best practices in abandoned mine land reclamation:...

Best Practices in Abandoned Mine Land Reclamation:

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Colorado Division of Minerals and Geology

published by the state of colorado

Department of Natural ResourcesDivision of Minerals and Geology

2002

For additional copies of this manual pleasecontact the Division of Minerals and Geology

at 303.866.3567 or by writingDivision of Minerals and Geology

1313 Sherman St

Rm 215

Denver CO 80203

This manual is also available as a PrintableDocument Format (PDF) file on the Internet

at www.mining.state.co.us/bmp.pdf

T A B L E O F C O N T E N T S

Introduction

Purpose 3How to Determine if an Area was Impacted

by Past Mining 4Past Mining and its Impact on You 6

MILL TAILINGS AND MINE WASTE

General Information

How to Test and Evaluate Drainages and Tailings in Previously Mined Areas 10

Solutions to Problems Created by Past Mining 11Flow Chart for Mine Waste Pile Remediation 12Flow Chart for Mill Tailings Remediation 13

Best Management Practices

Diversion Ditches 14Mine Waste Rock/Tailings Removal and

Consolidation 16Stream Diversion 18Erosion Control by Regrading 20Capping 22Vegetation 24Aeration and Settling Ponds 26Sulfate-Reducing Wetlands 28Oxidation Wetlands 30Treating Acid Mine Drainage 32

HAZARDOUS OPENINGS

General Information

Types of Openings 34Safeguarding and Reclamation Alternatives 35

Best Management Practices

Barriers 36Plugs 38Structural Seals 40

1

Most of the mining of gold, silver, lead, zincand other metals occurred in the ColoradoMineral Belt from 1860 to 1975, althoughsome mining operations are still active today.Mining practices during the early days allowedthe mine owners to simply abandon theirmines without consideration of the impact onstreams, water quality, slope stability and safe-ty. Often old mining properties within theColorado Mineral Belt contain abandonedmine workings, mine waste and/or mill tailings.

Best Practices in Abandoned Mine Land Reclamation

2

Introduction

Map of minerals found in Colorado

● coal ● uranium ● other minerals

Accessible mine openings and associat-

ed mine workings can be a safety haz-

ard and a liability on the part of the

landowner if someone is injured or

killed in them.

Mine waste is the rock taken from a

mine that is of no economic value.

Although some consider mine waste

piles to be aesthetically pleasing

because of their historic nature, these

piles are generally difficult to vege-

tate and may pollute adjacent streams.

Mill tailings are the waste product of

ore-processing facilities. Mill tailings

generally exit the mill as slurry and in

the past were deposited wherever con-

venient, usually in a stream valley.

Because mill tailings consist of very

small particles they are highly suscep-

tible to erosion or removal by wind and

water. In addition, areas covered by

mill tailings are generally difficult to

vegetate, due to the high concentra-

tion of heavy metals and acidity asso-

ciated with waste materials high in

pyrite.

Purpose of this Manual

This manual was compiled to assist people in:determining if an area has been impacted

by past mining;determining the extent of environmental

problems caused by past mining;providing options to address the environ-

mental and safety problems caused bypast mining, especially those posed bywaste rock dumps, mill tailings piles, andhazardous openings;

providing a list of contacts to acquire addi-tional information about reclamationpractices and current regulations gov-erning environmental problems associat-ed with properties mined in the past.

Introduction: Purpose of this Manual

3

accessible openings into the rock or soil;

piles of barren, unnatural-looking discoloredrock (often yellowish or reddish);

large areas of barren, brown or gray sandy orfine-grained material;

drainage from suspected mine openings (even if collapsed);

drainage from the base of a waste rock pile;

drainage from the low point of a mill tailings pile;


4

How do you determine if an area has been impacted by past mining?Walk the area and look for evidence of past mining activity, such as

pools of discolored (often orange/red) wateron barren, sandy or fine-grained soil;

areas of dead vegetation;

waste piles in winter after snowfall, when snowmelts more quickly than on surroundingareas;

Introduction: Past Mining and its Impact on You

5

If you suspect past mining activity, additionalinformation can often be obtained from thefollowing sources:

the town or county in which the property lies;mining/environmental groups in the area;county health departments;local watershed groups;local libraries;Colorado Division of Minerals and

Geology, Inactive Mine ReclamationProgram (303-866-3567)

Colorado Department of Public Healthand Environment, Water QualityControl Division (303-692-3500)

Bureau of Land Management MineralClaims Database (Public Room, 303-239-3600)

Old mine maps and maps showing locationsof old mills are sometimes available throughthese sources. Water quality information fromprevious testing is available through the Colorado Department of Public Healthand Environment, the county health depart-ment, local stakeholders groups and the stategovernment agencies listed above.

If you suspect that past mining has occurredin an area but cannot locate any informationabout mining in the area, it does not neces-sarily mean no mining occurred. Thousandsof unpatented claims and small exploratorymining operations throughout Coloradoexist, most of which were never recorded instate or local government offices.

Why should you be concerned if your propertywas impacted by past mining?In some cases, the impact of past mining onyour property may affect adjacent propertiesand/or nearby streams. In many cases, thisinitiates complaints from the local govern-ment or adjacent landowners. In other cases,government agencies may be involved ininvestigation and clean-up of a property adja-cent to yours. Additionally, if your propertyhas been impacted by past mining, you may berequired to participate in the clean-up plan.

Both state and federal agencies have regula-tions pertaining to abandoned and activemines.

Regulations are continually revised. Contactthe Colorado Department of Public Healthand Environment, Water Quality ControlDivision and the Environmental ProtectionAgency for details on the current regulationspertaining to mine and mill sites.

What are the problems caused by past mining?Historical mining operations cause problemsin three general areas:

Unsafe mine openings: Underground mines areaccessed either by vertical shafts, inclinedshafts or horizontal portals. A vertical shaftcan be hundreds of feet deep and may not beobvious until you are standing next to it. Inaddition, the ground next to the shaft may beunstable. Inclined shafts and portals aresomewhat less hazardous, but the groundaround them may also be unstable.

Inactive mines are not ventilated, and there-fore are likely to contain stale, oxygen-defi-cient air and possibly poisonous and evenexplosive gases. Old mine workings shouldNEVER be entered without properly trainedpersonnel equipped with the proper safetyequipment.


6

Past Mining and itsImpact on You

Drainage from an abandoned mine adit

Abandoned mine shaft with ineffective

fence and collapsing walls

Contamination of streams by acidic drainage: Acidicwater (commonly called acid mine drainage)forms from the chemical reaction of surfaceand ground water with rock containing sulfur.The product of this reaction is sulfuric acid,which then leaches metals (iron, copper, zinc,manganese, cadmium and lead) from mineral-ized rock and keeps the metals dissolved in thewater. This acidic metal-laden drainage canadversely impact aquatic and human healthwhen it enters the surface and groundwatersystems. Elevated levels of metals can cause fishand other aquatic life to die and drinking andagricultural water sources to be contaminated.

Much of the rock associated with mines andore deposits in the Colorado Mineral Beltcontains pyrite, a sulfur-bearing mineral, soacid mine drainage from past mining opera-tions is common. Acid mine drainage canform in mines and in water percolatingthrough waste rock dumps and mill tailingspiles.

Contamination of streams by excess sediment: Sedimentrelated to mining and milling activities con-sists of small particles that often contain highconcentrations of heavy metals. Because of thetoxic nature of this sediment, plants do notreadily grow on it, and as a result, it is easilyremoved and transported by water and wind.Mining-related sediment can contaminatestreams, rivers, wetlands and other riparianareas. Heavy metals in the sediments arereleased into the water in streams and ponds,poisoning the fish and other aquatic crea-tures. The mill tailings particles can destroyaquatic habitats by covering the stream bottomand suffocating the fish eggs, by filling inpools which serve as fish habitat. Sediment canalso affect suitability of the water for humanuses such as agriculture and drinking water.


7

Mill tailings being eroded by an

adjacent stream

Acid Mine drainage containing

heavy metals

What is the extent of the problems caused by pastmining on your property?Unsafe Mine Openings: Any open mine workingson your property are a potential liability. Suchopenings can be unstable and possibly containoxygen-deficient air or poisonous gases.These openings should be approached withcaution. Investigation of these openingsshould begin with a search for information atthe local library, county offices, local min-ing/environmental groups or the ColoradoDivision of Minerals and Geology, InactiveMine Reclamation Program. If access into anabandoned mine is necessary, the investiga-tion should be conducted by someone prop-erly trained and familiar with the necessarysafety precautions.

Draining Mine Openings: If drainage is comingfrom a mine opening on your property, it maybe contaminating adjacent streams. Warningsigns that the drainage may be acidic and con-tain metals include dead vegetation orred/orange staining on the rocks and soil inthe area where the drainage exits the mine.This drainage water should be tested to evalu-ate its pH (acidity) and metals content. Twosimple inexpensive tests are described laterand will provide a preliminary assessment ofthe nature and extent of contamination in thedrainage at your site.

Waste Rock Piles: The extent of the problemscaused by waste rock piles or dumps dependslargely on their location.

A waste rock pile located away from streamsand ponds that are well or moderately-wellvegetated with no visible staining of theground at the lower end, is probably not a sig-nificant problem to the environment andneeds no further action.

A waste rock pile located away from streamsand ponds that are not well vegetated andshows signs of staining and/or dead vegetationat the lower end, may be contributing metalsto the groundwater system.

A waste rock pile located in a stream ordrainageway may be contributing metals andlowering the pH of the stream as it percolatesthrough the rock.

A waste rock pile located directly below a col-lapsed or uncollapsed mine opening that isdraining may be contaminating the minedrainage further as it flows through andleaches the waste rock.

If there is drainage from a waste rock pile, thedrainage should be tested to evaluate its effecton adjacent streams and groundwater.Samples from above or upstream of the wastedump and below or downstream of the waste


8

Snowmelt and rainfall percolating

through old mine waste has killed the

vegetation downhill

Ineffective Barrier at an abandoned

coal mine allowing access to the

workings

dump should be tested using the simple inex-pensive tests suggested later for pH and met-als. The results should then be compared toassess the impact of the pile on the drainage.

Mill Tailings: Because mill tailings were general-ly in a slurry form when originally deposited,they are almost always located in a stream val-ley or depression where water collects.Evaluating the extent of the problem caused bytailings requires determination of their exactlocation, current condition and whether theyare being eroded and transported off the siteby wind or water. Some questions to be con-sidered are:

Are they wet or dry?

Are they located directly in a flowing stream?

Are they sitting in a depression filled with water?

Is there vegetation on the mill tailings? Is it alive or

dead?

Are there drainage paths on the surface of the tailings?

Are there pools of discolored water on the top of the

tailings?

Is there drainage coming from the lower end of the tail-

ings?

Is the water in the stream below the tailings cloudy?

Is there white, gray, or light brown fine sediment (tail-

ings) in amongst the rocks and pebbles of the stream

below the tailings?

Do the tailings create dust when the wind blows?

Tailings escaping from their present location: tailingscan escape either by erosion into a stream orby blowing in the wind, posing a problem.Likewise, if the water coming from the tailingsis contaminated, the tailings may be a prob-lem. Water pooled on the tailings and drain-ing from the lower end of the tailings and inthe stream below the tailings should be testedto evaluate the impact of the tailings on thesurrounding environment. The pH and met-als content of the tailings should also be test-ed. Three simple, inexpensive tests aredescribed on the next page. These will helpyou do a preliminary assessment of the natureand extent of the problem.


9

MOST IMPORTANT FOR ALL TESTS: Forany test, be sure to write down the date, time,exact sample location, results of your test andany observations you make at the sample loca-tion or during the test and save that informa-tion. It could save you money in the future.

1. A simple test of pH (how acidic the water is):

This test will provide an estimate of the pH ofthe water. The pH scale ranges from 0 to 14. ApH of 7 is neutral. A pH reading below 7 indi-cates the water is acidic. A pH reading above 7indicates the water is alkaline. Rainwater is nat-urally between pH 6 and 7 in most areas.Drainage directly affected by mining is oftenlow pH indicating that it is acidic, although insome drainages the pH is high, indicating alka-line conditions. This test can be done by pur-chasing pH or litmus paper at a drugstore,hobby shop, hardware store or scientific supplystore. Follow the directions on the litmus paperpackage and stick the paper into the drainagewater. If the resulting pH is either less than 5(acidic) or greater than 9 (alkaline), thisdrainage may be causing problems to the envi-ronment. If the water you are testing is in a fast-moving stream, get a small sample of the waterin a clean jar and then put in your pH (litmus)paper.

HINT: You probably will want to test duringboth low-flow (fall) and high-flow (spring)conditions and compare the results. Be sure towrite down the date, time, exact sample locationand results of your test.

2. A simple test to evaluate whether metals are present in

the water:

Often, a visual inspection of the drainage willindicate metals in the drainage. A red/orangecoating on the rocks indicates that the drainagecontains high iron. A black coating on the rocksindicates high manganese. A green/blue coat-

ing indicates either high copper or high silver.A white coating indicates high aluminum. Notethat other metals may also be present in lesserquantities, but their signature may be maskedby high iron or some other metal.

The following simple test of the drainage water can be per-

formed to indicate the presence of metals (however, it will not

differentiate which metals are present and which are not):

Obtain about one cup of the drainage in a cleandry glass jar or coffee cup. Add about one tea-spoon of baking soda, swirl the mixture around,then let it sit and watch to see if the baking sodawill completely dissolve. it will do so in good,clean water. However, if a fluffy sediment forms(precipitates) and collects at the bottom of thesample jar, that is an indication that there aremetals in solution in the water.

If metals are present, the next step is to have amore comprehensive test performed on thedrainage water by a water-testing lab. Call the labto find out about the procedure for sampling thedrainage. The new sample should be tested for atleast cadmium, copper, iron, lead, manganeseand zinc. This test is generally about $125.

3. A simple way to evaluate the contamination of the

tailings:

This method will allow you to test the pH andmetals content of mill tailings. Collect a sampleof tailings (about one cup) and place it in adoubled coffee filter over a strainer over a cleanglass or ceramic dish, jar or bottle. Pour aboutone cup of distilled water into the tailings andcollect the drainage that exits from the base ofthe coffee filter in the dish, jar or bottle. Testthis drainage using the two tests discussed abovefor pH and metals. Because the tailings will varyin degree of mineralization, you should collectand test samples from at least 10 locations in thetailings pile. Samples should be taken from


10

Three Simple,Inexpensive tests toEvaluate the drainageand Tailings in Previously Mined Areas

within the tailings (dig a hole!), as well as fromthe surface of the tailings.

What are feasible solutions to problems caused bypast mining?Feasible solutions to the impacts of past min-ing are called “Best Management Practices” orBMPs. Often, incorporation of only one BMPwill solve a particular problem. Sometimes,several BMPs must be incorporated. A list ofcommonly used BMPs is shown below. Thislist offers many different solutions that canapply to a wide variety of problems and involvevarying amounts of construction and mainte-nance, and a range of costs. Each of thesesolutions is described at the end of thisbrochure. In some cases, a description of theconstruction of the BMP is included.

Hydrologic Controls: Most hydrologic controls arepreventive measures. The goal of these BMPsis to inhibit the process of acid formationand/or heavy metal dissolution. If hydrologiccontrols can minimize or even eliminate waterfrom entering a mine or coming into contactwith sulfide rocks, waste rock or tailings, theycan be the best, most cost-effective reclama-tion approach because they eliminate thecause of the problem rather than treating thesymptoms.

BMP #1: diversion ditchesBMP #2: mine waste rock/tailings removal

and consolidationBMP #3: stream diversionBMP #4: erosion control by regradingBMP #5: cappingBMP #6: revegetation

Passive Treatment: Passive treatment generallyrefers to a range of drainage treatment tech-niques that do not require continuous electri-cal or chemical inputs or frequent mainte-

nance. These methods do not eliminate thecause of the problem, but in many cases, maybe the only feasible alternative to address theproblem.

BMP #7: aeration and settling pondsBMP #8: sulfate-reducing wetlandsBMP #9: oxidation wetlandsBMP #10: other BMPs to treat acid mine

drainage

Costs: Costs of BMPs vary widely from year toyear and location to location, however, a sheetshowing the general range of costs for some ofthe elements of the BMPs discussed in thisbooklet is available from the ColoradoDivision of Minerals and Geology, InactiveMine Reclamation Program.

What is the best solution for your problem?

General flow charts for determining possiblesolutions for mine waste and tailings pileproblems are provided in the next two pages.These charts are designed to guide you to pos-sible alternatives. Conditions at each site,however, will vary.

Who can you contact if you have questions?

Questions about the mining-related prob-lems discussed in this booklet should bedirected to the following agencies.

Colorado Division of Minerals andGeology

Inactive Mine Reclamation Program303-866-3567

Colorado Department of Public Healthand Environment

Water Quality Control Division303-692-3500

General Information: Solutions to Problems Created by Past Mining

11


12

MINE WASTE PILE REMEDIATION

Goal: Keep water away from mine waste

General Information

13

MILL TAILINGS REMEDIATION

Goal:Keep water away from mill tailings

BMP #1 - DIVERSION DITCHES

Applicable situations:waste rock pilesmill tailingsdraining mine openings

Description and purpose

Diversion ditches are effective where the qual-ity of rainwater, snowmelt or surface flow isdegraded by flowing over or through minewaste, tailings or into mine workings.Diversion ditches can also be used to interceptshallow groundwater that may enter a minewaste or tailings pile.

How to do It

A diversion ditch should be located upstreamof the contaminated waste rock or tailingspile, and should capture and channel theclean water from uphill around the problem,as shown in Maps A&B. Because the only goalof the ditch is to keep clean water away fromcontaminated rock or tailings, the length ofthe ditch depends on the size of the contami-nated pile and the topography of the site. Theends of the ditch should be in a place where

clean water will flow away from, and not comein contact with, the contaminated pile.

The size of the ditch generally depends on howmuch water is expected. The simplest ditchesare dug either by hand, using a backhoe, orusing the corner of a bulldozer blade to make atriangular cut. Care should be taken to dig deepenough to catch incoming shallow groundwateras well as water flowing on the surface whenusing any of these methods. The side walls ofthe ditch should be smoothed to a slope of 2:1(two feet horizontal to one foot vertical) or flat-ter to maintain stability, as shown in Drawing 1.

Ideally, the slope or gradient of the bottom ofthe ditch should be designed to encouragewater to flow freely, while not ponding, but


14

Best ManagementPractices

2 ft.

1 ft.DIVERSIONDITCH

UNCONTAMINATED WATERUNCONTAMINATED WATER

TAILINGS PILE

CONTAMINATEDWATER

STREAM FLOW STREAM FLOW

DIVERSION DITCH

TAILINGS PILE

CON

TAM

INATED

WATER

UNCONTAMINATED WATERUNCONTAMINATED WATER

DRAWING 1 (at top right)- Cross section of a diversion ditch showing side slopes at 2:1. To maintain stability, side slopes

should be at 2:1 or flatter. MAPS A & B (above)- Simplified views of a tailings pile and the quality of surface water flow-

ing into a nearby stream. (Also applies to waste rock piles.) Map A shows that uncontaminated surface water originating

uphill of the tailings pile will become contaminated after flowing across or through the contaminated pile. Map B shows that

a properly placed diversion ditch will channel the water originating uphill of the pile away from the pile to avoid becoming

contaminated. The amount of contaminated flow downhill of the tailings pile entering the stream is then greatly reduced.

Map A Map B

not flow so fast that water erodes and scoursthe ditch walls. In order to accommodate this,a minimum slope of 100:1 (100 feet horizon-tal to one foot vertical) and maximum slope of33:1 (33 feet horizontal to one foot vertical) isrecommended. The bottom of the ditchshould be smooth with no pits or holes.

The ditch should be vegetated to slow thewater flow and decrease the opportunity forerosion of the ditch by moving water. Seedingof the ditch walls and bottom is easiest duringlow flow times of the year such as late summeror fall. Recommendations for vegetation arediscussed in BMP #6 of this brochure.

If the slope of the ditch must be greater than33:1, then the ditch should be lined withriprap (medium to large rocks) to slow theflow of water and decrease the erosion andscouring along the ditch walls. If riprap isused, it is important to select rocks that arenot contaminated by mining and will notdegrade the water in the ditch. Often in high-altitude areas, suitable rocks can be found atthe base of steep talus slopes.

When to do it

Construction is generally easiest when per-formed during low flow times of the year, suchas late summer or fall.

Considerations

Although in most cases, water that flowsthrough a mine waste pile will degrade inquality, in a few cases water quality willremain the same or even improve. There-fore, it is important to sample the waterabove and below the pile to determine thechanges in water quality before doing anyditch construction.

Initial costs

Cost of diversion ditches will vary dependingon their length and the equipment used toconstruct them.

Maintenance

Periodic inspection and maintenance isrequired for continued effectiveness of diver-sion ditches. Water should flow smoothlyalong the base of the ditches and should notoverflow the ditch walls. Ditch maintenanceshould include cleaning debris out of theditches, checking that there is a constant dropin slope of the ditch bottom, and repairingerosion along ditch walls. Generally, inspec-tions should be conducted before and afterspring runoff and after major storm events.

Best Management Practices: Diversion Ditches

15

Diversion ditch in rocky area Diversion ditch lined with riprap

BMP #2 - MINE WASTE ROCK/TAILINGS REMOVAL

AND CONSOLIDATION

Applicable situationswaste rock located in direct contact with

flowing water or pondmill tailings located in direct contact with

flowing water or pond


The purpose of this BMP is to move the reac-tive material in the waste rock dump or tail-ings pile away from water sources. Reducingthe potential for water flow through the dumpor pile will decrease the formation of contam-inants, thereby reducing contamination tonearby water sources.

Removal and consolidation are effective wherethere are several small waste piles in an area,or where there is a large pile in direct contactwith flowing water. The method is simply toisolate reactive material away from watersources.

How to do it

An area must be found that is away from watersources and avalanche chutes that can hold thevolume of waste rock or tailings to be relocat-ed. The area must be cleared of topsoil andorganic material and contoured to hold thewaste rock or tailings. A compacted berm orsmall dam may be required on the down-

stream side if the material to be relocated issaturated or will tend to flow. Material exca-vated during preparation of the consolidationarea can be used to build the berm or set asideto be used later as a cap for the consolidatedpile. Relocation of the waste rock or tailingsmay require the use of backhoes, excavators,loaders and dump trucks depending on theamount of material to be removed and thedistance between the original site of the mate-rial and the consolidation area. The consoli-dated pile should be capped, preferably usingtopsoil and excavated material, and vegetatedto prevent erosion. Capping and vegetationtechniques are discussed in BMP#5 and #6.

Regrading and vegetation of the original siteof the waste rock or tailings should also beperformed to minimize erosion on the dis-turbed area. These are discussed in BMP #4and 6.

When to do it

The optimum time to do this BMP is duringthe driest time of the year (generally late sum-mer or fall), simply for ease of excavation andtransport.


16


Relocated mine waste prior to final

grading and capping

Bulldozer creating a pit for relocating

waste rock

Considerations

There are two major considerations in thisBMP:

the amount of waste rock or tailings to bemoved; and

the identification of an adequately large,relatively nearby, dry and safe area inwhich to place them.

Careful evaluation of both of these consider-ations is necessary to determine the bestcourse of action. Waste rock and tailings relo-cation can be expensive, depending on howmuch must be moved, how moist it is, andhow far it must be moved.

The other alternative in the case of waste rockor tailings located in a flowing stream is tomove the stream (see BMP #3 in thisbrochure). However, this is often also veryexpensive and may not provide a permanentsolution, depending on the configuration ofthe valley and the stream dynamics.

The other alternative in the case of waste rockor tailings located in a pond is to drain thepond, thus drying up the area.

Initial costs

Cost of this BMP will vary greatly dependingon the volume of material to be moved and the

distance between the original site and theconsolidation area.

Maintenance

Periodic inspection of the consolidated pile,especially the cap and berm or dam holdingthe material, should be conducted to ensurethat excessive erosion is not occurring.Prompt repair in eroded areas is essential tomaintaining this BMP.

Occasional visits to the site of the original pileshould be made, especially if the entire pilewas not removed. Additional work to protectthe remaining waste rock or tailings pile maybe necessary to reduce its exposure to water.

Best Management Practices: Mine Waste Rock/Tailings Removal and Consolidation

17

Consolidated waste rock site after

capping and revegetation

BMP #3 - STREAM DIVERSION

Applicable situationswaste rock pile in direct contact with flow-

ing stream with no place to remove andconsolidate pile;

mill tailings in direct contact with flowingstream with no place to remove and consolidate pile.


Stream diversion involves relocating a streamaway from a waste rock dump or tailings pile.Reducing the potential for water flow throughthe reactive materials in the dump or tailingspile will decrease the input of contaminantsinto the stream.

How to do it

The construction of this BMP depends large-ly on the configuration of the stream valley. Ingeneral, the valley must be wide and flat tomaintain a reasonable distance between thestream and the contaminated rock or tailingswhen finished. Also, the new stream align-ment should not be placed on bedrock andshould be slightly deeper than the existingstreambed to encourage the stream to stay inits new channel. Stabilizing measures may beneeded along the bank of the new streambedand could include willow plantings, emplace-ment of tree stumps, riprap and berms.

An effort should be made to make the envi-ronment of the new stream segment similar tothat of the abandoned stream segment. Nativevegetation should be planted or transplantedalong the new stream segment. Depending onthe length of the new stream alignment,meanders should be incorporated, especiallyif there were meanders in the original streamsegment.

The waste rock or tailings that is now in theabandoned streambed will still be susceptible toerosion from rainfall, snowmelt and wind, andtherefore should be capped and vegetated tominimize erosion (see BMP #5 and 6) .

When to do it

The optimum time to construct this BMP isduring the lowest flow of the stream (general-ly late summer or fall), simply for ease of con-struction.

Considerations

Initially, the major consideration for thisBMP is the presence of a suitable place toreroute the stream. With time, streams willfind the easiest way down a slope. Moving astream generally requires major excavationwork and often construction of stabilizingmeasures, such as extensive planting, bermsand riprapped banks. In addition, rerouted


18


New stream channel under

construction

Mine waste being eroded by a stream

streams will often move back into their origi-nal configuration during high flow events,because it was the easiest route down original-ly. Therefore, in most cases it is preferable (interms of initial construction costs and long-term maintenance costs) to move the wasterock pile or tailings pile away from the streamrather than to move the stream.

If stream relocation is the best option, theArmy Corps of Engineers should be contactedat the beginning of the planning process toobtain a 404 permit. The effect of streamrelocation on the surrounding area is animportant consideration and will be addressedas part of the 404 permit.

Initial costs

Costs for this BMP will vary depending on theconfiguration of the valley and the location ofthe waste rock or tailings with respect to thestream.

Maintenance

The new configuration of the stream shouldbe checked several times during the year,especially after high-flow events, such asspring run-off and flooding due to sum-mer/fall thunderstorms, to ensure that thestream is remaining in its new alignment.Areas of excess erosion and possible break-

through into the old stream alignment shouldbe repaired immediately.

Points of drainage from the old waste rock ortailings should be identified and sampledthrough time. Tailings would be expected tocontinue to dewater over several years becauseof their small grain size. If the drainage doesnot decrease over time, the possibility of aburied spring or mine opening should beconsidered, and the appropriate BMPs shouldbe installed.

Best Management Practices: Stream Diversion

19

Stream in new channel separated from

waste rock by relocated road

BMP #4 - EROSION CONTROL BY REGRADING

Applicable situationswaste rock pilesmill tailings


Erosion occurs as a result of many thingsincluding water, wind, frost and animal action.Generally slopes with less than three feet hori-zontal to one foot vertical are stable from erosion and conducive to vegetation growth.

Often an area that has been barren for a longtime is highly dissected by water erosion andmay be susceptible to wind erosion and frostaction. An area such as this requires regradingto make the surface more uniform and gentlysloping.

How to do it

Because the ultimate goal is to have a gentlysloping surface, natural debris, such as treetrunks and stumps, and metal debris shouldbe removed prior to regrading. If the naturaldebris is regraded into the new slope, the dirtabove the debris will settle as it decays andcould leave a hole or low spot allowing water topond. Pooled water can seep in and leachthrough the reactive waste rock or tailings, andresult in acidic drainage with high metals con-tent being discharged into the surroundingenvironment.

Regrading generally requires the use of heavyconstruction equipment, such as bulldozers,scrapers, loaders, backhoes and excavators tofill the holes and grade the slope. Note thatthe surface of the final slope should be moderately roughened to help in establishingvegetation, but not so rough as to promotepooling of water.

When to do it

The optimum time to construct this BMP isduring the driest time of the year (generallylate summer or fall), simply for ease of con-struction. Experience shows that wet tailingsare not conducive to heavy equipment traffic.

Considerations

This BMP is generally followed by vegetationof the waste rock or tailings if the waste rock ortailings is not too toxic and can support theestablishment and growth of vegetation (seeBMP #6). In cases in which the waste rock ortailings is toxic and cannot support vegeta-tion, regrading is followed by capping andvegetation (see BMP #5 and 6).

The potential for erosion can be reduced bycreating grooves across the slope (or perpendi-cular to the slope direction). This can be doneeasily on the last pass of the heavy equipment


20


Newly-reclaimed slope roughened to

help in establishing vegetation

Mired down in wet tailings!

using a track vehicle running up and down theslope.

Initial costs

Costs for regrading vary depending on the sizeand slope of the area, how much debris ispresent, and the wetness of the soil or tailings.

Maintenance

Periodic inspections should be conducted toidentify holes, pits and areas of erosion thatmay have formed due to scouring water, windor burrowing animals. These areas should berepaired quickly to minimize the chances forfurther erosion.

Best Management Practices: Erosion Control by Regrading

21

Gullies in a regraded slope

BMP #5 - CAPPING



Capping of waste rock or tailings is a protec-tive layer of soil, graded to promote runoffrather than infiltration into the reactivematerials. Any minor water or wind erosionthat occurs will remove soil from the cap andshould not disturb the contaminated wasterock or tailings. This will ultimately improvethe water quality downstream of the waste rockor tailings pile, by eliminating the source ofcontamination.

The cap will also provide an uncontaminatedsoil layer in which vegetation can grow.Vegetation of the cap will further protect thesoil and decrease erosion of the cap by slowingthe speed at which raindrops hit the soil.

How to do it

Caps range from simple to complex in designand vary widely in cost. The different types ofcaps depend on the toxicity of the material tobe capped and what materials are available ator near the site. In the majority of cases, sim-ple covers are adequate. Composite covers areused when the material is highly reactive ifmixed with surface water. Complex caps areused in situations of highly toxic materials andare often combined with liners under thetoxic material.

Simple cover: The simplest, least expensivetype of cap consists of soil obtained at the site.A minimum of six inches is desirable, becausesome erosion may occur before vegetation isestablished. One foot or greater is optimum.Often, the excavation of diversion ditches will

provide the necessary soil for a cap. Glacial tillor a good mix of clay, sand and organic mat-ter is ideal. Sometimes a site will have sand inone area and clay in another, which can bemixed. The cap should be graded to a gentleslope to encourage runoff. No extra effortshould be made to compact the soil. Thematerial will be sufficiently compacted by theequipment used to grade the cap. The surfaceof the slope should be left moderately rough-ened to enhance vegetation, but not so roughas to promote pooling of water. Once inplace, the cap should be vegetated (see BMP#6).

Composite cover: A composite cap has at leasttwo layers of different soil types. The lowerlayer lying next to the waste rock or tailings isfine-grained, high density and low perme-ability. The purpose of this layer is to inhibitwater from the surface from seeping into thecontaminated pile and forming acid drainage.The upper layer consists of coarser materialand is lower in density. The purpose of thislayer is to encourage plant growth. This capshould be vegetated once it is in place (seeBMP #6).

Complex cover: A complex cover consists ofinterlayered synthetic filter fabrics and fineand coarse material. The principles of this capare the same as the simple and composite caps,that is to inhibit water infiltration into the


22


Grading waste rock prior to capping

reactive material below and encourage plantgrowth on the top. The actual design andinstallation of these caps is site-specific andgenerally costly. If your site requires such acap, contact one of agencies listed in thisbrochure for assistance.

When to do it

Capping of the waste rock or tailings shouldbe performed immediately after regrading ofthe pile in order to minimize the opportunityfor erosion. Construction at high altitudes isgenerally easier in the dry seasons, such as latesummer or fall.

Considerations

Any type of cap will be susceptible to water andwind erosion, penetration of tree roots, ani-mal burrowing, and frost action.Consideration should be given to minimizingthe effects of these processes, such as fencingif animals are expected to be a problem.Generally, a vegetative cover on the cap helpsto minimize these effects.

The potential for erosion can be reduced bycreating grooves across the slope or perpendi-cular to the slope direction. This can be doneeasily on the last pass of the heavy equipmentusing a track vehicle running up and down theslope.

Initial costs

Costs vary depending on site topography andlocation of the capping material relative to thelocation of the pile. The primary cost is basedon equipment usage and may include dumptrucks, excavators, bulldozers, backhoes orloaders.

Maintenance

Periodic maintenance requirements includean occasional walk-through of the capped areato identify problems caused by erosion, treeroot penetration, and animal burrowing.Prompt repair of any problems will increasethe effectiveness and lifetime of this BMP.

Best Management Practices: Capping

23

Tailings capped, graded, and vegetated

Placing material on a composite cover

BMP #6 - VEGETATION



Vegetation planted on a waste rock or tailingspile helps to contain the reactive material byprotecting the pile from erosion and reducingthe amount of water that can infiltrate into thepile. In addition, vegetation growth providesnutrients to the soil cover and improves thewildlife habitat. Vegetation is often used incombination with other BMPs, protecting thesoil from erosion along diversion ditches and onareas that have been regraded and/or capped.

How to do it

Ideally, the surface to be vegetated shouldconsist of good uncontaminated soil, moder-ately roughened to allow the seeds to hold andsome moisture to collect. Roughening cansimply be the caterpillar tracks of heavy equip-ment that has been used at the site for regrad-ing. However, if the material beneath the soilcap is toxic, care must be taken not to rough-en the surface too much which could promoteponding and subsequent infiltration andleaching of the reactive material into the envi-ronment.

Fertilizer should be applied to enhance thesoil. If good uncontaminated soil is to be veg-etated, a commercial grade diammoniumphosphate (18-46-0) is generally adequate.This can be broadcast by hand or machine at arate of 300 pounds per acre. If vegetation is tobe performed directly on tailings with no soilcovering, mixing crushed limestone into thetailings or using a super phosphate fertilizer(0-58-0) at the same rate of 300 lbs. per acreis generally sufficient. Dry cow, horse orsheep manure, which is not caked or lumpyand has been stockpiled for at least one year,can be used instead of fertilizer, in which


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First-year growth at coal waste site

T A B L E O F S E E D S , T H E I R M I X E S , A N D P L A N T T Y P E SSeed Name (Scientific Name) Percent of Seed Mix Plant Type

Tufted Hairgrass (Deschampsia ceaspitosa) 20 Bunch grassSmooth Bromegrass (Bromus inermis) 20 Sod grassIntermediate Wheatgrass (Agropyron intermedium) 20 Sod grassKentucky Bluegrass (Poa pratensis) 15 Sod grassCreeping Foxtail (Alopecurus arundinaceous) 15 Sod grassHard Fescue (Festuca ovina) 10 Bunch grassCrested Wheatgrass (Agropyron cristatum) 10 Sod grassCicer Milkvetch (Astragalus cicer) less than 1 Leguminous forbWhite Clover (Trifolium repens) less than 1 Leguminous forbIndian Paintbrush (Castilleja spp.) less than 1 ForbShrubby Cinquefoil (Potentilla fruticosa) less than 1 Shrub

case it should be applied at a rate of 30 tonsper acre.

The seed mix used should be specific to theclimate of the site and should be similar to thenative vegetation. It should include a variety ofbunch grass, sod grass, legumes, forbs andshrubs, so that if one type fails, there will stillbe some vegetative cover on the area. Manyoptions are available. The scientific names ofthe seeds are given for ease of ordering. Forother seed mix options, contact your localCounty Extension Agent or Soil ConservationService representative.

After seeding, mulch should be applied overthe entire area to protect the seeds from waterand wind erosion while they sprout. A cover-ing of mulch will also retain moisture for theseeds, insulate the seeds from extreme tem-peratures and help to hold the seedlings inplace, so that they are less likely to be pushedout of the ground by frost in the fall.Certified weed-free hay, alfalfa or straw canbe used for mulch, depending on what isavailable and the cost. It should be applieduniformly at a rate of two tons per acre. It isbest to crimp the mulch into the soil to pre-vent it from blowing away. This can be doneusing a shovel to simply push ends of themulch into the ground, or by the caterpillartracks of a bulldozer or loader.

When to do it

Vegetation can be done anytime, althoughspring and fall are better because there ismore moisture available. Vegetation should beperformed soon after construction in an areais completed to protect the soil. Unprotectedsoil or tailings will quickly erode.

Considerations

Any vegetation program will be susceptible towater and wind erosion and frost action. Theuse of mulch will help to keep the seeds inplace and minimize the effects of frost on thenew seedlings.

Initial costs

Costs of vegetation will vary depending onacreage.

Maintenance

Periodic maintenance requirements includean occasional walk-through of the area toidentify problems caused by erosion and areasof non-growth. Prompt repair or reseeding ofproblem areas will help to stabilize the site andwill increase the effectiveness of this BMP. Ifyou suspect noxious weeds in your vegetation,contact your County Extension Agent forinformation on identification and controlmethods.

Best Management Practices: Vegetation

25

Regraded mill tailings site after

mulching

BMP #7 - AERATION AND SETTLING PONDS

Applicable situationstreating drainage from a mine opening


Aeration and settling ponds promote the pre-cipitation of heavy metals such as iron, zincand manganese through oxidation processes.This BMP is particularly effective for treatingmine drainage water that is high in total sus-pended solids (TSS) but has a pH close toneutral (7.0). Aeration is accomplished bychanneling the mine drainage over a series ofsmall waterfalls or drops, which will increasethe oxygen content of the water into a quietsettling pond, where the metals will drop out.

How to do it

Aeration is accomplished by making the waterturbulent. Turbulence can be initiated bychanneling the drainage down a steep slope,over rough slopes (such as ditches lined withriprap or large rocks) or over a series of dropsor small waterfalls.

A settling pond should be located at the baseof the aeration channel. Ideally, it is in a nat-urally low area, but not along or in flowingwater. An embankment at the lower end of thepond holds the water in the pond. This allowsclean water to flow over the top of theembankment back into the main stream

without eroding the dam. The embankment isgenerally composed of a mix of rock and soilwith larger rocks lining the upstream side andsmaller rocks on the top to discourage erosionas the water flows over the top.

Settling ponds should be designed so that thewater entering the pond will remain in thepond for a minimum of 24 hours beforebeing discharged. A 24-hour retention peri-od will allow the oxidized metals to precipi-tate. In order to design the pond for 24-hourretention, the expected flow into the pondmust first be measured. This can generally bedone with a bucket and stopwatch. Using thatflow rate (probably measured in gallons perminute), the amount of water that will flowinto the pond in a 24-hour period can be cal-culated. The pond should be large enough tohold at least that amount. An example calcu-lation for a settling pond is shown. (Note: onegallon equals 0.134 cubic feet.)

If, given the area on your site, it is not possi-ble to have a settling pond large enough toretain the water for at least 24 hours or theground is too rocky or hard to excavate to thenecessary depth and size, consider severalsmaller settling ponds at different elevations,which together will provide a total retentiontime of at least 24 hours.

When to do it

Construction of this BMP will be easiest during the lowest flow of the mine drainage.That is generally in the late summer or fall,however, flow at your site may differ.


26


settling pond at a Mill Tailings site

Considerations

This BMP is best used in situations in whichthe mine drainage water is high in total sus-pended solids (TSS) and has a pH of nearneutral (7.0). Therefore, sampling and test-ing to determine the pH and suspended met-als content of the drainage is advisable todecide if this BMP will work at your site.

Because this is a two-part system, consisting ofan aeration channel and settling pond,requirements for space are greater than forother BMPs.

Initial costs

Costs for this BMP vary depending on thedepth of soil cover and the topography of thesite. Construction of a settling pond at a rockysite may be difficult. A steep site may offergood possibilities for aeration of the drainage,but limited possibilities for a settling pond. Aflatter site may require creative thinking toaerate the drainage but provide plenty of areafor a settling pond.

Maintenance

The aeration channel should be periodicallyinspected to confirm that the drops andwaterfalls are effectively producing turbulencein the mine drainage. Prompt repair of any problems along the channel should bemade to ensure that the suspended metals in the drainage are adequately aerated andsubsequently dropped out.

Because metals will be precipitated ordropped out in the settling pond, the pondwill occasionally need to be cleaned out.Whenever the pond is half full of sediment, itshould be cleaned out and the sediment dis-posed of in an environmentally sound way.The metals content of the sediment from thepond should be tested. Based on that value,the sediment can be taken to a hazardous wastesite or buried in a lined and capped disposaltrench on the site.

Best Management Practices: Aeration and Settling Ponds

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E X A M P L E C A L C U L AT I O N FO R S I Z I N G A S E T T L I N G P O N DFO R 2 4 - H O U R R E T E N T I O N O F I N F L OW

step 1: Measure expected flow rate.

10 gallons/minute (gallons per minute or gpm)step 2: Convert gallons to cubic feet.

10 gallons x 0.134 cubic feet/gallon = 1.34 cubic feet (cu.ft.)step 3: Calculate expected flow for 24 hour period.

1.34 cu.ft./min. x 1440 min./24 hr. = 1930 cu.ft. flow in 24 hoursCONCLUSION: The pond must be able to hold 1930 cubic feet of water for 24-hourretention of 10 gpm flow. Therefore, width x length x depth of the pond in feet must beequal to or greater than 1930 cubic feet. One possible pond configuration is: width =20 ft.,length = 25 feet, depth = 4 ft., so the pond can hold 2000 cubic feet. However, there arecountless possible pond configurations. The area available at your site to build a pond willdetermine the dimensions of the pond.

BMP #8 - SULFATE-REDUCING WETLANDS

Applicable situationstreatment of drainage from waste rock pilestreatment of drainage from mill tailingstreatment of drainage from a mine opening


Sulfate-reducing wetlands will improve thequality of acid mine drainage using commonbacteria found in decomposing organics toremove the heavy metals. Sulfate-reducingbacteria (SRBs) utilize the oxygen in sulfatesfor respiration, producing sulfides. The sul-fides combine with heavy metals in thedrainage to form relatively insoluble metalsulfides, which precipitate or drop out. Thebacteria derive their energy from a carbonsource, most commonly cow manure ormushroom compost.

How to do it

Generally, a sulfate-reducing wetland isplaced behind a berm or small earthen dam.Depending on the grain size of the soil, thewetland cell behind the berm may need to belined with either compacted clay or a PVC orHDPE geomembrane liner. If the soil is fine-grained with very little rock, no liner is neces-sary. The system may leak temporarily, butshould seal off in a period of weeks.

A thin layer of gravel (about 3 to 6 inches) isplaced on the bottom of the cell (or on theliner) and perforated collection pipes areburied within this layer. A highly permeablegeotextile fabric, such as a loose weave erosionfabric, is placed on top of the gravel layer. Thisfabric must allow drainage into the gravel,while keeping the finer material above the fab-ric from piping into the gravel. The substrateor treatment layer is placed on the geotextile toa depth of about three to six feet. The substratecan consist of cow manure, mushroom com-post, sawdust or in some cases soils from thesite depending on their permeability.

The drainage enters at the top of the systembut must exit at the base of the system toensure that the drainage flows through thesubstrate material and is exposed to the SRBs.Mine drainage enters the system through apipe buried just beneath the top of the sub-strate or can simply be pooled on the surfaceof the substrate. A riser pipe, through whichtreated water will exit, is installed starting inthe gravel layer at the low end of the wetlandand angling up through the berm where it dis-charges. A schematic cross section of a sulfate-reducing wetland is shown in Drawing 2.

The size of the wetland depends on theamount of metals and pH of the drainage, thevolume of the drainage and the area availableto install the wetland. A general rule of thumb


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Drawing 2 - Schematic cross section of sulfate-reducing

wetland. Not to scale.

SUBSTRATE3–6 FT. THICK

PERMEABLEGEOTEXTILE

GRAVEL (3–6 IN. THICK)AND PERFORATED COLLECTION PIPES NATURAL FINE-GRAINED SOIL

OR LINER UNDER WETLAND

RISER PIPE

DISCHARGEFROM WETLAND

FLOW INTO WETLAND

ROCKS ON SLOPEPREVENT EROSION

is that five cubic yards of properly designedand installed wetland will treat one gallon perminute of mine drainage. Therefore, if thedepth of your wetland is three feet, and youare treating 10 gallons per minute ofdrainage, the total area of the wetland shouldbe about 150 square feet. The wetland canconsist of one large cell or be broken into sev-eral smaller cells in order to achieve the nec-essary area to treat the drainage.

When to do it

Construction of this BMP will be easiest dur-ing the driest time of the year.

Considerations

Sulfate-reducing bacteria prefer an environ-ment with a pH above 4.5. In situations wherethe pH of the drainage is below 4.5, designmodifications are necessary, such as channel-ing the drainage through a lined buried trenchfilled with two- to six-inch chunks of lime-stone prior to entering the wetland, or addinglimestone to the substrate in the wetland.

Some pooling on the cells is desirable,because it discourages plant growth. Plantswill introduce an additional source of oxygenand the system works best in an oxygen-defi-cient environment. However, pooling shouldnot approach the top of the berm.

Sulfate-reducing wetlands should generallynot be constructed near population centers,because these systems commonly produceexcess hydrogen sulfide, which can causeundesirable odors up to 1/2 mile away fromthe system. Note that when the system is firstinstalled, the treated water will be discoloredand may look worse than the untreated waterentering the system. This is normal andshould change after a few months.

Initial costs

Costs for installation of a sulfate-reducingwetland will depend on the size of the wetlandand the cost of obtaining and delivering thesubstrate materials.

Maintenance

Metals will precipitate as the drainage is treat-ed in the wetland. Wetlands, properlydesigned for the metals content of thedrainage being treated, generally have a life of20 to 30 years, after which time the accumu-lated metals will begin to slow the flow and thetreatment will not be as effective. This metalsludge must be removed and properly dis-posed of in either a landfill or an on-sitelined and capped trench, or it can be sold forremining if the metals content is sufficient.

Best Management Practices: Sulfate-Reducing Wetlands

29

Sulfate-reducing wetlands with

HDPE liners

BMP #9 - OXIDATION WETLANDS

Applicable situationstreatment of drainage from waste rock pilestreatment of drainage from mill tailingstreatment of drainage from mine openings


Oxidation wetlands are what most peoplethink of as “wetlands”. Metals, such as iron,manganese, and arsenic are precipitatedthrough oxidation by aquatic plants and algae.The plant materials provide aeration and,when they die, provide adsorption surfaces forthe metals and sites for algal growth. Algaehelp in the manganese removal process.

How to do it

An oxidation wetland looks like a marshy areawith slow water flow around typical wetlandvegetation, such as cattails and rushes. Thebase of the wetland should be unevenly gradedto allow mine drainage to flow through bothshallow (less than 10 inches) and deep (10 to20 inches) areas and around vegetationislands. Care should be taken to prevent highvelocity flow through the wetland. This wouldnot allow sufficient time for oxidation to takeplace and could cause channels to form in thewetland, decreasing the amount of time thedrainage spends in the wetland.

The size of the wetland depends on theamount of metals and pH of the drainage,volume of the drainage and the altitude of thesite. A general rule of thumb is that treatmentof one gallon per minute of drainage willrequire a 200 to 900 square foot wetland.The wetland can consist of one large cell or bebroken into several smaller cells in order toachieve the necessary area to treat thedrainage.

The wetland area should be filled with a mix-ture of gravel and organic material and plant-ed with cattails, bulrushes, sedges and rushes.These can be taken from another wetland siteand transplanted into the new wetland inclumps about a foot or so apart. Grass clip-pings and hay can be incorporated to providealgae.

Areas around the wetland disturbed duringconstruction should be vegetated as soon aspossible after construction to minimize ero-sion of the soil and sedimentation in thewetland.

When to do it

Construction of this BMP will be easiest during the driest time of the year.


30


Oxidation wetland containing peat

moss

Considerations

This treatment method is applicable where thepH of the mine drainage is approximately 6.5or higher and where the metals concentrationsare primarily a problem during the summermonths. Because this system depends mostlyon plants to oxidize the metals, the efficiencyof the system will decrease in the wintermonths.

Initial costs

Costs of this BMP depend primarily on thesize of the wetland and the equipment usedfor construction.

Maintenance

A periodic inspection of the wetland systemshould be conducted to ensure that the flow isspread throughout the wetland and channel-ization has not occurred. Channelizationproblems should be fixed as soon as possibleto achieve the maximum treatment this systemcan offer.

Metals will precipitate as the drainage is treat-ed in the wetland. Properly designed wetlandsgenerally have a life of 20 to 30 years, afterwhich time the accumulated metals will beginto slow the flow and the treatment will not beas effective. At this time, the height of theberm can be increased, which will allow con-tinued use of the wetland.

Best Management Practices: Oxidation Wetlands

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BMP #10 - BMPs TO TREAT ACID MINE DRAINAGE

There are BMPs that relate specifically to thetreatment of contaminated drainage frommine openings. These include diversion ofsurface waters, dilution, land application,bulkhead seals, anoxic limestone drains,aqueous limestone injection and mechanicalinjection of neutralizing agents. In general,these BMPs must be designed and engineeredto take into account the volume of water, waterchemistry, and mine configuration, areexpensive and require ongoing maintenance.Because of this, only a paragraph about eachof these BMPs is included here. If you needfurther information about these types ofBMPs, contact one of the agencies listed at theend of this report to obtain guidance.

Diversion of surface waters can sometimeswork to reduce the amount of clean waterinfiltrating into the mine workings and beingexposed to oxidizing pyrite. Obvious placeswhere water is entering the mine can some-times be identified during a site reconnais-sance. That surface water flow should bechanneled away from entering the mine.

Dilution involves mixing clean water withacidic mine drainage in a settling pond. Theresultant increase in pH causes some of themetals in solution to precipitate.

Dilution can be a cost-effective method oftreatment, because the neutralizing agent issimply uncontaminated water, however, thepercentage of metals precipitated is signifi-cantly less using this method than using mostother methods. This method is most effectivein removing iron, aluminum, copper, cadmi-um and lead, but has only slight effectivenessfor zinc and manganese.

Land Application is a method designed to usethe natural processes in soils and subsoils,such as plant uptake, evaporation and transpi-ration and soil exchange capacity, to combinewith and remove metals. This method can beused in places where mine discharge can bespread over a large area to infiltrate into rela-tively thick soils or unconsolidated deposits.Drainage should be neutral or near neutral in pH to avoid killing the plants where application occurs.

Bulkhead seals are used to control the forma-tion of acid mine drainage inside a mine. Abulkhead seal is installed in an adit to preventdischarge from the nearby portal. The work-ings of the mine will flood behind the sealinhibiting the oxidation of pyrite and therebydecreasing the amount of acidic water pro-duced. Bulkhead seals are expensive andrequire considerable geologic and engineer-ing investigation and characterization and aretherefore rarely used at inactive mines.

Anoxic limestone drains (ALDs) are used totreat acidic water discharging from an open orcollapsed mine opening. Acidic mine dis-charge is channeled through a buried trenchcontaining chunks of limestone, which arenaturally high in alkalinity. The limestonedissolves in the acidic water, raising the pH ofthe water. A settling pond is generally placedbelow the ALD to catch the metals that dropout of solution.

Aqueous lime injection is a passive method tointroduce neutralizing agents into minedrainage. Clean water is passed through apond containing a high pH (alkaline) materi-al (often lime). This high pH water is thenmixed with the mine drainage before it entersa settling pond, where the metals will dropout. This system can be cost effective if alka-


32


line waste such as kiln dusts or fly ash is read-ily available.

Mechanical injection of neutralizing agents isused to treat acidic drainage from mine open-ings. This system involves a wind, solar orhydro-powered mechanical feeder which con-tinuously dispenses neutralizing agents (suchas finely ground limestone) into the minedrainage. Introducing a high pH neutralizingmaterial into the low pH mine drainage willraise the pH of the mine water, thus allowingthe metals to drop out of solution. A settlingpond is required below the feeder to capturethe metals that precipitate out. This type ofsystem requires frequent maintenance andmay produce significant quantities of metalsludge.

Best Management Practices: Treating Acid Mine Drainage

Settling pond below a limestone

injection system

Small-scale pilot lime injection system

33

Full-scale limestone injection system

with limestone hopper, feeder system

and control panels

Safety hazards associated with inactive andabandoned mines account for several deathsand injuries throughout the country everyyear. Increased outdoor recreation, urbandevelopment, and general population growthinto rural areas enlarges the potential expo-sure of the general public to hazardous inac-tive and abandoned mine features. With a liti-gious society, liability concerns are becomingimportant considerations to public and pri-vate landowners. The major safety problemsassociated with inactive and abandoned minesare open shafts, stopes, and adits.

Shafts are vertical openings in the ground giv-ing access to the working area of a mine. Theyare often several hundred feet deep and anunwary person could easily stumble into thehole before seeing it. The openings are usual-ly unmarked and unfenced, sometimes half-hidden among old boards and mining equip-ment. Areas around old shafts are often com-posed of unconsolidated soil or weatheredrock which is apt to give way beneath theweight of a visitor. Some shafts have cribbingor timbers that appear sturdy but are, in fact,full of dry rot and extremely weak. Because old

mining districts are interesting to tourists andvisitors and access to many mining areas is rel-atively easy, these shafts pose a significant haz-ard.

Stopes, like open shafts, are hazardous becausethey are often deep and unstable around theedges. They are created as mining proceedsunderground and the ore body is removedfrom above and dropped into ore cars.Sometimes, stopes extend upward so near theground surface that it collapses into theunderground workings. Stope complexes oftenradiate great distances away from the mineentry. They are somewhat more dangerousthan shafts because there are often no struc-tures or dumps to announce their presence.

Adits are horizontal openings allowing access tothe mine workings. They pose a less immediatethreat to visitors than shafts simply because onecannot accidentally fall into an adit. Someadits, however, have winzes (internal verticalshafts) just inside the entry. Adits are muchmore inviting to casual explorers than verticalshafts since shafts usually cannot be enteredwithout special equipment. Some adits and


34

Hazardous Openings

Adit opening with timbered entryStope showing stulls supporting

hanging wall

shallow inclines still have supporting mineprops in place; others are driven into solidrock; still others have no props or solid roofsand look as if they could collapse at any time.The fact that an adit has remained intact formany years gives a false sense of security to thevisitor who, by some inadvertent action, maytrigger a collapse and literally bring the roofdown on his or her head. Another concern isthat idle mines often have very poor ventilation,resulting in the accumulation of potentiallyfatal quantities of gases.

Safeguarding and Reclamation Alternatives

Safeguarding hazardous inactive and aban-doned mine openings requires considerationof the fact that the site has not been main-tained for many years. Because the mine andthe area around the opening has been inactivefor a long time, nature has often taken a tollon any improvements that helped ensure asafe condition when the mine was producing.This can make construction of an effectivesafeguard fairly complicated.

Reclamation alternatives should consider thesize and stability of the opening, the type ofmaterial around it, its depth to competentrock, the effects of site drainage, mine ventila-tion, near surface mine workings, safety of con-struction, access, site disturbance during con-struction, requirements for protection ofthreatened/ endangered species and/or historicpreservation, and any other factors that mayaffect the reclamation method or the construc-tion effort.

Three general types of approaches are used forsafeguarding shafts, stopes, and adits.Barriers are designed to keep visitors awayfrom the hazard. Seals prevent entry to themine. Plugs eliminate the hazard altogether.

Alternatives should be evaluated for a numberof factors, such as:

Life span – will it be effective permanently,50 years, 10 years?

Degree of hazard elimination – Completely elim-inate it, provide a barrier or deterrent

Maintenance requirements – How prone is theclosure to vandalism and environmentaldegradation?

Construction safety – Is it safe for workers, anddoes it require special skills or equip-ment? Is methane being produced by themine? Is the mine atmosphere safe? Arethere overhanging and /or loose rocksaround the opening? Is this a uraniumor vanadium mine requiring specialhealth protection from radiation duringconstruction?

Environmental concerns – Water quality anddrainage. Is the site in a wetland area,near a steam? What will be disturbed toinstall the closure? Are there bats orother wildlife that may use opening forprotection? Will there be loss of vegetation?

Design concerns – Is the closure method feasi-ble to install? If competent rock is need-ed for anchoring grating or beddingconcrete caps, is it close to the surface?Access for equipment—Is the site accessi-ble by heavy equipment, or only by foot?Size of equipment needed – Depends onclosure method and site access?Availability of materials— Are materialseasily available and cost effective?Cultural resources – Is it in an historicarea, is the building significant, inruins?

Cost - Is the cost prohibitive? Reasonable?

General Information

35

BMP # 11 – BARRIERS


Barriers can be appropriate when the openingis too large for other alternatives and whenconstruction access is restricted. Barriersinclude fences of several types and grates madeof steel bars. Chain link and iron fences canbe effective at keeping casual visitors a safe dis-tance from hazardous openings. Steel grates,using industrial grade material similar to thatused for elevated walkways, can be installedover vertical openings or in the portal of hor-izontal openings. A locking door made out ofthe steel grating can be incorporated to allowcontinued access to the mine workings by thelandowner or authorized people. Alternativemethods involve placing a corrugated steelpipe in the adit and installing a grate on theouter end, or using a special grate of steel barsto allow for bat access.

Considerations

Barriers such as fences and grates should berecognized for exactly what they are – barriers.They are not intended to prevent entry by thedetermined visitor.

The advantages of fences are that they are safeto install with no exposure to the mine haz-ard, they disturb the site minimally, they areeasy to install, and they are relatively inex-pensive. The disadvantages of fences are thatthey are temporary, they don’t eliminate thehazard but just discourage access, they aresubject to vandalism, and they can be aesthet-ically intrusive in otherwise natural settings.When fences are used they must be located farenough away from the hazardous opening tosurvive erosion of the feature.

Steel grates, whether they are installed over avertical shaft or at the portal of a horizontalmine opening, are more permanent and moreof a deterrent than fencing. Advantages ofgrates are their somewhat long life (approxi-mately 50 years), total elimination of access tothe hazard, they involve little to no site distur-bance, they can be installed in remote or dif-ficult access situations, they allow continuedventilation of the mine workings, they can bedesigned to allow continued use of the mineby bats, and they are relatively low cost.Disadvantages include exposure to vandalismand corrosion over time, the necessity to pro-tect workers from falling, unstable roofs,unsafe mine atmospheres during construc-tion, and the need to have competent rock toanchor the grating in most situations.

Initial costs

The cost of fences and barriers will varydepending on their length or size, the accessi-bility of necessary construction equipment,and the strength of the materials used. Fencesare generally low cost with barbed wire beingthe cheapest, chain link being moderate incost, and ornamental iron fences being mostexpensive. Grates are moderate in cost.

Maintenance

Periodic inspection and maintenance isrequired for continued effectiveness of thistype of safeguard. They are especially suscep-tible to vandalism and the types of materialsused defines their ultimate longevity.


36


Best Management Practices: Barriers

37

Custom steel fence around an historic

headframe and shaft

Fabricating a steel grate with a

locking hatch

A steel grate barrier at an adit with

bars allowing bat access and a locking

door

An illustration of a steel grate barrier

with bat access

BMP # 12 – PLUGS


Plugs include backfills, monolithic plugs, andplugs utilizing polyurethane foam (PUF).They are designed to eliminate the hazardcompletely.

How to do it

Shafts, stopes, and subsidence features should bebackfilled using graded materials, i.e., placinglarge rock riprap in the bottom of the feature,followed by successively smaller diameter materi-als with a plant growth media on the surface toallow for revegetation. Adits should be backfilledwith a minimum depth of fifteen feet from theinner top of the fill to the outer top of the fill.

Monolithic plugs consist of pouring a four foot(4’) thick concrete cap over mine shafts that havecollapsed at the collar and have no apparentopening. The visible bottom of the usually shal-low pit is most likely a false plug that will fail inthe future. This work includes near surfaceexcavation, furnishing and installing riprap,furnishing and installing concrete, backfilling,and revegetating disturbed areas.

A PUF closure uses a column of polyurethanefoam placed several feet down into a verticalopening with mine waste or common fill mate-rial placed on top of it up to the level of the sur-rounding grade. The PUF plug is constructed inplace using a lightweight form lowered into theopening and specialized equipment to mix twoliquid components that immediately startexpanding into a quick-curing, solid mass.

Considerations

Plugs provide a positive, permanent, and main-tenance-free safeguard to hazardous mineopenings. Plugs can be constructed with on-sitemine waste, imported rock and material, con-crete, and polyurethane foam (PUF).

Backfilled shafts and adits are permanent, com-pletely eliminate the hazard, and are mainte-nance free. With proper equipment, construc-tion workers’ exposure to the mine hazard islow. If on-site material is used, waste piles maybe eliminated. Although the techniques used aregenerally low-tech using commonly availableequipment, care needs to be taken to ensure thatthe entire opening is filled with no void spacesremaining. Material placed in shafts must not beallowed to bridge and create temporary, unsup-ported plugs. Adits may need a bulkhead to sup-port backfill. Hand-placed material in adits isdifficult to compact and fill to the roof.Machines may need a special extension to getadequate closure. If any water is draining froman adit, a pipe or other method is required toprevent excessive water pressure on the plug.Material placed into shafts containing watermust be benign. In situations involving water,on-site mine waste material is probably notacceptable and material will have to be import-ed.

Monolithic plugs are also permanent, com-pletely eliminate the hazard, and are mainte-nance-free. Construction workers are notexposed to the hazard if no formwork isrequired. The technique disturbs only a smallarea around the shaft. The plug provides sup-port of sidewalls of the shaft near the surface.The plug remains functional even if caved mate-rial below the plug fails. It is critical that the


38


polyurethane foam being installed in a

cribbed shaft

deepest part of the plug be placed in contact withcompetent bedrock to prevent piping of uncon-solidated material around the concrete plug.Monolithic plugs are not appropriate for adits.

Polyurethane plug closures completely eliminatethe hazard, and are maintenance-free.Although it is a fairly new technique with onlyabout ten years of history, a properly installedPUF plug should be permanent. Workers caninstall the closure from ground-level and do notneed to go down the shaft. Once mixed, PUF isinert. It can be installed in openings that areinside historic structures without damaging thestructure. It can accommodate poor access situ-ations. PUF can also be used as formwork forconcrete closures. Disadvantages of PUF plugsare few: there is potential for vandalism if thePUF is exposed so a minimum of two feet of cov-ering material is required. Additionally, theunmixed chemicals used in the PUF are toxic soexposure to them and their fumes must be pre-vented during construction. Exposed PUF willsupport combustion and will degrade in ultravi-olet light so adequate covering materials againare important. Installation procedures are crit-ical to success of this closure method. PUF plugsare not appropriate for most adit closures.

Initial costs

The cost of plugs will vary depending on the typeof material used and the accessibility for neces-sary construction equipment. Costs of backfillplugs can be inexpensive if on-site material isused. The cost may be high if imported materi-al is required. The cost of a monolithic plug isgenerally low to moderate unless shoring isrequired to safely install it below the bedrockcontact. PUF closures involve high material costsbut relatively low installation costs.

Maintenance

An initial inspection of these closures should beconducted after one or two years to see if any settlement has occurred. If properlyinstalled, the closures should not require anymaintenance.

Best Management Practices: Plugs

39

Installing concrete for a monolithic

plug

Backfilling a shaft using riprap

Perspective cutaway drawing of

a precast concrete panel

BMP # 13 – STRUCTURAL SEALS


Structural seals include precast concrete pan-els and poured in place concrete slabsinstalled over vertical or near-vertical mineopenings. Bulkhead seals can be constructedin a horizontal opening or adit using pouredconcrete, concrete blocks, or native rock.Seals are designed to prevent access to all visi-tors. They can be removed only with heavyconstruction equipment.

Considerations

Seals using precast concrete panels or poured-in-place concrete slabs completely eliminateexposure to shaft and stope hazards and do notrequire maintenance. They are relatively per-manent, having a lifespan of approximately100 years. Construction involves workingaround the vertical openings but does notrequire entering the shaft. There is minimaldisturbance to the site. These closures canincorporate a locking hatch if access isrequired. Panels can be prefabricated forstandardized closures and both types of sealrequire minimal site-specific engineering.These caps need to be placed on competentrock to provide an adequate foundation forsupport. The caps must be large enough tooverlap all sides of the shaft an appropriatedistance. The caps will not prevent collapse ofthe shaft sidewalls. Access for bringing in pre-cast panels or concrete trucks is needed.

Bulkhead seals in adits are permanent, theyeliminate exposure to the hazard and requirelittle or no maintenance. They require mini-mal site disturbance and can be constructed toblend in with their surroundings. Standardconstruction techniques are used. They areparticularly good for poor access sites if nativematerials are used. They can also incorporatea locking hatch if access is required. If the aditis draining water, an adequately sized andproperly installed drain pipe is required.During construction, workers must be pro-tected against possible roof and rib falls anddangerous mine atmospheres. Bulkheads inadits must include keying into competentbedrock to prevent access around the sides.


40


Placing precast concrete panels over a

stope

Finishing construction of a native

rock bulkhead at an adit

Initial costs

Shaft seals using precast concrete panels arerelatively inexpensive due to the economies ofscale of panel production and the lower costof fabricating the panels in a central location.Cast-in-place concrete slabs are more costlydue to the need and difficulty of constructinghigh strength formwork in a remote locationand the usually difficult access for concretetrucks. Bulkhead seals at adits are fairly lowcost because on-site materials can often beused and most elements of the closure can betransported by hand.

Maintenance

Periodic inspection is recommended for thesetypes of safeguards. Although they are notparticularly susceptible to vandalism, they areoften very visible and attract attention. Themost likely cause of failure of these closures isfailure of the surrounding bedrock materialdue to natural weathering.

Best Management Practices: Structural Seals

produced by

Division of Minerals and GeologyBill Owens, Governor

Greg Walcher, Executive Director

Michael B. Long, Division Director

the State of Colorado Department of Natural Resources

for more in

formation

call us at 303.866.3567or write to us atDivision of Minerals and Geology1313 Sherman St.Room 215Denver, CO 80203

visit us online at www.mining.state.co.us

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