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Glenorchy City Council Derwent Park Stormwater Harvesting and Industrial Re-use

Project Aquifer Storage and Recovery (ASR) Environmental Effects

Report (EER) Supplement

April 2013

GHD | Report for Glenorchy City Council - Derwent Park Stormwater Harvesting and Industrial Re-use Project,

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Table of contents 1. Introduction ............................................................................................................................... 1

1.1 Purpose of this report ...................................................................................................... 1 1.2 Report Format ................................................................................................................. 1 1.3 Scope and limitations ...................................................................................................... 1

2. EER Response ......................................................................................................................... 2 2.1 Conceptual Hydrogeological Model.................................................................................. 2 2.2 Pilot ASR Modelling ......................................................................................................... 5 2.3 ASR Operation ................................................................................................................ 6 2.4 Water level and quality management and monitoring ..................................................... 10 2.5 General water level and quality monitoring and control .................................................. 13

Table index Table 1 Standing Water Levels (mAHD) ....................................................................................... 2

Table 2 Aquifer Hydraulic Properties ............................................................................................ 5

Table 3 Estimated short-term well yields ...................................................................................... 8

Table 4 Key requirements within the Derwent Park ASR risk management plan for progression to a Stage 4 operational assessment .......................................................... 16

Figure index Figure 1 Observed groundwater head contours (simple contours with no coastal control) .............. 3

Figure 2 Steady-state modelled groundwater head contours .......................................................... 4

Figure 3 ASR Bore locations (as at 27 April 2013). ........................................................................ 9

Figure 4 Dolerite and Tertiary clay aquitard (red) ......................................................................... 11

Figure 5 Proposed drilling traverse (red dashed line) ................................................................... 12

Figure 6 ASR Process flow chart ................................................................................................. 15

Appendices Appendix A – Annotated EER Response Requests

Appendix B – Preliminary, Proof of Concept Groundwater Model

Appendix C – Preliminary Subsidence Assessment

Appendix D – Revised EER Commitments


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1. Introduction 1.1 Purpose of this report

This report has been prepared to formalise the response to various requests for additional information on the Environmental Effects Report (EER)1 from the Environmental Protection Authority (EPA) on 21 December 2012 and additional feedback of 5 March 2013.

1.2 Report Format

As there several instances where multiple comments can be answered with the same additional information, in order to avoid unnecessary repetition the supplementary information has been presented with the response information presented in standard report format, rather than in the format of the request and answer. To enable tracking of responses, the requests for information have been reproduced in Appendix A with references to the relevant sections of this report that address the requests.

Commitments given in the EER have been amended and are presented in Appendix D as commitments 15 onwards.

1.3 Scope and limitations

This report has been prepared by GHD for Glenorchy City Council and may only be used and relied on by Glenorchy City Council for the purpose agreed between GHD and the Glenorchy City Council as set out in section 1.1 of this report.

GHD otherwise disclaims responsibility to any person other than Glenorchy City Council arising in connection with this report. GHD also excludes implied warranties and conditions, to the extent legally permissible.

The services undertaken by GHD in connection with preparing this report were limited to those specifically detailed in the report and are subject to the scope limitations set out in the report.

The opinions, conclusions and any recommendations in this report are based on conditions encountered and information reviewed at the date of preparation of the report. GHD has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared.

The opinions, conclusions and any recommendations in this report are based on assumptions made by GHD described in this report. GHD disclaims liability arising from any of the assumptions being incorrect.

GHD has prepared this report on the basis of information provided by Glenorchy City Council and others who provided information to GHD (including Government authorities), which GHD has not independently verified or checked beyond the agreed scope of work. GHD does not accept liability in connection with such unverified information, including errors and omissions in the report which were caused by errors or omissions in that information.

1 Glenorchy City Council (2012) Derwent Park Stormwater Harvesting and Industrial Reuse Project Aquifer Storage and Recovery Project Draft Environmental Effects Report June 2012

2 | GHD | Report for Glenorchy City Council - Derwent Park Stormwater Harvesting and Industrial Re-use Project, 32/16745

2. EER Response 2.1 Conceptual Hydrogeological Model

2.1.1 Upper and lower water table levels.

Groundwater static water levels (SWL), where available, range from approximately 0.93 mAHD to 19.78 mAHD. Available reduced levels water levels are summarised in Table 1 and contoured on Figure 1 (simple Krigged contours of average SWLs with no control data along coastal boundaries). The modelled (Section 2.2 and Appendix B) baseline steady state heads (Figure 2) which take in to account the interpreted geology show a similar distribution.

Table 1 Standing Water Levels (mAHD)

Well ID

Easting (mMGA)

Nothing (mMGA)

Ground elev (mAHD LIDAR)

SWL (mBTOC)

SWL (mAHD)

SWL Date

BH01 524294 5257169 9.81 4.20 5.61 8/03/2011 BH02 523835 5257138 13.79 0.97 12.82 20/04/2011 BH2A 523835 5257138 13.79 4.40 9.39 9/03/2011 BH03 524048 5257150 10.78 7.20 3.58 BH04 524312 5257271 6.06 6.00 BH05 524500 5257231 5.02 BH06 524661 5257213 6.40 3.30 3.10 1/05/2011 BH07 524678 5257175 6.03 4.40 BH08 524714 5257296 3.23 2.30 0.93 16/08/2011 BH09 524520 5256967 14.79 10.73 4.06 24/11/2011 BH10 524986 5256503 28.11 14.65 13.47 22/08/2011 BH11 524497 5257373 6.42 3.85 2.57 15/08/2011 BH12 524754 5257065 9.66 7.00 2.66 17/08/2011 BH13 524079 5257813 19.27 18.00 1.27 22/08/2011 BH14 523820 5257642 12.67 1.41 11.26 7/09/2011 BH15A 523546 5257270 16.48 2.30 14.18 4/09/2011 BH15P 523546 5257270 16.48 2.59 13.89 BH18 523980 5256811 15.87 BH20 524050 5256637 18.43 5.70 12.73 29/08/2011 BH22 524382 5255983 23.00 3.22 19.78 31/08/2011 BH23 524682 5257301 3.53 2.37 1.16 30/08/2012 BH24 524565 5257390 6.82 3.98 2.84 30/08/2012 BH25 524421 5257373 8.89 BH26 524635 5257301 3.32 0.93 2.39 31/08/2012 BH27 522549 5258045 9.76 1.70 8.06 12/09/2012 BH28 522821 5257984 7.63 BH29 522614 5257384 9.62 BH30 524337 5257207 8.27 4.13 4.14 31/10/2012 BH31 524435 5257207 7.54 3.38 4.16 31/01/2012 BH32 524486 5257283 4.37 1.55 2.82 1/11/2012


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Well ID

Easting (mMGA)

Nothing (mMGA)

Ground elev (mAHD LIDAR)

SWL (mBTOC)

SWL (mAHD)

SWL Date

BH33 524317 5257375 11.82 8.28 3.54 2/11/2012 BH34 523313 5257503 18.36 5.53 12.83 27/11/2012 BH35 523460 5257357 16.71 2.76 13.95 27/11/2012 BH36 523167 5257931 20.00 9.73 10.27 6/03/2012 BH37 523169 5257812 20.00 9.65 10.35 13/03/2013 BH38 523266 5258162 19.00 10.40 8.60 18/03/2013

Note coordinates are mostly hand-held GPS (E and N) and estimations from LIDAR elevations. Detailed survey is underway.

Figure 1 Observed groundwater head contours (simple contours with no

coastal control)


Figure 2 Steady-state modelled groundwater head contours

2.1.2 Recharge Areas

As discussed in the modelling report (Appendix B), the entire aquifer area is subject to varying amounts of recharge, depending on soil type and extent of development and paving. Additional recharge is likely to occur from leakage from stormwater drains as well as from the various rivulets during periods of low groundwater levels or high stream levels. The estimated recharge over the entire aquifer is in the order of 1 ML/d with leakage in and out of the rivulets approximately equal. The natural recharge is not critical, however, as the aquifer storage and recovery (ASR) system is planned to operate such that the average annual injection is approximately equal to the abstraction, within water level limitations noted below.


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2.1.3 Aquifer Hydraulic Properties

The aquifer hydraulic conductivities are summarised in Table 2. Additional pumping tests are underway.

Table 2 Aquifer Hydraulic Properties

Bore Transmissivity (m2/day)

Storage Coefficient Material

BH01 7 basalt BH02 10 sand BH06 89 6.7 x 10-5 basalt BH07 108 basalt BH09 36 basalt BH10 18 basalt BH11 197 2.7 x 10-4 basalt BH14 0.75 basalt BH15 100 - 101 sand BH20 5 - 6 sand BH27 12-16 sand BH34 0.12 - 0.8 sand BH35 42 - 199 sand

Pumping tests in the basalt aquifer provide estimated storativity “S” (confined storage) in the range 7x10-5 to 3x10-4, which means that for each metre decrease in head throughout the aquifer, approximately 7x10-5 to 3x10-4 m3 (0.07 L to 0.3 L) of water is released from storage from each square metre of aquifer. Over the entire 200 ha, this would equate to 0.14 to 0.6 ML of water per metre drop in confined head.

However, once the groundwater drops below the level of the top of the aquifer and becomes unconfined, the specific yield “Sy” dominates water release. Specific yield is typically between 0.1 to 0.3, for clean, well-sorted sands and can be similar in vesicular basalts. Values in fractured, but not vesicular basalt may be an order of magnitude or more lower. Based on the observations of highly vesicular basalt to the east and more in-filled, amygdaloidal basalt towards the interior of the basin, a lower value of 0.01 to 0.1 could be assumed, and 10 L to 100 L of water could be released per square metre from each metre drop in head, within the porous zones. If, based on the log of BH11, there is 24 m of vesicular basalt (the basalt to the west is thicker but less porous so the overall storage values may be similar) then each square metre of aquifer could, if totally drained, yield 240 L of water, or 0.5 GL to 5 GL over the full 200 ha. This is a theoretical yield and should not be taken as an estimate of available water, as it is unlikely that the wellfield would be spread over the entire aquifer, and the aquifer can never be completely drained. Given the relatively short injection and abstraction cycles proposed for the ASR system (nominally 30 days), only a relatively small proportion of storage would be required - less than half required even for the high demand rate of 7 ML/d and the low storage coefficient of 0.01.

2.2 Pilot ASR Modelling

The pilot operation is proposed to run at a peak abstraction rate in the order of 23 L/s. A preliminary Proof of Concept or Class 1 model, under the Australian Groundwater Modelling Guidelines (NWC 2012), has been run and documented separately (Appendix B). It was run for a maximum injection rate of 100 L/s and maximum abstraction rate of 40 L/s. mid way between the pilot and likely maximum abstraction rate. The model showed that with proper groundwater


level control under injection cycles, ASR operations were likely to be sustainable in terms of groundwater levels and prevention of seawater intrusion. A much more detailed model, incorporating the latest drilling results and the results of the pilot program, will be completed as part of the Stage 4 Operational Assessment. The reconstructed and calibrated model would be used to simulate the proposed ASR operations for a range of peak injection and abstraction rates, over several years of real rainfall and runoff data that incorporates both dry (10th percentile) and wet (90th percentile) years. It will also incorporate solute transport modelling if the pilot study indicates inflow of contaminated groundwater or sweater is a potential risk. It is assumed that approvals for expansion of the ASR system above the pilot scale system would be contingent upon acceptance of the Stage 4 works by EPA.

A detailed geological and hydrogeological model, compiling all of the drilling data to date and revised injection and abstraction scenarios, with modelling of contaminant transport from the landfill and coast is proposed after the results from the pilot operation are received.

Commitment 15. On completion and review of the pilot ASR project the data will be used to construct and calibrate a detailed groundwater flow and contaminant transport model and run predictive scenarios of the revised ASR operation.

2.3 ASR Operation

2.3.1 Pilot operation area

The pilot operation occupies approximately 23 ha or approximately 3 % of the estimated aquifer area of 750 ha. The extent of the final ASR scheme will depend on the harvestable water for injection and the consequent sustainable groundwater yield. It will however be confined to the 600 ha within the Glenorchy City Council

2.3.2 Water Treatment

Stormwater is first filtered through a fine screen that intercepts gross pollutants (above 3 mm in size) and a bypass pit that allows the first flush flows to bypass the harvesting system. The screened water then passes to a large pond/biofilter (Tank C) which has a floor made up of a layer of Hydrocon porous pavers, a geofabric and then a sand bed before being pumped to the ASR for storage.

Silts and fine debris will collect on the floor of the pond over time and reduce the efficiency of the filter and the rate of collection depends on the quality of the water being passed to Tank C. Whilst the floor area of the tank is large relative to the design flow rate, the floor will need to be cleaned once the collected material is sufficient to affect gravity flows to the pump station.

This will be by a process of pressure cleaning and eduction for offsite disposal rather than by backwashing or scouring. There is to be no uncontrolled discharge of collected materials to the stormwater system from Tank C under the normal operation of the system.

The initial operation of the system will require monitoring of the stormwater quality being passed to Tank C, the timing of the first flush bypass and the rate of debris build up within Tank C.

The output target for the system is a turbidity of less than 1 nephelometric turbidity units (NTU).

2.3.3 Likely Injection and Abstraction Rates

The peak, short-term abstraction rate of 76 L/s is an aspirational target of the final ASR system, although this may vary up or down depending on the number of potential water users, extent of aquifer and sustainable injection and abstraction yields. If higher injection rates are required to maintain groundwater levels, additional stormwater or other water sources may be required for aquifer injection. If none are available, abstraction rates will be reduced. Conversely, if


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groundwater demands were lower or water levels began to rise excessively, less injection would be required. The various estimated well yields are summarised in Table 3.

The pilot program is expected to operate at a peak dry weather groundwater demand of approximately 23 L/s to be extracted from BH06, BH11 and possibly one to two other wells, with injection in these wells and possibly some additional injection-only wells. All injection and abstraction wells will be constructed in accordance with the Minimum Construction Requirements for Water Bores in Australia February 2012 and will be licenced with DPIPWE prior to use.

On completion of the pilot program, results will be reviewed (including detailed modelling) to determine long-term abstraction and injection rates. Longer term rates will depend on the aquifer groundwater level at the time of injection or abstraction. Net flow of injection minus abstraction will be slightly positive over a 12-month period unless long-term monitoring indicates higher net abstraction or injection rates can be sustained.


Table 3 Estimated short-term well yields

Well ID ASR Grouping Proposed Well Function

Indicative yield (L/s)

BH01 Bunnings Basalt loop Monitoring BH02 Bunnings Basalt loop Monitoring

BH2A Bunnings Basalt loop Monitoring

(2ndry)

BH03 Bunnings Basalt loop Monitoring BH04 Bunnings Basalt loop Injection BH05 Bunnings Basalt loop NA BH06 Bunnings Basalt loop Extraction 9 BH07 Bunnings Basalt loop Injection 5 BH08 PoW Landfill Monitoring NA BH09 Southern feeders Extraction 1 BH10 Southern feeders Extraction 2 BH11 Bunnings Basalt loop Extraction 18 BH12 Cnr Brooker Ave Derwent Prk Rd Monitoring 1 BH13 Cnr Brooker Ave Elmsleigh Rd Monitoring <3 BH14 Goodwood Primary Monitoring <1

BH15A Central Alluvium Monitoring 5 BH15P Central Alluvium Extraction ~5-10 BH18 Central Alluvium Monitoring BH20 Central Alluvium Monitoring BH22 Central Alluvium Monitoring BH23 Bunnings Basalt loop Injection 2 BH24 Bunnings Basalt loop Extraction 6 BH25 Bunnings Basalt loop Extraction 3 BH26 Bunnings Basalt loop Extraction 20 BH27 KGV/Humphrey Riv Monitoring BH28 KGV/Humphrey Riv NA BH29 KGV/Humphrey Riv NA BH30 Bunnings Basalt loop Extraction 8 BH31 Bunnings Basalt loop Extraction 3 BH32 Bunnings Basalt loop Monitoring 2 BH33 Bunnings Basalt loop Extraction 2 BH34 Howard Road Alluvium Monitoring BH35 Lampton Ave Alluvium Extraction 5 BH36 Elwick Monitoring BH37 Elwick Monitoring BH38 Elwick Monitoring

Injection Only

Extraction and Injection

Monitoring

Pilot stage bores in bold

2 Salamanca Square Hobart TAS 7000 Australia T 61 3 6210 0600 F 61 3 6210 0601 E [email protected] W www.ghd.com

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MetresMap Projection: Transverse Mercator

Horizontal Datum: GDA 1994Grid: GDA 1994 MGA Zone 55

Glenorchy City CouncilDerwent Park ASR Assessment Stage 2

Figure 3

Job NumberRevision 0

32-16207

03 Apr 2013

Bore Locationso Date

Data source: Glenorchy City Council, Proposed Infrastructure, 2012; GHD, bore locations, 2013; Google, aerial imagery, 2012. Created by: jpulford

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2.3.4 Additional Surface Water Harvesting

Water Licence No. 9343 was issued to Council on 7 February 2013 for the extraction of up to 1,522 ML per annum from the Humphrey Rivulet. The bulk of this water, 1,151 ML, is to be taken from the rivulet during the “winter” period of May to October, with the remaining 371 ML during the drier “summer” parts of the year under the proviso that residual downstream flows within the Rivulet are not reduced by more than 50% during operation of the system. If the full allocation of water were to be used, the average winter supply is some 6.32 ML/d or 195% of the Stage 1 demand of the WTP. During the summer, the Rivulet could supply up to 62% of the WTP Stage 1 demand with the shortfall made up from the ASR.

During the winter period, it is envisaged that flows from the Rivulet will be pumped directly to the WTP whilst filtered stormwater will be directed to the ASR for storage. During the summer period, flows from the Rivulet will not be sufficient for the WTP requirements and are likely to be intermittent due to the need to maintain environmental flow rates within the Rivulet downstream of the offtake point. In this situation, the ASR would be used to supply the shortfall so as to maintain a constant supply of 3.24 ML/d to the WTP. The harvested water would also be available to provide supply for the hydraulic barrier injection wells along the Brooker highway (2.4.1) if required.

Commitment 16 Water from Humphrey Rivulet will be harvested in accordance with Water Licence No. 9343 including the condition that residual stream flows within the Rivulet are not reduced by more than 50% during operation of the system.

2.4 Water level and quality management and monitoring

Management of injection and abstraction rates will be required to prevent negative impacts from:

Inflow of contaminated or saline water;

Excessive water level rise causing waterlogging or soil salinity; and

Subsidence from excessive water level drawdown

2.4.1 Control of Contamination or Seawater Inflow

Operational water levels will be controlled to minimise inflow of saline water from the Derwent River by ensuring groundwater levels at BH8 and BH13 remain above sea level on average over the year and are below sea level for no more than 7 days. This will maintain a general seaward hydraulic gradient as well as preventing up-coning of deeper saline groundwater.

It was initially proposed to control saline and contaminated groundwater inflow by maintaining a positive hydraulic gradient (hydraulic barrier) from the edge of the borefield to Prince of Wales Bay using injection wells along the Brooker Highway, on the assumption that the basalt aquifer was fully connected with the Bay. However, recent excavation of the stormwater drain adjacent to BH08 and along the western edge of the Prince of Wales landfill intersected dolerite, with very little observed inflow even at elevations of less than 0.5 mAHD, separated from the basalt by a plastic clay layer. This clay layer has been identified between the basalt and dolerite in all boreholes. This indicates that the basalt aquifer in this area is isolated from the landfill and the coast by a continuous clay aquitard and underlying dolerite, with the possible exception of a small palaeochannel, backfilled with gravelly clay deposits approximately 90 m wide to the south of BH8 (Dolerite and Tertiary clay aquitard highlighted in red in Figure 4). Modelling (Appendix B) of inflows and abstractions above the proposed pilot rates indicate inflow of contaminated or saline water is unlikely due to the generally seaward hydraulic gradient being maintained without Brooker Highway “barrier” wells.


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Consequently, inflows of moderately contaminated groundwater from the landfill and adjacent hydrocarbon contaminated areas are likely to be small and be adequately diluted by groundwater from the rest of the well field. The combined groundwater flow will remain within the range of water quality treatable by the Water Treatment Plant (WTP).

The exact flow rate to maintain the mound is difficult to determine prior to the pilot testing. Based on test injection rates achieved in test bores, however, the required rate would be in the order of 1-10 L/s distributed along the eastern boundary of the basalt. If injection water is required during the summer months when filtered stormwater may not be available, this could be provided from the Humphrey2 Rivulet supply. Humphrey Rivulet has an average daily extraction rate of 2.03 ML/d via the ASR pressure main system (RM1 and the loop main) or from groundwater extracted from further towards the core of the aquifer in the aquifer.

Additional drilling is proposed along the eastern side of the Brooker Highway, along Gepp Parade (Figure 5), to better define the basalt aquifer and the landfill area

Commitment 17. Groundwater injection and abstraction will be managed to ensure average groundwater levels at monitoring wells BH8 and BH13 are maintained above sea level, to minimise inflow of saline or contaminated groundwater.

Commitment 18. Cary out geotechnical drilling to define the base of the basalt aquifer to the east of the Brooker Highway.

Figure 4 Dolerite and Tertiary clay aquitard (red)

2 Alternative spellings of Humphrey, Humphreys and Humphries are used on various published maps and databases. The Humphrey spelling has been adopted as it is used on the LIST database.


Figure 5 Proposed drilling traverse (red dashed line)


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2.4.2 Control of impacts on surface water bodies and groundwater dependant ecosystems

As noted in the EER, no groundwater dependent ecosystems have been identified in the area. Notwithstanding this, the project aim is to maintain environmental flows in both watercourses. Both Humphrey Rivulet and New Town Rivulet are relatively remote from the pilot extraction bore locations and it is considered unlikely that base flows in either stream will be significantly changed by the operation of the ASR. The preliminary modelling indicates drawdown in these areas is likely to be less than 0.2 m. Monitoring bore BH27 provides a means of measuring the change in water table levels adjacent to the Rivulets during the trial operation of the system.

As the ASR scheme is expanded, the abstraction bores will become closer to the streams, but abstraction and injection cycles, along with any licenced surface water abstraction, will be managed to base flows are maintained. Stream flow monitoring stations will be installed in both rivulets approximately adjacent to the cycleway on New Town Rivulet and adjacent to the surface water off take in Humphrey Rivulet.

Commitment 19. Stream flow monitoring stations will be installed in Humphrey Rivulet and New Town Rivulet and monitored to ensure dry weather stream flows are maintained to at least 50 % of historical flows.

2.4.3 Control of Subsidence

A preliminary assessment of subsidence was performed (Appendix C) based on non-geotechnical drilling to date. It confirmed that the risk of subsidence in the basalt is low but the alluvial aquifer may be sensitive to dewatering. Drawdown in the alluvial aquifer should be limited to approximately 5 m at a distance of 10 m from the bore (based on theoretical drawdowns calculated for the aquifer parameters if no monitoring wells are available) or at the nearest sensitive structure and subsidence monitored until a more detailed subsidence assessment, including drilling and interpretation of dedicated geotechnical boreholes, can confirm deeper drawdowns can be achieved without significant subsidence.

Commitment 20. Abstraction in the alluvial aquifer will be limited to levels likely to result in a drawdown no greater than 5 m below historical low levels at a distance of 10 m from the bore or at the nearest sensitive structure.

Commitment 21 A detailed subsidence assessment will be done to confirm safe levels of dewatering, above those in commitment 19, without sufficient subsidence to damage nearby structures.

2.5 General water level and quality monitoring and control

Water levels will be maintained such that they do not rise enough to cause waterlogging or soil salinity, nor fall low enough to cause subsidence in the unconsolidated alluvial aquifers. The general monitoring and management process is summarised in Figure 6

2.5.1 Water Level Monitoring

In Stage 1/Pilot scheme, groundwater levels will be automatically recorded and fed back in to the control system in all injection and abstraction wells and monitoring wells BH01, BH08, BH13, BH20 (or another bore closer to New Town Rivulet), BH23, BH27 and BH32. All other wells will be manually gauged at least monthly unless fitted with automatic data recorders (non-telemetered). As the project expands, all injection or abstraction wells will be similarly monitored, along with additional dedicated monitoring wells.


2.5.2 Water Level Controls

High water levels

In order to prevent waterlogging or salinization of soils, high water levels under injection cycles will be no higher than 2 m below ground surface in the injected well, controlled by automatic water level sensors, which will throttle back flows as they approach the level and cut off all injection at that level. A further limit will be that water levels in monitoring wells will remain at least 3 m below surface although higher or lower levels may be set on review of any additional baseline data obtained prior to commencement of pilot operations. Over pressurisation cannot occur, even in the event of failure of high water level controls, as the injection wells will be open to the atmosphere allowing discharge of excess water.

Low Water levels

Low water levels under abstraction will depend on each well. Generally, the lowest level will at least 2 m above the pump inlet or the base of the aquifer (as measured in the abstraction well) whichever is higher. As stage 1 operations are only within the basalt aquifer, subsidence due to aquifer dewatering of thick sediment sequences is not a significant risk.

In addition, it is proposed that water levels in BH08 will be retained at greater than 0 mAHD to prevent inflow of saline river water. During the pilot program, however, lower water levels will be allowed, in conjunction with close geochemical modelling, to assess the potential for interaction with seawater and groundwater beneath the former landfill.

Commitment 22. Flow rates and water levels will be continuously monitored in all injection and abstraction wells and water levels will be maintained within the range of between 2 m below ground surface and 2 m above the base of the aquifer (subject to subsidence constraints) to prevent waterlogging or pump damage.

2.5.3 Water Quality Monitoring

Various chemical parameters, including pH, EC, ORP, turbidity and hydrocarbon and mineral oils will be measured downstream from the junction of the various abstraction well lines and in the main ASR injection line and fed in to the control system. Investigation and shutoff levels will be set based on initial observations during the pilot study and the upper raw water limits required by the WTP process. Where concentrations in the combined abstraction lines exceed an investigation values, the individual abstraction lines will be manually sampled to determine the source of the exceedance. If an individual well exceeds adopted investigation values, it will be investigated and, if the shutoff level is exceeded, the individual well will be shut off and the source of contamination investigated. The groundwater monitoring bores noted in Section 2.5.1 will be monitored for the parameters and at the frequencies outlined for ASR injection water in Table 1 of the EER. A more detailed monitoring and management plan will be developed as part of the Stage 4 works for the full-scale operations.

Commitment 23. Groundwater quality will be continuously measured in the combined stream of the abstraction wells and in the injection stream and will be monitored in all abstraction wells and in nominated groundwater monitoring wells in accordance with Table 1 of the EER.

GHD | Report for Glenorchy City Council - Derwent Park Stormwater Harvesting and Industrial Re-use Project, 32/16745 | 15

Figure 6 ASR Process flow chart

Note Bypass refers to flow returned to stormwater drain and the biofilter is located in Pond C.

Core Components

Groundwater Injection

Harvest Humphrey Rivulet

Harvest Stormwater

Flow greater than WTP water

demand?

Ground waterabove min

level

Ground waterbelow max

level?

Barrier SWL > BH08?

Total > WTP water

demand?

Extract Groundwater

Inject Groundwater

No Injection. Excess water to bypass

Flow > Max injection

rate?

Excess to bypass

Harvest Humphrey Rivulet

Flow available in HR?

Reduce supply to WTP

Total > WTPwater

demand?

Full supply to WTP

Reduce supply to WTP

Flow > Biofilter capacity?

Biofilter

To biofilter with excess bypassing to Y

N

N

Y

N

Y

N

Y

N

NN

Y

Y

N

Y

Y

Y

N

Ground waterbelow max

level?Y N

Adjust HR take to achieve full WTP

supply

Inject excess flow to groundwater at defined

injection rate


2.5.4 Data storage and reporting

All water quality, flow and levels monitoring data will be stored in an electronic database and key parameters automatically plotted to provide early warning of potential exceedances. Data will be reviewed and reported at the sooner of quarterly or at the end or the pilot stage.

On completion of the pilot study, a detailed monitoring and management plan will be prepared, (Stage 4 Operational Management Plan) as outlined in the Stage 2 Pre-commissioning Assessment and is presented below in Table 4. This is consistent with the process given in Australian Guidelines 24 for Water Recycling: Managing Health and Environmental Risks (Phase 2) Managed Aquifer Recharge. It is appropriate to prepare the operational Management Plan at this stage as critical information on ASR performance will not be obtained until after completion of the pilot project.

Table 4 Key requirements within the Derwent Park ASR risk management plan for progression to a Stage 4 operational assessment

Element and key components Element 1: Commitment to responsible use and management of recycled water quality

- Ensure responsibilities of each agency are clearly defined and communicated (multiple agencies involved, project is the first of its kind) - Form stakeholder reference group and expert health reference group - Develop public engagement program

- Develop a recycled water policy to be implemented by GCC and DPIPWE with endorsement at senior management level (CEO) Element 2: Assessment of the recycled water system - Consider inadvertent or unauthorised uses of recycled water

- Revise assessment of the system as required; including system components, flow diagrams; catchment attributes, water quality data; and analysis of hazards and hazardous events - Develop assessment criteria for the SCADA data and implement Element 3: Preventative measures for recycled water management

- Identify alternative or additional preventative measures, e.g. UV disinfection and aeration for iron removal.

- Document preventative measures and strategies, removal efficiencies of pre-treatment systems and in-aquifer attenuation - Validate operation and contamination prevention by monitoring of water quality - Assess trigger values and link to operational procedures Element 4: Operational procedures and process control - Document all operational procedures within the risk management plan - Document monitoring protocols, including the frequency for each parameter

- Document the procedures for corrective actions when operational parameters are not met - Establish regime for equipment maintenance and performance assessment - Establish procedure for quality assurance of materials and chemicals Element 5: Verification of recycled water quality and environmental performance

- Assess the water quality monitoring in relation to operational and reporting requirements

- Document the location and frequency of sampling to ensure representative and reliable data - Establish and inquiry and response program for users


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- Develop reporting mechanisms and procedures for quarterly review of monitoring data

- Document the procedure for corrective responses to non -conformance or feedback from users Element 6: Management of incidents and emergencies

- Define a communication protocol including a list of key contacts and stakeholder agencies - Develop a public and media communication strategy - Define potential incidents and document response plans Element 7: Operation, contractor and end user awareness and training - Develop mechanisms to increase awareness of the recycled water system - Document training required and undertaken Element 8: Community involvement and awareness

- Assess requirements for effective involvement of users of recycled water and the community - Develop a comprehensive communication and education strategy, critical in preventing contamination of stormwater Element 9: Validation, research and development - Validate SCADA and other operating system

- Develop a research plan to address remaining knowledge gaps e.g. revised health risk assessment, infrastructure and aesthetics, public engagement and preliminary risk management plan for the catchment. Element 10: Documentation and reporting - Develop a records management system - Establish procedures for internal and external reporting Element 11: Evaluation and audit - Centralise all system information for ease of access - Develop procedures for annual and longer-term (3-5 years) performance review

- Establish procedures for internal and external auditing including communication of results Element 12: Review and continual improvement - Review by senior managers - Develop a recycled water quality management improvement plan

Commitment 24. All water quality, flow and levels monitoring data will be stored in an electronic database and key parameters automatically plotted to provide early warning of potential exceedances and reported at the sooner of quarterly or at the end or the pilot stage.

Commitment 25. On completion of the pilot study, a Stage 4 Operational Management Plan as outlined in in Australian Guidelines 24 for Water Recycling: Managing Health and Environmental Risks (Phase 2) Managed Aquifer Recharge, will be prepared.

GHD | Report for Glenorchy City Council - Derwent Park Stormwater Harvesting and Industrial Re-use Project, 32/16745

Appendices


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Appendix A – Annotated EER Response Requests

ENVIRONMENT PROTECTION AUTHORITY

Level6, 134 Macquarie Street, Hobart TAS GPO Box 1550, Hobart, TAS 7001 Australia

Enquiries: Ph: Email: Web: Our Ref:

Damien Blackwell 6233 2780 Fax 6233 6800 [email protected] www.epa.tas.gov.au EN-EM-EV-DE-112487_2:H113201

21 December 2012

Mr Mike Burdon Deputy Project Manager Derwent Park Stormwater Harvesting and Industrial Reuse Project Glenorchy City Council PO Box 103 GLENORCHY TAS 7010

Dear Mr Burdon

GLENORCHY CITY COUNCIL- AQUIFER STORAGE AND RECOVERY

EER SUPPLEMENT

I refer to the assessment of the above proposal by the Board of the Environment Protection Authority.

The period for public representations on the proposal has now ended and no public representations were received.

Comments on the project were received, however, from two Divisions of the Department of Primary Industries, Parks, Water and Environment. Details of the relevant comments are provided in the attached table.

While the Environmental Effects Report (EER) addresses a number of the agency comments, a number of issues raised will require further information before the assessment of the proposal can be completed.

Acting under delegation and in accordance with section 271(1) of the Environmental Management and Pollution Control Act 1994, I require you to prepare a supplement to the EER to address the State Government comments, as detailed in the attached table.

The EER Supplement should clearly identify where information or commitments made in the EER have been revised and replaced by the Supplement.

If you have any queries regarding the above, please contact the officer nominated at the head of this correspondence.

Yours sincerely

John Mollison A/GENERAL MANAGER

mailto:[email protected]







































http://www.epa.tas.gov.au/


















2

Encl. • Table containing:

(a) Summary of State Government comments

cc: Mr Peter Brooks, General Manager, Glenorchy City Council PO Box 103 GLENORCHY TAS 7010

[H113201_Comments summary table] Page 1 of 3

Glenorchy City Council/ Aquifer Storage and Recovery

Summary of Agency comments

DPIPWE Urban Water Policy Unit (UWPU)

1.2 Pre- treat within the wider SW system

1.2; 5-6 Scenarios [using various injection and extraction rates] for the following system thresholds should be run and results summarised and reported in the EER Supplement:

• Upper water table level adequate to prevent! minimise waterlogging/salinity risk.

• Lower water table level adequate to prevent surface stream depletion.

• Maintenance of Brooker Hwy groundwater 'mound' (ie positive hydrostatic head between ASR aquifer and former landfill site at POWB sportsfield).

• The process to maintain the groundwater mound that is intended to separate landfill site from ASR storage, particularly during dry periods when ASR aquifer is drawn down - particularly, where will Council source the water to maintain the mound?

• Briefly describe the monitoring system that will be applied to warn when above thresholds approached.

• Briefly detail the prescriptions for system management for each threshold.

• Assess/ discuss likely injection and production rates which will satisfy above thresholds.

UWPU notes that many of these should be addressed through production of a comprehensive groundwater model detailing various injection, storage and extraction scenarios, given assessed transmissivities. This will require further assessment using pump and injection tests on appropriate test bores. Section 2.2 and Appendix B

1.3 Mon'ing

1.3; 7-8 UWPU notes it may be necessary to draft and agree on a management plan to allow iterative development of the ASR system, particularly with reference to flow rates and magnitude of trigger levels for identified injection parameters. Section 2.5

Briefly outline Council's intended operational management and reporting systems for ASR, including any annual reporting and accident reporting for EPA. Section 2.5.3

Fig. 1; 11 Please specify source of water for the Brooker Hwy groundwater mound; pump or gravity injection to ASR storaQe? Section 2.4.1

2.2 Lndscp e, Heritag e & Eco Values

2.2; 12 Potential effects [of operating ASR] on Groundwater Dependent Ecosystems (base flows in adjacent streams- New Town and Humphries Rivulets) should be addressed. Briefly elaborate. Section 2.4.2

2 Proj area

2.4; 12-13 UWPU notes that some risks identified during ASR development [eg. Appendix 4, Section 6, GHD ASR Stage 2/Pre-commissioning assessment report] have not yet been adequately addressed. As such, UWPU requests that Council provide additional information to demonstrate how these risks will be managed, along with the following:

• Document the physical properties of all aquifers identified during the investigation phase and capacity of main aquifer to safely store proposed quantity of additional water [for subsequent extraction]. Section 2.1.3

• Assess and demonstrate the level of confinement between basalt and sedimentary aquifers, and the overall system.

• What proportion of the total aquifer will be used for ASR operations? Section 2.3.1

• What proportion of the operating area is currently filled by natural recharge processes (and what is available for additional ASR)? Section 2.3.1



Fig. 2; 14 Map will require updating, to include the current operating status for all test bores (capped, functioning or abandoned) and the final intended purpose for each bore, namely:

• Injection well • Abstraction well • Combined injection/abstraction well • Monitoring well Appendix E

With reference to water quality assessment; which individual/combination of bores will be monitored (or will the combined flow through the POWB supply pipe be used)? Section 2.5.3

App. 4 22 Subsidence risk is not assessed, specifically for unconsolidated aquifer materials - provide mitigation options. Appendix C and Section 2.4.3

28 Trial operation is supported, if appropriately controlled and monitored. Please provide more detail

about this trial with respect to controls. Section 2.4 No mention in EER of proposed Humphrey Rivulet abstraction and use of this water (licence application currently under consideration by DPIPWE's Water Management Branch). Please elaborate. Covered by WL9343

UWPU wishes to clarify that any substantial future changes of borehole construction details will need permit from DPIPWE's Water Management Branch.

DPIPWE -EPA 1.2 1.2; 5-6 How will proposed filter system (ie Hydrocon porous pavers/ sand filter ...) perform over time and does Division Pre- this filter system require backflushing or cleaning, which may then result in an aqueous or solid waste

treat stream? Please elaborate. within the wider sw system 13 Site 18-19 EER indicates that a series of injection only wells along Brooker Highway will be used to create a contam hydrostatic head between the intended aquifer and former landfill site at POWB sports field (to

minimise potential for migration of pollutants). Where will water used to create this mound be drawn from, particular during periods of dry weather/low rainfall? Please explain. Section 2.4.1

Section 2.3.2

GCC ASR project EER Supp V1: EPA Division comments Table: Review of EER Supp V1 received 20 February 2013 - feedback (to consider and address in next version of Supp) General Comments EER Supp V1 versus EER request for supplement With reference to the EER request for supplement issued to GCC 21/12/2012, EER Supp V1 lacks detail or clarity concerning the following points (as highlighted):

Briefly describe the monitoring system that will be applied to warn when above thresholds approached. Section 2.5

While inclusion of flowchart is beneficial, further elaboration/ explanation of this flowchart is required (ie briefly describe/ elaborate on each of the steps in the management/ monitoring system). Provision of (at least) the ranges of initial operating parameters (ie flow rates, water levels…) would be beneficial.

Briefly detail the prescriptions for system management for each threshold. Ditto above comment. Section 2.5

Assess/ discuss likely injection and production rates which will satisfy above thresholds. Is the figure of 76L/s (estimated short-term abstraction/ injection rate) the rate expected to ‘satisfy the above thresholds’ (ie the rate considered suitable/ realistic to minimise waterlogging/ salinity risk, surface stream depletion, aquifer contamination from POWB landfill)? The relationship between this figure and the system thresholds is not clearly established. UWPU notes that many of these should be addressed through production of a comprehensive groundwater model detailing various injection, storage and extraction scenarios, given assessed transmissivities. This will require further assessment using pump and injection tests on appropriate test bores. Section 2.2 and Appendix B As per the above note, UWPU maintains that system thresholds should be refined & validated via construction of a robust groundwater model. With reference to Supp (nominal page 2), it’s stated that production of hydrogeological model will be done after results of ‘pilot operation’ received. In Council’s view, what would a ‘pilot operation’ look like? What would be the parameters/ criteria that define a ‘pilot operation’? Ideally, if (as UWPU suggests) existing test bores are adequate for purpose of injection/ abstraction (& storage) tests, then robust groundwater model should be developed now (prior to conversion of test bores to production wells & full scale operation of ASR). Briefly outline Council’s intended operational management and reporting systems for ASR, including any annual reporting and accident reporting for EPA. Potential effects [of operating ASR] on Groundwater Dependent Ecosystems (base flows in adjacent streams - New Town and Humphries Rivulets) should be addressed. Briefly elaborate. Section 2.3 Inclusion of Table 3 [part g) recommendations for a draft management and reporting plan] is noted but represents only a high level, generic description of a management plan/ systems. Intended ‘operational management and reporting systems’ should be substantially developed/ defined prior to operating even a ‘pilot’ ASR process. More specific detail of operational management and reporting systems should be provided, with sufficient quantitative information and timings to show that ASR process is robust & environmental risks adequately addressed. Potential effects on Groundwater Dependent Ecosystems appears to be missing? Will GCC measure flows in the two rivulets during ASR operation? Please provide details.

What proportion of the total aquifer will be used for ASR operations? Supp does not appear to address this point. Please clarify/ elaborate. Section 2.3.4

What proportion of the operating area is currently filled by natural recharge processes (and what is available for additional ASR)?

Supp appears to contain little or no information concerning this point. Please explain/ address. Section 2.1.2

GCC ASR project EER Supp V1: EPA Division comments

2

Map will require updating, to include the current operating status for all test bores (eg. capped, functioning or abandoned) and the final intended purpose for each bore, namely:

Injection well Abstraction well Combined injection/abstraction well Monitoring well Figure 3

With reference to water quality assessment; which individual/combination of bores will be monitored (or will the combined flow through the POWB supply pipe be used)? EER contains a map (Figure 2) of ASR layout. This is the map that requires updating to show current operating status of all bores & final intended purpose for each bore. Contour map in EER Supp (Figure 1) is not this map. Updated map (ie updated Figure 2 from EER) could be linked/ associated with EER Supp Table 2 (knowing the coordinates of each bore is certainly useful). Table 1 in EER (p8) outlines a water quality monitoring regime for ASR process. As far as bores classed as ‘monitoring’ are concerned, are the parameters nominated in Table 1 (EER p8) those that will be measured at these bores? Please clarify what the intended monitoring regime & suite will be at ‘monitoring’ bores. Trial operation is supported, if appropriately controlled and monitored. Please provide more detail about this trial with respect to controls. Section 2.5 Will trial be conducted with production wells? More detail with respect to trial criteria/ parameters & controls is required. Refer also previous comment about defining the nature of intended ‘pilot’ operation. Other general comments Format (includes document control and references) EER Supplement (Supp) should include identifiers such as title, author, date, version number and the like in sufficient detail to allow good document control. Supp should also be set out more clearly, to make it easier to link request details with responses & therefore ascertain whether responses are satisfactory. Using each request point as a ‘header’ is likely to assist this process. Page numbering is also essential. Use a consistent font type, size. Miscellaneous

Commitments-it is noted that no additional commitments are identified in the EER Supp. However, several additional commitments seem possible. Eg. water levels will be maintained below historical high water levels or levels likely to cause soil salinity; drawdown in the alluvial aquifer will be limited to about 5m at a distance of 10m from an abstraction bore or the nearest sensitive structure & so on. Please review EER Supp & determine whether additional commitments are appropriate & re-populate commitments table (as provided in EER Part D-Management commitments) Appendix D

Use consistent terminology through the Supp (eg. is ‘biofilter’ same as ‘Tank C’?) Humphrey rivulet is ‘Humphreys’ rivulet Section 2.4.1.


3

Part Page; Paragraph (or section)

Comment or request

a) 1 Should tables 1 & 2 be consistent in terms of bore id? Table 1

presently contains far fewer bores than Table 2. Please explain discrepancy/ amend.

2; 1 ‘…as recent geological information confirms…’ please include/ append reference of this ‘recent geological information…’ & illustrate why landfill may be relatively isolated from aquifer targeted for injection & abstraction.

Explanation of why positive hydraulic mound might not be required (to limit contamination of main aquifer by former landfill site) is confusing, especially final sentence. Diagram/ figure may assist here with explanation.

2; 2 As indicated under General comments, a robust groundwater model (including how contaminants may move between landfill & main aquifer) should be developed prior to execution of ‘pilot’ operation. Again, define the nature of any ‘pilot’ operation.

b) 3; 1 ‘This area will be…’ d) 3; 3 Humphreys Rivulet (not Humphrey)

Is measurement of water level in bores near the two rivulets sufficient to monitor outcome of injection/ abstraction activity? How else might the effects of ASR on rivulet flows be gauged?

e) 3; 4 As indicated under General comments, further elaboration about

how the flow chart/ decision tree works is required. Eg. what precisely is ‘raw water’? (there are several refs to ‘raw water’ in the flowchart but not all instances appear to mean the same thing); is ‘bypass’ the high level overflow to POWB? ; what’s the material difference between ‘to raw water supply’ & ‘to raw water supply with excess bypass’? (two boxes immediately after the initial query ‘flow>biofilter capacity’). Check again for ‘internal consistency’.

f) 3; 5 What are units for ‘yield indicative’ column? L/sec?

Again, explain why tables 1 & 2 contain different number of bores, bore information.

g) 4; 1 As indicated under General comments, operational management

& reporting plan should be developed prior to ASR operation. Refine procedures/ protocols as operational experience, data is obtained. Consider removing/ appending Table 3 & replace with concise outline of operational management & reporting plan.

h) 6; 1 Remove ‘the’ at end of ‘…summarised in Table 4’.

Absence of some bore id’s from Table 4 suggests that conductivity info is not known at every bore-please explain.

Should Table 4 be populated with more storage coefficient data?

Yield per m2 (per 1m drop in head) is discussed-presumably yield correlates or is similar to that quantity of water that could be injected? A maximum, ‘safe’ volume of water that might be safely stored is absent. Section 2.1.3

i)


4

7; 1 Show (provide a figure) where the ‘alluvial’ aquifer is relative to basalt aquifer & relevant injection/ abstraction bores (how many bores are affected?) Appendix B

j) 7; 2 As previously indicated, elaborate about the ‘pilot’ or ‘trial’

operation criteria & parameters. E.g. which bores are involved? What are the target parameters (flows, water levels, quality), criteria & measurement ranges? Section 2.5.3

k) 7; 3 What is ‘WTP’? The reverse osmosis plant? Yes

With ref to WTP-what is Stage 1? Refers to flow and contaminant treatment capacity of WTP, which is not part of ASR process. Stage 1 is 20-30 L/s for saline groundwater, Stage 2 is nominally 70 L/s at <1000 mg/L.


Appendix B – Preliminary, Proof of Concept Groundwater Model

15 March 2013

Sam Ali Project Manager Glenorchy City Council PO Box 103 GLENORCHY TAS 7010

Our ref: 32/16745 59097 Your ref:

Dear Sam

Derwent Park Stormwater Re-use ASR Proof of Concept Groundwater Model

This letter outlines a ‘proof of concept1’ model to assess if operation of an aquifer storage and recovery (ASR) system, comprising a series of injection and abstraction wells in vesicular basalt at Derwent Park, is hydrogeologically feasible.

1 Introduction In order to assess the general feasibility of the concept of the proposed ASR system at the Pear Road, Gormanston Road Brooker Highway, rail reserve loop (Figure 1), a three-dimensional groundwater flow model was constructed and run to simulate one year of ASR operation. The model was developed to gain an understanding of potential general dynamic aquifer conditions and was not developed to predict actual water levels at particular locations.

1 Class 1 model under the Australian Groundwater Modelling Guidelines NWC 2012.

2

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Figure 1 Site location

2 Model construction The model was constructed using the Groundwater Modelling System (GMS) program. The 5-layer grid covered the area of the Derwent Park basalt and alluvium (Figure 2) with a grid spacing ranging from 2 m near the injection area, up to 20 m at the model fringes. The model layers were developed to represent the materials outlined in Table 1 and Figure 3. Material properties were based on the results of pumping tests outlined in the various drilling reports as well as published results for similar materials for the clay layers. The model surface was based on the Coastal Futures LIDAR data downloaded from LISTMAP, with anomalies associated with large industrial buildings removed. The upper two layers were set at 10 m and 20 m below ground surface and the base of the basalt/sand was based on interpolated drillhole data and outcrop elevations.

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Table 1 Model materials

Material Horizontal hydraulic conductivity “Kh” (m/d)

Vertical anisotropy (Kh/Kv)

Specific Storage (/m)

Specific Yield

Sandy Clay 0.001 10.0 5.0e-006 0.1

Clayey sand 0.1 3.0 5.0e-006 0.1

Sandy gravel 10.0 3.0 5.0e-006 0.1

Clayey gravel 1.0 3.0 5.0e-006 0.1

Weathered Basalt 0.2 1.0 5.0e-006 0.2

Basalt - Vesicular 20.0 1.0 5.0e-006 0.1

Basalt - Amygdaloidal

0.5 3.0 5.0e-006 0.01

Basalt - Massive 0.2 3.0 5.0e-006 0.01

Clay Wd Tuff 0.001 3.0 5.0e-006 0.1

Dolerite 0.05 3.0 5.0e-006 0.01

Triassic Sandstone - Weathered

0.001 10.0 5.0e-006 0.1

Quartzose Sand 5.0 3.0 5.0e-006 0.2

The model was originally developed with the simple geometry of

Layer 1 Thin surficial soils and sand;

Layer 2 Upper basalt with vesicular and amygdaloidal zones;

Layer 3 Lower massive basalt;

Layer 4 Green grey clay immediately below the basalt; and

Layer 5 Upper fractured Dolerite zone.

Results of recent drilling, identified that:

alluvial sands occupied a 60 m deep palaeochannel in the south

basalt pinched out with underlying clay; and

dolerite outcropping to the north and Prince of Wales Bay

Based on recent drilling results (GHD in prep), the model material zones were modified to crudely reflect the revised geology, but without modifying the layer elevations.

Figure 2 Model grid

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(EW section approximately midway through wellfield)

Figure 3 Model cross section

Recharge was constant over time and ranged from 0.00004 m/d heavily paved industrial areas on clay soils approximately to 0.002 m/d in parklands and residential areas on sandy alluvium. These rates equated to approximately 2% to 10% respectively to of annual rainfall (Figure 4).

The boundary along the Derwent shoreline was set as a constant head boundary (purple line Figure 5Figure 5) at 0 mAHD and Humphreys2 and New Town Rivulets were set as river cells (blue line in Figure 5) with a bed conductance of 10 m/day, a bed elevation set at the ground topography and a river level at 1 m above the bed level. All other boundaries were no-flow boundaries along the outcrop of the base of the basalt or alluvium.

Figure 4 Model recharge zones

2 Various spellings including Humphreys, Humphry and Humphries has been used on various maps and LIST databases.

“Humphreys Rivulet”, as used on the 1:25,000 topographic map, has been adopted for this document.

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Figure 5 Model boundary conditions (river = blue, constant head = purple)

3 Model calibration The baseline model was compared in steady-state against available average water level data. The model’s residual (difference between observed and modelled heads) statistics were

Mean Residual (Head) 2.46 m

Mean Absolute Residual (Head) 3.46 m

Root Mean Squared (RMS) Residual (Head) 4.65 m

Based on an observed water level range of 25.3 m this equates to a scaled RMS residual of 18%. Although this would be considered high for a formally calibrated model, it is adequate for a simple proof of concept model.

The plot of computed versus observed water levels (Figure 6) shows a relatively linear scatter, with better calibration in the areas of lower water levels, The more elevated areas, primarily in the sand

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aquifer to the south show a poorer calibration, possibly indicating either an underestimation of recharge or an overestimation of transmissivity either through overestimation of aquifer thickness or hydraulic conductivity. This is not surprising given the lack of modification of aquifer geometry in the alluvial areas. This calibration distribution is confirmed in Figure 7, which shows the location of monitoring locations and error bars. A green bar has a residual of less than 2 m, a yellow bar of between 2 m and 4 m and a red bar of greater than 4 m. It is likely that this calibration could be significantly improved by modifying the model geometry to reflect the geology observed in recently drilled boreholes.

Figure 6 Computed versus observed water levels (mAHD)

0

5

10

15

20

25

0 5 10 15 20 25

Computed vs. Observed ValuesHead

Com

pute

d

Observed

BH01

BH02

BH03

BH04

BH06

BH07

BH08

BH09

BH10

BH11

BH12

BH13

BH14

BH15

BH20

BH22

E

G

BH34

BH35

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Figure 7 Head calibration map (see text for description of symbols)

4 Simulation of ASR operations To assess the general feasibility of injecting stormwater flows and abstracting groundwater to makeup supply during periods where there is no stormwater flows, a transient model was run using daily stress periods, with 10 time steps in each stress period. The injection and abstraction rates were scaled based on daily rainfall for 2006, being a relatively dry year. The injection and abstraction rates were adjusted such that annual inflow equalled annual abstraction, injection was capped at 100 L/s and total abstraction was limited to 40 L/s (mid way between pilot scale flow rates and potential long-term requirements). This was distributed over 5 injection-only (I1-I5) and 5 combined injection-abstraction wells (AI1-AI5), as indicated on Figure 9. The general pattern was of short periods of injection followed by longer periods of

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extraction. The modelling does not take in to account the potential to inject water from sources other than stormwater but assumes there is adequate stormwater drain catchment area to provide the injection rates.

Figure 8 ASR flow rates

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Figure 9 ASR wells (flooded cells in blue)

Figure 10 Water levels - Mid ASR Field

3

4

5

6

7

8

Jan 2006 Apr Jul Oct Jan 2007

Cell Id: 49944

Val

ue

Time

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Figure 10 shows that the lowest water level was in mid-January (Figure 11) after which the water levels generally increased, with a peak level in mid-November (Figure 13). In this model case there was excess injected water, which, if left uncontrolled, leads to waterlogging (blue areas in Figure 13). In practice, however, the excess injection would be controlled by limitations to upper water levels in the injection wells, as well and the physical limitation of discharge from the open injection wells once water levels in the injection wells reached ground level if the water level controls failed. This model shows that, for the 40 L/s abstraction and 100 L/s injection scenario, there is excess water capacity.

Even in the period of lowest water levels in the well field (Figure 11), the hydraulic gradient between the wells and the adjacent landfill area to the northeast of the Brooker highway is essentially flat (less than 1/300), indicating there is little potential for significant inflow of contaminated groundwater. At the time of maximum drawdown, the 0.2 m drawdown limit (compared to the baseline steady-state conditions) extended approximately 300 m from the centre of the wellfield (Figure 12), indicating pumping induced changes to stream flow in either Humphreys or New Town Rivulets would be unlikely.

Figure 11 Low groundwater levels (18 January) (flooded cells in blue)

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Dark blue line is the 0.2 m drawdown contour

Figure 12 Maximum groundwater drawdown (18 January)

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Figure 13 High groundwater levels (18 November) (flooded cells in blue)

5 Conclusions The proof of concept model indicates that the proposed cycle of injection of stormwater flows and abstraction during periods of a shortfall of stormwater flows can achieve the general order of magnitude of abstraction, without excessive drawdown. With the appropriate injection and abstraction controls (based on upper and lower water levels) in place, the risk of waterlogging can also be managed. Consequently, the risk of significant impacts due to waterlogging or excessive drawdown during the pilot operations is very low.

To enable optimisation of abstraction and injection locations and rates, a more detailed model should be developed, reflecting the latest understanding of the geology of the aquifers, the locations of the current and proposed injection and abstraction wells and the latest proposed injection and abstraction rates. The model should be calibrated based on the results of the pilot ASR operation proposed for early 2013. It would also be prudent to incorporate contaminant transport modelling to assess the potential for inflow of contaminated or saline groundwater.

Regards

Robert Virtue Principal Hydrogeologist 03 6210 0726


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Appendix C – Preliminary Subsidence Assessment

31 January 2013

Sam Ali Project Manager Glenorchy City Council PO Box 103 GLENORCHY TAS 7010

Our ref: 32/16207 58803 Your ref:

Dear Sam

Aquifer Storage & Recovery Assessment Subsidence Assessment

A preliminary assessment of subsidence resulting from drawdown of the sedimentary and basalt palaeochannel aquifers in the Glenorchy and Derwent Park areas has been undertaken. This assessment has been undertaken in light of recent studies by GHD to determine the feasibility of using the aquifers in these areas to store and retrieve groundwater for industrial water supply during dry periods.

The subsidence assessment has been based on limited information and borelog information from previous boreholes drilled in the study area, which is defined by the borehole locations given in the GHD Figure, job number 32-16207, revision C, 30 November 2012 titled Short Term Bore Yields. Further, it should be noted that the previous boreholes were not undertaken to assess geotechnical parameters and all calculations have been based on a qualitative review of the borelogs.

The determination of subsidence has assumed typical engineering parameters based on the borelogs as discussed above, however the calculations have not modelled the surrounding geological model and have been based on the individual borelog profiles, hence the 3-dimensional effects of different materials and structures in the soils and rock has not been assessed. The assessment is therefore only a 1-dimensional assessment. The calculations are based on a nominated maximum drawdown value of approximately 2 m above the base of the aquifer. The estimated surface subsidence at selected boreholes is shown below (Table 1), which includes the assumed depths of drawdown:

Table 1 Estimated Surface Subsidence

Borehole 15 23 31 33 35

Lithology Sand/clay Basalt – fresh to weathered

Basalt – fresh to weathered

Sand/clay Sand/clay

Drawdown Depth (m) 23 7 35 40 17

Surface Subsidence (mm) 230 50 30 35 55

2 32/16207/58803

As discussed above, these subsidence estimates are based on assumed geotechnical parameters and a 1 dimensional subsurface model. It is likely that these estimates are in the order of 50% in error and a 3-dimensional analysis is recommended after obtaining geotechnical parameters for all the subsurface materials.

It is difficult to set an acceptable level of subsidence as this analysis only considers the 1-dimensional settlement and a more important criteria is the deflection of the surface and the near surface (underground utilities). As a guide Australian Standard AS2870,the Residential Slabs and Footings code provides a maximum limit of 10mm deflection over 2000mm length for full masonry construction. Hence with a 23m drawdown of the aquifer at Borehole 15 a surface subsidence of 230mm would be acceptable if it occurred over a radius of greater than 23m. This radial effect needs to be assessed with a further study using 3 modelling and possibly refinement

Alternatively the subsidence could be limited to 50mm at borehole 15 by restricting the drawdown to 5.5m below surface level. Such movements would be typical of that occurring from seasonal weather variations on a clay site as given in AS2870 for a Class H1 site which is common in the Hobart area.

The remaining locations gave subsidence values of less than 50 mm, with the exception of bore hole 35 with 55 mm) indicating the risk of settlement is low.

Please contact the undersigned for further advice or information.

Regards GHD Pty Ltd

Martin Schult Geotechnical Engineer 03 6210 0768

Appendix D – Revised EER Commitments

No. Commitment Completion Date By Whom 1 Council will put in place and implement

procedures to limit the spread of weeds and diseases.

Prior to, during and after construction

Council and contractors

2 A soil and water management plan will be prepared and submitted to the Director of the EPA prior to work commencing

Prior to any onground works commencing

Contractor

3 Accidental or undue contamination of the aquifer by injection of stormwater will be minimised by installing and implementing a water quality monitoring system.


Council

4 Glenorchy City Council will agree threshold limits for the WQMS with the EPA based on the existing quality of the groundwater in the aquifer

Prior to construction Council

5 A Risk Management Plan will be developed to manage pollutant hotspots within the catchment.


Council

6 Council will implement a program to manage pollutant hotspots within the catchment.

Prior to approval and construction

Council

7 A field mini lab will be procured and operatives trained in its use to help identify and manage pollutant hotspots within the catchment.

Prior to approval and construction

Council

8 No construction work will be undertaken in the immediate vicinity of the Moonah Primary School during term time

During construction Council and contractors

9 Council will communicate with surrounding properties regarding noise issues and working hours.

Prior to construction and then regularly during construction


10 Council will only undertake construction work during daylight operational hours as set by Council.

During construction Council and contractors

11 Council will put in place and administer appropriate road safety management, particularly in and around the Moonah Primary School.

Prior to and during construction


12 Specific site traffic arrangements will be agreed with Bunnings Warehouse.

Prior to the commencement of construction.

Contractor

13 All hazardous substances will be stored and handled in accordance with safe working practices and legislative requirements.

During construction Contractor

14 Site contamination assessments will be undertaken prior to any ground disturbance within the railway corridor and appropriate measures take to avoid the spread of contaminated material.

Prior to the commencement of construction.

Contractor

15 A detailed groundwater flow and contaminant transport model will be constructed and calibrated using the results of the pilot study and predictive scenarios of the revised ASR operation run.

On completion of the pilot study


16 Water from Humphrey Rivulet will be harvested in accordance with Water Licence No. 9343 including the condition that residual stream flows within the Rivulet are not reduced by more than 50% during operation of the system.

During operation Council

17 Groundwater injection and abstraction will be managed to ensure average groundwater levels at monitoring wells BH8 and BH13 are maintained above sea level, to minimise inflow of

During operation Council

New Commitments in blue.

saline or contaminated groundwater. 18 Carry out geotechnical drilling to define the base

of the basalt aquifer to the east of the Brooker Highway.

During Construction Council and Contractors

19 Stream flow monitoring stations will be installed in Humphrey Rivulet and New Town Rivulet and monitored to ensure dry weather stream flows are maintained to at least 50 % of historical flows.

Prior to operation of stream flow abstraction or pilot ASR.

Council and Contractors

20 Abstraction in the alluvial aquifer will be limited to levels likely to result in a drawdown no greater than 5 m below historical low levels at a distance of 10 m from the bore or at the nearest sensitive structure.

During Construction Council and Contractors

21 A detailed subsidence assessment will be done to confirm safe levels of dewatering, above those in commitment 19, without sufficient subsidence to damage nearby structures.

Prior to commencement of full-scale ASR


22 Flow rates and water levels will be continuously monitored in all injection and abstraction wells and water levels will be maintained within the range of between 2 m below ground surface and 2 m above the base of the aquifer (subject to subsidence constraints) to prevent waterlogging or pump damage

During operation Council and Contractors

23 Groundwater quality will be continuously measured in the combined stream of the abstraction wells and in the injection stream and will be monitored in all abstraction wells and in nominated groundwater monitoring wells in accordance with Table 1 of the EER.

Prior to and during operation


24 All water quality, flow and levels monitoring data will be stored in an electronic database and key parameters automatically plotted to provide early warning of potential exceedances and reported.

Quarterly and at the end of the pilot stage, then quarterly thereafter during the full-scale operation


25 A Stage 4 Operational Management Plan as outlined in in Australian Guidelines 24 for Water Recycling: Managing Health and Environmental Risks (Phase 2) Managed Aquifer Recharge, will be prepared.

On completion of the pilot study


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