summary of srrp technical reports

8/19/2019 Summary of SRRP Technical Reports

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Savage River Rehabilitation Project - Strategic Plan - December 2001

SUMMARY OF SRRP TECHNICAL REPORTSto 31 January 2002

This report is intended to provide a summary of the salient points arising from variousstudies and investigations that have relevance to the Savage River Rehabilitation Projectadministered by the Tasmanian Department of Primary Industries, Water andEnvironment.

It is not the Department’s intention to pass comment on the validity of the findings of each of the various reports summarised, though some minor introductory and editorialcomments are included (italicised and bracketed) for information purposes.

Many of the reports summarised herein can be viewed at the Environment Library, 5 th

Floor, 134 Macquarie St, Hobart. Documents that are unavailable in the library areavailable on departmental files, file reference nos. are provided, where applicable, in the project headings.

The location of various mine features and SRRP water monitoring sites is shown on the

map appended to this report.


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TABLE OF CONTENTS

SAVAGE R IVER MINE:.................................................................................................................................3

1995 Biological Survey .........................................................................................................................3

Report on OTD seeps ............................................................................................................................ 3

Survey of clay sources at the Savage River Mine .................................................................................. 4 Biological assessment of Main Creek and lower Savage River.............................................................5

Installation of flow gauging stations and water quality monitoring equipment on streams in the

vicinity of the Savage River Mine ..........................................................................................................6

Rehabilitation of disused tracks and other disturbances in the vicinity of the Savage River Township 6

Rehabilitation of historical disturbances associated with the Savage River Mine................................6

1999 SRRP Water Quality Review......................................................................................................... 7

Toxicity assessment of heavy metals in Savage River waters..............................................................10

Review of literature pertaining to engineered soil covers for the control of acid drainage arising from

mine wastes ......................................................................................................................................... 14

Monitoring and reporting of the effectiveness of the proposed soil cover for Hairpin Dump at the

Savage River Mine............................................................................................................................... 14

Design of an oxygen limiting clay cover for Hairpin Dump at the Savage River Mine ......................20

Magnesite lined drain adjacent to North Dump.................................................................................. 23 Hydrogeological study and evaluation of acid drainage remediation options....................................23

Desktop review of options for treatment of acidic discharges in Main Creek below B Dump............ 30

Provision of expert geochemical advice to the SRRP File: 071942................................................. 32

Develop engineering specifications for a water shedding cover on the upper levels of B Dump and

verify on-ground compliance during construction ..............................................................................34

Management of weeds on historical sections of the Savage River Mine site and adjacent to the lease

area in the former township ................................................................................................................ 35

Biological assessment of Main Creek and lower Savage River........................................................... 35

Evaluate use of Bauxsol at Savage River - dosing systems, mixing with magnesite, etc .....................35

Listing of dates of mining activity during PMI's operations ............................................................... 36

Trial desulphurisation of ABM tailings using falcon separator in Canada ........................................ 36

South Centre Pit groundwater study (draft) ........................................................................................ 36

Laboratory toxicant series using upper Savage River waters............................................................. 37

Prepare dam surveillance reports for OTD north and south and South Centre Pit............................ 38

The capping conundrum......................................................................................................................38

Water Quality on the ABM Lease and in the Savage River - A Review for the SRRP ......................... 38

Magazine Dump final report (draft).................................................................................................... 40

Feasibility study of the capture, diversion and treatment of acid discharges from North Dump........ 41

PORT LATTA PELLETISING FACILITY: ....................................................................................................... 44

Investigation of possible soil contamination adjacent to the Port Latta pelletising plant File: .........44

Rehabilitation of historical disturbances associated with the Port Latta Pelletising Facility ............ 45

Port Latta Dust Remediation............................................................................................................... 45

Removal, bio-remediation and disposal of historically hydrocarbon contaminated soils from the Port

Latta Pelletising Plant......................................................................................................................... 48

BIBLIOGRAPHY .........................................................................................................................................48


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Savage River Mine:

1995 Biological Survey

[Invertebrate sampling was undertaken during autumn of 1995 to support the

preparation of an Environmental Management Plan for the Savage River Mine by thethen operator of the mine, Pickands Mather & Co. International.]

Davies (1995) found that riffle abundance and diversity results at the upstream controlSavage River sites were not significantly different from the reference sites on adjacentstreams. By contrast both abundance and diversity of macroinvertebrates in rifflesdownstream of the Savage River Mine were significantly lower than for the upstreamcontrol sites. The severity of decline increased downstream with a slight recovery at thefarthest downstream site.

The picture was less clear for edge habitats because edge habitats at the downstream sitesshowed higher abundance and diversity than the riffle habitats, (which is the reverse of the trend at the upstream control sites). The farthest downstream site had the mostdegraded edge habitat. Possible reasons for the resilience of the downstream edge habitatswere suggested in the report.

Significant environmental impacts were observed throughout the river reach betweenBroderick Creek and some 30km downstream, “little recovery is occurring downstreamfrom the ameliorative action of inflowing tributaries”.

The overall conclusion of the report was “that severe degradation of water and/or habitatquality has occurred and/or is continuing to occur in the river”. “The degree of impact issufficiently severe to eliminate up to 90% of the major taxa of aquatic macroinvertebratesand to decrease overall abundance by up to 99% in the reach downstream of theconfluence with Main Creek.”

Report on OTD seeps

Thompson & Brett (1996) determined that OTD seepage flow rates varied between 1.25L/sec to 2.5 L/sec in the western collection drain, and from 0.42 L/sec to 0.83 L/sec in theeastern seepage collection drain.

Acidity loads were found to be relatively constant at 0.6 kg/min CaCO3 from the west

side and 0.15 kg/min CaCO3 from the east side.

Flow measurement weirs were installed on the outflows of both the eastern and western ponds into which the seepage collection drains discharge. From these weirs it was possible to determine the total flux of water and acidity from the OTD to the MCTD.

After subtraction of inputs from rainfall runoff from the surrounding catchment, it wasestimated that, in order to account for the observed total acidity flux, about 0.38 L/sec of


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acidic water must bypass the western seepage collection drain and enter the western pond. A further 2.1 L/sec must bypass the eastern collection drain and enter the eastern pond.

The total flow contribution from the OTD to the MCTD was estimated to be 6.5 L/sec, of

which 38% bypasses the collection drains. Total acidity load emitted from the OTD to theMCTD averages .027 kg/sec at a concentration of about 4000 mg/L.

Piezometers installed at various points along the OTD beach indicated the presence of agroundwater divide across the dam.

In situ permeability tests on the tailings beach gave results ranging from 10 -6 m/sec closeto the dam crest, falling to 10-7 m/sec further north, due the much finer tailings particlesize (slimes) further from the tailings discharge point.

A computer model was then constructed to fit the measured phreatic surface in the OTD.

Infiltration greater than 100m north of the dam crest modelled to effectively zero, while100% of incident rainfall on the southern dam embankment (which was constructed fromcoarse tailings) would be expected to infiltrate into the tailings.

Survey of clay sources at the Savage River Mine

File: 061611

This report (Thompson & Brett, 1998) describes potential sources of clay for remediationand revegetation purposes within and adjacent to the Savage River Mine.

Some 26 test pits were excavated into various prospective sources of clay. Weathering

depths were also assessed on the exposed walls of the mine pits to enable a determinationof clay volumes likely to arise under the mine plan.

Various engineering parameters of the sampled soils were reported. Soils were predominantly silts with laboratory permeability results ranging from 1.2 x 10-7 m/s to 3.2x 10-10 m/s.

The report suggested that over the life of the mine clay arisings would more-or-less balance with mine clay requirements (with excess in the early to middle years and adeficit toward the end of mine life). The report commented favourably on the logisticsand economics of extracting clay from ‘borrow’ pits in proximity to remediation sites.

Substantial reserves of good quality ‘clay’ adjacent to likely remediation sites weremapped to the south and west of B Dump, to the north of North West Dump and to thewest of North Dump.


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Biological assessment of Main Creek and lower Savage River

File: 060336

[Biological sampling undertaken in late 1997 and early 1998 coincided with the

recommencement of mining operations at Savage River after approximately 12 months of

inactivity. It may be of note that sediment levels arising from the mine would have beenrelatively low during the 12 months preceding the sampling.]

Invertebrates

Davies & Cook (1998) found that the abundance and number of taxa of macroinvertebrates in riffles at upstream control Savage River sites were not significantlydifferent from reference sites on other nearby streams. By contrast abundance andnumber of taxa of macroinvertebrates in riffles were significantly lower for sitesdownstream of the mine than for upstream control sites.

Main Creek, which was sampled for the first time in 1997/98, was found to be extremely

low in both abundance and diversity downstream of the Main Creek Tailings Dam.

Comparing the 1995 and 1998 edge and riffle data showed a decline in the reference sitesand mine precinct sites [possibly due to a general environmental change such as lowrainfall]. However, the riffle habitats at the farthest downstream sites showed evidence of recovery when compared to 1995 (i.e. a 3 fold increase in diversity). It was suggested thatthis recovery requires further confirmation.

The reach downstream of the confluence with Main Creek was the most degraded sectionof the Savage River during both 1995 and 1997/98.

Live pick macroinvertebrate data were entered into the AUSRIVAS bioassessmentmodels for northern Tasmania (a West Coast model was not available). AUSRIVASoutputs confirmed the extremely poor biological state of Main Creek, as well as the partial recovery in the condition of the lower Savage River sites.

The authors point out various difficulties surrounding the interpretation of AUSRIVASoutputs in relation to acid mine drainage and West Coast regional particularities. Nonetheless the AUSRIVAS outputs suggested that habitat degradation (e.g.sedimentation) may be substantially responsible for the observed aquatic impacts, withwater quality playing a less important role than at other acid drainage impacted sites.

The report recommended development of a West Coast AUSRIVAS model, as well asfurther study of the sediments in the lower Savage River (i.e. their origin and impacts).Use of field deployed stream mesocosms to compare habitat versus water quality effectswas also suggested.

Fish

Resident native and exotic fish were observed in the upper and lower Savage River,although fish fauna in the middle Savage River was severely depauperate, extremely low


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in abundance and probably non-resident. Presence of migratory fish species in the upper Savage implied that fish are able to pass through the mine precinct on occasion.

Similar diversity was observed in the lower Savage River and the lower Whyte River,with a number of native species and life stages present. Abundance in the lower Savage

was slightly less than in the lower Whyte (marginally statistically significant).

Installation of flow gauging stations and water quality monitoring

equipment on streams in the vicinity of the Savage River Mine

File: 061595(2)

Hydro-Electric Corporation (2000) prepared a summary of flow and water quality datafor the period December 1997 to January 2000.

The report describes the 12 SRRP monitoring stations and presents graphical and tabular summaries of the continuously recorded data. Time series graphs of water level, flow,

pH, conductivity and rainfall data are provided. Duration curves and flow percentilestatistics are also included.

Rehabilitation of disused tracks and other disturbances in the vicinity of

the Savage River Township

and

Rehabilitation of historical disturbances associated with the Savage

River Mine

File: 062569

A rehabilitation plan relating to the Savage River township (including former house lots,streets, and gravel pits) and various tracks and other disturbances in the vicinity of thetownship was prepared by Land Management and Rehabilitation Services Pty Ltd (1998).

The report includes an assessment of the rehabilitation potential of the project area.Generally, rehabilitation potential was classed as very low to moderate (lowest inquartzite areas). The former singlemen’s quarters was found to be impacted by aciddrainage and was considered to have an extremely low rehabilitation potential.Rehabilitation potential of disused tracks in moorland areas was generally consideredhigh due to the availability of stockpiled peat soil beside the tracks.

Measurable performance indicators were proposed for each rehabilitation potentialcategory. For example:

Targets for high rehabilitation potential areas: No stability problems, silt captured in drains2 plants per m2

At least 10 species presentGood coverage and generally healthy appearance


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Targets for very low rehabilitation potential areas:Possible silt movement in drains, captured in stable vegetated areas or structures1 plant per 3m

2

60% seedling survivalAt least 3 species presentLow coverage and showing signs of stress

An implementation plan detailing proposed drainage works, soil replacement works, seedapplication rates, fertiliser application rates and other revegetation treatments for eacharea is included in the document.

A final report on projects 010 and 011 was submitted in July 2001 (Land Management &Rehabilitation Services, 2001). The report summarises the treatments applied to each areaand provides a table of performance indicator measurements two years after the initial

treatment.

Overall the sites exhibited excellent stability. Survival of planted seedlings was in excessof 90%. Diversity exceeded targets in all areas. Average plant density was somewhatvariable, but on average exceeded the specified targets.

Maintenance treatments requested by DPIWE, including follow up fertiliser applicationto approximately 15,000 m

2 of slow growing areas, gorse control at gravel pit 1 andimprovement of drainage grips on the Whyte River access road were noted as beingcompleted by the time the final report was prepared.

During the course of the project some significant impediments to revegetation have beenidentified. Former building sites rehabilitated by PMI were found to have been coveredwith acid generating material. In many cases this toxic material was underlain at shallowdepth by concrete foundations which had not been correctly removed. Furthermore thetownship area has been colonised by numerous weed species and garden escapes. Theexotic grass Holcus lanatus was identified as a potential hindrance to successful re-establishment of native species in some sections of the township, due to its competitiveabilities.

The report includes a selection of ‘before’ and ‘after’ colour photographs of therehabilitated areas.

1999 SRRP Water Quality Review

This report (Koehnken & Ray, 1999) focused primarily on data for the calendar year 1998, which was a year of close to average rainfall in each month.

The report categorised the various monitoring sites as either ‘receiving’ sites or ‘source’sites for both Main Creek and the Savage River.


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Median conductivity readings ranged from 60 µS/cm in the upper river to 100-400 µS/cm

in the Savage River receiving group and 600 µS/cm in Main Creek. The source groups

were typically > 1000 µS/cm. Sulphate derived from acid drainage was considered to bethe major contributor to conductivity. Sulphate was also found to be naturally elevated

upstream of the mine.

Generally pH in the Savage River varied between 6.2 and 7.5, which is somewhat higher than for most streams in the Pieman catchment, probably due to the presence of carbonaterock strata in the Savage River catchment.

The two available upstream water samples indicated that background metal levels arelow, with the exception of iron and aluminium.

Among the receiving sites, Main Creek generally exhibited higher metal concentrationsthan the Savage River, except in the case of iron, which is thought to be influenced by the

settling out of iron rich sediments in the MCTD.

Among the source sites, metal concentrations were highest in the OTD seeps and NDD,with total and dissolved results being similar for these two sources. As may be expected,higher pH sources had a lower ratio of dissolved to total concentration for most metalspecies.

Analytical results for total copper and aluminium were found to consistently exceedANZECC (1992) guidelines at all sites except the MCTD, frequently by an order of magnitude. Nickel, and possibly zinc, may also exceed the ANZECC guidelines,depending upon the effect of hardness.

A consideration of the draft ANZECC (1999) trigger values suggested that ironmanganese and cobalt effects are also worthy of further investigation. The increase inionic strength of waters downstream of the mine also needs to be considered as a potential downstream impact.

High pollutant fluxes were found to be associated with high flows. Under median to highflow conditions, MCaSR was found to contribute about 40% of the copper flux exitingthe lease, with the remaining 60% exiting the lease on the Savage River side.

Table 1: Estimate of relative Mine Lease flux contribution by SRbSWRD and MCaSR

Parameter SRbSWRD (%) MCaSR (%)

Total Copper 61 39

Total Aluminium 64 36

Total Nickel 66 34

Total Iron 85 15

Total Manganese 64 36

Sulphate 71 29


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The overall flux balances between SRaDC, MCaSR and SRbSWRD were found to berelatively good considering the potential sources of error. The mine site and upstreamcatchment contributes the vast majority of metals, sediment and sulphate present atSRaDC, despite a doubling of water flux below the mine.

The OTD seeps were the single largest sources of acidity on the site, it was estimated thatthe MCTD neutralises an OTD acidity flux of 850 kg/day. Contaminant loads added tothe MCTD by the OTD seeps were found to be substantially retained within the alkalinetailings pond, with the exception of manganese and sulphate (the seeps accounted for only

1/3 of the sulphate flux exiting the MCTD). Therefore, acid drainage may be entering

the MCTD by other pathways.

Acidity concentrations in Main Creek underwent a 10 fold increase between MCTD andMCaSR, as a result of pollutant emissions in the hydrologically complex A Dump/BDump/MCTD dam wall area. Alkalinity was seen to rise again in the lower river

indicating that most of the acidity in Main Creek had been neutralised at that point, thiswould be consistent with the presence of carbonates downstream of the mine.

The report cited the risk of increased discharge of pollutants if the MCTD pH is notmaintained at or near neutral.

Relatively good surface water balances in the mine area negated the possibility of another major source of water in this area of the catchment. The key sources CPOF, BCbWRDand SRaPS were found to contribute about 75% of the measured pollutant fluxes atSRbWRD during summer and 55-70% during winter. Therefore some 25-45% is‘missing’, or as yet unquantified. Further monitoring of Brett’s drain was recommended.

Upstream of SRaPS, NDD and OTDN were found to be the largest contributors of pollutants. NDD was estimated to contribute 90% of the dissolved Copper at SRaPS withOTDN providing the remainder, however, for other parameters it was clear thatunidentified source(s) accounted for about 1/3 of the SRaPS flux.

A one off analysis of previously unmonitored seeps emanating from Horseshoe Dumpand North Dump estimated that together they would account for about half of theunidentified upstream source. The unidentified upstream component also includes thenatural inputs from upstream of the mine site, which is considered particularly significantin the case of iron and aluminium.

Broderick Creek was found to contribute 30% of the whole of site sulphate flux. Figure93 (reproduced below) compares the amount of acid drainage generated at each sourcesite (% sulphate) to the impact of that drainage (% combined metals released). The twomain groupings on the figure are referred to as neutralised acid drainage (CPOF, MCTD,BCbWRD) and unneutralised acid drainage (all other sites). Hypothetically it wasestimated that Broderick Creek would contribute an additional 55% of the current wholeof site pollutant loads if neutralisation by carbonate material in the Broderick Creek


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valley were to cease.

Toxicity assessment of heavy metals in Savage River waters

A suite of tests were performed by Davies et al (2001) to assess the likely toxicity of Savage River water under existing acid drainage conditions, following neutralisation of all acid drainage to pH 6.5, and following neutralisation of differing proportions of theacid drainage to pH 6.5.

Raw acid drainage was obtained from North Dump Drain. West Queen River water wasanalysed and found to be a reasonable surrogate for the waters of Savage River upstream

of the mine, provided that its alkalinity was adjusted to upper Savage River levels.Dilution ratios for the tests were selected based on flow data collected downstream of themine site. Each test included an unpolluted control. Reference toxicant series were alsoconducted using copper sulphate.

Test species included exotic and native fish, mayfly nymphs and algae.

Raw North Dump Drain acid drainage was found to cause high levels of fish mortality atdilutions ranging from 5.5:1 to 70:1 (these conditions are present in the Savage River greater than 50% of the time), however, resident fish have been found in the lower Savage River indicating that toxicity is being ameliorated by another factor.

No mortality occured over the same dilution range as in the above test when the aciddrainage was first neutralised to pH 6.5, though some minor toxicological impacts werestill present.

In a series of tests conducted at varying levels of alkalinity, greater than 11 mg/l of alkalinity coincided with substantially reduced toxicity to fish. Algae were significantlyimpacted only when both alkalinity and pH were low (3 and 5.2 respectively).


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Various ratios of untreated to treated acid drainage ranging from 100:0 to 25:75 (all at the50:1 dilution) showed negligible toxicological impacts. The principal reason for themassively reduced toxicity of the 100:0 ratio when compared to its equivalent in the firsttest was thought to be the increased pH in the partial neutralisation series (5.35 in test 1

compared to 6.35 in test 3).

Neutralisation using magnesite followed by limestone was compared with neutralisationusing limestone slurry alone. The authors concluded that there was no significantdifference between the two.

Fish avoidance trials were conducted in order to ascertain the potential for acid drainageeffected waters to form a barrier to fish migration. Raw acid drainage was avoided bytrout at dilutions < 5.7:1 (i.e. occurs less than 1 day in two years). Galaxias truttaceusshowed no substantial avoidance of acid drainage whether raw or partially treated, hencewhitebait runs are unlikely to be repelled by Savage River water quality.

A sample of actual lower Savage River water collected in August 2000 was found tocause a sub-lethal toxic response in algae (growth rate reduced to 47% of controls),however, the same batch of water did not produce measurable lethal or sublethal toxicityin fish or invertebrates.

Overall, alkalinity was found to be a significant factor controlling the toxicity of metalswithin the Savage River catchment. Significant reductions in environmental risk werefound to occur where the following conditions are met:

pH > 6Calcium > 15 mg/lMagnesium > 15 mg/lAlkalinity > 15 mg/l

Recent toxicological test work conducted at Mt Lyell was cited as the basis for the settingupper limits for individual pollutants as follows:

Copper < 35 µg/lAluminium < 350 µg/lSulphate < 100 mg/l

A discussion of Broderick Creek alkalinity was provided as an Appendix to this report.The available data suggested that there has been an increase in alkalinity concentrationsin Broderick Creek during ABM’s operations. The ABM flow-through appears tocontribute a large proportion of the total alkalinity exiting Broderick Creek.

Broderick Creek was found to contribute 25%, on average, of the alkalinity present in thelower Savage River, however, the Broderick Creek alkalinity contribution was found to be much more significant at times when alkalinity in the lower Savage River is low (i.e.at times when additional alkalinity may be of benefit).


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Broderick Creek water itself was found to induce a chronic non-lethal toxicologicalimpact on the growth of algae during a laboratory trial.

Multivariate analysis of data

[DPIWE scrutinised the available water quality data for the SRaDC and SRbWRDmonitoring sites and found that the combined targets established by Davies et al (2001)were achieved approximately 1-2% of the time. This was considered inconsistent with the

observed biological health of the middle and lower Savage River. The Contractor,

Freshwater Systems Pty Ltd, was requested to undertake further analysis of the data toascertain whether relationships between certain parameters would allow some targets to

be relaxed under defined conditions.]

Multivariate analysis of the previous results (excluding the algal data) was undertaken byDavies (2001) in order to derive thresholds that are interdependent. This reportacknowledged that the thresholds derived by Davies et al (2001) were too stringent.

Principal components analysis (“PCA”) was conducted to derive new variables (factors)that explain the observed data. These factors were then related back to the originalvariables.

PCA Factor 1 was found to clearly separate toxic and non-toxic conditions, with only twoexceptions. Upon investigation the exceptions were found to be a high sulphate case anda high aluminium case.

Factor 1 was very strongly correlated with pH, total Calcium, and dissolved Copper, eachof which is known to be important in describing toxic conditions in the Savage River.

Regression tree analysis provided essentially the same results, thereby backing up thesefindings.

The relationships between Calcium and dissolved Copper were examined in more detail,after excluding the two above-mentioned exceptions. The boundary between toxic andnon-toxic conditions (i.e. the NOEC line, see figure 3 reproduced below) could then bedefined by a mathematical relationship between total calcium and dissolved copper concentrations.


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0 10 20 30 40 50

20

40

60

80

100

120

140160

180

200

CuD

CaTDissolved copper (CuD) vs calcium (CaT) from toxicity tests, indicating nontoxic (O) and

toxic conditions (X). The line indicates the proposed toxicity threshold.

The change in copper toxicity threshold with increasing calcium is consistent withrelevant literature. SRRP environmental copper targets can therefore be relaxed wherecalcium (or hardness) is high.

As a result of the two above-mentioned exceptions, targets for dissolved aluminium and

sulphate of 610 µg/l and 450 mg/l respectively, are prescribed.

It was recommended that the revised environmental targets be applied irrespective of discharge or pH and that the focus for managing toxicity should be on hardness (and theCa:Mg ratio) rather than on alkalinity.

[DPIWE has since ascertained that the revised targets are currently achieved

approximately 78% of the time in the Savage River downstream of the mine]


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Review of literature pertaining to engineered soil covers for the control

of acid drainage arising from mine wastes

A review of literature pertaining to the effectiveness of covering dumps to reduce thegeneration and release of pollutants was undertaken jointly by DPIWE and ABM (Ray &

Ferguson, 2000 ).

Saturated covers are intended to hold water and thus reduce oxygen ingress to the rate atwhich it can diffuse through water. High rainfall and ready availability of clay would beexpected to facilitate the construction and operation of saturated covers at Savage River,however, very steep slopes and relatively low average oxidation rates may work againstthem.

Laboratory analysis and implied sulphate fluxes from dumps at Savage River suggest thataverage oxidation rates are generally in the moderate to low range. The report suggestedthat reducing a high oxidation rate dump to a low oxidation rate dump would be more

practically achievable than reducing a low oxidation rate dump to lower, because a verysmall amount of oxygen can maintain a low oxidation rate.

The report raised questions about the extent to which stored ferric iron compounds indumps could drive oxidation of pyrite and maintain low pH conditions even in theabsence of oxygen.

Covers comprised of other materials including; water, desulphurised tailings, organicmatter and alkaline substances were discussed briefly. Further investigation of desulphurised tailings covers and alkaline covers was recommended.

Applicability of saturated covers to Savage River was discussed. Water covers wererecommended where suitable redundant mine pits are available. Actual performance andeconomics of saturated soil covers on very steep slopes was queried. The potential for cover damage in the long term as a result of root penetration was also mentioned.

Monitoring and reporting of the effectiveness of the proposed soil cover

for Hairpin Dump at the Savage River Mine

Preconstruction Report

Thompson & Brett (2000a) point out that Hairpin Dump received waste rock from theeastern and western walls of North Pit between 1993 and 1994, making it a relatively

young dump. The western edge of Hairpin Dump sits above approximately 60m depth of waste rock that was dumped during earlier operations and is contiguous with the entireBroderick Dump complex.

Thompson & Brett ascertained from historical records that Hairpin Dump was built uponan earlier haul road, including the bend from which the name of the dump derives. It wasconsidered likely that the haul road would collect internal drainage within the dump anddirect it towards the south western corner of the dump, whereas pre-mine contours would


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have drained to the west. Excavations at the south western corner encountered seepagealong the former haul road and a sample was collected. Installation of a collection pit andmonitoring weir at this point was recommended.

Four temperature and oxygen probe holes were drilled 20 – 51m into Hairpin Dump

using reverse circulation percussion drilling. A fifth hole was drilled 55m into the pre-Hairpin Dump waste rock immediately west of Hairpin Dump. It was hoped that this holewould intercept water in a pre-mine gully, however, free water was not encountered.

Geological logging of the drill chips was recorded and composite samples were collectedfor analysis. The drill hole logging indicated that Hairpin Dump is comprised predominantly of serpentinised chloritic ultramafic and mafic rocks with abundantmagnetite.

The dump contents are described as large lumps of hard competent rock in a ductilematrix of clay and fine rock fragments. Chemically the system was said to be swamped

with iron, and alkali-generating carbonates were found to be at least as abundant assulphides.

Collection of free water from the base of the dump was not possible, therefore, a widerange assays were performed on a water extract from each drill chip sample (compositesample of each mineralogically similar section in the boreholes) to estimate thecomposition of pore water in the dump.

An attempt was made to develop a weak acid leach procedure to determine the amount of iron oxy-hydroxides in the dump, on the assumption that this would give a goodindication of the amount of oxidation that had taken place.

The authors acknowledge that the methods employed did dissolve a substantial amount of material not present in the dump pore water (confirmed by the high saturation indicescalculated for iron, aluminium and calcium).

The overall particle size distribution within the dump was estimated from two test pits.On average 50% of the dump material was found to be between 25mm and 1mm indiameter, and about 14% of the material was less than 1mm in size.

Bulk density, pore size distribution, specific heat, and specific gravity were alsodetermined. Thermal conductivity was considered a very important property for thermalmodelling of dump behaviour, however, various difficulties were encountered indetermining the parameters required to calculate it, hence an estimate from relevantliterature was used.

Analysis of the single water sample that may represent Hairpin Dump outlfows along theformer Haul Road, together with an estimate of average annual flow through the dump,suggested that current rates of contaminant release could continue for 1,000 yearsregardless of the oxidation rate of the dump. It was not considered appropriate to


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determine an oxidation rate from the estimated sulphate flux since 13% of the sulphur inthe dump is present in sulphate form.

Dump temperature was considered the best guide to the level of immediately past and present oxidation activity in the dump. The average oxidation rate of Hairpin Dump

waste rock to a depth of 20 metres was estimated from thermal modelling (ANSTO onedimensional model) to be 8.1 x 10-8 kg (O2) m-3 s-1. If this rate were to continue, the

remaining sulphide would be exhausted in about 20 years, however, it was noted that in practice the oxidation rate would be expected to decline over time.

Oxidation rates were found to be substantially higher in the uppermost 4 metres of each probe hole, despite the presence of ample oxygen and sulphides at lower depths. Theauthors were unable to present a conclusive rationale for this observation.

In many cases it was not possible to estimate oxidation rates from the rate of decline inoxygen levels immediately after completion of drilling because there was no measurable

decline. Oxygen appears to be freely available within much of the dump interior.

The report suggested that the evidence in respect of Hairpin Dump points strongly toadvective air movement (i.e. driven by wind and/or heat) as the primary means of oxygentransport in the dump. It was suggested that a cover that did no more than limit the meansof oxygen ingress to diffusion would reduce the oxidation rate substantially.

The time to completion of oxidation of all sulphide in the dump was estimated bycomparing sulphide content in oxidised and poorly oxidised sections of the dump ( i.e. >20 m from any dump surface). The data indicated that 4.6% of the sulphide content has been consumed per year since dump construction. At that rate oxidation would becomplete in 22 years.

Even if oxidation were to cease now it was estimated that it would take far greater than30 years to flush out the contaminants in the dump.

Estimation of the oxidation rate from sulphate plus sulphides currently in the upper 20metres of the dump suggested that oxidation would be complete in about 40 years. Thismethod is likely to underestimate the oxidation rate as some sulphate will have alreadyexited the dump.

Water extracts from within the dump and the single sample of dump outflow showedapproximately neutral pH. Metal contamination was present, but was minor compared tosome other sources at the mine site.

The theoretical Net Acid Producing Potential across the upper 20 metres of HairpinDump was calculated to be –14 kg H2SO4/t (i.e. net acid consuming). The realneutralising capacity may be even higher than assumed in the NAPP calculation as the NAG tests suggested that not all of sulphide present is reactive. It was thereforeconsidered likely that the dump effluent will become more alkaline with time.


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Five surface infilitration trials and three pit permeability trials were conducted on thedump surface. Surface permeability was estimated to vary from 1.3 x 10-7 m/s to 1.2 x 10-5 m/s depending on particle size of material. These values concur with site observationsof local runoff during moderately intense showers and penetration into coarser zones.

Sub-surface infiltration surveys were undertaken by excavating three test pits, filling withwater and recording the time taken for the water to infiltrate. Permeabilities wereestimated at 1.3 x 10-3 m/s (similar to medium sand)

Surface infiltration rates are much lower than sub-surface permeabilities, probably because of compaction of the dump surface during its use an equipment storage site,hence it is unlikely that significant areas of the dump would be able to reach saturation.

Four different types of cover were modelled using the SoilCover model for wet, averageand dry years. The time delay between inflow and outflow is predicted to be 6 months on

average.

A poor quality clay cap (porosity = 0.38, permeability = 10 -6 m/s) was predicted to causea slight increase in leachate volume (due to reduced evaporation) though the degree of saturation of the cover itself remained above 85% throughout the year. A good qualityclay (porosity = 0.35, permeability = 10-8 m/s) cap was estimated to reduce infiltration byaround 90% and the cover would be expected to remain close to saturation year round.

A target minimum permeability for the cover of 10-8 m/sec was recommended.

Overall the report found that while retardation of the oxidation rate of the dump may be possible via construction of a clay cover, in the case of Hairpin Dump this is not likely toresult in major environmental benefits. The results do suggest that regardless of oxidationrates, the potential for a major reduction in water flux does exist, with consequent potential for improvements in the economics of treatment of acid drainage.

The proposed Hairpin Dump clay capping trial provides an opportunity to confirm this behaviour through the installation of lysimeters and a leachate collection site. Assessmentof the oxygen limiting effects of the cover was also recommended on the basis of itsrelevance to other dumps at Savage River.

Peer Review

[Given the innovative nature of the methods employed during Thompson & Brett’sassessment of Hairpin Dump it was decided to subject the report to peer review]

Bennett et al (2001) strongly questioned Thompson & Brett’s recommendation to proceed with the capping of Hairpin Dump. The reviewers were of the opinion that pollutant generation rates from the dump had not been sufficiently quantified.

The reviewers noted that Thompson & Brett failed to determine a global oxidation rate


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for Hairpin Dump as required by the project brief.

The reviewers proceeded to estimate an internal oxidation rate of the dump material of 9.3 x 10-9 kg (O2) m

-3 s-1 based on the sulphate release rate that had been estimated byThompson & Brett (2000a).

The reviewers commented that Thompson & Brett erroneously attempted to correct for seasonal variation in temperature readings in the uppermost 10m of the dump. Bennett et al are of the view that at least 12 months of temperature data would be required toconfidently estimate oxidation rates from temperature data alone.

The reviewers provided a table of those estimates of internal oxidation rate from theThompson & Brett report which were considered reliable. The reviewers found noconvincing evidence to support Thompson & Brett’s suggestion that oxidation rates areconsistently higher in the uppermost 4-6m of the dump.

Bennett et al independently estimated the average oxidation rate of Hairpin Dump to be 1x 10-8 kg (O2) m-3 s-1, which is almost one order of magnitude lower than Thompson &

Brett’s estimate, but is very close to the result based on estimated sulphate flux.

The reviewer’s rejected Thompson & Brett’s ‘shrinking core’ model of Hairpin Dump onthe basis that hole BH4 appears to show oxygen diffusing into a ‘pod’ from both aboveand below.

The reviewers stated that any conclusions based on the one-dimensional model must bere-examined, as gas transport in Hairpin Dump can only be described using a two or three-dimensional model.

The reviewers challenged Thompson & Brett’s suggestion that advection is the predominant means of oxygen supply into Hairpin Dump, as they felt that diffusion alonewould be capable of explaining the observed field data.

The reviewers also queried the results of modelling using the SoilCover software program because the predicted degrees of saturation appear to be much higher than thefield measurements.

In conclusion the reviewers stated that the Thompson & Brett report does not present amodel of Hairpin Dump that can be used to quantify processes in the dump, to predictfuture behaviour of the dump or to quantify the effectiveness of a cover on present or future pollutant release rates

[Dr Stephen K Dobos was requested by DPIWE to peer review the geochemical aspectsof the Thompson & Brett report.]

Dobos (2001a) considered Thompson & Brett’s drilling, sampling and associatedgeochemical work to be of a generally high standard, though specific deficiencies were


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noted. Mineral paragenesis of the samples from the drilling is said to be ‘barely adequate’and rock texture or microstructure was not assessed. The nature and thicknesses of ‘rinds’of oxidation as functions of grainsize, rock type and position within the dump alsoreceived inadequate attention.

Dobos made the general observation that there are various potential sources of uncertainty involved in the interpretation of temperature and oxygen data from probeholes, and therefore commented favourably that Thompson & Brett’s conclusions werenot based solely on these measurements.

Dobos (2001a) points out that while Thompson & Brett identified that the Net AcidProducing Potential of the upper 20m of Hairpin Dump is on average –14kgH2SO4/tonne, the deeper sections of the dump, with an average NAPP of +29.7kgH2SO4/tonne are in fact likely to be acid forming. Dobos therefore questionsThompson & Brett’s assertion that alkalinity in the dump outflow will slowly increasewith time. The dump is ultimately likely be a net acid producer.

Thompson & Brett’s use of leachable iron as an indicator of degree of oxidation isquestioned on the basis that several minerals present at Savage River are likely to containleachable ferric iron, some minerals may even contain iron oxyhydroxides which do notresult from oxidation of pyrite. Furthermore Thompson & Brett did not adequately takeaccount of the net downward migration of oxidation products over the life of the dump.

The results of leaching with de-ionised water are also questioned since they representneither pure pore water nor pore waters plus all secondary reaction products. Chemicalmethods for estimation of oxidation rate are therefore said to be approximate at best, butare certainly considered worthy of further refinement.

Response to Peer Review

Thompson & Brett acknowledged the error in the estimation of oxidation rate via thermalmodelling, and consequently recalculated the average oxidation rate of the upper 20m of Hairpin Dump to be 5 x 10

-8 kg (O2) m

-3 s

-1. [This result lies approximately halfway

between Thompson & Brett’s initial estimate and that of Bennett et al] . This figure wasthen converted to a sulphide consumption rate for comparison with the chemical methodsused to estimate oxidation rate:

1. One Dimensional thermal modelling using ANSTO spreadsheet 0.49 kg S t-1 y-1

2. Oxidation rate derived from acid leached iron versus sulphide

content in poorly oxidised regions

0.42 kg S t-1 y-1

3.

Oxidation rate derived from current dump sulphide content versussulphide content plus sulphate content

0.40 kg S t-1 y-1

Despite the potential sources of error identified by the reviewers, the results are insurprisingly good agreement.

Thompson & Brett reiterated that estimation of oxidation rate using the modelled


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sulphate flux based on a single water sample would be meaningless as it is consideredunlikely that the sulphate release rate is in equilibrium with the sulphate generation rate.

The differing interpretations of the NAPP data result from differing definitions of HairpinDump. Thompson & Brett’s initial advice that effluent from the dump would become

more alkaline with time was based on modelling of the upper 20m of the dump. When thevery small number of deeper NAPP results (which are taken from waste rock which pre-dates the commencement of construction of Hairpin Dump in 1993) are taken intoaccount, it is possible that the total dump will be a net acid producer in the long term.

Thompson & Brett went on to identify several risks to the achievement of projectobjectives at Hairpin Dump. Overall it was felt that the existing and proposedinstrumentation of the dump before and after cover construction would be sufficient todetect and quantify any changes in oxygen flux and water flux into the dump resultingfrom cover construction. If necessary, complex three-dimensional modelling could beundertaken at a later date using data that is currently being collected.

Thermal modelling (draft)

[Sulphide Solutions was asked to undertake more detailed thermal modelling of Hairpin Dump]

Sulphide Solutions, (2002), undertook quasi-3D thermal modelling using a full year of temperature data from Hairpin Dump. A 2D heat conduction equation, with a termintroduced to account for heat loss in the third dimension, was applied to a cross sectionthrough probe holes BH1, BH3 and BH4.

The numerical modelling produced similar results to those observed in probe holes BH1,

BH3 and BH4. A pod of higher oxidation rate material in the vicinity of BH4 wasassumed to be either 5 or 10 metres in diameter. The diameter chosen did not alter theestimated average internal oxidation rate.

Using a thermal conductivity of 1.76 Wm-1

K -1

. Sulphide Solutions estimated an averageinternal oxidation rate of 2.1 kgO2m

-3s-1. Using a thermal conductivity of 2.5 Wm-1K -1

(as determined by Thompson & Brett 2000a), the average internal oxidation rate wasestimated to be 3.0 kgO2m

-3s

-1. [These figures are still 50% and 58% respectively lower

than Thompson and Brett’s revised estimate via 1D modelling.]

Design of an oxygen limiting clay cover for Hairpin Dump at the Savage

River Mine

Thompson & Brett (2001a) prepared a design for the proposed soil cover over HairpinDump. The design assumed that permeabilities of 10-7 to 10-8 m/s could readily beachieved on flatter accessible surfaces of the dump and that 10-6 to 10-7 m/s should beachievable on batter slopes with moderate compaction of the types ‘clay’ expected toarise during mining operations.


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Modelling of infiltration was found to be heavily affected by rainfall intensity. Infiltrationduring an average year modelled to 10% of incident rainfall where cover permeabilitywas 10-7 m/s, increasing to 56% where a low permeability overlay was provided for revegetation purposes. For a cover permeability of 10-6 m/s without an overlay, 50% of incident rainfall would be expected to infiltrate into the dump.

All modelled covers exhibited a high degree of saturation year round, suggesting thatoxygen transmission may be reduced even with higher permeability covers.

Stability analyses suggested that batter slopes of 1:2 would achieve a factor of safetyagainst slip failure of 1.117, which is considered acceptable.

Detailed design plans were also provided in the report.

Permeability is the important quality control parameter and will need to be tested in situfollowing placement and compaction of the clay.

Assessment of Soil Covers

Thompson & Brett (2002a) undertook a general assessment of soil covers in Tasmania asan extension to the Hairpin Dump contract.

In situ permeability and moisture content of existing soil covers and waste rock wasassessed at several locations at both Savage River and Mt Lyell.

Generally the cover materials were classed as low to moderate plasticity silts, severalexhibited a relatively high gravel content.

During construction of the Magazine Dump clay cap, laboratory compaction of samplesyielded permeability results ranging 1 x 10-7

m/sec to 6 x 10-9

m/sec. 10 field permeameter tests conducted at Magazine Dump on 23 November 2002 gave permeability results much higher than suggested by the earlier laboratory analysis:

Location Permeability MC%

Unripped flat areas 2.5 x 10-7 m/sec to 5.0 x 10-7 m/sec

Batters 2.6 x 10-4

m/sec to 8 x 10-6

m/sec

28.5 – 41.1

Clearly the reduced compaction on the track rolled batters has a significant effect on permeability. Moisture content was on average, slightly higher than optimum moisturecontent for the material, suggesting a high degree of saturation.

Combined data retrieved from the 6 lysimeters installed in Magazine Dump by ANSTOsuggested an infiltration rate through the cover of 11.2% of incident rainfall.

The OTD at Savage River was capped during 1996 with a moderately plastic silty clay.Once again permeability results were less than expected for the given material andcompaction methods:


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Location Permeability MC%

Bench 1.2 x 10-7 m/sec to 1.4 x 10-6 m/sec

Batters 5.5 x 10-6

m/sec

39 – 48.1

South West Dump was capped by ABM, using a tamping plate fitted to a hydraulic

excavator, to within 97% - 106% of maximum dry density. The material was classed as alow plasticity gravelly silty clay.

Location Permeability

Batters 1.0 x 10-7

m/sec to 2.2 x 10-6

m/sec

The South West Dump results appear quite reasonable in comparison to other dumps,especially in view of the poorer quality material used.

Waste rock at Hairpin Dump yielded the following permeability results:

Material Permeability

Surface gravels 1.2 x 10-5

m/sec to 8.0 x 10-5

m/secSurface clays 1.3 x 10-7 m/sec

Subsurface rockfill 1.2 x 10-3

m/sec to 1.5 x 10-3

m/sec

Thompson & Brett (2002b) undertook a water balance comparison before and after capping of Magazine Dump for the period December to April each year commencing1995.

After taking into account rainfall, evaporation and outflows from the dump, it appearsthat 2-3 times more water exits the dump over the summer period than would be expectedto enter it.

This could be explained by groundwater inflows to the dump of about 8,200m 3 during the period December to April. Changes in outflow over time suggest that the dump is slowlydrying out.

The results suggest that the Magazine Dump cover excludes about 60% of incidentrainfall. Given that the lysimeters indicate only about 10% infiltration through the dump plateaus, infiltration through the batters would need to be about 75% to give 60% overall(this means the batters leak about as much as they could, given likely evaporation lossesof around 25%).

This work confirms that where compaction is adequate, water shedding objectives (10 – 15% infiltration) are achievable. All covers also showed a high degree of saturationwhich may assist their oxygen barrier function.

Previous design work for clay covers at Savage River had specified permeability targetsof 10

-8 m/sec for flat areas, and 10

-7 m/sec for slopes. Based on the above work 10

-7 m/sec

is considered acceptable provided that drainage is good. It was therefore suggested thatcovers be designed to ensure at least 10% gradient on the upper surface of the clay cover.


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The erosion protection layer would need to be constructed from coarse rock rather thanrevegetation medium.

Magnesite lined drain adjacent to North Dump

[No report on the performance of this drain has been prepared. A brief assessment is provided in Coffey Geosciences (2000)]

Hydrogeological study and evaluation of acid drainage remediation

options

Surface Water Hydrology

Coffey Geosciences (2000) provides tables of estimated annual runoff pre- and post-mining for each section of the catchment. Monthly runoff coefficients determined using1998 stream flow data varied from 25% in March to 95% in August (average 63%), withrelatively good agreement between the 4 catchment areas considered. A preliminarySurface Water Management Plan that focused on drainage works to separate clean andcontaminated waters across the site was provided.

Hydrogeology

The hydrogeology section of Coffey Geosciences (2000) provides a brief description of the regional geology followed by a short summary of the findings of previoushydrogeological investigations by Piteau & Associates, Australian Groundwater Consultants and John Miedecke & Partners.

12 regional groundwater bores were drilled across the site. Groundwater levels were

measured and permeability estimated via a falling head test. A further 12 piezometerswere installed in the OTD.

Generally the site was characterised by low permeability rock types. Groundwater flow isexpected to be largely restricted to the edges of fault bounded blocks, with the majority of flow through the secondary fractures. Transmissivity was considered likely to be higher along the north-south regional foliation/structural trend. The main recharge areas were thought to be the weathered, near level ground on ridges(some of which are now covered by waste rock dumps). The main sinks were local creeksand rivers, with some flow to deeper fractures in unweathered rocks.

A conceptual hydrogeological model was presented.

Four groundwater aquifers were identified:• weathered chloritic schist (measured permeabilities ranged from 1 x 10-8 to 9 x 10-

6 m/sec),

•

weathered tertiary basalt (permeabilities from 4 x 10-6 to 9 x 10-6 m/sec),• metabasalt xenolith (4 x 10-6 m/sec), and


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• waste rock (characterised by high permeability and perched aquifers).

Order of magnitude groundwater flow volumes were presented. Estimated groundwater flow volumes from potential groundwater contamination sources were small incomparison to surface flows, however, contaminant flux may be locally significant where

contaminant concentrations are large.

Groundwater samples were submitted for chemical analysis. Total metal concentrationsin groundwater exceeded ANZECC (1992) guidelines for 3 or more metals at all bores.

Background copper, iron and aluminium concentrations in groundwater appear to benaturally elevated. GW4 results may indicate groundwater impact from oxidation of sulphides in undisturbed weathered schist (the unit of widest distribution). Bores adjacentto rock dumps produced results consistent with the impact of acid drainage.

Past and present analyses of South Centre Pit seepages were presented and discussed. The

study also reviewed past and present OTD data. It was suggested that virtually all seepageemanating from the OTD seeps enters the OTD within about 100m of the dam crest.

The report recommended a further year of regional groundwater monitoring to confirmthe above findings.

Acid Drainage Assessment

This report provides a brief summary of earlier work. Coffeys estimated, based on reports by Environmental Geochemistry International, that 55% of the waste rock at the SavageRiver Mine is likely to produce acid drainage, though it was noted that the Sulphidestended to react slowly and sometimes not all. A summary of the acid forming

characteristics of each of the major geological units is included.

OTD tailings and pore water geochemistry were assessed in some detail:

A general decline in water quality from north to south is apparent. Water quality appearsto be influenced by tailings grain size, with the highest acidity levels found in very coarsetailings. Sulphate levels where much higher than acidity levels, suggesting that acidityhas been consumed by dissolution of carbonate minerals. Various exceedances of theANZECC (1992) water quality guidelines were reported from the southern piezometers.

The waters of SRRP9, SRRP10, SRRP11 and SRRP12 (southern bores) are at gypsum

saturation. SRRP1, SRRP2, SRRP3 and SRRP7 (northern bores) are characterised bynear neutral pH and relatively low pollutant concentrations.

Groundwater recharge through the tailings was thought to be highest in the south westcorner of the OTD, based on pore water chloride concentrations.

The water quality data indicate that the tailings are being preferentially oxidised in thesouth west corner and southern end of the OTD. This is consistent with the observed


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particle size distribution (finer to the north), which is a result of the upstream methods bywhich the dam was constructed. The sandy materials at the southern end of the OTD aremore deeply oxidised. Oxidation depths varied from 16 – 35 cm. Depth profiles indicatedthat oxidation tends to be associated with coarse tailings layers, while silt/clay sizedtailings are generally more moist and consequently less weathered.

A brief summary of historical OTD reports is provided. Evidence of acid seepage fromthe OTD is said to have been documented as early as 1979, then in 1996 the rate of acidity flux from the OTD to the MCTD was estimated at 1070 kg/day.

The potential for seepage of acid drainage through the remnant soil profile under theeastern OTD embankment (south) [which is not captured by DPIWE’s monitoring weir]is said to be significant.

MCTD tailings were found by EGi to be potentially acid forming with NAPP valuesranging from 120 – 266 kg H2SO4/t. ABM commenced adding hard alkaline rock to the

mill feed for improved grinding performance during the Coffey study, but this is likely tocease when hard ore becomes available again.

Leachate emanating from dewatering bores on the RL 180 bench of the eastern wall of South Centre Pit was assessed and discussed. It is of interest that the pH of the pit watersis generally lower than the pH of the leachate from the dewatering bores.

Alkalinity and flow are generally higher in the south while metals (except copper) are

lower. Conductivity varied from 1700 – 2400 µS/cm and pH ranged from 6.3 – 7.4.Formation of ferric hydroxide precipitates at the outlet of some dewatering bores isindicative of generation of additional acidity through oxidation of iron on contact with the

atmosphere.

Seepage from B Dump (which lies to the south east) was not thought to be a major influence on the observed water quality in the dewatering bores, however, groundwater seepage may also occur below the water level in South Centre Pit.

A comparison of concentrations between bedrock seepage and surface seeps in thevicinity of North West Dump suggested that a lesser proportion of leachate from NWDump discharges to groundwater, compared to surface waters (this is consistent with the presence of a low permeability tertiary basalt cap under NW dump).

Pit void water profiles were discussed. The profiles showed no dramatic decline in pH(SCP ~5, CP ~6) with depth, though the deeper oxygen depleted layers exhibitedsubstantially higher conductivity and pollutant concentrations.

The report includes a discussion of the alkaline flow-through drain that is beingconstructed by ABM. Conductivity, alkalinity, sulphate, manganese and nickel werefound to significantly increase in the flow-through drain, while dissolved oxygen, totalsuspended solids and iron all decreased during transit.


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No assessment of the longevity of alkaline additions arising from the flow-through wasable to be made, though the drain does appear to be accumulating suspended sedimentand iron hydroxides.

The PMI flow-through did not appear to have any significant impact on water quality inBroderick Creek.

The trial magnesite drain adjacent to North Dump was not found to contribute significantamounts of alkalinity to the waters of the drain, however, the concentrations of aluminium, cobalt, nickel, manganese and zinc did fall along the drain.

The performance of this trial was thought to be influenced by the relatively high influent pH (~6.3), large size of the magnesite particles, sedimentation, and the short length of thedrain.

Previous NSR and DPIWE reports on water quality are summarised. Coffey Geosciencesthen modelled the annual pollutant fluxes by combining various sources of data. Sulphatewas taken to be a conservative and medium to long term indicator of acid generation andcopper was chosen to represent short-term pollutant source rankings. A number of limitations to the methods used were acknowledged.

The Coffey source rankings shown below are generally similar to the DPIWE rankingsexcept for the inclusion of SW Dump. Coffeys suggest that SW Dump may be a larger pollutant source than was previously thought.

Sulphate Rankings:Main Creek > SW Dump > Broderick Creek > Centre Pit > Crusher Gully > South Lens > North Dump Drain

CopperMain Creek >> North Dump Drain >> Crusher Gully > SW Dump > OTD > Centre Pit >Broderick Creek

Remediation Options:

The fourth section of Coffey geosciences (2000) focussed on remediation options atSavage River. The following set of key principles was applied to the development of remediation options:

• Focus on passive minimisation and control, with active treatment a last resort

• Sub-aqueous disposal is the most beneficial option

• Remediation techniques must aim to work 100% of the time

• Treatment sludges should be isolated from the Savage River

• Long term dump slope stability should be improved where practical and cost effective

B Dump


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1. Construct dams in Main Creek for the collection and pumping of waters to a centraltreatment facility (no changes to the dump itself)

2. Reshape and cap the top of B Dump with a low permeability cover plus erosion protection layer. Leachates to be collected in a magnesite lined drain for partialtreatment followed by collection in a holding pond and treatment or pumping to

central treatment facility3. Construct a carbonate flow-through drain in Main Creek, then fill in the valley toimprove geotechnical stability of dump batters and MCTD/ETD dam walls.

A Dump1. Collect and treat acid drainage with no change to dump (could be combined with

similar option for B Dump)2. Reshape and cap the top of A Dump and treat leachate. Magnesite lined permiter

drain may provide some pre-treatment3. Option 2 plus carbonate lined perimeter drain directing leachate to MCTD for

treatment.

4.

Push A Dump into South Centre pit after cessation of mining (water cover)

South West DumpOptions are considered limited due to steep slopes and proximity of the river to the toe of the dump. It is recommended that the impact of acid drainage from this dump be further evaluated before remediation options are considered in detail.

Crusher GullyWaste rock in this area will be substantially removed in the course of mining operations,nonetheless, the following options are suggested:1. Reshape and cap the dump, construct leachate collection drain near the base of the

dump with gravity drainage to South Lens Pit2.

Push waste rock from Crusher Gully into Centre Pit following cessation of operations3. Collect drainage in a cut off drain and pump it for treatment in a mine pit.

North Dump1. Collect leachate and transfer under gravity to a mine pit for treatment and sludge

retention (requires a suspended pipeline across the Savage River). Clean water east of the dump to be diverted via a directional bore hole.

2. Flatten the eastern slopes of the dump and extend the dump approximately 150 metresto the east and cap to divert clean water that currently enters the dump from the east.Install a magnesite lined collection drain along the western margin of the dump, possibly continue magnesite drain to South Lens Pit.

3.

Reshape dump using existing material.

Old Tailings Dam1. Construct a low permeability wedge embankment over the southern dam wall to

move the phreatic surface to the south. Construct embankments at ~150 metreintervals on the low permeability tailings beach to retain a water cover over most of the beach.


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2. Install a water powered treatment plant at the southern end of the OTD (requires a pipeline from northern pondage)

3. Cap the south west corner of the OTD.

Central treatment Plant

Four options for a centralised acid drainage treatment plant are presented:1. Dosing system, aerators, mixers, clarifiers and final polishing structure. Requiresongoing maintenance, pumping, electricity and sludge management.

2. Series of settlement dams with dosing structures at the inlets.3. Use of hydropower to operate treatment plant. Would probably not be sufficient to

pump all acid drainage on the site, or to crush local carbonate rock.4. Central slurry-producing facility located to permit slurry delivery under gravity to

various areas of the mine.

Smaller Treatment PlantsSome potential benefits of operating several distributed treatment plants are discussed.

Costs associated with treatment plants were estimated as follows:

Capital Cost Operating Cost p.a. Reagent Cost p.a.

Central treatment plant

$2.5 million $300,000 $250,000 -$400,000

Small hydro powered carbonate plants*

$150,000 -$250,000 each

$10,000 - $15,000each

$23,500 - $47,000

Small scale CaOdosing plants*

$150,000 -$250,000 each

$10,000 - $15,000each

$235,000 – $353,000

Small scale

Ca(OH)2 plants*

$180,000 -

$350,000 each

$10,000 - $30,000

each

$235,000 –

$353,000* Costs don’t include the cost of sludge storage facilities [the cost of which may exceed the cost of the plant by a considerable margin. For the central treatment plant it can beassumed that a mine pit would be available for low cost sludge disposal].

The potential effects of scaling and corrosion on pumping systems are raised, as is theissue of sludge management.

Several remediation options that were not considered viable are listed:

• Soil covers as oxygen barriers were excluded on the basis that they are rarelysuccessful, particularly in the very long term

•

In situ dosing of leachates without reshaping of dumps (due to slope instability)•

Caps without protection against erosion and root penetration

• A range of imported neutralising materials

Monitoring Data Assessment 2000 – 2001

Coffey Geosciences Pty Ltd (2001) prepared a brief summary of groundwater monitoringdata collected over the previous 12 months.


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Water level in the various groundwater bores was plotted against rainfall trend for the period of observations.

The rainfall trend peaks in mid July 2000 and troughs at the beginning of March 2001.Water level in the OTD piezometers was highest 1-2 months after the rainfall peak. The

water level trough was reached 0.5 to 1 months after the rainfall trough. The lag time wasgreatest in the southwestern corner of the OTD, which is the area with the coarsest grainsize.

Water level contours were seen to shift southwards during peak water levels, which inturn steepens the hydraulic gradient toward the MCTD. The report acknowledged the possibility that a gradient of water moving north may exist in some parts of the OTDduring high rainfall months.

Dataloggers installed in two of the OTD piezometers indicated that water levels varythrough about 2 metres and rise rapidly within 2-3 days of rainfall events.

Regional groundwater monitoring bores showed similar results, though water levelsgenerally responded more slowly than in the OTD. Groundwater levels were seen to peak between 1 – 3 months after rainfall and bottom out 1 – 2 months after the rainfall trough.

Bores GW8, GW9 and GW10 exhibited greater water level rises in July 2000 than nearby bores, probably because these three bores are located on flat, elevated areas that retainrainfall.

The continuously logged water level at GW8 varied through 10 metres over themonitoring period, indicating limited storage capacity. GW9 varied through 2 metres over the same period.

It was suggested that contaminated groundwater under B Dump and A Dump is morelikely to follow the steep east-west gradient toward Savage River and South Centre Pitthan to move north or south.

The authors concluded that the analytical data supplied by the DPIWE laboratory werenot sufficiently accurate for detailed analysis of water quality. Therefore the onlyassessment carried out was a comparison to the ANZECC 1992 water quality guidelines.

The majority of samples exceeded the ANZECC guidelines for pH, ferrous iron, total ironand copper. Aluminium and TDS also exceeded the guidelines for a significant number of samples.

The sites exhibiting the largest number of exceedances were ranked as follows:GW11 & SRRP11 > SRRP9 & SRRP12 > GW2 > GW5 > GW3 > SRRP10. Bores GW8,GW9 and GW10 appear to represent background water quality (i.e. not affected bymining). Groundwater from the background bores generally exceeds the ANZECCguidelines for copper, zinc, iron and pH. All other bores are significantly impacted by


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sulphide oxidation.

Cobalt, though not included in the 1992 ANZECC guidelines, is significantly elevated ingroundwater and may also be of significance to aquatic ecosystems

Desktop review of options for treatment of acidic discharges in MainCreek below B Dump

[Chemical treatment of Main Creek was considered a potentially viable option given that its alkali demand is less than 2 tonnes/day and dramatic reductions in volumetric flow

were anticipated following ABM’s planned diversion of the tailings dam decant toTownsends Creek.]

Thompson & Brett Pty Ltd (2000b) assessed the feasibility, at desktop level, of providingtreatment facilities at various locations.

Thompson and Brett’s prior hydrological knowledge of the Savage River site was appliedto the Main Creek catchment to predict a mean flow in Main Creek above TownsendsCreek of 46 l/s after the Townsends Creek decant becomes operational (or a peak monthly flow of 93 l/s based on a 1:100 year event of 72 hours duration). The reportidentified the potential for further large reductions in peak flow through capping of disturbed areas and diversion of runoff from the undisturbed eastern slopes of the MainCreek valley.

The pros and cons of constructing treatment plants at each major source of acid drainageversus a centralised treatment facility to which acid drainage is pumped were discussed.The expense of installing a clarifier, flocculant mixing plant and other equipment at each

distributed acid source must be weighed against the cost pumping non-thickened sludgeto a stable disposal receptacle. Both of these options need to be compared with thealternative of pumping acid drainage to a central treatment facility.

The report identified the potential to utilise ABM’s existing tailings thickener, along withthe latent alkalinity content of the tailings, to neutralise acid drainage. It was suggestedthat following cessation of operations locally available magnesite or limestone couldreplace tailings as the source of alkalinity, with the thickener continuing to be used to produce sludge. Options to employ the Green Precipitate process or to operate a partialsludge recycle loop to gain the benefits of a High Density Sludge were also raised.

Co-disposal of neutralisation sludges with tailings was considered the best sludgedisposal option during the mine life (subject to test work and long term pH control of thewaters of the MCTD). If available a disused mine pit could provide a suitable post-mining receptacle for non-thickened sludge (subject to resource sterilisation issues).Being naturally alkaline, North Pit is the preferred pit for sludge disposal.

Static treatment at North Pit was also considered. Under this option partial neutralisationof acid drainage would be achieved by passing acid drainage over the carbonate rich east


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wall of north pit. Further neutralisation with local or imported reagents would still berequired in North Pit pond.

Cost comparisons between three identified treatment ‘packages’ were provided. The keyassumptions upon which the costings are based are summarised below:

• Flood storage in Main Creek requires a 10-15 metre high dam and a 1.0 km accessroad.

• Cost of electricity is 17 c/kwh.• Reagent cost is $200/tonne (slaked lime).• Allowance for a full time locally based operator with vehicle and equipment is

included.• Equipment maintenance costs are set at 2.5% of capital.• A sinking fund for capital replacement after 25 years is included.• An approximate capital cost of a treatment plant with clarifier was estimated to be

$2.5 million. This figure was nominally halved where ABM mill facilities were to be

utilised in construction of the plant.• The discount rate is 4%• The operating period is 50 years

The options are summarised in the table below1

Option Neutralisation method Sludge disposal

Sludge pumped to ABMtailings thickener

1. Treatment in MainCreek

Conventional limetreatment.

Sludge pumped to North Pit

By mixing with alkalinetailings

To ABM tailings dam2. Treatment at ABM mill/ North Pit

Batch treatment with limein North Pit

Sludge permitted to settle North Pit pond

Pump sludge to ABM mill/tailings dam.

3. Treatment plant at North Pit

Conventional lime reagent.Possible benefit of naturalalkalinity not costed. Sludge permitted to settle

North Pit pond

Each of the above options was costed under five peak monthly flow scenarios:a) the current situation (93 l/s), b) Capping of B Dump with diversion of surface waters (63 l/s)c) Includes scenario b) plus in-filling and capping of the Main Creek valley

adjacent to B Dump(36 l/s)d) Includes scenario c) plus diversion of runoff from the eastern slopes of the

Main Creek valley (10 l/s)e) Includes capping and diversion as per d) but also assumes a 50% reduction in

acid loading resulting from reduced oxygen ingress (10 l/s)

1 Shaded cells indicate altered procedures post-mine life


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The up-front capital cost and net present value of each option over a 50-year operating period is summarised below:

Option Scenario a)2

Scenario c)3

NPV Capital alone NPV Capital alone

1 $13,155,682 $3,830,000 $10,111,612 $2,330,000

2 $15,021,087 $2,657,750 $7,310,034 $1,630,4213 $16,008,926 $4,340,000 $11,340,5920 $2,580,000

Clearly operating costs account for a large proportion of the overall project cost. The potential benefits of ABM’s contribution may have a value of several millions of dollars[e.g. 1a minus 2c]. These benefits accrue both during mine life (e.g. provision of operators, alkaline tailings and infrastructure) and may also continue post-mine life (e.g.construction of diversion drains and clay caps).

A considerable body of further test work was recommended in the report. Particularly asrelates to the potential use of tailings or locally available carbonate rocks for treatment of

acid drainage.

The potential for hydropower generation was discussed briefly. From the final MCTDoutfall height of 335 metres, it was estimated that 666 kW could be generated adjacent tothe Savage River. This is about three times the likely power consumption rate of theenvironmental works.

Approximate costs of the power-generating infrastructure are estimated. When comparedto the electricity price currently paid by ABM, the hydropower generation scheme wouldrun at a loss. Post-ABM, the Crown may be faced with higher commercial electricityrates making the scheme considerably more attractive. The potential value of any excess

power generated and sold to other consumers may be boosted by ‘greenhouse credits’,however, such sales are subject to long term maintenance of the 40km transmission lineto Waratah.

Notwithstanding the potential for future generation of electricity, current MCTD outflowswould be sufficient to drive a turbine pump to lift Main Creek above Townsends Creek toa treatment plant.

Provision of expert geochemical advice to the SRRP File:071942

[An independent expert geochemist was appointed to provide specific geochemical

support to the SRRP. The expert geochemist’s advice regarding the ABM flow-through

2 Costings for scenario a) exclude any ABM contribution.

3 Costs for scenario c) include anticipated savings arising from ABM’s contribution over a 15year period. Scenario c) has been selected to denote the lower end of the scale on the basis that the very low flow rates assumed for scenarios d) and e) may not be practically achievable in the

long term due to seepage from the Main Creek Tailings Dam.


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was then sought]

Dr Stephen Dobos (2001b) noted that a substantial portion of the alkaline flow-throughdrain being constructed by ABM in the Broderick Creek valley is made of calcite-chlorite-quartz schist which is generally 10% or more calcite and approximately 1%

sulphide.

The limited available water quality data indicated a substantial increase in alkalinity inthe flow-through drain (both Ca and Mg rise significantly), but only a minor increase in pH was observed. Aluminium and iron concentrations decrease significantly, thoughcopper and sulphate increase. The overall environmental outcome is consideredfavourable.

The central issue was considered to be the longevity of the alkalinity additions if blindingand passivation of carbonates occurs within the flow-through. The increase in magnesiumduring transit was considered noteworthy on the basis that magnesium carbonates are less

likely to be blinded by epsomite than calcite is by gypsum. The source of magnesium isnot known but it could come from magnesite, dolomite or the breakdown of chlorite.

Performance of both oxic and anoxic limestone drains is said to rapidly diminish due to both blinding and physical blockage. The relatively high quality of influent to the flow-through is said to improve the prospects for ABM’s flow-through. Dobos guessed that theABM flow-through should perform for at least 20 years.

Some potential measures to prolong and possibly increase alkalinity additio