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HEDIN ET AL.: TREATMENT F ACID MINE DRAINAGEWITH LIMESTONETable1. Comparativeost of limestoneandalkaline chemicalscommonlysed n the treatment f acid minedrainage.

Cost per kmoleChemical of OH-Material composition equivalentSLimestone CaC03 $ 0.6~Hydrated ime Ca(OH)~ 2.64Ammonia NH3 5.61Soda ash NaCO~ 15.16Caustic soda NaOH 21.56

Chemical osts fromSkousen t al. (1990). Limestonecost is basedon a95% CaCO3ontent at $13 Mg3.

MATERIALS AND METHODSStudy Sites

HoweBridge Anoxic Limestone DrainThe ALDt the Howe ridge site treated acidic water thatupwelled rom an abandoned xploration well. In October of1991, the well was cappedand a PVC ipe was attached thattransferred the minewater 15 m horizontally to the ALD.Asampling port was installed in this transfer pipe to allow

buried with spoil (Table 2, Fig. 1).and Z, were installed in the ALDtthe ALDffluent, respectively.Water discharged from the Morzontal 30-cmdiam. pipe that was laend of the limestone bed. Flow atepipe outlet. BetweenOctober of 19water levels in the ALD ere controbottomof this pipe, which was 0.6limestone. The pore volumeof the this period was estimated as 12 50riser wasconnectedo the effluent piin the ALDo the top of the limestovolume f the flooded limestone to

Water Sampling andWater sampleswere collected moplacedwithin the ALDsnd from he fiALDs.The samplingwells were conPVC ipes that were perforated at tsection of each pipe sat within the pipe extended hrough substrate tha

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1340 J. ENVIRON.QUAL., VOL. 23, NOVEMBER-DECEMBER994Vegetated-crown

Mine ~cWell g limestone-~.

z S~CTION

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HEDIN ET AL.: TREATMENT F ACID MINE DRAINAGEWITH LIMESTONE350-300.250.200150100500

A 500400

1~~ 300-

---- 200-~ 100-

I I I I I I 0

~5o B

~ I 250-T

o--n Morrison ALDo--o Howe Bridge AL

O0

Dec dun Dec 1990 1991 1991Samplin

Fig. 3. Effluent concentrations of alkaMorrison ALDs. Data collection at of ALD onstruction.

in these parametersndicated hatof mine water within the ALD

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1342 J. ENVIRON.QUAL., VOL. 23, NOVEMBER-DECEMBER994Table . Meanoncentrationsf water onstituents t the Morrison LD, ctober990 o May 993. Concand cidity as CaCOs)nd lowas L min- . Standardeviations re shownn parentheses, is sampleizexcept K, n = 6, anddissolvedoxygen DO),n =

Pre-ALD~ Seep W Well Y WelpH 4.6 (0.6):~ 5.3(0.2) 6.1(0.1) 6.2Alk 5 (6):~ 23 (12) 201 (42) 269(AI NA 1 (

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HEDIN ET AL.: TREATMENT F ACID MINE DRAINAGEWITH LIMESTONETable 5. Carbon dioxide partial pressures (kPa) and saturation indices IAPIK~p) for the ALD ampling statiusing WATEQ4FBall et al., 1987).

COz CaCO~ MgCOa CaMg(COah FeCO~Station kPa(log(atm)) log(SO log(SI) log(SI) log(SOHoweBridge

Irdtuent 6.39( - 1.20) - 2.65 - 3.19 - 5.91 - 0.51Well 1 7.51( - 1.13) - 1.93 - 2.51 - 4.51 + 0.16Well 2 8.05( - 1.10) - 1.45 - 2.08 - 3.60 + 0.57Well 3 6.39( - 1.20) - 1.12 - 1.79 - 2.99 + 0.86Well 4 6.69( - 1.18) - 1.10 - 1.77 - 2.94 0.87Effluent 7.87( - lAD - 1.24 - 1.90 - 3.21 + 0.75MorrisonSeep W 9.24( - 1.04) - 3.22 - 3.57 - 6.86 - 1.06Well Y 13.05( - 0.89) - 1.25 - 1.86 - 3.18 + 0.61Well Z 13.99( - 0.86) - 0.94 - 1.64 - 2.65 0.78Effluent 11.37( - 0.95) - 0.82 - 1.54 - 2.43 + 0.83

ALDsby increasing the equilibrium concentrations ofalkalinity (Hem, 1985) and by increasing the ratecalcite dissolution (Bemer and Morse, 1974).In both systems, calcite dissolution occurred predomi-nantly in the first half of the ALDs. ittle calcite dissolu-tion occurred in the second half of either ALD Fig.

the dilution-adjusted decrease calculated as 28 mg L-1. At 6.8 L min- 1 and over the 30-moin concentration is equivalent tof Fe. While we suspect that resulted from siderite format

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1344 J . E N V I R O N . Q U A L . , V O L . 2 3 , N O V E M B E R - D E C E M B E R 1994Table 6. Mean concentrationsof water constituentsat theHowe BridgeandMorrison passive treatmenL-' (alkalinity as CaCOj). is thesample size.Allstandard deviationswere less than50 of the meSamplingpointHowe BridgeALD inf luentA L D f f l u n tPond f f l u n tWetland effluentMorrisonS e e p WA L D f f l u n tPond f f l u n tWetland f f l u n t

n

171717172134242 4

PH

5.66.25.66.15.36.36.36.6

A lk331612 3862 32713457

C a1592111822 341192 30162164

2 792 77195802161515

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SHIPITALOET AL.: WATER IN EARTHWORM BURROWS & PAN LYSIMETERS