Wastewater and stormwater minimisation in a coal mine

Journal of Cleaner Production 8 (2000) 23–34www.elsevier.com/locate/jclepro

Wastewater and stormwater minimisation in a coal mine

H.B. Dharmappa*, K. Wingrove, M. Sivakumar, R. SinghDepartment of Civil, Mining and Environmental Engineering, University of Wollongong, Wollongong 2522, Australia

Received 12 January 1999; accepted 23 September 1999

Abstract

This paper presents a case study on the application of cleaner production principles in the mining industry. The water balanceprepared for the case study showed that less than 20% of the wastewater generated by the colliery is discharged off-site. Theremaining 80% of the wastewater is recycled back into the colliery. Modeling of the stormwater system showed that 75% of theclean runoff becomes contaminated through poor management practices. It was also found that the present system of stormwatermanagement causes the process wastewater management system to fail in wet weather. Improved process and stormwater manage-ment systems are proposed. Relatively simple alterations to the operation of the coal wash filtration dams are expected to reducethe periods of inefficient operation of these dams by 95% and the pumping cost by 30%. The use of stormwater diversion channelsand retention basins reduces the overflow volumes of the process wastewater treatment dams in 5 year average recurrence interval(ARI) storms by 100%. The paper also includes several recommendations for reducing the production of process wastewater atsource and off-site disposal of wastewater. 2000 Elsevier Science Ltd. All rights reserved.

Keywords:Stormwater; Wastewater; Coal mines; Mine environment; Waste minimisation; Cleaner production, management and treatment

1. Introduction

As industrialisation takes a leap ahead, resulting inhigh pollution loads, there is a growing concern aboutthe quality of the living environment. This calls for moreinnovative efforts to protect the environment. Now, theindustries are expected to pro-actively reduce the amountof pollutants discharged into the environment. Inaddition, the environmental management is nowregarded as an essential element of an organisation’soverall management plan as opposed to a stand-aloneand sideline issue in the past. Towards this end, tra-ditional ‘end-of-pipe treatment’ is grossly inadequate. Itis a fact that the end-of-pipe treatment only transfers thepollution from one form to the other. For example, con-trol of air pollution results in the water pollution, whichin turn results in soil pollution and, ultimately, all thepollutants end up joining the water body.

To counter the above shortcoming and to preserve thehigh quality of the environment the new concept called

* Corresponding author. Tel.:+61-2-42214492; fax: +61-2-42213238.

E-mail address:[email protected] (H.B. Dharmappa)

0959-6526/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.PII: S0959-6526 (99)00309-1

Cleaner Production (CP), or Low or Non-Waste Tech-nology (LNWT) is being introduced in many countries. CPrefers to technology designed to prevent waste emission atthe source of generation itself. The philosophy behind thisis ‘to produce better while polluting less’ [1]. In practicethis technology and its application go by many othernames such as clean technology, waste minimisation, pol-lution prevention, waste recycling, resource utilisation,residue utilisation, etc. [2]. CP minimises or totally elimin-ates the emission of pollutants to the environment. Whileinvesting little on the process, it is possible to save a lotof money on waste treatment and disposal. Often the capi-tal return period is less than 2 years.

The mining industries have also caught up with theabove principles of waste management. They are parti-cularly concerned about the wastewater being generated attheir facilities. The main objective of this paper is to exam-ine the opportunities for minimising the overall quantity ofwastewater and stormwater from an underground miningindustry, located in New South Wales, Australia.

2. Strategies for liquid effluent management

The collieries produce liquid, solid and gaseouseffluents. However, in this study only the liquid effluents

24 H.B. Dharmappa et al. / Journal of Cleaner Production 8 (2000) 23–34

are considered for applying cleaner production prin-ciples. The effluents from the collieries can be con-sidered to be consisting of four components:

O Mine waterO Process wastewaterO Domestic wastewaterO Stormwater

Two main methods through which the cleaner pro-duction can be achieved in any industry are [3]:

O Source reductionO Recycle/reuse

It is possible to apply both of the above methods in orderto achieve wastewater minimisation in a mining industry.The goals for cleaner production in a typical collieryinclude:

O Mine water managementO to minimise the mine water productionO to reduce the degree of contaminationO to recycle/reuse in the underground mining

O Process wastewater managementO to minimise the fresh water requirementsO to improve effluent qualityO to increase reuse potential of effluentO to optimise treatment system

O Domestic wastewaterO to minimise the water consumptionO to treat the wastewater to meet the local standardsO to prevent faecal contaminationO to reuse/recycle within the colliery

O Stormwater managementO to reduce degree of contamination and quantity

contaminatedO to ensure quality of colliery effluents are main-

tained and process water treatment systemefficiency is not compromised by runoff

Not many studies are found in the area of application ofsource reduction principles for the wastewater manage-ment in collieries. However, some studies [4,5] havereported the application of wastewater recycle/reuseprinciples in order to achieve cleaner production goalsin collieries. Singh et al. [4] showed, for one of themines in the Illawarra region (Australia), that the townwater consumption can be reduced by about 50% (from1500 to 740 m3/d) with a corresponding saving in thecost of AUS$0.245 million/yr. However, in this studythe issues related to stormwater management were notconsidered.In the present study the cleaner production principleswere applied to both wastewater and stormwater man-agement. It was proposed to manage the wastewater

through in-plant recycle/reuse and the stormwaterthrough source reduction. The concepts were demon-strated using a case study.

3. Case study

An underground coalmine is selected for the casestudy. The location and the production details of the col-liery are shown in Table 1. The existing water manage-ment is shown in Fig. 1. The water requirement for vari-ous operations is given in Table 2.

4. Wastewater management

4.1. Quantity and quality of wastewater

Mine water discharge. The main pollutants of theaquifer inflow are dissolved minerals from the aqu-iferous rock strata. It is not practically feasible to preventthe contamination of this water. However, the analysesshowed that the non-filterable residue (NFR) levels ofthis stream are extremely low (Table 3). In order toreduce the quantity of aquifer inflow, the following tech-niques can be implemented:

O use retreat mining techniques;O advance dewatering of aquifer using surrounding

borehole pumps; andO seal fractures, fissures and cavities with grout.

Bathhouse wastewater. The bathhouse effluent is pre-dominantly contaminated by coal fines from the mineworkers and soaps used in their showering. Detergentsand disinfectants are also used to clean the bathhouse.To minimise these pollutants, workers should removeloose coal fines before surfacing from underground andbiodegradable soaps and detergents should be used. Thequantity of bathhouse wastewater can be reduced byusing water saving shower roses and hose nozzles. Theflowrate and the non-filterable residue (NFR) levels ofthe bathhouse effluent are given in Table 3.

Pit-top operational wastewater. The majority of the

Table 1Location and production details of the colliery

Items Parameters

Location Illawarra, AustraliaCoal seam WongawilliProduction rate—raw 0.4 MT/yrProduction rate—washed 0.3 MT/yrMining method Continuous minerOn-site washery Yes

25H.B. Dharmappa et al. / Journal of Cleaner Production 8 (2000) 23–34

Fig. 1. The existing wastewater treatment system at the colliery.

Table 2Water requirement by the colliery

Activity Quantity Quality requirements(m3/d)

Office (drinking and 0.05 Fresh waterkitchen)Workshop 1.0 Low NFRa, low salts, near

neutralBathhouse 3.0 Low NFR, low salts, near

neutralUnderground operations 200 Low NFR, low salts, near

neutralWashery 1590 Low NFR, near neutralStockpile sprays 4.2 Low NFR, near neutralTruck washing 0.17 Low NFR, near neutralRoad dust suppression 2.5 Low NFR, near neutralTotal 1800.92

a NFR—non-filterable residues.

Table 3Flowrates and NFR levels for different wastewaters

Wastewater source Flowrate (m3/d) NFR (mg/l)

Washery effluent 300 400–13,650Bathhouse effluent 3 4–157Minewater discharge 3000 0.4–7

pit-top operational water is used to control dust. Methodsto reduce the need for using water spraying to controldust include:

O sealing frequently used roadways;O improving the truck loading system to minimise spill-

age of coal products;O using air-vacuum systems to remove and capture coal

fines from trucks covering small material stockpilesand laden trucks; and

O providing wind breaks for large material stockpiles.

If implemented, these methods would reduce both thequantity and pollutant levels of the pit-top wastewater.

Washery wastewater. Wastewater from the washeryincludes the liquid effluent and the slurry tailings. Theliquid effluent is a result of truck washing, machineryand work area wash down and pipe leakages. As such,the wastewater generated generally consists of a largeamount of NFR as shown in Table 3. This wastewaterstream can be reduced by:

O using air-vacuum methods for truck, machinery andwork area cleaning;

O maintaining pipes and connections to prevent leak-ages; and

O using water saving hose nozzles for any necessarywash down activities.


The slurry tailings effluent is a waste product from thecoal washing process. The colliery currently sells someof these fine ‘rejects’ as a lawn treatment material.Further development of this market as well as the devel-opment of other marketable uses for this material wouldchange its status from waste product to saleable product.

4.2. Process wastewater reuse and disposal

Currently, the colliery discharges approximately 600m3/d of treated wastewater from the main dam. Thisquantity represents less than 20% of the volume of waterremoved from under ground. This reflects that a signifi-cant amount of wastewater is already being reused forcolliery operations. The aquifer inflow water meets allof the colliery’s water needs with the exception of drink-ing and kitchen water requirements. Due to healthreasons, it is not appropriate to use the aquifer inflowwater for either of these purposes. Thus the only optionfor increasing the reuse on site is for additional purposes.The colliery rehabilitation program involves extensiverevegetation of large areas of land. The aquifer inflowwater would be suitable as a water source for this pro-gram. However, the volumes of water involved wouldnot significantly reduce the quantity of off-site discharge.

Currently the colliery does not specifically make itssurplus water available to external industries. The waterwould be suitable for use by many local industries,which do not require potable quality water for their oper-ations such as:

O irrigation water for local farms, parks, golf courses,green belts or lawns

O industrial cooling waterO industrial wash down waterO industrial boiler feed waterO vehicle washing waterO dust suppression waterO industrial and public fire fighting supplies.

The water could be conveyed by pipeline off site ortransported off site by tanker trucks. Depending on theuse of the water, it may or may not be necessary for thewater to be neutralised. This option of increasing off-site utilisation of the water is considered to be the mostfeasible and most significant method of reducing the off-site discharge of wastewater from the colliery. Assuminga saleable market can be established, the sale price of thewater would provide an estimated income of the order ofAUS$150/d or AUS$40,000/yr. This would at leastcover treatment costs and may provide additional profitfor the colliery.

4.3. Process wastewater pumping system

The existing pumping system at the colliery is shownin Fig. 2. The main inefficiency of this system is con-

sidered to be the allowance of the underground dischargeto flow by gravity to the main dam and then be pumpedback up to the washery. This section accounts forapproximately 25% of the total cost of pumping systemexpenses and could be eliminated by the simple layoutchanges as shown in Fig. 3. If the discharge from Pump1 is directly conveyed (by gravity) to the washery, Pump3 would become redundant and an energy saving of$27/d or approximately $7000/yr would be made. Inaddition, the NFR load of the water would be lower thanthe water, which is allowed to flow down to the maindam, as the water can pick up the soil particles alongthe way. To implement such a scheme it may be requiredto construct a holding tank, to ensure that the washeryhas a constant supply of water. The cost of such a tankwould need to be estimated, however it is expected thatthe pay-back period would be minimal (could be lessthan a year) and in the long term, substantial energy sav-ings would result. It is important to note that the maindam pump would still need to be operational as it isnecessary to have a surface supply to the fire fightingtanks in case the underground fires inhibit the use of theunderground pumps.

The pumping of the effluent from intermediate damto the settlement dam provides an additional inefficiency.When the filter dams are operating well there is no needfor further treatment of the filter dam effluent. Additional‘treatment’ of this wastewater stream by the intermedi-ate, settlement and main dams ultimately results in anincrease in the NFR content (Table 4). This is due tothe picking up of sediments during the transfer of waste-water from one dam to the other. Thus, it is less pollutingto discharge to the natural creek system directly fromthe filter dams. Pump 2 accounts for over 10% of thetotal pumping costs. However, when the filter dams arenot operating well, further treatment by the intermediateand main dams is necessary to reduce the NFR contentof the wastewater stream. In this case, use of the inter-mediate, settlement and main dams is necessary. Asshown in Fig. 3, it is recommended that the effluent fromthe filter dams is discharged by gravity directly to thenatural creek system when the filter dams are operatingwell. With this modification, it is estimated that the fre-quency of use of Pump 2 would be reduced to 3 daysevery second month. This corresponds to 18 days/yr,which costs approximately $230/yr (amounting to 7% ofthe total operating cost of Pump 2). Thus a saving ofapproximately $3000/yr or 93% would result.

An overall reduction of approximatelyAUS$10,000/yr in pump operating costs would resultfrom the suggested improvements. This represents areduction of more than 30% in pumping costs.


Fig. 2. The existing pumping system at the colliery.

Fig. 3. Proposed pumping system for the colliery.


Table 4Treatment efficiency achieved in the settling dams

Treatment dam Effluent NFR concentration

Tailings dams Decrease by.99%Filter dams Decrease by.99%Intermediate dams Slight increaseSettlement dams Slight increaseMain dams Decrease by.45%Stabilisation pond Increase by.50%

5. Stormwater management

The investigation into the existing stormwater man-agement system at the colliery indicated two main prob-lem areas: (i) hydraulic overloading of the process was-tewater treatment dams during storm conditions; and (ii)allowance of essentially uncontaminated runoff to flowdownhill and become contaminated.

An improved system of stormwater management hasbeen devised with the goal of reducing, or ideally, elimi-nating these problems. The goals for the improved sys-tem are thus to:

O Reduce the pollutant levels in contaminated runoff;O Reduce the quantity of contaminated runoff; andO Ensure that the process water treatment system

efficiency is not compromised in storm conditions.

Based on the topography and land uses (Fig. 4) thecatchment area of the colliery is classified into several

Fig. 4. Land use and pit-top operations at the colliery.

sub-catchments as shown in Fig. 5. These sub-catch-ments are grouped together into clean and dirty regionsas shown in Table 5. It should be noted that regions C1and C2 are separated by a cliff line and C2 and C3 areseparated by a ridge line. Similarly, D1 and D2 are sep-arated by a ridge line. The grouping allows managementoptions to be applied as it is considered more feasibleto manage the runoff in regions as opposed to individualsub-catchments.

5.1. Pollution prevention of stormwater

Many management practices are available to reducethe pollutant levels in runoff. These practices are ofteninexpensive and relatively simple but can be very effec-tive. Management practices appropriate for the collieryare provided below in two categories of low and highcontamination potential sub-catchments.

5.1.1. Low contamination sub-catchmentsTo ensure runoff from low contamination potential

areas remains uncontaminated, it is imperative that theflow be diverted away from high contamination areas.This can be achieved through the use of [6]: catch drains;interceptor dykes; berms; open channels; and pipelines.

Presently, runoff from area 1A is the only ‘clean run-off’ which is diverted to prevent its contamination. Run-off from this area represents approximately 12% of thetotal clean runoff volume and 8% of the total runoff vol-ume. If all of the clean runoff were diverted away fromhigh contamination areas, the total volume of contami-


Fig. 5. Classification of land use and drainage routes for pit-top operations.

Table 5Stormwater management regions

Region Runoff quality Contributing sub-catchments Comments

C1 Clean 1A, 2A, 4A Runoff easily divertedC2 Clean 4B Runoff easily divertedC3 Clean 1B, 7B, 9B Runoff easily divertedC4 Clean 6A, 7A, 8A Runoff not easily diverted (drains by gravity to main dam)D1 Dirty 3A, 5A Runoff easily divertedD2 Dirty 2B, 3B Runoff easily divertedD3 Dirty 5B, 6B, 8B Runoff not easily diverted (contains process water treatment dams)

nated runoff would be reduced by more than 50%. Thisis a substantial reduction in the quantity of stormwatercontamination.

Although considered ‘clean’, runoff from low con-tamination sub-catchments contains soil particles. Thequantity of soil particles picked up by the runoff can bereduced by:

O Increasing the vegetative ground cover this hasadditional benefits of absorbing rainfall energy, rootsholding soil in place, increasing absorptive capacityof the soil, reducing the runoff quantity as well asacting as a filter to catch sediments. Areas 4A, 4B,7B and 9B are largely open grassland. The introduc-tion of shrubs and trees is appropriate.

O Installing straw bale barriers and check dams in diver-sion channels to decrease the channel flow velocityand thereby allow sediments to settle out of the flow.A reduction of channel flow velocity would alsodecrease any erosion caused by the flow downstream.

5.1.2. High contamination sub-catchmentsThe contamination of runoff in these areas can be gre-

atly reduced by minimising the possibility of runoffcoming into contact with pollutants. Methods appropri-ate for the colliery include [6]:

O The containment of drips, overflows, leaks or othermaterial releases from vehicles, workshop areas, the


washery, and the conveyor belt. This can be achievedthrough dikes, drip pans and sumps.

O Enclosing material storage areas with curbing barriersto divert runoff around the polluted areas. This isespecially suitable for the washery and workshopareas. This can be supplemented by covering the areasto prevent precipitation falling into the curbed area.This however, requires greater capital investment.

O Ensuring trucks are well positioned to minimise spill-age of materials during loading and unloading oper-ations.

O Cleaning up or recovering a substance after it hasbeen released or spilled to reduce the potential impactof the spill before it reaches the environment.

O Controlling wind dispersion of particles through theuse of water spraying, coverings and wind breaks.The colliery only has water sprays in place on its maincoal product stockpile. Additional sprays should beplaced on three other big material stockpiles, whichare currently unprotected from the wind. Water spray-ing has the advantage of confining the pollutantswithin an area, however it does lead to contaminationof that water, which thus requires treatment.

O Trucks operating within the site should be covered inwindy conditions or sprayed with the water.

O The site roads are currently water sprayed daily. It isappropriate for those roads, which are most heavilyused are properly sealed to collect the runoff.

A major source of contamination for these areas is thecoal product and waste material stockpiles. Due to thesize of the stockpiles, methods to minimise the runoffcontamination from these areas, such as covering, wouldbe very expensive and thus considered impractical. It is,however, suggested to prevent runoff from other areasentering the stockpile areas. Runoff from the stockpileareas is highly contaminated by coal fines and shouldbe treated. Similar argument holds for the process watertreatment dam areas.

5.2. Stormwater management options

The main aim of managing the clean water runoff isto ensure that the runoff remains uncontaminated. Inaddition, it is desirable to remove the soil loading fromthe runoff and control the release of the runoff off siteto prevent downstream siltation and flooding. The mainaim of managing the dirty water runoff is to ensure thatthe runoff does not compromise the process water treat-ment system. It is also desirable to remove the coal finesload and control the release of the runoff off site to pre-vent downstream siltation and flooding. Managementoptions which would achieve, or partially achieve, thesegoals are outlined in the following sections in increasingorder of complexity and cost [7].

5.2.1. Option 1This option involves the use of diversion channels to

collect clean and dirty stormwater runoff and convey itdirectly to the natural creek system. The clean and dirtywater diversion channels may or may not be combined.For clean runoff, as the contamination is soil particlesonly, the effect on the receiving environment could argu-ably be acceptable. The use of diversion channels would,however, accumulate the flows and thus increase the riskof downstream flooding. Thus this option does not achi-eve the objectives of minimising flooding and siltationof the natural creek system. For dirty runoff, the optionis considered undesirable as it would result in the dis-charge of significant quantities of coal fines into thenatural river system. This option is however preferableto the existing method of management of both clean anddirty runoff.


collect clean and dirty stormwater runoff and convey itto the existing process water sedimentation dams (i.e.the intermediate, settlement or main dams). The cleanand dirty water diversion channels may or may not becombined. This option would provide some detention ofthe stormwater runoff, however the process water treat-ment dams have quite limited freeboard volumes. Thusthis option would run a high risk of hydraulically over-loading the process water treatment system and result inthe discharge of poorly treated process water as well aslimited stormwater treatment. However, it is possible toincrease the effective freeboard volume of the intermedi-ate dams. Thus there would be some scope to utilise theintermediate dams primarily as stormwater detentionbasins. This is the only manner in which this option ofdiverting clean or dirty stormwater to the existing treat-ment dams is considered feasible.


collect clean and dirty stormwater runoff and convey itto the process water sedimentation dams, where thesedams have been modified to increase their maximumcapacity and thus increase their freeboard volume. Theclean and dirty water diversion channels may or may notbe combined. This option involves significant structuralalterations to the sedimentation dams to increase themaximum capacity of the process water sedimentationdams. This increase can be achieved by raising theheight of the dam walls or by increasing the depth of thedams. Due to the size of the main dam, any significantalterations are considered to be of major capital expenseand hence not preferred. There is, however, some scopeto inexpensively increase the depth of both intermediateand settlement dams through excavation. Increasing theheight of the dam walls of the settlement and eastern


intermediate dams could also be relatively easily achi-eved. The additional freeboard volumes, which are esti-mated to be feasible are summarised in Table 6. Detailedcalculations are provided in Wingrove [7]. With suchmodification of the process water treatment dams,Option 3 is considered viable for both clean and dirtystormwater runoff.

5.2.4. Option 4This option involves the use of separate diversion

channels to collect clean and dirty stormwater runoff andconvey it to purpose-built clean and dirty stormwaterdetention basins. The detention basins would slowlyrelease the clarified stormwater into the natural creeksystem or into the process water sedimentation dams.This option would achieve all of the performance objec-tives exceptionally well. However, the land spacerequired and the construction costs involved are con-sidered to hinder the viability of this option. Sub-catch-ment 9B is the only area whose natural topography lendsitself to the construction of a detention basin. Completeexcavation or complete construction of dam walls wouldbe required in all other sub-catchments. If the estimatedcapital cost is justifiable, Option 4 is considered to behighly desirable.

5.2.5. Option 5This option is similar to Option 4 in that it involves

the use of separate diversion channels to collect cleanand dirty stormwater runoff and convey it to purposebuilt detention basins. However, in this option the storm-water is slowly released into holding tanks or dams tostore the clarified water for future use. As the collieryhas a surplus of water as opposed to a shortage, thisoption is considered to be unnecessary.

All of the above options are superior to the existingmanagement method which allows 88% of clean runoffto become contaminated and resulting in the failure ofthe existing process water treatment system. The diver-sion of all runoff away from the process water treatmentdams, and in particular the filter dams (filter dam wallscan collapse and be washed downstream due tooverloading) should reduce or eliminate this problem.The most appropriate and cost effective of these options

Table 6Freeboard volumes of modified process water treatment dams

Process water treatment dam Freeboard volume (m3)Existing Additional Total

feasible

Intermediate dam (east) 600 2120 2720Intermediate dam (west) 800 1800 2600Settlement dam 0 3000 3000

depends on the volume of runoff from the catchmentarea.

5.3. Clean stormwater runoff management

This section quantifies the volume of clean stormwaterrunoff, which is considered capturable and determinesthe detention times required for the soil particles to beremoved from this runoff.

Ideally, all clean runoff should be captured anddiverted. This is somewhat unrealistic due to the top-ography of the colliery site and the practical locationsof diversion channels. The total capturable volume rep-resents approximately 75% of the total volume of runofffrom low contamination areas. The total volume of run-off discharged from the four clean regions is summarisedin Table 7. Detailed calculations are provided in Wing-rove [7]. To remove soil particles from stormwater adetention time of 2 h is typically used [8]. Consideringthe modeled storm duration and the peak flowrates [7]the required detention volumes are estimated for each ofthe clean regions as in Table 7.

5.4. Dirty stormwater management

This section quantifies the volume of dirty stormwaterrunoff that is considered capturable and determines thedetention times required for the coal fines to be removedfrom this runoff. The quantification is based on the run-off volumes [7]. Similar to that of clean stormwater man-agement discussed in Section 5.3, the capturable volumeof the dirty stormwater is summarised in Table 8. Thedetention volume required for each region is also sum-marised in Table 8.

5.5. Improved stormwater management

A preferred method of management of the clean anddirty stormwater runoff has been devised. This methodis a combination of the five options outlined in Section5.2 and considers the runoff volumes established in Sec-tions 5.3 and 5.4. In all regions, the 10 yr ARI runoffvolume is considered to be the minimum design para-meter. Catering for the 20 yr ARI is considered to betoo conservative. The method is shown schematically inFig. 6 and outlined in the following sections. It shouldbe noted that the conceptual location of the diversionchannels and the detention basins is largely governed bythe topography of the site.

5.5.1. Detention basin designThe main design considerations for stormwater deten-

tion basins are the detention time and overflow rate. Thedetention volumes established in Tables 7 and 8 arebased on a 2 h detention time. An appropriate basin vol-ume is adopted using the 10 yr ARI detention volume


Table 7Total discharge volumes and detention volumes for low contamination regions

Region Contributing sub-catchments Total inflow (m3) Detention volume (m3)20 yr ARI 10 yr ARI 5 yr ARI 20 yr ARI 10 yr ARI 5 yr ARI

C1 1A, 2A, 4A 17,727 9371 5744 328 262 196C2 4B 6342 3356 2061 79 64 48C3 1B, 7B, 9B 31,634 16,724 10,240 396 317 237C4 6A, 7A, 8A 10,933 5812 3603 202 162 123

Table 8Total discharge volumes and detention volumes for high contamination regions

Region Contributing sub-catchments Total inflow (m3) Detention volume (m3)20 yr ARI 10 yr ARI 5 yr ARI 20 yr ARI 10 yr ARI 5 yr ARI

D1 3A, 5A 17,160 9162 5749 317 256 196D2 2B, 3B 9003 4835 3064 113 92 71D4 5B, 6B, 8B 21,742 11,096 6952 272 210 161

as the minimum design volume. The detention time foreach basin is thus greater than 2 h for the 5 and 10 yrARI storms and slightly less than 2 h for the 20 yr ARIstorm. To determine the area and depth of the basins theoverflow rate design criterion is used. In this criterion,it is desirable to have the overflow rate (vo) of the deten-tion basin to be less than the settling velocity (vs) of theparticles in the stormwater. The settling velocity of thesoil particles has been estimated to be 0.98 m/h (detailedcalculations are provided in [7]). The surface areas ofthe detention basins have been adopted such as to ensurevo is less thanvs. Table 9 summarises the design para-meters for the suggested detention basins. It should benoted that although five new detention basins are sug-gested for construction, the relatively small volume ofthe basins would result in low construction costs. Con-struction could be carried out by plant equipment alreadyowned by the colliery. The detention basins, which col-lect the clean stormwater runoff could be omitted andthe net effect on the natural creek system would besuperior to the effect resulting from the existing storm-water management methods. However, the benefits ofdetention basins are considered to far outweigh the costs,and thus their use is highly recommended.

5.6. Effect on process water treatment system

By implementing the measures outlined above, a sub-stantial quantity of stormwater would be diverted awayfrom the process water treatment dams. This would sig-nificantly reduce the hydraulic loading of these dams andthus the wet weather efficiency would approach the dryweather efficiency. Table 10 summarises the percentagereductions of the volume of stormwater discharged into theprocess water dam sub-catchments and the corresponding

reductions in overflow volumes from these sub-catch-ments. The following points can be noted from Table 10:

O The improved stormwater management would sub-stantially reduce the overflow volumes from all dams.

O The existing method of stormwater management isconsidered to cause the process water treatment damto fail due to higher overflow rates. Under theimproved method, the process water treatment systemwould maintain acceptable efficiency for even the 20yr ARI storm.

O For the 5 yr ARI storm, there would be no overflowfrom the process water treatment dams.

O For the 10 yr ARI storm, there would be no overflowfrom the intermediate dams and the filter dams. Thevolume of overflow from the main and settlementdams would be reduced by over 70% compared to theoverflow, which results from the existing manage-ment.

O For the 20 yr ARI storm, the overflow volume fromthe filter dams would be reduced by 95% comparedto the overflow which results from the existing man-agement. It is particularly important to maintain treat-ment efficiency of the filter dams as they play a verysignificant role in the removal of NFR from the pro-cess wastewaters. The overflow volume from theintermediate dams would be reduced by over 70% andthe overflow from the main and settlement damswould be reduced by approximately 50%.

The above significant decreases in overflow volumesindicate notably improved wet weather efficiency of theprocess water treatment system. The correspondingreduced impact on the receiving natural creek environ-ment would also be significant.


Fig. 6. Improved storm water management system for the colliery.

6. Conclusions

This paper presents a case study, which highlights thebenefits of applying waste minimisation in collieries.Both, source reduction and recycle/reuse principles of

cleaner production are applied. Source reduction con-cepts were applied to segregate the stormwater into cleanand dirty components. The dirty stormwater is then pro-posed to be diverted using diversion channels and treatedwith detention basins. These modifications were found to


Table 9Detention basin design parameters

Influent Basin Discharge to Max. capacity Surfaceare (m2) Avg. depth Detent. time (h) Overflow (m/h)region location (m3) (m)

20 yr 10 yr 5 yr 20 yr 10 yr 5 yrARI ARI ARI ARI ARI ARI

C1 4A Off site 300 200 1.5 1.83 2.29 3.07 0.82 0.65 0.49C2 4B Off site 80 80 1.0 2.01 2.51 3.35 0.50 0.40 0.30C3 9B Off site 350 233 1.5 1.77 2.21 2.95 0.85 0.68 0.51D1 5A Settlement dam 270 180 1.5 1.70 2.11 2.76 0.88 0.71 0.54D2 3B Intermediate dam 100 100 1.0 1.77 2.18 2.82 0.56 0.46 0.36

Table 10Effect of improved stormwater management on process wastewater treatment

Sub- Process water Increase in process Reduction of stormwater discharge into Reduction of process water treatmentcatchment treatment dams water treatment dams sub-catchment (%) dams overflow volumes (%)

freeboard volume (%)20 yr ARI 10 yr ARI 5 yr ARI 20 yr ARI 10 yr ARI 5 yr ARI

8A Main and settlement 43 28 28 27 47 73 1005B Filter dams 0 65 65 65 95 100 1006B Intermediate dams 280 54 74 217 71 100 100

reduce the overflow volumes of the process wastewatertreatment dams in 5 year average recurrence interval(ARI) storms by 100%, with reductions of 70–100%achievable for a 10 yr ARI storm.

Improved process water management systems are pro-posed. Relatively simple alterations to the operation ofthe coal wash filtration dams are expected to reduce theperiods of inefficient operation of these dams by 95%.The operating cost of process water pumping can bereduced by 30% resulting in a saving of operating costof the pumps by about AUS$10,000/yr.

As highlighted in this paper, often there is significanteconomic benefit resulting from the application of wasteminimisation. In addition, there is always a major benefitto the environment.

The principles and procedures used to develop theimproved methods of wastewater management for thecolliery selected in the case study can be, to some extent,applied to other coal mines by incorporating some sitespecific conditions.

Acknowledgements

The assistance provided by the mine management inproviding the information is greatly appreciated. Sincere

thanks to Mr Joe Shonhardt, University of Wollongong,for his help during the initial stages of the project. Theassistance extended by Ms Joanne George and Mr NormGal during laboratory analysis is gratefully acknowl-edged.

References

[1] Overcash MR. Techniques for industrial pollution prevention—acompendium for hazardous and non-hazardous waste minimis-ation. Michigan: Lewis Publishers Inc, 1986.

[2] Martin L. Waste reduction: the case for stopping wastes at theirsource. UNEP: Indust Envir 1986;9(4):35–7.

[3] Freeman H. Hazardous waste minimisation. New York: McGrawHill, 1990.

[4] Singh RN, Dharmappa HB, Sivakumar M. Wastewater qualitymanagement in coal mines in the Illawarra region. InternationalConference on Mining and the Environment, Bandung, Indonesia,6–7 March, 1996:9.1–9.16.

[5] Sivakumar M, Morton SGS, Singh RN. Mine water managementand control in an environmentally sensitive region. Mine WaterEnvir 1994;13(1):27–40.

[6] USEPA. Stormwater management and technology. USA: NoyesData Corporation, 1993.

[7] Wingrove K. Wastewater management in Illawarra coal mines. BEthesis, University of Wollongong, Wollongong, Australia, 1996.

[8] Field R, O’Shea M, Chin KK. Integrated stormwater managemet.Michigan: Lewis Publishers Inc, 1993.

Wastewater and stormwater minimisation in a coal mine

Documents