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1Q\ 8905 
 
 Bureau of Mines Information Circular/1982 
 
 Acid Mine Drainage: 
 
 Control and Abatement Research 
 
 By Ann G. Kim, Bernice S. Heisey, 
 
 Robert L. P. Kleinmann, and Maurice Deul 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 8905 
 
 Acid Mine Drainage: 
 
 Control and Abatement Research 
 
 By Ann G. Kim, Bernice S. Heisey, 
 
 Robert L. P. Kleinmann, and Maurice Deul 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 James G. Watt, Secretary 
 
 BUREAU OF MINES 
 Robert C. Norton, Director 
 

 This publication has been cataloged as follows: 
 
 Acid mine drainage. 
 
 
 (Bureau of Mines information circular ; 8905) 
 
 
 Bibliography: p. 21-22. 
 
 
 Supt. of Docs, no.: I 28.27:8905. 
 
 
 1. Acid mine drainage. I. Kim, Ann G. II. Series: 
 
 Information 
 
 circular (United States. Bureau of Mines) ; 8905. 
 
 
 -TN2^7U4- [TD899,M5] 622s [628.1'6832] 
 
 82-19724 
 

 
 
 CONTENTS 
 
 Abstract 
 
 Introduction 
 
 The acid mine drainage problem 
 
 Chemistry of formation and control 
 
 Bureau of Mines acid mine drainage research 
 
 Mine sealing 
 
 Acid mine drainage treatment 
 
 At-source control of acid mine drainage 
 
 Summary and recommendations 
 
 References 
 
 ILLUSTRATIONS 
 
 1. Ground water percolating through pyrltlc material produces sulfuric acid 
 
 and iron compounds which are eventually discharged into surface streams. 
 
 2. In solutions Inoculated with 0.2 ml of T. ferrooxidans and 0.1 ml each of 
 
 T. ferrooxldans and Metallogenium , the decrease in pH is greater than in 
 sterile controls. 
 
 3. Plot of acidity and total dissolved iron versus pH measured in laboratory 
 
 simulations of a coal refuse pile shows the rapid production of acid and 
 1 ron at low pH 
 
 4. In abandoned mines below drainage, natural flooding can be used to exclude 
 
 air, limiting pyrite oxidation 
 
 5. A wet seal with an air trap allows water to leave the mine while prevent- 
 
 ing air from entering 
 
 6. Subsidence cracks over an underground mine may allow surface water and air 
 
 to enter a sealed mine 
 
 7 . Although the oxygen level in a sealed mine may be lower than that of nor- 
 
 mal air, it may be sufficient to support oxidation for long periods of 
 t Ime 
 
 8. Flow diagram of hydrated lime treatment process for acid mine drainage.... 
 
 9. Although the unit cost decreases with capacity, the total capital costs 
 
 may range between $500,000 and $2 million for a conventional treatment 
 process. 
 
 10. Limestone treatment produces a denser sludge in 1 day than lime neutrali- 
 
 zation produces in 43 days 
 
 11. Limestone treatment, which Includes neutralization, aeration, and set- 
 
 tling, is less expensive and produces a dense crystalline sludge 
 
 12. In acid mine drainage neutralized with limestone, the rate of ferrous iron 
 
 oxidation is 10 to 25 ppm/mln 
 
 13. The sequencing batch reactor Incorporates fill, aerate, settle, and dis- 
 
 charge cycles to optimize the rate of ferrous iron oxidation by bacteria 
 
 14. Most sludge from acid mine drainage treatment is retained in ponds, pumped 
 
 into abandoned sections of deep mines, or dumped in refuse areas. 
 
 15. The rate of acid production was approximately that of sterile controls 
 
 when detergent was used to limit bacterial activity in a laboratory 
 
 s tudy 
 
 16. Controlled release of detergents can be used to reduce acid production 
 
 from spoil piles by 50 to 95 pet compared with an untreated control 
 
 TABLES 
 
 1 . Water control practices 
 
 2. Variation in composition of mine effluent before and after sealing 
 
 3. Bureau of Mines conservation and development program — acid mine drainage.. 
 
 Page 
 
 1 
 
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 4 
 
 6 
 
 6 
 
 11 
 
 15 
 
 18 
 
 21 
 
 10 
 
 11 
 
 11 
 
 12 
 12 
 14 
 14 
 14 
 
 15 
 16 
 
 17 
 19 
 
 20 
 
ACID MINE DRAINAGE: CONTROL AND ABATEMENT RESEARCH 
 
 By Ann G. Kim, ' Bernice S. Heisey,^ Robert L, P. Kleinmann,"' and Maurice Deul'' 
 
 ABSTRACT 
 
 Acid drainage from underground coal mines and coal refuse piles Is one 
 of the most persistent industrial pollution problems in the United 
 States: This Bureau of Mines report reviews the acid mine drainage 
 problem generally and describes research currently underway to combat 
 it. 
 
 INTRODUCTION 
 
 In the last 15 years there has been little improvement in the number 
 of streams adversely affected by acid mine drainage. The Bureau of 
 Mines has developed a comprehensive program of acid mine drainage re- 
 search oriented toward both active and abandoned mines. It includes im- 
 proved prediction of acid potential, improved mine planning, at -source 
 control of acid formation, improved reclamation, improved water treat- 
 ment techniques, and assessment of ground water contamination in major 
 mining districts. 
 
 Controlling the acid at its source by limiting pyrite oxidation is a 
 major objective of the program. The Bureau of Mines is investigating 
 methods of slowing reaction kinetics by limiting oxygen, inhibiting 
 iron-oxidizing bacteria, or otherwise influencing reaction chemistry. 
 The Bureau has recently developed and field-tested a practical method of 
 bacterial inhibition which is effective in reducing acid drainage from 
 coal refuse piles. Since this technique is probably not applicable to 
 abandoned underground mines, improved methods of mine sealing are 
 required. 
 
 Bureau of Mines research into treatment of acid mine drainage is ori- 
 ented toward improving water treatment efficiency and developing low- 
 maintenance treatment systems. Current areas of investigation include 
 improved iron oxidation efficiency, limestone neutralization, disposal 
 of acid mine drainage sludge, and development of an artificial bog 
 treatment system. 
 
 'Research chemist. 
 ^Writer-editor . 
 ■^Supervisory geologist. 
 ^Research supervisor. 
 All authors are with the Pittsburgh Research Center, Bureau of Mines, Pitts- 
 burgh, Pa. 
 
THE ACID MINE DRAINAGE PROBLEM 
 
 Acid drainage from underground coal 
 mines and coal refuse piles is one of the 
 most persistent industrial pollution 
 problems in the United States. Pyrite in 
 the coal and overlying strata, when ex- 
 posed to air and water, oxidizes, produc- 
 ing ferrous ions and sulfuric acid. The 
 ferrous ions are oxidized and produce an 
 hydrated iron oxide (yellowboy) and more 
 acidity. The acid lowers the pH of the 
 water, making it corrosive and unable to 
 support many forms of aquatic life. The 
 iron oxide forms an unsightly coating on 
 the bottom of streams, and further limits 
 the ability of aquatic life to survive in 
 streams affected by acid mine drainage. 
 
 Before coal is mined, very little of 
 the pyrite is exposed to the conditions 
 necessary to produce acid drainage. The 
 mining and coal cleaning process exposes 
 the pyrite to surface or ground waters 
 and allows pyrite oxidation to occur. A 
 ton of coal containing 1 pet pyritic sul- 
 fur has the potential of producing 
 33 pounds of yellowboy and over 60 pounds 
 of sulfuric acid. However, the rate of 
 acid production varies, and abandoned 
 mines and refuse piles can produce 
 acid drainage for more than 50 years. 
 The drainage, if discharged into sur- 
 face streams or ponds, constitutes an 
 extensive, expensive, and persistent 
 
 -Water percolating 
 
 ^^&§^BM 
 
 FIGURE 1. - Ground water percolating through pyritic material produces sulfuric acid and iron com- 
 pounds which are eventually discharged into surface streams. 
 
environmental problem (fig. 1). Federal 
 law (37)5 now requires that water dis- 
 charge from active coal mines have a pH 
 between 6 and 9 and places limits on the 
 total iron, manganese, and suspended sol- 
 ids. Controlling acid mine drainage from 
 active mines usually requires expensive 
 water treatment and the necessity of han- 
 dling very large volumes of water. Con- 
 trolling drainage from abandoned mines is 
 even more difficult due to location, 
 water volume, and the general limitation 
 on public funds available for work in 
 this area. The Bureau of Mines research 
 program in acid mine drainage addresses 
 the problems of both active and abandoned 
 mines. 
 
 In 1936, it was estimated ( 17 ) that 
 more than 9 million tons of sulfuric acid 
 were discharged annually from coal mines 
 into the streams of Pennsylvania. Now, 
 although Federal and State regulations 
 specify water quality standards for coal 
 mine discharges, acid mine drainage re- 
 mains a problem. The most comprehensive 
 survey of the extent of acid mine drain- 
 age pollution was conducted by the Feder- 
 al Water Pollution Control Administration 
 in 1967 (^, 8^). Drainage basins through- 
 out the Appalachian Region, in Pennsyl- 
 vania, West Virginia, Maryland, Ohio, 
 Kentucky, Virginia, Tennessee, Alabama, 
 and Georgia, were sampled for various 
 water quality parameters including acid- 
 ity, to determine the extent of water 
 pollution caused by coal mine drainage. 
 At that time, 10,500 miles of streams 
 were significantly degraded by coal mine 
 drainage, and further analysis of the 
 data showed that approximately half, or 
 5,740 miles was affected by acid mine 
 drainage ( 11 ) . 
 
 Since that time, no Federal agency has 
 undertaken a survey of this scale; cur- 
 rent mine drainage assessments are re- 
 stricted to statewide estimates. Direct 
 comparisons between current State data 
 and those collected in the 1967 study 
 cannot be made, because of differences in 
 
 ^Numbers in parentheses refer to items 
 in the list of references at the end of 
 this report. 
 
 the intensity of sampling and variation 
 in the criteria used to classify a stream 
 as degraded. However, current water 
 quality data, obtained from State envir- 
 onmental agencies of the Appalachian Re- 
 gion, do indicate that there has been 
 little overall improvement in streams 
 affected by acid mine drainage. 
 
 In Pennsylvania, which annually pro- 
 duces approximately 82 million tons of 
 coal (22), there are 2,795 miles of major 
 streams that fail to meet current water 
 quality standards ( 32 ) , Drainage from 
 abandoned mines contributes to at least 
 70 pet of the total. Although projected 
 figures for 1983 indicate a slight de- 
 crease in stream miles that will not meet 
 water quality standards, no decrease in 
 the drainage pollution related to mining 
 is expected. 
 
 In Ohio, where annual coal production 
 was nearly 42 million tons (22) , a 1979 
 study conducted by the Ohio Environmental 
 Protection Agency indicates that acid 
 mine drainage affects 1,075 miles of 
 streams (30). In Maryland, where annual 
 coal production was just over 2-1/2 mil- 
 lion tons ( 22 ) , the Maryland Bureau of 
 Mines currently estimates that 450 miles 
 of streams are affected by acid mine 
 drainage (9), much of it related to min- 
 ing in neighboring States. In Tennessee, 
 where annual coal production is nearly 
 11-1/2 million tons (22), acid mine 
 drainage was estimated to affect 994 
 miles of streams, according to the Divi- 
 sion of Water Quality Control of the Ten- 
 nessee Department of Public Health (35). 
 In Kentucky, the Department for Natural 
 Resources and Environmental Protection, 
 Division of Abandoned Lands, has compiled 
 data for 1978-80 which show that of a to- 
 tal of more than 2,100 miles of streams 
 within the Eastern Coalfield affected by 
 coal mine drainage, only 77 miles are 
 acid (12). The low proportion of acid 
 streams in this area of Kentucky is 
 apparently related to the abundance of 
 limestone in the coal-bearing rocks. 
 
 Although rigorous comparisons cannot 
 be made, the more recent data indicate 
 that the extent of acid mine drainage 
 
pollution is of the same order of magni- 
 tude as that measured in the 1967 study. 
 Government regulation has done much to 
 upgrade the quality of discharges from 
 active mining operations, but most acid 
 mine drainage comes from abandoned mines, 
 which are not regulated. In spite of in- 
 creased efforts to control it, acid mine 
 drainage continues to be a major problem. 
 
 Present regulations stipulate that acid 
 drainage from active mines and refuse 
 piles must be chemically treated for as 
 long as it is discharged from the mine or 
 pile. These mandatory standards have 
 generated research needs in the following 
 areas: More efficient treatment methods. 
 
 the disposal of sludge produced by treat- 
 ment, engineering methods to reduce acid 
 formation and other at-source methods of 
 control, control of acid formation and 
 erosion from spoil piles, and improved 
 water management techniques. In addi- 
 tion, there is no systematic, cost- 
 effective method of reducing the acid 
 load from mines already abandoned and 
 from mines to be abandoned in the future, 
 although an estimated 80 pet of acid mine 
 water comes from abandoned mines and 
 spoil piles. This area particularly re- 
 quires a concentrated research effort if 
 there is to be significant improvement in 
 the quality of many streams. 
 
 CHEMISTRY OF FORMATION AND CONTROL 
 
 Prevention and/or control of aciiJ mine 
 water depends on an understanding of the 
 chemical, biological, and geological fac- 
 tors that influence its formation, which 
 is best described as a series of chemical 
 reactions. Acid mine water is produced 
 by the oxidation of the pyrite (FeS2) 
 normally present in coal and the adjacent 
 rock strata. The oxidation of pyrite is 
 usually described by the reaction below 
 in which pyrite, oxygen, and water form 
 sulfuric acid and ferrous sulfate: 
 
 2Fe, + 7O9 + 2HoO = 4H+ + 2Fe2+ + 4S02-. 
 
 Oxidation of the ferrous iron produces 
 ferric ions according to the following 
 reaction: 
 
 2Fe2+ + 1/2 O2 + 2H+ = 2Fe3+ + H^O. 
 
 When the ferric ion hydrolyzes, it pro- 
 duces an insoluble ferric hydroxide (yel- 
 lowboy) and more acid: 
 
 Fe3+ + 3H2O = Fe(0H)3 + 3H+. 
 
 Although this summary is correct at pH 
 above about 4.0, it is only one of three 
 different reactions systems, which vary 
 in significance with pH (14). Also 
 
 significant in the oxidation of pyrite is 
 a bacterium, Thiobacillus ferrooxidans . 
 
 At near-neutral pH (stage 1), the rates 
 of oxidation by air and by T. ferrooxi- 
 dans are comparable. This stage is typi- 
 cal of freshly exposed coal or refuse. 
 Despite the high concentration of pyrite, 
 the rate of oxidation either by oxygen or 
 by T. ferrooxidans is relatively low, and 
 the natural alkalinity of ground water 
 may effectively neutralize the acid 
 formed at this stage. 
 
 When the neutralizing capacity of the 
 environment is exceeded, acid begins 
 to accumulate and the pH decreases 
 (stage 2). As the pH decreases, the rate 
 of iron oxidation by oxygen also de- 
 creases. But at the lower pH of stage 2, 
 the rate of iron oxidation by T. ferroox- 
 idans increases. The action of the bac- 
 teria causes increased acid production, 
 which serves to further lower pH 
 (fig. 2). 
 
 As the pH in the immediate vicinity of 
 the pyrite falls to less than 3, the in- 
 creased solubility of iron and the de- 
 creased rate of Fe(0H)3 precipitation 
 affect the overall rate of acid produc- 
 tion (stage 3). At this point, ferrous 
 
lU 
 
 UJ 
 
 z 
 o 
 
 a: 
 
 UJ 
 
 I- 
 
 X 
 
 Q. 
 
 6 - 
 
 5 - 
 
 3 - 
 
 2 - 
 
 1 
 
 1 1 1 1 y^ 
 
 - 
 
 v/"^^ Sterile 
 
 1 
 
 ^£. 
 
 „-^'^ ^Inoculated 
 
 1 1 1 1 1 
 
 I 
 
 4 5 
 
 INITIAL pH 
 
 8 
 
 FIGURE 2. - In solutions inoculated with 0.2 ml 
 of T. ferrooxidans(^) and 0.1 ml each of T. ferro- 
 
 oxi dans and Metallogenium {B), the decrease in pH 
 is greater than in sterile controls (C). 
 
 iron is oxidized by T. ferrooxidans and 
 the ferric ion in turn oxidizes the 
 pyrite: 
 
 FeS2 + 14Fe5+ + 8H2O = 15Fe2+ 
 
 + S02- + 16H+. 
 4 
 
 In this third stage, the rate of acid 
 production is high (fig. 3) and is lim- 
 ited by the concentration of ferric ions. 
 Inhibition of T. ferrooxidans would pre- 
 vent ferric oxidation of pyrite and 
 should therefore reduce acid production 
 by at least 75 pet. 
 
 When untreated acid mine drainage is 
 mixed with surface waters, it has a dele- 
 terious effect upon the receiving stream, 
 usually making it unsightly and inhos- 
 pitable to most forms of aquatic life. 
 Most organisms cannot tolerate an acid 
 environment. Also, the ferrous iron in 
 acid mine drainage consumes the oxygen in 
 a stream, and the precipitated ferric hy- 
 droxide covers the streambed, limiting 
 the oxygen available to benthic organ- 
 isms. The acidity and total solids ad- 
 versely affect aquatic life, and heavy 
 metal ions present in some mine waters 
 have an increased toxicity in acid 
 
 IfiOO - 
 
 6,000 - 
 
 O 
 O 
 o 
 
 " 5,000 - 
 en 
 
 e 
 
 ^f 4,000 
 
 CO 
 
 X 
 
 Q 3,000 - 
 F 
 
 V 
 
 Q 2,000 
 
 o 
 
 < 
 
 1,000 
 
 Acidity- 
 
 ron 
 
 ^-i^ I il I 
 
 2,000 
 
 1,800 
 
 1,600 
 
 1,400 
 
 ,200 
 
 1,000 
 
 o 
 on 
 
 800 
 
 600 
 
 400 
 
 200 
 
 I 2 3 4 5 6 7 
 
 pH 
 
 FIGURE 3. - Plot of acidity and total dissolved 
 iron versus pH measured in laboratory simulations 
 of a coal refuse pile shows the rapid production of 
 acid and iron at low pH. 
 
 solutions (6). In streams severely pol- 
 luted with acid mine drainage, there are 
 usually no complex aquatic plants, no 
 fish, few if any benthic invertebrates, 
 and only a few species of algae. In some 
 cases, the invertebrates and algae that 
 can survive grow to nuisance proportions. 
 
 When acid mine drainage is produced in 
 an active mine, environmental laws re- 
 quire that it meet minimum standards be- 
 fore it is discharged into surface 
 streams. According to the Federal Water 
 Pollution Control Act, water from coal 
 mines must have a pH between 6 and 9 and 
 must contain no more than an average of 
 3.5 ppm and a maximum of 7 ppm iron, no 
 more than an average of 2 ppm and a maxi- 
 mum of 4 ppm manganese, and no more than 
 70 ppm total suspended solids. 
 
 Standard acid mine drainage treatment 
 methods Involve neutralization of the 
 acid by the addition of a base, oxidation 
 
of ferrous iron in an aeration tank, or 
 pond, and precipitation of iron compounds 
 in a settling pond. Manganese, unless 
 present in high concentrations, is usu- 
 ally removed with the iron. 
 
 The chemistry of the basic treatment 
 method is relatively straightforward. 
 Neutralization is the reaction of the 
 acid with a base: 
 
 H2SO4 + Ca(0H)2 = CaS04 + 2H2O. 
 
 If limestone is used as the neutralizing 
 agent, the reaction is 
 
 H2SO4 + CaCOj = CaS04 + H2O + CO2. 
 
 To remove the ferrous iron, the neutral- 
 ized water is aerated to produce ferric 
 ions, which react with the base to form 
 insoluble ferric hydroxides: 
 
 Fe2(S04)3 + Ca(0H)2 = Fe(0H)3 + CaS04. 
 
 With limestone as the neutralizing agent, 
 the reaction is 
 
 Fe 2 (504)3 ■•" 3CaC03 + 3H2O = 2Fe(0H)3 
 3C0- 
 
 + 3CaS04 + 
 
 '2* 
 
 Other alkaline agents can be used, but 
 because of cost, ease of handling, or 
 other environmental effects, lime is most 
 commonly used. Other methods that have 
 been suggested for treating acid mine 
 drainage include reverse osmosis, ion ex- 
 change, and flash distillation. However, 
 these are not treatment methods per se, 
 but methods for producing potable water 
 that were suggested for acid mine drain- 
 age only where there is no alternative 
 source of potable water. With these 
 methods a concentrated acid brine or 
 sludge must be disposed of, and because 
 of technical problems and high cost, 
 processes like these are not commonly 
 considered as reasonable alternatives to 
 neutralization. 
 
 BUREAU OF MINES ACID MINE DRAINAGE RESEARCH 
 
 Methods to reduce the pollution from 
 ferruginous acid water from coal mines 
 and spoil banks usually involve either 
 reducing the rate of acid formation or 
 increasing the efficiency of mine water 
 treatment. Although acid mine drainage 
 has been a problem for many years, there 
 have been few significant innovations in 
 its prevention and control. The Bureau 
 of Mines was involved in much of the acid 
 mine drainage research conducted before 
 1970 (r7_, ^, 26). The Bureau performed 
 analytical studies to determine the acid- 
 ity, composition, and corrosivity of acid 
 mine water. Sources of and variations in 
 acid mine drainage, the effect of pyrite 
 content, rock dusting, and chemical neu- 
 tralization also were investigated. In 
 addition, the Bureau of Mines was a major 
 contributor to the development of mine 
 seals during the 1930' s. 
 
 During the 1970' s the Bureau of Mines 
 had only a limited acid mine drainage 
 program as other Federal agencies, such 
 as the Environmental Protection Agency 
 (EPA), assumed primary responsibility for 
 water pollution research. Because of the 
 
 continuing problems in acid mine drainage 
 control, the Bureau of Mines has recently 
 developed a comprehensive program of 
 acid mine drainage research. This pro- 
 gram is directed toward several areas, 
 including improved prediction of acid 
 potential, improved mine planning, at- 
 source control of acid formation, im- 
 proved reclamation, improved water treat- 
 ment, techniques to control acid drainage 
 at abandoned mines and waste piles, and 
 assessment of ground water contamination 
 in major mining districts. 
 
 MINE SEALING 
 
 In 1928 it was reported that mines 
 sealed by natural caving produced less 
 acid than unsealed mines in the same lo- 
 cality (19). It was assumed that limit- 
 ing the amount of air and water entering 
 the mine reduced the rate of acid forma- 
 tion. After a 1-year field study, an ex- 
 tensive mine sealing program was under- 
 taken in 1933 through the Works Progress 
 Administration and the Civil Works Admin- 
 istration. Records indicate that seal- 
 ing did produce favorable results in 
 
West Virginia, Ohio, and Pennsylvania 
 (36). However, the Federal sealing pro- 
 grams were short term and did not provide 
 funds for maintaining the seals. Lack of 
 maintenance, natural deterioration, van- 
 dalism, and subsequent mining combined to 
 reduce the long-term effectiveness of the 
 mine sealing program. 
 
 Despite the lack of long-term monitor- 
 ing, mine sealing is considered a stan- 
 dard method for reducing acid formation 
 from coal mines (27, 29). In mines lo- 
 cated below drainage, natural flooding is 
 used to cover the pyritic material and 
 exclude air (fig. 4). When the air sup- 
 ply is eliminated, it is assumed that the 
 pyrite is no longer oxidized. If the 
 water pool is stable and the additional 
 hydraulic pressure creates no downdip 
 
 Vjj=f. 
 
 drainage problems, flooding is considered 
 adequate. 
 
 This effect is currently being observed 
 in the Northern Field of the Pennsylvania 
 Anthracite Region ( 7^) > where flooded 
 workings underlie approximately 43,000 
 acres. The Bureau of Mines is currently 
 studying the hydrology and geochemistry 
 of this large mine pool complex because 
 the pool is well established, having 
 started to form over 30 years ago. Owing 
 to its size and flow characteristics, 
 water draining from the mines remained 
 acid until only a few years ago, cast- 
 ing some doubt on the effectiveness of 
 flooding. However, our study has shown 
 that the water in the mine pools has now 
 recovered and is in fact slightly 
 alkaline. 
 
 T<t-, 
 
 
 FIGURE 4. - In abandoned mines below drainage, natural flooding can be used to exclude 
 air, limiting pyrite oxidation. 
 
In deep mines above drainage, flooding 
 is generally ineffective owing to seepage 
 through surface fractures and the 
 tendency of the water to migrate to other 
 discharge points. In such mines, con- 
 ventional seals are airtight and/or 
 watertight masonry walls hitched into the 
 roof, bottom, and ribs of mine openings 
 (fig. 5). Subsidence fractures that 
 extend from the mine through the caved 
 overburden to the surface serve as open 
 pathways for the migration of air and the 
 drainage of surface water (fig. 6). To 
 effectively seal these mines, it is also 
 necessary to backfill and grade all 
 fractures that extend from the mine to 
 the surface. Although aerial photography 
 and infrared scanning can be used to 
 locate zones of high permeability, this 
 process is expensive and not sen- 
 sitive enough to delineate relatively 
 small subsidence fractures. Indiscern- 
 ible joints and subsidence fractures can 
 affect the overall effectiveness of a 
 mine sealing project by allowing a mine 
 to "breathe" (fig. 7). Monitoring by the 
 Bureau of Mines has shown a general cor- 
 relation between the oxygen level in the 
 mine, the differential pressure across 
 mine seals, and changes in the barometric 
 pressure (28). 
 
 Because most mine sealing evaluations 
 are based on short-term observation, the 
 Bureau is now evaluating the long-term 
 effectiveness of mine sealing in several 
 areas. For example, at Moraine State 
 Park grouted double bulkhead seals were 
 used in an area where an artificial lake 
 was built over 10 years ago. In this 
 area, water discharged from sealed areas 
 has a total mean acid load of 206 lb/day 
 10 years after sealing, compared with 540 
 lb/day before sealing. The discharge 
 rate varies between 250 and 500 gpm, and 
 the total iron has a mean value of 
 53 lb/day at present, compared with 
 46 lb/day prior to sealing (21). Over 
 the 10-year period the variation in dis- 
 charge rate, acidity, alkalinity, and 
 total iron has declined, indicating that 
 a mine pool has been created as a result 
 of sealing. In the Highland Fuel Mine 
 area (Butler County, Pa.) water samples 
 
 are obtained from discharge points and 
 from observation holes behind the seals. 
 The discharge from the sealed area varies 
 from 25 to 80 gpm, and the pH of the 
 water is approximately 4. Total iron in 
 the discharge averages 12 to 14 ppm. 
 Water samples from the mine pool behind 
 the seals have an average pH above 6 and 
 a higher total iron content. 
 
 Recent inspection of wet, dry, and 
 hydraulic and/or bulkhead seals con- 
 structed 13 years ago in abandoned mines 
 near Elkins, W, Va. , has shown that five 
 of the clay seals have deteriorated, al- 
 lowing acid seepage to kill vegetation on 
 the slopes below the seal. Yellowboy 
 precipitate has restricted the drainage 
 opening of one wet masonry block seal. 
 Water quality in at least one stream 
 receiving discharge from the sealed mines 
 has not improved significantly since the 
 mines were sealed. 
 
 The Bureau's evaluation of mine seals 
 installed approximately 10 or more years 
 ago has indicated several serious prob- 
 lems with conventionally constructed 
 seals. First, completely sealing a mine 
 above drainage is very difficult and may 
 be very expensive. Complete sealing re- 
 quires that all zones of high permeabil- 
 ity be located and sealed. The usual 
 procedure is to locate subsidence frac- 
 tures , cover the area with a compacted 
 clay blanket, and regrade it. To be ef- 
 fective, this procedure requires that all 
 fractures be located and that no further 
 subsidence occur. The evidence indicates 
 that surface sealing is rarely effective 
 for long periods. Another problem with 
 mine sealing is that masonry seals re- 
 quire continued maintenance. Even if 
 seals are adequately built and main- 
 tained, the improvement in water quality 
 directly attributable to the sealing pro- 
 cess has not been adequately determined. 
 
 To improve the effectiveness of mine 
 sealing, the Bureau of Mines is studying 
 sealed mines to determine factors con- 
 trolling changes in water quality and is 
 developing techniques to build more 
 efficient, less expensive seals. In 
 
Hitch- 
 
 /y///A/ ,, /i, ^ //•/,,/ . 
 
 ,_ Hitchx ^ 
 
 J — . C-4 
 
 ELEVATION-A 
 
 Roof rock 
 
 FIGURE 5. - A wet seal with an air trap allows water to leave the mine while 
 preventing air from entering. 
 
 FIGURE 6. - Subsidence cracks over an underground mine may allow surface 
 water and air to enter a sealed mine. 
 
10 
 
 22 
 
 O 14 
 
 KEY 
 
 — Sealed mine I 
 
 — Sealed mine 2 
 
 15 20 
 
 TIME, months 
 
 FIGURE 7. - Although the oxygen level in a 
 sealed mine may be lower than that of normal air, 
 it may be sufficient to support oxidation for long 
 periods of time. 
 
 addition to monitoring discharge rates 
 and water quality parameters, at some 
 sites drawdovm testing will be used to 
 determine aquifer capacity and water 
 level fluctuations. Subsidence areas 
 will be surveyed during and after draw- 
 down testing. The collection of rainfall 
 data and the use of fluorescent dye to 
 determine the direction and velocity of 
 ground water flow in the mine pool will 
 also be used to determine the factors 
 that affect water quality when mines are 
 sealed conventionally. 
 
 The Bureau also is involved in a demon- 
 stration of pneumatic stowing of lime- 
 stone as a method of producing more 
 effective mine seals at a cost equal to 
 or less than that of conventional seals. 
 Observations of mine seals to date indi- 
 cate that seals constructed of cement 
 block and grout do not substantially im- 
 prove water quality, may not effectively 
 contain impounded water, and are subject 
 to failure and/or leakage. The construc- 
 tion of a competent seal requires that it 
 be permanently attached to the roof, 
 
 ribs, and floor. Frequently the failure 
 of conventional seals is due to collapse 
 of weak strata over the seal. Pneumatic 
 stowing produces a highly compacted lime- 
 stone plug which supports roof and ribs. 
 Movement of surrounding strata will cause 
 further compaction of the limestone. 
 Concrete or other additives to the lime- 
 stone can be used to produce a stronger 
 seal. If appropriate, the limestone seal 
 can be constructed to allow low flows 
 of mine water. If the water is only 
 slightly acid, passage through the lime- 
 stone can effectively neutralize it. In 
 a field trial of pneumatic stowing, the 
 limestone seals were found to be satis- 
 factory in terms of the safety of con- 
 struction, the strength of the seal, and 
 the cost. Long-term monitoring of these 
 seals is planned to determine their 
 effect on water quality. 
 
 In deep mines, the construction of mine 
 seals limits the water discharge rate and 
 creates a mine pool covering some or all 
 of the pyritic material. If inundation 
 is to be an effective method of con- 
 trolling acid drainage, outcrop barrier 
 pillars must be capable of withstanding 
 the hydrostatic head created by the im- 
 pounded water. In general. Federal and 
 State regulations on mine closure do not 
 deal directly with criteria for outcrop 
 barriers used to flood the mine. A 
 Bureau of Mines contract report (31) de- 
 tails the factors that affect the com- 
 petency and stability of outcrop barri- 
 ers. According to the study, an outcrop 
 barrier should be wide enough to prevent 
 seepage, have sufficient overburden to 
 prevent a blowout, and provide a stable 
 slope. Curtain grouting, compartmental- 
 ized barriers, and relief wells can be 
 used to reinforce outcrop barriers. 
 
 In mines that have been successfully 
 inundated, water quality is often good in 
 the mine pool but generally acid after 
 seeping through the barrier. Use of a 
 relief well system, as suggested in the 
 contract report (31) , would remove water 
 from the mine pool prior to its exposure 
 to pyrite-bearing coal and would also 
 limit the hydrostatic head that the out- 
 crop barrier would have to withstand. 
 Properly designed outcrop barriers could 
 
11 
 
 reduce acid formation in abandoned mines 
 and allow maximum coal removal. 
 
 Oxygen may also be a limiting factor in 
 coal refuse piles and some surface mines. 
 The Bureau of Mines is currently using 
 soil gas probes to study oxygen diffusion 
 characteristics in coal refuse piles; 
 preliminary results indicate that pyrite 
 oxidation is limited to a near-surface 
 layer. A similar study will soon be ini- 
 tiated in an abandoned surface mine. 
 Followup research will concentrate on 
 current reclamation methods to determine 
 if any reduce oxygen diffusion or result 
 in the consumption of oxygen, thus limit- 
 ing acid formation. 
 
 ACID MINE DRAINAGE TREATMENT 
 
 Many factors influence the quantity and 
 quality of water handled by a mining 
 operation, but it is not unusual for a 
 single mine to treat Ijnillion gallons of 
 acid water per day. Water from coal 
 mines is usually treated by chemical neu- 
 tralization. At present, lime is the 
 most commonly used neutralizing agent. 
 Generally, a small volume of mine water 
 is added to powdered lime to produce a 
 slurry which, added to the raw mine 
 water, raises the pH to between 7 and 9. 
 The water is aerated to oxidize the fer- 
 rous iron and is then transferred to a 
 settling pond for precipitation of the 
 iron compounds (fig. 8). Although com- 
 monly used, lime neutralization has sev- 
 eral inherent problems. Lime is a 
 caustic material and can produce water 
 with an unacceptably high pH. Lime 
 treatment produces a flocculant precipi- 
 tate that does not form a dense, easily 
 handled sludge. Research by EPA failed 
 to produce any economical improvement in 
 sludge disposal methods. The Bureau is 
 evaluating the technology and economics 
 of current sludge disposal practices to 
 determine the most promising area of re- 
 search. Sludge disposal problems, and 
 high cost (fig. 9) are the principal rea- 
 sons for seeking improved acid mine 
 drainage treatment methods. 
 
 Row cool 
 mine water 
 
 Lime 
 
 storage 
 
 bin 
 
 Flash 
 mixer 
 
 Lime 
 screw 
 feeder 
 
 Oxidation 
 tank 
 
 Sludge 
 
 collection 
 
 pump 
 
 Settling 
 
 lagoon 
 
 I 
 
 1 ' 
 
 
 
 Settling 
 
 lagoon 
 
 2 
 
 
 Settling 
 lagoon 
 
 3 
 
 
 
 
 
 1 e 
 
 Plant 
 effluent 
 
 FIGURES. - Flowdiagramofhydrated lime treat- 
 ment process for acid mine drainage (34). 
 
 CAPACITY, gal/d 
 
 1,000 
 
 500 
 
 ;I00 
 
 50 
 
 J I I I I 
 
 J I I I I I II 
 
 J I I I I I I 
 
 10^ 
 
 CAPACITY, mVd 
 
 10^ 
 
 FIGURE 9. - Although the unit cost decreases 
 with capacity, the total capital costs may range 
 between $500,000 and $2 million for a convention- 
 al treatment process (34), 
 
12 
 
 As an alternative treatment method, the 
 Bureau has developed a neutralization 
 process using limestone instead of lime 
 (4^, 61, ]A, l]_, 24-25). Limestone is 
 readily available and costs less than 
 lime, and limestone treatment produces a 
 dense crystalline sludge (fig. 10). In 
 the Bureau treatment process, very fine 
 (5 to 10 ym) limestone is produced by wet 
 autogenous grinding in a tube mill. The 
 limestone slurry is mixed with the acid 
 mine drainage, and the drainage is aer- 
 ated to remove carbon dioxide and to oxi- 
 dize the ferrous iron (fig. 11). The 
 gypsum-iron oxide sludge separates from 
 the drainage in settling ponds. Although 
 limestone treatment has the advantages of 
 lower material costs, simplicity of plant 
 design and operation, the use of a less 
 hazardous material, and a denser, sludge, 
 its use is limited by the rate at which 
 ferrous iron is oxidized. With limestone 
 neutralization, the pH of the treated 
 
 12 
 
 0) 
 
 a 
 S 10 
 
 E 
 
 o 
 o 
 
 E 
 
 LiT 
 
 UJ 
 
 o 
 
 Q 
 
 _l 
 CO 
 
 8 
 
 
 
 KEY 
 P^ Lime 
 
 [//^ Limestone 
 
 IS 
 
 :V,Ti>1^(: 
 
 
 "SUM 
 
 
 ^S 
 
 5 43 
 SETTLING TIME, days 
 
 FIGURE 10. - Limestone treatment produces a 
 denser sludge in 1 day than lime neutralization 
 produces in 43 days. 
 
 drainage is between 6.8 and 8.0 and the 
 iron oxidation rate ranges from 10 to 
 25 ppm/min (fig. 12). 
 
 To minimize the power and land require- 
 ments for aeration, the Bureau is inves- 
 tigating the use of catalysts to increase 
 the rate of ferrous iron oxidation at low 
 pH. A laboratory study by the Bureau of 
 Mines indicated that activated carbon was 
 an effective catalyst in the oxidation of 
 ferrous iron (23). In batch tests, the 
 ferrous iron content of acid mine drain- 
 age flowing through an aspirated column 
 of activated carbon was reduced from over 
 700 ppm to less than 10 ppm in approxi- 
 mately 1 minute. In these tests, approx- 
 imately 5,000 ml of the acid drainage was 
 passed through the 200 grams of activated 
 carbon before the catalytic effect was 
 noted. During this period the pH of the 
 effluent was higher than that of the mine 
 drainage feed. Since the increase in 
 iron oxidation rate was observed after 
 the pH of the drainage showed substan- 
 tially no change, the onset of the cata- 
 lytic effect was attributed to acid con- 
 ditioning the carbon, 
 
 A pilot-scale field study was conducted 
 (33) to study the effect of activated 
 carbon on the ferrous iron oxidation rate 
 using a three-stage continuously stirred 
 reactor. Continuous agitation of the 
 carbon in the mine water provided more 
 efficient water-carbon contact and pre- 
 vented channeling and/or fouling. A weir 
 device at the top of the reactor con- 
 trolled carbon loss. In this system the 
 ferrous iron oxidation rates were not as 
 high as those reported in the previous 
 laboratory study. Acid conditioning the 
 carbon did not significantly affect the 
 iron oxidation rate. When the pH of the 
 influent water was adjusted to 5, the 
 rate of iron oxidation increased, but not 
 to the levels reported in the laboratory 
 study. When comparing the rate data from 
 the field and laboratory studies, it was 
 considered possible that the high iron 
 oxidation rate reported was due to the 
 growth of iron-oxidizing bacteria on the 
 carbon rather than to direct catalysis by 
 the carbon. T. ferrooxidans is an aero- 
 bic bacterium which derives energy from 
 
13 
 
 Mine discharge 
 from borehole 
 
 Makeup limestone 
 Autogenous tube mill, 25 rpm, ^^^^ 3 in by 
 7,500- to 9,000-1 b limestone load, ' 
 
 about 80 pet C0CO3 
 
 Limestone slurry sump, ['] 
 6to8.7lb/min U / 
 
 <400"mesh size 
 
 Mine water analysis : 
 PH, 2.8 
 Fe**, 36 ppm 
 Total Fe, 360 ppm 
 Acidity, 1,690 ppm 
 
 Effluent 
 pH, 5.7 
 
 Aeration pond 
 
 Weir 
 Effluent pH, 6.8 
 Fe, 3 ppm 
 
 Sedimentation pond 
 
 Discharge to main lagoon 
 pH, 7.0 
 
 Fe, < I ppm 
 
 FIGURE 11, - Limestone treatment, which includes neutralization, aeration, and settling, is 
 less expensive and produces a dense crystalline sludge. 
 
 the oxidation of ferrous iron in acid 
 mine drainage. It is possible that the 
 activated carbon provides a substrate to 
 which the bacteria adhered. However, 
 recent laboratory tests showed no signif- 
 icant bacterial activity or catalytic 
 action. 
 
 The Bureau is also funding an investi- 
 gation of the growth of iron-oxidizing 
 bacteria on clay particles (5,000 mg/l) 
 in a sequencing batch reactor. In this 
 test bacteria are grown on clay particles 
 in a ferrous sulfate solution containing 
 appropriate inorganic nutrients. The re- 
 actor, a system of fill, aerate, settle, 
 and discharge cycles (fig. 13), is de- 
 signed to produce an effluent with a Fe2+ 
 concentration of less than 10 mg/l. The 
 retention of bacteria on the clay par- 
 ticles is dependent upon the ferrous iron 
 content. If the Fe2+ content of the 
 
 system decreases to 5 mg/l, the bacteria 
 are desorbed from the clay and removed 
 from the reactor in the discharge cycle. 
 Using the sequencing batch reactor, a 
 ferrous iron oxidation rate of approxi- 
 mately 290 mg/l/hr has been reported for 
 estimated bacterial populations of ap- 
 proximately 5 X 10^ cells/ml. 
 
 The disposal of sludge produced by neu- 
 tralization of acid mine drainage is ex- 
 pensive and potentially one of the most 
 persistent problems in its treatment. As 
 a preliminary step, the current sludge 
 disposal practices of 33 treatment plants 
 were assessed to determine the magnitude 
 of sludge production, current disposal 
 practices, and constraints on their usage 
 (1). The primary sludge disposal problem 
 involves the large volume of sludge gen- 
 erated and the scarcity of approved dis- 
 posal sites. The four most commonly used 
 
lA 
 
 800 
 
 700 - 
 
 600 - 
 
 500 - 
 
 I 
 
 Q. 
 
 ^ 400 
 
 300 - 
 
 200 - 
 
 100 
 
 1 -r 
 
 1 I 1 
 
 1 
 
 - \\ 
 
 
 - 
 
 \ \ 
 
 \ 
 
 ~ 
 
 - \ \ 
 
 \ N 
 \ S 
 \ N 
 
 - 
 
 ^^ 
 
 \ 1 1 >^ ^^ 
 
 4-^ 
 
 10 15 20 
 
 MIXING TIME, mm 
 
 25 
 
 ■30 
 
 35 
 
 FIGURE 12. - In acid mine drainage neutralized 
 with limestone, the rate of ferrous iron oxidation is 
 10 to 25 ppm/min» 
 
 V////.m^///////////////////777Zy 
 
 Settle 
 
 2 4 6 8 10 
 
 BATCH REACTOR SEQUENCING CYCLE TIME, hr 
 
 12 
 
 FIGURE 13. - The sequencing batch reactor in- 
 corporates fill, aerate, settle, and discharge cycles 
 to optimize the rate of ferrous iron oxidation by 
 bacteria. 
 
 methods of sludge disposal are deep mine 
 disposal, retentzion in ponds, incorpora- 
 t:ion in coal refuse piles, and surface 
 burial. The amount of land required for 
 disposal is usually the determining fac- 
 tor in the overall cost, although trans- 
 portation, equipment, maintenance, and 
 labor are also significant (fig. 14). 
 The development of methods to efficiently 
 and economically increase the density of 
 the sludge would substantially reduce the 
 cost of sludge disposal. 
 
 Although there are other methods poten- 
 tially applicable to acid mine drainage 
 
 Deep mine 
 
 Retained in pond 
 
 Refuse area 
 
 Burial on site 
 
 33 AMD plants surveyed 
 Total area: 214 acres 
 
 KEY 
 ^3 Pet AMD plants 
 Pet total acreage 
 Average area, acres 
 
 I I Maximum area per 
 
 site, acres 
 J L 
 
 100 
 
 20 40 60 80 
 
 FIGURE 14. - Most sludge from acid mine drain- 
 age (AMD) treatment is retained in ponds, pumped 
 into abandoned sections of deep mines, or dumped 
 in refuse areas. 
 
 treatment, such as ion exchange, reverse 
 osmosis, and flash distillation, the Bu- 
 reau is not currently investigating 
 these. Most of these processes are high 
 in cost, have high power requirements, 
 and produce a highly concentrated toxic 
 brine or sludge which is more difficult 
 to dispose of than the original sludge. 
 The Bureau's research program in treating 
 acid drainage from active mines is di- 
 rected toward development and demonstra- 
 tion of a complete limestone treatment 
 system, including a suitable catalyst for 
 rapid oxidation of ferrous iron and 
 sludge disposal. 
 
 The Bureau is also investigating a low- 
 cost, low-maintenance treatment system 
 for small streams contaminated by acid 
 drainage from abandoned mines. Conven- 
 tional treatment is not applicable be- 
 cause of the low flow rate and the remote 
 rural location. It has been observed 
 that bogs containing sphagnum moss and/or 
 cattails remove iron by ion exchange and 
 precipitation (10). Subsequent neutrali- 
 zation at limestone outcrops completes an 
 effective natural treatment system. 
 Artificial duplication of this natural 
 process could improve water quality in 
 many small streams. 
 
 The Bureau will test the practicality 
 of duplicating this natural treatment 
 system at a low-flow acid drainage dis- 
 charge point in Northern Appalachia. 
 
15 
 
 The system will include an artificial 
 sphagnum moss bog followed by limestone 
 rubble. The system is designed so that 
 the drainage will pool in the moss, but 
 will not raise the upstream water level 
 enough to allow the water to flow around 
 the treatment system. Monitoring the pH, 
 Eh, temperature, iron and sulfate concen- 
 trations, and total acidity of the stream 
 above and below the artificial bog will 
 determine its effect on water quality. 
 The monitoring will extend over at least 
 6 months so that the effect of uncon- 
 trollable parameters such as ambient tem- 
 perature, rainfall, and stream flow rate 
 can be determined. If this low-cost, 
 low-maintenance system proves to be ef- 
 fective, it could be used to restore many 
 small streams in rural areas. 
 
 AT- SOURCE CONTROL OF ACID MINE DRAINAGE 
 
 Of the millions of dollars spent on 
 acid mine drainage each year, the major 
 portion is spent on treatment. But 
 treatment is not the best solution to 
 most acid mine drainage problems. Treat- 
 ment has the disadvantage of being nec- 
 essary for as long as the acid discharge 
 continues and thus requires manpower, 
 surface facilities, and a sludge disposal 
 area indefinitely. 
 
 West Virginia (16). Sodium lauryl sul- 
 fate was applied at rates of 20 to 55 gal 
 of 30-pct solution per acre, with a dilu- 
 tion range between 1:100 and 1:1000. 
 Application rates were based on labora- 
 tory adsorption tests; dilution rates 
 were dictated by site characteristics. 
 At each site, drainage pH rose from ap- 
 proximately 2.5 to 5.5 or higher, with 
 similarly dramatic decreases in acidity, 
 iron, and sulfates. 
 
 One disadvantage of the detergents is 
 that their effectiveness is limited; re- 
 population of the bacteria typically 
 occurs in 3 to 4 months. To provide 
 long-term control, the surfactants have 
 been incorporated into rubber pellets 
 (16) which can be applied early to a 
 refuse pile or pyrite mine spoil. These 
 pellets gradually release the surfactant 
 into infiltrating rain water. In labora- 
 tory studies (fig. 15) and pilot-scale 
 tests (fig. 16), controlled release of 
 sodium lauryl sulfate reduced acid pro- 
 duction 50 to 95 pet (14). Full-scale 
 field tests are now in progress. 
 
 Another potential approach to at-source 
 control of acid production requires the 
 establishment of an alkaline environment. 
 As already discussed, pyrite oxidation is 
 
 Since acid drainage results from the 
 oxidation of pyrite associated with coal 
 and overburden strata, limiting the rate 
 of pyrite oxidation would reduce the 
 amount of acid formed. T. ferrooxidans 
 normally catalyzes the pyrite oxidation 
 and accelerates the initial acidification 
 of freshly exposed coal and overburden. 
 Inhibiting bacterial activity, therefore, 
 would limit the rate of acid production 
 and, in combination with proper reclama- 
 tion, would reduce substantially the to- 
 tal amount of acid produced. Of the mul- 
 titude of potential bactericidal agents, 
 certain biodegradable anionic surfactants 
 (detergents) have been found to control 
 T. ferrooxidans in an economical and 
 environmentally safe manner (15). 
 
 Field tests were recently conducted 
 by the Bureau of Mines on both active 
 and abandoned coal refuse piles in 
 
 5,0001^ 
 
 1,000 
 
 3,000 
 
 2,500 
 
 E 
 
 Q. 
 CL 
 
 - 2,000 ^ 
 
 _j 
 
 1,500 
 
 1.00 
 
 1,000 
 
 0.25 0.50 0.75 
 AMOUNT OF CONTROLLED 
 RELEASE MATERIAL, g 
 
 FIGURE 15. - The rate of acid production was 
 approximately that of sterile controls when deter- 
 gent was used to limit bacterial activity in a lab- 
 oratory study. 
 
16 
 
 35.000 
 
 g"^ 30,000 
 
 o 
 o 
 
 E 
 
 ro" 
 00 
 
 X 
 
 Q. 
 
 Q 
 
 O 
 < 
 
 5,000 - 
 
 70 100 130 
 
 AGE OF COAL REFUSE PILES, days 
 
 FIGURE 16. - Controlled release of detergents can 
 beused to reduce acid production from spoil piles by 
 50 to 95 pet compared with an untreated control. 
 
 slow at near-neutral pH. A source of 
 alkalinity such as lime, if added to 
 recently exposed pyritic material, will 
 retard or prevent acidification. The Bu- 
 reau of Mines is currently investigating 
 the possibility of reestablishing a radi- 
 cally alkaline environment, albeit tem- 
 porarily, to determine if this will slow 
 pyrite oxidation to the point where lime- 
 stone will be sufficient to maintain 
 near-neutral pH. 
 
 Water handling procedures for under- 
 ground coal mines generally combine grav- 
 ity flow and collection with pumping from 
 sumps to surface treatment and/or dis- 
 posal areas. To minimize the formation 
 of acid water, properly placed sumps and 
 pumping systems can reduce the time the 
 water is in contact with pyritic materi- 
 als. The size and location of sumps is 
 also governed by the ability to discharge 
 water on the surface with minimum power. 
 
 depends upon 
 t ration of 
 a treatment 
 control 
 reduce 
 
 Since on the average it requires 0.5 kwhr 
 to pump 1,000 gal of water against a 100- 
 ft head, gravity drainage and an effi- 
 cient pump are most cost effective. The 
 capacity of water treatment facilities 
 flow rate and the concen- 
 pollutants. In designing 
 system, using infiltration 
 and efficient water handling to 
 the amount of water flowing 
 through the mine and minimize the amount 
 of acid formed can result in substantial 
 savings in water treatment costs. 
 
 A recent Bureau of Mines contract study 
 examined current state-of-the-art methods 
 of water diversion and overburden de- 
 watering in Appalachian bituminous coal- 
 fields (3). It was found that most water 
 enters underground mines either through 
 water-bearing strata in contact with the 
 coal seam, from surface seepage, through 
 faults and fractures, or from abandoned 
 workings. If surface water is the 
 source, runoff diversion, regrading, soil 
 sealing, and streambed modifications are 
 possible control methods. The influx of 
 ground water may be controlled by reduc- 
 ing the permeability of overlying strata, 
 sealing abandoned mines , and well de- 
 watering in advance of mining. Although 
 all of these methods have been tried to 
 some extent (table 1), their successful 
 application depends largely upon geologic 
 and hydrologic conditions. In general, 
 the standard approach to handling the in- 
 flux of water into underground mines con- 
 sists of collecting the water and pumping 
 it back to the surface. At present it 
 appears that water diversion and over- 
 burden dewatering are, at best, sup- 
 plements to traditional water handling 
 procedures. Such methods have the 
 advantages of helping to control large 
 influxes of water that could affect pro- 
 duction and reducing the cost of water 
 treatment. 
 
TABLE 1. - Water control practices (2) 
 
 17 
 
 Water control 
 practice 
 
 Application 
 
 Limits of control 
 
 Field experience 
 
 
 
 SURFACE WATER CONTROLS 
 
 
 Runoff 
 
 diversion. . . 
 
 Prevents infiltration into 
 
 Effective if mine inflow 
 
 Used with varying 
 
 
 
 soil, mine openings, out- 
 
 is due to infiltration. 
 
 success. 
 
 
 
 crops, rock fissures, strip- 
 
 May increase stream flow. 
 
 
 
 
 pings, cave-ins, surface 
 
 
 
 
 
 cracks, and subsidence areas. 
 
 
 
 Surface 
 
 ! regrading,. 
 
 Eliminates ponding and im- 
 
 Depends on drainage area. 
 
 Used at strip mine 
 
 
 
 proves drainage. Applicable 
 
 annual precipitation. 
 
 sites. Can be very 
 
 
 
 near surface mines or other 
 
 rate of infiltration in- 
 
 effective if mine 
 
 
 
 large land disturbances. 
 
 to soil. May increase 
 stream flow. 
 
 water is due to 
 ponding of water 
 over mine. 
 
 Soil sealing 
 
 Prevents infiltration 
 
 Prevents infiltration into 
 
 Limited success. 
 
 
 
 into soil by reducing 
 
 soil only. Not effective 
 
 
 
 
 permeability. 
 
 in sealing fractures or 
 other flow conduits. 
 
 
 Stream 
 
 channeling. . 
 
 Prevents inflow to mines from 
 streams, especially in areas 
 of vertical fractures, 
 subsidence, or high 
 permeability. 
 
 Can prevent large quan- 
 tities of water from 
 entering a mine. 
 
 Very effective. 
 
 
 GROUND WATER 
 
 CONTROLS 
 
 
 Grouting and/or 
 
 Reduces permeability of over- 
 
 Effective in limiting in- 
 
 Effective in curtail- 
 
 grouting curtains. 
 
 lying strata by sealing fis- 
 
 flow via direct conduits. 
 
 ing water inflow 
 
 
 sures, fractures, and perme- 
 
 
 during shaft sink- 
 
 
 able formations. 
 
 
 ing. Also used to 
 cement localized 
 areas of water in- 
 flow such as faults 
 and joints. 
 
 Borehole sealing... 
 
 Prevents inflow to mines 
 
 Sealing ineffective after 
 
 Effective in reducing 
 
 
 through boreholes from sur- 
 
 roof collapses. 
 
 inflow through 
 
 
 face water sources and/or 
 
 
 boreholes. 
 
 
 overlying aquifers. 
 
 
 
 Subsurface soil 
 
 Prevents infiltration through 
 
 Sealing efficiency re- 
 
 No demonstrations of 
 
 sealing. 
 
 the soil by reducing 
 
 duced if area frac- 
 
 this technique. 
 
 
 permeability. 
 
 tured. Most sealants 
 are uneconomical. 
 
 
 Mine sealing 
 
 Prevents water from escaping 
 
 Seals may lose effective- 
 
 Effective in reducing 
 
 
 an abandoned mine and infil- 
 
 ness with time, depending 
 
 or eliminating flow 
 
 
 trating active workings. 
 
 on construction method 
 
 from abandoned mines 
 
 
 
 and strata changes. 
 
 into active mines. 
 
 
 
 Seals may cause ground 
 
 
 
 
 water levels to rise, 
 
 
 
 
 causing surface damage. 
 
 
 
 
 Breached seals may prove 
 
 
 
 
 hazardous to adjacent op- 
 
 
 
 
 erating mines. 
 
 
 Well dewatering .... 
 
 Intercepts aquifers and 
 
 Requires favorable geo- 
 
 Limited success. 
 
 
 controls the movement 
 
 logic conditions. 
 
 Used in reducing 
 
 
 and discharge of 
 
 
 water handling re- 
 
 
 groundwater. 
 
 
 quirements in mine. 
 
18 
 
 In coal mines where fracture-dominated 
 inflow is localized, intercepting water 
 entering through faults and fractures may 
 be feasible. Water flowing through such 
 fracture zones is essentially surface 
 water and would not normally require 
 treatment. The Bureau has awarded a 
 contract to conduct a pilot study on 
 controlling fracture-dominated inflow. 
 The study will develop design criteria 
 for, and determine the cost effectiveness 
 of, intercepting nonacid water flowing 
 through localized fractures and trans- 
 porting it to the surface. Economic and 
 engineering analysis of this process 
 should determine if it would reduce the 
 cost of treatment substantially. 
 
 Coal storage piles and refuse piles may 
 also be sources of ground water contam- 
 ination (38). Rainfall percolating 
 through such piles may leach acid and/or 
 other toxic ions and carry them into 
 
 ground water. The Bureau has awarded a 
 contract to assess the extent of ground 
 and surface water contamination from coal 
 storage piles. Methods to prevent con- 
 tamination of ground water include sur- 
 face collection, impoundment, and treat- 
 ment of runoff water. Preliminary cost 
 estimates and a discussion of beneficial 
 and adverse effects will be included. 
 
 Another area of concern is the effect 
 of large-scale lignite mining in western 
 Tennessee on ground water resources. At 
 present there are few data available on 
 the effects of mining upon ground water 
 in the alluvial plain, in both shallow 
 and deep aquifers. To gather data, four 
 wells and two pits have been dug to de- 
 termine ground water levels, movement, 
 and chemistry. A contract report will 
 assess the hydrologic impact of lignite 
 mining. 
 
 SUMMARY AND RECOMMENDATIONS 
 
 The Federal Water Pollution Control Act 
 of 1972 set effluent standards for coal 
 mines, requiring treatment for acid mine 
 drainage. Although these standards have 
 been in effect for almost a decade, there 
 has not been significant improvement in 
 the water quality of many streams af- 
 fected by mine drainage. This lack of 
 improvement is related to the amount of 
 acid drainage flowing from abandoned 
 mines. 
 
 It has been known for years that air, 
 water, bacteria, and pyrite are essential 
 elements in acid production, yet at pres- 
 ent there is no standard method or pro- 
 gram for limiting the formation of acid 
 mine drainage. Controlled release of 
 anionic surfactants appears to be 
 applicable to near-surface sources of 
 acid production but not to long-term 
 treatment of underground mines. Mine 
 sealing, which is supposed to limit acid 
 production in abandoned mines, has been 
 only marginally successful (table 2). 
 Bureau of Mines studies indicate that 
 surface reclamation and seals at mine 
 openings do not retard the passage of air 
 into a mine. In many cases, seals used 
 
 to flood a mine or the surrounding strata 
 cannot withstand the continuous hydraulic 
 pressure, resulting in failure of the 
 seal or seepage around it. The Bureau is 
 now evaluating mine seals in several are- 
 as in order to determine relevant chemi- 
 cal, geological, and engineering param- 
 eters and to determine the long-term 
 effect of mine sealing on water quality. 
 
 Mine sealing is relevant not only to 
 abandoned mines, but also to operating 
 mines that will close in the future. At 
 the present, mines must eliminate acid 
 production or treat acid drainage in- 
 definitely. It is possible that bond 
 forfeiture may become a realistic eco- 
 nomic alternative to the long-term cost 
 of water treatment. In this area, there 
 is need for development of low-cost seals 
 that will maintain their integrity in- 
 definitely. Other methods such as con- 
 trolled roof collapse, water diversion, 
 bacterial inhibition, and improved drain- 
 age should be investigated to determine 
 their usefulness in reducing the forma- 
 tion of acid in mines that are no longer 
 operating. 
 
19 
 
 TABLE 2. - Variation in composition of mine effluent before and after sealing 
 
 Mine 1 
 
 Before 
 
 Low 
 
 High 
 
 After 
 
 Low 
 
 High 
 
 Mine 2 
 
 Before 
 
 Low 
 
 High 
 
 After 
 
 Low 
 
 High 
 
 2.9 
 75 
 655 
 203 
 109 
 13 
 
 3.2 
 
 1,290 
 
 2,260 
 
 1,242 
 
 520 
 
 508 
 
 PH 
 
 Total acidity (as CaCOj)! , .ppm. . 
 
 Sulfate (as SO4 ) ppm. . 
 
 Calcium (as CaCO^) ppm.. 
 
 Magnesium (as MgCOj ) ppm. . 
 
 Total iron (as Fe203) ppm.. 
 
 lEnd point = pH 8.2 at 60° C. 
 
 Improved prediction of acid drainage 
 potential is being investigated in order 
 to eliminate or minimize the formation of 
 acid mine drainage. At present, core 
 samples are analyzed for total sulfur and 
 potential alkalinity, or tested with slow 
 leaching methods. These procedures have 
 not been correlated with acidity mea- 
 surements in the field, and they are gen- 
 erally acknowledged as only an approx- 
 imation of potential acid problems. 
 Available techniques will be tested at 
 sites where the extent of acid production 
 is known, to determine their accuracy and 
 possibly develop modifications. Rapid- 
 leaching tests will also be examined for 
 their applicability to the determination 
 of acid potential. Accurate methods of 
 predicting acid potential of coal and 
 overburden will allow better permitting 
 by State agencies, improved mine plan- 
 ning, and improved reclamation. 
 
 In operating mines, the need to treat 
 large volumes of acid drainage is a 
 problem. Currently, lime neutralization 
 with aeration is the standard method of 
 treating acid mine drainage. This method 
 is relatively expensive, requires hand- 
 ling a caustic substance, and produces a 
 sludge with poor settling characteris- 
 tics. The Bureau has developed and is 
 now improving a treatment system using 
 limestone. Limestone treatment is less 
 expensive, uses a noncaustic material, 
 and produces a denser sludge. Routine 
 use of the system requires the rapid oxi- 
 dation of ferrous iron at acid or neutral 
 pH. In an initial field study, activated 
 
 3.0 
 45 
 
 356 
 
 36 
 
 76 
 
 5 
 
 5.5 
 490 
 1,180 
 625 
 336 
 160 
 
 2.3 
 
 80 
 
 349 
 
 125 
 
 76 
 
 33 
 
 3.2 
 1,210 
 2,520 
 760 
 530 
 670 
 
 2.85 
 
 20 
 
 152 
 
 70 
 
 7 
 
 23 
 
 3.70 
 
 1,170 
 
 2,375 
 
 725 
 
 502 
 
 720 
 
 carbon did not have the anticipated 
 catalytic effect on the iron oxidation 
 rate. Presently, studies are underway to 
 determine if iron-oxidizing bacteria 
 grown on activated carbon can increase 
 the rate of iron oxidation in acid mine 
 drainage. A study using bacteria grown 
 on clay particles in a sequencing batch 
 reactor has the same purpose. The 
 develop-ment of an effective oxidation 
 step will allow full-scale testing of the 
 limestone treatment process. At present, 
 other methods of treating acid mine 
 drainage are not economically or tech- 
 nically practical. Limestone treatment 
 seems to be one alternative that could be 
 technically feasible and economically 
 superior to lime treatment, although at 
 present it is primarily applicable to 
 waters with a low ferrous iron content. 
 It also has the advantage of being read- 
 ily adaptable to reclaiming streams 
 affected by drainage from abandoned 
 mines. A passive system using sphagnum 
 moss and limestone will be tested as a 
 means of improving water quality in low- 
 flow streams. 
 
 It is apparent that 10 years of man- 
 dated water treatment have not produced a 
 significant improvement in overall water 
 quality. Although treatment of acid 
 drainage from active mines prevents fur- 
 ther deterioration, the majority of mine 
 water pollution originates from abandoned 
 mines. At present there is a need to 
 develop methods for reclaiming polluted 
 streams and for at-source control of 
 acid production. Research is needed to 
 
20 
 
 develop limestone treatment into a prac- 
 tical alternative to lime neutralization. 
 To address these and other acid mine 
 drainage pollution problems, the Bureau 
 of Mines is conducting research in bac- 
 terial inhibition to control acid genera- 
 tion, improved water handling to reduce 
 acid load, development of improved mine 
 seals, rapid biological oxidation of fer- 
 rous iron, improved sludge disposal prac- 
 tices, low-maintenance treatment of small 
 streams, reclamation techniques to reduce 
 
 acid drainage formation, and limestone 
 treatment of acid drainage (table 3). 
 
 Work in these research areas comprises 
 a comprehensive approach to solving many 
 of the longstanding problems associated 
 with acid mine drainage. Improved treat- 
 ment methods, at-source control methods, 
 and stream reclamation methods resulting 
 from the Bureau's research program will 
 make a significant contribution to up- 
 grading water quality in mining areas. 
 
 TABLE 3. - Bureau of Mines conservation and development program — acid mine drainage 
 
 Research area 
 
 Prediction of acid mine drainage: 
 
 Prediction of acid potential 
 
 Prediction of water infiltration 
 
 Integration of predictive technology and premine planning 
 
 At-source control technology: 
 
 Inhibition of acid-forming bacteria: 
 
 Surface mines and refuse piles 
 
 Tailings piles 
 
 Extension of bacterial inhibition to underground mines where 
 
 applicable 
 
 Alkaline treatment of coal refuse 
 
 Placement of phritlc overburden 
 
 Water handling procedures, including diversion and dewatering 
 
 At-source control technology for inactive or abandoned mines: 
 
 Daylighting 
 
 Effect of flooding on acid production, limiting parameters 
 
 Improved mine seals 
 
 Feasibility study — underground disposal mine refuse in a flooded mine 
 
 Demonstration of above if feasible 
 
 Reclamation of acid seeps (burnout) on revegetated mine sites 
 
 Water treatment: 
 
 Enhanced oxidation of iron 
 
 Limestone neutralization 
 
 Improved sludge disposal 
 
 Assessment studies: 
 
 Ground water contamination by acid-producing metal ore mines and 
 t ai lings ponds 
 
 Economic analysis — recovery of metals from tailings or streams 
 
 Manuals : 
 
 Premine planning to minimize acid drainage 
 
 At-source control of acid drainage 
 
 Proposed 
 time frame, 
 fiscal years 
 
 1981-85 
 1981-84 
 1984-86 
 
 1981-83 
 1983-84 
 
 1983-86 
 1982-83 
 1982-85 
 1981-85 
 
 1982-85 
 1982-85 
 1981-86 
 1982-83 
 1984-85 
 1982-85 
 
 1981-86 
 1984-86 
 1982-84 
 
 1982-86 
 1983-85 
 
 1985-86 
 1985-86 
 
21 
 
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22 
 
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 35. Tennessee Department of Public 
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 37. U.S. Code of Federal Regula- 
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 105 pp. 
 
 INT.-BU.OF MINES, PGH., PA. 26485 
 
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