Protecting the Blue Lake from land use impacts · September 2009 Protecting the Blue Lake from land...

September 2009

Protecting the Blue Lake from land use impacts

Report for the Centre for Natural Resource Management Project ID: CNRM043714

J Vanderzalm, P Dillon, D Page, S Marvanek, S Lamontagne, P Cook, H King, J Dighton, B Sherman and L Adams

Water for a Healthy Country Flagship Report series ISSN: 1835-095X

Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills.

CSIRO initiated the National Research Flagships to address Australia’s major research challenges and opportunities. They apply large scale, long term, multidisciplinary science and aim for widespread adoption of solutions. The Flagship Collaboration Fund supports the best and brightest researchers to address these complex challenges through partnerships between CSIRO, universities, research agencies and industry.

The Water for a Healthy Country Flagship aims to achieve a tenfold increase in the economic, social and environmental benefits from water by 2025. The work contained in this report is collaboration between CSIRO and the Centre for Natural Resource Management, South East Natural Resource Management Board (previously SENRCC and SECWMB), SA Water Corporation, SA EPA, DWLBC, SARDI, City Council of Mount Gambier and District Council of Grant.

For more information about Water for a Healthy Country Flagship or the National Research Flagship Initiative visit www.csiro.au/org/HealthyCountry.html

Citation: Vanderzalm, J., Dillon, P., Page, D., Marvanek, S., Lamontagne, S., Cook, P., King, H., Dighton, J., Sherman, B., Adams, L. 2009. Protecting the Blue Lake from land use impacts. CSIRO: Water for a Healthy Country National Research Flagship.

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CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

Cover Photograph:

From CSIRO’s ScienceImage: www.scienceimage.csiro.au File: PDC00391_028.jpg

Description: Aerial photograph of the Blue Lake at Mount Gambier, SA. View to the South with Mount Gambier urban area in foreground.

Photographer: Willem van Aken © 2006 CSIRO

Protecting the Blue Lake from land use impacts Page iii

ACKNOWLEDGEMENTS Financial support for this project is provided by the Centre for Natural Resource Management (CNRM Project ID CNRM043714). The authors also acknowledge in-kind support from the South East Natural Resource Management Board (previously SENRCC and SECWMB), SA Water Corporation, SA EPA, DWLBC, SARDI, City Council of Mount Gambier and District Council of Grant. Unpublished water quality data for the Blue Lake and the groundwater in the Blue Lake Capture Zone was provided by the SA EPA and DWLBC.

Thanks to all those that participated in the ‘In-lake Processes’ Research Workshop including Phil Gorey (EPA), Helen King (EPA), David Duncan (EPA), Glenn Harrington (DWLBC), Saad Mustafa (DWLBC), Jeff Lawson (DWLBC), Nigel Fleming (SARDI), Andrew Telfer (Australian Water Environments), Fred Leaney (CSIRO) and Jeff Turner (CSIRO).

Additional thanks to Bob Schuster (CSIRO) for preparing the C, N and P diagrams; Ray Correll (CSIRO) for his advice on analysing trends in water quality; Jeff Lawson, Greg Jones (DWLBC) and Carl Smith (EPA) for collecting SF6 samples; Jordan Clark (University of California) for advice on SF6 tracer test and analysis of duplicate samples; Grant Pearce (DWLBC) and dive team for collecting lake sediments; CSIRO Land and Water laboratories in Adelaide and Canberra for analysis of the lake sediments; Shane Snyder (Southern Nevada Water Authority) for undertaking trace organic chemical analysis; David Holliday (CSIRO) and the City of Mount Gambier (CoMG) staff for assisting with the SF6 tracer test; and Toney Hirnyk (CSIRO) for help making the sampling equipment used in the ‘in-lake’ attenuation studies. Finally the authors appreciate the suggestions of Jeff Lawson (DWLBC) and Andy McPharlin (DWLBC, formerly SA Water) over the duration of the project, but especially when reviewing the report.

Protecting the Blue Lake from land use impacts Page iv

EXECUTIVE SUMMARY The Blue Lake is an important resource to Mount Gambier, and the surrounding region, primarily as the drinking water supply but also as a tourist attraction due to its vibrant blue colour in the summer period. The main source of recharge to the Blue Lake is groundwater from the unconfined, karstic Gambier Limestone underlying the urban area aquifer. This groundwater recharge is susceptible to potential contamination from urban land use, including urban stormwater which is discharged directly into the unconfined aquifer. Thus it is imperative to understand the impact of land management practices on the quality and quantity of water in the Blue Lake and its surrounding groundwater capture zone. A risk assessment approach was used which is consistent with the Australian Drinking Water Guidelines (NHMRC–NRMMC, 2004) and the Australian Guidelines for Water Recycling (NRMMC-EPHC-AHMC, 2006). This methodology is capable of dealing with the uncertainties regarding the potential hazard loadings and residence time in the karstic aquifer, which are necessary to quantify time-dependent attenuation processes.

This significant task is the focus of the Centre for Natural Resource Management (CNRM) funded project entitled ‘Protecting the Blue Lake from land use impacts (part B)’. The aim is to provide management authorities with detailed understanding of the management practices that can be implemented within the catchment area which will protect the water quality of Blue Lake and is outlined by the following objectives:

1. Define the existing water quality in the Blue Lake and in the groundwater system feeding Blue Lake.

2. Establish conditional targets for water quality and water balances within the Blue Lake catchment area.

3. Assess benefits for protecting water quality by altering the location of the extraction of municipal water supply.

4. Assess and quantify the potential contamination sources from existing activities within the capture zone.

5. Define pathways for contamination to reach the Blue Lake and the potential mechanisms for attenuation within the capture zone.

6. Undertake a risk assessment to prioritise the land use activities against potential risks to water quality in the capture zone.

7. Evaluate protective strategies, including the available management options, to address land uses activities identified as a significant risk.

This study compares the historical water quality for the Blue Lake and the groundwater in the unconfined Gambier Limestone aquifer to water quality target values. The existing water quality data for Blue Lake does not show any potential for breach of water quality guideline values. Trace metal and metalloids illustrate some historical peaks in concentration. However there is no evidence to suggest rising concentrations within Blue Lake. Data regarding anthropogenic organic compounds in Blue Lake are rare. Thus it is recommended that any positive analytical detection warrants further investigation, including repeat sampling and analysis.

Existing water quality guidelines are appropriate for monitoring major ions and metals in Blue Lake. However, it is recommended that provision be made in the monitoring programmes to identify deviations from current trends so that they can be verified promptly. Targets have been proposed to manage nutrient concentrations in Blue Lake. These will allow identification of any alteration in trends in nutrient concentrations in the lake, which will allow the cause/s of any change to be determined and appropriate action decided upon. However a new program is required to set a baseline regarding the algal numbers and speciation within the lake.

Protecting the Blue Lake from land use impacts Page v

A preliminary review of the alternative sources for town water supply to Mount Gambier indicated that the sources of highest priority for further examination are continued extraction from the unconfined aquifer via Blue Lake, directly from the unconfined aquifer (not via Blue Lake) or from the confined aquifer. Surface water sources are limited by the expense associated with infrastructure and while indirect stormwater reuse is currently in operation, direct reuse (without aquifer storage) would also require new infrastructure. This evaluation reiterates the importance of protecting the water quality in the Blue Lake and its capture zone as the most likely sources of water supply for Mount Gambier into the future.

An experimental program was undertaken to develop the understanding of natural attenuation processes in the system, both within the aquifer and in Blue Lake itself. A sulfur hexafluoride (SF6) applied tracer test was used to examine the potential for contaminants to migrate quickly to the lake via karst features. This study showed that it is possible for recharge via stormwater drainage wells to reach Blue Lake in approximately two years.

The chemical composition of lake sediments, collected in the water column and from the lake floor, was used to understand the in-lake removal of potential contaminants. Many inorganic species exhibited the highest concentration in sediments collected in the water column during the winter months, due to their association with organic matter. In contrast, the lead concentrations were greatest during the warmer period of high carbonate production. Lead concentrations in the lake floor sediments were lower than in the water column, suggesting they are solubilised in the water column.

The inorganic species concentrations in the most recent lake floor sediments was generally comparable to those found settling in the water column during the periods of high carbonate production. The lake cores suggested that the rate of carbonate precipitation has increased with time and this effectively dilutes the concentration of most of the inorganic species. The particulate settling flux, which is currently governed by the annual carbonate cycle, provides a mechanism to remove inorganic species from the water column. Regardless of their association with either organic or inorganic carbon, trace inorganic chemicals are removed from the water column to the lake floor. As a result some inorganic species exhibit lower concentrations in the Blue Lake than in the groundwater, which provides the lake recharge.

A risk assessment based on a GIS urban land use map focused on current land use and the high risk activities identified in a qualitative risk assessment undertaken within the preceding project, ‘Protecting the Blue Lake from Land Use Impacts Part A’. The land use and contaminants (N, P, atrazine, simazine) in the agricultural area are currently being assessed within a companion CNRM project ‘Primary production to mitigate water quality threats’.

The risks posed by the current urban land use on the water quality of Blue Lake were assessed using an urban land use map and a quantitative risk assessment. Dry cleaners and their use of tetrachloroethene (PCE) were deemed as a high risk activity in the urban area. PCE contamination of the aquifer should be minimised by best practice procedures such as spill containment and response plans, bunded storage areas and possible well-head protection/treatment for bores likely to be affected. It is proposed that this be applied to all dry cleaning activities regardless of other activities within the catchment.

While inorganic species can be filtered or adsorbed during aquifer passage, these processes may not be permanent and thus efforts to minimise their concentration prior to recharge are recommended. Based on the existing stormwater quality data, inorganic species are predominantly associated with particulate matter. Possible management options include installation of treatment devices capable of capturing the fine fraction particulates in particulate matter. Particulate removal will also serve to removal particle bound organics such as PAHs.

Currently, there are a number of programs in place to protect water quality, which could be improved by a number of activities including:

Protecting the Blue Lake from land use impacts Page vi

Develop a risk management plan for the Blue Lake and the groundwater in its capture zone. This would build on the risk assessment conducted in this study and be consistent with the Australian Guidelines for Water Recycling (NRMMC-EPHC-AHMC, 2006).

Conduct research to define appropriate management actions if the current level of understanding is insufficient. This is currently underway for nitrate contamination from agricultural land use and on-site wastewater treatment through two CNRM funded projects. However an additional research program is required to understand the nitrogen and phosphorus cycles in Blue Lake, in relation to the potential for algal blooms and to define any management actions needed for phosphorus contamination.

Develop a program to improve the potential for stormwater treatment prior to discharge in the high priority spill and surface runoff catchments. This should encompass appropriate street sweeping and cleaning/maintenance schedules for existing treatment steps, in conjunction with examination of measures to enhance the existing stormwater treatment. The economic feasibility of providing improved treatment will be assisted by focusing efforts on the high risk catchments initially, equating to a small number of triple chamber settling pits (<30).

Focused industry inspections for the high risk activities to assess the strategies for managing water quality included in a community engagement (e.g. WaterCare) program.

Protecting the Blue Lake from land use impacts Page vii

TABLE OF CONTENTS Acknowledgements ..................................................................................................... iii

Executive Summary..................................................................................................... iv

1. Introduction ......................................................................................................... 1

2. Mount Gambier’s water quality condition......................................................... 2 2.1. Outline of available data and methodology for analysis ........................................... 2 2.2. Comparing water quality data to water quality guideline values............................... 5 2.3. Chloride, sodium, potassium and sulfate.................................................................. 6 2.4. Nutrients.................................................................................................................... 9 2.5. Metals and metalloids ............................................................................................. 13 2.6. Trace organics ........................................................................................................ 17 2.7. Summary of water quality condition........................................................................ 18

3. Setting and applying water quality targets ..................................................... 19 3.1. In-lake processes affecting Blue Lake water quality............................................... 19

3.1.1. Light and its influence on the colour of Lakes......................................................19 3.1.2. Carbon, Nitrogen and Phosphorus cycles ...........................................................20 3.1.3. How Blue Lake works ..........................................................................................23 3.1.4. Summary of in-lake processes ............................................................................27

3.2. Alternative extraction scenarios.............................................................................. 29 3.3. Target condition values........................................................................................... 30

3.3.1. Targets ................................................................................................................30 3.3.2. Prioritising unknowns regarding in-lake processes..............................................31

3.4. Summary of water quality targets ........................................................................... 32

4. Attenuation studies........................................................................................... 33 4.1. Attenuation studies methodology............................................................................ 33

4.1.1. Travel time estimates ..........................................................................................33 4.1.2. In-lake treatment processes ................................................................................38

4.2. Attenuation studies results...................................................................................... 40 4.2.1. Travel time estimates ..........................................................................................40 4.2.2. In-lake treatment processes ................................................................................41 4.2.3. Summary of attenuation studies ..........................................................................49

5. Assessing risks to Blue Lake from urban land use risks.............................. 50 5.1. Risk assessment methodology ............................................................................... 50 5.2. GIS development for the urban area ...................................................................... 50 5.3. Prioritisation of risk activities................................................................................... 55 5.4. Comparison of risk rankings to existing water quality data..................................... 58 5.5. Fate of potential contaminants................................................................................ 60

5.5.1. Copper, chrome and arsenic (CCA) ....................................................................60 5.5.2. Benzene, toluene, ethylbenzene and xylene (BTEX) ..........................................60 5.5.3. Phenanthrene, fluoranthene and pyrene (PAHs).................................................60 5.5.4. Tetrachloroethene (PCE).....................................................................................60 5.5.5. Diffuse Hazards ...................................................................................................61

5.6. Quantitative risk assessment.................................................................................. 61 5.7. Summary of risk assessment.................................................................................. 63

6. Management options for protection of Blue Lake water quality................... 64 6.1. Current management.............................................................................................. 64 6.2. Non-structural measures ........................................................................................ 64

Protecting the Blue Lake from land use impacts Page viii

6.3. Structural measures................................................................................................ 65 6.4. Management options .............................................................................................. 66

6.4.1. Monitoring and evaluation ...................................................................................70 6.5. Summary of management options.......................................................................... 73

7. Summary and recommendations..................................................................... 73

References .................................................................................................................. 76

Appendix 1 In-lake processes research workshop notes....................................... 80

Appendix 2 Summary of qualitative risk assessment............................................. 88

Appendix 3 Estimating the importance of various sources to contaminant loads89

Appendix 4 Trace organic analysis undertaken by Southern Nevada Water Authority............................................................................................................................ 90

Appendix 5 Timeline of events in Mount Gambier .................................................. 92

Appendix 6 Draft risk management framework ....................................................... 93

Protecting the Blue Lake from land use impacts Page ix

TABLES Table 1 Summary of sampling locations utilised for the evaluation of water quality in Blue

Lake.................................................................................................................................. 2 Table 2 Range of water quality parameters and the time interval monitored within the Blue

Lake, the unconfined Gambier Limestone aquifer and Mount Gambier’s stormwater...... 3 Table 3 Drinking water and aquatic ecosystem guideline values for development of target

values for the Blue Lake (ANZECC and ARMCANZ, 2000; SA EPA, 2003; NHMRC-NRMMC, 2004)................................................................................................................. 5

Table 4 Summary of water quality data for the Blue Lake, the unconfined Gambier Limestone aquifer and Mount Gambier’s stormwater. ....................................................................... 6

Table 5 Blue Lake water balance and estimated quantities of in-lake removal capacity....... 22 Table 6 Annual limnological, biological and chemical observations in Blue Lake. ................ 28 Table 7 Summary of preliminary review of potential sources for town water supply in Mount

Gambier.......................................................................................................................... 29 Table 8 Targets indicators and measurements proposed for Blue Lake and its groundwater.

........................................................................................................................................ 30 Table 9 Prioritising unknowns regarding in-lake processes and future water quality for Blue

Lake................................................................................................................................ 32 Table 10 Injection locations used for the sulfur hexafluoride (SF6) tracer test....................... 35 Table 11 Concentration and total mass of sulfur hexafluoride (SF6) discharged into the

injection bores. ............................................................................................................... 36 Table 12 Program of monitoring sulfur hexafluoride (SF6) in the groundwater of the Gambier

Limestone unconfined aquifer. ....................................................................................... 37 Table 13 Details of the six core samples collected from the base of Blue Lake on 29/3/08 and

sub-sampled for analysis................................................................................................ 39 Table 14 Mass of sediment collected in traps 15 m, 40 m, 70 m below the surface of Blue

Lake and the calculated rate of settling of particulate matter through the water column.41 Table 15 Chemical composition of the sediments settling within Blue Lake.......................... 42 Table 16 Chemical composition of core NL10 (North) from Blue Lake.................................. 46 Table 17 Data sources used for GIS development................................................................ 51 Table 18 Urban land use and associated risk activities incorporated into urban area GIS. .. 51 Table 19 Locations of activities included on urban area GIS................................................. 52 Table 20 Points system to prioritise stormwater catchments relevant to risk activities. ........ 56 Table 21 Catchments with scores ≥7 for the surface runoff and/or the spill pathways. ......... 56 Table 22 Potential contaminants within stormwater catchments deemed as high risk.......... 57 Table 23 Results of Mann-Whitney rank sum test comparing stormwater quality for high and

low risk catchments. ....................................................................................................... 59 Table 24 Input data for assessment of risk posed by organic hazards in stormwater. .......... 62 Table 25 Draft Management Options to address the risks to Blue Lake water quality. ......... 67 Table 26 Industry sites included on the GIS Land Use Map recommended for detailed

assessment. ................................................................................................................... 70 Table 27 Draft water quality monitoring plan required to support the proposed management

options. ........................................................................................................................... 72

Protecting the Blue Lake from land use impacts Page x

FIGURES Figure 1 Map of Blue Lake showing the location of sampling points. ...................................... 3 Figure 2 Chloride trend in Blue Lake. ...................................................................................... 7 Figure 3 Sodium trend in Blue Lake. ....................................................................................... 7 Figure 4 Major ion chemistry of Blue Lake and selected groundwater observation bores. ..... 8 Figure 5 Potassium trend in Blue Lake.................................................................................... 9 Figure 6 Sulfate trend in Blue Lake. ........................................................................................ 9 Figure 7 Nitrogen (as nitrate) trend in Blue Lake................................................................... 10 Figure 8 Nitrate concentrations in Blue Lake (BL), Mount Gambier’s groundwater (GW),

stormwater (SW) and potential from wastewater (WW) (based on the assumption that all TKN is converted to nitrate)............................................................................................ 11

Figure 9 Filterable Reactive Phosphorus (FRP) trend in Blue Lake. ..................................... 11 Figure 10 Dissolved organic carbon trend in Blue Lake. ....................................................... 12 Figure 11 Chlorophyll a trend in Blue Lake............................................................................ 12 Figure 12 Boron trends in Blue Lake. .................................................................................... 13 Figure 13 Arsenic trend in Blue Lake..................................................................................... 14 Figure 14 Chromium trend in Blue Lake. ............................................................................... 14 Figure 15 Copper trend in Blue Lake..................................................................................... 15 Figure 16 Lead trend in Blue Lake......................................................................................... 16 Figure 17 Nickel trend in Blue Lake....................................................................................... 16 Figure 18 Zinc trend in Blue Lake.......................................................................................... 17 Figure 19 Conceptual diagram for carbon (organic and inorganic) processes in Blue Lake.

DIC=dissolved inorganic carbon, DOC=dissolved organic carbon, PIC=particulate inorganic carbon, POC=particulate organic carbon........................................................ 21

Figure 20 Conceptual diagram for nitrogen processes in Blue Lake. DON=dissolved organic nitrogen, PON=particulate organic nitrogen. .................................................................. 21

Figure 21 Conceptual diagram for phosphorus processes in Blue Lake. sol P=soluble phosphorus, part P=particulate phosphorus................................................................... 22

Figure 22 Blue Lake conductivity and temperatures profiles with depth January 2004 to January 2005 (unpublished data from SA EPA and DWLBC)........................................ 23

Figure 23 Annual cycling of Chlorophyll a in Blue Lake......................................................... 24 Figure 24 Bicarbonate and calcium cycling in Blue Lake, shown for recent data (2001-2005).

........................................................................................................................................ 25 Figure 25 Scanning electron micrograph of 10 μm calcite crystals coated in organic material,

including a diatom. Sample was collected in a sediment trap 15 m below the lake surface (Telfer, 2000). .................................................................................................... 26

Figure 26 Recent stratigraphic assessment in the vicinity of the Blue Lake (Lawson and Hill, in press).......................................................................................................................... 26

Figure 27 Approximate location of sulfur hexafluoride (SF6) injection bores in relation to the location of Blue Lake, the zone of ‘karst influence’ (Lawson, unpublished data) expected to impact on Blue Lake from flow through karst features and the regional groundwater flow direction................................................................................................................... 34

Figure 28 Mobile apparatus used to prepare the sulfur hexafluoride (SF6) tracer prior to discharge of tracer into bores. ........................................................................................ 36

Figure 29 Sampling apparatus to collect particulates within Blue Lake (Telfer 2000). .......... 38 Figure 30 Grant Pearce collects sediment cores from the base of Blue Lake on 29/3/08

(photo Dr Richard Harris; ABC South East SA, 2008 http://www.abc.net.au/local/stories/2008/04/03/2207124.htm)....................................... 39

Figure 31 Settling rate (mg/day) for particulate matter and carbonate collected at 15 m, 40 m or 70 m below the surface of Blue Lake. ........................................................................ 42

Figure 32 Settling rate (ng/day) for the inorganic components of the particulate matter collected at 15m, 40m or 70m below the surface of Blue Lake. ..................................... 43

Protecting the Blue Lake from land use impacts Page xi

Figure 33 Comparison of core samples collected from the northern edge (NL10) and centre (CL10) of the Blue Lake indicating variation in the sediment banding............................ 44

Figure 34 Total 210Pb and excess 210Pb versus depth for cores NL10 (North) and CL10 (Centre). ......................................................................................................................... 45

Figure 35 Estimated relationship between age and depth for core NL10 (North).................. 45 Figure 36 Accumulation rate of a) sediment and calcium carbonate and b) aluminium, iron,

phosphorus and organic matter in core NL10 (North) with depth................................... 47 Figure 37 Change in lake surface elevation and rate of water extraction for Blue Lake 1880-

2000 (Herczeg et al., 2003). ........................................................................................... 48 Figure 38 Blue Lake in 1894 (Mount Gambier Public Library, 2009)..................................... 48 Figure 39 Accumulation rate of inorganic constituents in core NL10 (North). ....................... 49 Figure 40 Framework to assess the impact of land use activities on water quality. Target

values can be based on potable and environmental water quality guidelines................ 50 Figure 41 Risk activities within the Mount Gambier urban area (all pathways). .................... 53 Figure 42 Risk activities within the Mount Gambier urban area with the potential to impact

water quality through surface runoff. .............................................................................. 54 Figure 43 Risk activities within the Mount Gambier urban area with the potential to impact on

water quality through spills. ............................................................................................ 54 Figure 44 Risk activities within the Mount Gambier urban area with the potential to impact on

water quality through infiltration...................................................................................... 55 Figure 45 Stormwater catchments potentially impacted by surface runoff prioritised by risk

activities contained. ........................................................................................................ 57 Figure 46 Stormwater catchments potentially impacted by spills prioritised by risk activities

contained. ....................................................................................................................... 58 Figure 47 Location of existing stormwater quality data for Mount Gambier in relation to high

and low risk catchments. ................................................................................................ 59 Figure 48 Degradation pathway of chlorinated ethenes from tetrachloroethene to ethene

(after Hunkeler et al., 2005)............................................................................................ 61 Figure 49 Change in risk as simulated stormwater based organics are attenuated in the

groundwater and the Blue Lake. The risk indicator = simulated median concentration/target value. 1E-20 was substituted for values of zero in this figure........ 63

Figure 50 Typical triple chamber settling pits (SA EPA, 2005). ............................................. 66 Figure 51 Treatment of stormwater using up-flow polypropylene (PPL) media (Lee et al.,

2004). ............................................................................................................................. 68

Protecting the Blue Lake from land use impacts Page 1

1. INTRODUCTION The Blue Lake is an important resource to Mount Gambier, and the surrounding region, primarily as the drinking water supply but also as a tourist attraction due to its vibrant blue colour in the summer period. The main source of recharge to the Blue Lake is groundwater from the unconfined, karstic Gambier Limestone aquifer underlying the urban area. This groundwater recharge is susceptible to potential contamination from urban land use, including urban stormwater which is discharged directly into the unconfined aquifer. Thus it is imperative to understand the impact of land management practices on the quality and quantity of water in the Blue Lake and its surrounding groundwater capture zone. A risk assessment approach was used which is consistent with the Australian Drinking Water Guidelines (NHMRC–NRMMC, 2004) and the Australian Guidelines for Water Recycling (NRMMC-EPHC-AHMC, 2006). This methodology is capable of dealing with the uncertainty in regarding the loadings of potential hazards and residence time in the karstic aquifer, which are necessary to quantify time-dependent attenuation processes.

This significant task is the focus of the Centre for Natural Resource Management (CNRM) funded project entitled ‘Protecting the Blue Lake from land use impacts (part B)’. The aim is to provide management authorities with detailed understanding of the management practices that can be implemented within the catchment area which will protect the water quality of Blue Lake and is outlined by the following objectives:

1. Define the existing water quality in the Blue Lake and in the groundwater system feeding Blue Lake.

2. Establish conditional targets for water quality and water balances within the Blue Lake catchment area.

3. Assess benefits for protecting water quality by altering the location of the extraction of municipal water supply.

4. Assess and quantify the potential contamination sources from existing activities within the capture zone.

5. Define pathways for contamination to reach the Blue Lake and the potential mechanisms for attenuation within the capture zone.

6. Undertake a risk assessment to prioritise the land use activities against potential risks to water quality in the capture zone.

7. Evaluate protective strategies, including the available management options, to address land uses activities identified as a significant risk.

Initially Section 1 compares the historical water quality for the Blue Lake and the groundwater in the unconfined Gambier Limestone aquifer to water quality target values. Such assessment looks for incidences in breach of water quality targets or increasing trends, which may indicate a long-term potential to exceed target values.

Following the assessment of existing water quality data, Section 2 develops the understanding of in-lake processes and establishes conditional targets for water quality and water balances within the Blue Lake catchment area. This section also reviews the feasibility of using alternative sources of drinking water supply to supplement or replace the extraction from the Blue Lake.

Section 3 describes the field studies undertaken to understand the fate of potential hazards in the aquifer and Blue Lake by developing the current understanding of travel times in the aquifer and in-lake treatment processes.

A risk assessment based on a GIS urban land use map is discussed in Section 4. The focus is on current land use and the high risk activities identified in a qualitative


risk assessment undertaken within the preceding project, ‘Protecting the Blue Lake from Land Use Impacts (part A)’. The agricultural land use and associated impact on the high priority hazards (N, P, atrazine, simazine) is currently being assessed within a companion CNRM project ‘Primary production to mitigate water quality threats’.

Finally, Section 5 outlines the recommended management options to provide greater protection to the quality of Blue Lake from the potential urban land use hazards. These recommendations and current precautionary measures have been combined to produce a draft risk management framework (Appendix 6).

2. MOUNT GAMBIER’S WATER QUALITY CONDITION

2.1. Outline of available data and methodology for analysis The historical water quality data for the Blue Lake was obtained from seven sampling locations between 1968 until 2005 (Table 1 and Figure 1). The water quality within the Blue Lake is monitored by SA Water from the surface of the lake at the pumping station. The frequency of this sampling varies from fortnightly to annually depending on the parameter under consideration. The SA EPA has monitored water quality in the Blue Lake at four depths (surface, 20 m, 40 m and 60 m) on a 3 monthly basis at various sampling locations between 1974 and 2005. The water quality data presented in this report was attained from the SA Water and EPA database, a compilation of analytical results from the Australian Water Quality Centre (AWQC) (electronic format, unpublished data). The full range of parameters in the database and the time interval of available data are presented in Table 2. Numerous completed and ongoing research projects may also provide additional water quality data for the Blue Lake and the groundwater in its capture zone but have not been included in this summary. Water quality data preceding 1968 may be available, but have not been included in this analysis. The reliability of historical analytical and sampling methodologies should always be taken into consideration and has previously been the cause for exclusion of early data (pre 1968).

The water quality data (SA EPA, unpublished data) for the unconfined aquifer within the Blue Lake Protection and Capture Zone (BLPCZ) is available between 1981 and 2005 (Table 2). The SA EPA undertakes groundwater quality monitoring on an annual basis in summer, while DWLBC monitor groundwater salinity on a biannual basis, in spring and autumn. It is recognised that stormwater recharge is a major contributor to groundwater recharge under the urban area. Thus, stormwater quality data obtained from a study undertaken by Emmet (1985), the City Council of Mount Gambier (URS, 2000; 2003) and a recent CSIRO study (Wolf et al., 2006) is also examined.

Table 1 Summary of sampling locations utilised for the evaluation of water quality in Blue Lake.

Sampling location Interval used for evaluation Comment

Pumping station 1968-2005 surface sampling – SA Water

Site 1 1974-1985 depth sampling – SA EPA


Site 2A 1981-1992 depth sampling – SA EPA





Figure 1 Map of Blue Lake showing the location of sampling points.

Table 2 Range of water quality parameters and the time interval monitored within the Blue Lake, the unconfined Gambier Limestone aquifer and Mount Gambier’s stormwater.

Blue Lake Unconfined aquifer Stormwater

Colour 1968-2005 Conductivity 1968-2005 1981-2005 1978-1982, 2004 Total dissolved solids 1974-2005 1981-2005 Suspended solids 1968-1981 1978-1982, 1999-2002,

2004 pH (lab) 1968-2005 1981-1998 1978-1982 pH (field) * * 2004 Turbidity 1968-2005 2004 Temperature (lab) 1983-2005 Temperature (field) * * 2004 Dissolved oxygen (field) * 2004 Hardness 1974-2005 1995-1996 Alkalinity 1974-2005 1995-1996 Chloride 1968-2005 1995-2005 2004 Bicarbonate 1968-2005 1995-2002 2004 Sulfate 1968-2005 1981-2002 2004 Bromide 1983-1986 Fluoride 1968-2005 1995-1996 Iodide 1984-2004 Calcium 1968-2005 1995-2002 2004 Magnesium 1968-2005 1995-2002 2004 Sodium 1968-2005 1981-2002 2004 Potassium 1972-2005 1981-2002 Aluminium-total 1995-2005 1995-2005 2004 Aluminium-sol 1995-2005 1995-2005 2004 Antimony 1997, 2001-2004 Arsenic 1989-2005 1995-2005 1978-1982, 1999-2002,

2004 Boron 1968-2005 2005 2004 Barium 2001-2004 Beryllium 1997, 2001-2004

Table 2 continued


Blue Lake Unconfined aquifer Stormwater

Cadmium 1968-2004 2004 Chromium 1989-2005 1995-2005 1982, 1999-2002, 2004 Copper 1989-2005 1995-2005 1978-1982, 1999-2002,

2004 Iron 1968-2005 1981-2005 2004 Lead 1991-2004 1995-2005 1978-1982, 1999-2002,

2004 Manganese 1986-2004 Mercury 1968-2004 Molybdenum 1995-2004 Nickel 1995-2004 1999-2002, 2004 Selenium 1995-2004 Silver 1997, 2001-2004 Tin 1997, 2001-2004 Zinc 1991-2005 1995-2005 1978-1982, 1999-2002,

2004 Ammonium 1968-2005 1981-1994 1978-1982, 2004 Nitrate 1968-2005 1981-2005 1978-1982, 1999-2002,

2004 Nitrite 1968-2005 1981-2005 1978-1982, 2004 Total Kjeldahl nitrogen 1968-2005 1981-2005 1978-1982, 1999-2002,

2004 Total phosphorus 1968-2005 1981-2005 1978-1982, 1999-2002,

2004 Filterable reactive phosphorus 1968-2005 1981-2005 1978-1982, 2004 Silica 1968-2005 1995-1996 Cyanide 1997, 2001-2004 Cyclohexane hexachloride 1997 Dissolved organic carbon 1983-2005 1986-1994 2004 Total organic carbon 1968-1995 1978-1982 Adsorbable organic halides 1995-2005 1996-2005 Benzene, toluene, ethylbenzene, xylene

* * 1999-2002

Pesticides 1997, 2001-2005 1996-2005 1978-1982, 1999-2002 Phenols 1968-2005 * 2004 Polycyclic aromatic hydrocarbons

* 1999-2002, 2004

Total petroleum hydrocarbons * * 1999-2002, 2004 Chlorophyll a and b 1993-2005 E-coli and coliforms 1983-2005 Heterotrophic Fe bacteria 1997-2002 Free carbon dioxide 1974-2005 1995-1996 Alpha and beta activity 1987-2004 Water isotopes 1992-2004 * 1999-2002 * data available but not attained, bold indicates parameter measured at the time of data collation (Oct. 2005)


2.2. Comparing water quality data to water quality guideline values

Existing data for the Blue Lake can be compared with water quality targets based on human health and aquatic ecosystem protection (Table 3). Commonly, the suggested aquatic ecosystem trigger values (SA EPA, 2003; ANZECC & ARMCANZ, 2000) are far more stringent than the drinking water guideline value (e.g. Cu in Table 3). It is also apparent that there can be considerable variation in the values recommended for aquatic ecosystem protection (e.g. Cu, Ni) or the target concentration may be below the current analytical detection limit (e.g. atrazine).

Table 3 Drinking water and aquatic ecosystem guideline values for development of target values for the Blue Lake (ANZECC and ARMCANZ, 2000; SA EPA, 2003; NHMRC-NRMMC, 2004).

Current Blue Lake (mg/L)

Drinking water (mg/L) Aquatic ecosystem (mg/L)

80th %ile 90th %ile Health Aesthetic SA EPA, 2003

ANZECC & ARMCANZ, 2000 a

Total dissolved solids

370 500

Chloride 90 250

Sodium 60 180

Sulfate 20 500 250

Total phosphorus 0.02 0.02 0.5 (0.1 soluble)

0.025 (0.01 sol)

Nitrate as N 3.6 3.8 11 (infants)

22 (adults)

5 (total N) 0.7 a

3.4 b

Total organic carbon

1.3 (sol) 1.6 (sol) 15

Boron 0.09 0.14 4 0.37

Arsenic 0.001 0.002 0.007 0.05 0.024 as As(III)

Chromium(VI) 0.01 (total)

0.015 (total)

0.05 0.001 0.001

Copper 0.013 0.015 2 0.01 0.0014

Lead 0.001 0.003 0.01 0.005 0.0034

Nickel 0.06 0.07 0.02 0.15 0.011

Zinc 0.04 0.05 3 0.05 0.008

Atrazine <0.0005 <0.0005 0.0001c,d 0.3 0.013

Simazine <0.0005 <0.0005 0.0032

a 95% protection, b 90% protection c or limit of detection, d below available limit of detection

Water quality data for the Blue Lake, the unconfined Gambier Limestone aquifer and Mount Gambier’s stormwater has been summarised by presenting the median concentration, the range of values observed and the number of samples available for a selected suite of parameters. Time series graphs of the water quality data for Blue Lake are presented in Figure 2-18. These graphs include all sampling locations without any smoothing of the data set by taking annual averages.

This comparison of existing water quality data with suggested water quality targets will be used as a base to recommend further data analysis required to determine specific target values for the Blue Lake and inputs (if applicable).


Table 4 Summary of water quality data for the Blue Lake, the unconfined Gambier Limestone aquifer and Mount Gambier’s stormwater.

Blue Lake Unconfined aquifer Stormwater (mg/L) n median range n median range n median range

TDS 1073 360 320-400 238 390 96-890 37 51 22-120 Cl 770 86 63-105 206 75 6-230 35 5 2-24 Na 760 59 52-74 73 58 4-99 10 8 7-12 K 770 3 2-5 82 2 0.1-23 10 1 1.0-2.3 SO4 750 18 2-30 67 12 2-33 10 8 4-15 TKN 690 0.2 0.01-5 165 0.2 <0.05-3 120 1 <0.02-5 NO3-N 1500 3 0.01-6 180 9 0.3-88 112 0.1 <0.02-5 TP 890 0.009 <0.005-2.7 240 0.1 0.006-3.5 121 0.3 0.1-9 FRP 595 <0.005 <0.005-0.2 240 0.01 <0.005-3 37 0.09 <0.005-0.7 B 110 <0.04 <0.005-0.2 22 <0.04 <0.05-0.08 10 0.08 <0.04-0.1 As 139 <0.001 <0.001-0.005 205 0.002 <0.001-0.02 47 <0.005 <0.005-0.1 Cr 149 <0.005 <0.005-0.03 209 0.005 <0.003-0.8 90 0.005 <0.001-0.06 Cu 150 <0.005 <0.005-0.05 149 0.005 <0.001-3 99 0.01 <0.001-0.2 Pb 43 0.001 <0.0005-0.008 208 0.004 <0.0005-

0.06 99 0.01 <0.001-0.9

Ni 30 0.001 <0.0005-0.07 63 0.003 <0.001-0.06 Zn 121 0.02 <0.003-0.1 204 0.03 <0.003-1 99 0.1 0.01-2 TOC 27 25 7-60 DOC 295 1 0.08-5 210 1.1 0.1-8 11 9 6-19 Atrazine (μg/L)

53 <0.5 <0.5-0.5 140 <0.5 <0.5-1 75 <0.5 <0.5-12.4

Simazine (μg/L)

53 <0.5 <0.5-0.5 140 <0.5 <0.5-0.5 75 <0.5 <0.5-5.3

n=number of samples

2.3. Chloride, sodium, potassium and sulfate There is no indication of any potential for water quality in the Blue Lake to breach drinking water guideline values for chloride, sodium, sulfate or the aggregate measure of total dissolved solids.

Chloride and sodium in the Blue Lake have declined since the 1970s, with the most recent data showing concentrations that are comparable to the median groundwater concentrations (Table 4; Figure 2-3). Stormwater recharge, with a median chloride concentration of 5 mg/L, is considerably fresher than groundwater of the unconfined and confined aquifers and thus is not likely to lead to increased salinity in Blue Lake. It is difficult to calculate the portions of each end-member in Blue Lake using chloride signatures due to the uncertainty in the evolution of groundwater signatures (Lamontagne and Herczeg, 2002). The chloride concentration in the unconfined aquifer has a median of 75 mg/L, but is extremely variable (Table 4). Data for the past decade shows variability between 6 (Unit no. 7022-0293 GAM12, possibly due to stormwater recharge) and 230 mg/L (Unit no. 7022-2846 BLA17, shallow well in the city area). Long-term water quality data available for 1972, 1982, 1995 and 2005 illustrate lower chloride concentrations in the shallower monitoring bores (currently defined as intersecting Unit 1). Major ion chemistry shows clustering for water quality from the Blue Lake and groundwater bores intersecting lower intervals of the Gambier Limestone aquifer (Unit no. 7022-2846, intersecting Unit 3) (Figure 4).


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Cl (

mg

/L)

all data

site 6-40mDrinking water guideline value 250 mg/L (aesthetic)

Figure 2 Chloride trend in Blue Lake.

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Na

(m

g/L

)

all data

site 6-40mDrinking water guideline value 180 mg/L (aesthetic)

Figure 3 Sodium trend in Blue Lake.


Figure 4 Major ion chemistry of Blue Lake and selected groundwater observation bores.

Within Blue Lake, potassium concentrations are relatively constant at 3 mg/L (Figure 5), while sulfate peaked in the 1980s, declining to a fairly level 18 mg/L (Figure 6). Turner (1979) relates the variability in groundwater major ion chemistry in the vicinity of the Blue Lake to the influence of volcanic soils overlying the Gambier Limestone. In close proximity to Blue Lake (<1 km) groundwater is enriched in sulfate, sodium and potassium, leading to considerable variability in their concentrations in the groundwater. In addition, groundwater can be affected by contamination such as sewer leaks. The maximum groundwater potassium of 23 mg/L in Unit no. 7022-2910 (BLA18), associated with a site of suspected sewage contamination, is comparable to the potassium concentration within wastewater (Wolf et al., 2006).

80 60 40 20 20 40 60 80

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Ca Na+K HCO3 Cl

Mg SO4

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LegendLegend

C Blue Lake

K 7022-1532

L 7022-1538

H 7022-2823

D 7022-2828

A 7022-2846

L 7022-290

E 7022-60


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K (

mg

/L)

all datasite 6-40m

Figure 5 Potassium trend in Blue Lake.

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SO

4 (m

g/L

)

all datasite 6-40 to 50m

Drinking water guideline value 250 mg/L (aesthetic)

Figure 6 Sulfate trend in Blue Lake.

2.4. Nutrients Nutrient contamination, as nitrate, within the Gambier Limestone is a major water quality concern in the region (Dillon, 1988; Lamontagne and Herczeg, 2002). Diffuse (fertilizer application) and point sources (septic tanks, dairy waste plumes) have resulted in a median groundwater nitrate concentration of approximately 9 mg/L N (40 mg/L NO3

-) within the unconfined Gambier Limestone (Table 1) and an increasing concentration in Blue Lake (Figure 7). Nitrate in the Blue Lake is not expected to


breach drinking water guidelines in the near future (~30 years). However groundwater nitrate may continue to increase as polluted areas of the aquifer will require centuries to reach a new equilibrium. Similarly, land-use changes will continue to alter nitrogen inputs to the groundwater. Thus it becomes difficult to project the future concentration of nitrate in Blue Lake when the input concentrations are uncertain. There does seem to be a trend toward higher nitrate concentrations at around 40 m below the lake surface which may be influenced by in-lake removal processes (discussed in section 2.1.2). This trend toward higher nitrate at 40 m may be an indication of groundwater inflow at this depth but may also be influenced by chemical stratification within the sub-units of the Gambier Limestone. Application of chemical signatures to quantify the contribution of each sub-unit to the inflow into Blue Lake is the topic of an independent research program (J. Lawson, pers. comm.).

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NO

3-N

(m

g/L

)

pumpsurface to 10m20 to 30 m40 to 50m60+m

Drinking water guideline value 22 mg/L as N (adults)Aquatic ecosystem target value 0.7 (95% protection)- 3.4 (90% protection) mg/L as N

Figure 7 Nitrogen (as nitrate) trend in Blue Lake.

An isolated maximum nitrate of 87 mg/L as N in groundwater beneath the city recorded in Unit no. 7022-2910 (BLA18) is attributed to septic contamination from the original hospital in Mount Gambier. This concentration is comparable to the magnitude of sewage TKN loadings (Figure 8) and supports the hypothesis that all forms of nitrogen input will be converted to nitrate under the aerobic conditions of the Gambier Limestone unconfined aquifer with little potential for attenuation. There is limited opportunity for examination of groundwater quality within the sub-units of the Gambier Limestone aquifer. Two sets of observation wells have discrete open intervals at three depths mainly intersecting Unit 1 (Unit nos. 7022-2823 and 7022-7721); Unit 3 (Unit nos. 7022-7724 and 7022-7722) of the Greenpoint Member; and the lower dolomitic Camelback Member (Unit nos. 7022-7725 and 7022-7723). Nitrate is highest in the shallower wells which predominantly intersect Unit 1 (12 to 27 mg/L N), exceeding the drinking water guideline. Unit 3 (4 to 6 mg/L N) and the Camelback member (2 to 8 mg/L N) are similar in concentration to the Blue Lake. Disposal of stormwater, lower in nitrogen than the groundwater, has the potential to lower the groundwater nitrate concentration recharging the Blue Lake.


BL GW SW WW

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NO

3-N

mg/

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BL=Blue Lake GW=groundwater

SW=stormwater WW=waste water

Max.

75 percentile

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25 percentile

Min.

Figure 8 Nitrate concentrations in Blue Lake (BL), Mount Gambier’s groundwater (GW), stormwater (SW) and potential from wastewater (WW) (based on the assumption that all TKN is converted to nitrate).

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FR

P (

mg

/L)

pumpsurface to 10m20 to 30m40 to 50m60+m

Aquatic ecosystem target value 0.01-0.1 mg/L soluble

Figure 9 Filterable Reactive Phosphorus (FRP) trend in Blue Lake.

While nitrogen loadings are generally greater than phosphorus, both are important factors in determining the water quality of the receiving water body. Currently the Blue Lake is oligotrophic, with algal production thought to be limited by phosphorus availability (Telfer, 2000; Lamontagne and Herczeg, 2002). Phosphorus mobility in the carbonate aquifer is low and thus the 80th percentile for total phosphorus in the Blue Lake is below the recommended aquatic ecosystem trigger values. Despite some peaks in FRP around 1980 and 1990, there is no indication of increasing phosphorus in the lake (Figure 9). Given the nitrate concentrations within Blue Lake, it appears feasible that the low phosphorus concentrations in Blue Lake limit excessive algal production (Lamontagne and Herczeg, 2002).


Dissolved organic carbon (DOC) in Blue Lake shows an increase up until 1990 and then a decline to the current median of 1 mg/L (Figure 10). Nonetheless, the peak of 5 mg/L is well below the suggested target values for total organic carbon (TOC). While chlorophyll a, an indicator of primary production, is quite variable within the Blue Lake, there is no sign of an increasing trend (Figure 11). The annual cycle of chlorophyll a is considered in section 2.1.3. Phosphorus and organic carbon in stormwater were predominantly in particulate form. The concentrations were generally higher in stormwater than in the groundwater, with some incidence in excess of the water quality guidelines. Thus, stormwater discharge could impact on the nutrient status of the Blue Lake.

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DO

C (

mg

/L)


Aquatic ecosystem target value 15 mg/L total organic carbon

Figure 10 Dissolved organic carbon trend in Blue Lake.

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loro

ph

yll a

(u

g/L

)

pump

site 6-surface to 10m

site 6-20 to 30m

site 6-40 to 50m

site 6-60m

Figure 11 Chlorophyll a trend in Blue Lake.


2.5. Metals and metalloids The metal and metalloid water quality data for Blue Lake is limited. There is no warning of a rising trend for boron, arsenic, chromium, copper, lead, nickel or zinc. A change in analytical technique in 2001 has generally affected the detection limit for the metals and metalloids. Metals and metalloids in stormwater are predominantly associated with particulates; however chromium, copper and zinc have a significant soluble component (Wolf et al., 2006). The concentrations measured in stormwater illustrate a potential to breach guideline values, especially when stringent environmental values are considered.

Arsenic, chromium, copper, lead and zinc all exhibit higher median and peak concentrations in the groundwater than in Blue Lake. Note, nickel is not monitored in the groundwater and the number of boron analyses is too small to make this comparison. It is possible that metal concentrations are lowered in the lake through in-lake removal processes.

Boron concentrations in stormwater and wastewater are approximately 0.1 mg/L (Table 4; Figure 12). A recent study showed no potential for boron adsorption to carbonate aquifer material (Vogel, 2005). Thus it follows that boron concentrations in Blue Lake up to 0.2 mg/L, coincide with the maximum concentration observed in wastewater. Arsenic data for the Blue Lake is consistently below the drinking water guideline, which in this case is lower than the aquatic ecosystem targets (Figure 13).

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B (

mg

/L)


Drinking water guideline value 4 mg/L Aquatic ecosystem target value 0.37 mg/L

shift likely due to change in analytical detection limit

Figure 12 Boron trends in Blue Lake.


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As

(mg

/L)

pumpsite 6-surfacesite 6-20msite 6-40msite 6-60m

Drinking water guideline value 0.007 mg/LAquatic ecosystem target value 0.02-0.05 mg/L

Figure 13 Arsenic trend in Blue Lake.

Arsenic, chromium, copper, lead, nickel and zinc concentrations in the lake rise in the 1990s, but then decline (Figure 13-18). It is difficult to assess the stringent aquatic ecosystem water quality criteria for chromium (0.001 mg/L as Cr(VI)), which is below detection with the current analytical technique and does not speciate Cr(VI) and Cr(III). In 1995, 40 kL of copper chrome arsenate (CCA) was spilled at a softwoods site in Mount Gambier, to the north-west of Blue Lake. A link between contamination events and marginally elevated chromium and copper concentrations in the Blue Lake in March and October 1995 and again in September 1997 may confirm preferential pathways to the lake and warrants further investigation.

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(mg

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Drinking water guideline value 0.05 mg/L as Cr(VI)Aquatic ecosystem target value 0.001 mg/L as Cr(VI)

Figure 14 Chromium trend in Blue Lake.


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Drinking water guideline value 2 mg/LAquatic ecosystem target value 0.001-0.01 mg/L

Figure 15 Copper trend in Blue Lake.

Recent data indicates higher copper concentrations from the pump than other locations in the lake, suggesting addition from the pump itself. The copper concentrations measured in the centre of the lake are below both the recommended aquatic ecosystem targets. Following the peak in the 1990s, lead, nickel and zinc concentrations measured in Blue Lake are below all water quality targets. Note that the incidence of higher nickel concentrations sampled from the centre of the lake in 1995 (0.05 to 0.07 mg/L), has resulted in an 80th percentile concentration above the drinking water guideline, whereas nickel concentrations from the pump are consistently below the target. The shift toward lower zinc concentrations post 1990s may have been influenced by lower input concentrations, in response to measures such as settling pit installation on all stormwater drainage bores. The analytical detection limits for copper, chromium and zinc vary between the current monitoring sites, with more sensitive detection reported for site 6 using ICP-MS (0.001, 0.003 and 0.003 mg/L respectively) compared to samples from the pump using ICP (0.03, 0.03 and 0.01 mg/L respectively). The current detection limits would not allow peaks in chromium and copper, such as those observed in the 1990s, or breach of aquatic ecosystem guideline values to be identified.


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Figure 16 Lead trend in Blue Lake.

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pumpsite 5,6


Figure 17 Nickel trend in Blue Lake.


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(m

g/L

)pumpsite 6-surfacesite 6-20msite 6-40msite 6-60m

Drinking water guideline value 3 mg/LAquatic ecosystem target value 0.008-0.05 mg/L

Figure 18 Zinc trend in Blue Lake.

2.6. Trace organics Data for trace organic concentrations in Blue Lake is sparser than for the inorganic suite. In some cases, a specific chemical or group of chemicals has been monitored over a discrete time interval (e.g. cyclohexane hexachloride, phenols). Stormwater recharge is known to introduce total petroleum hydrocarbons and polycyclic aromatic hydrocarbons to the groundwater. However these species have very low mobility and are generally degradable, and thus are not likely to reach the Blue Lake.

Pesticides can also enter the groundwater though stormwater recharge in urban areas, along with infiltration in rural areas. Pesticides can be quite mobile, but are generally susceptible to degradation. Thus the likelihood of pesticide migration to Blue Lake will depend on the specific chemical used and the residence time within the aquifer.

Analyses for a suite of pesticides, including atrazine and simazine, are available for the Blue Lake quarterly since 1997 (n=53). In all cases the concentration are reported at or below the analytical detection limit, predominantly 0.5 μg/L. The current ADWG for atrazine is 0.1 μg/L, which suggests a more sensitive detection should be sought.

Of 140 pesticide samples collected from the unconfined aquifer there were five instances where atrazine exceeds 0.5 μg/L (Unit nos. 7022-0252 GAM21 and 7022-1538 GAM23 only), while simazine is consistently at or below 0.5 μg/L. Atrazine and simazine are mostly below 0.5 μg/L in Mount Gambier’s stormwater (65 of 75 samples), but peak concentrations of 12 and 5 μg/L respectively have been measured. Analysis of degradation by-products would prove useful in understanding the rate of attenuation within the aquifer.


2.7. Summary of water quality condition The major ion chemistry (examined for chloride, sodium, potassium and sulfate) in Blue Lake does not show any potential for breach of water quality guideline values. Australian Drinking Water Guidelines (ADWG) (NHMRC-NRMMC, 2004) for total dissolved solids (500 mg/L), chloride (250 mg/L), sodium (180 mg/L) and sulfate (250 mg/L) are adequate for the Blue Lake.

It is difficult to use major ion chemistry to quantify the water balance (ie stormwater contribution) due to the variability in groundwater signatures. The current understanding of the water balance is outlined in section 2.1.3.

The analytical methodology and detection limits should be consistent within the catchment. This applies to all sampling locations in Blue Lake, for the groundwater monitoring and also any monitoring for assessment of potential inputs. Currently, lower detection limits are available for Cu, Cr and Zn sampled from site 6 using ICP-MS (0.001, 0.003 and 0.003 mg/L respectively) compared to samples from the pump using ICP (0.03, 0.03 and 0.01 mg/L respectively). It is recommended that the more sensitive detection limit be chosen.

Trace metal and metalloids illustrate some historical peaks in concentration. However there is no evidence to suggest rising concentrations within Blue Lake. Recommended water quality targets are the ADWG for arsenic (0.007 mg/L), the ANZECC and ARMCANZ (2000) aquatic ecosystem target for boron (0.4 mg/L) and the SA EPA (2003) aquatic ecosystem targets for copper (0.01 mg/L), lead (0.005 mg/L), nickel (0.15 mg/L), and zinc (0.05 mg/L). The recommended water quality target for chromium is the lower of the two current detection limits, 0.003 mg/L.

Data regarding anthropogenic organic compounds in Blue Lake are rare. Thus it is recommended that any positive analytical detection warrants further investigation, including repeat sampling and analysis.

Currently, the 80th percentile nitrate concentration in Blue Lake (3.6 mg/L as N) exceeds the suggested ANZECC and ARMCANZ (2000) aquatic ecosystem targets, but is within the SA EPA (2003) value for total nitrogen (5 mg/L). Nitrate concentrations within the lake remain lower then the median groundwater concentration (9 mg/L as N) but are rising. In contrast, the total phosphorus concentrations in the lake are lower than all the possible target values, possibly limiting excessive biological activity. Setting conditional targets for nutrient concentrations in Blue Lake and groundwater in the capture zone relies on greater understanding of the inputs to the lake and the in-lake processes that may alter their concentrations. When aquatic ecosystem protection is the priority, it is essential to understand the critical nutrient loadings that can be tolerated. This is particularly relevant for limiting nutrients, where a marginal increase in input loading has the potential to alter the nutrient status of the system. Target condition values for nutrients are considered in more detail in section 2.

It is suggested that anomalous water quality data be verified at the time of receipt. This may be as simple as checking the result with the laboratory or may require repeat sampling and analysis. This would ensure that outliers (such as those observed for Cu and Cr) are genuine and can be used to support an improved understanding of anthropogenic effects on water quality.


3. SETTING AND APPLYING WATER QUALITY TARGETS The National Water Quality Management Strategy (ANZECC and ARMCANZ, 2000) provides a framework for setting and applying water quality targets via the following steps:

Defining the Primary Management Aims

Determining Water Quality Guidelines

Defining Water Quality Objectives

Monitoring/Assessment/Management Response.

Each step requires scientific and consultative inputs. This section formulates the scientific input for the framework.

The primary management aims are based on protecting the assumed environmental values for Blue Lake as follows:

Maintaining a supply of water fit for use after disinfection as a drinking water supply for Mount Gambier

Maintaining the annual colour change and clarity of the lake

Prevention of algal blooms.

3.1. In-lake processes affecting Blue Lake water quality A ‘Blue Lake In-lake Processes’ research workshop was held at CSIRO Waite campus 28-29 November, 2005 to develop a multidisciplinary understanding of the in-lake processes impacting on water quality. The outcomes of this workshop are presented in this section (2.1) with detailed meeting notes available in Appendix 1.

3.1.1. Light and its influence on the colour of Lakes

The colour of lakes is a function of a number of physical processes, including:

The amount of light impinging on the lake

The angle of the light impinging on the lake

The optical properties of the water.

The lake colour that we observe from the surface is primarily a function of how much light is back-scattered (see below) from the lake. In part, lakes often appear more ‘colourful’ in summer because:

More photons impinge on the lake surface

When the sun is higher in the sky, a lower proportion of photons are reflected from the lake surface and thus more can be back-scattered once in the lake.

The colour that will be preferentially back-scattered depends on the optical properties of the water. Water, solutes, phytoplankton and suspended particles tend to absorb and scatter light at different wavelengths. Most of the light that is absorbed is converted into heat (except for a small portion used in photosynthesis). Scattering of light is the ability of water, solutes, and particles to change the direction at which light is travelling. Pure water tends to scatter light in the blue range, small particles (such as CaCO3 crystals)


scatter light in the blue-green range and dissolved organic matter scatter in the yellow-brown range. At higher concentrations, suspended particles will tend to dominate the light absorption and scattering. Phytoplankton tend to give a green colour to lakes, suspended organic matter a yellow-green colour and mineral particles (clays, CaCO3 crystals) can give a white to yellow-brown colour.

3.1.2. Carbon, Nitrogen and Phosphorus cycles

To appreciate the potential for contaminant attenuation in Blue Lake, it is important to understand how the processes within Blue Lake operate and interact. Organic and inorganic carbon cycling will affect the aqueous chemistry of the lake and thus the conceptual diagram for carbon is presented in Figure 19. Conceptual diagrams for nitrogen and phosphorus, the parameters viewed as inherent for aquatic ecosystem protection, are presented in Figure 20-21. In these conceptual diagrams, ‘pumping’ refers to water abstraction and not to any naturally occurring physical process. The key processes in these cycles include algal uptake and recycling, mineral equilibrium, microbial cycling within the water column and at the sediment-water interface, and sedimentation. Estimates for components of these cycles are outlined in Table 5.

Collection of sediment cores from the lake bottom in conjunction with suspended sediment from within the lake indicates that carbon dioxide loss from the surface is the most significant component of the carbon cycle (Herczeg et al., 2003). Comparing the carbon flux measured in traps suspended at 15, 40 and 70m below the surface, with that accumulated in the sediment, indicates that 88 per cent of dissolved inorganic carbon (DIC) and 96 per cent of dissolved organic carbon (DOC) is recycled within the lake.

Quantification of the components of the nitrogen cycle indicates approximately 2 mg/L of N removal via in-lake processes, when compared to the groundwater inputs (Lamontagne and Herczeg, 2002). However, the pathways contributing to this removal have not been confirmed. Uncertainties in the N balance include determining the nitrogen species utilised for algal biomass production, measuring the difference between gross and net algal uptake and the subsequent removal through sedimentation. Also, the rates of denitrification and mineralisation of organic matter, likely to occur at the sediment-water interface, are unknown.

To date, the phosphorus cycle in Blue Lake has not been examined. It is accepted that P inputs from groundwater will remain low due to adsorption on the carbonate aquifer. Also in-lake algal uptake and precipitation of calcium phosphates serve as removal mechanisms. It is suspected that atmospheric deposition to the lake surface and erosion of the caldera could be significant sources of P to the lake, but these have not been quantified. While improbable, shock loadings of P to the lake (from spills, accelerated erosion, etc.) could pose a temporary water quality problem to the lake by fostering algal blooms.


Figure 19 Conceptual diagram for carbon (organic and inorganic) processes in Blue Lake. DIC=dissolved inorganic carbon, DOC=dissolved organic carbon, PIC=particulate inorganic carbon, POC=particulate organic carbon.

Figure 20 Conceptual diagram for nitrogen processes in Blue Lake. DON=dissolved organic nitrogen, PON=particulate organic nitrogen.


Figure 21 Conceptual diagram for phosphorus processes in Blue Lake. sol P=soluble phosphorus, part P=particulate phosphorus.

Table 5 Blue Lake water balance and estimated quantities of in-lake removal capacity.

Parameter Estimate Source Groundwater input 3.5-4.5x106 m3/yr Groundwater outflow 0-1 x106 m3/yr Precipitation 0.5x106 m3/yr Evaporation 0.7x106 m3/yr Pumping removal 3.6x106 m3/yr

Barr et al., 2000; Lamontagne and Herczeg, 2002; Herczeg et al., 2003; ongoing work DWLBC

Gaseous invasion inorganic C 217 t/yr Gaseous evasion inorganic C 388 t/yr Groundwater input inorganic C 346 t/yr Groundwater outflow inorganic C 28 t/yr Pumping removal inorganic C 139 t/yr Inorganic C to sediments 10.8 t/yr Organic C to sediments 2.2 t/yr

Herczeg et al., 2003

Precipitation input NO3-N 0.05 t/yr Groundwater input NO3-N 22 t/yr Groundwater outflow NO3-N 1-2 t/yr Pumping removal NO3-N ~10 t/yr Total in-lake removal NO3-N 8-10 t/yr

Lamontagne and Herczeg, 2002

In-lake N removal attributed to organic matter in sediments

0.22 t/yr estimated from OC (Herczeg et al., 2003) using C:N ratio of 10:1

In-lake P removal attributed to organic matter in sediments

0.02 t/yr estimated from OC (Herczeg et al., 2003) using C:P ratio of 100:1

t=tonne


0.6 0.62 0.64 0.66 0.68 0.70

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3.1.3. How Blue Lake works

Physical limnology

Currently, Blue Lake has a warm monomictic stratification regime, with the warm surface layer overturning once a year to mix the lake. In stratified lakes, the warm low density upper layer is known as the epilimnion, the gradient between the low density layer and a deeper high density layer is the thermocline or metalimnion, and the area below the thermocline is the hypolimnion. Nutrients and carbon dioxide that enter the lake in groundwater will accumulate in the hypolimnion and metalimnion when the lake is stratified. These high concentrations will be mixed with the epilimniotic water when the lake destratifies.

The temperature profiles from January 2004 to January 2005 (Figure 22) illustrate the commencement of stratification from September when the lake is well mixed through to the highly stratified condition in summer (shown for January). The surface layer depth is 10 to 15 m in spring and summer, with a slight deepening in late March to early April. Little vertical mixing occurs below the thermocline, although the lake appears to be well mixed horizontally throughout the year. Chemical stratification (inflow or the influence of chemical signatures from sub-units of the aquifer) is shown between 35 and 50 m below the lake surface (~ -24 to -39 m AHD) in the conductivity profiles and as small kinks in the temperature profiles. Inflow rises up and alters the conductivity profile in the 15 to 30 m depth range. It is believed that peak summer extraction will not alter the thickness of the surface layer as the sun’s heat will rapidly replace any heat that is removed through pumping.

Figure 22 Blue Lake conductivity and temperatures profiles with depth January 2004 to January 2005 (unpublished data from SA EPA and DWLBC).


Biology

The factors limiting phytoplankton primary production in lakes are:

Water column mixing and stratification

Grazing by zooplankton and sedimentation losses

Light environment

Nutrient availability.

Blue Lake is oligotrophic, or low in nutrients, with phosphorus thought to be the nutrient limiting algal biomass growth. Chlorophyll a concentrations are an indicator of phytoplankton or biomass abundance. Typically, oligotrophic lakes have concentrations less than 10 μg/L (Wetzel, 1983). Annually, the chlorophyll a concentration in Blue Lake is highest at the depth of groundwater entry (40 m), indicating this depth provides both an adequate nutrient supply from groundwater inflow and also light penetration from the lake’s surface (Figure 23). This depth could be the best tradeoff for phytoplankton in summer, between light and nutrient availability. There is also a seasonal trend in the surface layer chlorophyll a concentration, indicating the maximum primary production in winter when phosphorus is recycled from the bottom waters (July to August) and the minimum when the lake is stratified in spring/summer (November to January) (Telfer, 2000). In winter algae are dispersed through the mixed lake, while in summer algae are restricted to below the thermocline. Algal genera identified in Blue Lake include Closterium, Sunedra, Glenodinium and Surirella (Allison and Harvey, 1983).

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Figure 23 Annual cycling of Chlorophyll a in Blue Lake.

Chemistry

The mechanism for the annual colour change, from aqua in May through to October to a vibrant blue in December to March (summer), has been discussed by various researchers (Tamuly, 1970; Telfer, 2000; Turoczy, 2002). It is generally accepted that there is an annual calcite precipitation cycle (Figure 24), which has a role in clarifying the lake in around November, and precedes the colour change from aqua to blue. Such precipitation events are typical of hardwater bodies (Morse et al., 2003; Dittrich and Obst, 2004), which act to maintain equilibrium according to the following equation:


CO2 + H2O + CaCO3 Ca2+ + 2HCO3-

An important influence on the calcium carbonate equilibrium is the partial pressure of carbon dioxide (pCO2). An increase in pCO2 (and acidity) leads to carbonate dissolution, while conversely a decrease in pCO2 will induce oversaturation and then precipitation. Temperature and pressure also affect this process as gas solubility reduces under higher temperatures but increases under higher pressures. Thus it follows that higher pCO2 would be expected in the hypolimnion, which is cooler and under higher pressure than in the warm epilimnion. During stratification, the carbonate equilibrium reaction is expected to operate in both directions in response to vertical variability in the chemical environment through the profile.

In the Blue Lake, precipitation occurs in response to carbon dioxide evasion (diffusion to the atmosphere) from the warmer surface layer. Oversaturation can also occur in response to carbon dioxide consumption during primary production (Dittrich and Obst, 2004). However this does not appear to be a significant driver in Blue Lake as we see calcium precipitation in the surface layers when algal biomass production is low.

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Figure 24 Bicarbonate and calcium cycling in Blue Lake, shown for recent data (2001-2005).

Turoczy (2002) reported the highest calcium carbonate concentration within the lake in August, corresponding to a period of low clarity (Telfer, 2000). The lowest concentration of suspended calcium carbonate was in the summer blue period, when the lake clarity was highest. He also found the calcium carbonate concentration to peak after the lake had mixed (holomixis) and suggested this was due to an influx of calcium from redissolution of carbonate in the hypolimnion after remix. Calcium precipitation is potentially very important for water quality with the possibility for removal of both inorganic and organic chemicals, through coprecipitation (Figure 24). This process may be important in regulating contaminants entering Blue Lake via sorption in the organic phase (applicable to anthropogenic organic chemicals) or coprecipitation (inorganic chemicals). The coating visible on the calcite particles may also contain clays (Telfer, 2000), which have a high adsorption potential.


Figure 25 Scanning electron micrograph of 10 μm calcite crystals coated in organic material, including a diatom. Sample was collected in a sediment trap 15 m below the lake surface (Telfer, 2000).

Blue Lake water balance

The current understanding of the Blue Lake water balance is summarised in Table 5. Recent work (Li et al., 2000) has defined seven units within the Gambier Limestone aquifer. Units 1 through 5 are alternating aquifers and aquitards within the Green Point member, overlying the Camelback and Greenways members (Figure 26). However the extent of these units varies spatially and is controlled by an eastward dip in all units and extensive faulting. The Camelback unit outcrops to the northwest of Blue Lake, but as this dips additional overlying units are observed (J. Lawson, unpublished data). Lake inflow is believed to be, coincident with the dolomitic Camelback layer of the aquifer at around 50 m below the lake surface (-39 m AHD). The contribution of individual stratigraphic units to lake inflow is currently under investigation (J. Lawson, pers. comm.). To the south of Blue Lake, it is possible that U1 provides flow into Blue Lake, while the Camelback member shows outflow.

Figure 26 Recent stratigraphic assessment in the vicinity of the Blue Lake (Lawson and Hill, in press).


It has been estimated that up to 15 per cent of the annual groundwater inflow originates from the confined Dilwyn aquifer (Barr et al., 2000). However, this estimate does not consider the salinity variations within the unconfined aquifer. Due to the fault through Blue Lake, there is potential for underflow from the Gambier Limestone to the Dilwyn formation, which could then move upwards into Blue Lake. Contaminant inputs to Blue Lake will vary depending on the contribution to inflow from the unconfined and confined aquifers and also the stratigraphic units within the unconfined aquifer.

3.1.4. Summary of in-lake processes

The annual limnological, biological and chemical cycles are summarised in Table 6. From this, a simple explanation of how Blue Lake works has been formulated.

The water in Blue Lake is clear due to several important natural cleaning processes. Groundwater entering the lake is cleaned or ‘treated’ as it moves through the limestone aquifer. The aquifer removes organic matter, which can give water a yellow to brown stain. It also takes out phosphorus and this limits the amount of algae that is produced in the lake. In addition to this, the clear water in Blue Lake turns vibrant blue in summer for two reasons. Firstly, the higher position of the sun in summer than in winter means more light hits the surface of the lake. This also increases the blue light that can be scattered back out from the lake by small particles. Secondly, during spring, the surface of the lake warms, dissolved carbon dioxide is released, the pH increases and this water becomes over-saturated in calcite and this begins to precipitate out. Tiny calcite crystals form and as these fall down to the bottom of the lake they capture organic material, and clean the water. Each year a new layer of calcite about 3 mm thick and organic material 1 mm thick settles on the bottom of the 70 m deep lake. By summer the lake is stratified with its warmest water in the top 15 m and the coolest at the bottom, below 50 m, and the lake looks its bluest. The highest algal concentrations are found 40 to 50 m below the surface, suggesting this depth provides the optimum balance between their light and nutrient requirements. Towards autumn gradual cooling of the surface water triggers deeper mixing bringing water with a high dissolved carbon dioxide concentration to the surface where it is released and a second round of calcite precipitation and cleaning occurs. Further deepening and cooling of the surface layer causes calcite precipitation rates to reduce, leading to a lower clarity and the colour change from vibrant blue to aqua. By August the whole lake is well mixed and the temperature is uniform throughout. Then the cycle begins again. On average over an annual cycle, nitrate-N concentration is reduced relative to groundwater inputs by 2 mg/L and dissolved inorganic carbon (DIC) by 30 mg/L.

In relation to protecting aquatic ecosystems, it is known that passage through the limestone aquifer ensures phosphorus inputs are low in normal inflows to Blue Lake. However, there are many unknowns in the N, P, OC balances, including the effects of caldera management (erosion) on P inputs and in-lake recycling of P. Other unknowns include the origin of and age distribution of water entering lake and changes in in-lake processes since European settlement.


Table 6 Annual limnological, biological and chemical observations in Blue Lake.

Physical limnology Biology Chemistry

Jul Algal biomass production at maximum, algae dispersed

Uniform chemical profiles through water column

Aug Lake completely mixed Highest suspended CaCO3 due to resuspension

Sep Warmer weather brings onset of stratification

Oct 10-15m warm surface layer, little mixing below thermocline

Nov Algal biomass production at minimum

Calcite precipitation begins, milky colouration at edges of lake

Dec High clarity

Calcite precipitation due to enhanced CO2 evasion from warm surface layer, highest flux of sediments, CaCO3 and organic C

Jan 10-15m warm surface layer

Summer calcite precipitation at surface with subsequent dissolution in the water column due to higher pCO2

Feb Algae restricted below thermocline when stratified

Mar Surface layer deepens slightly Second peak in CaCO3 production as deeper mixing brings supersaturated water to the surface

Apr

May

Cooling of lake surface in early winter causes deepening of mixed surface layer, clarity reduction

CaCO3 precipitation low

Jun


3.2. Alternative extraction scenarios It has been identified that a protection measure for the water quality in the Blue Lake is the potential attenuation capacity of the unconfined aquifer. Additional protection could also be provided by increasing the residence time of the groundwater in the aquifer matrix before it enters the Blue Lake. By reducing the volume of water extracted from the Blue Lake the residence time within the aquifer and the lake itself may possibly be increased. However it is unclear if the decreases in lake level are also increasing the hydraulic gradient towards the lake

The main objective for considering alternative sources of water supply to Mount Gambier is to assess the benefits for protecting water quality by altering the location of the extraction of the municipal water supply. This is based on the principle that the extraction of water from the Blue Lake is decreasing the residence time of the groundwater in the aquifer. There has been no conclusive information to indicate that the extraction of the water from the Blue Lake is inducing the flow of contaminants towards the lake.

Regionally, groundwater levels in the unconfined aquifer have been influenced by factors such as climate change, groundwater extraction, land clearance and urbanisation. The knowledge about the relationship of each of these factors to groundwater levels is important. Thus a specific research project is being undertaken to try and separate the effects of climate change from anthropogenic influences on the water levels in the Blue Lake, using a continuous time series model (H. King, pers. comm.).

A preliminary review of the alternative sources of potable water supply to Mount Gambier indicates that the sources of highest priority for further examination are continued extraction from the unconfined aquifer, directly or via Blue Lake and extraction from the confined aquifer (Table 7). Surface water sources are limited by the expense associated with infrastructure and while indirect stormwater reuse is currently in operation, direct reuse (without aquifer storage) would also require new infrastructure.

Table 7 Summary of preliminary review of potential sources for town water supply in Mount Gambier.

Potential source Issues Priority

Unconfined aquifer (via Blue Lake)

Declining water level Future water quality

High

Unconfined aquifer (not via Blue Lake)

Allocations Water protection area no longer appears in council development plan

High

Confined aquifer Allocations Sustainability of extraction

High

Eight Mile Creek Infrastructure expensive Extraction may have undesirable impacts on groundwater dependent ecosystem (ie saline intrusion)

Low

River Murray Infrastructure expensive Low Glenelg River Infrastructure expensive

Currently resource is stressed and no abstractions allowed Low

Stormwater reuse Direct reuse requires new infrastructure as current system is based on flood protection Not a new source, indirect reuse already occurs via Blue Lake

Low


3.3. Target condition values

3.3.1. Targets

From the evaluation of existing water quality data for the Blue Lake and its groundwater system (section 1), it was evident that existing water quality guideline values such as those in the Australian Drinking Water Guidelines (NHMRC–NRMMC, 2004) could be adopted for some parameters, but others such as nutrients require targets to be set. It is necessary that these target values reflect the intended state of the Blue Lake in order to ensure that the environmental values discussed at the start of this section are achieved and will continue to be achieved in the foreseeable future (Table 8).

Table 8 Targets indicators and measurements proposed for Blue Lake and its groundwater.

Target Indicator Measurement

1. Maintain a factor of safety on drinking water guidelines (aside from pathogens) so that action can be effective in time if monitoring shows undesirable trends.

Pumped water quality meets all NWQMS drinking water quality criteria (aside from pathogens) including a factor of safety (annual mean concentrations <80th %ile of historical values).

SA Water sampling methods, frequency and analytes as required by SA Department of Health. Changes to reporting required.

2. Maintain nutrient levels in Blue Lake within or lower than the current range of concentrations (that have been shown to support the above environmental values).

Annual mean [TP] <80th %ile of historical values (0.02 mg/L). Increase in mean [NO3

- ] <10% over a 5 year interval. [NO3

-]1997=3.5 mg/L [NO3-]2002= 3.4

mg/L. Annual mean [DOC] <80th %ile of historical values (1.3 mg/L).

Key nutrients are measured by SA Water monthly from pump pontoon and EPA 4 monthly from site 6 (4 depths). Changes to reporting required.

3. Maintain or improve groundwater quality on the perimeter of the lake and in specific locations associated with contaminant sources that may adversely affect future achievement of target values, so that management can be effective before targets are infringed.

Annual mean concentrations <80th %ile of historical values. Increase in mean [NO3

-] <10% over a 5 year interval.

EPA to monitor selected wells in aquifer units considered to replenish BL and to represent different land management in the BL g/w catchment. Changes to reporting required. A review of the current g/w program is recommended (analytes, location, frequency).

4. Maintain lake in oligotrophic state. Maintain biotic species and numbers within lake within range pertaining to targets 1 and 2.

Chlorophyll a <5 μg/L (based on current data and ANZECC and ARMCANZ, 2000).

Chl a: SA Water monthly from pump pontoon and EPA 4 monthly from site 6 (4 depths). Changes to reporting required. New program required to obtain baseline data for algal counts and phytoplankton speciation.

5. No acceleration in decline in lake level. No target has yet been set for maximum annual pumping volume or minimum desirable lake level.

Decline in lake level <10% of depth over a 10 year period. Lower limit for lake level and groundwater level for long-term needs to be set (e.g. >0 m AHD).

SA Water continues to record lake levels and pumping. In addition DWLBC continually record lake level. Existing program is adequate.


Indicators reflect whether the target has been met. Failure of an indicator should trigger a review of the data, and repeated failure of an indicator suggests initiation of a study to evaluate the cause of the decline in quality, its potential longevity, means of resolution and management responses. Measurement suggests who would take the measurements which would be used to form the indicators. In all cases, the 80th percentile of historical water quality is used as the upper bound for the target value.

Currently there is no data on algal counts for Blue Lake and thus it is not possible to set an indicator for noting change in biotic numbers (target 4). A new program is required to set a baseline for future comparison of algal speciation and numbers.

3.3.2. Prioritising unknowns regarding in-lake processes

The condition of the lake has been studied extensively but the natural attenuation processes for various contaminants that reach the lake are currently not well understood. Contaminant sources in the Blue Lake catchment are mitigated by land and water management, residuals are conveyed to Blue Lake via aquifers which may provide further attenuation, and finally in Blue Lake natural processes may further reduce contaminant concentrations. As a final treatment step, water extracted from the lake for public water supply is disinfected at the SA Water chlorination plant.

In the context of managing risks to the environmental values of the lake, the in-lake processes play only a relatively small role in water treatment. However this may be a very important role, especially if the lake were to be perturbed so that the current attenuating processes no longer occurred or the aquatic ecosystem, geochemistry, or even limnology became unstable and the future water quality could then deteriorate unpredictably.

A qualitative assessment of the short- and long-term risk to the environmental value of Blue Lake was undertaken for a range of water quality issues (Appendix 1). Nitrate was considered a medium risk over the long-term due to the rising concentrations in Blue Lake. However agricultural land use management, and the resultant nitrogen loadings to the aquifer, is a greater influence on the nitrate concentration in Blue Lake than the role of in-lake processes. In-lake processes may be significant in regulating the risk from water quality issues due to anthropogenic organic chemicals, metals, or an algal bloom and thus enables the importance of addressing unknowns regarding in-lake processes to be ranked (Table 9). Rather than break this down to individual processes, this has been expressed in relation to the various nutrient or water cycles and balances affecting lake behaviour and water quality.

Consequently a study of in-lake treatment processes (section 4) was designed to understand the removal of inorganic chemicals (nutrients, metals and metalloids) during the annual calcite precipitation cycle. This included sampling and analysis of sediments in the water-column and from the lake bottom to assess recycling at the sediment-water interface and accumulation on the lake floor. While this study addresses some of the moderate-high priority unknowns regarding in-lake processes, a number of knowledge gaps remain.


Table 9 Prioritising unknowns regarding in-lake processes and future water quality for Blue Lake.

Unknown Effects Why important Relative priority

P balance components and processes

Ecosystem, colour P is limiting nutrient for algae in Blue Lake

High

Water balance Loadings to lake Volumes from each aquifer (Greenpoint units, Camelback and unknown) and changes in Dilwyn contribution unknown. Source areas not yet well defined. Lake outflows unknown.

High Some aspects covered in Blue Lake A project. Gaps will require new project.

Nutrient cycling processes at the sediment-water interface

Redox status, metals, organics, nutrients

Field and laboratory experiments are required to quantify the C, N and P biogeochemical processes at the sediment-water interface.

High

C balance components and processes

Colour Calcite precipitation strips organics and metals from water column

Moderate

Inputs of metals and anthropogenic organics

Accumulation in sediments on lake floor

Possibilities for inferring loadings and travel times from contaminant sources in catchment and to indicate the possibility for remobilisation, which will assist with the water balance.

Moderate

Biological communities

Algal species Not a priority problem but monitoring now will set up good benchmarks for the future assessment of this indicator (as required for target 4).

Moderate

N balance components and processes

Drinking, (minor ecosystem effects)

Trending upwards slowly, at almost 50% of 11mg/L guideline value for infants, forestry and more intensive agriculture so continued increase likely

Low

Future status of processes P, N, C

Algal communities and colour

Stability limits of algal systems defined, but unlikely to be of value unless a spill and shock loadings occur

Low

3.4. Summary of water quality targets Existing water quality guidelines are appropriate for monitoring major ions and metals in Blue Lake. However, it is recommended that provision be made in the monitoring programmes to identify deviations from current trends (based on the 80th percentile of historical data), so that they can be verified promptly.

Targets have been proposed to manage nutrient concentrations in Blue Lake. These will allow identification of any alteration in trends in nutrient concentrations in the lake, which will allow the cause/s of any change to be determined and appropriate action decided upon. However a new program is required to set a baseline regarding the algal numbers and speciation within the lake.

Concurrently reviewing the in-lake processes and the associated uncertainties has allowed the future research focus to be targeted to priority tasks. The priority knowledge gaps were deemed to be the understanding of the local hydrostratigraphy, the phosphorus cycle and nutrient cycling at the sediment-water interface. Treatment


provided by the annual calcite precipitation contributes to the understanding of nutrient cycling and the phosphorus cycle and is addressed within this project. The remaining knowledge gaps require additional programs.

In summary, the main recommendations and the agency responsible are:

Lower detection limits for analysis of Cu, Cr and Zn in samples collected from the pump, to 0.001, 0.003 and 0.003 mg/L respectively (SA Water)

Change reporting for water quality data, to include comparison to 80th percentile of historical concentrations for all parameters and more detailed quantification of change for key parameters (SA Water, SA EPA, DWLBC)

Review groundwater monitoring program as new information arises from hydrostratigraphy work (DWLBC)

Develop new program to obtain baseline data regarding algal counts and phytoplankton speciation in Blue Lake (SA Water/SA EPA).

4. ATTENUATION STUDIES Field studies were undertaken to understand the fate of potential hazards in the aquifer and Blue Lake by developing the current understanding of the travel times in the aquifer and the potential for in-lake treatment processes. Travel time estimates were based predominantly on a sulfur hexafluoride (SF6) tracer test with some assessment of chemical signatures that may indicate residence time. In-lake treatment processes were evaluated by determining the composition of sediments collected in the water column and from the lake floor.

This work contributes to objective 5 to ‘define pathways for contamination to reach Blue Lake and the potential mechanisms for attenuation within the capture zone’, which provides the necessary input data for the risk assessment.

4.1. Attenuation studies methodology

4.1.1. Travel time estimates

Sulfur hexafluoride (SF6)

The regional hydraulic gradient in the Mount Gambier area is to the south-west, but it is very low in the city area (~0.00014) with localised reversal of the flow direction reported (Lawson et al., 1993; Telfer, 1999). Karst features are oriented in the north-west to south-east direction (Lawson et al., 1993). Migration through these karst features provides an opportunity for contaminants to move quickly to the Blue Lake. However the degree of connection between fractures themselves and of the fracture network with the Blue Lake is not known.

Flow into the Blue Lake is believed to be via the Camelback member of the Gambier Limestone unconfined aquifer and the top of this unit is located at approximately 50 m below the lake level (-39 m AHD). There are few observation bores completed in the dolomitic unit only, thus hydraulic data to examine flow in this unit is limited. Downhole flow metering indicated the majority of flow in a 0.5 m thick interval tens of metres below the water table but details of the bore locations were not given (Telfer and Emmett, 1994).

Sulfur hexafluoride (SF6) was injected into 24 bores situated 1-3 km on the northern side of Blue Lake in August 2005 (Table 10; Figure 27). While some injection sites were located in the direction of regional groundwater flow, the majority of injection


sites were within a zone oriented in the NW to SE direction to enhance the opportunity for observing migration through preferential flow paths (J. Lawson, unpublished data). The injection bores consisted of 22 stormwater drainage bores and 2 groundwater observation bores, and were predominantly completed in the Camelback member.

The SF6 tracer solution was prepared in the field by recirculating approximately 400 L of water from a rainwater tank through a gas mixing tube, where SF6 was bubbled into the water (Figure 28). The 400 L of SF6 tagged water was gravity fed into the injection bore and then followed by 300-600 L of water to push the tracer into the aquifer. The injected concentrations were determined from the average of duplicate samples taken during the discharge of tracer into the bore (start, mid, end). Between 1.0-2.4x10-2 mol of SF6 was injected into each injection location (Table 11). A minimum of 15 per cent of tracer from an individual injection well would need to reach the Blue Lake to achieve a SF6 concentration that could be measured, a scenario that is most likely for preferential flow through karst features.

Figure 27 Approximate location of sulfur hexafluoride (SF6) injection bores in relation to the location of Blue Lake, the zone of ‘karst influence’ (Lawson, unpublished data) expected to impact on Blue Lake from flow through karst features and the regional groundwater flow direction.

SF6 injection Karst influence Drainage bore

Regional GW flow

N

1 km

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Table 10 Injection locations used for the sulfur hexafluoride (SF6) tracer test.

City of Mount Gambier (CoMG) stormwater drainage network

DWLBC observation bore

Unit No Easting Northing Approx depth

Location Re-sampled Aug 07

Bore no Catchment no 7022- (m)

298 324 8199 478622 5813988 43 Commercial St West Yes

151 328 2976 478865 5813638 49 White Ave opposite Ritana Rd Yes

220 319 5665 479333 5813763 50 Charles St Yes

19 333 2851 479498 5813507 52 corner Thurston St and Brown Rd Yes

317 427 6992 479296 5813102 67 Webb St Yes

141 357 0926 479105 5813037 80 corner Kalimna Ave and Shepherdson Rd Yes

376 355 8698 479605 5812885 75 Earl St Yes, hydrocarbon evident

123 365 2964 479995 5813005 87 Wehl St South Yes

366 377 1992 479960 5813500 49 Commercial St West Yes

180 379 4445 479728 5813705 42 Ellis St Yes

56 313 1958 479538 5813995 45 Umpherston St No, sealed with bitumen

210 47 5652 481265 5812358 89 Boandik Terrace Yes

364 63 8116 481017 5812467 88 Crouch St South Yes

246 117 1454 481585 5813180 76 Byrne St Yes

102 408 1447 481026 5813686 71 Frew Park Yes

195 416 5651 480232 5813675 53 Wehl St South Yes

29 84 1460 481665 5812835 87 corner Davison St and Commercial St East Yes

276 39 6632 480578 5812344 88 corner Ferrers St and Gwendoline St Yes

252 316 6584 478750 5813200 76 Sheperdson Rd Hastings Reserve Yes, bitumen evident

239 66 6091 481091 5812617 71 Heriot St Yes

114 101 1479 481190 5812655 78 corner Tandara St and Harrald St Yes

SGIC‡ 69 3685 480495 5812930 96 SGIC carpark No, cars parked over access

BLA156 7725 481605 5812567 96 Sturt St Yes

BLA164 6998 478075 5814258 35 Commercial St West Yes ‡ CoMG drainage bore no unknown


Figure 28 Mobile apparatus used to prepare the sulfur hexafluoride (SF6) tracer prior to discharge of tracer into bores.

Table 11 Concentration and total mass of sulfur hexafluoride (SF6) discharged into the injection bores.

Injection Resampling Aug-07

Bore no SF6 (pmol/cm3) % saturation*

SF6 mass injected

SF6 concentration‡ SF6 mass recovered

concentration stdev (mol)† (pmol/cm3) (mol)†

298 5.27E+04 9.43E+03 17.6 2.1E-02 2.87E-04 9.2E-10

151 3.64E+04 6.70E+03 12.1 1.5E-02 7.99E-03 3.2E-08

220 4.53E+04 1.09E+04 15.1 1.8E-02 1.39E-03 6.0E-09

19 5.70E+04 6.44E+03 19.0 2.3E-02 1.25E-02 1.4E-07

317 3.34E+04 4.46E+03 11.1 1.3E-02 8.99E-04 5.3E-09

141 4.33E+04 5.04E+03 14.4 1.7E-02 1.18E-03 8.6E-09 376 5.49E+04 2.75E+03 18.3 2.2E-02 9.16E-04 7.2E-09

123 4.53E+04 4.81E+03 15.1 1.8E-02 <1E-04 nd

366 3.85E+04 3.97E+03 12.8 1.5E-02 1.39E-03 5.2E-09

180 4.01E+04 3.97E+03 13.4 1.6E-02 2.25E-03 9.3E-09

56 5.98E+04 1.05E+03 19.9 2.4E-02 nd nd

210 3.15E+04 3.29E+03 10.5 1.3E-02 <1E-04 nd

364 3.21E+04 1.16E+03 10.7 1.3E-02 1.64E-04 1.1E-09

246 2.51E+04 1.37E+03 8.4 1.0E-02 1.46E-04 8.5E-10

102 3.50E+04 1.02E+03 11.7 1.4E-02 <1E-04 nd

195 2.84E+04 9.23E+02 9.5 1.1E-02 2.57E-03 1.1E-08

29 3.53E+04 9.61E+03 11.8 1.4E-02 1.29E-04 7.9E-10

276 3.94E+04 4.98E+03 13.1 1.6E-02 3.42E-04 2.3E-09

252 5.29E+04 9.47E+03 17.6 2.1E-02 3.46E-04 2.0E-09

239 2.54E+04 2.38E+03 8.5 1.0E-02 1.05E-01 6.1E-07

114 3.64E+04 3.28E+03 12.1 1.5E-02 3.74E-03 2.3E-08

SGIC 3.43E+04 7.40E+03 11.4 1.4E-02 nd nd

BLA156 3.80E+04 1.56E+03 12.7 1.5E-02 4.96E-03 1.8E-06

BLA164 4.02E+04 2.24E+03 13.4 1.6E-02 1.30E-03 1.2E-08 *based on saturation=3E-4 mol/dm3; †based on ~400 L of injection; ‡after well purged; nd=not determined


The program to monitor the migration of SF6 in the aquifer consisted of monitoring in the Blue Lake and in the groundwater of the Gambier Limestone unconfined aquifer. Water samples were collected from the Blue Lake at monthly intervals from a site in the centre of the lake (site 6) at 4 depths (surface, 20 m, 40 m, 60 m below the surface) and at weekly intervals from the pump pontoon (approximately 5 m below the surface) from September 2005 (~260 samples). SF6 analysis was undertaken by Gas Chromatography at CSIRO Land and Water Adelaide, with a detection limit of approximately 10-13 mol/L (10-4 pmol/cm3). Additional monitoring was undertaken at 3 depths (8 m, 40 m, 60 m) at 4 sites along the northern side and 1 in the south-western corner in October 2008. Quality control included sending a selection of samples (~20) for analysis at the University of California to a lower detection limit of 5x10-14 mol/L (5x10-5 pmol/cm3).

Groundwater was sampled for SF6 analysis during the DWLBC annual monitoring programs in early 2006 and 2007 (6 and 18 months after injection); and in conjunction with sampling events in October 2006 and August 2007 (Table 12). Groundwater from twenty-two of the injection sites was sampled 2 years after injection, in August 2007, to examine the migration of the tracer from the injection site. These samples were collected over a time series (~ 5 minute intervals) from the commencement of pumping until at least 3 well volumes had been purged. Electrical conductivity was recorded during sampling. Two of the injection sites could not be accessed during the August 2007 sampling event.

Table 12 Program of monitoring sulfur hexafluoride (SF6) in the groundwater of the Gambier Limestone unconfined aquifer.

Location Feb-06 Oct-06 Jan/Feb-07 Aug-07

DWLBC sampling Sampling trace organics DWLBC sampling Re-sampling inj. sites

BLA006 9/02/2006 1/02/2007

BLA008 7/02/2006 23/01/2007

BLA017 9/02/2006 5/02/2007

BLA018 7/02/2006 9/10/2006

BLA020 7/02/2006 23/01/2007

BLA042 2/02/2006 1/02/2007

BLA076 6/02/2006 22/01/2007

BLA082 6/08/2007

BLA114 9/02/2006 24/01/2007

BLA134 2/02/2006 23/01/2007

BLA143 2/02/2006

BLA154 9/10/2006

BLA155 2/02/2006 1/02/2007

BLA160 6/02/2006

BLA162 2/02/2006 1/02/2007 15/08/2007

BLA165 9/02/2006 15/08/2007

BLA169 15/08/2007

BLA170 2/02/2006 24/01/2007

BLA171 6/02/2006

BLA178 7/02/2006 15/08/2007

BLA179 7/02/2006 6/08/2007

GAM008 1/02/2006 23/01/2007

GAM009 7/02/2006 22/01/2007

GAM021 7/02/2006 22/01/2007

GAM023 1/02/2006

GAM060 7/02/2006 24/01/2007

GAM112 6/02/2006

GAM252 15/08/2007

GAM254 6/02/2006


Trace organic chemicals

Trace organic chemicals have been used to identify the presence of human wastewater contamination in environmental samples (Glassmeyer et al., 2005; Drewes et al., 2008) owing to their potential to persist in the environment over long time scales and to be detected at low concentrations (ng/L and below). In addition, some chemicals can be attributed to a time of use, which suggests they may be used as potential indicators of residence time since discharge into the groundwater system. The utility of trace organic chemicals as ‘time tracers’ was investigated during May 2005 and October 2006, by screening a small number of water samples for a suite of organic chemicals of varying origin (Appendix 1). This screening was undertaken when trace organic analysis was available through additional projects.

Blue Lake was sampled in May 2005 for trace organic analysis to ng/L at the Southern Nevada Water Authority (SNWA). This was followed in October 2006 with samples of Mount Gambier’s wastewater, Blue Lake and two groundwater bores (BLA018 and BLA154) suspected to be impacted by sewage effluent and industrial waste respectively also analysed at SNWA.

An approximate time-line of development in Mount Gambier that may have impacted on the water quality of Blue Lake and the surrounding groundwater can be found in Appendix 2.

4.1.2. In-lake treatment processes

Sediment traps

Sediment traps (100 mm diameter) were installed in the Blue Lake at depths of 15 m, 40 m and 70 m below the surface according to the method used by Telfer (2000) (Figure 29). This allows collection of material settling from the summer epilimnion (15 m), the base of the photic zone (40 m) and reaching the base of the lake (70 m) (Telfer 2000). Sediment was collected in 8 intervals between 11/10/06 and 18/10/07.

The sediment collected from each depth interval was analysed by CSIRO Land and Water Laboratories, Adelaide for B, Fe and P with detection limits of 10-20, 20 and 10 mg/kg respectively; As, Cr, Cu, Mn, Ni, Pb, and Zn with a detection limit of 0.1 mg/kg for all species by ICP-OES and ICP-MS; and inorganic C by calibrated manometry, measuring the volume of carbon dioxide evolved by reaction with hydrochloric acid (HCl) with an approximate detection limit of 5 % as CO3.

Figure 29 Sampling apparatus to collect particulates within Blue Lake (Telfer 2000).

Lake core sampling

Core samples were collected from the Blue Lake floor by a dive team (Dive Leader Grant Pearce, DWLBC) on 29 March 2008. The core samples were collected by hand by pushing 60-100 mm diameter PVC tubes into the lake bottom and then capping both ends (Figure 30). Care was taken to keep the cores upright and minimise disturbance of the sediment samples during sampling and


retrieval from the lake. Six cores were collected in total, with three cores collected from two locations in the lake, either in the centre (CL) at a depth of 72 m or on the northern edge (NL) at a depth of 65 m. The visibility at the bottom of the lake varied greatly between the two locations; with greater visibility on the northern edge (G. Pearce, pers. comm.). Core samples were collected at a radius of 10, 20 or 30 m from the line of descent (Table 13).

Figure 30 Grant Pearce collects sediment cores from the base of Blue Lake on 29/3/08 (photo Dr Richard Harris; ABC South East SA, 2008 http://www.abc.net.au/local/stories/2008/04/03/2207124.htm).

Table 13 Details of the six core samples collected from the base of Blue Lake on 29/3/08 and sub-sampled for analysis.

Site description Core ID Diameter (mm) Total length (mm) No. sub-samples Northern wall NL10 60 260 35 10, 20, 30m from NL20 60 240 35 the line of descent NL30 100 260 39 Centre of lake CL10 60 285 43 10, 20, 30m from CL20 60 285 45 the line of descent CL30 60 225 33

The cores were sectioned based on visual changes in colour and texture and samples from one of each set of three cores (CL10 and NL10) were submitted for elemental analysis (n=78) and dating (n=37) analyses at CSIRO laboratories.

The core sample sediment was analysed at CSIRO Land and Water laboratories, Adelaide for moisture content by gravimetry; Al, Fe and P with detection limits of 20, 20 and 10 mg/kg respectively; As, B, Cd, Cr, Cu, Mn, Ni, Pb, and Zn with a detection limit of 0.1 mg/kg for all species by ICP-OES and ICP-MS; inorganic C by measurement of carbon dioxide evolved by reaction with hydrochloric acid (HCl) with a detection limit of 0.1 %; organic C and organic N by high temperature combustion following removal of inorganic C with detection limits of 1 % and 0.1 % respectively.


210Pb dating of sediment cores was analysed by gamma spectrometry at the CSIRO Land and Water Laboratories, Canberra.

4.2. Attenuation studies results

4.2.1. Travel time estimates

Sulfur hexafluoride (SF6)

The SF6 monitoring program in Blue Lake, on a weekly basis from the lake’s surface and on a monthly basis at four depths in the centre of the lake, indicated that SF6 reached Blue Lake after approximately 2 years. Samples of Blue Lake collected since August 2007 show very low levels of SF6, approximately 2x10-4 pmol/cm3, marginally higher than the analytical detection limit. Following this, approximately 40 per cent of samples from Blue Lake collected between August 2007 and October 2008 had SF6 concentrations between 10-4 and 1.5x10-3 pmol/cm3. Movement from any of the injection sites to Blue Lake in 2 years indicates a groundwater flow velocity of 0.5-1.5 km/year through karstic flow.

Re-sampling the injection bores provided varying results with concentrations after the injection site was purged (3 well volumes) varying from <10-4 to 0.1 pmol/cm3 (bore no. 29; Table 11), but predominantly around 1x10-3 pmol/cm3. The highest SF6 concentration, of 28 pmol/cm3, was sampled from BLA156 at the commencement of pumping and rapidly reduced to 5x10-3 pmol/cm3

when three well volumes had been extracted. A simple approximation, calculating the SF6 concentration that would result if the total amount of tracer was diluted by the volume of water within the aquifer, produced concentrations around 0.6-5 x10-3 pmol/cm3 (based on a porosity of 0.1-0.25 and an aquifer thickness of 30-100 m). While the SF6 concentration remaining in the injection bores is comparable to the estimate resulting from dilution in the aquifer, SF6 was not measured in all samples of groundwater taken, indicating the tracer has not been evenly dispersed through the aquifer. The range of residual SF6 concentrations remaining in the injection sites after 2 years indicates there is considerable variability in the volume of water each bore discharges as would be expected given the range in catchment area for each bore (1-58 ha). The SF6 concentration remaining in BLA164 was an order of magnitude lower than in BLA156 despite starting with similar injected concentrations. As these bores do not receive stormwater discharge, the SF6 concentration is altered by local groundwater flow and illustrates the variable nature of groundwater movement in the karstic aquifer.

Trace organic chemicals

A suite of over 20 organic chemicals was detected within Mount Gambier’s wastewater, which was sampled adjacent to the hospital to increase the likelihood for detection of pharmaceuticals. However there was little detection of organic chemicals in samples taken from the groundwater or Blue Lake (Appendix 4).

An atrazine concentration of 7 ng/L was detected in Blue Lake (measured in samples collected in May 2005 and October 2006). This lies within the range of concentrations found in two groundwater samples (0.33 and 26 ng/L) and Mount Gambier’s wastewater (38 ng/L) in October 2006 but is far below the detection limit of 500 ng/L commonly reported for atrazine in environmental samples and also below the Australian drinking water quality guideline value of 100 ng/L (NHMRC-NRMMC, 2004). Fluoranthene, one of the three polycyclic aromatic hydrocarbon (PAH) species previously reported in Mount Gambier’s stormwater was present in Blue Lake at 6.1 ng/L (May 2005), similar to the stormwater concentrations of 2.3-6.7 ng/L (n=4) reported with passive samplers (Komarova et al., 2005). Caffeine was also measured at a concentration of 37 ng/L, consistent with previously reported environmental samples such as drinking water (12 ng/L) sourced from surface water in the USA (Trenholm et al., 2006). Iopromide was not detected in the sample collected from the Blue Lake in October 2006, despite a previous detection at 12-34 ng/L (Wolf et al., 2006). Bisphenol A and nonyphenol were present in the groundwater samples and


sulfamethoxazole was present in BLA154 only. Due to the lack of detections within Blue Lake, trace organic chemicals were not used as indicators of residence time in this system.

4.2.2. In-lake treatment processes

Sediment traps

The sediment traps indicated similar particulate matter settling rates at 3 depths in Blue Lake, from 2-27 mg/d at 15 m, 1-31 mg/d at 40 m and 2-26 mg/d at 70 m (Table 14; Figure 31). The settling rates were highest in the warmer months (October-April) and lowest in the cooler period of the year (May-October), with the April-May samples illustrating a transition between the two periods. The particulates collected in the traps comprised 30 to 62 per cent carbonate (Figure 32), with the lowest carbonate contribution during winter coincident with the lower settling rates.

Table 14 Mass of sediment collected in traps 15 m, 40 m, 70 m below the surface of Blue Lake and the calculated rate of settling of particulate matter through the water column.

Sample name

Collection interval Days 15 m collection trap 40 m collection trap 70 m collection trap

Mass (mg)

Rate (mg/day)

Mass (mg)

Rate (mg/day)

Mass (mg)

Rate (mg/day)

Nov-06 11/10/2006-23/11/2006

43 654 15.2 769 17.9 680 15.8

Dec-06 23-11/2006-10/1/2007

48 1155 24.1 1477 30.8 1269 26.4

Feb-07 10/1/2007-28/2/2007

49 1323 27.0 1180 24.1 957 19.5

Mar-07 28/2/2007-16/4/2007

47 992 21.1 1337 28.5 na na

May-07 16/4/2007-29/5/2007

43 482 11.2 368 8.6 411 9.6

Jun-07 29/5/2007-18/7/2007

50 212 4.2 131 2.6 208 4.2

Aug-07 18/7/2007-30/8/2007

43 189 4.4 77 1.8 93 2.2

Sep-07 30/8/2007-18/10/2007

49 99 2.0 51 1.0 86 1.8

Due to low mass recovered from each depth in the Jun07, Aug07 and Sep07 sediment traps, these three sampling intervals were combined for chemical analysis and are discussed collectively as the the ‘winter’ sampling interval. Most of the inorganic chemicals quantified within the water column sediment (As, Cr, Cu, Fe, Mn, Ni, P, Zn) exhibited their highest concentration during winter, when carbonate settling was low and organic matter was dominant (Table 15). In contrast, the lead concentration was highest in the Nov06 sample (October-November). While boron was highest in the Feb07 sample, variable detection limits make it difficult to link this to the rate of carbonate production. While the concentration data suggests the inorganic species are predominantly associated with organic matter, the settling flux was governed by the carbonate cycle and was greatest during the warmer months (Figure 32). Thus, the annual carbonate precipitation cycle provides the mechanism to remove inorganic species from the water column.


0

5

10

15

20

25

30

35

10/10/06 29/11/06 18/1/07 9/3/07 28/4/07 17/6/07 6/8/07 25/9/07 14/11/07

Mid-point of collection interval

Ra

te (

mg

/da

y)15m

40m

70m

15m-CO3

40m-CO3

70m-CO3

Figure 31 Settling rate (mg/day) for particulate matter and carbonate collected at 15 m, 40 m or 70 m below the surface of Blue Lake.

Table 15 Chemical composition of the sediments settling within Blue Lake.

Sample name Days As B Cr Cu Fe Mn Ni P Pb Zn CO3

mg/kg % Nov-06 15m 43 1.4 <20 4.6 3.3 1900 19 1.7 96 91 13 61.9 40m 1.7 <20 5.5 4.6 1800 22 2.4 151 43 14 53.7 70m 1.9 <20 7.1 6.0 1800 46 4.0 240 112 27 54.0 Dec-06 15m 48 1.5 <20 7.9 3.7 1800 11 1.8 116 17 7.7 53.1 40m 1.9 <20 6.5 4.9 1900 13 2.0 88 21 9.8 60.4 70m 1.5 11 7.5 4.3 1700 16 1.9 110 14 4.9 52.3 Feb-07 15m 49 1.6 21 18 2.8 1900 10 3.6 79 22 6.6 56.7 40m 1.6 39 11 3.9 1800 11 1.9 143 18 9.5 59.0 70m 2.4 30 13 6.1 1900 24 2.9 176 21 16 57.5 Mar-07 15m 47 1.8 <20 8.5 6.4 2000 9.2 1.8 115 17 10 58.3 40m 2.2 <20 9.4 4.4 1700 11 2.0 180 12 6.6 59.0 70m 1.8 <20 4.3 4.6 1500 7.9 1.2 84 1.2 1.3 54.8 May-07 15m 43 1.0 <10 8.1 2.0 2500 11 1.9 200 15 25 60.9 40m 1.1 <10 8.6 2.1 2750 12 2.2 220 13 15 56.9 70m 0.9 <10 9.6 2.1 2620 16 2.8 300 18 10 58.8 Jun-07† 15m 142 4.0 20 16 11 3670 48 7.1 890 21 70 30.0 40m 5.1 20 21 14 5550 120 9.3 1350 33 55 35.0 * 70m 3.8 10 18 11 4830 158 8.5 1080 38 35 30.0 † Jun-07, Aug-07 and Sep-07 combined for elemental analysis due to low mass of individual samples; * only Jun-07 sample as insufficient mass was available from Aug-07 and Sep-07 samples


Figure 32 Settling rate (ng/day) for the inorganic components of the particulate matter collected at 15m, 40m or 70m below the surface of Blue Lake.

0

10

20

30

40

50

60

70

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

As

(ng/

day)

15m

40m

70m

0

100

200

300

400

500

600

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Cr

(ng/

day)

15m

40m

70m

0

10000

20000

30000

40000

50000

60000

70000

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Fe

(ng/

day)

15m

40m

70m

0

20

40

60

80

100

120

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Ni (

ng/d

ay)

15m

40m

70m

0

20

40

60

80

100

120

140

160

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Cu

(ng/

day)

15m

40m

70m

0

100

200

300

400

500

600

700

800

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Mn

(ng/

day)

15m

40m

70m

0

1000

2000

3000

4000

5000

6000

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

P (

ng/d

ay)

15m

40m

70m

0

200

400

600

800

1000

1200

1400

1600

1800

2000

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Pb

(ng/

day)

15m

40m

70m

0

50

100

150

200

250

300

350

400

450

500

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

Zn

(ng/

day)

15m

40m

70m

0

100

200

300

400

500

600

700

800

900

1000

10/10/06 29/11/06 18/01/07 9/03/07 28/04/07 17/06/07 6/08/07 25/09/07

B (

ng/d

ay)

15m

40m

70m


Lake core sampling

The cores collected from the two sampling locations showed variation in their banding and deposition of sediment (Figure 33).

The volumetric porosity of the core samples ranged from 0.66-0.83, on average 0.76; with a corresponding volumetric dry bulk density of 0.17-0.34 g/cm3, on average 0.23 g/cm3. The dry bulk densities are higher than reported in cores collected by cold finger techniques reported by Herczeg et al., 2003 (0.09-0.17 g/cm3), due to drainage and loss of water after sampling.

CL10

NL10

199119701908 1926 1950

CL10

Figure 33 Comparison of core samples collected from the northern edge (NL10) and centre (CL10) of the Blue Lake indicating variation in the sediment banding.

The total and excess 210Pb concentrations in the sediments of cores NL10 and CL10 showed a typical exponential decline in 210Pb over the top 100 mm of the core (Figure 34). However higher concentrations were measured in the top of the northern core (NL10), with a maximum excess 210Pb of 93 Bq/kg. This is consistent with the previous concentration of 83 Bq/kg excess 210Pb reported at the top of a core collected in 1994 (Herczeg et al., 2003). The 210Pb concentrations measured on the centre core (CL10) suggest that the most recent material may have been lost during sampling and thus the following discussion will focus on the northern core (NL10).


0

50

100

150

200

250

300

0 20 40 60 80 100 120

Total 210Pb

dept

h (m

m)

North

Centre

0

50

100

150

200

250

300

0 20 40 60 80 100

Excess 210Pb

North

Centre

The relationship between age and depth was estimated using the constant rate of supply (CRS) model (Binford 1990) (Figure 35). The uncertainty associated with this method increases with depth and therefore the age estimates below approximately 140 mm are not considered reliable. This method assumes a constant rate of groundwater inflow to Blue Lake.

The elemental composition of the core samples is shown in Table 16 and indicates that many species show low concentrations in the more recent sediments, possibly due to dilution by the large amount of carbonate sedimentation occurring.

Figure 34 Total 210Pb and excess 210Pb versus depth for cores NL10 (North) and CL10 (Centre).

1800

1820

1840

1860

1880

1900

1920

1940

1960

1980

2000

2020

0 20 40 60 80 100 120 140

Depth (mm)

Est

ima

ted

year

Figure 35 Estimated relationship between age and depth for core NL10 (North).


Table 16 Chemical composition of core NL10 (North) from Blue Lake.

ID & depth Al As B Cd Cu Cr Fe Mn Ni P Pb Zn N CO3

(mm) mg/kg %

C77 5 2610 2.4 6.7 <0.1 3.1 7.3 2858 48 7.0 330 3.8 10.9 2.3 89.6

C76 10 2097 2.6 6.6 <0.1 2.9 14 2978 39 10.9 376 2.3 8.5 2.2 91.5

C75 20 1895 1.5 6.5 <0.1 2.5 6.2 2042 36 6.7 300 2.3 8.0 2.5 92.2

C74 25 1781 1.5 6.4 <0.1 2.6 6.2 1822 35 6.6 259 3.3 8.6

C73 30 1710 1.6 6.4 <0.1 3.0 7.2 1722 35 7.9 253 3.9 9.1 2.7 93.6

C72 40 1565 1.3 5.2 <0.1 2.3 5.4 1659 38 8.3 209 5.0 12.5 2.1 93.3

C71 45 1290 1.6 4.5 <0.1 2.9 5.2 1502 38 7.3 175 5.1 11.2 2.2 94.6

C70 50 2998 1.6 6.2 <0.1 3.5 7.5 2605 53 7.1 261 4.9 14.1 1.6 90.7

C69 55 3947 1.6 6.7 0.1 3.6 7.7 3065 61 6.8 285 4.9 13.4 0.6 89.8

C68 60 5214 1.6 7.5 0.1 3.2 7.9 3922 70 6.9 349 5.4 14.3 1.4 88.3

C67 65 4525 1.5 7.3 <0.1 3.7 6.8 3405 70 6.5 342 5.2 14.0 1.4 86.7

C66 70 4565 1.3 7.5 0.1 3.4 6.6 3354 74 7.0 358 6.1 16.5 1.5 87.8

C65 78 6466 2.2 8.9 0.1 4.7 17 4710 93 13.9 432 7.2 18.2 1.5 84.9

C64 86 8399 3.6 10.5 0.1 4.0 9.7 7360 109 7.8 482 6.6 20.1

C63 91 9357 4.5 11.2 <0.1 3.9 11 10845 107 9.4 502 5.0 18.6 1.0 72.3

C62 100 12105 3.6 14.6 0.1 4.8 14 10935 115 10.8 630 5.8 21.6

C61 110 11159 2.9 12.5 0.1 4.3 13 9260 115 9.4 597 5.1 20.6 1.1 71.7

C60 120 10762 3.7 11.0 0.1 4.7 12 9118 117 9.1 576 5.6 18.3

C59 130 10825 3.3 10.9 0.1 3.7 12 9767 118 8.3 570 4.4 17.4 1.2 76.6

C58 135 11145 4.1 11.4 0.1 4.9 12 9802 119 8.9 581 6.6 19.4

C57 140 13793 4.3 13.5 0.2 5.6 13 11019 132 9.2 720 6.4 18.7

C56 150 10767 4.9 12.2 0.1 5.4 13 11053 118 9.0 618 6.5 16.2 1.2 75.1

C55 155 5881 4.5 9.1 <0.1 7.9 9.2 5588 91 9.2 412 6.2 12.6

C54 160 6413 3.3 9.5 <0.1 3.7 8.7 6139 87 7.2 456 4.7 11.8 1.5 81.0

C53 170 5729 3.4 8.5 <0.1 3.4 7.8 5516 79 7.6 441 4.1 10.4 1.5 82.9

C52 180 4575 2.6 8.6 <0.1 3.4 7.7 4250 77 8.1 433 1.2 8.1 1.5 80.8

C51 185 4838 2.5 8.7 <0.1 3.4 7.8 4333 77 8.2 462 1.2 8.6

C50 195 3546 1.9 8.8 <0.1 3.3 7.1 3406 78 8.3 471 1.0 7.3

49 205 3159 3.4 8.6 0.1 4.6 9.1 3343 71 10.9 414 1.1 7.1 2.0 87.2

C48 215 4988 3.2 10.7 <0.1 4.8 10 4598 80 10.6 568 1.4 11.0

C47 225 3226 2.9 9.2 0.1 3.1 8.8 3138 67 10.1 366 0.9 8.1 1.8 85.4

C45 235 2866 2.5 8.2 <0.1 1.9 5.4 3457 65 6.1 305 0.6 5.9 1.6 87.8

C44 245 4245 2.6 9.3 <0.1 4.2 8.8 3740 72 9.0 557 1.3 9.7

C43 250 5134 2.2 9.5 <0.1 3.2 9.6 4086 68 8.4 531 1.1 10.6 1.8 85.3

C42 260 5011 2.2 9.8 <0.1 3.3 9.0 4057 70 8.6 527 1.9 10.3 Aluminium, iron and manganese concentrations in the sediments are strongly correlated (R2>0.92) due to their origin as naturally occurring soil elements. Phosphorus concentrations were also correlated with aluminium concentrations (R2=0.73) and the carbonate content (inverse relationship; R2=0.89). Manganese, and boron concentrations in the sediments show an inverse relationship with the carbonate content (R2>0.81), arsenic exhibits a weaker inverse correlation (R2=0.62) while the other trace species show only a slight inverse trend. The inverse relationship between the metal species and the carbonate content indicates that carbonate precipitation has diluted the concentration of inorganic species within the lake sediments. However the precipitation cycle and associated carbonate sedimentation provides a mechanism for contaminant removal to the lake floor.

Most of the trace elements were present in the lake sediments at comparable concentrations to the sediments collected in the water column. For example, the arsenic concentrations in the profile were lowest in the upper 70 mm, from around 1960 onwards. These concentrations were comparable to those reported in the sediment traps during the summer period of high carbonate production. In contrast the lead concentrations in lake sediments were considerably lower than in the sediment traps suggesting considerable dissolution of lead in the water column prior to


sedimentation. The previous discussion on sediment traps suggested lead removal was associated with carbonate production, 88 per cent of which is recycled in the water column (Herczeg et al., 2003). Nickel concentrations in the sediment were similar to the higher concentrations evident in the winter sediment traps (associated with organic matter). However the majority of trace elements did not show such high concentrations in the lake sediment. Cadmium concentrations were <0.1-0.1 mg/kg through the core sample.

The accumulation rate of lake sediments ranged from 0.027 to 0.086 g/cm2 yr, and increased with time (Figure 36). This is largely influenced by increasing accumulation rate of calcium carbonate which has increased with the shorter residence time in Blue Lake due to extraction for water supply (Figure 37). The accumulation rate of aluminium, iron, phosphorus and organic matter (Figure 36) all peak at 100-120 mm, corresponding to a period from the late 1800s when settlement occurred. Land clearing and soil erosion may explain the increase in accumulation of the soil minerals around the 1900s (peak Al, Fe, Mn, P and minimum carbonate content). Figure 38 illustrates considerable land clearing had occurred in the vicinity of Blake Lake by 1894, thus exposing the volcanic soils around the lake. Higher input of phosphorus leads to increased organic matter production and accumulation, illustrating the importance of caldera erosion on algal growth. Aside from lead, the inorganic constituents of the core sample also exhibit a peak accumulation rate corresponding to this interval, either due to their origin in volcanic soils or accumulation in organic matter (Figure 39). These inorganic also showed a strong relationship with organic matter in sediments collected in the water column. The peak in lead accumulation rate occurs around 60 mm in depth (1950-1960) but this can not be linked to stormwater quality as unleaded petrol was not used until 1986. This lead peak may be related to the use of lead pipes in plumbing.

0

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0.00 0.02 0.04 0.06 0.08 0.10

accumulation rate (g/cm2 yr)

dept

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m)

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appr

ox y

ear

sedimentCaCO3

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0.00 0.20 0.40 0.60 0.80

accumulation rate (mg/cm2 yr)

dept

h (m

m)

AlFeP x10Organic matter /10

Figure 36 Accumulation rate of a) sediment and calcium carbonate and b) aluminium, iron, phosphorus and organic matter in core NL10 (North) with depth.

a) b)


Figure 37 Change in lake surface elevation and rate of water extraction for Blue Lake 1880-2000 (Herczeg et al., 2003).

Figure 38 Blue Lake in 1894 (Mount Gambier Public Library, 2009).


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0.0000 0.0002 0.0004 0.0006 0.0008


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0.0000 0.0005 0.0010 0.0015


dept

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Mn /10Zn

Figure 39 Accumulation rate of inorganic constituents in core NL10 (North).

4.2.3. Summary of attenuation studies

A sulfur hexafluoride (SF6) tracer test indicated that it is possible for stormwater recharged directly into the unconfined aquifer via stormwater drainage wells to reach Blue Lake in approximately 2 years. Detection in Blue Lake in this timeframe indicates there is migration through karst features. It is recommended to continue refining the understanding of residence time in the aquifer by monitoring travel time indicators such as SF6 from the applied tracer test and additional dissolved gas tracers such as 3He.

Due to the lack of detections within Blue Lake, trace organic chemicals were not used as indicators of residence time in this system.

Most of the inorganic species exhibited the highest concentration in sediments collected in the water column during the winter months, due to their association with organic matter. In contrast, lead and boron concentrations were greatest during the warmer period of high carbonate production. Lead concentrations in the lake floor sediments were lower than in the water column, suggesting they are solubilised in the water column. The inorganic species concentration in the most recent lake floor sediments was generally comparable to those found settling in the water column during the periods of high carbonate production. The lake cores suggested that the rate of carbonate precipitation has increased with time in response to increasing extraction rates and this effectively dilutes the concentration of most of the inorganic species. The particulate settling flux, which is currently governed by the annual carbonate cycle, provides a mechanism to remove inorganic species from the water column. Regardless of their association with either organic or inorganic carbon, trace inorganic chemicals are removed from the water column to the lake floor. As a result some inorganic species exhibit lower concentrations in the Blue Lake than in the groundwater, which provides the lake recharge.


5. ASSESSING RISKS TO BLUE LAKE FROM URBAN LAND USE RISKS

5.1. Risk assessment methodology The risk assessment framework (Figure 40) relies on examining potential hazards and their attenuation mechanisms (factors that alter input concentration) in comparison to water quality target values. This approach is consistent with the Australian drinking water guidelines (NHMRC- NRMMC, 2004) and the guidelines for water recycling (NRMMC-EPHC-AHMC, 2006).

This method can incorporate both potable water quality guidelines (NHMRC-NRMMC, 2004) and aquatic ecosystem water quality criteria (ANZECC and ARMCANZ 2000; SA EPA 2003) by selecting the most sensitive target value. The measurement of risk can range from a simple qualitative assessment through to a fully quantitative assessment, depending on the input data available. Furthermore, the risk assessment can be iterative, adding complexity as the supporting input data develops. The quantitative risk assessment (QRA) was performed using the @RiskTM software. The risk assessment can accommodate varying detail in input data. The initial risk assessment assumes a very conservative approach in response to data limitations. However for a quantitative assessment, the degree of confidence increases as the uncertainty associated with input parameters, such as aquifer residence time, decreases.

Figure 40 Framework to assess the impact of land use activities on water quality. Target values can be based on potable and environmental water quality guidelines.

5.2. GIS development for the urban area Hazard identification was undertaken by identifying high risk activities in the urban area using a GIS map. The data sources used to develop the urban area GIS are detailed in Table 17. Service stations and commercial transportation locations were derived using council information, in GIS layers and also complied through the Watercare program (K. Climie, pers. comm.), in combination with Telstra directories. Activity street addresses were matched to the property cadastre. All activity locations were confirmed manually in June 2006. The qualitative risk assessment undertaken within Protecting the Blue Lake from land use impacts (Part A) was used to develop the land use map (Appendix 2).


Table 17 Data sources used for GIS development.

Source Information

City Council of Mount Gambier GIS layers: properties roads stormwater catchments and bores planning zones petrol stations vehicle crash sites cooling towers (included dry cleaners) Watercare unlicensed activities database

SA EPA GIS layer: EPA licensed activities AISUWRS project GIS layer: Sewer leaks Telstra directories Service station addresses

Commercial transportation addresses (for fuel storage)

Land use within the urban area, deemed as risk activities to Blue Lake, that are incorporated into the GIS are shown in Table 18. More than one land use may have the same risk activity. For example, service stations, the timber industry and works depot sites are all associated with fuel storage, while fuel storage is also specified as a land use. The fuel storage land use category contains fuel depots and commercial transportation sites.

Table 18 Urban land use and associated risk activities incorporated into urban area GIS.

Land Use Risk activity Chemicals of concern Qualitative risk assessment

Pathway‡

Sewers Sewer leak nutrients, pathogens, metals, solvents

L-M I

Fuel storage Fuel storage hydrocarbons M-H I, SR, SP Service stations Fuel storage hydrocarbons M-H I, SR, SP Timber industry Timber treatment copper chrome arsenic (CCA)†,

creosote† M-H I, SR, SP

Fuel storage hydrocarbons M I, SR, SP Dry cleaners Chemical storage perchloroethylene (PCE),

tetrachloroethylene (TCE) H I, SR, SP

Works depots Bitumen storage polycyclic aromatic hydrocarbons (PAH)

M I, SR

Fuel storage hydrocarbons M I, SR, SP Road transport High density traffic hydrocarbons, metals not included SR High risk traffic

accidents hydrocarbons, solvents not included SP

†Site specific, ‡ I=infiltration, SR=surface runoff, SP=spill

The potential pathway/s for contamination are infiltration (I), surface runoff (SR) and spill (SP). Initially all locations undergoing a specific activity are associated with the same pathway, regardless of site specific interventions or barriers. This allows urban stormwater catchments to be ranked based on the importance of stormwater pre-treatment (SR risks) or spill containment (SP risks). The specific locations for each activity are documented in Table 19.

Activities from the qualitative risk assessment that are not included on the GIS include:

intensive irrigation as it is not significant in the urban area;

septic tanks as distribution is low density; and

unlicensed landfill as the specific location is not known.


Table 19 Locations of activities included on urban area GIS.

Land Use Business/Activity name Address

Sewers Sewer leak as per AISUWRS GIS layer Dry cleaners Mr Clean 88 Jubilee Highway West Nari Dry Cleaners 2 Ferrers Street Park Dry Cleaners 157 Commercial Street West South East Laundry 8 Anthony Street Fuel storage AA Scott Pty Ltd 209-211 Jubilee Highway West Associated Hemmings Pty Ltd 11 Avey Road Caltex Depot 40 Margaret Street I Moretti 23 Wireless Road K & S Freighters Pty Ltd 141 Jubilee West Highway MTU Detroit Diesel Australia Pty Ltd Jubilee Highway West Peter Whitehead Pty Ltd 389 Commercial Street West Sneaths Transport 18-20 Graham Road South West Freight 13 Graham Road Service stations Ampol 230 Commercial Street Ampol 141 Commercial Street West Asco Oil 251Commercial Street West BP Australia Ltd 221 Jubilee Highway Caltex 141 Jubilee Highway West Caltex 29 Penola Road Mobil 2 Scott Court Mobil 115-116 Commercial Street Mobil 197 Commercial Street West Mobil 190 Jubilee Highway East Mobil 82-84 Jubilee Highway West Pick Avenue 26 Pick Avenue Scott’s Agencies (within Mobil Fuel Depo) 211 Jubilee Highway West Shell Fuel Link 2/34 Bay Road Shell 96 Commercial Street West Woolworths Petrol 108-110 Commercial Street East Timber industry Carter Holt Harvey Wood Products 15 White Avenue Carter Holt Harvey Wood Products (CCA

use) 170 Jubilee Highway East

Carter Holt Harvey Wood Products Lot 1, Commercial Street West Green Triangle Forest Products (creosote

use) Jubilee Highway McDonnell Industries Pty Ltd Suttontown Road Whiteheads Timber Sales Pty Ltd (CCA

use) Lewis Avenue Works depots District Council of Grant 324 Commercial Street West Gambier Earth Movers 29 Avey Road Mount Gambier City Council 265 Commercial Street West WFC Contracting 8,14 & 20 Tolmie Street Road transport High density traffic Commercial Street Jubilee Highway Pick Avenue Penola Road Traffic accidents Commercial Street/Penola Road Commercial Street/Wehl Street South Jubilee Highway/Penola Road Jubilee Highway/Wehl Street North Jubilee Highway/Pick Avenue

Stormwater discharge, from both industrial and residential areas, was ranked as medium to high risk in the qualitative risk assessment. In the land use map, stormwater discharge is treated as a pathway rather than a land use. This allows each stormwater catchment to be assessed in relation to the activities it contains.


The entire parcel of land is attributed to the land use/risk activity, regardless of the actual footprint of the activity. Thus fuel storage associated with transportation or timber industry sites may be depicted as affecting a larger area than fuel storage at a service station. Where an activity is identified as a line source (high density traffic) or a parcel of land, all stormwater catchments intersected are highlighted as catchments affected. Point locations of high risk traffic accidents and centre lines of high density traffic roads are given a 5m buffer to encompass all the catchments impacted. Sewer leak information obtained from the AISUWRS project was expressed in kL/year/asset. This was converted to kL/year/m by dividing the leak rate by the length of each asset. This effectively distributes the leak across the asset, rather than attributing it to one large leak. All leaks ≥ 1 kL/year/m are shown. The high risk traffic accident locations are the four highest ranked ‘vehicle crash sites’ from the Council’s GIS layer, in conjunction with an additional recommendation (Steering Committee meeting 15/6/06).

The following series of figures (Figure 41-44) illustrate the risk activities included in the urban area GIS in relation to their potential pathway for contamination.

Figure 41 Risk activities within the Mount Gambier urban area (all pathways).


Figure 42 Risk activities within the Mount Gambier urban area with the potential to impact water quality through surface runoff.

Figure 43 Risk activities within the Mount Gambier urban area with the potential to impact on water quality through spills.


Figure 44 Risk activities within the Mount Gambier urban area with the potential to impact on water quality through infiltration.

5.3. Prioritisation of risk activities The initial GIS prepared highlights numerous catchments that are affected by land use. This is refined by including site specific information to the activities. Each activity location included is attributed with additional data to prioritise the stormwater catchments for treatment relevant to the surface runoff and spill pathways.

Stormwater catchments are given a cumulative score, from the number and nature of the chemical hazards contained within each catchment area (Table 20). The catchments considered as the greatest potential risk are those with the highest cumulative score. Owing to the lack of data, scoring does not take into account additional measures for environmental protection such as physical barriers or education programs. Further assessment of the impervious and pervious cover and environmental protection within the catchment will follow for high priority catchments in Task 5. High density traffic is only scored once per catchment regardless of the number of applicable roads contained.

For the stormwater runoff pathway, 16 catchments score 7 or above, and for the spill pathway 12 catchments score above 7 (Table 21). A considerable number of the higher ranking categories are a priority for the two pathways assessed, surface runoff (Figure 45) and spill (Figure 46). The seventeen stormwater catchments within the urban area of Mount Gambier deemed as highest risk for the surface runoff and/or spill pathways, based on the land use activities, are shown in Table 21, and the hazards present are summarised in Table 22. Notably, two high-risk catchments do not contain a bore and overflow is not reported. Thus infiltration is more important for catchment number 16 and 7.

The hazards in the urban area of Mount Gambier were identified as benzene, ethylbenzene, toluene and xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), copper chrome arsenic (CCA) and tetrachloroethene (PCE; also known as perchloroethylene and tetrachloroethylene). These hazards were deemed as risk agents for the surface runoff and spill pathways. While these species can also infiltrate to the groundwater, it is assumed that the loads will be far less than the surface and spill pathways.


Diffuse impacts within the Blue Lake Capture Zone will impact on the quality of groundwater (and ultimately Blue Lake) via infiltration. The hazards identified from diffuse impacts in the capture zone were nitrogen, atrazine and simazine (Fleming, 2006).

Table 20 Points system to prioritise stormwater catchments relevant to risk activities.

Activity Scoring

Fuel storage Petrol/diesel - score 3

Timber treatment CCA – score 5

Creosote and pentachlorophenol– score 3

Chemical storage PCE – score 5

High density traffic Hydrocarbons, metals – score 3

Traffic accidents Hydrocarbons, solvents – score 5 Note: higher score indicates higher potential risk from hazard

Table 21 Catchments with scores ≥7 for the surface runoff and/or the spill pathways.

Catchment no.*

Pathway Area (ha) Bore/s Overflow

69 SR, SP 57.8 95 (Cave Garden), 205, 338, 239, 81

overflow to c73 (low risk catchment)

8 SR, SP 23.4 private bore

16 SR, SP 7.5 no bore-field

282 SR, SP 7.1 148

10 SR, SP 2.7 13 receives overflow from c166 (high density traffic)

284 SR, SP 34.4 private

294 SR, SP 6.1 79

9 SR, SP 51.9 55-private bore

381 SR, SP 10.9 182 (Engelbrecht Cave), 377

72 SR 9.5 92

293 SR 8.6 212

319 SR 7.1 220

311 SR 5.9 158, 202

280 SR 5.4 291, 292

7 SR, SP 35.5 no bore-field

423 SR, SP 3.1 119

408 SP 19.7 10, 72, 102, 199, 355 receives overflow from c409, c412 (high density traffic)

* Catchment numbers shown in bold are high priority for both pathways (surface runoff and spill)


Table 22 Potential contaminants within stormwater catchments deemed as high risk.

Catchment* Surface Runoff Spill

BTEX PAH CCA PCE BTEX PAH CCA PCE

69

8

16†

282

10

284

294

9

381

72

293

319

311

280

7†

423

408 * shading indicates catchment ranked as high risk for pathway † no drainage bore in catchment

Figure 45 Stormwater catchments potentially impacted by surface runoff prioritised by risk activities contained.


Figure 46 Stormwater catchments potentially impacted by spills prioritised by risk activities contained.

5.4. Comparison of risk rankings to existing water quality data A comparison was made been between the available water quality data for stormwater in four catchments deemed as high risk (69, 280, 282, 381) and ten catchments deemed as low risk (56, 84, 96, 99, 155, 239, 256, 325, 357, 382) (Figure 47). The high and low risk data sets were compared using a Mann-Whitney rank sum test SigmaStat 3.5 (Systat Software Inc, 2006) for the parameters with sufficient data available. The parameters considered were suspended solids (SS), total phosphorus (TP), total nitrogen (TN), nitrate (NO3-N), total chromium (Cr-t), total copper (Cu-t), total lead (Pb-t), total nickel (Ni-t), total zinc (Zn-t) and total petroleum hydrocarbon (TPH).

Several of these were shown to be statistically different (P-value ≤0.005) between the high and low risk catchments (Table 23). This supports the notion that water quality is related to risk for most species. It is not surprising that TN or nitrate-N is not significantly different between high and low risk catchments as the assessment was not based on these parameters.


Figure 47 Location of existing stormwater quality data for Mount Gambier in relation to high and low risk catchments.

Table 23 Results of Mann-Whitney rank sum test comparing stormwater quality for high and low risk catchments.

Parameter High risk catchments Low risk catchments P-value Significant difference

Range (mg/L) Median (mg/L)

Range (mg/L) Median (mg/L)

SS 4-1680 (30) 108 0.5-4840 (64) 31 <0.001 TP 0.02-7 (32) 0.41 0.01-9.2 (64) 0.19 0.003 TN 0.09-5.3 (32) 1.14 0.02-9.0 (55) 0.79 0.09 × NO3-N 0.02-4.8 (30) 0.17 0.02-5.3 (56) 0.09 0.68 × Cr-t <0.001-0.059 (24) 0.011 <0.001-0.053 (61) 0.002 <0.001 Cu-t 0.009-0.23 (27) 0.033 <0.001-0.13 (61) 0.009 <0.001 Pb-t 0.01-0.88 (27) 0.034 0.0008-0.064 (60) 0.008 <0.001 Ni-t 0.001-0.048 (20) 0.004 <0.001-0.059 (54) 0.002 0.007 × Zn-t 0.084-2.4 (27) 0.34 0.007-0.43 (62) 0.076 <0.001 TPH 70-2890 (20) 620 70-1570 (37) 295 <0.001

(n) number of observations


5.5. Fate of potential contaminants

5.5.1. Copper, chrome and arsenic (CCA)

The storage and use of CCA wood preservatives within the city area, results in a risk to the quality of the underlying groundwater. The mobility of these species will be affected by precipitation as carbonates, complexation by organic matter or sorption to charged surfaces of iron oxides or clays (Telfer, 1994). As these removal mechanisms are reversible and may have limited capacity, discharge of CCA to the aquifer should be minimised.

Arsenic concentrations are predominantly reported as below the analytical detection limit in samples of Mount Gambier’s stormwater (n=34), and for samples with measurable concentrations (n=26), concentrations have not exceeded the 7 μg/L drinking water guideline value. Chromium and copper have been detected more frequently in stormwater samples and the medians for Cu-total and Cr-total equal the target values of 10 μg/L and 3 μg/L respectively. The peak concentrations for soluble copper and chromium are 14 and 10 mg/L respectively. In both instances these values meet the drinking water guideline values but exceed the SA EPA aquatic ecosystem target values.

Removal of copper, chromium and arsenic has been illustrated by analysis of the Blue Lake sediments and also by maintenance of acceptable concentrations within the lake. However the contributing removal processes for inorganic species, such as precipitation, sorption or ion exchange, are reversible and therefore not applied within a quantitative risk assessment.

5.5.2. Benzene, toluene, ethylbenzene and xylene (BTEX)

Benzene, toluene, ethylbenzene and xylene (BTEX) are common groundwater contaminants owing to leakage from storage tanks and spills during transport and handling (NRC, 2000). BTEX compounds are lighter than water (LNAPLs) and spread horizontally along the water table, with diffusion into the water table. Despite being a minor constituent of fuel products, the high solubility of BTEX produces a major contribution to the dissolved phase once fuels are in contact with water (Chapelle, 1993).

BTEX can readily degrade to carbon dioxide under aerobic and anaerobic conditions, thus explaining the absence of these compounds in known contamination sites (Chapelle, 1993; 1996; NRC, 2000). Aerobic conditions are the most favourable for complete degradation of all BTEX components (NRC, 2000). This is reflected in the short half-lives for groundwater and surface water, which are predominantly less than one month (Table 24).

5.5.3. Phenanthrene, fluoranthene and pyrene (PAHs)

Polycyclic aromatic hydrocarbons (PAH) are sparingly soluble and are predominantly removed through sorption. Despite their low solubility PAH species with 4 rings or less are found in leachate from bitumen/asphalt (Brandt and de Groot, 2001; Kriech et al., 2002). The contribution to leachate declines with size and water solubility of the PAH, as does the tendency for degradation (Chapelle, 1993). Degradation proceeds slowly and is limited to PAH in the dissolved phase (NRC, 2000).

The three PAHs selected for examination in the risk assessment are intermediate in size (3-4 rings) and have been detected in Mount Gambier’s stormwater. PAH guidelines for drinking water quality focus on benzo[a]pyrene as it is a known carcinogen. However it is also a 5-ring species that is unlikely to be present in the aqueous phase.

5.5.4. Tetrachloroethene (PCE)

Natural attenuation of chlorinated ethenes is achieved under mixed anaerobic and aerobic conditions. Chlorinated ethenes are strong oxidants and can be dechlorinated under reducing conditions (Hunkeler et al., 2005). Progression through dechlorination, from tetrachloroethene to


ethene, (Figure 48) can be achieved by reductive dissolution, but requires a methanogenic condition for completion. Alternatively a combination of mild reduction (PCE→TCE→DCE) and oxidation (DCE→VC→ethene) can effectively degrade chloroethenes (Chapelle, 1996; Bradley, 1999; Witt et al., 2002). PCE is volatile and would not be expected to persist in Blue Lake (Barber and Davis, 2001).

Figure 48 Degradation pathway of chlorinated ethenes from tetrachloroethene to ethene (after Hunkeler et al., 2005).

5.5.5. Diffuse Hazards

Preliminary nitrogen leaching fluxes have been calculated for the two zones within the BLPCZ as a function of the land use and the soil type using the LEACHM (Leaching Estimation and Chemistry Model) (J. Hutson, pers. comm.; unpublished data CNRM Project 54116). Urban residential land use was not assessed as a high risk activity for nitrogen loads to the groundwater due to the low nitrogen concentration of urban stormwater.

5.6. Quantitative risk assessment The quantitative risk assessment for the potential organic contaminants was undertaken in the following steps:

starting with a simulated stormwater, based a uniform distribution between zero and the solubility limit of each species (Table 24);

then calculating the quality of groundwater recharging Blue Lake (simulated groundwater). This was based on attenuation in the aquifer through 45 to 65 per cent dilution and degradation for the given range of half-lives. The groundwater concentration used for dilution was assumed to be zero, based on the lack of detection of any trace organics in the ambient groundwater; and

finally calculating the resultant concentration in Blue Lake (simulated Blue Lake) after degradation and volatilisation for the given range of half-lives.

A residence time of 18 months to 20 years was used for the calculation of degradation in the aquifer. While the closest injection location was approximately 1 km from Blue Lake, there are few drainage bores within 1 km of the lake and the topography of the city means that surface runoff will


move away from the lake (downhill). A residence time of 6 to 10 years (Herczeg et al., 2003) was used for the calculation of degradation and volatilisation in Blue Lake. The risk assessment is based on current land use and does not incorporate historical contamination events. However the risk assessment will be tested using a historical case study.

For the urban hazards the simulated stormwater quality used in the risk assessment was far in excess of either measured concentrations or literature values for stormwater. Benzene began as the stormwater species with the highest risk due to the potential for high concentrations in solution (Figure 49). However the degradation of benzene in an aerobic aquifer is so rapid that predicted concentrations in the groundwater are approaching zero, which in turn results in zero concentrations in Blue Lake. Benzene thus becomes the lowest risk contaminant considered. The other BTEX compounds illustrate similar behaviour.

While tetrachloroethene (PCE) also has high solubility, it is a more persistent species. Based on the half-life range used (360 days), dilution and degradation in the aquifer appear sufficient to reduce PCE concentrations to the target value. Additional treatment within Blue Lake leads to further reduction.

Despite starting with median concentrations orders of magnitude greater than those recorded for Mount Gambier, calculated medians for the three PAHs (phenanthrene, fluoranthene and pyrene) in both the groundwater and Blue Lake are below the aquatic ecosystem target of 3 μg/L. Pyrene, with the highest resistance to degradation (Table 24), produced concentrations that are close to the current analytical capabilities for trace concentrations (0.1 μg/L).

Table 24 Input data for assessment of risk posed by organic hazards in stormwater.

Guideline (µg/L) Mount Gambier stormwater

Solubility limit

Half-life (days) (3)

Drinking water (1)

Aquatic ecosystem (2)

(µg/L) (mg/L) (3) Aquifer Lake*

Benzene 1 - <1 1790 10-16 5-16

Ethylbenzene 3a - <2 152 6-10 3-10

Toluene 25a - <2 524 7-28 4-22

Xylene 20a - <4 180 14-100 7-28

Phenanthrene - 3 0.0026-0.014 1.2 32-400 0.13-1.0

Fluoranthene - 3 0.0022-0.0077 0.27 120-880 0.9-2.6

Pyrene - 3 0.0018-0.0057 0.13 420-3800 0.03-0.1

Tetrachloroethene 50 - not monitored 150 360 180-360 a aesthetic, * surface water half-life is based on degradation and volatilisation (1) NHMRC and NRMMC, 2004; (2) SA EPA, 2003; (3) Appendix 1 Attenuation Processes Report


1.E-20

1.E-17

1.E-14

1.E-11

1.E-08

1.E-05

1.E-02

1.E+01

1.E+04

1.E+07

Benzene Ethylbenzene Toluene Xylene Phenanthrene Fluoranthene Pyrene PCERis

k in

dic

ato

r =

Me

dia

n c

on

ce

ntr

ati

on

/Ta

rge

t v

alu

e

Stormwater (median simulated) Groundwater (median simulated) Blue Lake (median simulated)

Figure 49 Change in risk as simulated stormwater based organics are attenuated in the groundwater and the Blue Lake. The risk indicator = simulated median concentration/target value. 1E-20 was substituted for values of zero in this figure.

5.7. Summary of risk assessment Dry cleaners and their use of PCE are a high risk activity in the urban area. Not all dry cleaners were captured in the high risk catchments (i.e. it may have been the only activity in the catchment). PCE contamination of the aquifer should be minimised by best practice procedures such as spill containment and response plans, bunds around storage areas and possible well-head protection/treatment for bores likely to be affected. It is proposed that this be applied to all dry cleaning activities regardless of other activities within the catchment.

Currently dilution is the only attenuation considered sustainable for the inorganic species. Based on the existing stormwater quality data, inorganic species are predominantly associated with particulate matter. While there is a street sweeping program in place, this is effective in removing gross pollutants but has little effect on the prevention of fine material and urban runoff contaminants from entering receiving water (Walker and Wong, 1999). Possible management options include installation of treatment devices capable of capturing the fine fraction particulates in particulate matter. Particulate removal will also serve to removal particle bound organics such as PAHs.


6. MANAGEMENT OPTIONS FOR PROTECTION OF BLUE LAKE WATER QUALITY

6.1. Current management

6.2. Non-structural measures The Blue Lake Management Plan (BLMC, 2006) provides a five year natural resource management plan for the Blue Lake and the surrounding area, to protect the quality and quantity of water available for Mount Gambier in addition to maintaining an aquatic ecosystem that is a valuable tourist attraction to the region. A number of specific activities have been undertaken under the guidance of the plan, including:

Development of a specific guideline for the management of stormwater in Mount Gambier (SA EPA, 2005). This document provides advice on the best management practices available and is predominantly aimed at new developments not the retrofit of existing infrastructure.

The Blue Lake WaterCare Program focussing on community awareness and education (http://www.bluelakewatercare.com/; program ceased 2009). The WaterCare officer works with local industry, schools and community groups to raise their awareness of water management practices. A prominent example of this work is the drain stencilling program to increase understanding of stormwater entering the Blue Lake. The WaterCare program has developed a register of approximately 170 industry locations in Mount Gambier with the potential to discharge contaminants but do not require an EPA licence.

Council policies on restricted traffic in the vicinity of Blue Lake, on-site wastewater treatment, stormwater management in new developments and emergency response to prevent spills from entering the stormwater drainage network.

Additional control of contaminant release to the environment is achieved by:

EPA activities under the Environment Protection (Water Quality) Policy, site licensing, guidelines (e.g. bunding and spill management, responsible pesticide use and the stormwater management series) and response to grievances from the community.

SA Water trade waste discharge agreements, trade waste guidelines (including those for bunding requirements and the laundering industry), CCTV inspections of sewer mains and sewer spill response plans. There are currently approximately 200 trade waste agreements, which are subject to regular audits. Sewer spills are generally small scale, contributing around 200 L in total per year (A. McPharlin, pers. comm.).

Modification to drainage well permits issued by DWLBC to include a referral to seek advice from the EPA regarding stormwater discharge requirements.

Industry best practice legislation and codes of practice administered by SafeWork SA (eg Petroleum Products Act).

KESAB Clean Site education program.

Recent and current research projects contribute to the understanding of the importance of the potential pathways to contamination in the BLPCZ (Fleming, 2006; Wolf et al., 2006). ‘Primary production to mitigate water quality threats’ will quantify the nitrogen and pesticide loadings to groundwater under land use and soil type combinations encountered in the region.


The City of Mount Gambier (CoMG) currently use a street sweeper with a water spray jet and vacuum that is also equipped with a vacuum hose for removing debris from side entry pits (to 1.2 m) at the following frequencies:

Central business district: daily

Main highways: 1-2 weekly

Residential and industrial areas: 6 weekly

Problem areas/spills: as required

A footpath sweeper is also used daily in the central business district.

Street sweeping is deemed an effective means of gross pollutant removal and is generally used for aesthetic improvements. Street sweeping efficiency improves with particle size but has limited removal of particles less than 300 µm and no effective removal of particles less than 125 µm (Walker & Wong, 1999). As suspended solids in road runoff are predominantly below 1 mm and contaminants, such as metals and organics, are associated with sediments less than 300 µm (Walker & Wong, 1999) conventional street sweeping, such as undertaken in the CoMG, has limited effect on the prevention of urban runoff contaminants from entering receiving water. However, Galloway & Laffan (2007) reported that frequent (daily) street sweeping contributed to greater overall stormwater treatment when comparing the treatment provided by street sweeping and gross pollutant traps in three sub-catchments in Manly, NSW.

The CoMG has also undertaken stormwater quality monitoring as a condition of their licence to discharge stormwater to the aquifer (URS, 2003). Currently, the CoMG’s routine stormwater monitoring program has been halted under advice from the SA EPA pending recommendations from this research program (H. King, pers. comm.).

6.3. Structural measures The predominant form of stormwater treatment in Mount Gambier is the triple chamber settling pit (Figure 50), receiving stormwater from the roadside entry pits and discharging to stormwater drainage bores. While triple chamber systems provide some capacity for storage and removal of gross pollutants, they have limited capacity for removal of fine sediments and hydrocarbons and are recommended for catchments up to 0.25 hectares (SA EPA, 2005). However, the high risk catchments for surface runoff and spills vary in size from 3 to 58 hectares and the contaminants of concern are either hydrocarbons or metals, both of which are generally associated with fine sediments.

Continuous deflective separation (CDS) units, which are on-line gross pollutant traps, are located prior to stormwater discharge to the sinkholes in the Cave Gardens, O’Halloran Terrace and Boandik Terrace. The efficiency of CDS units and triple chamber settling pits relies on frequent cleaning. With around 500 stormwater drainage bores in the city area, it is not practical for the City of Mount Gambier (CoMG) to comply with the recommended schedule for cleaning of 3-6 monthly (SA EPA, 2005).


Figure 50 Typical triple chamber settling pits (SA EPA, 2005).

6.4. Management options Some management options to protect the quality of the Blue Lake against the potential water quality issues determined from the quantitative risk assessment based on high risk urban land use activities (section 3) and impacts on water quality (section 2) are presented in Table 25. In some instances, further information is required before specific options can be defined. The principles behind these management options are as follows:

Prevention is preferred to treatment. Water quality controls are situated as close to the pollutant source as possible. Target the pollutants identified as highest priority (Target Condition Report and Preliminary

Risk Assessment). Target the sources in order of importance. Measure what you manage to verify that management controls are implemented. Monitor stormwater and groundwater to validate that Blue Lake is protected and to provide

early warning. Establish the effectiveness of selected existing and pilot control measures to maximise the

combined measures for a given level of investment. Review the data periodically (e.g. every 5 years) to revise the risk assessment, monitoring

program (locations, frequency, analytes) and management plan.

Protecting the Blue Lake from land use impacts CNRM043714 Page 67

Table 25 Draft Management Options to address the risks to Blue Lake water quality.

Issue Risk^ Dominant sources* Management actions Comment

Nitrate Low-Moderate

Agricultural land use (ie grazing, crops, forestry, fertilizer application)

On-site wastewater treatment systems (OWTS)

Fertilizer application (urban area)

Sewer leaks

Restrict land use activities/fertilizer application in high risk areas‡

Review OWTS effectiveness to develop management action – CNRM054154 (07/08)

Encourage responsible use (urban)

Program to progressively remediate sewer leaks

Levett et al., 2009

Existing program - WaterCare

SA Water responsible

Algal blooms Low Changing N:P ratio in BL

Spills

OWTS

Sewer leaks

Develop understanding of nutrient balance and cycles in Blue Lake

Restrict chemical transport in the vicinity of Blue Lake

Review OWTS effectiveness CNRM054154 (07/08)


Knowledge gap to be addressed

Existing program City of Mount Gambier (CoMG)

Levett et al., 2009


Anthropogenic organics

Low Spills – industrial and traffic

Urban runoff, particularly in high risk catchments†

Leaking storage

Pesticide leaching

Sewer leaks

OWTS


Improve quality of runoff to discharge - non structural measures (including industry best practice)

Improve quality of runoff to discharge - structural measures

Program to remediate leaking storage tanks

Encourage responsible use

Program to remediate sewer leaks, trade waste restrictions


Existing program CoMG

Existing programs - WaterCare, WorkSafe SA, EPA

New program required

Industry specific

Include in WaterCare


Levett et al., 2009

Metals Low Industrial spills

Urban runoff, particularly in high risk catchments†

Sewer leaks

OWTS


Promote industry best practice – structural and non structural measures

Improve quality of runoff to discharge - non structural measures

Improve quality of runoff to discharge - structural measures

Program to remediate sewer leaks, trade waste restrictions


Existing program CoMG

Existing programs - WaterCare, WorkSafe SA, EPA

As above

New program required


Levett et al., 2009

Pathogens Low OWTS

Sewer leaks

Urban runoff



Improve quality of runoff to discharge - non structural measures

Levett et al., 2009


WaterCare – ongoing programs ^as estimated in Appendix 1, *sources in order of importance as estimated in Appendix 3, †as identified in GIS Urban Land Use Map, ‡ as identified in CNRM ‘Primary production to mitigate water quality threats’, WaterCare program ceased 2009.


For the agricultural impacts it is envisaged that the outcomes of ‘Primary production to mitigate water quality threats’ will recommend the appropriate land use management to minimise the risk to groundwater. Preliminary modelling indicates that the nitrogen load to groundwater from grazing is far greater than any other land use in the BLPCZ, predominantly due to the large coverage of this activity. Irrigated pastures (legumes and vegetables) contribute leachate with the highest nitrogen concentration, but are less significant in coverage.

The AISUWRS project advised that sewer leaks be progressively repaired, focusing on the older infrastructure in the city centre (Wolf et al., 2006). The treatment effectiveness of on-site wastewater treatment systems (OWTS) in the area was found to be highly variable, with some systems discharging poor quality effluent. However there was no clear evidence for impact on the quality of groundwater sampled from household bores at the time of OWTS sampling (Levett et al., 2009). Management recommendations were based on improving the treatment performance of these systems through improvements to council policy and operational procedures in conjunction with a program for community engagement (Alexander et al., 2008; Levett et al., 2009).

While the Gambier Limestone aquifer and the Blue Lake provide passive water quality treatment, it is not possible to control their function. Thus, it is desirable to minimise the contaminant loadings to the groundwater by optimising the engineered pre-treatment steps. It is recommended that the existing programs to manage stormwater quality in the CoMG be modified. The more frequent street sweeping routes (daily to weekly) should be reviewed to ensure all roads within the high risk catchments are included. Advances in technology, such as the small-micron surface sweepers, with improve the capability of street sweeping to remove finer particles (Walker and Wong, 1999) should be considered when upgrades in machinery are required. In addition CDS/triple chamber pit cleaning and maintenance should be undertaken 3-6 monthly where possible in the high risk catchments (SA EPA, 2005).

An additional program could be developed to design and test modifications to the current triple chamber settling pits to enhance pollutant removal. Initial modifications may be to ensure all pits are fitted with a shroud over the outlet pipe, as shown in Figure 50, to prevent floatable material such as oils and light hydrocarbons entering the drainage bore.

Further modifications require additional resources to determine the most effective means of treating the quantity and quality of stormwater received. Lee et al., (2004) report the design of a stormwater treatment device using sedimentation followed by upward flow through a polypropylene (PPL) media (Figure 51), which effectively removes >60 per cent of suspended solids and heavy metals and <40 per cent of COD and PAHs. Triple chamber pit retrofits could assess the possibility of adding a filtration step, though media such as gravel, PPL or activated carbon, to facilitate improved treatment while maintaining suitable flow. Alternatively an adsorbent sock or boom, such as used in liquid spill protection, could be added to the treatment step (e.g. Absorb Environmental Solutions).

Figure 51 Treatment of stormwater using up-flow polypropylene (PPL) media (Lee et al., 2004).


Clearly modifications of this type provide an opportunity for some innovative treatment steps (e.g. Uni of Massachusetts, 2004) and require specialist expertise in urban hydrology considering both water quality and quantity aspects. Any modification must ensure that the role of drainage bores in providing flood protection is not compromised. While the retrofit is based on the requirements of the high risk catchments, provision should be made for staged upgrades to the low risk catchments, which may be as simple as fitting a shroud over the outlet pipe. High flow bypass measures and subsequent treatment should also be considered to optimise the treatment.

The risk assessment is based on the type and number of land use activities within a given catchment. It does not consider site specific controls, such as treatment or containment, which may reduce the residual risk. For example, modern service station design can incorporate several facets to prevent the opportunity for hydrocarbon contamination including monitoring of storage tank levels, double containment of storage, separating the paths for spills and stormwater in the refuelling area and the capacity to contain tanker spills. Such infrastructure provides an additional barrier to contamination through an opportunity to reduce contamination prior to well-head treatment.

Further development of the risk assessment requires an assessment of the infrastructure and programs to manage water quality at the individual locations of high risk activities. Industry sites within high-risk catchments are a high priority for further inspection (Table 26). Most of these site visits could be achieved within a program similar to the SENRMB/CoMG ‘WaterCare’ program which ceased in 2009; aimed at providing focused industry inspections, suggestions for improved water quality management where appropriate and recognition of high quality operation. While not discussed explicitly in this report, the site inspections and modifications to site infrastructure would also address risks to the groundwater via infiltration.


Table 26 Industry sites included on the GIS Land Use Map recommended for detailed assessment.

Land Use Business/Activity name Address

Dry cleaners Mr Clean 88 Jubilee Highway West Nari Dry Cleaners 2 Ferrers Street Park Dry Cleaners 157 Commercial Street West South East Laundry‡ 8 Anthony Street Fuel storage AA Scott Pty Ltd 209-211 Jubilee Highway West Associated Hemmings Pty Ltd 11 Avey Road K & S Freighters Pty Ltd 141 Jubilee West Highway Peter Whitehead Pty Ltd 389 Commercial Street West Sneaths Transport 18-20 Graham Road South West Freight 13 Graham Road Service stations Ampol 230 Commercial Street Ampol 141 Jubilee Highway West BP Australia Ltd 221 Jubilee Highway Caltex 141 Commercial Street West Caltex 29 Penola Road Mobil 115-116 Commercial Street Mobil 197 Commercial Street West Mobil 190 Jubilee Highway East Mobil 82-84 Jubilee Highway West Scott’s Agencies (within Mobil Fuel Depot) 211 Jubilee Highway West Shell Fuel Link 2/34 Bay Road Shell 96 Commercial Street West Woolworths Petrol 108-110 Commercial Street East Timber industry* Carter Holt Harvey Wood Products 15 White Avenue Carter Holt Harvey Wood Products (CCA

use) 170 Jubilee Highway East

Carter Holt Harvey Wood Products Lot 1, Commercial Street West Green Triangle Forest Products (creosote

use) Jubilee Highway Whiteheads Timber Sales Lewis Avenue Works depots Gambier Earth Movers 29 Avey Road *EPA licensed sites not included in the WaterCare program; ‡a high risk activity but not within the ‘high risk’ stormwater catchments

6.4.1. Monitoring and evaluation

To comply with the HACCP philosophy for managing water quality (NHMRC-NRMMC, 2004; NRMMC-EPHC-AHMC, 2006) and the principles outlined above, the management options needs to be supported by monitoring programs and evaluation as detailed below.

Record of repeat inspection of industry sites (annual basis) to review barriers to contamination in place and uptake of recommendations made through the appropriate programs (such as the previous WaterCare program). WaterCare records indicate that of 121 sites visited, 20 have had repeat visits and another site, Cummings (auto repairs), has been visited three times due to the proactive approach of the manager. Four of the 20 businesses in particular, McCormick’s Bus Company, AJ & DF Ward (car restoration and supplies), South East Auto Trade and Auto Repairs and Hire had notable improvements regarding oil use and storage. These visits were more than a year apart and allowed the businesses enough time to improve on previously highlighted issues (C. Kinloch, pers. comm.). In 2005, Blue Lake Watercare awarded six Best Practice Grants funded by the South East Natural Resources Management Board, of which four were taken up and completed. Dean and McCabe Windmills and Rock Valley Mechanical both received assistance to install oil-water plate separators, and bunded and roofed oil storage areas; C&R


Machining installed roofing and bunding in an oil storage area; and Auspine Nursery installed rainwater tanks to keep stormwater on the property and reuse it. In the latest, 2007 round of grants, five have been awarded. One of the grants was won by previous recipients Dean and McCabe Windmills, to assist with the purchase of a spray paint booth. The other projects successful in 2007 include stormwater retention and reuse at Patch Properties, Yahl Industrial Estate and Gambier Contracts Incorporated and the purchase and installation of an oil-water separator at South East Electric Motor Rewind. The grants assist concerned businesses to make improvements which would prove expensive for the individual to address in the short term. The grants complement the WaterCare approach of encouraging good stormwater management through education and example, and promoting “best practice” (C. Kinloch, pers. comm.).

Documentation of street sweeping and treatment device maintenance and modification. Implementation of improved treatment techniques could be assessed against the schedule for retrofitting high and low risk catchments.

The performance of treatment retrofits can be monitored by measuring the quality of stormwater discharging into bores at a small number of test sites. Groundwater quality in the city area should also be monitored for a complimentary suite of water quality parameters. Total petroleum hydrocarbon (TPH) has frequently been quantified in Mount Gambier’s stormwater and is likely to be a useful indicator of treatment performance. High priority metals and metalloids (As, Cu, Cr) need to be monitored in the total and soluble phase. As trace organics are not easily quantified using grab sampling, passive sampling techniques as utilised previously in stormwater drainage bores in Mount Gambier for PAHs are recommended (Komarova et al., 2006).

Monitoring water quality impacted by all contaminant pathways (Table 27). The general urban groundwater monitoring could also include signature species for various point sources, such as sewage or historical contaminant plumes. This plan also incorporates reinstatement of the CoMG stormwater monitoring program. The 10 catchments recommended for the stormwater monitoring program include those deemed as high risk catchments with existing water quality data (69, 282, 381, 281); residential catchments with existing water quality data (357, 99) and new monitoring locations identified as high risk with respect to the current urban land use (10, 293, 311, 319 or 72).

The National Guidelines for Water Recycling (NRMMC-EPHC-AHMC, 2006) adopt a risk management framework which is comprised of 12 elements. Stormwater recycling and its contribution to Blue Lake recharge can be assessed in relation to this framework (Appendix 5). It is recommended that this framework be developed and adopted in the future.


Table 27 Draft water quality monitoring plan required to support the proposed management options.

Monitoring station type

No Frequency Analytes Comment Status

Stormwater drainage wells

10 6 monthly N, P, major ions, organics, metals, pathogens

Passive sampling for organics (selected locations).

Program to be reinstated in catchments 69, 282, 381, 281, 357, 99 10, 293, 311, 319 or 72.

Triple chamber settling pits

6 2 monthly (for test period only)

metals, organics, suspended solids

To test effectiveness of stormwater pre-treatment strategies.

New program required for test period only.

Sewer (Finger Point WWTP)

1 3 monthly N, P, major ions, organics, metals

Existing program.

On-site wastewater treatment discharge/leachate

60

12

Once

3 monthly

N, P, major ions, organics, metals, pathogens

Add source signature species if applicable. New program

required.

Groundwater – general urban

5 12 monthly N, P, major ions, organics, metals

Groundwater – industrial

5 12 monthly N, P, major ions, organics, metals,

Review existing program. Add 2 bores on Lake Terrace (completed in Camelback and Unit 3).

Add Cl, SO4, HCO3, Ca, Mg, Na, K, TDS, pH (field), temp (field).

Groundwater – rural 5 12 monthly N, P, major ions, organics, metals, pathogens*

Add source signature species if applicable.

Passive sampler use in selected locations to complement use in stormwater drainage wells.

Existing program -Greater Mt Gambier bores. Add pH (field data)

Blue Lake 1 3 monthly

EPA/SA Water monitoring suite

Add source signature species if applicable

Existing program – may need revision.

*where groundwater is used for drinking


6.5. Summary of management options In summary, improved management of water quality impacts on Blue Lake from land use activities in the BLPCZ requires management options to address all the potential pathways for contamination. Currently, there are a number of programs in place to protect water quality, which could be improved as recommended below:

Conduct research to define appropriate management actions if the current level of

understanding is insufficient. This is currently underway for nitrate contamination from agricultural land use and on-site wastewater treatment through two CNRM funded projects. However an additional research program is required to understand the nitrogen and phosphorus cycles in Blue Lake, in relation to the potential for algal blooms and to define any management actions needed for phosphorus contamination.

City of Mount Gambier (CoMG) to develop a program to improve the potential for

stormwater treatment prior to discharge in the high priority spill and surface runoff catchments. This should encompass appropriate street sweeping and cleaning/maintenance schedules for existing treatment steps, in conjunction with examination of measures to enhance the existing stormwater treatment. The economic feasibility of providing improved treatment will be assisted by focusing efforts on the high risk catchments initially, equating to a small number of triple chamber settling pits (<30).

Focused industry inspections for the high risk activities to assess the strategies for

managing water quality in a program similar to the previous WaterCare program. Triple chamber pit retrofits made by CoMG could also be recommended to private bore operators.

In addition, these actions should be supported by monitoring programs and evaluation processes. Water quality monitoring programs need to be modified and/or developed to provide suitable evaluation of the management activities.

7. SUMMARY AND RECOMMENDATIONS The existing water quality data for Blue Lake does not show any potential for breach of water quality guideline values. Trace metal and metalloids illustrate some historical peaks in concentration. However there is no evidence to suggest rising concentrations within Blue Lake. Data regarding anthropogenic organic compounds in Blue Lake are rare. Thus it is recommended that any positive analytical detection warrants further investigation, including repeat sampling and analysis.

Currently, the 80th percentile for nitrate in Blue Lake (3.6 mg/L as N) exceeds the suggested ANZECC and ARMCANZ (2000) aquatic ecosystem targets, but is within the SA EPA (2003) value for total nitrogen (5 mg/L). Nitrate concentrations within the lake remain lower then the median groundwater concentration (9 mg/L as N) but are rising. In contrast, the total phosphorus concentrations in the lake are lower than all the possible target values, possibly limiting excessive biological activity. Setting conditional targets for nutrient concentrations in Blue Lake and groundwater in the capture zone relies on greater understanding of the inputs to the lake and the in-lake processes that may alter their concentrations. When aquatic ecosystem protection is the priority, it is essential to understand the critical nutrient loadings that can be tolerated. This is particularly relevant for limiting nutrients, where a marginal increase in input loading has the potential to alter the nutrient status of the system. Targets for input concentrations can be derived from the critical loadings for the lake.

Existing water quality guidelines are appropriate for monitoring major ions and metals in Blue Lake. However, it is recommended that provision be made in the monitoring programmes to


identify deviations from current trends (based on 80th percentile of historical data), so that they can be verified promptly. Targets have been proposed to manage nutrient concentrations in Blue Lake. These will allow identification of any alteration in trends in nutrient concentrations in the lake, which will allow the cause/s of any change to be determined and appropriate action decided upon. However a new program is required to set a baseline regarding the algal numbers and speciation within the lake.

It is suggested that anomalous water quality data be verified at the time of receipt. This may be as simple as checking the result with the laboratory or may require repeat sampling and analysis. This would ensure that outliers (such as those observed for Cu and Cr) are genuine and can be used to support an improved understanding of anthropogenic effects on water quality. In addition, analytical methodology and detection limits should be consistent within the catchment, including all sampling locations in Blue Lake, for the groundwater monitoring and also any monitoring for assessment of potential inputs. Currently, lower detection limits are available for Cu, Cr and Zn sampled from site 6 using ICP-MS (0.001, 0.003 and 0.003 mg/L respectively) compared to samples from the pump using ICP (0.03, 0.03 and 0.01 mg/L respectively). It is recommended that the more sensitive detection limit be chosen.

A preliminary review of the alternative sources for town water supply to Mount Gambier indicated that the sources of highest priority for further examination are continued extraction from the unconfined aquifer via Blue Lake, directly from the unconfined aquifer (not via Blue Lake) or from the confined aquifer. Surface water sources are limited by the expense associated with infrastructure and while indirect stormwater reuse is currently in operation, direct reuse (without aquifer storage) would also require new infrastructure. This evaluation reiterates the importance of protecting the water quality in the Blue Lake and its capture zone as the most likely source of water supply for Mount Gambier into the future.

Concurrently reviewing the in-lake processes and the associated uncertainties has allowed the future research focus to be targeted to priority tasks. High priority knowledge gaps were deemed to be the understanding of the local hydrostratigraphy, the phosphorus cycle and the biogeochemical processes at the sediment-water interface. An experimental program was undertaken to develop the understanding of natural attenuation processes in the system, both within the aquifer and in Blue Lake itself. A sulfur hexafluoride (SF6) applied tracer test was used to examine the potential for contaminants to migrate quickly to the lake via karst features. This study showed that it is possible for recharge via stormwater drainage wells to reach Blue Lake in approximately 2 years.

The chemical composition of lake sediments, collected in the water column and from the lake floor, was used to understand the in-lake removal of potential contaminants. Many inorganic species exhibited the highest concentration in sediments collected in the water column during the winter months, due to their association with organic matter. In contrast, the lead concentration was greatest during the warmer period of high carbonate production. Lead concentrations in the lake floor sediments were lower than in the water column, suggesting they are solubilised in the water column.

The inorganic species concentrations in the most recent lake floor sediments was generally comparable to those found settling in the water column during the periods of high carbonate production. The lake cores suggested that the rate of carbonate precipitation has increased with time and this effectively dilutes the concentration of most of the inorganic species. The particulate settling flux, which is currently governed by the annual carbonate cycle, provides a mechanism to remove inorganic species from the water column. Regardless of their association with either organic or inorganic carbon, trace inorganic chemicals are removed from the water column to the lake floor. As a result some inorganic species exhibit lower concentrations in the Blue Lake than in the groundwater, which provides the lake recharge.

The risks posed by the current urban land use on the water quality of Blue Lake were assessed using an urban land use map and a quantitative risk assessment. Dry cleaners and their use of tetrachloroethene (PCE) were deemed as a high risk activity in the urban area. PCE contamination of the aquifer should be minimised by best practice procedures such as spill containment and response plans, bunded storage areas and possible well-head


protection/treatment for bores likely to be affected. It is proposed that this be applied to all dry cleaning activities regardless of other activities within the catchment. The other hazards identified from the urban land use map were benzene, toluene, ethylbenzene and xylene (BTEX) and polycyclic aromatic hydrocarbons (PAH). However natural treatment is expected to remediate any incidence of contamination from these hazards.

While inorganic species can be filtered or adsorbed during aquifer passage, these processes may not be permanent and thus efforts to minimize their concentration prior to recharge are recommended. Based on the existing stormwater quality data, inorganic species are predominantly associated with particulate matter. Possible management options include installation of treatment devices capable of capturing the fine fraction particulates in particulate matter. Particulate removal will also serve to removal particle bound organics such as PAHs.

Currently, there are a number of programs in place to protect water quality, which could be improved by a number of activities:

Adopt a risk management plan for the Blue Lake. This would build on the risk assessment conducted in this study to outline the monitoring, evaluation, supporting programs.

Conduct research to define appropriate management actions if the current level of understanding is insufficient. This is currently underway for nitrate contamination from agricultural land use and on-site wastewater treatment through two CNRM funded projects. However an additional research program is required to understand the nitrogen and phosphorus cycles in Blue Lake, in relation to the potential for algal blooms and to define any management actions needed for phosphorus contamination.

City of Mount Gambier (CoMG) to develop a program to improve the potential for stormwater treatment prior to discharge in the high priority spill and surface runoff catchments. This should encompass appropriate street sweeping and cleaning/maintenance schedules for existing treatment steps, in conjunction with examination of measures to enhance the existing stormwater treatment. The economic feasibility of providing improved treatment will be assisted by focusing efforts on the high risk catchments initially, equating to a small number of triple chamber settling pits (<30).

Focused industry inspections for the high risk activities to assess the strategies for managing water quality in a program similar to the previous SENRMB/CoMG WaterCare program. Triple chamber pit retrofits made by CoMG could also be recommended to private bore operators.

Finally, it is recommended that the risk management framework within the Australian Guidelines for Water Recycling (NRMMC-EPHC-AHMC, 2006) be developed and adopted for Blue Lake and its groundwater. The current management of stormwater recycling for recharge to the Blue Lake Mount Gambier’s drinking water supply is summarised in relation to the 12 elements of the framework in Appendix 5.

.


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APPENDIX 1 IN-LAKE PROCESSES RESEARCH WORKSHOP NOTES Date: Mon 28th-Tues 29th November, 2005 Venue: Prescott Building Level 4 Meeting Room, CSIRO Waite Campus Attendees: Phil Gorey (EPA), Helen King (EPA), David Duncan (EPA), Glenn Harrington (DWLBC),

Saad Mustafa (DWLBC), Jeff Lawson (DWLBC), Nigel Fleming (SARDI), Andrew Telfer (Aus Water Env), Peter Dillon (CSIRO), Sébastien Lamontagne (CSIRO), Fred Leaney (CSIRO), Jeff Turner (CSIRO), Jo Vanderzalm (CSIRO), Brad Sherman (CSIRO) – phone hookup

Day 1: Monday 28th November, 2005 Nutrients and Ecosystems - Sébastien Lamontagne Factors limiting primary production in lakes: The amount of light Water column mixing and stratification Grazing and sedimentation losses Nutrient availability Major nutrients are N, P and S although S is rarely a limiting nutrient. Minor nutrients are Fe, Si, Mo and vitamins. Redfield ratios most lifeforms are about 106C:16N:P Can use ratios to estimate limiting nutrients: N:P > 16 P-limitation N:P < 16 N-limitation Mineralisation - conversion of nutrient from organic into inorganic compounds. Gross and net mineralisation rates can be hard to separate in the environment, but compare the change from year to year (net) vs total amount in and amount out (gross). Mineral weathering - conversion of nutrients from particulate inorganic into dissolved inorganic form, mainly P, Si, C. Mineral precipitation - reverse of weathering. Atmospheric deposition - wet = rainfall, dry = particle aerosols, gaseous deposition Bulk collectors sample wet deposition and some poorly defined fraction of dry deposition. Nitrogen - various redox states. Fixation = using N2 to produce organic N. Denitrification = NO3 into N2 or N2O. Nitrogen cycling (see diagram) - DOC from catchment generally high C:N ratio whereas that produced in lake is richer in N. Not sure whether lakes are net sinks or sources of N. Remixing can be a driver for degassing. Algae (PON) grow in upper part of water column (photic zone), preferring N from NH4

+, but can also use NO3-. PON subsides to bottom (sediments). Takes quite a while

(about 0.5m per day) so get a lot of decomposition and nutrient recycling. Microbial recycling and denitrification in sediments. Algae can gain N though fixation from the atmosphere when N is a limiting nutrient. Benthic zone important for recycling decaying nutrients settling through the lake. Temperature stratification of lake epilimnion = warm, low density layer at top of lake, metalimnion (aka thermocline) = greatest change of temperature, hypolimnion = area below thermocline, cool, high density lower layer of lake. Algae like to live in the thermocline - nutrients are greater at lower depths while light is greater at upper levels. Things to do for balancing the N budget - measure denitrification rates, measure mineralisation rates at the sediment/water interface, estimate gross and net algal uptake and sedimentation rates, determine if pumping influences the stratification regime and, indirectly, sedimentation and denitrification rates. DO declines to around 50% saturation at 60m below lake surface (AT), indicating there is a move to anoxic conditions. Martin Mingis (PhD thesis) measured N2 and N2O emissions and nitrification/denitrification rates from a lake using 15N labeled pools of N (difficult). Possible to measure denitrification rates with peepers (diffusison


chambers) placed at the water-sediment interface of using bulk chemistry to calculate budget in hypolimnion when stratified. Phosphorus - only one major chemical form as phosphate (PO4

3-). Insoluble, can form a variety of minerals. Negative charge, sorbs onto surfaces. Mobility and availability sensitive to redox conditions as dissolution of iron oxides can release previously sorbed phosphate. Soluble P is the fraction that passes through a 0.45 μm filter. Most P is in the particulate form in the water column. Very strong demand and internal cycling for phosphate in lakes. Phosphorus cycle (see diagram) - Erosion of the bank (caldera) could be a significant source of phosphorus to the lake (and can possibly be managed). Also could be pollen from pine plantations, seen as yellow scum on the surface and from insects deposited to the lake. Emergence of insects as a loss from the lake? (e.g. Midges/mosquito larvae). Could measure the level of enzyme activity in lake to determine the degree of P limitation. The key part of the P cycle is the efficiency of the sedimentation process and how fast it occurs (how quickly the P goes out of circulation). Formation of carbonate P minerals and physical loss of algae through sedimentation are 2 major loss processes. P can be released when sediments become anoxic. It is possible to build a preliminary P budget using current data and best guesses. Additional information that could be useful includes: Determining the degree of P limitation in the Blue Lake Determine the critical load for P to maintain lake in an oligotrophic state or "noxious algal bloom-free" state Determine how changes in stratification regime could influence the P cycle. Paleoecological analysis of cold finger cores (tape peel) could give information regarding changes in algal communities/primary production. (Action: Jo to follow up work of Derek Vogelscene, with George Ganf Adelaide Uni, on phosphorus limitation). George Ganf reported that this bioassay work was undertaken some time ago (before the advent of computers) and never written up. Therefore I have not been able to obtain any information on the outcomes. Please advise if you have any knowledge of this work. Carbon cycle (see diagram) - On-going slow rain of small calcium carbonate crystals through the water column gives a physical filtering effect for algae. Water flux into and out of the lake is a major pathway of carbon (as DIC), but atmospheric exchange is also important. By pumping we have increased the rate of water loss and water replenishment. The carbonate forming factors are still present in the lake, so the rate of carbonate formation has increased about threefold in the last 200 years. 90% of the upper sediments (from cold finger core) is inorganic C as opposed to organic C. Nick Turoczy's research - Jo Vanderzalm Turoczy et al., (in prep) Depth and seasonal dependence of groundwater entry into the Blue Lake, Mt Gambier, Australia. 18O and NO3

- evenly mixed through depth across the lake in winter. Peak in NO3- and 18O at 40m depth in

summer, suggested as evidence of groundwater intrusion from all sides of lake (centre, north, south, east, west). Peak in NO3

- concentration occurs about a month after the peak in pumping rate. However, discussion pointed out that horizontal mixing would lead to this effect rather than entry around the lake. N. J. Turoczy (2002). Calcium chemistry of Blue Lake, Mt Gambier, Australia, and relevance to remarkable seasonal colour changes, Arch. Hydrobiol, 156(1): 1-9. Highest suspended CaCO3 occurs in August, but is fine and does not settle until later in the year when production rates increase. Blue Lake In-lake processes and the nitrogen budget - Andrew Telfer Observations from ~1991-1994. Winter - low pumping, lake fully mixed, grey colour, groundwater inflow occurring and algae dispersed. Spring (November) - moderate pumping, input of heat, lake begins to stratify, peak calcite precipitation and tannin removal through coprecipitation on nucleation sites.


Summer (February) – continued heat to the upper water column, moderate calcite precipitation but occurring in a thicker column of water (deeper surface layer), thermocline, algae constricted below thermocline, blue colour. Colour deepens as summer progresses because column of clear water deepens. Autumn (May) - moderate pumping, algae and tannins mixed back into upper layer as circulation deepens, lake going grey colour. Calcite production is low over winter. Chlorophyll a (a measure of living species) is relatively constant at 40m depth, consistent with nutrient inflow. As the water column warms, the surface Chl a concentration decline as the algae go deeper to obtain nutrients. There is evidence of NO3

- reduction at the bottom of the lake in winter (just prior to mixing) and to a lesser extent in February. The potential of upward flow through the Dilwyn Formation contributing to these profiles was discussed. It was determined that there is little evidence for upward flow from the Dilwyn to Blue Lake. Ca isopleths peak below thermocline, DO around 40% of saturation. Calcite crystals ~10 μm diameter. A estimate of in lake N consumption at ~8 Tonne/year. Summer – lot more light coming out of water and more blue in water. Spring – less light coming out of water and also more green light present. An isotope record of changes in water and carbon budgets of the Blue Lake, South Australia - Fred Leaney Mackereth core (1980s) 13C, 14C and 18O of carbonate - 28,000 year hydrological history of the lake and levels controlled by sea level changes. Cold Finger core (early 2000s) 210Pb, 226Ra, 13C and 18O - changes in the water and carbon balance of the lake (1880-2000) Water residence time has reduced from 21 years in the 1880's to around 8 years now (1990s).13C balance gave a DIC residence time from 3.8 years originally to 2.2 years now. Not a linear relationship between the reduction in water and DIC residence times as DIC is affected by groundwater inflow and gaseous exchanges. Groundwater delivery rate of nitrate and predicted change in nitrate concentration in the Blue Lake, South Australia - Sebastien Lamontagne This project aimed to: review trends for NO3

- in the Blue Lake determine past NO3

- loading rates from groundwater attempt a short-term forecast for changes in NO3

- concentration in the lake. Change in mass of NO3

- from year to year = groundwater input + atmospheric deposition - in-lake consumption - pumping withdrawal - groundwater outflow. In-lake consumption is based on a mass transfer coefficient, taken from the literature at between 2.4 and 6.4 m/year for an oligotrophic lake. In-lake consumption 8-9 Tonne/year (agrees with independent calculation of AT). Forecast for NO3

- concentration - assumes that the rate of increase for groundwater NO3- will persist for the

next 30 years. Also forecast for different pumping regimes (high, low, and current). Forecast for next 30 years if groundwater continues to increase in NO3

- concentration is that lake water will continue to increase but still be drinkable in 30 years time. Largest impact on NO3

- concentration is the pumping rate - less pumping = longer residence time and more capacity of the lake to clean NO3

- from the water. Physical limnology - Brad Sherman Meteorology drives the seasonal stratification. Wind speeds from the Mount Gambier airport are higher than expected on the lake surface. There is no obvious trend in seasonality of wind speed. Penetrative convection is likely to be the most important surface mixing driver. Pan evaporation shows high evaporation in spring summer and autumn. Thermal stratification commences by early Spring. The surface layer depth is 10 to 15 m thick in spring and summer (approximately October to March). The deepest surface mixing layer is just before sunrise as the


cooling energy at the surface drives mixing deeper into the water column. Late March/early April the surface layer becomes slightly deeper. Little mixing occurs below thermocline. A small kink in the electrical conductivity profile at 32 m may reflect groundwater intrusion (chemical stratification). Inflow between 35 and 50m depth - small inflection point in temperature gradient = bottom of intrusion with little mixing below. Inflow rises up and alters conductivity profile in the 15 to 30m depth range. Chlorophyll data (Telfer, 2000) suggests a brief period only of complete mixing in August. Prefers chemical indicators to temperature indicators because can get isothermal water columns with no mixing. Inflows - hydrostratigraphy consistent with temperature and conductivity indicators of inflow level. As zone at the base of the lake may only be mixed for a short period it would be interesting to put an oxygen electrode down the bottom to record anoxic events. The water is pumped from the lake surface (4 GL/year) and most pumping takes place during summer when lake is warmest so the pumping is taking heat from the lake. Pumped water may be about 5 degrees warmer than the inflowing groundwater. If taking 7m off height of water column, this would remove about half of the surface mixing layer. Over summer there is a net fall in water level, have had about 2-3m decline in water level over the last 30yrs. The mixed layer depth will basically remain the same because the sun is so powerful that it will just heat it up again. You may get a little bit of cooling but not a huge amount. There is strong feedback between the temperature of the surface layer and the air temperature. Lake surface will not radiate as much heat at night if slightly cooler on surface and will tend to heat up again to an equilibrium temperature. Would be surprised if mixed layer/thermocline depth is significantly impacted by intrusion of groundwater. Optical properties (ie increased algal growth) would shift thermocline position as the clearer the water, the weaker the temperature gradient because more light percolates down into the water column. Thus, strong temperature gradient closer to the surface exist in water bodies where water is very turbid. Chlorophyll data indicates high concentrations below the thermocline. Not uncommon to have subsurface chlorophyll maxima like this, particularly if the only nutrient supply is coming through the groundwater intrusion. Divers report distinct bounds of production. Additional information from diver’s observations (reports by Peter Horne): Visibility dramatically reduced below thermocline January 1985. Visibility poor 25 to 40m in January 1987. Visibility reasonably constant during July, 1985. Stalagmite formations at 45m on the NE face. Sponge like spires, consisting of calcite tubes, at 20m in thermocline on N side. Upward migration of plankton at night. Biology reported in Blue Lake: Algae – Closterium, Sunedra, Glenodinium, Surirella, Rhizoclonium, Ulothrix, Zygnema, Blue-green algal mats?, Chara, Chrysophota (diatoms), Bacillariophycae Zooplankton – copepods Amphipods Molluscs Profiles at different locations around the lake (centre, north, south, east, west ) are very consistent. This is very typical because horizontal diffusion is 5 orders of magnitude greater than vertical diffusion (Action: Jo feedback to Nick T). Look for the movement pattern of a warm intrusion going straight up (with entrained water) until in equilibrium with surrounding water, and then moving towards the centre of the lake. Would need to look for this pattern. Could use a tracer to test the movement. Conceptual model of in-lake processes – Jo Vanderzalm A conceptual model of in-lake processes was discussed and modified. The final draft and a simple common English summary is incorporated in the Target Condition report. Knowledge gaps Further monitoring of sediment traps/sediment via cores would be useful to understand the sedimentation process and what effect it has on in-lake processes. Collection of data could be improved for biological processes. Potential to measure the partial pressure of carbon dioxide as a measure of primary production. Would first look at and synthesise information from current sampling programme (3 times per year) before embarking on a new monitoring programme.


Day 2: Tuesday 29th November, 2005 Hydrostratigraphy - Jeff Lawson Gambier Limestone consists of Green Point (Units 1-5), Camelback and Greenways Members. U1-U5 of Green Point are alternating aquifers and aquitard. However marl content of aquitards is variable and they can act as aquifers. The extent of these members varies spatially. New bore on Lake Terrace Site is missing U1. NW (city area), Camelback Unit outcrops. Moving eastward additional units are added on top of the Camelback until to the NE all units are present. Geophysics has been used to identify faulting, which seem to be under surface sand dunes around Mt Gambier. The high gradient zone to the NE of Blue Lake is due to faulting. The Tartwarp fault is actually a double fault. Also evident is high level of fracturing at the top of the Camelback unit with porosity increasing from an average of around 12% in U3 and U4 to an average and maximum of 17% and 32% respectively in the Camelback. Plan to use geophysical tools on all bores used for SF6 injection in January 2006. 80m displacement of the top of the Dilwyn formation is evident at the fault in Blue Lake. There is potential for underflow from the Gambier Limestone to the Dilwyn, which could then move upwards and into Blue Lake. Possible flows to the lake from the south in Unit 1, whereas Camelback shows outflow. Boundaries of the Blue Lake Capture Zone may need to be revised. Setting and applying water quality targets - Dave Duncan NWQMS National Water Quality Management Strategy provides a framework for setting targets. The key questions include: What do we value? What are the threats to these values? What must we do to maintain these values? What will it cost and are we willing to pay for everything? What values will we pay to protect? Each step for setting targets requires scientific input and consultation. The steps are: Primary management aims Determine water quality guidelines Define water quality objectives Monitoring/assessment/management response. The outcome of consultation is clearly defined statements of environmental values and management responses. It is important to focus on processes, not just water quality, what are/are not threats and the critical control points to monitor/manage the system. Assess all possible affecting factors and discard those which will have no effect on the desired environmental values and environmental objectives. Determine target for those factors which are important to the desired values and objectives. Water quality - Jo Vanderzalm Water quality trends in Blue Lake for C, N, P in comparison to possible water quality criteria from the ADWG (drinking), SA EPA’s EPP (aquatic ecosystem) and NWQMS (aquatic ecosystem). EPP aquatic ecosystem water quality criteria are generally higher than the NWQMS as the EPP is based on a value that will cause harm while the NWQMS is based on a value to protect against harm. Generally looking at 2nd most stringent value in NWQMS (to protect 95% of species) for a slightly disturbed ecosystem. Bicarbonate annual cycle with lower concentrations evident in summer. DOC well within suggested criteria, peak evident in 1990’s. Chl a peak in winter at pump, higher at 40m (in agreement with AT data). NO3

- trending upwards potential to exceed suggested AE criteria (TN 5 mg/L). May be lower values coinciding with DOC peaks. NH4

+ is variable peaking in early summer and could provide additional information regarding N cycling. Also higher in 1990’s, cause of this peak needs to be considered for information regarding in-lake cycling.


Total dissolved phosphorus should be considered, not just filterable reactive phosphorus (FRP). FRP low, peak in 1990s. (Action: Jo to confirm analytical details with AWQC). Discussion of setting targets considered. No current microbiological raw water quality targets (SA Water now have no raw water targets, only end-of-tap values). P concentration is critical, but probably will continue to be cleaned up in transit to lake. NF CNRM project to examine management changes to maintain N concentrations in groundwater at moderate levels. DD urged caution with adopting drinking water guidelines as these are the critical upper bounds. Suggested a tiered management approach with more detailed monitoring implemented after initial trigger is met. High risk factors need to be addressed. Targets need to warn of approaching critical levels rather than saying that a disaster has already arrived. PD possible treatment of stormwater drainage, sewage leaks to be addressed. PG can base trigger targets on a statistical analysis of existing levels, which provides something to report against. The likely time-frame between a land management change and impact on Blue Lake water quality was discussed with estimates of 40 to 200 years from modeling work (Dillon, 1988) and Cl response to stormwater inputs (AT). Any target which involves high costs including opportunity costs of foregone industry, requires a justifiable need for the target. Specify a framework for what works now and how to assess a monitoring framework for changes in water quality. Get an assessment of likely ecological impacts of various pollutants, catastrophic events, etc. Blue Lake Management Plan assesses some of these risks - start by reviewing the risks and responses in the management plan. e.g. management of traffic around the blue lake, emergency response for spills down stormwater drains. (Action: Jo to report on work by Mia Thurgate on stromatalites in Blue Lake or other aquatic ecosystem work). Changes in drivers that affect blue lake water quality - Sébastian Lamontagne There are gaping holes in our knowledge regarding the ecology. Need to set up the N balance, P and C balances of the lake. Need institutional ownership of Blue Lake from a limnological/ecological perspective. This will allow future experiments to be designed to provide mutual benefit/input for all relevant aspects. Extend the type of work done by AT in the 1990’s. How important is the permanent sedimentation of N? From Herzecg et al., net N sedimentation = 180 kg N/yr. Most N is recycled either in the water column or on the surface of the sediment. Denitrification - wide range of rates in literature, 0.3-3 tons N/yr, ammonium deposition 30-60 kg N/yr. WSIBal – Jeff Turner Water, conservative Solute and environmental Isotope mass Balance is a transient lumped mass balance model using simultaneous solutions coupled to balances for water, a conservative solute and environmental isotopes. It provides a 3 way constraint to understand the water level in lakes and has been applied to Blue Lake up until 1995. It can also be coupled to a geochemical model. Currently run with fixed inputs for Cl and isotopic signatures. Isotopic signatures of unconfined and confined aquifers similar and therefore not useful in determining their relative contributions to Blue Lake. Future runs will include sensitivity analysis to examine the importance of varying the Cl inputs. Groundwater outflow stopped at the point of maximum pumping (1976-1986) but has since returned. 8-10 year lake residence time. Groundwater outflow evident in ‘bore 4’ on the southern side of Blue Lake, identified by evaporated isotopic signature. Possible to add another conservative solute such as F (data exists). JT suggested repeating work of Ramamurthy using uranium to determine the contributions from the confined and unconfined aquifers. General discussion related to setting targets for Blue Lake and the significance of in-lake processes when compared to land management choices followed. The short- and long-term risks to water quality in Blue Lake are evaluated in the Table below. The outcomes and a structure for setting targets for Blue Lake, along with indicators are incorporated into the Target Condition Report.


Issue Short Term Risk

Long Term Risk

Reasons behind risk assessment & controls available

Nitrate* Low Moderate

Intensifying dairy and horticulture increase nitrate leaching to g/w. Forest expansion reducing recharge from low N input areas, offset to some degree by increased recharge of low N stormwater in expanding Mt Gambier. Hence N conc in g/w feeding BL is more likely to increase than stay constant. Upward trend of N in BL to ~4 mgN/L cf 11 mg N/L drinking guideline. N attenuation capacity in lake limited by organic cycle which is limited by P (not N). Main control is land management – addressed in companion CNRM project (Project leader Nigel Fleming). It was noted that the steepest increase in NO3 in BL was in 70s when pumping rates from BL were highest. Possibility that greater induction of water from upper units of Greenpoint Formation with higher NO3 concentrations occurred. More hydrogeological and groundwater quality information would help resolve this.

Algal blooms*

Low Low Limestone aquifer is effective at stripping P which is the limiting nutrient for algal growth in BL. P balance is yet to be done e.g. sources include pollen, insects, bird droppings, caldera erosion and vegetation control programs, and groundwater inflow. Shock P loadings from fertiliser or other chemical spills need to be considered. Anecdotal evidence suggests that when lights temporarily installed on pontoon local algal blooms occurred due to lights attracting insects, that would fall in the water attracting fish, that attracted cormorants, whose excreta provided enough nutrients for small algal bloom at the pontoon. When use of lights was discontinued the bloom disappeared. Several periods of slightly elevated FRP in lake may be related to factors above (e.g. lights, vegetation control, forest fires) and their timing should be followed up to see if any relationship exists. Control: aquifer acts as good control for P removal in g/w although effectiveness for drainage water entering Camelback directly was questioned. Prevention of fertiliser or other chemicals containing P from entering the lake directly or via drainage water would help to prevent shock loadings.

Anthropogenic organics*

Low Low Existing source controls such as for hydrocarbons, PAHs, and pesticides in the stormwater system and in agricultural chemical practices are likely to be effective in reducing concentrations of these reaching the g/w and the lake. Calcite precipitation with co-precipitation of POC is likely to strip these from the water column, where they would be bound up in benthic sediments on the floor of the lake. Those that can degrade under anaerobic conditions may subsequently be attenuated. There has been no detection of these in the lake water and sediment cores may reveal whether they have ever reached the lake and been removed. Prevention of pesticide spills would protect aquatic ecosystem.

Metals* Low Low As for anthropogenic organics, if metals reach the lake they are likely to be found in the sediments. Evidence of some elevated concentrations of Cu and Cr in lake water on at least one occasion in the mid-1990s suggests this record should be found in lake sediments, which may be able to provide a history of such events.

Endocrine disruptors*

Low Low Any EDCs of sewage origin are considered to be very dilute, and to have no consequences for human health. Their effect on lake organisms is expected to be very small and like other trace organics will be stripped during calcite precipitation.

Pathogens* Low Low Even pathogens entering drainage wells and traveling via Camelback karst features are likely to have a travel time adequate


Issue Short Term Risk

Long Term Risk

Reasons behind risk assessment & controls available

for removal. This will be better known when SF6 results for the first 6 months are analysed. However pathogens affecting humans are a food source to environmental organisms, and will not affect the aquatic ecology. Disinfection is required by SA Water prior to distribution of the water and if there are any remaining pathogens they will be removed then. The lake is not considered as requiring protection for recreational bathing, which would conflict with its use as a drinking water source.

* in-lake processes expected to contribute to removal from Blue Lake


APPENDIX 2 SUMMARY OF QUALITATIVE RISK ASSESSMENT


APPENDIX 3 ESTIMATING THE IMPORTANCE OF VARIOUS SOURCES TO CONTAMINANT LOADS Issue Source Approx.

load Comment

N Agricultural land use On-site wastewater treatment (OWTS) Fertilizer application (urban area) Sewer leaks

550 T/yr 60 T/yr 30 T/yr 6 T/yr

LEACHM calc (J. Hutson, pers.comm.) LEACHM calc for rural residential (J. Hutson, pers.comm.) 500 ha public open space, 59 kg/ha from irrigated sown grass (J. Hutson, pers.comm.) Assume sewer leaks add 1% of groundwater recharge (Wolf et al.,, 2006)

P (algal blooms) Changing N/P in BL Spills OWTS Sewer leaks

? ? 2 T/yr 0.2 T/yr

Currently P limitation is thought to prevent algal blooms Shock loading directly to lake Based on N:P molar ratio of 16:1, mass ratio of 37:1, removal in aquifer is likely to be high

Anthropogenic organics

Spills Urban runoff Pesticide leaching Leaking storage Sewer leaks OWTS

Various species – qualitative assessment

Shock loading directly to lake or aquifer Directly to aquifer Diffuse source Industrial contaminants Domestic and industrial waste Domestic waste

Metals Industrial spills Urban runoff Sewer leaks OWTS

Various species – qualitative assessment

Shock loading directly to lake or aquifer Directly to aquifer Domestic and industrial waste Domestic waste

Pathogens OWTS Sewer leaks Urban runoff

1017 cfu 1016 cfu 109 cfu

Assume an order of magnitude > sewer leak Based on wastewater 107 /100 mL cfu Assume 1% of stormwater recharge is contaminated


APPENDIX 4 TRACE ORGANIC ANALYSIS UNDERTAKEN BY SOUTHERN NEVADA WATER AUTHORITY

Description Blue Lake 40 m Travel Blank Travel Blank Travel Blank

Sample Date 12/05/2005 12/05/2005

Analyte ppt ppt ppt ppt

Hydrocodone <1.0 <1.0 <1.0 <1.0

Trimethoprim <1.0 <1.0 <1.0 <1.0

Acetaminophen 4.0 <1.0 <1.0 <1.0

Caffeine 37 <10 <10 <10

Erythromycin-H2O <1.0 <1.0 <1.0 <1.0

Sulfamethoxazole <1.0 <1.0 <1.0 <1.0

Fluoxetine <1.0 <1.0 <1.0 <1.0

Pentoxifylline <1.0 <1.0 <1.0 <1.0

Meprobamate <1.0 <1.0 <1.0 <1.0

Dilantin <1.0 <1.0 <1.0 <1.0

TCEP <10 <10 <10 <10

Carbamazepine <1.0 <1.0 <1.0 <1.0

DEET <1.0 <1.0 1.2 1.1

Atrazine 7.7 <1.0 <1.0 <1.0

Diazepam <1.0 <1.0 <1.0 <1.0

Oxybenzone <1.0 <1.0 <1.0 <1.0

Estriol <5.0 <5.0 <5.0 <5.0

Ethynylestradiol <1.0 <1.0 <1.0 <1.0

Estrone <1.0 <1.0 <1.0 <1.0

Estradiol <1.0 <1.0 <1.0 <1.0

Testosterone <1.0 <1.0 <1.0 <1.0

Progesterone - APCI <1.0 <1.0 <1.0 <1.0

Androstenedione <1.0 <1.0 <1.0 <1.0

Iopromide <1.0 <1.0 <1.0 <1.0

Naproxen <1.0 <1.0 <1.0 <1.0

Ibuprofen <1.0 <1.0 <1.0 <1.0

Diclofenac <1.0 <1.0 <1.0 <1.0

Triclosan <1.0 <1.0 <1.0 <1.0

Gemfibrozil <1.0 <1.0 <1.0 <1.0

-BHC <5.0 <5.0 <5.0 <5.0

-BHC <5.0 <5.0 <5.0 <5.0

-BHC <5.0 <5.0 <5.0 <5.0

Diazinon <5.0 <5.0 <5.0 <5.0

-BHC <5.0 <5.0 <5.0 <5.0

Aldrin <5.0 <5.0 <5.0 <5.0

Chlorpyrifos <5.0 <5.0 <5.0 <5.0

Fluoranthene 6.1 <5.0 <5.0 <5.0

Dieldrin <5.0 <5.0 <5.0 <5.0

BDE #28 <10 <10 <10 <10

BDE #47 <10 <10 <10 <10

BDE # 100 <10 <10 <10 <10

BDE #99 <10 <10 <10 <10

BDE #154 <10 <10 <10 <10

BDE #153 <10 <10 <10 <10

BHT 2599 3337 1955 2969

Bisphenol A <100.0 163 <100.0 <100.0

Nonylphenol (sum) 910 194 22000 10380

NDMA <2.5 <2.5 27 <2.5


Description

MG001,

BLA018

(Ground Water)

MG002,

BLA154

(Ground Water)

MG003,

Blue Lake

MG004, Wastewater

pump station adjacent

hospital

MG005,

Trip Blank

Sample Date 9/10/2006 9/10/2006 11/10/2006 11/10/2006 9/10/2006

Electrical conductivity (us/cm) 1620 767 646 - -

pH 7.23 7.43 7.42 - -

Temperature (°C) 16 16 15.3 - -

SWL (m) 33.8 29.4 - - -

Analyte ppt ppt ppt ppt ppt

Sulfamethoxazole <0.25 1.6 <0.25 5500 <0.25

Atenolol <0.25 <0.25 <0.25 2400 <0.25

Trimethoprim <0.25 <0.25 <0.25 2900 <0.25

Fluoxetine <0.50 <0.50 <0.50 4.8 <0.50

Norfluoxetine <0.50 <0.50 <0.50 <2.5 <0.50

Meprobamate <0.25 <0.25 <0.25 <1.25 <0.25

Dilantin <1.0 <1.0 <1.0 7.7 <1.0

Carbamazepine <0.50 <0.50 <0.50 780 <0.50

Atrazine 0.33 26 7.1 38 <0.25

Diazepam <0.25 <0.25 <0.25 <1.25 <0.25

Linuron <0.50 <0.50 <0.50 <2.5 <0.50

Atorvastatin <0.25 <0.25 <0.25 410 <0.25

o-Hydroxy atorvastatin <0.50 <0.50 <0.50 640 <0.50

p-Hydroxy atorvastatin <0.50 <0.50 <0.50 890 <0.50

Risperidone <0.25 0.34 <0.25 <1.25 <0.25

Enalapril <0.25 <0.25 <0.25 98 <0.25

Gemfibrozil <0.25 <0.25 <0.25 6100 <0.25

Bisphenol A 280 90 20 380 34

Simvastatin <0.25 <0.25 <0.25 <1.25 <0.25

Simvastatin hydroxy acid <0.25 <0.25 <0.25 14 <0.25

Diclofenac <0.25 <0.25 <0.25 150 <0.25

Naproxen <0.50 <0.50 <0.50 4600 <0.50

Triclosan <1.0 <1.0 <1.0 340 <1.0

BHA <25 <25 <25 464 <25

BHT <25 <25 <25 103 <25

DEET <25 <25 <25 162 <25

octylphenol <25 <25 <25 <25 <25

Benzophenone <25 <25 <25 98 <25

-BHC <10 <10 <10 <10 <10

-BHC <10 <10 <10 <10 <10

-BHC <10 <10 <10 <10 <10

TCEP <50 <50 <50 671 <50

Fyrol PCF <50 <50 <50 2900 <50

Diadzinon <10 <10 <10 <10 <10

-BHC <10 <10 <10 <10 <10

Traseolide <25 <25 <25 <25 <25

Galaxolide <25 <25 <25 1750 <25

Tonalide <25 <25 <25 <25 <25

Vinclozolin <10 <10 <10 198 <10

Metolachlor <10 <10 <10 <10 <10

Musk Ketone <25 <25 <25 <25 <25

Octachlorostyrene <10 <10 <10 <10 <10

Butylbenzyl phthalate <50 51 <50 264 <50

Methoxychlor <10 <10 <10 <10 <10

Dioctyl phthalate 56 63 54 486 <50

Nonylphenol 537 258 <50 766 <50

Iopromide <5.0 <5.0 <5.0 <25 <5.0


Appendix 5 Timeline of events in Mount Gambier

1800 Mount Gambier's mountain named

1840 Settlement

1845 Police station

1847 Hotel, general store, post office, police barracks

1850 Agricultural farming

1855 First 1/4 acre township allotments sold

1858 School

1861 Newspaper

1863 Council

1867 Flour processing (added oat processing in 1875)

1876 Native tree nursery

1879 Railway

1880 Forestry

1880s Hand dug drainage wells

1882 Old Town Hall constructed

1884 Pumping station Blue Lake

1892 Cave gardens constructed

late 1800 Manufactured coal gas plant

1883 Reticulated water supply began

1930-1950 Numerous small slaughterhouses and cheese processors operated

1940s Drainage wells drilled

1954 Declared city

1954 Pine Industries site making furniture components

1963 Ceased manufactured coal gas

1963 Tempered liquified petroleum (TPG) at coal gas site

1960s Panelboard production commenced

1966 Pine Industries site opened Green Mill and began using pentachlorphenol (PCP)

1970 Sewer system

1970s Rubbish dump in city ceased

1970s Saleyards ceased

1970-1990 Industrial contamination

1973 Drainage wells have silt traps

1976 Water Resources Act

1977 Pentachlorophenol spill into drainage bore at Pine Industries site

1980 Ceased tempered liquified petroleum (TPG)

1980s Fuel spill in the Cave Gardens

1980-1990 Creosote spills

1993 Pine Industries ceased using pentachlorophenol (PCP)

1995 CCA spill

1997 Ceased Orchard Road landfill

2001 Blue Lake Management Plan

2004 Risk analysis

2005 EPA Guideline Stormwater Management


APPENDIX 6 DRAFT RISK MANAGEMENT FRAMEWORK Table A6.1 Draft framework for managing the recycled stormwater component in recharge to Blue Lake, Mount Gambier’s drinking water supply. Framework element and components Activity Element 1: Commitment to responsible use and management of recycled water Components: Responsible use of recycled water Recycled water policy Regulatory and formal requirements Engaging stakeholders

Stormwater discharge to the groundwater recognised as a major component of the recharge to Blue Lake Commitment from State and Local government to protect Blue Lake and its aquifer system - Blue Lake Management Plan (2001; 2006) SA EPA (2005) guideline for the management of stormwater in Mount Gambier in new developments Water Quality Environmental Protection Policy SA EPA Licence arrangements

Element 2: Assessment of the recycled water system Components: Identify intended used and source of recycled water Recycled water system and analysis Assessment of water quality data

Environmental values of Blue Lake include drinking water supply, maintaining the annual colour change and clarity, prevention of algal blooms Stormwater discharge to the groundwater is a major component of the recharge to Blue Lake (Section 2.1.3 Blue Lake water balance) Stormwater quality indicates potential to breach water quality guidelines for inorganic chemicals, nutrients, trace organic chemicals No evidence of degradation in Blue Lake water quality from long-term stormwater discharge Nitrate levels in Blue Lake are increasing but not due to stormwater discharge (Section 1 this report)

Hazard identification and risk assessment Hazard identification based on the current urban land use identified risks from BTEX, PAHs, PCE, CCA in stormwater discharge (Section 4 this report) Knowledge gap identified regarding P cycle in Blue Lake, could impact on algal blooms (Section 2 this report)

Element 3: Preventative measures for recycled water management Components: Preventative measures and multiple barriers Critical control points

Chlorination of Blue Lake (human health) Stormwater pre-treatment includes gross pollutant removal through street sweeping and three-chambered settling pits Industry best-practice Community awareness (e.g. drain stencilling) Potential modifications include improved pre-treatment (fine material, organic contaminants) in high risk stormwater catchments (Section 5 this report) Aquifer and lake storage

Element 4: Operational procedures and process control Components: Operational procedures Operational monitoring Corrective action

Prevent gross contamination stormwater – spill response actions, council maintenance of stormwater pre-treatment Monitoring recommendations based on groundwater and Blue Lake quality (Section 2 this report) Disinfection, post-treatment measures if necessary (human health)


Equipment capability and maintenance Materials and chemicals

Stormwater pre-treatment measures – maintenance schedule, suggest upgrade in high risk catchments Material used for stormwater treatment and drainage well construction suitable for function

Element 5: Verification of recycled water quality Components: Recycled water quality monitoring Application and discharge site monitoring Satisfaction of users of recycled water Short-term evaluation of results Corrective action

Stormwater quality monitoring undertaken (1971-1982; 1999, 2002, 2004) Groundwater quality monitoring undertaken annually Blue Lake water quality monitoring undertaken at various frequencies, based on parameter/s of interest Recommendations for monitoring program and evaluation of results (Section 2 this report) Corrective action depends on the exceedence

Element 6: Management of incidents and emergencies Components: Communication Incident and emergency response protocols

Protocol for managing spills that could impact on stormwater quality

Element 7: Operation, contractor and end user awareness and training Components: Operator, contractor and end use awareness and involvement Operator, contractor and end user training

Drillers – appropriate drainage well construction (material and depth) WaterCare program - Industry education regarding stormwater quality and impacts on reuse Industry best practice

Element 8: Community involvement and awareness Components Community consultation commendation and education

WaterCare program - Community education regarding stormwater quality and impacts on reuse

Element 9: Validation, research and development Components Validation of processes Design of equipment Investigative studies and research monitoring

Water quality monitoring within Blue Lake Stormwater treatment device – design and test new device or retrofit of existing infrastructure P cycling, aquifer residence time, contaminant attenuation, hydrostratigraphy

Element 10: Documentation and reporting Components Management of documentation and records Reporting

All results to be recorded and stored Results reported on an annual basis to EPA/NRMB (via Blue Lake Management Committee)

Element 11: Evaluation and audit Components Long-term evaluation of results Audit of recycled water management

Reporting (Section 2 this report) Blue Lake Management Committee

Element 12: Review and continual improvement Components Review by senior managers

Blue Lake Management Plan review

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