The management of recharge and quality of the underground water in the Klerksdorp area with specific reference to post closure at the Stilfontein Gold Mine (1952-2000)

by

ANET SPANGENBERG

MINI DISSERTATION

Submitted in partial fulfillment of the requirements for the degree

MASTER OF SCIENCE

in

GEOGRAPHY AND ENVIRONMENTAL MANAGEMENT

in the

FACULTY OF SCIENCE

at the

RAND AFRIKAANS UNIVERSITY

STUDY LEADER: DR. J.F. DURAND ASSISTANT STUDY LEADER: DR. J.M. MEEUWIS

OCTOBER 2000 Contents: Page List of tables 4 List of figures 5 Acknowledgements 6 Abstract 7

Introduction 8

Problem Statement 11

Study area 13 3.1 Geology 13 3.2 Dykes and Sills 15 3.3 Regional climate 15 3.4 Land use 15 3.5 Natural vegetation 17 3.6 Surface water 18 3.7 Groundwater 19 3.7.1 Depth of water table 26 3.7.2 Presence of boreholes 28 3.7.3 Geohydrology of the Dolomites 29 3.7.4 Possible impacts of mining on the groundwater 30 3.8 Interaction of surface water and groundwater 31 3.9 Groundwater recharge 34 3.10 The gold mining industry 37 3.10.1 Stilfontein mine water balance 38 3.10.2 Interaction of mine water with groundwater 39 3

Contents continued Page

Literature review 41

Data collection and methodology 43

Discussion of results 44 6.1 Recharge of aquifers 44 6.1.1 Rainfall 44 6.1.2 Rainfall vs. Pumping 45 6.2 Aquifer Recharge 52 6.3 Water Quality 52

Conclusions 58

Recommendations 59

References 60 4

I. List of tables Page

Table 1: Groundwater abstraction by mines 2 1

Table 2: Contaminants, sources and areas affected 3:3

Table 3: Rainfall: After Rosewarne vs. Composite of the rainfall 46

Table 4: Annual Rainfall; "Shallow" "Deep" Water Levels 47

Table 5: Pumping ex-Stilfontein Mine 50

Table 6: Groundwater flow in the Stilfontein Gold Mine 52

Table 7: Modified hydrologic balance after Enslin (1971) 54

Table 8: Margaret Shaft water quality: 1997-2000 55 5

IL List of figures Page

Figure 1: The study area: Klerksdorp, Stilfontein and Hartebeestfontein 10

Figure 2: Site map of Stilfontein Gold Mining Company 14

Figure 3: General geology of the study area 16

Figure 4: Surface water features of the Stilfontein Mine 20

Figure 5: Stilfontein Rainfall: modified Rosewarne (1982) 22

Figure 6: Stilfontein Gold Mine: Volumes Pumped 23

Figure 7: Stilfontein Gold Mine: Monthly Pumping vs Annual Rainfall 24

Figure 8: The various elements of recharge and interrelationships 35

Figure 9: Stilfontein Mine Water Balance 39

Figure 10: Hartebeestfontein Gold Mine: Rainfall vs. Deep Water Table 48

Figure 11: Hartebeestfontein Gold Mine: Rainfall vs. Shallow Water Table 49

Figure 12: Stilfontein Gold Mine: Annual Pumping vs Annual Rainfall 51

Figure 13: Flow of groundwater 53

Figure 14: Margaret Shaft Water Quality: Time Series 56

Figure 15: Koekemoer Spruit: EC vs Sulphate Time Series 57 6

III. Acknowledgements

I would like to express my thanks:- To the Stilfontein Gold Mine Management & Staff for all the information made available to me and for their hospitality during site visits; To Dr. Stoch for his knowledge and patience; To my study leaders Dr. Durand and Dr. Meeuwis for their attention to detail, research experience, guidance and advice. I would also like to thank my long suffering parents and Malcolm for all their love and support, without which this thesis would never have seen the light of day. Any merit in this treatise is due to Divine guidance, the errors are my own. 7

IV. Abstract

Mining has taken place in the Klerksdorp area since gold was discovered in 1887 and the conglomerates were mined in the Town lands. The mining history of Stilfontein goes back to 1888 when the Strathmore Reef was discovered and worked.

During the early period no attention was paid to the impact of mining on the environment. Since the 1992 Rio Conference the focus has shifted to sustainable development and environmental well-being.

This study investigates the present surface and ground water situations at Stilfontein Mine with the view to making informed management decisions for the pre- and post- closure periods. Recommendations are based on the observations and discussions.

Samevatting

Sedert 1887 vind mynbedrywighede in the Klerksdorp omgewing plaas waar konglomerate op die Town lands gemyn is. Die geskiedenis van Stilfontein strek van 1888 toe die Strathmore rif ondek en gemyn is.

Uit die staanspoor is daar Been aandag geskenk op die aanslag van die mynbedrywighede op die omgewing nie. Sedert die 1992 Rio Konferensie het die klem verskuif na volhoubare ontwikkeling en omgewingsgesondheid.

Die studie ondersoek die huidige oppervlak en groundwater toestand van die Stilfontein Myn met die ingeligte besluitneming as doel ten opsigte van die voor- en namynsluiting..speriodes. Aanbevelings is op die waarnemings en bespreekings gegrond. 8

1. Introduction

There are four major gold mines active in the Klerksdorp area, namely Stilfontein, Hartebeestfontein, Buffelsfontein and Vaal Reefs (KMMA, 1997). Many changes to the mine business structures have taken place over the years. To ensure the safety of the underground mine workers, some mines had to dewater the overlying aquifers.

This study will focus on the Stilfontein Mine, as it was and is still the mine responsible for the major extraction of ground water in the area (Figure 1). The other mines do not pump significant volumes of ground water, as owing to the nature of the geology, they are relatively dry when compared to Stilfontein (Rosewarne, 1982).

During January 1992, Stilfontein Gold Mine ceased underground production owing to the decline in the economy and gold market. Underground mine closure meant that Margaret Shaft could stop pumping the ground water, but was obliged to continue in accordance with an agreement with Hartebeestfontein Gold Mine.

It was estimated that if Stilfontein were to cease pumping, the mine void would fill with water within three months. The danger, however, exists that water from Stilfontein Mine, will flood the workings of the neighbouring mines. Hartebeestfontein Mine does not have the pumping capacity and necessary equipment as the need never arose to handle large volumes of water (Hodgson, 1990).

As Stilfontein Mine is situated upstream from the other mines in the area in respect of the hydraulic gradient, water entering Stilfontein will eventually flow into Hartebeestfontein Mine then to the Buffelsfontein Mine and finally flood the Vaal Reefs Mine. This is due to the fact that the areas between the mine rock pillars, which were rich in gold ore, had been mined out. As a result, there are underground connections between the mines. Underground connections are also maintained between mines, which serve as escape routes during emergencies. 9

Due to the North/South dip in the ore body, Vaal Reefs Mine is currently mining at levels 'deeper than the neighbouring mines. If Vaal Reefs were to pump substantial volumes of ground water, the capital and running costs would be high, as additional pumping equipment would have to be installed at great depths.

The Klerksdorp mines have addressed the concerns about the water situation. The need for cooperation is dealt with by a "Water Forum", for without this cooperation it would not be possible to implement an integrated water management policy.

In the Stilfontein area, various dolomitic aquifers are utilized by farmers, homeowners, informal settlements and industries. Because of the demand on freshwater more focus is now placed on the sustainability of the ground water resources.

Stilfontein Mine has dewatered a valuable resource and the water currently being pumped can be utilized more efficiently (DWAF, 200). The aquifer in the Koekemoer Spruit area, a sub-catchment of the Vaal River, is impacted on by a number of active and abandoned mines. Past, present and the anticipated future impacts of mining needs to be identified to manage and mitigate the negative and amplify the positive impacts.

It is advisable that management decisions be taken by well-informed managers, using adequate information based on accurate data. Legend:

CI Dams /V Rivers A/ National Routes A Other Routes Frit Towns

MINE WASTE SOLUTIONS

Source: I

ENVIROGREEN

Figurel: The study area of Klerksdorp,

Orkney, Stilfontein and

Hartebeestfontein

Scale: 10000 0 10000 20000 Meters 2. Problem Statement

While in operation, it was necessary for Stilfontein Mine to pump water to the surface to prevent the mine from flooding and to ensure the safety of the underground workers. Currently only Margaret Shaft is pumping water to prevent Hartebeestfontein Mine from flooding. Hartebeestfontein Mine carries the cost of both the pumping of water and the maintenance of the pumps.

The problems which may arise from dewatering dolomitic compartments, are, inter alia, water pollution, the formation of dewatering cones (the localized lowering of water tables) and the potential for accelerated sinkhole formation. All these phenomena can influence the drainage patterns of the river catchments involved.

This study, will focus on:

the recharge of the aquifers; the impact the discharge water on the Koekemoer Spruit area; the quality of the ground water pumped to the surface as well as the water discharged into the Koekemoer Spruit and determining. the suitability of water for alternative use.

By quantifying the recharge, the mine will be able to establish the volume of water that it will have to pump from underground after the recharge via the Koekemoer Spruit is eliminated and seepage from tailings dams, no longer in use, has declined, or ceased.

Recharge by rainfall [EU] may, however, continue to be a problem. If this recharge can be intercepted and prevented from entering the Stilfontein Mine, the water pollution will be reduced, as contact with the stope surface and mine water rich in sulphates which have an acid forming capacity, will be avoided. Reducing recharge also translates into savings in pumping costs and maintenance. 12

Enslin (1971) established rainfall recharge values for large areas of South Africa. These

values are used in this study as a baseline assumption. It follows that the impacts of

changed water regimes on the ground water is established before the Stilfontein mine

water is used to monitor the Stilfontein No 2 tailings dam. This exercise will confirm the

volume of water that the Stilfontein Mine has recirculated, at great cost.

Currently an average of 26 MI/day of groundwater is being discharged into the

Koekemoer Spruit. Although it is claimed that the Koekemoer Spruit was non-perennial,

the indications are that it was a perennial stream fed by the Stilfontein "eye". However,

since discharge from Margaret Shaft is being fed into the spruit, it has again taken on the

characteristics of a perennial stream, with an extensive wetland that reduces the volume

of water destined for the Vaal River water body. The importance of the Vaal River

necessitates that the water quality of the Koekemoer Spruit be regularly sampled and

analysed in order to establish the impact of a spruit on a major river system.

At one stage Stilfontein Mine used to pump an average of 40-60 MI/day to the surface. A

portion of this water was used by mine personnel, some was gravity fed to farmers, while the mine used a significant volume as process water in the gold plant. • Lately the

Hartebeestfontein Mine uses a substantial volume of Margaret Shaft groundwater. This water is also used on the Golf Course and supplied to a Nursery. The mine estimates that there is a 26 MI/day surplus, which is discharged directly into the Koekemoer Spruit.

This discharge is done according to permit No. 8M, issued on 26 October 1992, by the

Department Water Affairs and Forestry, which authorises the release of 40 096 m 3/d to the Koekemoer Spruit whilst 3 082 m 3/d may be supplied to third parties.

Connely el al (1989) estimated that an average of 20 MI/day found its way back to the mine workings. If the water quality of this 26 MI/day is suitable and complies with water standards it can be used to supplement drinking water for Khuma Township, or the water could be used for agriculture. The mine will thereby prevent recycling of water, save on cost _related. to maintenance_of equipment and electricity, and generate income should the sale of water be a feasible alternative. 13

3. Study area

The Stilfontein Gold Mine is situated in the Northwest Province, adjacent to the town of Stilfontein and about 15 km east of Klerksdorp and 5 km west of Khuma. Orkney lies some 25 km to the southwest with Potchefstroom 30 km to the east. The Koekemoer Spruit, which flows from North to South, bisects the study area and drains the sub- catchment into the Vaal River. This catchment is indicated in figure 4.

Stilfontein mine (Figure 2) came into production in July 1952. Underground mining operations ceased in January 1992, owing to the prevailing adverse economic climate as well as a substantial decline in ore reserves on the principal reef horizon. Since the cessation of underground mining activities in January 1992, however, Margaret Shaft, has been used for the purpose of manning, serving and maintaining the major pump installation on 10 1 /, and 16 I I, level (s). In the late 1990's the mine considered closure. However, despite the depressed gold price, with the change in management and improved recovery techniques the life of the mine may be extended for about ten to fifteen years.

3.1 Geology With the exception of a central portion, the entire mine surface area is underlain by dolomites of the Chuniespoort Group, which have an approximate north-south strike and an easterly dip of 15-25 degrees. The central southern part of the lease area is overlain by an outlier of Karoo sediments, elongated in an east-west direction, between 120 m and 350 m wide and up to 190 m deep.

The principal reef mined, was the Vaal Reef, which occurs within the quartzites of the Central Rand Group, at depths between 300 m and 2 000 m below the surface. The reef sub-outcrops against the Black Reef, at the base of the dolomites, in the eastern part of the mine boundary, where the Vaal Reef is truncated by the Ventersdorp Lava Succession (EMPR, 1998).

Legend: A/ Remaining extent of SGM A, EMP Area M Footprint ELT -7 Tailings Dams cP( o o b Powerline Servitude o Road Reserve • A 1346 Pelonorni

S lanai ein

1 35 a

...... A1 i f :wiz,- Arawa 1111111► 111014, /Ma ilk an MU. MINE WASTE SOLUTIONS

1325,8 99 Source: i 46

31:1F011. ENV IROGREEN 0000

Figure 2: Site map of Stilfontein Gold Mining Company

•

r NDSJA: HARTEsEEs-fFoNTEIN;

Nr.6 Stag • '''''' I -

snourpx 0 000A1011 Scale: ... • ..... ...... ; 700 0 700 1400 Meters 15

3.2 Dykes and Sills Most of the faulting on the mine trends in a SW-NE direction and is normal, with throws both to the north and south of between 10 and 250 m (EMPR, 1998). A Kimberlite-type dyke and the Pilanesberg dyke strike approximately N-S and occur in the central and western parts of the mine respectively (Figure 3). The Kimberlite-type dyke acts as a conduit, allowing for the flow of water from the overlying dolomite into the mine's workings (L&W, 1993b). The major faults found in the area also have a general N-S strike. The overlying dolomite is between 300 m and 500 m thick.

3.3 Regional Climate The climate of the study area is typical of the South African 'Highveld', with warm to hot, rainy summers and cold, dry, sunny winters. Temperatures average about 30 degrees Celsius in summer and 18 degrees Celsius in winter (EMP, 1998).

The average rainfall in South Africa is approximately 480 mm, about half the world average of 860 mm, which makes South Africa reliant on a limited water resource (Odendaal, 1991). Rainfall in South Africa decreases from east to west (Department of Transport, 1954). Rainfall in the Klerksdorp area occurs mainly as thunderstorms and showers, with an annual average of between 600 and 625 mm. More than 50 per cent of the Mean Annual Precipitation occurs in the six-month period October to March (EMPR, 1998).

3.4 Land use Apart from mining activities to the south of the lease area and municipal development at Stilfontein and Khuma, the remainder of the existing land is used for auicultural purposes (EMPR, 1998). • ci (/)

2000) og reen, ir Env ce: Sour ( a are dy stu f the o logy eo l g Genera

3: u re ig F I7

3.5 Natural vegetation Stilfontein Gold Mine lies in the western portion of the grassveld basin of South Africa. The vegetation in the area is part of the 'Cymbopogon-Themeda veld', Type 48 of Acock's description (1985).

The rocky nature of the area and the low effectiveness of the rainfall supports the typical Karoo ecosystem, which has developed on the dolomitic terrain. In general, the vegetation consists of isolated thorn and Karee trees with a ground cover mixture of grass types and shrubs. The environment in the proximity of the Koekemoer Spruit is more 'vlei' like, and therefore characterised by dense stands of reeds and a well-established around cover of grass.

Some dominant species identified by the EMPR (1998) are: Common Name Scientific Name Ground cover Turpentine grass Cymbopogon plurinodis Rooigras Themeda triandra Herringbone grass Pogonarthria sciitarrosa

Shrubs B loubos Taaibos Buffalo thorn Ziziphus /77 urcorrata

Trees Kameeldoorn Acacia erialaba Karee Rhus lancea Wild Olive Olea africana

Flowers Aloe Aloe Deyviana transvalensis Large Witchweed Striga elegans Orange River Lily Crinum bulphispernuin 18

3.6 Surface water The main watercourses and streams in the area are shown in figure 4. The affected catchment is the Koekemoer Spruit while the receiving water body is the Vaal River system. Excess underground water, not allocated by the mine, is discharged into the Koekemoer Spruit, part of which ultimately ends up in the Vaal River (IWQA, 1995).

The Koekemoer Spruit originates on the farms Rooipoort and Lustfontein about 28 km north of the point where the Koekemoer Spruit crosses the N12, just to the east of the tailings dam complex (Figure 4). The Kromdraai Spruit, a tributary of the Koekemoer Spruit originates to the north of the Koekemoer Spruit and drains to the east of the Koekemoer Spruit until it joins the latter stream about 3.5 km to the north of the point where the Koekemoer Spruit crosses the N12. From the confluence with the Kromdraai Spruit no other stream of note joins the Koekemoer Spruit until it flows into the Vaal River about 16.5 km further downstream in the vicinity of Buffelsfontein Gold Mine about 6 km, downstream of Vermaasdrift (Envirogreen, 2000).

The demand for potable water is increasing owing to an increase in population and the need to reticulate the rural areas. To conserve water, there is an increasing awareness for optimized use, especially under the larger consumers like the mines (Odendaal, 1991). The strategies employed involve recycling the existing water supply and the minimization of water losses through evaporation and seepage (Ahmad, 1991; Cooper, 1991).

Apart from the impact on the receiving water environments and the legal requirement to reduce effluent and, thereby, pollution, these reductions would result in a concomitant reduction of the water supply needed by the Mine. The Department of Water Affairs and Forestry holds the view that effluent should be considered as a water resource (DWAF, 1986). In any reclamation strategy, like water resource allocation, reuse, recycling, or seepage collection, poor water quality, or deterioration in existing water quality places a limitation on water use. 19

The discharged ground water will need treatment before it can be considered fit for use. Generally, the treatment processes are mainly aimed at reducing high salinity levels by one, or more processes of desalination. Suspended solids are removed by filtration and settling. Water can be conditioned to reduce scale and corrosion by neutralization. Cyanide and radioactivity concentration can also be reduced by applying a variety of different techniques (Pulles et al, 1996).

The costs of water treatment usually limits the use thereof. For example, expensive treatment of mine water, to reduce high conductivity and sulphates, makes the water too expensive to be used by the mine, or sold to rural areas like the Khuma Township.

3.7 Ground water Rosewarne (1982) examined the water abstraction from the Buffelsfontein, Hartebeestfontein, Stilfontein and Vaal Reefs mines. Table 1 shows that the Stilfontein Mine pumped about half of the total amount abstracted from mine workings by the four mines in the area. Only Buffelsfontein Mine pumped water directly from the dolomite (Rosewarne, 1982). The well field consisted of six wells, which were situated south of the tailings dams and interlinked into a main supply line, with a volume of 2.8 MI/day.

In his study Rosewarne (1982) concluded that quantities of water pumped from Stilfontein mine showed a sharp rise at the beginning of 1976 (Table 5). Rosewarne claimed that the increased inflow was as a result of a higher seasonal rainfall and resultant recharge. It appears that Rosewarne did not appreciate the impact of mining on the hydrological cycle.

Experience with mining in the Carletonville area showed that as the stoping area of the mine increased, so did the .volume of the water reporting to the mined underground slopes. Wolmerans (1984) explained that the increased volume was due to the increased number of underground fissures intercepted. According to Wolmerans & Guise-Brown (1978) the increase in pumping at the Venterspost mine was directly related to the increase in the stoping area.

Legend: M Quartemary Catchments Aif Rivers 0 Goundwater Monitoring Points

- .... ■•■ 1.1 f f 111011.1.- Ardraa 11113kWIlh. AM MRS. i1111.1■11. MINE WASTE SOLUTIONS

I Source:)

ENV IROGREEN

-- . Figure 4: Surface water features

of the Stilfontein Mine . . . : .

..0 • ,

Scale: 3000 0 3000 6000

Meters 21

Table 1: Groundwater abstraction by mines Mine Operating shafts Groundwater abstraction (average MI/day) from mine workings from dolomite Buffelsfontein 4 (Pioneer, Oranje, 14.4 2.8 Eastern & Southern) Hartebeestfontein 6 (Nos. 2, 4, 5, 6, 7 13.1 - & 8) Stilfontein 4 (Toni, Charles, 49.2 - Scott & Margaret) Vaal Reefs 9 (Nos. 1-9) 19.7 - Total 96.4 2.8 (Source: Rosewarne, 1982)

For the Stilfontein mine. the long-term average rainfall was calculated from the Rosewarne (1982) data and data obtained from the Department of Agriculture for Stilfontein (van der Merwe. 2000, Personal Communication). Unfortunately the data for the period 1987 to 1993 were not available. For this reason a composite of the data received from a number of rainfall stations was constructed.

Nothing can be deduced from either the long-term average, or the annual fluctuations of rainfall (Figure 5). In constructing a linear trend, however, it is noticed that there is a gradual cyclic decrease in the rainfall, - which must translate into a decrease in the natural recharge. Figure 6 shows an obvious increase in the volume of underground water pumped, as the annual averages are less variable, with a positive trend. The positive trend is the overall trend. It is not accurate due to the initial dewatering but levels out later as the water levels are only maintained. For the first period the mine was dewatering and a time period had to elapse before an equilibrium could be established since no records of flows of the springs are available. A pattern was established for latter records showing a more discernable pattern.

Overlaying pumping on rainfall over the period from 1952 to 2000, shOws the increase in water pumped from the underground workings in contrast with the gradual decrease in annual rainfall (Figure 7). By plotting seven-year averages. the variability is smoothed to show the fluctuating pattern of the rainfall. tN CV

E E E E u_ act

C C

O O

•t- ( Pmi ) ewnion : L a Pumped l Stilfontein Gold mine: Volumes [ww] IleJulell 0 0 a C■1 0 co co O ll fa in C Ra l a nu

O An s

E v V

_se o_ ing co —

E mp 000 2

_se E E c7) CL Pu . SE >, COX CL c hly E t Li_ 0 > E 1959 to Ce ° .E Mon

ca e: - a3 a) a) c c a.c 2 < Min ld Go in te n ilfo St

O O CO IP/I II euinion 25

Apart from the natural recharge of the dolomite, factors controlling the inflow of groundwater to mine workings can be attributed to: fissures, or structures of sufficient depth to act as conduits for groundwater flow the thickness of Ventersdorp Lava (impermeable) between the dolomite and the gold bearing Witwatersrand Supergroup, and the presence of dykes, which may act as impermeable barriers as in the case of the Pilansberg dyke, or as water bearing conduits as with the Kimberlite-type dykes.

According to Rosewarne (1982) most of the water flowing into the mine void originates from the eastern area. This was explained as follows: the eastern mine workings are at the shallowest depth, 400 m as compared to 1800 m in the west, the dolomite directly overlies the Witwatersrand Formation, the fissures in this area are well developed, the Kimberlite-type dyke is water bearing, and there are no impermeable dykes to retard the groundwater flow.

Hartebeestfontein, Buffelsfontein and Vaal Reefs are relatively dry mines owing, to impermeable Ventersdorp lavas, which lie between the dolomite and the mining operations.

The pre-mining water table in the area had a gentle downward gradient towards the south with the dolomitic compartments designated A and B in the L & W (1993a) study (Figure 3, Envirogreen, 2000). Originally the direction of ground water flow was influenced by the N-S trending mega joints/fractures, which in turn, were interlinked with minor water bearing slots and joints.

The advent of mining and the need to dewater had a severe impact on the hydrological profile. The stopes, tunnels and haulages, which act as conduits for the groundwater in the rock fractures directed the water to the shafts from where the water was pumped to the surface. The result was the artificial cones of water table depression, which 26

developed in dolomitic compartment B, while compartment A shows less impact from mining with the original North/South gradient towards the Vaal River, as shown in figure 3.

Compartment B (figure 3), which lies in the eastern part of the mine has a Kimberlite- type dyke that strikes N-S. According to L&W Consulting Environmentalists (1993b) the Kimberlite dyke, which can act as a conduit directs the natural flow of water from the overlying dolomite into the mine's workings via the stopes and tunnels. The Pilanesberg dyke is shown by a solid line while the Kimberlite dyke, which runs virtually below the Koekemoer Spruit, is shown by a dashed line (Figure 3), the blue arrows shows the directions of groundwater flow.

The presence of the Kimberlite dyke below the Koekemoer Spruit explains its recharge potential. In addition to the spruit, seepage from the unlined slimes, evaporation and return water dams of all the mines, serve as points of recharge as they overlie intrinsically permeable soils. Presently ground water is only being pumped from Margaret shaft of the Stilfontein Mine (EMPR, 1998).

It is not uncommon for water in mines where mining activities have ceased, to show a gradual improvement with time owing to stratification and the reduced potential for pyrite oxidation. It is therefore not unreasonable to expect the quality of the ground water being pumped at Margaret Shaft to follow the same trend. De Lange and Pulles (1992) investigated the suitability of Stilfontein water as a substitute for the present domestic water supply at Hartebeestfontein and concluded that the water was not suitable as potable water but that the quality was improving.

3.7.1 Depth of water table An outlier of Karoo shales directly overlies the dolomite rocks in an elongated east-west direction across the centre of the Hartebeestfontein/Stilfontein lease area. This Karoo outlier is between 120-350 m wide and up to 190 m deep. The 27

groundwater in the shale is associated with fractures, joints and dykes within the weathered impermeable shales.

The permanent water table is approximately 20 m below surface in places. The overall groundwater potential of these shales is poor (L & W, 1993b). Dolomite covers the major area of compartment A, which has three aquifers, viz.

An upper-perched water aquifer, which developed at varying depths above the permanent water table with isolated pockets of groundwater trapped within confined solution slots, or chert bands within the upper dolomite profile. Variable depth to this shallow water table can be expected in the dolomites. The permanent aquifer developed within the interconnecting solution slots, joints and faults. Water tables commonly occur at levels slightly above the Vaal River water level. • A deep-seated aquifer generally related to isolated water bearing features such as faults or dykes. It is important to note however that these water-bearing features are in some way interconnected with the permanent and perched dolomite aquifers above (L&W, 1993b).

The EMPR (1998) refers to the three distinct water tables in the Stilfontein Mine area, where the first two comprise regional water rest levels as measured outside the impacted minim environment: The first of these represents the perched water level at the interface between the soils/weathered rock and the solid bedrock below. This water table, which is characteristic of the upper weathered sediments of the Karoo outlier, appears to fluctuate seasonally.

The second water table is found in the fractured rock aquifers of the Karoo Sequence, or in the solution slots and joints in the dolomites of the Chuniespoort Group. '7 8

Both these fore-mentioned water bodies/aquifers are subject to surface recharge, either natural, or artificial. The third water table is controlled by the artificial aquifer which is the void created by mining and the level will depend on the controlled flooding of the mine workings. In some low-lying areas there is a perched water table that varies between 1 to 3 metres below ground level. The permanent, natural water level varies from 5 metres to more than a 100 metres below ground level depending on the underlying geology. (L & W, 1993b)

3.7.2 Presence of boreholes A large number of boreholes can be found in the study area. Most of these are exploration boreholes sunk by the mining companies while others are associated with the farming community. Unfortunately there is no reliable inventory of these boreholes in terms of geology, depth and/or water supply.

The Stilfontein Gold Mine currently monitors four boreholes (de Bruin, 2000). The positions of these borehole are indicated in Figure 4 as: ( 1) Borehole SHC I (Depth: 18.5 m below ground level) This borehole is situated in the CHEMWES plant area and the water quality recorded in this borehole can be classified as Ca-Mg-SO 4 type water with low alkalinity. The presence of sulphate in the samples reflects the impact of mining and shows that there is a pollution plume spreading from the plant. (2) Borehole 'PLOT' (Depth: 5.5 m below ground level) This borehole is situated to the east of the tailings dam complex and appears not to be situated in any potential plume pathway arising from the tailings darn complex (Envirogreen, 2000). Dolomitic water is typically characterised by a Ca-Mg-HCO3 type water and relative low TDS and associated sulphate concentration. Envirogreen (2000) state that this water sample, with a TDS of 637 mg/I and sulphate content of 126 mg/I suggested no adverse effects from mining. This statement is in contradiction of the Ca-Mg-HCO 3 type that this water is supposed to represent but also in contradiction of the findings of 29

Kent (1958) and Keersmaekers and Aldridge (1967) who undertook extensive investigations into the quality of dolomitic water. The most likely source of the sulphate is the abandoned New Machavie mine which lies upstream in the headwaters of the Kromdraai Spruit. Borehole CW 8 (Depth: 7.3 m below ground level) and Borehole SCR 9 (Depth: 23.6 m below ground level). These two boreholes are addressed together for the following reasons: Both are situated close or within the potential pollution plume pathways from the tailings dam complex, and Both are characterised by a Ca-Mg-SO 4 type water with an associated relatively low alkalinity.

The above water quality is typically that of leachate from gold tailings dams. Relative low Fe and Mn concentrations (<8 mg/I) suggest that the groundwater is not acidic. From the composition of the water it appears that enough buffer capacity is still available to neutralise any acidity from the tailings dam complex (Envirogreen, 2000).

3.7.3 Geohydrology of the Dolomites Dolomite is a rock composed of calcium-magnesium carbonate and exceptionally soluble. Percolating groundwater enriched with carbon dioxide forms a weak carbonic acid. The result is typical solution of the bedrock along joints, fissures and faults with the formation of the characteristic dolomitic cavities and karstic landscapes.

The system of solution slots, caverns and fractures is linked to a greater, or lesser degree to form a network of water bearing conduits, which if below the water table, act as major water conduits. Fluctuation of the water table over geological time largely controls the dissolution of the dolomites in a horizontal plane. The presence of one, or more of these features causes accelerated leaching of the dolomite along their margins. 30

Major faults, joints, or dykes contacts may result in primary conduits for water flow. The relative permeability difference between Karoo sediments and dolomites at surface results in accelerated leaching of the contact margins, which can be important recharge zones to the dolomite aquifers (L&W, 1993b).

Typically dolomite aquifers are highly transmissive, with a high recharge potential, while the shallow bedrock environment around the mine has a low storeativity. Recharge to the unconfined dolomite aquifers occurs predominantly via the highly permeable materials developed at surface or within slots. The infiltration rate of dolomites is assumed to be in the order of 6 per cent of mean annual precipitation (Enslin. 1971). Due to the variable nature of the chemical weathering of dolomite, the yields of boreholes in the dolomite are also extremely variable (L&W, 1993b)

3.7.4 Possible impacts of mining on the ground water The mining activities, past and present, have affected both the yield and the water quality of the catchment:

Water quality and quantities have been affected in Compartment B. In Compartment A, water quality, is the primary cause for concern, with the effect on the yield being relatively minor. Hence the importance to the Pilanesberg dolerite dyke as a groundwater barrier. The yield of Compartment A has been affected, but only in so far as the addition of poor quality water to the system is concerned (L&W. 1993b).

The extensive dewatering of Compartment B has measurably . affected the water yield in the affected zone. The availability of groundwater is dependent on recharge from rainfall, streams and other surface, or shallow sources and is locally controlled by topography. In the case of the mining environment, the most important impact is that of the artificial recharge effected by slimes dams, settling 31

ponds, processing plants and other surface mining activities and the pumping of water entering the mine voids.

Compartment B is affected by the same sources of recharge and pollution as Compartment A and thus the quality of water can be expected to be similar. However, the important difference in Compartment B, with respect to the affected area, is the presence of a dewatering cone as depicted in figure 3. The dewatering cone developed as a result of the dewatering of Stilfontein Mine workings. During the operational phase, Stilfontein Gold Mine dewatered the underground workings to continue and extend underground mining operations.

In Compartment B, therefore, the main impact has been the result of the lowering of the ground water level, on cessation of pumping by the mine the water level will return to its original level. In Compartment A, the water levels in the immediate vicinity of the slimes dams and the evaporation area, have been affected as a result of the recharging effect of the surface water elevating the water levels.

The nature of gold mining leads to a change in water quality. How this change affects the use of this water downstream depends on what has, or has not been done to the water. Those elements of concern to the natural environment and which are sourced from mining activities are summarized in Table 2 along with a summary of the affected natural systems (Pulles et al, 1996).

3.8 Interaction between surface water and groundwater Two areas of significance have been identified: I. Continuous seepage to Compartments A and B from tailing dams and return water dams together with run-off from rock dumps, has created an artificial recharge by polluted water to the dolomite aquifer below. As a result, a shallow water table has been created in this area (Hodgson, 1990). 32

The impacts resulting from these sources of seepage are: Degradation of the dolomite aquifer water quality Localised rise in the groundwater levels (L & W, Aug 1993)

Prior to the cessation of mining on Stilfontein mine, some of the water was pumped from underground and discharged into the Koekemoer Spruit. Approximately 50 per cent of this discharge water again infiltrated the dolomite-dewatering cone, resulting in the recirulation of water. There have also been minor contributions from sources of irrigation, for example the golf course and farmers, although these are considered to be of minor significance (Hodgson, 1990).

Natural recharge ultimately defines the long term, abstractable volume of water from an aquifer (Sami & Murray, 1998). Recharge rates for aquifers must be estimated before groundwater resources can be evaluated and before the consequences of withdrawal from aquifers can be forecast (Walton, 1970). Extensive research on recharge estimation methods has been done (Bredenkamp et al, 1995). Connelly et al. (1989) compiled a sizeable bibliography, which pays particular attention to soil properties and their relation to groundwater recharge.

According to Connelly et al (1989) groundwater recharge is one of the most difficult of all hydrological components to determine, especially in fractured rocks and in arid regions where regions can be extremely variable in space and time. The process of recharge from rainfall is determined by inter-related, complex factors, which include virtually the entire hydrological cycle. 33

Table 2: Contaminants, sources and areas affected

Contaminant Typical source Areas affected Metals Pyrite oxidation in underground Sediment, groundwater, surface Iron stopes & surface rock & sand waters, macrophytes and biota Manganese dumps & slimes dams & defunct Zinc mines with dissolution of metals Lead Copper Sulphate Pyrite oxidation in underground Sediment, groundwater, surface stopes & surface rock & sand waters dumps & slimes dams & defunct mines with production of sulphates. Cyanide Spillage from: plant areas, Sediment, groundwater, surface ruptured slimes delivery pipeline waters, macrophytes and biota and slimes dams Suspended solids Inadequate underground setting, Sediment, groundwater, surface runoff from surface rock, sand waters, biota dumps & slimes dams Sodium Fissure water addition of sodium Sediment, groundwater, surface based neutralization chemicals waters macrophytes and biota. Chlorides Fissure water Sediment, groundwater, surface waters, macrophytes & biota Nitrogen compounds Waste explosives in underground Groundwater, surface waters stopes, gaseous by-products from explosives, sewage and contaminated runoff from hostels Phosphates Sewage and contaminated runoff Groundwater, surface waters from hostels Acidity Pyrite oxidation Groundwater, surface waters macrophytes and biota Radio nuclides Pyrite oxidation in underground Sediment, groundwater. surface stopes & surface rock and sand waters, macrophytes and biota dumps & slimes dams with dissolution of radio nuclides Microbes Faecal contamination of u/g mine Sediment, groundwater, surface Faecal coliforms service water, poorly treated waters, macrophytes, biota Coliphages sewage, run-off from hostel areas, livestock grazing (Source: Pulles et al, 1996)

Bredenkamp et al (1995, p.3) undertook a major review of the existing literature methods of calculating_ recharge and concluded that: "Contrary to the general view that groundwater estimation is extremely complex, recharge conforms, for large time intervals, to simple relationships, by means of which most problems in the appraisal and management of groundwater resources can be adequately addressed". 34

3.9 Groundwater Recharge In nature the hydrological cycle represents the balance between water accretion and loss. Rainfall is the primary source of the water, which dissipates as evapotranspiration, surface runoff and seepage into the aquifers. In simple terms, groundwater recharge represents the portion of rainfall which reaches an aquifer irrespective of whether it follows a preferential flow path via fractures, or drains through a column of soil, or infiltrates from free water in river channels, ponds or dams (Lloyd, 1986). The complexity of the different elements of recharge and their interrelationships can be appreciated from the presentation of Lloyd (1986) shown in figure 8.

Sami & Murray (1998) gave a broad overview of rainfall recharge. When rain falls to earth, a fraction is intercepted by trees, plants and buildings. The proportion, which does not reach the ground, is lost by evaporation (interception loss). During frequent and brief low intensity events, interception loss may absorb a large fraction of the total rainfall. As a result, such events are the least effective from a water resource recharge point of view.

During heavier rainfall events, water that reaches the ground surface may follow several pathways. A component of it evaporates immediately from the soil surface, while some infiltrates into the soil and the remainder is lost through runoff. Rainfall may enter the ground at a maximum rate defined as the infiltration capacity. Permeability is controlled by soil texture and structure, as well as surface conditions and storm duration. Water entering the soil replenishes soil moisture if it is below field capacity. Field capacity is defined as the maximum volume of water that can be retained by a soil against gravity. This water is available to be used by plants, or may evaporate directly through capillary action.

As field capacity is approached, soil water flow becomes increasingly important. Water may flow laterally above a less permeable layer until it reaches a stream channel, or it may continue downward contributing to recharge. Since infiltration capacities and field capacities define thresholds, which control the movement of water through the soil, they are important attributes to consider in groundwater recharge studies (Sami & Murray, 35

1998). The proportion of water that ultimately enters the aquifer, therefore depends on the overlying soil. The yield potential of an aquifer is a function of the aquifer's permeability and storage capacity.

Precipitation • Virgis Evaporation III Evaporation from Precipitation surface 40 Reaching Surface

Runoff and 1 I • Infiltration Interflow into soil Evapo- Transpiration 11P' Transmission Sheet runoff Localised Soil moisture 4 A Losses & floodout Donding storage 1 Concentration Evapo- Vertical In joints transpiration Infiltration Direct recharge

Lateral & Vertical Vertical infiltration Evapo- infiltration ration Evaporation Indirect Indirect Recharge Indirect recharge recharge

Figure 8: The various elements of recharge and interrelationships (Lloyd, 1986)

The importance of reliable estimations of groundwater recharge needs no emphasis, as it is probably the most crucial aspect of any groundwater study undertaken: To ascertain the volume of water that could be abstracted on a sustainable basis To ensure proper management of the aquifer To develop reliable simulations of water quality changes in an aquifer To study the propagation and dispersion of contaminants (Bredenkamp et al, 1995). 36

In view of the difficulties in obtaining a reliable estimate of recharge at every locality, the expression of recharge as a function of rainfall seems the only practical way to obtain an initial value of recharge, in respect to both its long-term replenishment and annual variability (Grieske, 1992). This was the view of Enslin (1971) who put forward a rainfall / recharge relationship with which to estimate the groundwater resources of the Republic of South Africa. One of the most important contributions of Bredenkamp's study is the conclusion that the cumulative rainfall departures from average rainfall conditions pioneered by Wentzel (1936) can be an excellent indicator of the hydrological response in an area. It also provides a simple technique for checking the reliability of groundwater level data series and of filling in missing values, or extending a record (Bredenkamp et al, 1995).

Bredenkamp et al (1995) states that recharge at a given time is reflected some time later as a change in the groundwater level. This lag in response is a complicating factor but one, which is largely eliminated if periods of significant rainfall are followed by a dry season. This is the case in most semi-arid regions that tend to be characterised by well- defined seasonal rainfall patterns. Hence the advantage of deriving estimates of groundwater recharge from a water balance based on an annual, or a moving 12-month average. A direct relationship between the annual run-off and precipitation was found to apply to dolomitic springs: as there is a linear response between rainfall and spring flow. Bredenkamp et al. (1995) claims that there is a connection between the groundwater levels in the aquifer and the cumulative rainfall departure from the average precipitation.

In determining aquifer recharge complex calculations can be simplified by using the following values: Karoo aquifers R* = 1.5 % of MAP** (mm) where MAP is less than 700 mm/d Granitic aquifers R = (MAP)2/ 20 000 [mm] 37

Hard rock sedimentary aquifers in mountainous catchments R = 0.73 (MAP — 600) [mm], where MAP is less than 1 100 mm Dolomitic aquifers Because of the impact of mining, extensive research has been done on dolomite over many years (Wolmerans, 1984). Where possible a recharge value should be obtained, or extrapolated from recharge values established at nearby dolomitic aquifers (Bredenkamp et al, 1995). Kalahari sand and shale aquifers R = 0.8 % of MAP

*R — recharge to the aquifers is measured in millimeters per annum, **MAP — mean annual precipitation and

According to Simmers (1988) no single estimation technique has been identified which does not give suspect results.

3.10 The Gold Mining Industry Water is a fundamental necessity for mining, both in terms of the quantity as well as the quality (Pulles et al, 1996). Water in the gold mining industry is used underground in drilling operations, for dust suppression, environmental cooling, condenser circuits on refrigeration plants and in hydropower (Niles, 1992). Additionally, water is used to transport the ore after it has been crushed and milled. The addition of water allows the ore to be gravity concentrated and thickened; it allows a cyanidation process to be performed, followed by either filtration or carbon-in-pulp recovery, and it transports waste materials to the slimes dams. Potable water is supplied to the hostels, residential areas and surface plants (Niles et al, 1996).

The actual volume of water used varies from mine to mine. Some mines have large amounts of fissure water, which need to be disposed of, others have to purchase large volumes of clean water, and others recirculate much of the water and so have only to purchase make-up water. 38

Water discharged from mines falls into two main groups, active and passive. In terms of active discharge, this can be sourced from the sewage treatment works, from dewatering of the mine and overflows from holding reservoirs and dams. Passive discharge includes seepage from residue deposits (both to surface and to groundwater systems). Seepage from discard dumps and abandoned mines are often acidic and normally have high concentrations of salts and metals as a result of pyrite oxidation (Best, 1985). Elements of concern are sulphates, sodium, chloride, aluminium, cadmium, nickel and other heavy metals (Hart, 1985).

3.10.1 Stilfontein Mine Water Balance Stilfontein mine kept a record of their internal water balance for June 1999 (Figure 9), the data by courtesy of Stilfontein Mine (de Bruin. 2000). Although ground water is used by the mine itself and supplied to the Hartebeestfontein mine and other consumers. most of the water finds its way into the Koekemoer Spruit and then back into the mine. The volume pumped equals 1061 MI/month and the volume released into the Spruit equals 802.2 MI/month which means that only 25 per cent was being_ used for the 1998/1999 period.

Previously the water balance was different and shortly it is going to change once more. There are plans afoot to recover the gold in the Number 2 Tailings Dam. All the surplus water from the Margaret Shaft will be committed to this project, which will run for about five years, from July 2001.

This change in use will mean that no water will be discharged into the Koekemoer Spruit. It is anticipated that the volume being pumped by Margaret Shaft will reduce in proportion to the reduction in the artificial recharge. As the tailings on dam number 2 are to be transferred to the now dormant tailings dam number 5, the activity is exclusively on compartment A (Figure 3). The groundwater quality of compartment A may be impacted upon and will need to be closely monitored.

39

Stilfontein Gold Mine Limited Water Balance Per month average over 12 months (ending June 1999) Volumes for September 2000 Megalitres per month

Margaret Shaft 1061 020 SGM & Slimes dams

13.4 Stilfontein Mine Consumers 6.2 0.329

OMV A 10.4 2i ). 6

WEIR Reservoir Parties 12.8 ► 12.5

Elartebeestfontein 209.7 217.3 Sewage 11.7 Golf course

V 12.5 10.04 Koekemoer Spruit 802.2

Figure 9: Stilfontein Mine Water Balance (* Values not available)

3.10.2 Interaction of mine water with groundwater The exposure of underground ore bodies created an aerobic atmosphere that facilitated the chemical weathering of sulphide minerals such as pyrites, which in turn, led to the typical pollution of mine water. There is seepage of polluted water from the surface and perched water through the working and along natural and mining fissures. The mine water, which .is pumped to the surface -is contaminated and impacts on the quality of the surface and groundwater.

Prior to 1956 every conceivable step was taken to prevent water from entering underground working places. At Venterspost mine in the Far West Rand an 40

`impervious umbrella" was established by the injection of cement through boreholes drilled into the hanging of ore bodies. Although this method successfully stopped water from inundating a stope during the period of active mining its efficacy was temporary. A survey of the hanging of stoped areas proved that doming fractures extended beyond the effective limits of the umbrella. Water inflow increased as stoping advanced and soon exceeded natural replenishment. The same trend was experienced at nearby West Driefontein Mine (Wolmerans, 1984).

The water pumped from underground was discharged on surface and allowed to seep back into the mine workings. Chemical and radioactive tracers proved that the water recirculated within a few days to depths beyond 1 100 meters. Excessive seepage of water within a dolomitic environment was well known to be the major cause for the formation of sinkholes. These factors together with the dangers attached to mining beneath aquifers having astronomical storage capacities forced mining and government executives to adopt a policy whereby some of the dolomite compartments could be systematically dewatered (Wolmerans & Guise-Brown, 1978).

As Ions as the surrounding mines continue to operate, there will be continued dewatering of the affected dolomitic compartment and the status quo of the compartment will remain approximately as it is at present. It is assumed that because boundary pillars between mines are likely to have been crushed, there is some degree of hydraulic continuity existing between the underground workings of the various mines. The danger also exists that the stability of the dolomites will be affected, resulting in the formation of karstic features. such as sinkholes and dolines. The closest community is the township of Khuma, which is situated on the Ecca formation, within the dolomite series, a formation well known for dolomitic stability problems. Such karstic features could be reactivated, or new features added, as a result of further dewatering (L & W, Aug 1993). 41

4. Literature review Enslin (1971) determined rainfall recharge for catchments in the Western Transvaal by relating the size of the catchment to the annual rainfall in order to estimate the sustainable yield. The importance of the work done by Enslin from the 1950s to the 1970s vests in his vast experience in the field of Geohydrology. It is to his work that Bredenkamp et al (1995) refer in their "Manual of Quantitative Estimation of Groundwater Recharge and Aquifer Storativity" in evaluating the pioneering work done in hydrology. The full extent of the dolomites, some 18 500 km 2, was covered and rainfall recharge values calculated. In fact Enslin (1970) advocated the use of a rainfall/recharge relationship for the entire country.

Rosewarne (1982) extended the research done in the area between Johannesburg and the Boskop dyke to include an appraisal of the dolomite of the Far West Rand including Potchefstroom to the Vaal River. The aim of this study was to obtain more detail on the geology of the area, ground and surface water quality as well as the early impacts of mining activities on the water resources of the area.

Conrielly, Abrams and Schultz (1989) investigated rainfall recharge of groundwater for the Water Research Commission. The main objectives of the study was to gain an understanding of the recharge process and to establish better estimates for ground water recharge from rainfall through improved methodology and numerical modelling.

Hodgson (1990) was asked by the Klerksdorp Mine's representatives to investigate the influx of water into the Stilfontein Mine. He established a correlation between rainfall and the amounts of water pumped by Stilfontein Mine.

Steffen, Robertson and Kirsten was contracted by the Hartebeestfontein Gold Mine to - assess the water balance of Koekemoer Spruit to (I) identify the mechanisms of water losses in the reach of the Koekemoer Spruit between the Stilfontein Gold Mine and the Vaal River and 42

(2) the recharge of water from Koekemoer Spruit back into the underground workings of Stilfontein Gold Mine (Morris, Schultz and le Roux, 1992).

L&W Consulting Environmentalists completed a baseline study on the regional groundwater of the Klerksdorp area in 1993(b). In this study the impact of mining on the underground and surface water was identified as well as the basic geohydrology and recharge sources. (L&W, 1993a).

A two-phased groundwater investigation of the Klerksdorp gold field was undertaken by Anglo American Civil Engineering Department (ANMERCOSA, Jan & Dec 1996) on behalf of the Klerksdorp mine Managers Association during 1995. This study was prompted by a report by the Institute for Water Quality Studies (IWQA, 1995), which identified that the seepage of contaminated water from the dolomitic aquifer, which underlies the Klerksdorp gold field, was adversely impacting on the quality of water in the Vaal River.

In 1997 a forum to develop a water management strategy for the Klerksdorp Gold Field was convened to investigate possible means of ameliorating ground water contamination due to mining activities. Problem areas were identified; as well as further investigation and feasibility studies needed to determine how practical the solutions for long and short- term problems would be (KMMA, 1997).

Pulles, Howard and de Lange (2000) completed the first phase of a study to assess the long-term risks concerning water in the Klerksdorp, Orkney, Stilfontein and Hartebeestfontein (KOSH) gold mining region. Various risks such as short and long-term water pollution from both surface residue deposits (tailings darns and waste rock dumps) and the underground workings were identified. The aim of the study was to provide the status of available information on the potential pathways existing between the various aspects giving rise to contamination in the area. 43

5. Methodology To achieve the objectives of the problem statement various methods were used. A literature study was done to evaluate the different rainfall recharge models suggested and techniques used. Rainfall data was obtained for the Stilfontein and Hartebeestfontein area, the Department of Water Affairs and Forestry, while historical data was also obtained from published studies, for example Rosewarne (1982). Even though data was obtained from various sources no complete sets were available. For this reason composites were created to give an overall impression of the rainfall in the area. The results were displayed in graphical format and conclusions drawn from them.

The Stilfontein Mine maintains a database on pumping, rainfall and water quality with some data from 1910. All relevant data from the mines were made available for this study. Water quality testing is done regularly as part of the compliance of permits and regulations set by the various Departments. Owing to the pyrite content of the ore there is a massive presence of sulphate in the mine water, the presence of which overshadows the combined effect of all the other constituents. Individually the other constituents are only present in relatively small quantities. Only Total Dissolved Solids (TDS). conductivity (EC) and sulphates (SO4) were evaluated to determine the extent of water pollution and to monitor.the water quality status.

These same components where evaluated in respect of the Koekemoer Spruit water, which is regularly monitored by both the Mine and DWAF. Water quality of both Margaret Shaft and Koekemoer Spruit is presented in a graphic format from which conclusions were drawn.

Grab water samples were taken from a few boreholes on the properties of some farmers and field measurements of conductivity taken to check the upstream water quality. There is a close relationship between TDS and sulphate from the pyritic ore body, in the KOSH area. As conductivity is dependent on the total dissolves solids, only EC was measured for these samples. 44

6. Discussion of results 6.1 Recharge of the Aquifers 6.1.1 Rainfall: It may be assumed that the major part of the groundwater, which can be exploited, originates from the infiltration of rain, which seeps into the underground in the immediate vicinity of the precipitation area, or lower down in the catchment area after flowing in small streams and concentrating in vleis, hollows and basins (Enslin, 1971).

Bredenkamp et al (1995) found after comparing existing systems, concluded, that the lumped approach to ground water analysis provided better results than conceptual modeling, which he did not rate highly. He found that using an annual basis he could determine the linear relationship above the threshold value of rainfall that would apply to the recharge of the aquifer as this accommodates the time lag association with the adjustment of the water level. Bredenkamp et al (1995) therefore discarded the shorter daily, weekly or monthly time steps in favour of a 12-month period.

No complete records of rainfall figures were available for the time periods investigated. Instead of patching data, a composite was created (average values created by combining the data from a number of rainfall stations). This was compared with data obtained from Rosewarne's research. The deviation between Rosewarne, the composite and Stilfontein is extremely variable. Comparing the averages between different time series, different averages are obtained. It is noticed that even sites in close proximity have variable results and averages; it is therefore deduced that large areas, with a considerable recharge area, necessitates multiple stations. Rosewarne's values are markedly higher for reasons unknown (Table 3). It is felt that a composite gives a better estimate of rainfall, over a larger area, than just one test station.

Table 4 contains information supplied by Cornelissen (2000) on which figures 10 and 11 are based. These graphs reflect the impact of rainfall on the levels of the perched aquifers in the area. Two aquifers were identified at a neigbouring mine, one relatively 'deep' and one relatively "shallow'. 45

Two graphs were derived from the data in Table 4. The available rainfall data was plotted against the fluctuations of the deep water table (Figure 10) and shallow water table (Figure 11) overlain by the respective seven year moving averages. The moving averages indicate that when rainfall increases there is a consequent increase in the level of the water tables, with an interval between them. The variability of the rainfall is out of phase with the flux in the water tables, which readjust according to the rate recharge. These graphs illustrate the existence of a direct relationship between rainfall and recharge and the 'lag' between these events, which confirms the recommendation of Bredenkamp et al (1995) to use "lumped" data.

6.1.2 Rainfall vs. Pumping: The foregoing relationship can be extrapolated to mimic the relationship between rainfall and pumping of the Margaret Shaft. In Figure 12 pumping data from Stilfontein Mine and the rainfall of the area are plotted against each other. A seven-year moving average is calculated to amplify the trends in irregular data sets. From the graph it can be noted that where there is an increase in seasonal rainfall, the trend of pumped volumes follows, sometime later owing to the lag between rainfall and recharge. These patterns confirm the views of Enslin (1971).

Please note that for the first period, 1952 to 1966, no direct relationship between rainfall and amounts pumped exists (Table 5). The reason for the apparent anomaly is that the development of the underground workings of the mine was in progress. The inflow increases as the area being exploited increases and only stabilized when the maximum inflow had been reached. Where inflow equates to volume pumped, the effect of rainfall on inflow becomes obvious. (Figure 12) Table: 3 Rainfall: After Rosewarne vs Composite of the Rainfall 46

Year Rosewarne l Stilfontein l Composite 11% Deviation 1 l% Deviation 2 1959 Calculated 985 593 66.2 1960 Calculated 1016 703 44.6 1961 Calculated 925 597 55.1 1962 Calculated 768 679 13.0 1963 Calculated 611 621 -1.6 1964 Calculated 726 491 47.8 1965 Calculated 648 419 54.7 1966 Calculated 934 680 37.4 1967 Calculated 871 796 9.4 1968 687 493 39.3 1969 615 655 -6.1 1970 723 520 38.9 1971 860 599 43.6 1972 600 532 12.9 1973 770 781 -1.4 1974 860 760 13.2 1975 1070 740 748 43.1 -1.1 1976 628 1027 788 -20.3 30.4 1977 1045 805 587 78.1 37.2 1978 628 585 418 50.1 39.8 1979 910 798 531 71.2 50.2 _ 1980 1048 597 466 125.0 28.3

Ave 815 612 37

1981 824 541 52.3 1982 579 452 28.1 1983 549 386 42.3 1984 472 435 8.5 1985 463 467 -0.8 1986 629 602 4.6 1987 580 418 38.6 1988 856 795 7.8 1989 779 762 2.2 1990 418 388 7.7 1991 526 562 -6.4 1992 488 400 21.8

Ave 651 l 541 22 aoie: 4 /Annual rcainraii; snaiiow veep" Water Levels 4+1

Year Total Rainfall (mm) 1960 703 1961 597 1962 679 1963 621 Shallow Borehole (m) Deep Borehole (m) 1964 491 14.6 45.0 1965 419 13.4 62.7 1966 680 14.2 73.3 1967 796 14.2 69.9 1968 493 13.9 81.1 1969 655 14.4 90.5 1970 520 15.2 93.7 1971 599 15.2 92.1 1972 532 14.5 92.2 1973 781 14.6 90.0 1974 760 14.3 77.8 1975 748 13.3 69.4 1976 788 10.8 37.6 1977 587 10.7 39.5 1978 418 10.9 36.1 1979 531 11.4 43.8 1980 466 11.7 56.8 1981 541 11.0 59.2 1982 452 11.7 67.7 1983 386 13.2 86.1 1984 435 14.7 103.1 1985 467 15.1 126.3 1986 602 14.7 143.0 1987 418 14.6 136.8 1988 795 13.6 141.7 1989 762 12.3 141.1 1990 388 1991 562 1992 400

Average l 578 CO V (w) toga a 0 0 a a a a a N CD O cv v- CD 03 '1.. 1-

le b Ta ter Wa Deep s v l fa in Ra

Mine: ld Go

in te beesffon te Har

(ww) lle.jumj ienuuv rn .ct

( w) tpdaa

LC) OD a)

ble Water Ta Water low l Sha ll vs fa in Ra e: ld Min Go

in ffonte es tebe Har

O a O co CO Lf) (ww) pelumi ienuuv Table: 5 Pumping ex-Stilfontein Mine 50

Annual Composite I Year Pumping kl/d RF mm Rainfall 1952 3182 641 1953 5535 706 1954 7092 672 1955 7501 662 1956 10323 1071 1957 10910 994 1958 12198 540 1959 20227 727 593 1960 27930 1121 703 1961 34900 806 597 1962 33733 891 679 1963 32483 773 621 1964 29722 642 491 1965 28040 488 419 1966 35980 773 680 1967 36750 893 796 1968 33837 711 493 1969 29065 789 655 1970 27600 690 520 1971 26900 606 599 1972 25827 849 532 1973 26317 778 781 1974 29083 718 760 1975 34377 945 748 1976 46733 1268 788 1977 44517 641 587 1978 50083 908 418 1979 48200 870 531 1980 49850 780 466 1981 54850 1132 1982 51767 756 1983 42383 898 1984 40417 584 1985 44050 490 1986 40870 522 1987 41007 560 1988 41300 772 1989 60090 1990 60777 Missing 1991 45008 ala 1992 40612 1993 39647 766 1994 .36369 - 447 1995 31095 627 1996 32139 923 1997 34050 899 1998 35414 711 1999 33473 592

Average I 33629 1 764 I 612

74; Dm] Ileiu!e21

Ts 4- C Tu" W el= C C < N > a) C a E

2000 a_= ru c= 1952 to c < ii c _ 0 o c .12c ..-0 co

Vep/ppdatunioA 52

6.2 Aquifer Recharge: According to Rosewarne (1982) most of the ground water emanates from the eastern side of the mine. He estimated the inflow of water to be 27.96 MI per day (Figure 13). The proportions are indicated in table 6.

Table 6: Groundwater flow in the Stilfontein Gold Mine Site kl/hr MI/d A 500 12 B 340 8.16 C 80 1.92 45 1.08 E 110 2.64 F 40 0.96 G 50 1.2 0/0 East of dyke 22.08 79 Total 27.96 Balance 5.88

Enslin previously calculated the infiltration rate of the rainfall into the dolomite at 5.5 per cent of the average annual rainfall (33mm of 600mm), which translates to 26 MI per day for the 291 km 2 catchment. For the catchment to produce 30 Ml per day, with an annual average rainfall of 600 mm per annum, the recharge would have to exceed 6.2 per cent (Table 7).

6.3 Water quality: It appears that since cessation of mining the water quality of Margaret Shaft (Table S & Figure 14) has improved. Conductivity, sulphates and Total Dissolved Solids has improved by seven percent. indicating that the pollution has decreased due to the cessation of mining activities. This improvement in water quality is also supported by the analyses of sample taken from Koekemoer Spruit, which shows a decline in both - conductivity and sulphates (Figure 15). Water pumped from Margaret Shaft is currently only suitable for industrial processes and saline agriculture. Although the trend of groundwater quality leans to improvement, it is unlikely that, unless stratification takes place, the water quality can be used for urban purposes without expensive amelioration. • ▪

1:•• 4 c• - ' • ...;F;41•-• :,.. ST 2 ; 41 , •L • 14 iti t 1 • .7. ••• .• • rt ;••••• 4 • 1. ••• 0 .., i. • • : ' 11;41. • • • I )•• 6 x+67 000m i ' — i. ' • • M '400 0 M a w 1111 8 4a-1 1° 1 41 ii r° L MN a r ', Me aka ... II 01 i la 4 M4 la•,W 1••?fil "0aM I llam• .U ._ 0 rlis•"....._ " 10001. • 14 IMO eft4.al; •.... i ' ■ 144 44/67,21111110011 6ftr. aula so 1.•:" 4- !Ii. p...4'. '.... r..- I511 s ....111111111111111121: -••••• ■•••••- 0•1171.17221.1•3111• 11441'.. 7—"IIIIV VII";V ia. ; . vvvvvvvvvvvvvvvvyvvv • vvvvvvvvvvyaggyvvv vvttyw V v v v v v v Ijoittlh 900 m vvvvvvvvvvvv VW "et vvvvvvvv -1200m v.v v ' • ...... ; 1500m

x+68 000 tri • -1900m

...... . . . . . . . . . . ,,. .. .. • . . "+4"•- • ...•' ' f. *°' Et TIO - e="`::•*''0:. g 0 tik . ..."" . a iaigtai • 4

x + 69 000 m

•••1 4§T3ei i • 7. "t.1.7.•••.' 1 • • 4•-•:4 felt — • Jr:\ . . . . • . 16 Mvrgarat- a9e 1, • . • Scot; sildttidyke • Scot :.■.4. •\' . 7. x + 70 000 m 1. • . 4•• eC • 51. 5 • - • •%•.'

•••• 1N.,. •

LrL741.,..7:1 E.Sr 1f. ° 4/s, /-1,:, . L-\.: \. • • I NI. • • 0 '' . •. (I) N■_:. . Hit.8 • 0, AC Cr . . ty ; .HB 9 *.,$:117' . 1.• • . •,„,•,..• • •• • • • • • • " l• • REFERENCEIVERKLARING : • • • •.7.;:..V a. }.1 -- • —if/Ei 2—. . . . • • ' " • • 0 Va al Reif..Sub.:Outcrop against Black Reef Sub-dagsoom van Vaalrif teen Swaririf. • I , • •1•• ••• ' . • • .. • ... Gebied van maksimum invioei van ...... Airoa oflrOkimilm inflow of fissure wafer-4:400 idik i •• :with approximate quantify •••-•-- • ---L--•spleetwafer en benaderde hoeveelheid. . . • • • • .;.1 .% • .... .. 4 . . • Areiplified':.diabram showing flow of' fis- Vereenvoudigde diagram van soled - • $ -•••-•••• —1•• Groundwater flow (Source: Rosewarne, 1982) sure wafet?;... . wafervloei 1/820 • / Figure 13: - Kiniberlite 4. •• • • • - . Kimbirliet • ,4* • Known-WalirAearing . i.diabase . Bekende waterdraende H8160 H8 5 - - _ ., — • —4: Epi-diabaas -. -- 1issur .- gangsplete - - L'-•• 1 1 r / :,.9dy kes reccia zone a _ • _ , Breksiesone Scale 1: 25 000 /•17 ► -1 I • 1 - • Vonerde /7.r.ruer), . . it). I .. • "%. 1 I .. • .. ...Wef•IN a 1 ' . si Ory/ Drool . - - . t ...... : -.-- ...-z• : -t- • -- 7-• • • I- Watergebiede /- • ' • / 00se. s;iire'cilTieas. . • s • se • - '• i 4,.'!. w.. wet • Onknowia 1 -I

; • Serpi : gat. !—__OitbeicecidT / • ,'

Tr 11■=111/ ? C%• CNI

O ble 1.6

0 ta s le

(r) b (D CO O II C 0 C 0 O CO >. 4-, ta O (0 O CD C) O trs O C CD ter O O cr X (7) to C X O X C) zr CNI Cr CNI E 0 wa E E

0 Is

ls CO CIO ti co CO r- 0 0 co CD O O O cs- Cc) O O cs- Cr) 0 r-- cs- N-- cs- a C a CV X C X X

N. hdrawa C)

Wit -cs .rs cr .-..-_- co E

zU) W N Lim CD Dc) (Z) O W CO L O X X a x u-

w E E N- z E E c°

0 CO C O 0 CO Ca

'ts co ti 0 O (r) o Ir)

0 X ti rIE E

›- CD a E E O E O c2 E

,===mr...■

E O E rn E U— C C

O O ? O O a- O cts her co 2 .1•11MINI ■■• is hig is C C .5 C in C ion >, te >, C C a) t C C a) a) O c O (4) c (.) .(7) a) a) a) fon a) C C C C t C C C O C (7) a) a) O a) a) O O a) O a) O O a) filtra O a) O a) C I- a) C I- .o I- s:s O _o O bees O a) a) E co E ci) te cc f in

cis i Ci) co t Har Wha /11••■••■ .111■111. Table: 8 Margaret Shaft Water Quality: 1997 - 2000 55

Date EC TDS SO4 97/02/09 200 1590 809 97/04/30 227 1729 839 97/05/30 220 1724 818 97/06/30 203 1549 800 97/07/31 195 1770 819 97/09/30 209 1600 674 97/10/31 197 1538 684 98/01/30 199 1638 767 98/02/27 197 1673 933 98/03/31 193 1681 820 98/04/30 195 1408 860 98/05/29 195 1615 872 98/06/30 198 1692 938 98/07/31 196 1566 785 98/08/31 195 1732 727 98/09/30 193 1764 756 98/10/30 187 1604 674 99/02/26 186 1353 735 99/03/11 190 1475 840 99/03/31 182 1572 730 99/04/30 185 1412 754 99/05/31 187 1530 760 99/06/30 185 1408 672 99/07/30 184 1532 668 99/08/31 183 1512 626 99/09/30 184 1359 944 00/02/03 176 1443 718 00/03/02 182 1486 676 cG U)

[1/6w] amichns a a a a a a 0 0 O O a a a a 0 O O CD CO r.- co to '4- otr) 1111 O W..' r !.. r 1-

ies r Se

e im T

: lity a Qu ter Wa

ft Sha

t e ar rg Ma

•90, va, qt— O O a ea 'Tr CV CO CO CNI CV CV CV [w/Stu] AMARonpuo3 11 ul

(Ow) sawyclins

0 0 0 Or) CO CO ch

.1= w E I- Btu .c 0. U) 000 2

w 5 to 9 :;.; 19

U) C) O E a) a) 0

o - . _ o U) 0 it) 0 tN r (w/S110 3 IL 58

7. Conclusions This study reconfirms the relationship between rainfall and recharge, which was clearly established by comparing rainfall with pumping. This study supports the findings of Enslin (1971) and Bredenkamp et al (1995) that data modeling has a low priority. An understanding of the geohydrology, will serve management better as the decisions taken will be based on an understanding of the geohydrology to benefit the mine, rather than transpose ill understood data through complex algorithms. If the mines are able to devise a strategy to keep most of the natural recharge (26 Ml per day), out of the underground workings, the pumping will be reduced to a bare minimum, with substantial concomitant saving.

Planned actions of the mine to rework the no 2 slimes dam, using the surplus water to monitor the tailings in order to extract the gold, will stop the -±24 MI/day discharge into Koekemoer Spruit eliminating, any recycling in the process for the next five to ten years. It is anticipated that the Koekemoer Spruit will once again become a non-perennial stream, which will have a serious impact on the artificial wetland. A concomitant benefit will be that the water quality of the Vaal River will be positively affected.

Although mining has a negative impact on the surrounding environment, a gradual improvement in water quality is anticipated due to the down scaling. Even though the water quality of Margaret Shaft appears to have improved, the discharge is still only suitable for secondary use. A supply of current water to Khuma Township, without suitable amelioration, is not advised.

From the information garnered, it is obvious that the mine will be able to save a considerable amount of water and by implication costs if it were to implement an integrated strategy on water management. If pollution is contained, the mine will be able to exploit a more favourable water resource. Should interested and affected parties insist on radical measures to force the regulations, this may lead to job losses followed by mine closure and consequently no improvement. 59

8. Recommendations Preventing the percolation of rainfall into the underground workings is desirable for two reasons; one being a reduction in volumes of water being pumped and the other is the prevention of polluting a valuable resource. Surface runoff as well as drainage occurs from North to South in the Stilfontein area. If this runoff can be intercepted, by allowing the rainfall to percolate underground before reaching the porous compartments, the impermeable dyke will prevent water from entering the workings. Boreholes can be sunk into this 'shallower' water table in order to extract water of better quality and at a shallower depth. If interception does not significantly reduce the volume of water reporting underground, this water, according to the conductivity (65mS/m) is of a potable standard and would be suitable for supply to formal and informal settlements. There is a significant recycling of Margaret Shaft water. It is suspected that there is faults/fissures in Koekemoer Spruit. If discharge is to continue it is recommended that a pipeline, or other method be used to bypass this 'fault' and to discharge outside the area of supply to Stilfontein's underground workings. It is recommended that dewatering continue at Stilfontein Mine. The motivation being that Stilfontein has the capacity and facilities to maintain pumping. Margaret Shaft is pumping water from a relatively shallow depth compared to Vaal Reefs, which mines at considerable depths. Costs of bringing water to surface from such depths are astronomical. The mines will however have to negotiate the most economic and environmentally sustainable path to follow. Total dissolved solids (TDS), conductivity (EC) and sulphates (SO4) were chosen as the basis of an evaluation program for water quality because of the statistical correlation between them and the cost implication of maintaining a sophisticated monitoring program. It is, therefore, recommended that it is only necessary to establish the TDS, EC and SO4 values for routine monitoring. Where the profile of the water quality has been established and this is relatively stable, bi-annual sampling is considered to be adequate. 60

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