Acid Mine Drainage

Mod­i­fied and updat­ed by Chris­t­ian Wolk­ers­dor­fer based on a text pub­lished by the Office of Sur­face Min­ing Recla­ma­tion and Enforce­ment (OSMRE).

Acid mine drainage (AMD) has been a detri­men­tal by-prod­uct of coal min­ing for many years. At present, acid mine drainage con­tin­ues to pose a poten­tial prob­lem in some areas, despite improved pre­dic­tion and pre­ven­tion tech­niques.

Acid Mine Drainage Research

Acid mine drainage (AMD) has been the sub­ject of inten­sive research since the 1960s. Research efforts have pro­ceed­ed recent­ly through the Mine Drainage Tech­nol­o­gy Ini­tia­tive (MDTI), the Inter­na­tion­al Net­work of Acid Pre­ven­tion (INAP), the Mine Envi­ron­ment Neu­tral Drainage (MEND) pro­gram and the Inter­na­tion­al Mine Water Asso­ci­a­tion (IMWA). The major areas of research on AMD are Pre­dic­tion of AMD and Prevention/Mitigation.

The fol­low­ing is an overview of infor­ma­tion on some major acid mine drainage top­ics.

Factors controlling the formation of AMD

The for­ma­tion of acid drainage is a com­plex geo­chem­i­cal and micro­bial­ly medi­at­ed process. The acid load ulti­mate­ly gen­er­at­ed from a mine site is pri­mar­i­ly a func­tion of the fol­low­ing fac­tors:

Pyrite Weathering

Chemistry of Pyrite Weathering

A com­plex series of chem­i­cal weath­er­ing reac­tions are spon­ta­neous­ly ini­ti­at­ed when sur­face min­ing activ­i­ties expose spoil mate­ri­als to an oxi­diz­ing envi­ron­ment (Deutsch, 1997). The min­er­al assem­blages con­tained in the spoil are not in equi­lib­ri­um with the oxi­diz­ing envi­ron­ment and almost imme­di­ate­ly begin weath­er­ing and min­er­al trans­for­ma­tions. The reac­tions are anal­o­gous to “geo­log­ic weath­er­ing” which takes place over extend­ed peri­ods of time (i.e., hun­dreds to thou­sands of years) but the rates of reac­tion are orders of mag­ni­tude greater than in “nat­ur­al” weath­er­ing sys­tems. The accel­er­at­ed reac­tion rates can release dam­ag­ing quan­ti­ties of acid­i­ty, met­als, and oth­er sol­u­ble com­po­nents into the envi­ron­ment. The pyrite oxi­da­tion process has been exten­sive­ly stud­ied and has been reviewed by Nord­strom (1979). For pur­pos­es of this descrip­tion, the term “pyrite” is used to col­lec­tive­ly refer to all iron disul­fide min­er­als.‌‌‌‌‌‌‌

The fol­low­ing equa­tions show the gen­er­al­ly accept­ed sequence of pyrite reac­tions:

2 FeS₂ + 7 O₂ + 2 H₂O → 2 Fe²⁺ + 4 SO₄^2- + 4 H⁺

4 Fe²⁺ + O₂ + 4 H⁺ → 4 Fe³⁺ + 2 H₂O

4 Fe³⁺ + 12 H₂O → 4 Fe(OH)₃ + 12 H⁺

FeS₂ + 14 Fe³⁺ + 8 H₂O → 15 Fe²⁺ +2 SO₄^2- + 16 H⁺

In the ini­tial step, pyrite reacts with oxy­gen and water to pro­duce fer­rous iron, sul­fate and acid­i­ty. The sec­ond step involves the con­ver­sion of fer­rous iron to fer­ric iron. This sec­ond reac­tion has been termed the “rate-deter­min­ing” step for the over­all sequence.

The third step involves the hydrol­y­sis of fer­ric iron with water to form the sol­id fer­ric hydrox­ide (fer­ri­hy­drite) and the release of addi­tion­al acid­i­ty. This third reac­tion is pH-depen­dent. Under very acid con­di­tions of less than about pH 3.5, the sol­id min­er­al does not form and fer­ric iron remains in solu­tion. At high­er pH val­ues, a pre­cip­i­tate forms, com­mon­ly referred to as “yel­low boy.”

The fourth step involves the oxi­da­tion of addi­tion­al pyrite by fer­ric iron. The fer­ric iron is gen­er­at­ed by the ini­tial oxi­da­tion reac­tions in steps one and two. This cyclic prop­a­ga­tion of acid gen­er­a­tion by iron takes place very rapid­ly and con­tin­ues until the sup­ply of fer­ric iron or pyrite is exhaust­ed. Oxy­gen is not required for the fourth reac­tion to occur.

The over­all pyrite reac­tion series is among the most acid-pro­duc­ing of all weath­er­ing process­es in nature.

Microbiological Controls

The pyrite weath­er­ing process is a series of chem­i­cal reac­tions but also has an impor­tant micro­bi­o­log­i­cal com­po­nent. The con­ver­sion of fer­rous to fer­ric iron in the over­all pyrite reac­tion sequence has been described as the “rate-deter­min­ing step” (Singer and Stumm, 1970). This con­ver­sion can be great­ly accel­er­at­ed by a species of bac­te­ria, Acidithiobacil­lus fer­rox­i­dans. This bac­te­ria and sev­er­al oth­er species thought to be involved in pyrite weath­er­ing are wide­spread in the envi­ron­ment. A. fer­rox­i­dans has been shown to increase the iron con­ver­sion reac­tion rate by a fac­tor of hun­dreds to as much as one mil­lion times (Singer and Stumm, 1970; Nord­strom, 1979).

The activ­i­ty of these bac­te­ria is pH-depen­dent on opti­mal con­di­tions in the range of pH 2 to 3. Thus, once pyrite oxi­da­tion and acid pro­duc­tion have begun, con­di­tions are favourable for bac­te­ria to fur­ther accel­er­ate the reac­tion rate. At pH val­ues of about 6 and above, bac­te­r­i­al activ­i­ty is thought to be not rel­e­vant or com­pa­ra­ble to abi­ot­ic reac­tion rates. The cat­alyz­ing effect of the bac­te­ria effec­tive­ly removes con­straints on pyrite weath­er­ing and allows the reac­tions to pro­ceed rapid­ly. The role of microbes in pyrite oxi­da­tion is described in more detail by Klein­mann et al. (1981) and Nord­strom (1979).

Depositional Environment

Pale­oen­vi­ron­ments under which coal-bear­ing rocks formed can be char­ac­ter­ized into three gen­er­al cat­e­gories: marine; fresh­wa­ter; and brack­ish. Stud­ies of Penn­syl­van­ian-age coal-bear­ing rocks have shown that the pale­oen­vi­ron­ment can be used to broad­ly define acid drainage poten­tial (Skousen et al., 1998, Brady et al. 1988; Horn­berg­er et al. 1981). Rocks formed in brack­ish water con­di­tions are gen­er­al­ly most prone to acid pro­duc­tion; fresh­wa­ter sys­tems usu­al­ly pro­duce non-acid water, and marine sys­tems pro­duce vari­able drainage qual­i­ty. In some coal mea­sures, the pale­oen­vi­ron­ment varies lat­er­al­ly and ver­ti­cal­ly with­in a sin­gle mine site and is a con­trol­ling fac­tor in the inher­ent dis­tri­b­u­tion of pyrite and car­bon­ates.

Acid/Base Balance and Reaction Rates

Drainage and spoil qual­i­ty are a prod­uct of two com­pet­ing process­es: acid for­ma­tion from pyrite oxi­da­tion, and gen­er­a­tion of alka­lin­i­ty from the dis­so­lu­tion of car­bon­ates and oth­er basic min­er­als.

The acid gen­er­a­tion process con­sists of three phas­es: ini­ti­a­tion; prop­a­ga­tion; and ter­mi­na­tion. The ini­ti­a­tion phase can begin as soon as pyrit­ic mate­ri­als are exposed to an oxi­diz­ing envi­ron­ment, how­ev­er, the acid load gen­er­at­ed is rel­a­tive­ly small. In the prop­a­ga­tion phase, acid pro­duc­tion increas­es rapid­ly. In the ter­mi­na­tion phase, acid pro­duc­tion grad­u­al­ly declines. The actu­al times asso­ci­at­ed with these phas­es are, at present, ill-defined, but appear to be on the order of years to decades. Mod­el­ling pre­dic­tions and com­par­i­son to a lim­it­ed num­ber of field sites indi­cate the peak acid load occurs 5 to 10 years after min­ing, fol­lowed by a grad­ual decline over 20 to 40 years (Ziemkiewicz et al., 1991, Hart et al., 1991). The same stud­ies project very long decay curves for coal refuse (beyond 50 years) before acid leachate is deplet­ed. Reli­able acid generation/depletion pre­dic­tions for under­ground mine dis­charges are not avail­able.

The over­all acid-pro­duc­ing process can pro­ceed very rapid­ly with few chem­i­cal con­straints. In con­trast, dis­so­lu­tion or reac­tion rates of many com­mon min­er­als are gen­er­al­ly slow due to sol­u­bil­i­ty lim­i­ta­tions. Pro­duc­tion of alka­lin­i­ty tends to attain a con­stant val­ue or lev­el off with time so that the rate of acid pro­duc­tion com­mon­ly may exceed the pro­duc­tion of alka­lin­i­ty.

The trends in reac­tion rates can be off­set or enhanced by the mass bal­ance between acid and alka­line-pro­duc­ing min­er­als. A gen­er­al rela­tion between acid and basic min­er­als and resul­tant drainage qual­i­ty is described as fol­lows:

• Low pyrite, low base con­tent – Drainage may con­tain low lev­els of acid­i­ty, or maybe non-acid. Low con­cen­tra­tions of dis­solved met­als.
• Low pyrite, high base con­tent – Drainage is alka­line with low con­cen­tra­tions of dis­solved met­als.
• High pyrite, low base con­tent – Drainage is acid with high con­cen­tra­tions of dis­solved met­als.
• High pyrite, high base con­tent – Drainage is usu­al­ly alka­line, occa­sion­al­ly acid, with high con­cen­tra­tions of dis­solved met­als.

The con­di­tions most con­ducive to acid for­ma­tion are high pyrite con­tents with lit­tle base mate­r­i­al present. Con­verse­ly, an excess of base rel­a­tive to pyrite is most like­ly to pre­clude acid for­ma­tion. Sites con­tain­ing low quan­ti­ties of pyrite and bases pro­duce the most vari­able drainage qual­i­ty and are the most dif­fi­cult to assess with pre-min­ing pre­dic­tive tech­niques.

Lithologic Controls

Lithol­o­gy or rock type also influ­ences spoil and drainage qual­i­ty. Phys­i­cal char­ac­ter­is­tics of the rock, such as poros­i­ty, and acces­so­ry min­er­als can exert var­i­ous con­straints or enhance­ments to the over­all chem­i­cal weath­er­ing process. For exam­ple, pyrit­ic sand­stones tend to release their acid load rapid­ly (Ziemkiewicz, 1991). Argilla­ceous rocks tend to release their acid load over a longer peri­od of time. Acces­so­ry min­er­als (clays and oth­er sil­i­cates) may dis­solve, form new min­er­als, or atten­u­ate the acid and alka­line weath­er­ing prod­ucts.

Mineralogical Controls

The min­er­al pyrite occurs in sev­er­al dif­fer­ent mor­pho­log­i­cal forms and a range of grain sizes. The “fram­boidal” form is con­sid­ered high­ly reac­tive and is char­ac­ter­ized by a small grain size and large sur­face area (Caruc­cio et al., 1977). Pyrite can occur in grain sizes rang­ing from invis­i­ble to the eye up to sev­er­al inch­es. Fram­boids and oth­er fine-grained pyrites with a large sur­face area are much more chem­i­cal­ly reac­tive than the coars­er forms (Evan­gelou, 1995). The reac­tiv­i­ty of fine-grained pyrites reflects the fact that acid-gen­er­at­ing reac­tions occur at the min­er­al sur­face.

Mine site Hydrologic Conditions

Mine site hydrol­o­gy plays a crit­i­cal role in deter­min­ing drainage qual­i­ty, yet the flow mechan­ics of ground­wa­ter in spoils are among the least under­stood aspects of AMD. The prod­ucts of pyrite oxi­da­tion are free acid and sol­u­ble acid salts. If no per­co­lat­ing water is present, the acid salts gen­er­at­ed from the lim­it­ed avail­able mois­ture sim­ply reside with­in the spoil. When excess mois­ture is present, the acid weath­er­ing prod­ucts are dis­solved and trans­port­ed with the water mov­ing through the mate­r­i­al.

The chem­istry of ground-water dis­charges can vary depend­ing on the degree of flush­ing (Sny­der and Caruc­cio, 1988) and the time since the last pre­cip­i­ta­tion event. Ground-water dis­charge can be “flashy” or rapid shal­low inter­flow asso­ci­at­ed with high-inten­si­ty short-dura­tion pre­cip­i­ta­tion events or base flow. Under­ground mine dis­charges that drain from large-vol­ume pool stor­age typ­i­cal­ly exhib­it a mut­ed or sea­son­al response to pre­cip­i­ta­tion pat­terns.

The posi­tion of a water table with­in the spoil also influ­ences drainage qual­i­ty. Water table ele­va­tions in spoils fluc­tu­ate in response to sea­son­al con­di­tions form­ing a zone of cyclic wet­ting and dry­ing. This pro­vides opti­mal con­di­tions for the oxi­da­tion and sub­se­quent leach­ing of pyrite and asso­ci­at­ed weath­er­ing prod­ucts. Ground-water flow paths and the loca­tion and ele­va­tion of sat­u­rat­ed zones are often dif­fi­cult to pre­dict in mine spoils.

Numer­ous chem­i­cal, phys­i­cal and bio­log­i­cal fac­tors inter­act to con­trol the qual­i­ty of mine drainage. Although the basic process­es of acid mine drainage for­ma­tion are uni­ver­sal, the impor­tance of any sin­gle con­trol­ling fac­tor is fre­quent­ly spe­cif­ic to mine site con­di­tions.‌‌

Prediction of AMD‌

Pre­dic­tion of acid gen­er­a­tion based on geo­chem­i­cal analy­sis has been prac­tised for about 25 years. The most wide­ly used method, Acid/Base Account­ing (Sobek et al., 1978), quan­ti­ta­tive­ly bal­ances pyrite against car­bon­ates and oth­er alka­line mate­ri­als. Its orig­i­nal use was to iden­ti­fy top­soil sub­sti­tutes and root zone media, not a quan­ti­ta­tive pre­dic­tor of drainage qual­i­ty. As a water qual­i­ty pre­dic­tor, it has been accu­rate in some instances and mis­lead­ing in oth­ers (Erick­son and Hei­den, 1988). Research has, there­fore, con­tin­ued on improv­ing pre­dic­tive meth­ods.

A vari­ety of sim­u­lat­ed weath­er­ing tests have been devel­oped and stud­ied as drainage qual­i­ty pre­dic­tors (Caruc­cio, 1967; Sturey et al., 1982; Ren­ton et al., 1988) Test details dif­fer, but all meth­ods attempt to mim­ic cyclic wetting/drying and flush­ing of spoil piles. Cur­rent­ly, there is no con­sen­sus on which method most accu­rate­ly reflects field con­di­tions. Ques­tions have also arisen regard­ing the length of lab­o­ra­to­ry test time and extrap­o­la­tion to field weath­er­ing time.

It has been observed that pyrites of dif­fer­ent ori­gins can exhib­it vary­ing lev­els of reac­tiv­i­ty. Lab­o­ra­to­ry stud­ies have been con­duct­ed (Ham­mack et al., 1988) to deter­mine why cer­tain pyrites are more chem­i­cal­ly reac­tive. “Evolved gas analy­sis,” which involves the ther­mal decom­po­si­tion of sul­fur com­pounds under con­trolled con­di­tions, has been used to char­ac­ter­ize pyrite reac­tiv­i­ty. The basic premise is that low­er tem­per­a­ture decom­po­si­tion reflects unsta­ble and more reac­tive pyrite. Cur­rent research efforts (Sheetz, 1990) are focused on X‑ray dif­frac­tion stud­ies of sub­tle dif­fer­ences in crys­tal struc­ture and pos­si­ble trace inclu­sions in the crys­tal lat­tice, in com­bi­na­tion with evolved gas analy­sis. The goal of these research efforts is to iden­ti­fy the con­trol­ling fac­tors and devel­op a repro­ducible test that dis­crim­i­nates reac­tive and non­re­ac­tive pyrites.

Com­put­er mod­els are anoth­er approach to the pre­dic­tion of acid gen­er­a­tion. Most of these mod­els incor­po­rate a num­ber of chem­i­cal and phys­i­cal para­me­ters to describe the chem­i­cal reac­tions of acid gen­er­a­tion, micro­bial catal­y­sis and leach­ing (trans­port) of the weath­er­ing prod­ucts (Jaynes, 1991; Schar­er et al., 1991). Many of these para­me­ters are dif­fi­cult to mea­sure or must be esti­mat­ed and ver­i­fi­ca­tion is gen­er­al­ly lack­ing. One mod­el uses a “lumped vari­able” approach, rather than a large num­ber of indi­vid­ual para­me­ters (Rymer et al., 1990; Hart et al., 1991). One com­bined vari­able esti­mates acid gen­er­a­tion, and a sec­ond vari­able accounts for the leach­ing of weath­er­ing prod­ucts. This mod­el is still under­go­ing test­ing and ver­i­fi­ca­tion.

Prevention/Mitigation of AMD

Research on acid pre­ven­tion and mit­i­ga­tion has focused on three main areas: chem­i­cal inhi­bi­tion of the acid-gen­er­at­ing reac­tions; inhi­bi­tion of the microbes respon­si­ble for cat­alyz­ing the acid-gen­er­at­ing reac­tions; and phys­i­cal or geot­ech­ni­cal treat­ments to min­i­mize water con­tact and leach­ing.

Chemical Methods

Alkaline Addition

Alka­line place­ment strate­gies involve either mix­ing direct­ly with pyrit­ic mate­r­i­al or con­cen­trat­ed place­ment to cre­ate a high­ly alka­line envi­ron­ment. Direct mix­ing places alka­line mate­ri­als in inti­mate con­tact with pyrit­ic spoil to inhib­it acid for­ma­tion and neu­tral­ize any gen­er­at­ed acid­i­ty in situ. Alka­line addi­tion case stud­ies have been report­ed by Brady et al., 1990. “Alka­line recharge” employs trench­es loaded with alka­line mate­r­i­al, usu­al­ly a com­bi­na­tion of sol­u­ble sodi­um car­bon­ate and crushed lime­stone.

The strat­e­gy is to charge infil­trat­ing waters with high dos­es of alka­lin­i­ty suf­fi­cient to over­whelm any acid pro­duced with­in the back­fill. This approach is high­ly depen­dent on the place­ment of the alka­line trench­es to pro­vide max­i­mum inflow to the acid-pro­duc­ing zones. An alka­line recharge case study has been report­ed by Caruc­cio and Gei­del (1989). A third vari­ant of the alka­line place­ment tech­nique is encap­su­la­tion with alka­line mate­r­i­al above and below the acid-pro­duc­ing zone.‌

Alkaline Agents‌

The ben­e­fits of adding lime (cal­ci­um car­bon­ate) and oth­er alka­line agents have long been rec­og­nized in mit­i­gat­ing acid drainage. How­ev­er, the com­plex chem­istry of spoil mate­ri­als has giv­en vary­ing lev­els of effec­tive­ness in alka­line addi­tion stud­ies.

Direct mix­ing and con­tact with pyrit­ic mate­ri­als appear most effec­tive but an opti­mum lime-to-pyrite ratio remains unknown.

Indi­rect treat­ments such as alka­line recharge (Caruc­cio and Gei­del, 1989) and bore­hole injec­tion (Aljoe and Hawkins, 1991; Lad­wig et al., 1985) have also yield­ed mixed results. Field stud­ies of alka­line addi­tion (Brady et al., 1990) have been con­duct­ed but it has been dif­fi­cult to iden­ti­fy defin­i­tive cause-and-effect rela­tion­ships. Fur­ther research is con­tin­u­ing in this area.

Phosphate

The appli­ca­tion of rock phos­phate is anoth­er tech­nique under study as a pyrite oxi­da­tion inhibitor (Ren­ton et al., 1988; Evan­gelou et al., 1991). Pyrite weath­er­ing ulti­mate­ly pro­duces free fer­ric iron which acts to oxi­dize addi­tion­al pyrite, thus estab­lish­ing a cyclic and self-prop­a­gat­ing series of reac­tions. Dis­so­lu­tion of rock phos­phate in acid media releas­es high­ly reac­tive phos­phate ions, which will com­bine with iron to form insol­u­ble iron phos­phate com­pounds. The for­ma­tion of insol­u­ble iron phos­phates would halt or inhib­it the cyclic reac­tion of iron and pyrite. Phos­phate treat­ment has effec­tive­ly reduced acid gen­er­a­tion in lab­o­ra­to­ry stud­ies; one field study showed a reduc­tion of about sev­en­ty per cent in acid load com­pared to a con­trol (Meek, 1991).

For rea­sons not yet com­plete­ly under­stood, an appli­ca­tion rate of about two to three per cent rock phos­phate pro­vides the most effec­tive con­trol. Thor­ough mix­ing of phos­phate and pyrit­ic mate­r­i­al also appears nec­es­sary for effec­tive treat­ment. Fur­ther research is con­tin­u­ing in this area.

Coatings and Sealants

Oth­er ongo­ing research activ­i­ties focus on the sur­face chem­istry of pyrite and the devel­op­ment of var­i­ous types of seal­ers, coat­ings and inhibitors to halt acid pro­duc­tion.

Biological Agents/Bactericides

The cat­alyt­ic role of bac­te­ria in pyrite oxi­da­tion has been well doc­u­ment­ed (Klein­mann et al., 1981). Many com­pounds have been screened as selec­tive bac­te­ri­cides and the anion­ic sur­fac­tants sodi­um lau­ryl sul­fate and alkyl ben­zene sul­fonate are con­sid­ered to be the most reli­able inhibitors. The appli­ca­tion of bac­te­ri­cides has reduced acid load­ing in field exper­i­ments. Bac­te­ri­cides are gen­er­al­ly water sol­u­ble and will leach from the spoil. Cur­rent­ly, the time required for the leach­ing of bac­te­ri­cides is uncer­tain. It is also unclear whether the sul­fur and iron oxi­diz­ing bac­te­ria will repop­u­late the spoil and cat­alyze the acid-pro­duc­ing reac­tions when the bac­te­ri­cide is deplet­ed.

Physical or Geochemical Treatments

Controlled Placement‌

Con­trolled place­ment (spe­cial han­dling) is a pre­ven­ta­tive mea­sure involv­ing the place­ment of pyrit­ic or alka­line mate­r­i­al dur­ing min­ing to min­i­mize or neu­tral­ize the for­ma­tion of AMD. Accord­ing to the gen­er­al­ly accept­ed chem­i­cal equa­tions for pyrite oxi­da­tion, oxy­gen and water are nec­es­sary to ini­ti­ate acid for­ma­tion. Exclu­sion of either reac­tant should pre­clude or inhib­it acid pro­duc­tion. Place­ment of pyrit­ic mate­r­i­al encom­pass­es either an attempt to exclude oxy­gen, usu­al­ly by com­plete sub­mer­gence below the water table; or an attempt to iso­late the mate­r­i­al from water con­tact to avoid leach­ing of acid salts. Place­ment of alka­line mate­ri­als has a twofold role:

1. inhi­bi­tion of the acid-form­ing reac­tions by main­tain­ing neu­tral to alka­line pH; and
2. neu­tral­iza­tion of any acid formed.

Submergence

Sub­mer­gence relies on sev­er­al physi­co-chem­i­cal phe­nom­e­na for suc­cess. Oxy­gen dif­fus­es very slow­ly and has lim­it­ed sol­u­bil­i­ty in water. For this approach to suc­ceed, a stag­nant or no flow con­di­tion and a rel­a­tive­ly thick sat­u­rat­ed zone appear crit­i­cal. Stag­nant flow con­di­tions lead­ing to the devel­op­ment of anox­ic (oxy­gen-free) con­di­tions and a sat­u­rat­ed thick­ness on the order of sev­er­al tens of feet appear to effec­tive­ly cur­tail oxy­gen dif­fu­sion. This approach is most suc­cess­ful in large mines in flat ter­rain where ground-water gra­di­ents are low, the sat­u­rat­ed zone is thick, and aquifers are of large are­al extent. Ham­mack and Wat­zlaf (1990) con­clud­ed that a water cov­er to main­tain oxy­gen below a par­tial pres­sure of one per cent is nec­es­sary to inhib­it pyrite oxi­da­tion.

Sub­mer­gence is gen­er­al­ly not used in the hilly ter­rain of Appalachia, where gra­di­ents and flow veloc­i­ties are too great to achieve stag­nant, anox­ic con­di­tions. In these sit­u­a­tions, sub­mer­gence may be coun­ter­pro­duc­tive and actu­al­ly enhance the pro­duc­tion and leach­ing of acid prod­ucts. Sub­mer­gence or flood­ing is also applied to pre­vent AMD from under­ground mines. Key con­sid­er­a­tions include:

• Whether the mine is locat­ed above or below drainage.
• The abil­i­ty of mine seals and out­crop bar­ri­ers to pre­vent seep­age.
• Poten­tial for mine seals and out­crop bar­ri­ers to fail under hydraulic pres­sure.

In gen­er­al, flood­ing to pre­vent AMD is believed to be more suc­cess­ful in below-drainage mines. It is assumed that com­plete flood­ing elim­i­nates oxy­gen and halts or severe­ly cur­tails acid gen­er­a­tion, the mine pool is sta­ble and lit­tle or no dis­charge occurs (Kim et al., 1982).

Flood­ing of above drainage mines is also prac­tised typ­i­cal­ly through the use of “wet” seals, which allow water to drain but exclude air entry. Kim et al., 1982 con­clud­ed that seal­ing and flood­ing above drainage mines does reduce acid load­ing but is tech­ni­cal­ly more dif­fi­cult and less effec­tive than oth­er meth­ods in AMD pre­ven­tion. Mon­i­tor­ing stud­ies of sealed mines indi­cate a gen­er­al decrease in pol­lu­tant load­ing 10 to 25 years after min­ing (Borek et al., 1991), but it is unclear if the decreas­es were due to mine seal­ing or “nat­ur­al phe­nom­e­na”. While pol­lu­tant load­ing decreased, and water qual­i­ty remained well out­side accept­ed water qual­i­ty stan­dards for mine drainage.

OSM’s rules do not specif­i­cal­ly address cri­te­ria for out­crop bar­ri­er thick­ness for flood­ing under­ground works. A con­sen­sus “stan­dard” engi­neer­ing design approach to out­crop bar­ri­ers and seals is also lack­ing. A con­tract report to the U.S. Bureau of Mines (Dames and Moore, 1981) dis­cuss­es the fac­tors affect­ing the sta­bil­i­ty of out­crop bar­ri­ers. Out­crop bar­ri­ers should be wide enough to pre­vent seep­age and have suf­fi­cient over­bur­den to pre­vent fail­ure (blowout). Cur­tain grout­ing, relief wells and com­part­men­tal­ized bar­ri­ers are sev­er­al of the tech­niques sug­gest­ed for con­trol­ling AMD dis­charges.

Isolation Above the Water Table‌

Place­ment of pyrit­ic mate­r­i­al above a water table is an attempt to iso­late the mate­r­i­al from con­tact with water and pre­clude the leach­ing of acid-weath­er­ing prod­ucts. Com­paction and cap­ping with clay or oth­er mate­ri­als may also be employed to reduce per­me­abil­i­ty. In prac­tice, it has proven very dif­fi­cult to com­plete­ly iso­late spoil mate­ri­als from water con­tact. Clay caps and oth­er flow bar­ri­ers are prone to leak­age, and the spo­radic infil­tra­tion of rain or snowmelt may peri­od­i­cal­ly leach the spoil. The cap­ping approach can be extend­ed to com­plete encap­su­la­tion on the top, bot­tom and sides as a fur­ther effort to iso­late the mate­ri­als from water con­tact. Skousen et al., 1987 give a gen­er­al review of iso­la­tion and cap­ping and oth­er pre­ven­tive tech­niques for han­dling pyrit­ic spoil.

Encapsulation/Physical Barriers

Tech­niques to iso­late or encap­su­late pyrit­ic mate­r­i­al include the use of fly ash, cement, ben­tonite, and oth­er clays; these are a few of the mate­ri­als stud­ied as sealants and flow bar­ri­ers by Skousen et al. (1987) and Bow­ders and Chi­a­do (1990). Suc­cess­ful appli­ca­tion of these meth­ods in the field is heav­i­ly depen­dent on good engi­neer­ing and con­struc­tion prac­tices and site con­di­tions. Oth­er inves­ti­ga­tions have attempt­ed bore­hole injec­tion to iso­late buried pyrit­ic mate­r­i­al. Research is ongo­ing in this area and may esca­late as sol­id waste dis­pos­al rules become more strin­gent.

Water Management

Water man­age­ment strate­gies both dur­ing and after min­ing are anoth­er option for reduc­ing acid gen­er­a­tion. Water man­age­ment can include the fol­low­ing:

• Active min­ing oper­a­tions can incor­po­rate diver­sions to route sur­face drainage away from pyrit­ic mate­r­i­al or through alka­line mate­r­i­al.
• Spoil mate­r­i­al can be placed and rough-grad­ed to pre­vent pond­ing and sub­se­quent infil­tra­tion.
• Prompt removal of pit water can lessen the amount and sever­i­ty of acid gen­er­at­ed.
• Pol­lut­ed pit water can be iso­lat­ed from non-con­t­a­m­i­nat­ed sources (no com­min­gling) to reduce the quan­ti­ty of water requir­ing treat­ment.
• Con­struct­ed under­drain sys­tems can be used to route water away from con­tact with acid-form­ing mate­r­i­al.

Spe­cial han­dling (con­trolled place­ment), alka­line place­ment and water man­age­ment strate­gies alone or in com­bi­na­tion can sub­stan­tial­ly reduce or mit­i­gate the gen­er­a­tion of acid drainage. Opti­mal strate­gies are site-spe­cif­ic and a func­tion of geol­o­gy, topog­ra­phy, hydrol­o­gy, min­ing method and cost-effec­tive­ness.

Mine-spoil Hydrology‌

Although some­times not con­sid­ered an AMD research top­ic, mine spoil hydrol­o­gy plays a cru­cial role in deter­min­ing drainage qual­i­ty. Rel­a­tive­ly few stud­ies of hydro­ge­o­log­ic process­es have been con­duct­ed in the con­text of con­trol­ling mine drainage qual­i­ty, and it is a sub­ject in need of fur­ther inves­ti­ga­tion. Much use­ful research has been con­duct­ed in pre­dic­tive and pre­ven­ta­tive acid drainage tech­niques. No uni­ver­sal­ly effec­tive tech­nolo­gies have yet been devel­oped, how­ev­er.

Treatment Methods and Costs

The least cost­ly and most effec­tive method of con­trol­ling Acid Mine Drainage is to pre­vent its ini­tial for­ma­tion. This usu­al­ly can be accom­plished by appli­ca­tion of the prin­ci­ples and pro­ce­dures described in the pre­vi­ous sec­tion and care­ful mine plan­ning.

On occa­sion, despite the appli­ca­tion of sound min­ing and recla­ma­tion prin­ci­ples, Acid Mine Drainage will be formed and must be treat­ed to meet exist­ing Fed­er­al and State stan­dards before it is released from the mine site. Pri­or to open­ing the mine, the oper­a­tor should eval­u­ate the poten­tial for cre­at­ing Acid Mine Drainage that would require treat­ment and should become famil­iar with the extent of the costs that such treat­ment might impose. Con­sid­er­a­tion should also be giv­en to the pos­si­bil­i­ty that treat­ment might have to be con­tin­ued well into the future, specif­i­cal­ly until such time that the dis­charge meets efflu­ent stan­dards with­out treat­ment.

Treat­ment, as nor­mal­ly applied to Acid Mine Drainage, involves chem­i­cal neu­tral­iza­tion of the acid­i­ty fol­lowed by pre­cip­i­ta­tion of iron and oth­er sus­pend­ed solids. Treat­ment sys­tems include:

1. equip­ment for feed­ing the neu­tral­iz­ing agent to the Acid Mine Drainage
2. means for mix­ing the two streams (Acid Mine Drainage and neu­tral­iz­ing agent)
3. pro­ce­dures for ensur­ing iron oxi­da­tion
4. set­tling ponds for remov­ing iron, man­ganese, and oth­er co-pre­cip­i­tates

A num­ber of fac­tors dic­tate the lev­el of sophis­ti­ca­tion of the treat­ment sys­tem that is nec­es­sary to ensure that efflu­ent stan­dards will be met. These fac­tors include the chem­i­cal char­ac­ter­is­tics of the Acid Mine Drainage, the quan­ti­ty to be treat­ed, cli­mate, ter­rain, sludge char­ac­ter­is­tics, and the pro­ject­ed life of the plant. The chem­i­cals usu­al­ly used for Acid Mine Drainage treat­ment include lime­stone, hydrat­ed lime, soda ash, caus­tic soda, and ammo­nia. The fol­low­ing dis­cus­sion high­lights some of the char­ac­ter­is­tics of each of these neu­tral­iz­ing agents.

Limestone (calcium carbonate)

The cal­ci­um con­tent of lime­stone should be as high as pos­si­ble (Dolomitic lime­stones are less reac­tive and gen­er­al­ly inef­fec­tive in treat­ing Acid Mine Drainage.) Advan­tages of using lime­stone include low cost, ease of use, and for­ma­tion of a dense, eas­i­ly han­dled, sludge. Dis­ad­van­tages include slow reac­tion time, loss in effi­cien­cy of the sys­tem because of coat­ing of the lime­stone par­ti­cles with iron pre­cip­i­tates, dif­fi­cul­ty in treat­ing Acid Mine Drainage with a high fer­rous-fer­ric ratio, and inef­fec­tive­ness in remov­ing man­ganese. Lime­stone treat­ment is gen­er­al­ly not effec­tive for acidi­ties exceed­ing 50 mg/L.

Hydrated Lime (calcium hydroxide)

Hydrat­ed lime is nor­mal­ly the neu­tral­iz­ing agent of choice by the coal min­ing indus­try because it is easy and safe to use, effec­tive, and rel­a­tive­ly inex­pen­sive. The major dis­ad­van­tages are the volu­mi­nous sludge that is pro­duced (when com­pared to lime­stone) and the high ini­tial costs that are incurred because of the size of the treat­ment plant.

Soda Ash (sodium carbonate)

Soda ash bri­quettes are espe­cial­ly effec­tive for treat­ing small Acid Mine Drainage flows in remote areas. Major dis­ad­van­tages are high­er reagent cost (rel­a­tive to lime­stone) and poor set­tling prop­er­ties of the sludge.

Caustic Soda (sodium hydroxide)‌

Caus­tic soda is espe­cial­ly effec­tive for treat­ing low flows in remote loca­tions and for treat­ing Acid Mine Drainage hav­ing a high man­ganese con­tent. Major dis­ad­van­tages are its high cost, the dan­gers involved with han­dling the chem­i­cal, poor sludge prop­er­ties, and freez­ing prob­lems in cold weath­er.

Ammonia

Anhy­drous ammo­nia is effec­tive in treat­ing Acid Mine Drainage hav­ing a high fer­rous iron and/or man­ganese con­tent. Ammo­nia costs less than caus­tic soda and has many of the same advan­tages. How­ev­er, ammo­nia is dif­fi­cult and dan­ger­ous to use and can affect bio­log­i­cal con­di­tions down­stream from the min­ing oper­a­tion. The pos­si­ble off-site effects are tox­i­c­i­ty to fish and oth­er aquat­ic life forms, eutroph­i­ca­tion and nitri­fi­ca­tion. Fish species gen­er­al­ly exhib­it low tol­er­ance to union­ized ammo­nia and tox­i­c­i­ty lev­els can be affect­ed by pH, tem­per­a­ture, dis­solved oxy­gen and oth­er fac­tors. A more com­plete review of ammo­nia treat­ment of mine drainage is giv­en by Faulkn­er (1991). Ammo­nia use is not allowed in all States and, where per­mit­ted, addi­tion­al mon­i­tor­ing is required.

Constructed Wetlands

Con­struct­ed wet­lands uti­lize soil- and water-borne microbes asso­ci­at­ed with wet­land plants to remove dis­solved met­als from mine drainage. Ini­tial design and con­struc­tion costs may be sub­stan­tial, rang­ing into tens of thou­sands of dol­lars. Unlike chem­i­cal treat­ment, how­ev­er, wet­lands are pas­sive sys­tems requir­ing lit­tle or no con­tin­u­ing main­te­nance. This is a rel­a­tive­ly new treat­ment tech­nol­o­gy with many spe­cif­ic mech­a­nisms and main­te­nance require­ments not yet ful­ly under­stood. Opti­mum siz­ing and con­fig­u­ra­tion cri­te­ria are still under study. Sea­son­al vari­a­tions in met­als removal effi­cien­cy have been not­ed with less­er amounts removed in cold weath­er. Wet­lands are gen­er­al­ly more effec­tive in remov­ing iron than man­ganese. The great­est util­i­ty of wet­lands appears to be in the treat­ment of small flows of a few gal­lons per minute.

Treatment Costs

For Acid Mine Drainage treat­ment costs, OSM has devel­oped AMDTreat, a com­put­er pro­gram to cal­cu­late long-term costs for treat­ing mine drainage, avail­able for down­load at: www.osmre.gov

Technical references on Acid Mine Drainage‌

Aljoe W.W. and J.W. Hawkins, 1991, “Hydro­log­ic Char­ac­ter­i­za­tion and In-Situ Neu­tral­iza­tion of Acidic Mine Pools in Aban­doned Under­ground Coal Mines,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence on the Abate­ment of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al, Cana­da, Vol­ume 1, p 69–90.

Borek S. L., T. E. Ack­man, G. P. Wat­zlaf, R. W. Ham­mack, J. P. Lip­scomb, 1991, “The Long-Term Eval­u­a­tion of Mine Seals Con­struct­ed in Ran­dolph Coun­ty, W.V. in 1967,” in Pro­ceed­ings Twelfth Annu­al West Vir­ginia Sur­face Mine Drainage Task Force Sym­po­sium, April 3–4, 1991, Mor­gan­town, West Vir­ginia.

Bow­ders, J. and E. Chi­a­do, 1990, ” Engi­neer­ing Eval­u­a­tion of Waste Phos­phat­ic Clay for Pro­duc­ing Low Per­me­abil­i­ty Bar­ri­ers,” in Pro­ceed­ings 1990 Min­ing and Recla­ma­tion Con­fer­ence and Exhi­bi­tion, Vol­ume 1, p 11–18, West Vir­ginia Uni­ver­si­ty.

Brady, K. B., M. Smith, R. Beam and C. Cravot­ta III, 1990, “Effec­tive­ness of Addi­tion of Alka­line Mate­ri­als at Sur­face Coal Mines in Pre­vent­ing and Abat­ing Acid Mine Drainage: Part 2 Mine Site Case Stud­ies,” in Pro­ceed­ings of the 1990 Min­ing and Recla­ma­tion Con­fer­ence and Exhi­bi­tion, Vol­ume 1, p 227–242, West Vir­ginia Uni­ver­si­ty.

Brady K.B., J.R. Shaulis and V.W. Sek­ma, 1988, “A Study of Mine Drainage Qual­i­ty and Pre­dic­tion Using Over­bur­den Analy­sis and Pale­oen­vi­ron­men­tal Recon­struc­tions, Fayette Coun­ty, Penn­syl­va­nia,” in Con­fer­ence Pro­ceed­ings, Mine Drainage and Sur­face Mine Recla­ma­tion, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9183, p 33–44.

Caruc­cio F. T. and G. Gediel, 1989, “Water Man­age­ment Strate­gies in Abat­ing Acid Mine Drainage – Is Water Diver­sion Real­ly Ben­e­fi­cial?,” in Pro­ceed­ings 1989 Multi­na­tion­al Con­fer­ence on Mine Plan­ning and Design, Uni­ver­si­ty of Ken­tucky, Lex­ing­ton, Ken­tucky.

Caruc­cio, F.T., J.C. Ferm, J. Horne, G. Gei­del, B. Bagenz, 1977, “Pale­oen­vi­ron­ment of Coal and Its Rela­tion to Drainage Qual­i­ty,” pre­pared for U.S. Envi­ron­men­tal Pro­tec­tion Agency, EPA-600/7–77-067, Cincin­nati, Ohio.

Caruc­cio F. T., 1967, “An Eval­u­a­tion of Fac­tors Influ­enc­ing Acid Mine Drainage Pro­duc­tion from Var­i­ous Stra­ta of the Alleghe­ny Group and the Ground Water Inter­ac­tions in Select­ed Areas of West­ern Penn­syl­va­nia,” Ph.D. Dis­ser­ta­tion, The Penn­syl­va­nia State Uni­ver­si­ty, State Col­lege, Penn­syl­va­nia.

Dames and Moore, 1981, “Out­crop Bar­ri­er Design Guide­lines For Appalachi­an Coal Mines,” pre­pared for the U.S. Bureau of Mines, Con­tract J0395069, Bureau of Mines Open File Report 134–81.

Deutsch, W. J., Ground­wa­ter Geo­chem­istry: Fun­da­men­tals and Appli­ca­tions to Con­t­a­m­i­na­tion, 1997, CRC Press, N.Y., 221 p.

Erick­son P. and R. Hei­den, 1988, “Eval­u­a­tion of Over­bur­den Ana­lyt­i­cal Meth­ods as a Means to Pre­dict Post-Min­ing Coal Mine Drainage Qual­i­ty,” in Con­fer­ence Pro­ceed­ings Mine Drainage and Sur­face Mine Recla­ma­tion, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9183, Vol­ume 1, p 11–20.

Evan­gelou, V., U. Sain­ju and E. Por­tig, 1991, “Some Con­sid­er­a­tions When Apply­ing Limestone/Rock Phos­phate Mate­ri­als on to Acid Pyrit­ic Spoils,” in Pro­ceed­ings Twelfth Annu­al West Vir­ginia Sur­face Mine Drainage Task Force Sym­po­sium, April 3–4, 1991, Mor­gan­town, West Vir­ginia.

Evan­gelou, V.P., 1995. Pyrite Oxi­da­tion and its Con­trol. CRC Press, N.Y., 293 p.

Faulkn­er, B. (ed.), 1991, “Hand­book for Use of Ammo­nia in Treat­ing Mine Waters,” West Vir­ginia Min­ing and Recla­ma­tion Asso­ci­a­tion, Charleston, West Vir­ginia.

Ham­mack R. W. and G. R. Wat­zlaf, 1990, “The Effect of Oxy­gen on Pyrite Oxi­da­tion,” in Pro­ceed­ings of the 1990 Min­ing and Recla­ma­tion Con­fer­ence and Exhi­bi­tion, Vol­ume 1, p 257–264, West Vir­ginia Uni­ver­si­ty.

Ham­mack, R. W., R. Lai and J. R. Diehl, 1988, “Meth­ods for Deter­min­ing Fun­da­men­tal Chem­i­cal Dif­fer­ences Between Iron Disul­fides from Dif­fer­ent Geo­log­ic Prove­nances,” in Con­fer­ence Pro­ceed­ings Mine Drainage and Sur­face Mine Recla­ma­tion, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9183, p 136–146.

Hart, W. M., K. Batarseh, G. P. Swaney and A. H. Stiller, 1991, “A Rig­or­ous Mod­el to Pre­dict the AMD Pro­duc­tion Rate of Mine Waste Rock,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence On The Abate­ment Of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al, Cana­da, Vol­ume 2, p 257–270.

Hart W.H., K.I. Batarseh, G.P. Swaney and A.H. Stiller, “A Rig­or­ous Mod­el to Pre­dict the AMD Pro­duc­tion of Mine Waste Rock,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence on the Abate­ment of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al Cana­da, Vol­ume 2, p 257–270.

Horn­berg­er, R.J., R.R. Parizek and E.G. Williams, 1981, “Delin­eation of Acid Mine Drainage Poten­tial of Coal Bear­ing Stra­ta of the Pottsville and Alleghe­ny Groups in West­ern Penn­syl­va­nia,” Research Report OWRT Project B‑097-PA, the Penn­syl­va­nia State Uni­ver­si­ty, Uni­ver­si­ty Park Penn­syl­va­nia.

Jaynes, D. B., 1991, “Mod­el­ing Acid Mine Drainage from Reclaimed Coal Strip Mines,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence on the Abate­ment of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al, Cana­da, Vol­ume 2, p 191–210.

Kim, A., B. Heisey, R. L. P. Klein­mann and M. Duel, 1982, “Acid Mine Drainage: Con­trol and Abate­ment Research,” U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 8905.

Klein­mann R.L.P., D.A. Crerar and R.R. Pacel­li, 1981, “Bio­geo­chem­istry of Acid Mine Drainage and a Method to Con­trol Acid For­ma­tion,” Min­ing Engi­neer­ing, March 1981.

Lad­wig, K., P. Erick­son and R. Klein­mann, 1985, Alka­line Injec­tion: An Overview of Recent Work,” in Con­trol of Acid Mine Drainage, Pro­ceed­ings of a Tech­nol­o­gy Trans­fer Sem­i­nar, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9027.

Meek A., 1991, “Assess­ment of Acid Pre­ven­ta­tive Tech­niques at the Island Creek Min­ing Co. Ten­mile Site,” in Pro­ceed­ings Twelfth Annu­al West Vir­ginia Sur­face Mine Drainage Task Force Sym­po­sium, April 3–4, 1991, Mor­gan­town, West Vir­ginia.

Nord­strom, D. K., 1979, “Aque­ous Pyrite Oxi­da­tion and the Con­se­quent For­ma­tion of Sec­ondary Iron Min­er­als,” in “Acid Sul­fate Weath­er­ing,” Soil Sci­ence Soci­ety of Amer­i­ca Spe­cial Pub­li­ca­tion No. 10, p 37–56.

Ren­ton, J., A. H. Stiller and T. E. Rymer, 1988, “The Use of Phos­phate Mate­ri­als as Ame­lio­rants for Acid Mine Drainage,” in Con­fer­ence Pro­ceed­ings Mine Drainage and Sur­face Mine Recla­ma­tion, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9183, p 67–75.

Ren­ton, J. J., T. E. Rymer and A. H. Stiller, 1988, “A Lab­o­ra­to­ry Pro­ce­dure to Eval­u­ate the Acid Pro­duc­ing Poten­tial of Coal Asso­ci­at­ed Rocks,” Min­ing Sci­ence and Tech­nol­o­gy, Vol 7, p 227–235, Else­vi­er, Ams­ter­dam.

Rymer, T., A. Stiller, W. Hart and J. Ren­ton, 1990, “Some Aspects of SSPE/PSM Mod­el­ing for Quan­ti­ta­tive Assess­ment of Dis­turbed Hydro­log­ic Sys­tems,” in Pro­ceed­ings 1990 Min­ing and Recla­ma­tion Con­fer­ence and Exhi­bi­tion, Vol­ume 1, p 61–68, West Vir­ginia Uni­ver­si­ty.

Schar­er, J. M., V. Gar­ga, R. Smith and B. E. Hal­bert, 1991, “Use of Steady State Mod­els for Assess­ing Acid Gen­er­a­tion in Pyrit­ic Mine Tail­ings,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence on the Abate­ment of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al, Cana­da, Vol­ume 2, p 211–230.

Sheetz, B.E., 1990, “Improv­ing The Char­ac­ter­i­za­tion Of Sul­fur In Over­bur­dens and Coals Using State-of-the-Art Tech­nol­o­gy,” First Annu­al Progress Report to the Office of Sur­face Min­ing, Grant 996421, Mate­ri­als Research Lab­o­ra­to­ry, the Penn­syl­va­nia State Uni­ver­si­ty, Uni­ver­si­ty Park, Penn­syl­va­nia.

Singer, P.C. and W. Stumm, 1970, “Acid Mine Drainage: The Rate Deter­min­ing Step,” Sci­ence 167; p 1121–1123.

Skousen, J. G., K. Poli­tan, T. Hilton and A. Meek, 1990, “Acid Mine Drainage Treat­ment Sys­tems: Chem­i­cals and Costs”, in Green Lands, Vol 20, No.4, p 31–37, Fall 1990, West Vir­ginia Min­ing and Recla­ma­tion Asso­ci­a­tion, Charleston West Vir­ginia.

Skousen, J. G., J. C. Sencin­div­er and R. M. Smith, 1987, “A Review of pro­ce­dures For Sur­face Min­ing and Recla­ma­tion in Areas with Acid-pro­duc­ing Mate­ri­als,” in coop­er­a­tion with The West Vir­ginia Sur­face Mine drainage Task Force, the West Vir­ginia Uni­ver­si­ty Ener­gy and Water Research Cen­ter and the West Vir­ginia Min­ing and Recla­ma­tion Asso­ci­a­tion, 39 p, West Vir­ginia Uni­ver­si­ty Ener­gy and Water Research Cen­ter.

Sny­der, D. T., and F. T. Caruc­cio, 1988, ” The Par­ti­tion­ing of Flow Com­po­nents of Acidic Seeps from Sur­face Coal Mines and the Iden­ti­fi­ca­tion of Acid Pro­duc­ing Hori­zons with­in the Back­fill,” in Con­fer­ence Pro­ceed­ings Mine Drainage and Sur­face Mine Recla­ma­tion, U.S. Bureau of Mines Infor­ma­tion Cir­cu­lar 9183, p 59–66.

Sobek A. A., W. A. Schuller, J. R. Free­man and R. M. Smith, 1978, “Field and Lab­o­ra­to­ry Meth­ods Applic­a­ble to Over­bur­dens and Mine­soils,” pre­pared for U.S. Envi­ron­men­tal Pro­tec­tion Agency, EPA- 600/2–78-054, Cincin­nati, Ohio.

Sturey C. S., J. R. Free­man, T. A. Keeney, and J. Sturm, 1982, “Over­bur­den Analy­sis by Acid-Base Account­ing and Sim­u­lat­ed Weath­er­ing Stud­ies as a Means of Deter­min­ing the Prob­a­ble Hydro­log­ic Con­se­quences of Min­ing and Recla­ma­tion,” in Pro­ceed­ings Sym­po­sium on Sur­face Min­ing, Hydrol­o­gy, Sed­i­men­tol­ogy, and Recla­ma­tion, Uni­ver­si­ty of Ken­tucky, Lex­ing­ton, Ken­tucky.

Tetch­er J. J., T. T. Phipps and J. G. Skousen, “Cost Analy­sis For Treat­ing Acid Mine Drainage from Coal Mines in the U.S.,” in Pro­ceed­ings Sec­ond Inter­na­tion­al Con­fer­ence on the Abate­ment of Acidic Drainage, Sep­tem­ber 16–18, 1991, Mon­tre­al, Cana­da, Vol­ume 1, p 561–574.

Ziemkiewicz, P., J. Ren­ton and T. Rymer, 1991, “Pre­dic­tion and Con­trol of Acid Mine Drainage: Effect of Rock Type and Amend­ment,” in Pro­ceed­ings Twelfth Annu­al West Vir­ginia Sur­face Mine Drainage Task Force Sym­po­sium, April 3–4, 1991, Mor­gan­town, West Vir­ginia.