6ICARD_The Brukunga Pyrite Mine a Field Laboratory for Acid Rock Drainage Studies

7/24/2019 6ICARD_The Brukunga Pyrite Mine a Field Laboratory for Acid Rock Drainage Studies

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The Brukunga Pyrite Mine A Field Laboratory for Acid Rock Drainage Studies

G F Taylor 1 and R C Cox 2

ABSTRACTThe Brukunga pyrite mine was operated from 1955 to 1972 to supplyfeedstock for sulfuric acid production in the South Australian fertilizer industry. Iron sulfide ore, mined by Nairne Pyrite Ltd, was finely crushedand concentrated onsite with the concentrates being sent by road and railto Port Adelaide for roasting. Waste rock was dumped at two locations onthe western side of Dawesley Creek and the tailings pumped to avalley-fill storage facility on the eastern side. Production of 1.5 Mtconcentrate resulted in 3.5 Mt tailings and 8 Mt waste rock. The site has

been administered by the South Australian Government since August1977 and a lime treatment plant has been operated on the site sinceSeptember 1980.

Environmental issues arising from these operations included: diversion of Dawesley Creek to accommodate the waste rock dumps; dumping of low-grade sulfidic ore in waste rock dumps at the angleof repose immediately adjacent to Dawesley Creek; exposed fresh sulfide mineralisation in the quarry floor; tailings storage facility dam wall constructed by upstream up-lift

using tailings and waste rock; an acid water pond sited on the tailings; and pollution of natural drainage.

As a result, the minesite rapidly became a source of acid drainage and potential contaminants (sulfate, Al, Fe, Mn, Cd, Zn, and Ni).

Various Government bodies have been responsible for considerableeffort and expenditure in reducing the flow of acid seepage andcontaminants into Dawesley Creek. Presently an estimated 60 per cent of seepage from the waste rock dumps, tailings storage facility and quarry iscollected and neutralised prior to discharge into the creek. Tailings have

been covered with waste rock, biosolids, neutralisation sludge and soil

and planted with grasses, shrubs and trees to reduce rainfall infiltration.Monitoring of water flows, water quality and riparian ecosystems ison-going. Consultants have been engaged to develop cost-effectiveremediation techniques and a five-member Brukunga Mine SiteRemediation Board was appointed to oversee remediation of the site andliaise with the community. Construction has commenced on the diversionof Dawesley Creek, and plans are being developed for the relocation of waste rock back to the quarry benches and upgrading of theneutralisation plant.

The paper examines operations, environmental monitoring,remediation, research and community involvement with respect to current

best practice.

INTRODUCTION

After the end of WWII, sources of sulfur for manufacture of

superphosphate were limited and with the prospect of limitedsupplies in the future, prices were high. This, together with aguarantee by the Commonwealth Government to pay a subsidy if the price of sulfur fell below a certain fixed price, the savings of foreign exchange and the opportunity to establish a localindustry, led the South Australian Government to encourage andsponsor the formation of Nairne Pyrites Pty Ltd (Doherty, 1978).The company was formed in August 1951 and comprisedWallaroo Mt Lyell Fertilizers Ltd, Adelaide Chemical and

Fertilizer Co Ltd, Cresco Fertilizer Ltd with BHP Co Ltd asquarry and treatment plant operations (Armstrong and Betheras,1952).

Investigation into a suitable source of pyrite was commenced by Enterprise Exploration Co Pty Ltd and later taken over by Nairne Pyrites Pty Ltd. A suitable source was discovered 5 kmnorth of Nairne, close to the existing rail and relatively close toPort Adelaide where a sulfuric acid plant was constructed. Themine commenced operations in 1955 and was shut-down in 1972when the Commonwealth Government withdrew the Sulfur Bounty because a supply of relatively low-cost sulfur becameavailable from Canadian sour gas wells. To support the miningoperations, the township of Brukunga was built by the South

Australian Housing Trust. Today it is essentially a residentialsettlement of 220 persons.Although the company maintained a caretaker staff at the

mine, they were unable to check the gradual deterioration of thearea and the resultant increase in contamination of DawesleyCreek due mainly to acid rock drainage (ARD). Communityconcerns led the South Australian Department of Mines tocommission Australian Mineral Development Laboratories(AMDEL) to study and propose a solution to this contaminant

problem (Doherty, 1987). Administration of the rehabilitation of the mine became the responsibility of the South AustralianDepartment of Mines. Design, construction and subsequentmaintenance of the rehabilitation works was undertaken by theEngineering and Water Supply until 1998, when responsibilityreverted to the Department of Mines (now Office of Minerals andEnergy Resources, Primary Industries and Resources SA).

THE BRUKUNGA MINE

The Brukunga minesite occurs 50 km east of Adelaide in an areaof rolling hills of the eastern Mount Lofty Ranges. Host rocks arethe Talisker Calc-siltstone of the Cambrian Lower KanmantooGroup, consisting of a metamorphosed phyllite with calc-phylliteinterbeds (Gravestock and Gatehouse, 1995). Sulfide-rich bandsare common in the lower part of the formation particularly in the

Nairne Pyrite Member, which hosts several small-scale base-metal deposits.

Iron-sulfide mineralisation occurred as three steeply-E-dippingconformable lenses separated by waste beds. Each of the 15 -

30 m thick ore zones consisted of iron sulfide-bearing muscoviteschists and gneisses with minor lenses of calcsilicate and quartz plagioclase metasediments. The waste zones consisted of quartz plagioclase granofels and minor calcsilicate granofels, muscoviteschists and gneisses. The lenses outcropped as ferruginousgossans with weathering to a depth of 18 m (La Ganza, 1959).Mineralization was pyrite and pyrrhotite with minor sphalerite,chalcopyrite, galena and arsenopyrite, sources of arsenic,cadmium, copper, zinc, antimony, lead, nickel, tin, barium,cobalt, manganese and sulfate (Burtt and Gum, 2000a and b).

Mining was undertaken by quarrying into the eastern flank of ahillside which forms the western side of a valley traversed byDawesley Creek, a tributary of the Bremer River, Today, thequarry is approximately 1800 m long (N-S) and 150 m wide andconsist of an exposed foot-wall and main bench with two deepslots excavated to access deeper ore (Figure 1). Waste rock was

placed in two large dumps on the western side of Dawesley

6th ICARD Cairns, QLD, 12 - 18 July 2003 93

1. CSIRO, Environmental Project Office, PMB No 2, Glen Osmond SA5064.

2. Regulation and Rehabilitation Branch, Mineral Resource Group,Office of Mineral and Energy Resources, PIRSA, GPO Box 1671,Adelaide SA 5001.

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Creek and a much smaller dump on the eastern side (Figure 1).Material containing more than five per cent sulfide was regardedas ore and processed on site. The concentrates were transported

by road to Nairne and thence by rail to Port Adelaide where theywere converted to sulfuric acid and then superphosphate for SAsagriculture industry. Tailings were deposited in a valley-fill

storage facility on the eastern side of Dawesley Creek (Figure 1).The surrounding countryside has been largely cleared of native

vegetation and supports grazing, dairying and other pastoralindustries. The climate is essentially Mediterranean with coolwet winters (600 mm annual rainfall) and warm-hot dry summers(pan evaporation 1100 to 1400 mm/annum).

94 Cairns, QLD, 12 - 18 July 2003 6th ICARD

G F TAYLOR and R C COX

FIG 1 - Brukunga Mine Site layout and Sampling locations.


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ENVIRONMENTAL ISSUES

During mine operation, the company was forced to providealternative water supplies to landholders adjacent to DawesleyCreek when acid drainage contaminated their water supply.During 1972, complaints were received concerning dead fish inLake Alexandrina, the discharge point of the Bremer River, andconcern was expressed over the long-term effect on the important

Angas-Bremer Irrigation areas (Smith and Hancock, 1992).Although this catchment hosts a numbers of old mines(Kanmantoo, Bremer, Kitticoola, Aclare, Wheal Ellen andStrathalbyn; Both 1990) and the outcropping 100 km long NairnePyrite Member, environmental attention is focussed on theBrukunga Mine.

There are a number of factors which have resulted in theBrukunga minesite being classified together with Rum Jungle,Mt Lyell, Captains Flat and Mt Morgan as major sources of ARDin Australia. Each of these factors is discussed below.

Diversion of Dawesley Creek

As mining operations progressed there was insufficient space between the mine and Dawesley Creek to dispose of the waste

rock. Consequently two westerly intrusions of the creek were buried and the creek diverted to accommodate the SouthernWaste Dump. The buried channel is both a source of water flowing into the waste rock and a conduit for acid seepageseeping back to the existing channel.

Waste rock dumps

There is approximately 8 Mt waste rock deposited in two maindumps (Figure 1) with the Southern Dump being the largest. Asmall Eastern Dump is reported to contain little acid-generatingmaterial whereas the two major dumps average two per centsulfide as pyrite (Blesing et al , 1974). Rainfall infiltration has not

been measured directly, but seepage data (EGi, 1995) suggest anoutflow of 38 Ml/annum or in excess of 50 per cent of incidentrainfall, despite some surface compaction by vehicular traffic.Some of this seepage is undoubtedly due to the former sectionsof Dawesley Creek buried under the southern dump.

Monitoring of temperature profiles and pore gas oxygenconcentrations (Bennett, 1994) suggested a sulfate generationrate of 400 tonnes per annum whereas measurement of seepagerate and sulfate concentrations indicates a sulfate generation rateof 1000 tonnes per annum. Part of the seepage is collected insumps located at the toe of the dumps, but some of it finds itsway around and into Dawesley Creek. Waste rock from the minehas been used elsewhere on site, notably in construction of thetailings dam wall and to fill surplus neutralisation sludge dams atthe back of the tailings storage facility. EGi, 1995 estimated that65 per cent of ARD on site is generated by the waste rock

dumps.

Exposed quarry bench

The remainder of the three iron sulfide lodes are exposed on thequarry bench and the two deeper slots. This is subject to aerialoxidation, rainfall, seepage from the 70 - 85 m high westernhighwall of the quarry and flow through Days Creek which allincrease the volume of contaminated water and have resulted insome minor ponding on site. The exposed walls have oxidisedand are covered by dark red-brown iron oxides, whilst the pondsare surrounded by a number of evaporative mineral precipitates.The rocks of the walls and benches have low permeability andthe estimated 15 per cent contribution to total sulfate generationis more likely to be from sheet wash and drainage to Dawesley

Creek via Days Creek and ephemeral channels.

Tailings storage facility

Approximately 3.5 Mt tailings averaging 1.8 per cent sulfide,mainly as pyrrhotite, are held in a valley-fill storage facility onthe eastern side of Dawesley Creek. This TSF abuts the southernend of the Brukunga township.

The starter dam wall was built from soil and rock directly ontothe natural valley floor. It was subsequently raised 12 levels

using the up-stream beached-sand method and by 1967 a heightof 35 m has been reached. The downstream slope of the dam wallwas armoured using waste rock, some of which was potentiallyacid generating.

Initial toe seepage from the TSF was estimated at between80 ML/a and 100 ML/a (AMDEL Report No 1015) and this wasreduced by treatment and removal of the acid-lake to 40 ML/a by1991. Closure of precipitate drying dams in 1998 and 2000 andthe establishment of vegetation has further reduced seepage to 34ML/a in 2001 (Figure 2). The TSF accounts for approximately25 per cent of total sulfide generation with seepage due torainfall infiltration, valley flow and discharge from a spring

buried beneath the tailings.

Ponding on tailings surface

Following closure of the mine, the TSF became a major sourceof acid seepage into Dawesley Creek. To prevent this, theseepage was collected at the toe and pumped to astorage/evaporation pond at the back of the TSF. This resulted inrecycling and concentrating of the seepage liquor.

After studies by AMDEL into the best way to treat the acidconditions a lime neutralisation plant was commissioned in 1980to eliminate the accumulated acid water and to treat seepagecollected from the TSF and the mine site. The plant produces aneutralisation sludge consisting of gypsum with hydroxides of heavy metals. After thickening the sludge is pumped to holding

ponds at the back of the TSF where excess water either seepsinto the tailings or evaporates.

Soil and water contamination

There were no baseline studies of surface or groundwaters or downstream soils prior to mining at Brukunga. Contributions tosoil and water contamination from other potential sources eg theupstream Bird-in-Hand gold mine (1881intermittent to 1937) and

a considerable strike length of the mineralised Nairne Pyrite


THE BRUKUNGA PYRITE MINE A FIELD LABORATORY FOR ACID ROCK DRAINAGE STUDIES

Annual Rainfall and Seepage for Brukunga

0

20000

40000

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80000

100000

120000

1 9 7 5

1 9 8 8

1 9 8 9

1 9 9 0

1 9 9 1

1 9 9 2

1 9 9 3

1 9 9 4

1 9 9 5

1 9 9 6

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1 9 9 9

2 0 0 0

2 0 0 1

2 0 0 2

s e e p a g e ( k i l o l i t r e s )

0

100

200

300

400

500

600

700

800

900

1000

r a i n f a l l ( m m / y r )

seepage

rainfall

FIG 2 - Annual seepage from toe of the tailings storage facilitytogether with annual rainfall at Brukunga.


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Member were unknown prior to mining. Current monitoring program results (Table 1) record the mine site contribution to thecontamination of the waters of Dawesley Creek. Comparisonwith waters in the Creek upstream of the mine (Dawesley u/sPeggy Buxton; Table 1) record a marked decrease in pH andsignificant increases in acidity, sulfate and trace elements levels.Although not included in Table 1, cadmium concentrationsimmediately below the mine ranged from 0.0004 mg/L in August

winter dilution 1997 to 0.2 mg/L in February 1998 summer lowflow. Average winter and summer values exceed therecommended ANZECC Water Quality Guidelines for livestock watering by two and ten times respectively. Concerns raised by alocal landholder alleging possible impact of cadmium on 1993calving rates led to PIRSA commissioning a detailedretrospective desktop study (McLaughlin and White, 1999).

In 1992 a resident of Brukunga raised concern for the presenceof white crystalline precipitates beneath a house in the township,which resulted in studies by SA Housing Trust and SA HealthCommission determining the salts to be mixtures of magnesium,iron and aluminium sulfates. An health risk assessmentconcluded that elevated levels of some elements did not cause ameasurable health risk but contact with the salts should beminimised by remedial actions such as covering with mulch,lawn, or paving.

Cover materials

Both neutralisation sludge from the plant and biosolids fromwaste water treatment plants are used as part of the on-goingrehabilitation of the minesite. Both contain elevated levels of avariety of heavy metals and concern was raised that they may actas additional sources of contamination of water in DawesleyCreek. PIRSA engaged Australian Water Technologies toundertake an investigation of the use of biosolids andneutralisation sludge to determine the potential for heavy metalsand nutrients to move off-site.

Noise, dust, odoursThe waste lime used in the neutralisation plant sometimesreleases a faint acetylene smell when the pulp is freshly agitated.The odour is perceivable only when standing in close proximityto the lime tank.

Wet sludge from residential septic tanks is used on the TSF.The sludge arrives in 8000 L tankers on an average of 35 loads

per month. To eliminate any odour, noise or dust problems, or traffic disturbance to Brukunga residents, cartage occurs onweekdays only and enters the site prior to the township. Thesludge is spread thinly amongst trees and rapid drying of thesludge reduces any odour. Biosolids from SA Water Corporations waste water treatment plants have been mixed withimported soils for rehabilitation. Deposition and spreading isconducted only when climatic conditions are favourable.

Noise generated by vehicular traffic is restricted to daylighthours only. The neutralisation plant which operates on a 24-hour

basis in winter is powered by electric motors which minimisesnoise levels. The occasional use of diesel motors is conductedduring daylight hours and is short-term in duration.

In April 2000 an asphalt seal was applied to the compoundyard to reduce dust derived from vehicle movements. At thesame time, Watts Road leading to the compound, was sealed tothe entrance gates. Much of the delivery traffic is routed onto thesite through a gate below the TSF and out of sight of thetownship Vegetation of the TSF and other parts of the site hasminimised dust derived from formerly disturbed or bare surfaces.

Municipal impact Not all contamination of Dawesley Creek is attributable to theBrukunga Mine. The headwaters of Dawesley Creek are adjacentto the township of Woodside with discharge from its SepticTreatment Ponds being released to the catchment. An antiquatedcommon septic system, built at Brukunga in 1956, enabledeffluent to overflow into Dawesley Creek leading to odour andturbidity and surface frothing. From 2000 the town sewage was



Parameter(mg/L) except pH

Mine cuts Tailings Dawesleys u/sPeggy Buxton

Dawesley d/s(KAN 2)

Waste dumpR/O and Seep

pH 2.53.0

2.3 7.5 3.04.5

2.53.0

Acidity 40008000

7000 0 2001000

40006000

SO4 500010 000

8000 80100

10002000

60009000

Fe 10002500

4000 1.5 1030

200600

Al 400800

50


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pumped to the Mt Barker STP, thus reducing local odour andcontamination of Dawesley Creek. The creek is also subject tothe impacts of any waterway through agricultural land increased nutrient levels from fertilisers and animal wastes andsuspended solids.

SummaryAn annual Environment Protection Authority site licenceestablished the accepted monitoring requirements in 1996 andrequires regular water monitoring and reporting, and thedevelopment and revision of an Environmental ImprovementProgram for remediation work conducted on the site. These arediscussed separately below.

MONITORINGMonitoring of various parameters falls into two categories:ongoing and short-term/information gathering. The objectives of an on-going water monitoring program, contained in Condition100-1 of the EPA Site Licence No 10577, are:

1. Determine the annual and seasonal lodes of heavy metalsentering Dawesley Creek from the site by measuring the

stream flow and the concentration upstream anddownstream of the site.

2. Determine the extent of impact of the site (the zone of impact) on Dawesley Creek and the Bremer River byundertaking a biological (macroinvertebrate) monitoring

program every three months.

3. Determine the temporal and spatial variations of pH andheavy metal concentrations within the zone of impact byundertaking a monthly sampling program at a selection of fixed sites within the zone for the purpose of assessingcompliance with the water quality guidelines for the

protection of aquatic ecosystems as given in the AustralianWater Quality Guidelines for Fresh and Marine Waters,1992.

Water qualityData collected from the monitoring program are collated in anannual report by PIRSA for the EPA. Some data from the 2001

program are reproduced below to illustrate load, temporal andspatial variations, and impact as measured by species richness.Figure 3 shows that there are significant quantities of sulfate,aluminium, cadmium, manganese, iron, nickel and zinc from themine site in Dawesley Creek. The loads vary from year to year

but do not correspond directly with the water flow.Water samples are taken monthly at eight locations one

upstream of Brukunga and one in Nairne Creek as controls andsix others located in Dawesley Creek or influenced by its flowdown to the Bremer River. Samples are analysed for pH, TDS,

conductivity, Cu, Fe, Pb, Mn, Al, Ni, Cd, Zn, Cr and sulfate.Figure 4 shows improvements in pH, sulfate and cadmium levelsdownstream from the mine (Site 2) for 2002 compared with theaverages for the previous four years 1998-2001. During the hotand dry summer months, pH is at its lowest (3 - 3.5) and thecontaminant levels at their greatest. In the latter half of the year dilution from winter rains results in increased pH (4 - 4.5) andcontaminant levels drop to values, which approximate to theANZECC guideline for livestock. Figure 5 shows monitoringdata for the same three properties at Site 12, which is in MtBarker Creek below the confluence of Dawesley/Mt Barker Creeks. These show a dramatic improvement in pH (7.5 - 8) withlittle variation throughout the year (except for September 2001)when there was very heavy rainfall. Sulfate values aresignificantly lower than immediately below the mine and areconsistent throughout the year. Cadmium values are an order of magnitude lower but are highly variable throughout the year.

Impact of acid drainage from the Brukunga Mine on theecosystem of Dawesley Creek is assessed by quarterlymacroinverterbrate monitoring using a standard sweep net(250 mm mesh) using the standard method for edge habitat. Theresults are presented as species richness, which is a measure of thediversity of the macroinverterbrate community. A large number of species indicates lower stress on the environment. Figure 6 showsthe mean and standard deviation species richness for six sites for the period 1996 - 2001. Figure 7 shows the temporal variation inspecies richness at three of the sites. Figure 6 clearly shows theimpact on ARD on Dawesley Creek downstream of the mine. Theaverage value at Peggy Buxton Road is less than that in NairneCreek due to eutrophication by run-off from grazing land anddischarge from a wastewater treatment plant in the headwaters of Dawesley Creek. Temporal variations (Figure 7) indicateimproving conditions with a gradual increase in species richnesssince 1996 at each of the three sites, with an increase throughoutthe year downstream of the mine

Water in the collection ponds below the tailings dam wall,together with the seepage water from the TSF is monitored on aquarterly basis.

Depth to water table

Early concerns about the stability of the tailings dam wall led tothe establishment of seven monitoring boreholes in the22-hectare surface of the TSF. The depth to water is monitoredmonthly and the data graphed to show temporal variations. Over the long term, the depth to water has increased indicating acontinual drying of the tailings, demonstrating the success of therehabilitation strategy. The bores located along the front edgeand in the middle of the TSF show no significant seasonalvariation whereas those located at the shallow upper end of thevalley show a rise in winter and a fall in summer.

In 1996, an electrical and electromagnetic survey of the TSFwas conducted (Buselli and Hnang, 1996) which indicatedsources of fresh water at the SE corner of the TSF and another onthe northern edge. The latter coincides with a presumedfreshwater spring.

EcologyIn addition to the species richness monitoring there has beenmonitoring of algal activity, benthic diatoms, freshwater shrimp,aquatic fungi and microbial communities by ANSTO, FlindersUniversity and University of Adelaide (Markich and Wojcik,1999; Markich, 2000). The results are in agreement with themacroinverterbrate monitoring. Much of the data generated bythis three-year monitoring has been utilised by the ANSTO codeAQUARISK (Twining et al , 2000) to quantify the ecological risk to aquatic species in Dawesley Creek. There was good agreement

between the impact quantified using the code and fieldobservations.

Groundwater hydrologyThe groundwater hydrology of the quarry, areas to the west andwaste rock dumps has been assessed on several occasions (AGC,1989; EGi, 1995). Hydrology is controlled by the structuralgeology of the area, which consists of competent quartzites andmetasiltstones dipping to the east at 60. There is some fracturingand jointing at a different orientation. EGi (1995) concluded that: the permeability and transmissivity of the sequence is low; groundwater movement is probably controlled by vertical

fractures; bedding planes may also have an influence; storage coefficients are probably low; and the fracture system is heterogeneous and is difficult to map.

This suggests that there is little seepage of contaminatedgroundwater into Dawesley Creek.




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FIG 3 - Calculated annual load of contaminants in Dawesley Creek. Note: chromium, copper and lead were not graphed because a highnumber of samples are recorded as being below the detection limit of the analysis technique. Using this data can result in high calculated

loads that are not real.


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0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

p H

Maximum

Av er age

Wi n t e r

Summer

Minimum

Lower limit ANZECC guideline f or ir r igation pH 4.5

01,0002,0003,0004,0005,0006,0007,0008,0009,000

10,000


C o n c e n t r a t i o n ( m g / l i t r e )

1992ANZECCr ecommendedguidli nef or li vestock1,000mg/l itr e

Maxi mum

Average

Wi n t e r

Summer

Mini mum

0.00

0.05

0.10

0.15

0.20

0.25



1992 ANZECCrecommended guidlinefor livestock0.01 mg/litre

Maximum

Average

Winter

Summer

Minimum

FIG 4 - 2002 results against four year average Dawesley Creek as it leaves the Brukunga Mine site ( a ) pH, ( b ) sulfate and ( c ) cadmium.


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4.0

6.0

8.0

10.0

12.0


p H

Lower limit ANZECC guideline f or ir r igation pH 4.5

Maximum

Av er ageWinter

Summer

Minimum

U pper li mit AN ZECC gui del in e f o r i r r i gati on pH 9 .0

01,0002,0003,0004,0005,0006,0007,0008,0009,000

10,000



1992ANZECCr ecommendedguidli nef or li vestock1,000mg/ li tr e

Maxi mum

Average

Winter

Summer

Mini mum

0.00

0.05

0.10

0.15

0.20

0.25



1992ANZECC recommendedguidline for livestock0.01mg/litre

Maximum

Average

Winter

Summer

Minimum

FIG 5 - 2002 results against four year average Mt Barker water downstream of the Brukunga Mine site ( a ) pH, ( b ) sulfate and ( c ) cadmium.


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Soils and stream sedimentsA program of soil and stream sediment sampling was undertakenalong the Dawesley-Bremer catchment to determine the extentand magnitude of potential heavy metal contamination (Burtt andGum, 2000a and b, 2001). The study was undertaken to answer concern raised by various persons fearing an accumulating slugof metals downstream of the mine. Arsenic, cadmium, copper and zinc were found to be consistently elevated above ANZECC(1992) guidelines and required further study whereas antimony,lead, nickel and tin were occasionally elevated. The majority atthe contamination is confined to the top 20 cm of the soil profile.At the junction of Mt Barker Creek and the Bremer River,contamination was found to a depth of 1 m. At this site, mixingof acid water with alkaline water of Mt Barker Creek precipitatesthe heavy metals. Downstream of this site, heavy metalconcentrations in soils quickly drop to background values.Precipitated heavy metals are deposited in stream sediments and

point bar deposits, which are reworked during flood eventsresulting in sporadic deposition further downstream. The initialstudy identified elevated Cd in soil at Langhorne Creek, whichwas followed by more detailed sampling of soil and vegetation.Soil metal values were found to be below detection or at

background levels, except for some sites in close proximity to theBremer River.

Another small soil sampling program was conducted inresponse to an alarmed local resident on an area located behindresidences in Brukunga and adjacent to Dawesley Creek (Burttand Gum, 2001). The area contains varying amounts of introduced fill, which has been spread and covered withintroduced topsoil and vegetated. Apart from three slightlyelevated arsenic values, no concerns were identified.

Oxidation ratesThe oxidation rates within the waste rock dumps and TSF weredetermined by ANSTO (Bennett, 1994) using temperature and

pore gas oxygen concentration profiles. The results show that thewaste rock dumps are well aerated and oxidation is occurringthroughout the dumps. The calculated sulfate generation rate is400 tonnes per annum for each dump and that this will occur for at least another 300 years. Oxygen measurements in the tailingsindicate that oxidation is occurring in the top 3 m and theoxidation rate is limited by the oxygen supply rate.

ENVIRONMENTAL MANAGEMENTSince closure of the mine in 1972, there have been manymeasures to reduce ARD and improve the quality of water inDawesley Creek and stabilise and rehabilitate the 123 ha of disturbed land. During the 1970s AMDEL conducted extensiveresearch for the SA Department of Mines on seepageremediation which led to the installation of a water treatment

plant, seepage collection sumps and pump back system, coveringand revegetating the tailings and dam wall, minor works on thewaste dumps, installation of a dewatering well in the highwall,spreading of sewage sludge and neutralisation sludge andinfilling of sludge dams.

Water collectionAcid seepage was originally collected at the toe of the TSF andreturned to a 15 ha acid lake at the top of the tailings dam, for evaporation. The lake added to the seepage from the foot of thedam wall and increased contaminant load. Seepage from themine site is collected at the base of the rock dumps, in eightsumps along the west bank of Dawesley Creek and surfacerun-off from the quarry is collected and pumped to the retentiondams. Calculations show that approximately 60 per cent of theseepage from the minesite is collected for treatment in theneutralisation plant, the remainder enters Dawesley Creek. Toimprove interception of acid seepage, the sumps were deepenedin 2001 and probes reset to keep collection points nearer to dry.The tweaking of seepage collection wells is ongoing and isthought to be the main factor in the decreasing contaminationlevels monitored in water leaving the mine site.

Neutralisation plantA neutralisation plant was commissioned in September 1980 totreat the acid seepage and to eliminate the 15 ha acid lake locatedon the tailings. The design capacity of the plant is 20 kL/hour butduring periods of high flow it is operated at 30 kL/hour with aconsequent reduction in efficiency of the thickener tank. Thismeans that more water is pumped to the sludge holding ponds,and more unsettled particles go the clarifying pond. Lime sludgeis obtained as a waste product from the production of industrialacetylene gas. Lime is added at a rate to achieve a pH = 9 in thethickener to ensure precipitation of the majority of dissolvedmetals, particularly cadmium and manganese.



FIG 6 - Dawsley Creek system-mean and standard deviation species richness six sites: 1996 - 2001.


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FIG 7 - Species richness and pH.


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Sludge from the plant is pumped to evaporation ponds at the back (east) end of the TSF. The dried sludge (mainly gypsumwith some iron oxyhydroxides) is then used as cover materialthroughout the site. The number of evaporation ponds has beendecreased over the past four years by backfilling with waste rock from the Northern rock dump. This has led to a reduction in thequantity of acid seepage at the toe of the tailings dam wall.

Treated water is clarified in two ponds and released into

Dawesley Creek at a near neutral pH.

Rehabilitation of the TSFRehabilitation of the TSF commenced with trial plantings byAMDEL in 1976. Waste rock and gravel and untreated sewagesludge were applied directly to the tailings. This was sown withgrasses and 18 different species of native trees and shrubs andtreated with lime and fertiliser, but not watered. Subsequently,the TSF has been completely covered with waste rock, soil,neutralisation sludge and biosolids, and planted with grasses anda variety of native shrubs and trees. This has been done

progressively, involving local school children in the planting of tube stock in June and July. The tube stock is watered for threeyears and applications of septic sludge provides nutrients and the

microbes for soil development. Revegetation has been verysuccessful with trees now well established and some regeneratingfrom seed.

The rehabilitation of the dam wall commenced in 1993 with progressive dozing in 1994 and 1995 to reshape and contour thewall followed by covering with soil and biosolids. Success of theTSF rehabilitation is measured by a reduction in seepage fromthe toe of the dam wall and by an increase in depth-to-water inthe tailings, which is attributed to the establishment of anevapotranspiration cover. Other factors such as the formation of anetwork of hardpans 1200 mm below the tailings surface,reduced lateral flow into the tailings, a reduction in the number of sludge ponds on the surface and potentially a reduced flowfrom the spring have contributed.

Rehabilitation of waste rock dumps

No effective rehabilitation of the two main rock dumps hasoccurred mainly because of the ruggedness and steepness of thesides. Some upper surface compaction has occurred due tovehicular traffic. Vegetation of the dumps was trialled in the1970s by seeding with pinus radiata from a helicopter. Apartfrom scattered pines (which can tolerate low pH environments)the trial was unsuccessful and these two dumps remainessentially bare. Small quantities of sewage sludge depositedover the side, mainly as a convenient location for the disposal of wet sewage sludge in winter, have resulted in grassing of smallareas. It is difficult to assess the effects as the area covered isvery small compared with the extent of the heaps.

The much smaller Eastern Dump (Figure 1) has beencompletely covered with neutralisation sludge, soil and biosolids,self seeded with grasses and planted out with tube stock.Although this revegetation has been successful, there is nomonitoring to assess infiltration rates, oxidation rates andseepage characteristics.

Rehabilitation of quarry faces

Present efforts are directed at rehabilitation of small areas of thequarry site. As all surplus sludge ponds on the TSF have been

backfilled, the neutralisation sludge is now deposited on thequarry bench at the southern end. The sludge has been heaped toform regular shaped bunds, which are topped with soil, mulch,

pea-straw, biosolids and horse manure. The first tube-stock was

planted in June 1999 to retain precipitation, reduce surface

erosion and to improve the aesthetics of the site. The trees haveestablished well in the gypsum sludge and will form a partialscreen for the exposed high foot wall of the quarry.

In May 2001, the old metallurgical plant site was spread withimported soils, horse manure and sown to pasture grasses. InJune 2001, Urrbrae High School students planted out the areawith tube stock. Results to date have been encouraging.

An area on the east side of Dawesley Creek affected byseepage from the retention pond was rehabilitated by installationof a French drain and planting with eucalyptus tube-stock. Arecent application of pea-straw resulted in surrounding grasscover and provided a boost in growth of the trees, which had

been stagnant for several years.

RESEARCH

The Brukunga minesite has been the focus of a variety of research by post-graduate students from local universities andANSTO, CSIRO, AWT, and AWQC. Four major studies wereundertaken to assess the environmental impacts of the mine andrehabilitation measures (McLaughlin and White, 1999; Schultze,2000; Australian Water Technologies, 2000, Burtt and Gum,

2000a and b, 2001) each of which is referred to above. The study by McLaughlin and White (1999) was in response to allegedinfertility in livestock on pasture downstream to the mine.

Because of concerns raised by some local residents for the useof biosolids and neutralisation sludge around the site, AustralianWater Technologies were commissioned by PIRSA to examinetheir impact on the environment. In particular, they wererequested to examine their erodibility, solubility and potential asa source of heavy metals. AWT (2000) found that there isminimal risk of any heavy metals contained in the sedimentsused in rehabilitation contaminating water in Dawesley Creek.Over time the water holding capacity of biosolids may decreaseas organic matter decomposes, which may lead to greater erodibility.

Other research has been related to post-graduate studies or as acontribution to larger studies such as oxidation rates in sulfidicminewastes (Bennett, 1994) or the development of an ecologicalrisk assessment protocol for aquatic ecosystems (Twining, 1999,2000). In addition to the work of ANSTO and CSIRO, there have

been numerous studies of the impact of contamination includingcadmium and zinc in soils (Nardecchia, 1997), aquatic fungi(Wojcik, 1999; Edwards, 2000) algal esterase (Regal et al , 1999),

benthic diatoms (Sincock, 2000) and freshwater shrimp(OBrien, 1999). Studies directed at the remediation of ARD andminesite rehabilitation include the role of sewage sludge inreducing ARD (Girdham, 1994), use of sulfate-reducing bacteriato remediate ARD (Elliott, 1995), the use of a rotating biologicalcontactor to remediate ARD (Wilde, 1995) and the developmentof hardpans/cement in mitigating ARD (Agnew, 1994, 1998).

One student (Haibo, 1994) examined the environmentalmanagement practices at Brukunga and concluded that at thetime, they were unsatisfactory.

PIRSA is presently sponsoring three research projects: thedevelopment of a porous reactive wall to remove contaminatesfrom acid water (Masters, Uni SA), ecotoxicology of the minesite (PhD, Adelaide Uni) and the application of hyperspectralremote sensing to AMD monitoring (PhD CSIRO).

ENVIRONMENTAL IMPROVEMENT PROGRAMAs part of License No 10577 issued by the EPA, PIRSA isrequired under condition 100-20 to submit an EnvironmentalImprovement Program (EIP). PIRSA has just completed arevision of the plan (PIRSA, 2002), which is intended to cover three-year period until 31 December 2004.




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Within the revised EIP are three major new initiatives toimprove the water quality in Dawesley Creek. These are:

1. diversion of Dawesley Creek;

2. additional lime treatment capacity; and

3. relocation of waste rock.

The program is budgeted to cost $26 M over a ten-year period.

Diversion of Dawesley Creek

To achieve significant short-term improvement in water qualityfor downstream water users it was recommended that flow inDawesley Creek be diverted past the mine site by construction of large diameter pipe and open channel conduit. The diversion, at a

budget cost of $2.6 million will enable the mine site, ie thesource of pollution, to be essentially isolated from the creek flow.

The diversion conduit will carry normal creek flow, particularly summer flow, which becomes highly concentrateddue to the low rainfall and high evaporation rates experiencedthrough summer. A proportion of the acid pools that form alongthe original creek bed will be collected and pumped to theretention ponds for lime treatment.

During winter significant dilution occurs due to the increase inrun-off from winter rains, which can reduce contamination levelsto those acceptable for livestock use. Completion of the diversion

project by winter 2003 and continued operation of the existingseepage interception pump-network are expected to result in asignificant improvement in water quality in Dawesley Creek.

Additional lime treatment capacityThe Second Stage major initiative is to tender for design andconstruction of a second lime treatment plant at a budget cost of $2.5 million. This will effectively double the peak treatmentcapacity from 30 KL/h to 60 KL/h, enabling the additionalwinter pollution captured from the mine site to be treated and tomeet high demand at other times of peak flow.

The second plant is to be designed and installed over athree-year period from 2003 to 2005. It is planned to locate the

plant adjoining to the existing plant for logistic reasonsassociated with sludge handling and to consolidate plantsupervision. Operation of a second plant will significantlyincrease operating costs for the site from $650 000 to around$800 000 and hence this is seen mainly as a holding situation for implementation of the third stage initiative.

Before a commitment is made to proceed with the constructionof the second plant a review of monitoring results for DawesleyCreek will be undertaken. Favourable monitoring resultsobserved in winter 2001 indicate that small tweaking of the

pump collection system has reduced pollution levels. Additionalimprovements achieved by the operation of the creek diversion

may be sufficient to reduce pollution to satisfactory holdinglevels for downstream water users.

Relocation of rock dumpsThe Third Stage major initiative is the relocation of theeight-million tonne rock dumps, containing an estimated two per cent sulfur, away from Dawesley Creek and the blending of introduced limestone marl during compaction in the old quarry.The budget cost of the project is $21 million and is planned tooccur over a period of seven years.

It will be necessary to establish that rock relocation can besuccessfully performed and that the proposed technique will havethe desired affect of halting acid seepage. The proposal willrequire re-evaluation before commitment is made to such a high

cost proposal.

Relocation will create separation between dump and creek-lineenabling more effective seepage collection to be implemented.The import of limestone marl is to provide in situ alkalineconditions to neutralise continuing acid reactions. Thecompaction of the dump will enable the surface to be shaped at1:3 slopes and dressed with quarry rubble for planting out withvegetation. A trial dump should be constructed to determine theeffectiveness of this solution prior to full commitment.

On completion of rock relocation the amount of seepage will be reduced to a manageable amount with the majority of acidcollection occurring from the sand-tailings dam. Water neutralisation will be wound back and the planting of vegetationand maintenance of property will become the dominant

preoccupation for care of the 123 ha site.

Community consultationThe township of Brukunga is surrounded on three sides by the123 ha minesite. Its present population is 220, most of whocommute to other centres of population for employment.Agriculture and rural living is the main activity within thecatchment, few rely on Dawesley Creek with water sourced from

property bores and dams and roof catchment for household use.

A technical committee, the Brukunga Taskforce wasestablished in July 1999 in response to heightened publicconcern following a directive issued by the EPA requiringsignposting, issue of notices to landowners and the publication of warnings regarding contaminated water in Dawesley Creek. InMay 1999, the Deputy Premier and Minster for PrimaryIndustries, Natural Resources and Regional Developmentestablished the Brukunga Mine Site Remediation Board(BMSR). This Board superseded the Taskforce and is structuredto ensure strong community involvement and ownership indecisions. Its first objective is to achieve a water quality inDawesley Creek that is suitable for domestic consumption, stock and primary production purposes.

BMSR Board activitiesThe Board has met on a regular basis since February 2000 andinvites the public to attend meetings on a quarterly basis todiscuss and respond to items of interest. It organises letter-dropsto local resident regarding progress with initiatives. Residentswere invited to a walk-through inspection of the site of thediversion project. This was followed by a special meeting todiscuss the preliminary alignment for the creek diversion andhear any concerns.

BMSR Board newsletterThe Board produces a public newsletter Lets Talk and to datehas produced seven issues. The Board maintains a circulation listof landowners, interested persons, political and scientific

organisation for the forwarding of newsletters. Copies are alsoleft at the local store.

Informal liaisonVarious technical and professional visits are made to the siteincluding visitors from South Africa, Japan and PR China. Sitevisits have been included in major conferences in Adelaide:Minerals Council of Australian Environmental Workshop,Australian Geological Convention and International DamConference. The site is used extensively by local universities andsome secondary schools for instructional purposes.

Project Officers from PIRSA Rural Solutions consult with property owners downstream of Brukunga and negotiate on behalf of PIRSA Minerals Resources Group for the installation

of fences along the creek, the aim of which is to exclude




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livestock. Inspection tours of the site have been conducted for small groups of local and interested residents including two localLandcare Groups.

Aboriginal heritageThe mine site lies within the traditional lands of the Peramangk Aboriginal people and Brukunga is an Aboriginal word meaningplace of hidden fire. Brukunga is highlighted in Aboriginalmythology in the story of Tjirbrukes travels and on his death his

body became the hill of iron pyrites (Harris 2002).

COSTSThe cost for operating the plant (neutralisation plant, sumps, sump

pumps) and maintaining the 123 ha Brukunga site for 2001 - 2002was $650 000. This included salaries of two site personnel andengineering support ($150 000), EPA licence ($12 900), water monitoring program ($67 300), power consumption ($25 200),waste lime and flocculant ($77 800), neutralisation sludgerelocation ($85 700) and overall maintenance ($205 300).

CONCLUSIONS

The Brukunga Pyrite Mine operated when little was understoodabout the environmental impacts of AMD. Consequently, mine

planning, operations and decommissioning resulted in a number of environmental issues which contributed to acid generation andcontamination of Dawesley Creek. Over a period of nearly threedecades, State Government departments have undertaken avariety of measures to reduce the impact of AMD on DawesleyCreek, with apparent positive outcomes. Recently, with theassistance of the community, more effective measures have beendeveloped and a diversion channel is under construction.

ACKNOWLEDGEMENTSPrimary Industries and Resources SA provided much of theinformation for this paper and gave permission for its

publication. Peter Grindley has continued to collect and maintaindata about the mine, wastes and Dawesley Creek. His knowledgehas been invaluable to those responsible for the management of the site and the many visitors to it.

REFERENCESAGC, 1989. Brukunga Mine Rehabilitation. Conceptual plan. Report to

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Agnew, M, 1998. The formation of hardpan within tailings as a possibleinhibitor of acid mine drainage, contaminant release and dusting.PhD thesis. The University of Adelaide.

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Armstrong, A and Betheras, F, 1952. Nairne pyrite deposit explanation.SA Dept of Mines report, pp 98-107.

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Burtt, A C and Gum, J C, 2000a. Soil and stream sediment sampling of the Dawesley-Bremer Catchment for potential environmentalcontaminants. PIRSA Report Book 2000/00002.

Burtt, A C and Gum, J C, 2000b. The Dawesley-Bremer Catchment:Phase 2 sampling program for potential environmental contaminants.PIRSA Report Book 2000/00019.

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Elliott, P, 1995. The use of sulfate-reducing bacteria to remediate acidmine drainage. B.Biotech (Hons) thesis. Flinders University of SouthAustralia.

Girdham, J L, 1994. The role of sewage sludge in decreasing acid minedrainage. BSc (Hons) thesis. The University of Adelaide.

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Nardecchia, D, 1997. Investigation of heavy metal contamination andremediation in a rural site. Honours thesis, University of Adelaide.

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Documents

6ICARD_The Brukunga Pyrite Mine a Field Laboratory for Acid Rock Drainage Studies