Coal Mining and Production

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Coal Mining and Production

Industry Description and Practices

Coal is one of the world's most plentiful energyresources, and its use is likely to quadruple bythe year 2020. Coal occurs in a wide range offorms and qualities. There are two broadcategories: (a) hard coal, which includes cokingcoal (used to produce steel) and otherbituminous and anthracite coals used for steamand power generation; and (b) brown coal (sub-bituminous and lignite), which is used mostly

as on-site fuel. Coal has a wide range ofmoisture (2-40%), sulfur (0.2-8%), and ashcontent (5-40%). These can affect the value ofthe coal as a fuel and cause environmentalproblems in its use.

The depth, thickness, and configuration ofthe coal seams determine the mode ofextraction. Shallow, flat coal deposits are minedby surface processes, which are generally lesscostly (per ton of coal) than underground minesof similar capacity. Strip mining is one of themost economical surface processes. Here

removal of overburden and coal extractionproceed in parallel strips along the face of thecoal deposit, with the spoil being depositedbehind the operation in the previously minedareas. In open pit mining, thick seams (tens ofmeters) are mined by traditional quarryingtechniques. Underground mining is used fordeep seams. Underground mining methodsvary according to the site conditions, but allinvolve the removal of seams followed by moreor less controlled subsidence of the overlyingstrata.

Raw coal may be sold as mined or may be

processed in a beneficiation/washing plant toremove noncombustible materials (up to 45%reduction in ash content) and inorganic sulfur

(up to 25% reduction). Coal beneficiation isbased on wet physical processes such as gravityseparation and flotation. Beneficiation producestwo waste streams: fine materials that aredischarged as a slurry to a tailingsimpoundment, and coarse material (typicallygreater than 0.5 millimeters (mm) that is hauledaway as a solid waste.

Waste Characteristics

Key impacts of surface mining are typicallymassive disturbances of large areas of land andpossible disruption of surface and groundwaterpatterns. In some surface mines, the generationof acid mine drainage (AMD) is a majorproblem. Other significant impacts includefugitive dust and disposal of overburden/wasterock.

In underground mines, the surfacedisturbance is less obvious, but the extent ofpossible subsidence can be very large. Methanegeneration and release can also be a problem

under certain geological conditions. Ifgroundwater systems are disturbed, thepossibility of serious pollution from highlysaline or highly acidic water exists. Impacts maycontinue long after mining ceases.

The following table presents the levels ofliquid effluents, solid waste, and dust generatedfor the major mining techniques.

Beneficiation plants produce large volumesof tailings and solid wastes. Storage andhandling of coal generates dust at rates whichcan be 3 kilograms (kg) per metric ton of coalmined, with the ambient dust concentration

ranging from 10 to 300 micrograms per cubicmeter (g/m3)(above the background level) atthe mine site.

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Coal Mining and Production 342

Loads Per Unit of Production*

ParameterSurface mining

(t/1000t coal produced)Underground mining

(t/1000t coal produced)

Mining Techniques Contour Area Conventional Longwall

Liquid effluents 0.24 1.2 1 1.6

Solid waste 10 10 3 5

Dust 0.1 0.06 0.006 0.01

Source: Based on Edgar, 1983

* (Note: Local conditions will form the basis for choosing the appropriate mining method)

Pollution Prevention and Control

Early planning and careful design of operationsare the key to minimizing pollution associatedwith mining activities. Specific responsibilities

should be assigned for the implementation andmonitoring of environmental measures. Beforemining begins, a mining plan and a mineclosure and restoration plan must be preparedand approved. These plans define the sequenceand nature of extraction operations and detailthe methods to be used in closure andrestoration. These plans should be updatedregularly (every three to five years) as miningprogresses.

Development Plan

This plan defines the sequence and nature ofextraction operations and details the methods tobe used in closure and restoration. At aminimum, the plan must address the following:


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343 Coal Mining and Production

Removal and proper storage of topsoil. Early restoration of worked-out areas and

of spoil heaps to minimize the extent of openareas. Diversion and management of surface and

groundwater to minimize water pollutionproblems. Simple treatment to reduce thedischarge of suspended solids may also benecessary. (Treatment of saline groundwatermay be difficult.) Identification and management of areas

with high potential for AMD generation. Minimize the of generation of AMD by

reducing disturbed areas and isolating drainagestreams by avoiding contacts with sulfurbearing materials. A water management plan for operations

and post-closure including minimization of

liquid wastes by methods such as recyclingwater from tailings wash plant. Minimization of spillage losses by proper

design and operation of coal transportation andtransfer facilities. Reduction of dust by early revegetation

and by good maintenance of roads and workareas. Specific dust suppression measures maybe required for coal handling and loadingfacilities such as minimizing drop distances,covering equipment, and wetting storage piles.Release of dust from crushing and other coalprocessing and beneficiation operations should

be controlled. Controlling the release of chemicals(including floatation chemicals) used inbeneficiation processes. Minimization of the effects of subsidence

by careful extraction methods in relation tosurface uses. Control of methane, a greenhouse gas, (to

less than one percent by volume) to minimizethe risk of explosion in closed mines. Recovermethane where feasible. When methane contentis above 25 percent by volume, it normallyshould be recovered. Development of suitable restoration and

revegetation methods, appropriate to thespecific site conditions. Proper storage and handling of fuel and

chemicals used on-site to avoid spillages.

Mine Closure and Restoration Plan

The plan should include reclamation of openpits, waste piles, beneficiation tailings,sedimentation basins, and abandoned mine,mill, and camp sites. Mine reclamation plansshould incorporate the following: Return of the land to conditions capable of

supporting prior land use, equivalent uses, orother environmentally acceptable uses. Use of overburden for backfill and topsoil

(or other plant growth medium) forreclamation. Contour slopes to minimize erosion and

runoff. Plant native vegetation to prevent erosion

and encourage self-sustaining development of aproductive ecosystem on the reclaimed land. Management of post-closure AMD and

beneficiation tailings.

Budget and schedule for pre- and post-abandonment reclamation activities.Upon mine closure, all shaft openings and

mine adits should be sealed or secured.There is a need to reserve money over the

life of the mine to cover the costs associatedwith mine closure. The amount of money andthe type of financing required will depend on anumber of factors such as the projected life ofthe mine, the nature of the operations, thecomplexity of environmental issues, thefinancial and environmental managementcapacity of the borrower/project sponsor, and

the jurisdiction in which the mine is located.The mine reclamation and closure plan, thetiming of its submission, and its financingshould be discussed and agreed with theborrower/sponsor as early as possible.

Target Pollution Loads

Implementation of cleaner production processesand pollution prevention measures can provideboth economic and environmental benefits. Thetarget loads presented in the WasteCharacteristics Section should be used as a

guide for pollution prevention purposes. Thefigures relate to each of the productionprocesses before the addition of pollutioncontrol measures.

There is a need to reserve money over thelife of the mine to cover the costs associatedwith mine closure. The amount of money andthe type of financing required will depend on a


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Liquid Effluentsnumber of factors such as the projected life ofthe mine, the nature of the operations, thecomplexity of environmental issues, thefinancial and environmental managementcapacity of the borrower/project sponsor, andthe jurisdiction in which the mine is located.The mine reclamation and closure plan, thetiming of its submission, and its financingshould be discussed and agreed with theborrower/sponsor as early as possible.

Settling ponds to catch stormwater and toreduce suspended solids should be provided forall effluent before discharge from the site.

Where treatment of AMD or other effluentsis required, the following effluent levels shouldbe achieved during operation and after mineclosure.

Acid Mine Drainage and Liquid Effluentsfrom Coal MiningEmission Guidelines

Parameter

Maximum valuemilligrams per liter

(mg/L) except for pH)

pH 6 - 9

Total suspended

solids*

50

Oil and grease 10

Iron 3.5

Total metals 10

Emission levels for the design and operation ofeach project must be established through theEnvironmental Assessment (EA) process, basedon country legislation and the PollutionPrevention and Abatement Handbook as applied to

local conditions. The emission levels selectedmust be justified in the EA and acceptable toMIGA.

The following guidelines present emissionlevels normally acceptable to the World BankGroup in making decisions regarding provisionof World Bank Group assistance, includingMIGA guarantees; any deviations from theselevels must be described in the projectdocumentation.

* A level of 35 mg/L should be the monthly average.

Ambient Noise

Noise abatement measures should achieveeither the following levels or a maximumincrease in background levels of 3 dB(A).Measurements are to be taken at noise receptorslocated outside the project property boundary.

The guidelines are expressed asconcentrations to facilitate monitoring. Dilutionof air emissions or effluents to achieve these

guidelines is unacceptable.All of the maximum levels should be

achieved for at least 95% of the time that theplant or unit is operating, to be calculated as aproportion of annual operating hours. Ambient Noise

Maximum Allowable Leq(hourly), in dB(A)

Receptor Daytime

07:00 - 22:00

Nighttime

22:00 - 07:00

Residential;institutional;

educational

55 45

Industrial;commercial

70 70

Air Emissions

Controls may be required on individual sourcessuch as ventilation exhausts if they have asignificant effect on ambient particulate levels.If coal crushers or dryers are used, fabric filtersor other systems should be used to recover coal

and reduce particulate emissions to levels below50 milligrams per normal cubic meter(mg/Nm3).

The emission requirements given here can beconsistently achieved by well-designed, well-


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operated and well-maintained pollution controlsystems.

Monitoring and Reporting

Frequent sampling may be required duringstart-up and upset conditions. All wastewaterdischarges from the operations should bemonitored weekly for pH, total suspendedsolids, and oil and grease. A full analysiscovering iron and other trace metals should becarried out quarterly. Where salinity is apotential problem, appropriate parameters(chloride, total dissolved solids (TDS),conductivity) should be monitored.

Ambient air levels of particulate material,including PM10 (particles less than 10 microns insize), in and around mining operations should

be measured quarterly. Methane levels shouldbe monitored where appropriate, at leastannually even after mine closure.

Monitoring data should be analyzed andreviewed at regular intervals and comparedwith the operating standards so that anynecessary corrective actions can be taken.Records of monitoring results should be kept inan acceptable format. These should be reportedto the responsible authorities and relevantparties, as required, and provided to MIGA ifrequested.

Key Issues

The following box summarizes the keyproduction and control practices that will leadto compliance with emission guidelines.

Develop and implement a comprehensive

environmental and mine management plan

to include:

- Restoration and rehabilitation of disturbed areas.

- Minimize land subsidence.

- Identification and management of AMD sources.

- Water management for operations and post-closure

conditions.

- Management and sealing of pyrite containing piles

to reduce AMD formation.

- Develop and implement a post-closure plan to

include:

Restoration of disturbed areas.

Long-term geotechnical and geochemical stability

of waste piles.

Restoration of acceptable long-term surface- and

groundwater flow patterns.

Further Information

The following are suggested as sources ofadditional information (these sources areprovided for guidance and are not intended tobe comprehensive):

Edgar, T.F. 1983. Coal Processing and PollutionControl. Houston: Gulf Publishing.

Hartman, Howard L. (ed.) 1992. SMEEngineering Handbook. 2nd ed., Vol.2. Littleton,Colorado: Society for Mining, Metallurgy, and

Exploration.

World Bank, Environment Department. 1996."Pollution Prevention and Abatement: CoalMining." Technical Background Document.

Coal Mining and Production

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