ENGEOLAB ccrhdhv.co.za/media/June-2013/E02.JNB.001204_Volksrust... · 2013. 5. 20. · Jacques du...

Members : P.G. Hansmeyer Pr.Sci.Nat.,B.Sc (Hons.) Eng. Geol., T.S. Mathibela, G.N. Shabangu, J. du Preez Pr. Sci. Nat., B.Sc (Hons) Geohydrology

WITBANK: Posbus/P.O. Box 4177 Witbank 1035

Tel: (013) 656 0719 Fax: (013) 656 0737 E-mail: [email protected]

MTUNZINI: Posbus/P.O. Box 521 Mtunzini 3867


HILTON: Posbus/P.O. Box 307 Hilton 3245


ENGEOLAB cc Earth Science Consultants Civil Engineering Soil Testing Reg. No. 2002/014257/23

PAULPIETERSBURG: Posbus/P.O. Box 672 Paulpietersburg 3180

Tel: (013) 656 0720 Fax: (086) 512 8867 Cell: 082 339 6111 E-mail: [email protected]

26 October 2012

The Project Manager OOuurr RReeff:: LLLL11998888

TOWB Trading CC

Volsrust

2470

Attention: Mr. Kobus Kok email to: [email protected]

Phone: 082 7088 536

RREE:: GGEEOOHHYYDDRROOLLOOGGIICCAALL RRIISSKK AASSSSEESSSSMMEENNTT –– PPRROOPPOOSSEEDD SSMMAALLKKLLOOOOFF TTRRUUCCKK SSTTOOPP DDEEVVEELLOOPPMMEENNTT,, VVOOLLKKSSRRUUSSTT

Dear Sir,

The preliminary phase of the geohydrological investigation, done at a desktop level based on

existing data, followed by a limited field investigation for the proposed truck stop and associated

filling station development has been completed. Please find herewith our results and

recommendations inferred from available information sources and field results.

I trust that this meets with your immediate requirements in this regard.

Yours Faithfully

Jacques du Preez

Hydrogeologist (Pr Sci Nat - BSc Hons)

ENGEOLAB cc - Hilton (KwaZulu-Natal)

Cell: 083 628 3263

ENGEOLAB cc

PPRREELLIIMMIINNAARRYY AASSSSEESSSSMMEENNTT OOFF AANNTTIICCIIPPAATTEEDD GGEEOOHHYYDDRROOLLOOGGIICCAALL CCOONNDDIITTIIOONNSS FFOORR TTHHEE PPRROOPPOOSSEEDD TTRRUUCCKK SSTTOOPP && SSEERRVVIICCEE SSTTAATTIIOONN

DDEEVVEELLOOPPMMEENNTT OONN PPOORRTTIIOONN 99 OOFF TTHHEE FFAARRMM SSMMAALLKKLLOOOOFF NNOO..112222––HHSS,, VVOOLLKKSSRRUUSSTT,, MMPPUUMMAALLAANNGGAA

PPRROOJJEECCTT NNOO:: LL1988 DDAATTEE:: OCTOBER 2012 J. Du Preez Pr.Sci.Nat.

LL1988: Assessment of the Geohydrological Conditions for the proposed Smalkloof Truck Stop & Service Station, Volksrust – Preliminary Report OCTOBER 2012 – ENGEOLAB CC

2

INDEX PAGE NO

1. INTRODUCTION ...........................................................................................................4

2. SCOPE OF WORK..........................................................................................................4

3. INVESTIGATION METHODOLOGY ..................................................................................5

4. PRELIMINARY SITE ASSESSMENT – SMALKLOOF TRUCK STOP & SERVICE STATION ...........5

4.1 SITE DESCRIPTION..................................................................................................... 6

4.2 SITE SOILS AND GEOLOGY.......................................................................................... 7

PRELIMINARY GEOHYDROLOGICAL EVALUATION .............................................8

4.3.1 DESKTOP INVESTIGATION.................................................................................8

GROUNDWATER FLOW.......................................................................................................... 8

GROUNDWATER RECHARGE .................................................................................................. 8

GROUNDWATER LEVELS ........................................................................................................ 9

CURRENT GROUNDWATER USE .............................................................................................. 9

AQUIFER PARAMETERS ......................................................................................................... 9

HYDROCHEMICAL TRENDS OF GROUNDWATER...................................................................... 10

RESOURCE CLASSIFICATION & RESERVE DETERMINATION ....................................................... 10

REMOTE SENSING – IDENTIFICATION OF GEOLOGICAL FEATURES............................................. 12

FIELD INVESTIGATION RESULTS ........................................................................12

4.3.2 HYDROCENSUS..............................................................................................12

4.3.3 GEOPHYSICAL INVESTIGATION ........................................................................14

4.3.4 AQUIFER ASSESSMENT – CONCEPTUAL MODEL ................................................15

4.3.5 RISK ASSESSMENT, AQUIFER POTENTIAL VULNERABILITY & POLLUTION RISK ......16

4.3.6 FLOOD LINE DETERMINATION.........................................................................17

5. GAP ANALYSIS – DETAILED AQUIFER ASSESSMENT.......................................................17

5.1 CONTROLLED BOREHOLE TEST PUMPING .................................................................. 18

5.2 BOREHOLE DRILLING............................................................................................... 19

6. CONCLUSIONS ...........................................................................................................21

7. RECOMMENDATIONS.................................................................................................23

10. REFERENCES - INFORMATION CONSULTED ..................................................................26


3

LIST OF TABLES & FIGURES

TABLE 1: Reserve Determination – Groundwater Allocation ............................................................... 10

TABLE 2: Aquifer Index, Yield & Class............................................................................................... 11

TABLE 3: Hydrocensus –Verification of Existing Boreholes ................................................................. 13

TABLE 4: Geophysical Investigation Summary: Traverses & Proposed Drilling Positions .......................... 15

Figure 1: Locality Map................................................................................................................. 28

Figure 2: Regional Geology Plan (from 2728 Frankfort Geological series) .................................. 29

Figure 3: Effective Catchment and Quaternary Catchment V31B................................................ 30

Figure 4: Inferred Geological lineaments and Geophysical Traverses......................................... 31

Figure 5: Hydrocensus Results ................................................................................................... 32


4

PPRREELLIIMMIINNAARRYY AASSSSEESSSSMMEENNTT OOFF GGEEOOHHYYDDRROOLLOOGGIICCAALL CCOONNDDIITTIIOONNSS FFOORR TTHHEE PPRROOPPOOSSEEDD TTRRUUCCKK SSTTOOPP && SSEERRVVIICCEE SSTTAATTIIOONN

DDEEVVEELLOOPPMMEENNTT OONN PPOORRTTIIOONN 99 OOFF TTHHEE FFAARRMM SSMMAALLKKLLOOOOFF NNOO..112222––HHSS,, VVOOLLKKSSRRUUSSTT,, MMPPUUMMAALLAANNGGAA

1. INTRODUCTION

Following an appointment by TOWB Trading and on behalf of the Mr. Kobus Kok, Engeolab cc

was requested to assess the geohydrological aspects and characteristics of the area in and

around the proposed Smalkloof Truck stop & service station. The site is located on Portion 9

of the farm Smalkloof No. 122-HS in the Volksrust district, Pixley ka Seme Municipality in

Mpumalanga Province.

As a specialist study, the geohydrological investigation forms part of the environmental

impact assessment process. This is required to determine the potential contamination risk

from the proposed development which includes a “Truck Stop” as part of phase 1 of the

development and a “Service / Filling Station” as part of future developments.

The aims and objectives of the preliminary assessment of the anticipated geohydrological

conditions are to assess available information, identify data gaps and highlight any

environmental constraints pertaining to the development in terms of the geohydrological

aspects. The need for detailed aquifer assessment will also be made following this preliminary

assessment in order to ultimately classify the proposed site from a geohydrological

perspective as suitable or unsuitable for the proposed facility.

2. SCOPE OF WORK

The initial scope of work relates to the hydrogeological review of all the available existing

data in terms of site suitability, by determining the impact of the proposed development in

terms of the geohydrological component and to assess and highlight potential issues and

risks, their significance, and recommend mitigation measures for normal operating times as

well as potential breakages and spills.

The following key steps make up the phased approach of the investigation:

i. Desktop Investigation;

ii. Site Assessment;

iii. Geophysical Investigation;

iv. Preliminary Risk Assessment;

v. Detailed aquifer assessment by means of: Borehole drilling and aquifer testing;

vi. Augmented risk assessment


5

The preliminary geohydrological assessment of the site was conducted in accordance with the

following guidelines:-

• DWAF proposed requirements for geohydrological component of site investigation

and reporting for underground storage facilities;

• DWAF minimum requirements for water monitoring at waste management facilities,

Second Edition, dated 1998;

• South African National Standard, SANS 10089-3:2010, Part 3. The installation,

modification and decommissioning of underground storage tanks, pumps, dispenses

and pipework at service stations and consumer installations.

3. INVESTIGATION METHODOLOGY

The investigation area will be limited to an area of 5km around the proposed development,

however where possible additional borehole data was included in the report. The

investigation methodology comprised the following:-

• A desktop and aerial photographic interpretation of the site;

• Assessment of the cover soils and residuum through a review of the available

geotechnical data conducted by Duncan Hemingway & Partners Consulting civil &

structural engineers;

• A walk-over survey and site assessment coupled with a hydro census of existing

boreholes in a 1km radius of the proposed site.;

• A geophysical survey comprising magnetic and electromagnetic traverses;

• Aquifer assessment by means of anticipated geohydrological conditions;

• Risk assessment of the inherent pollution potential associated with a service station’s

fuel spill potential as well as the treatment and disposal of sewerage and domestic

waste.

4. PRELIMINARY SITE ASSESSMENT – SMALKLOOF TRUCK STOP & SERVICE STATION

An assessment of the available information combined with the brief field investigation results

was used to determine the current site conditions and status quo. This can be used as

background value against which all future monitoring results can be exacted.

It is understood that the proposed service station will eventually comprise a stop-over for

motorists, motor cyclists and truckers to stock up with food stuff and beverages from the


6

kiosk and to fill up with fuel provided from underground storage tanks. The service station

will be easily accessible along the north-eastern boundary from the R23 tarred road to

Standerton. Storm water and surface run-off will be channelled via existing unlined drainage

channels towards the south-western boundary formed by the R23.

4.1 SITE DESCRIPTION

The investigation focuses on portion 9 of the farm Smalkloof No. 122-HS, Volksrust,

located some 3.5km North-West of Volksrust along the R23 between Volksrust and

Standerton. The site is located within the jurisdiction of the Pixley ka Seme Local

Municipality, Mpumalanga Province and is indicated on Figure 1 below and attached

as Appendix A.

Fig 1: Locality Plan

In general, the Volksrust area is regarded as moist, sandy grassland region with an

annual precipitation of around 856mm and fall within the Highveld Grassland

physiographic region. The area is blanketed by deep sandy loam and even clayey soils

derived from in-situ decomposed Mudstone and Shale of the Volksrust Formation.

Vegetation on the proposed site currently comprises various alien tree and indigenous

grass species. It appears that an informal Blue Gum tree plantation previously

occupying a portion of western section the area earmarked for development has


7

recently been removed and remnants can be seen on site. Refer also to Plate 1 below

which indicates the current site conditions

Plate 1: Southerly view across the proposed Plate 2: South-westerly view across the proposed site.

site with TP 1 in the foreground.

Topographically, the majority of the site has very soft slopes; run-off from rainfall

drains into small surface dams to the south-west of the site and then into the streams

to the south-east and east of the site. The expected regional drainage from site is in a

South-easterly direction towards the Mahawane River, which eventually drains

through Volksrust town in a south-easterly direction towards the Slang River, a

tributary of the Buffalo River some 9km south-east of the site.

4.2 SITE SOILS AND GEOLOGY

According to the 2728 Frankfort Geological series, the area under investigation is

underlain by transported and residual soils derived from the in situ decomposition of

mudstone and shale of the Volksrust Formation. To the higher lying north of the site,

olive-green and grey mudstone and sub-ordinate sandstone of the Normandien

Formation can be found capped by younger Dolerite sills. Commonly found in the

study area are younger dolerite intrusions (denoted as Jd) in the shape of dykes and

sheets (sills). The appended Figure 3: Regional Geology shows the different geological

formations.

Most notably, no major regional geological features intersect the site on a local level.

The aforementioned conditions were confirmed through the geotechnical

investigation results obtained from the Duncan Hemingway Geotechnical report into

site conditions and concluded that the soils are relatively consistent across the site

and consist a shallow (0.45m) layer of dark brown colluvium followed by relatively

deep (at least 3m) layer of red-brown becoming light grey silty clays with varying

expansive properties, derived from in-situ decomposed or completely weathered

Mudstone / Sandstone.


8

PRELIMINARY GEOHYDROLOGICAL EVALUATION

4.3.1 DESKTOP INVESTIGATION

Making use of the available information, a conceptual model will be proposed

for the aquifer and catchment within which the proposed development is

located. This is done by collecting available data for the quaternary catchment

and then streamlining the data by verification of the results through field

observations. The data is then collated into this preliminary geohydrological

report indicating site conditions, geology, geological structural features, available

relevant geohydrological information, inferred water quality trends and

groundwater movement aimed at eventually determining the site suitability in

terms of the proposed development. A brief description of the results of desktop

data search is given below.

RESULTS:

Using the Hydrogeological Maps and available GRDM software data sets

provided by DWA, the groundwater resource potential was characterized for the

various stratigraphic units occurring in the project area.

In general, a lack of thick sequences of permeable geological units either

consolidated or unconsolidated occur in the study area and hence secondary

permeability is of prime importance for groundwater flow and storage.

Reasonably thick sequences of clay and sandy loam soils can also be expected.

GROUNDWATER FLOW

The regional and local geology coupled with topography dictates the

groundwater and surface water flow. The geology of the area comprises mainly

Mudstone and shale with a negligible dip, however due to the topography the

flow is expected to be in a south-easterly direction toward the lower lying

Buffalo River located some 9km south-east of the site.

Groundwater flow is predominantly through fractured and jointed bedrock,

therefore the aquifers are considered secondary aquifers, but no significant deep

seated aquifers appear to be present.

Note: a detailed determination of groundwater flow direction is beyond the

scope of this project as this would require accurate groundwater level, test

pumping data and hydraulic parameters. The flow direction is based on

topographical and geological features solely.

GROUNDWATER RECHARGE

Groundwater recharge is an estimate of the percentage of mean annual

precipitation (MAP) that enters the sub-soil and ultimately percolates downward

to the groundwater table. In the project area recharge is entirely rainfall


9

dependant and is estimated at 3-5% of the MAP, which is about 856mm.

Precipitation which does not recharge the groundwater table runs off directly to

surface water courses or evaporates before infiltration.

Factors on site that may affect the amount of precipitation reaching the water

table and recharging the groundwater flow systems include:-

• high water holding capacity of the soils – especially if the rainfall events are

short and relatively infrequent;

• shape and slope of ground surface - rainfall on steep slopes will tend to run

off quickly;

• type and density of vegetation cover.

On site the recharge rates appear to be moderate as a result of soft side slopes

and therefore slower run-off and higher infiltration, coupled with the occurrence

of moderate impermeable clayey silt residuum.

GROUNDWATER LEVELS

No existing borehole records could be obtained from the available Department

of Water Affairs’ National Groundwater Archive (NGA) or GRIP data bases within

a 3km radius of the proposed site. However, data from the DWA’s GRDM

software data set indicates the average water level depth as 12.9m below

ground level (mbgl). Groundwater levels in general follow the topography and

are generally deeper in higher lying areas and shallower near drainage areas like

local streams. Local exceptions may however occur.

CURRENT GROUNDWATER USE

Despite the apparent lack of existing borehole data, the lack of formal water

supply in the study area necessitates the use of groundwater either as direct or

indirect source. Most farm homesteads in the area are expected to use

groundwater directly from boreholes or springs while some river abstractions

are used for both domestic or irrigation purposes.

AQUIFER PARAMETERS

The two parameters that determine any aquifer’s properties are transmissivity

(T) and storativity (S). Transmisivity is the rate at which water moves through the

aquifer as a result of the hydraulic gradient and storativity is the aquifer’s ability

to release water from storage (mostly from the matrix). Transmisivity is the

product of hydraulic conductivity and the aquifer depth.

No available records means no indication of the aquifer parameters. However,

GRDM data set indicates the expected range of Transmissivity values can be

estimated between 1 and 20m2/d. However, the geometric mean T-value

proposed by the available information is around 10m2/d.


10

HYDROCHEMICAL TRENDS OF GROUNDWATER

The lack of existing water quality data for groundwater sources limits the

hydrochemical model of the area, however we highlight the following based on

information supplied by the GRDM software data set.

o TDS value of approximately 416mg/l

These water quality values are proposed as background values and therefore a

level for comparing future water quality results in order to determine water

quality trends.

RESOURCE CLASSIFICATION & RESERVE DETERMINATION

Using the Groundwater Resource Directed Measures software data set (GRDM),

the quaternary catchment within which the study area falls was assessed. As part

of the V31B quaternary catchment, which comprises 508.3km2 with an estimated

mean annual precipitation of 856mm/annum, an estimated baseflow of

12.0Mm3/annum and a recharge of 51mm/annum or 26.07million m

3/annum,

the study area seems to be relatively unstressed in terms of groundwater

abstraction according to South African Reserve Determination classification

system. The current use is estimated to be very low (0.12M m3/annum based on

current records, but not confirmed by a detailed hydrocensus) resulting in the

total allowable groundwater abstraction of 13.61 million m3/annum for the

entire catchment based on the simple formula = Recharge - (Baseflow + Current

Abstraction).

Using the same formula, but this time for the effective catchment i.e. the

portion that contributes to the expected allocation for the site investigated

(some 3.4km2), yield the estimated recharge of 0.17 million m

3/annum minus

baseflow of 0.08 million m3/annum plus current use (estimated to be very low

0.001M m3/annum based on current records, again not confirmed by a detailed

hydrocensus) results in the total allowable groundwater abstraction of

0.0869million m3/annum or 238.2 m

3/day (9.925 m

3/hr) for the effective

catchment.

Figure 3 attached as Appendix A indicates the quaternary catchment V31B as

well as the effective catchment for the study area, while groundwater allocation

calculations are given in Table 1 below

TABLE 1: Reserve Determination – Groundwater Allocation

DELINEATION OF RESOURCE UNIT Total Catchment V31B Effective catchment

Total area [km²] 508.3 3.4

Protected area [km²] 0 0

Effective area [km²] 508.3 3.4


11

DELINEATION OF RESOURCE UNIT Total Catchment V31B Effective catchment

RESOURCE CLASSIFICATION

Abstraction [Mm³/a] 0.12 0

Recharge [Mm³/a] 26.07 0.17

Stress Index [%] 0.460299 0

Present Status Category

B – Localized, low levels of

contaminations

A - Unmodified, pristine

conditions

Vulnerability C B

QUANTIFICATION OF THE RESERVE

Human Need:

Population 50265 335

Basic human need [l/d/p] 25 25

Basic human need total [Mm³/a] 0.458668 0.003057

Recharge:

Recharge [Mm³/a] 26.07 0.17

Baseflow:

Baseflow [Mm³/a] 12 0.08

Reserve:

Reserve as % recharge 47.78929 48.85699

Allocatable groundwater [Mm³/a] 13.61133 0.086943

Current Abstraction [Mm³/a] 0.12 0

Yield as well as strike depths from boreholes drilled into the Volksrust Formation

vary greatly but normally classify as low (


12

REMOTE SENSING – IDENTIFICATION OF GEOLOGICAL FEATURES

Upon completion of the data search, the desktop study entailed the use of

geological maps for the area as well as aerial photographic interpretation for the

specific area under investigation. Possible lineaments, geological structures

intersecting the designated area were identified. These can be targeted for

subsequent field investigation, using geophysical methods. These features form

the primary drilling targets as groundwater movement is perceived to be

concentrated along these features, especially in a secondary (fracture rock)

aquifer scenario as found in the study area.

Even though no major geological features were observed during the desktop

phase, possible minor geological lineaments inferred from the aerial

photographs were identified for potential geophysical investigation.

Included is a map indicating possible lineaments identified during the desktop

study. Refer also to Figure 4: Site Map in Appendix

FIELD INVESTIGATION RESULTS

A Field verification including a walk-over survey of the site and hydro census of existing

borehole sources together with the aforementioned mapping will assist in developing a

conceptual model for the aquifer and catchment within which the development is

proposed.

4.3.2 HYDROCENSUS

To confirm the proposed geohydrological model of the area, the existing data of

relevant groundwater resources identified through the desk study and reported

by the client, were verified and recorded on site using a handheld Global

Positioning System (GPS) and photographed. The results obtained are discussed

in more detail below.

RESULTS:

The data base search for existing groundwater sources yielded NO EXISTING

BOREHOLES in a 3km radius of the proposed site.

A brief hydrocensus was then conducted within a one kilometre (1km) radius of

the proposed site by means of a drive-over survey. A total of six existing

boreholes were identified on site.

These boreholes, some equipped and in working condition, others vandalized,

unequipped and not working are summarized in Table 2 below and indicated in


13

plate 2 below. Appendix C also contains photographic evidence of existing

sources and site conditions.

Plate 2: From left to right and then top to bottom BH 1, BH 2, BH 3, BH 4, BH 5, BH 6

A summary of the coordinates and relevant available information is indicated in Table

3 below and on Fig 5 attached as Appendix A.

TABLE 3: Hydrocensus –Verification of Existing Boreholes

Source Name

Latitude S (WGS 84)

Longitude E

Depth (mbgl)

Yield (l/s)

Water level

(mbgl)

Equipment Type

Equipment Condition Application Water Quality

BH 1 27 19 56.3 29 51 43.6 Unknown Unknown Unknown

Mono Direct drive Pump

Not Working

Stock Watering

Unknown

BH 2 27 20 21.7 29 51 51.6 4.78m Unknown Dry None Not

Working Stock

Watering Unknown


Mono Direct drive Pump

Not Working

Stock Watering

Unknown

BH 4 27 20 15.9 29 51 39.6 Unknown Unknown Unknown Unknown Unknown Domestic Unknown


Submersible Pump

Working Domestic Unknown


Submersible Pump

Working Domestic Unknown


14

4.3.3 GEOPHYSICAL INVESTIGATION

As per the Department of Water Affairs’ (DWA) requirement, a remote sensing

investigation was carried out on site in order to identify potential geological

structures intersecting the proposed site. A second purpose of the geophysical

investigation is to guide the location of boreholes for the installation of a

groundwater monitoring network.

Methods:

Considering the geology of the area (mainly fractured rock region – sedimentary

rock and intrusive igneous Dolerite), the most suitable and cost-effective

geophysical techniques for groundwater exploration, the Magnetic and

Electromagnetic methods were employed. This entailed the geophysical

verification of geological structures identified during the remote sensing. Details

of the geophysical methods are described below:

Magnetic Method

This method measures the total field component of the earth’s magnetic

field. A G5 Proton Magnetometer was used. The different magnetic

susceptibilities of the various rock types result in contrasting magnetic

signatures. Magnetic data may be interpreted to represent dykes, geological

contacts and faults, which may have a bearing on the occurrence, storage

and movement of the groundwater. The abundance of magnetic rock types

(dolerite dykes and sills) in the project area deems this technique very

effective.

A default station interval of 5m was adapted in order to delineate possible

geological structures.

Electromagnetic Method

The apparent conductivity of the underlying geology can be measured using

a Geonics EM 34-3, a horizontal loop frequency domain electromagnetic

instrument. This property is proportional to the amount of weathering

encountered in the underlying geology. Anomalies indicate lateral changes in

the conductivity and facilitate the detection of conductor type targets. The

20 and 40m spacing were employed to investigate various depths. For

resistive terrains (low conductivities), the vertical depth of exploration over

homogeneous or horizontally stratified earth for coil separation of 20 and

40m are 30 and 60m (horizontal coils) and 15 and 30m (vertical coils)

respectively. The lateral extent of the volume of the earth, which is sensed,

approximates the vertical depth and small changes in conductivity (5 to

10mS/m) are readily and accurately measured.


15

Results:

Geophysical Traversing and Proposed Drilling Sites

The remote sensing portion of the investigation indicated a few minor geological

lineaments i.e. no prominent fault zones or Dolerite Dykes, but rather localized

lineaments. Using the results of the aerial photographic interpretations in

combination with geophysical techniques, three (3) geophysical traverses

(Denoted as T1, T2 and T3) were conducted, recording NO GOOD POTENTIAL

drilling site based on geophysical anomalies. The results of these traverses

(attached as Appendix B) are summarized in Table 4 below.

TABLE 4: Geophysical Investigation Summary: Traverses & Proposed Drilling Positions

Geophysical

Traverse

Site at

Station:

Latitude

(WGS 84)

Longitude Geological Site Type Priority

T 1 No Site Start S27° 20’ 12.3”

End S27° 20’ 23.5”

Start E029° 51’ 40.4”

End E029° 51’ 52.8”

Mudstone and Shale. None

T 2 No Site Start S27° 20’ 20.3”

End S27° 20’ 22.9”

Start E029° 51’ 51.6”

End E029° 51’ 48.5”


T3 No Site Start S27° 20’ 13.3”

End S27° 20’ 16.0”

Start E029° 51’ 44.5”

End E029° 51’ 41.8”


4.3.4 AQUIFER ASSESSMENT – CONCEPTUAL MODEL

The proposed conceptual model based on available information comprises:

• A shallow (0.45m) layer of dark brown colluvium followed by relatively

deep (at least 3m) layer of red-brown becoming light grey silty clay derived

from in-situ decomposed or completely weathered Mudstone / Sandstone,

which is unsaturated and with a low hydraulic conductivity. A seasonal

aquifer perched on the bedrock probably forms in this layer, especially

after high rainfall events. Flow would be expected to follow the surface

contours closely.

• The next tens of meters will be highly to moderately weathered, fractured

Mudstone bedrock with low hydraulic conductivity. The permanent

groundwater level resides in this unit and is about 10 – 50mbgl. The water

level is influenced by regional topography and for the site it would be in

general south-easterly. See also Figure 3.

• Below a few tens of meters the fracturing of the aquifer is less frequent

and the fractures less open due to increased pressure. This results in an

aquifer of low hydraulic conductivity and very slow groundwater flow

velocities. As in the previous unit the flow is expected to be south-easterly.


16

Fracturing of the bedrock could consist of both minor dolerite structures (even

though none were observed on site) and/or minor pressure-relieve joints.

Groundwater, originating from the vertical infiltration of rainwater through the

upper layers (s) up to groundwater level, will flow mostly horizontally in the

directions as discussed above. Water flow volumes and velocities will, on

average, decrease gradually with depth.

4.3.5 RISK ASSESSMENT, AQUIFER POTENTIAL VULNERABILITY & POLLUTION

RISK

In order to determine the impact of the proposed development in terms of the

geohydrological component, one has to assess the aquifer potential,

characteristics and significance. This will in turn be used to determine the

vulnerability, highlight potential issues and risks, their significance, and lastly

provide a means of recommending mitigation measures for normal operating

times as well as potential breakages and spills.

Results:

The sustainable volume of groundwater or groundwater potential of the aquifer

underlying the proposed site was calculated using the GRDM software which

uses the hydraulic characteristics (transmissivity and blow yields) as well as the

annual replenishment of groundwater reserves by infiltration of rainwater to the

subsurface or simply called “Recharge”. However, the volume of groundwater

that can be extracted sustainably for a long period is limited by the recharge

over the area.

Using the various methods available for calculating the recharge, the estimated

recharge varies from 3% to 6% of mean annual precipitation (MAP of

856mm/annum). Due to the relatively thick and continuous clay layer overlying

the area, the method based on soil information is preferred which proposes a

recharge value of 3% of MAP or some 238.2 m3/day (9.925 m

3/hr) for the

effective catchment from groundwater sources within the proposed Volksrust

truck stop area. This recharge value is crucial, because should more groundwater

be extracted than the recharge over the area, a regional lowering of the

groundwater table will result with negative influence on neighbouring users.

Slow infiltration or surface run-off is further aided by these low permeable cover

soils and underlying silty clay residuum.

The low recharge rates, low permeable residuum and low groundwater potential

aquifer of limited aerial extent, lowers the risk of groundwater pollution.

However, insufficient hydrochemical and geohydrological records results in

numerous assumptions in terms of the water quality and quantity. Groundwater


17

sources can be preliminary summarized as neutral, fresh, soft with slightly

elevated TDS value. Therefore, in our opinion it can be expected that despite the

slightly higher TDS values, pollution has not taken place and the effective

catchment can be classified in terms of quality as moderately modified with low

levels of localized contamination as per section 4.3.1.

The most significant pollution threats to groundwater resources associated with

the proposed development are:- • Domestic waste generated from the kiosk and the subsequent potential for

leachate formation;

• Spillage that may occur during refuelling;

• Leaking underground storage tanks and fittings resulting in possible

hydrocarbon contamination;

• Dysfunctional sewerage plant and sewerage spills.

Management of leachate formation from domestic waste and discharge of treated

effluent water together with sufficient fuel spill control measures should, in our

opinion maintain the ‘low’ aquifer vulnerability status and ensure a minimal risk of

groundwater pollution.

4.3.6 FLOOD LINE DETERMINATION

As part of DWA requirements, a 1 in 100 year flood line determination should be

carried out on any rivers and streams in the vicinity of the site. No substantial

rivers are found on or near the proposed site.

In fact, a flood line determination was carried out by Messrs. S.E. Lauterbach &

Associates which confirmed that the 1:100 year flood line is not applicable for

site Portion 9 of Smalkloof No. 122-HS as the closest stream is located 400m

eastwards of the site, with an altitude difference of approximately 5 metres.

Refer to Appendix D.

5. GAP ANALYSIS – DETAILED AQUIFER ASSESSMENT

In terms of the detailed aquifer assessment, data gaps identified by the desktop and

preliminary investigation include a lack of controlled test pumping of existing boreholes and

drilling details or borehole logs. This could assist in determining geohydrological conditions

not identified by the desk study.


18

The following is highlighted in terms of information gaps:

• Site specific aquifer characteristics, such as hydraulic conductivity, storage capacity

and specific groundwater flow directions, geochemical trends could not be confirmed

through actual field data. As none of the existing boreholes sources could be sampled

in terms of water quality.

• No water levels could be determined on site and no controlled test pumping data was

available. Data had to be inferred making general assumptions based on the available

desktop data.

5.1 CONTROLLED BOREHOLE TEST PUMPING

Even though the aquifer seems relatively unstressed, controlled borehole yield pump

tests should be completed for the existing/operational boreholes. The test pumping

procedures to be carried out on site should be in accordance with the SABS’

standards: Development, Maintenance and Management of Groundwater Resources –

Part 4: Test-Pumping of water boreholes; SA Code of Practice Ref SABS 0299-4: 2003

and should comprise of the following:

Step Discharge Test

The tests consists of three (3) to four (4) steps of 60 minutes each as part of initial

the step-drawdown test followed by the recovery monitoring. The steps are

conducted at increasing rates and the drawdown measured to ascertain the

potential borehole yields.

On completion of the step drawdown and recovery tests, constant discharge tests

are conducted at a constant rate for a period of 24 hours and recovery was

measured.

Constant Discharge Test

A constant discharge test is performed to assess the productivity of the aquifer

according to its response to the abstraction of water. This test entails pumping the

borehole at a single pumping rate which is kept constant for an extended period of

time. In this instance the boreholes should be pumped for 24 or 48 hours.

Recovery Monitoring

This test provides an indication of the ability of a borehole and groundwater

system to recover from the stress of abstraction. This ability can again be analysed


19

to provide information with regards to the hydraulic properties of the

groundwater system and arrive at an optimum yield for the medium to long term

utilization of the borehole.

Other notes:

• When additional boreholes are located within relatively close proximity to the

tested borehole possible interference (i.e. hydraulic continuity) must be

monitored.

Data obtained during the yield test is used to:

- determine the hydraulic parameters of transmissivity and specific capacity;

- determine the sustainable yield of the individual boreholes after allowing for the

effects of barrier boundaries and interference between different abstraction

boreholes

5.2 BOREHOLE DRILLING

Borehole drilling has two distinct purposes, one being the soil and rock profiling to

determine subsurface characteristics and deeper seated aquifer/s beneath the site

and two for the subsequent monitoring and sampling of groundwater and seepage as

part of the proposed monitoring network, determining groundwater flow directions

and determining initial groundwater quality.

To detect any changes in the aquifer system monitoring of water levels and flow rates

is imperative. The monitoring of the discharge rates and drawdown levels of the

groundwater is of paramount importance should long term exploitation of these

respective secondary aquifers be considered.

• Plastic conduit pipe (32 or 25mm Ø) should be strapped to the riser pipes to

allow monitoring of static and dynamic water levels (manually with a dipper or

electronically through a pressure sensor) prior to start-up, during and at the

end of each daily pump cycle.

• Around the storage tanks it is important to place shallow monitoring wells to

ensure any potential leakage from the lagoon is detected in time. These wells

must be of uPVC or HDPE material and have an internal diameter of at least

50mm. It is recommended that a minimum of one up gradient and two down

gradient wells be installed.


20

• The depth of the well must be at least 2m below the depth of the storage tanks

See Figure below for typical monitoring well design.

Typical monitoring well design required around storage tanks

*adapted from Goodspeed Environmental Services


21

6. CONCLUSIONS

The desktop phase and field verification of the hydrogeological study for the proposed site

concluded:

• In general, the proposed site is located in an area that is regarded as moist, sandy

grassland region with an annual precipitation of around 856mm and fall within the

Highveld Grassland physiographic region.

• The area is blanketed by deep sandy loam and even clayey soils comprising a

silty/clayey overburden (typically not less than 77% and up to 94% silt and clay) that

are normally medium active with plasticity indexes of around 25-30 derived from

completely weathered and/or transported Mudstone of the Volksrust Formation,

which is unsaturated and with a low hydraulic conductivity and permeability.

• The next tens of meters will be highly to moderately weathered, fractured

Mudstone/sandstone bedrock with low hydraulic conductivity. The permanent

groundwater level resides in this unit and is about 10 – 50mbgl. The water level is

influenced by regional topography and for the site it would be in general south-

easterly. See also Figure 3.

• Below a few tens of meters the fracturing of the aquifer is less frequent and the

fractures less open due to increased pressure. This results in an aquifer of low

hydraulic conductivity and very slow groundwater flow velocities. As in the previous

unit the flow is expected to be south-easterly

• Below this (approx >50 -100mbgl) the fracturing of the aquifer is less frequent and the

fractures less open due to increased pressure. This results in an aquifer of low

hydraulic conductivity and very slow groundwater flow velocities. As in the previous

unit the flow is expected to be south-easterly.

• No major or minor geological features were observed during the desktop phase and

this was confirmed by the geophysical investigation results.

• Average water level depth is approximately 12.9m below ground level (mbgl) and

groundwater levels in general follow the topography.

• Despite the apparent lack of existing borehole data, the lack of formal water supply in

the study area necessitates the use of groundwater either as direct or indirect source.

Most farm homesteads in the area are expected to use groundwater directly from

boreholes or springs.

• There are six (6) existing boreholes in a 1km radius of the site. Three are perceived to

be operational and equipped with submersible pumps (refer BH 4, Bh 5 & BH 6). These

are located on adjacent properties and the applications are believed to be for

domestic water supply purposes. The other 3 are either, unequipped and collapsed or

not operational even though equipped (refer to BH 1, BH 2 & BH 3).

• The majority of the existing boreholes have proper concrete seals at the surface to

prevent any ingress into the borehole.

• No test pumping data was available for the existing boreholes. Even though the


22

geometric mean Transmissivity value proposed by the available information is

expected to be around 10m2/d, the recharge is slightly limited by the thick and

continuous (protective) clay layer overlying the area. The method based on soil

information proposes a recharge value of 3% of MAP or some 238.2 m3/day

(9.925m3/hr) from groundwater sources within the effective catchment area for the

proposed site. This can only be confirmed by test pumping and regular, accurate

monitoring of water levels and flow volumes.

• None of the boreholes have any identification on them in the field. The Department of

Water Affairs has a formal numbering system for boreholes and it is suggested the

local office be contacted to register these wells and for numbers. It is important that

these numbers be marked on the boreholes in the field.

• The moderate recharge rates, low permeable residuum and aquifer of limited aerial

extent, lowers the risk of groundwater pollution. Areas with increased permeability

(where the clay layer has been altered or removed) could lead to increased recharge

rates and faster infiltration.

• Limited existing Hydrochemical records indicate that the quality monitoring from

groundwater sources can be summarized as neutral, fresh, soft with elevated TDS

values

• In our opinion it can be expected that the proposed development poses a low

potential pollution risk, pollution has not taken place and the catchment / effective

catchment and even the proposed site can be preliminary classified as largely

unmodified or pristine water quality. The current hydrological and hydrochemical

characteristics are not expected to change significantly in the near future, provided

that the current abstraction and contamination loads remain similar.

• In terms of the National Water Act (Act 36 of 1998), under the General authorization,

which allows a person to take water for reasonable domestic use directly from any

water resource to which he or she has lawful access, no licence or registration is

required for the domestic portion. It also allows a person to take water for small

gardening (not for commercial purposes) and the watering of animals (excluding

feedlots) on land owned or occupied by that person, from any water resource which is

situated on or forms a boundary of that land, if the use is not excessive in relation to

the capacity of the water resource and the needs of other users.

• For the industrial use portion though, water use must be registered and in terms of

the abstraction, a water use license may be required. All water users instructed to

register have the statutory obligation to do so. There are strict penalties, prescribed in

the Act, for those who do not comply. In future, when water users are required to

apply for licences, those who did not register will lower their chances of getting a

licence to use water.


23

7. RECOMMENDATIONS

The recommendations made at this stage aim to provide an understanding of aquifer parameters

and development potential therefore providing a better projection of available resources and the

set up for a management and monitoring system to limit pollution potential.

Based on the aforementioned conclusions, the following legal, management, preventative

and monitoring measures are proposed:

Legal Requirements:

In order to meet the statutory obligation in terms of the National Water Act (Act 36 of 1998),

we recommend that:

All sources of abstraction be registered with the Department of Water Affairs;

For the proposed truck stop & service station (industrial use portion), water use, water

storage and waste water discharge license applications should be discussed with the

appointed environmental experts and submitted even though the development is

expected to fall within the general authorization limit of 45m3/ha/a.

Monitoring Requirements

To detect any changes in the aquifer system, as well as potential pollution derived directly or

indirectly from the proposed development, monitoring of water levels and flow rates, water

quality and trends, is imperative.

Water Level Monitoring:

The monitoring of the abstraction rates and drawdown levels of the groundwater is of

paramount importance should long term exposure to potential hydrocarbon contamination

and /or exploitation of the secondary aquifers be considered.

In our opinion, sufficient existing boreholes are found in reasonable proximity of the

proposed site and therefore, no additional boreholes are currently required.

The following measures are recommended:

The existing production boreholes (BH 2, BH 3, BH 4, BH 5 & BH 6) should be properly test

pumped in terms of SANS guidelines, slug tested, or even existing data sourced to confirm

hydraulic parameters.

The existing production boreholes’ static water level, maximum drawdown abstraction

level, recovery water level and critical water level obtained from the initial test should be

monitored monthly to confirm hydraulic parameters, seasonal fluctuations and

sustainability.

For monitoring purposes, a Plastic conduit pipe (32 or 25mm Ø) should be strapped to the

riser pipes to allow monitoring of static and dynamic water levels (manually with a dipper

or electronically through a pressure sensor) prior to start-up, during and at the end of

each daily pump cycle.

Optional monitoring recommendations are: a flow-meter to be installed in the delivery


24

lines of the production boreholes to record daily and total abstractions. Hour-meters to

be included in the control panel to allow pump performance monitoring.

Shallow monitoring wells must be installed around the storage tanks to ensure any

potential leakage from the lagoon is detected in time. These wells must be of uPVC or

HDPE material and have an internal diameter of at least 50mm. It is recommended that a

minimum of one up gradient and two down gradient wells be installed. The depth of the

well must be at least 2m below the depth of the storage tank.

Piezometers must be installed in all wells and water level monitoring carried out and

recorded either manually or with data loggers.

Water Quality Monitoring

The existing production boreholes and monitoring wells should be sampled regularly in

terms of water quality (SANS 241) guidelines for domestic use.

Initially, quarterly groundwater quality monitoring of production wells and monitoring

wells is recommended.

A proper groundwater quality monitoring program must be implemented as soon as

possible, where initial sampling and analysis should allow for all major chemical, physical

and bacteriological constituents as per (SANS 241). Follow-up sampling could monitor

elements in excess only as well as for traces of hydrocarbon contamination.

Where water is supplied for human consumption, guidelines in terms of a water service

provider should be adhered to.

An early warning system must be considered for placement within the monitoring wells

or beneath the storage tanks.

Wellheads on boreholes down gradient of the proposed facility must be constructed to

prevent any ingress of surface water either from a spill or flooding.

General Management Requirements

The hydrochemical and water level values obtained from the new data sets should be

instituted as the “starting” status.

Precautions should be taken to ensure that surface run-off, potential leaks or spills do not

flow into any of the existing or monitoring boreholes and for this purpose we propose a

concrete apron around each borehole casing and inside the pump house structure.

No major lowering of the water table should take place through increased groundwater

abstraction as that could increase the hydraulic gradient and therefore accelerate

pollutant transport times.

The monitoring data should be reviewed by a hydrogeologist to establish performance

and water quality trends.

Preventative Requirements

Occasional or uncontrolled discharge of contaminants on the site could have a marked influence

on recharge, especially in the top unsaturated clayey residuum and shallow weathered bedrock

zones.


25

The current neutral, unpolluted hydrochemical characteristics can be impacted by increased or

uncontrolled contaminant handling or other processes associated with the proposed

development. Management and discharge of treated effluent water together with sufficient

waste spill control measures should, in our opinion maintain the unpolluted, ‘stable’ aquifer

vulnerability status and ensure a minimal risk of groundwater pollution provided that:

construction of the new facilities does not change the nature of the “protective” clayey

overburden to such a degree (more permeable) that fast infiltration becomes possible

resulting in increased pollutant transport times.

The base of the fuel tank excavations should be flat and free from rocks and other foreign

objects and covered by 150mm thick backfill of acceptable quality, compacted to

specification with the correct backfill material and prepared using accepted construction

practices to ensure stability of underground tanks.

To lower the potential for leachate formation, domestic waste should be placed in a

water tight container and disposed of on a regular basis.

Precautions should be taken to ensure that surface run-off, potential leaks or spills do not

flow into the sewer system without first passing through a simple gravity separator /

settlement pond or similar protective installation.

Submersible pumps should be fitted with leak detectors that check the integrity of the

pipework.

The drive way areas around the dispensers/pumps where spillage may occur during

refuelling should be graded to allow effluent to first pass through a gravity separator.


26

10. REFERENCES - INFORMATION CONSULTED

As part of the desktop investigation, the following geological and hydrogeological data

sources were consulted:-

- Geological Map Sheet 2728 Frankfort to a scale of 1:250 000, Department of

Mineral and Energy Affairs, 1988

- Topographical map sheet 2729BD to a scale of 1:50 000.

- Aerial photographs in digital format, Google Earth 2012.

- A layout plan of the site in electronic format from S.E Lauterbach & associates

Professional Land Surveyors, September 2012.

- Report on the anticipated geotechnical conditions, Duncan Hemingway &

Partners, dated 12 september 2012

- GRIP data set obtained from the Department of Water Affairs (DWA).

- National Groundwater Archive (NGA) data set obtained from the Department

of Water Affairs (DWA).

- DWAF proposed requirements for geohydrological component of site

investigation and reporting for underground storage facilities;

- DWAF minimum requirements for water monitoring at waste management

facilities, Second Edition, dated 1998;

- South African National Standard, SANS 10089-3:2010, Part 3. The installation,

modification and decommissioning of underground storage tanks, pumps,

dispenses and pipe work at service stations and consumer installations.

Prepared by:

……………………….

Jacques du Preez

Hydrogeologist (Pr Sci Nat - BSc Hons)

ENGEOLAB cc - Hilton (KwaZulu-Natal)

Tel: +(27)13 – 656 0720

Fax: +(27)33 - 343 1226/ 086 582 0667

Cell: 083 628 3263

E-Mail: [email protected]


27

AAPPPPEENNDDIIXX AA

Maps and Figures

ENGEOLAB cc

Figure 1: Locality Map

ENGEOLAB cc

Figure 2: Regional Geology Plan (from 2728 Frankfort Geological series)


30

Figure 3: Effective Catchment and Quaternary Catchment V31B


31

Figure 4: Inferred Geological lineaments and Geophysical Traverses


32

Figure 5: Hydrocensus Results

ENGEOLAB cc

AAPPPPEENNDDIIXX BB

Geophysical Data

CLIENT: TOWB Trading

T1=530mENGEOLAB CC

T1=530mLINE :SE-NWDIR:VolksrustDISTRICT :SmalkloofBOREHOLE NO:

No SiteDRILL SITE:Portion 9 of Smalkloof N122-HSFARM:SmalkloofVILLAGE:VolksrustREGION:

-10

0

10

20

30

40

50

60

70

Co

nd

uctivity (

mS

/m)

-50 50 150 250 350 450 550

EM-34

-10

0

10

20

30

40

50

Conductivity (

mS

/m)

-50 50 150 250 350 450 550

EM-34 (40 m Coil Spacing)

-1000

-500

0

500

1000

Ma

gn

etic (

nT

) -

28

00

0

-50 50 150 250 350 450 550

Distance (m)

Total Field Magnetic


T2=130mENGEOLAB CC

T2=130mLINE :NE-SWDIR:VolksrustDISTRICT :SmalkloofBOREHOLE NO:

No SiteDRILL SITE:Portion 9 of Smalkloof N122-HSFARM:Smalkloof Truck StopVILLAGE:VolksrustREGION:

0

20

40

60

80

100

120

140

Co

nd

uctivity (

mS

/m)

-50 50 150 250 350

EM-34

0

20

40

60

80

100

120

140

Conductivity (

mS

/m)

-50 50 150 250 350


200

400

600

800

1000

1200

1400

1600

1800

Ma

gn

etic (

nT

) -

28

00

0

-50 50 150 250 350

Distance (m)



T3=120mENGEOLAB CC

T3=120mLINE :SW-NEDIR:VolksrustDISTRICT :SmalkloofBOREHOLE NO:

No SiteDRILL SITE:Portion 9 of Smalkloof N122-HSFARM:SmalkloofVILLAGE:VolksrustREGION:

0

10

20

30

40

50

60

70

Co

nd

uctivity (

mS

/m)

-50 50 150 250 350

EM-34

0

10

20

30

40

50

Conductivity (

mS

/m)

-50 50 150 250 350


0

50

100

150

200

250

300

350

Ma

gn

etic (

nT

) -

28

00

0

-50 50 150 250 350

Distance (m)



37

AAPPPPEENNDDIIXX CC

1:100 Year Flood line Determination

S.E. LAUTERBACH & ASSOCIATES PROFESSIONAL LAND SURVEYORS

Siegfried Ewald Lauterbach B.Sc. (Survey) PrL.(S.A.) M.I.P.L.S.

Brigitte Lauterbach B.Sc. (Geomatics) PrL. (S.A.) M.I.P.L.S.

Cadastral Surveys ● Engineering & Topographical Surveys

Sectional Title Consultants ● Township Planning Consultants

______________________________________________________________________________________________

Tel: (034) 3125761 / 2 ~ Fax: (034) 3125419 ~ Email: [email protected]

P O Box 407, Newcastle, 2940 ~ 32 Ayliff Street, Newcastle

______________________________________________________________________________________________

Our Ref: RT-122-9 Your Ref:

28 September 2012

Kobus Kok

TOWB Trading CC

Volksrust

Email: [email protected]

Dear Sir,

Portion 9 of Smalkloof No. 122 - HS

Pixley ka Seme Municipality

We confirm herewith that the 1:100 floodline is not applicable to the site, as the

closest stream is 400m eastwards, with an altitude difference of approximately 5

metres.

Yours faithfully,

SE. Lauterbach
mailto:[email protected]:[email protected]

ENGEOLAB ccrhdhv.co.za/media/June-2013/E02.JNB.001204_Volksrust... · 2013. 5. 20. · Jacques du...

Documents

Transcript of ENGEOLAB ccrhdhv.co.za/media/June-2013/E02.JNB.001204_Volksrust... · 2013. 5. 20. · Jacques du...