Water quality and flow data from a pumped, mostly flooded, and a free draining, mostly unflooded coal mine-pools were analyzed for temporal trends. Both mine-pools began discharging acidic drainage, with pH 900 mg/L, and sulfate (SO4 -2 ) values of about 2,500 to 4,000 mg/L, less than one year after closure. Each site had an initial flushing period, lasting about 2 years in the unflooded mine, and 8 years in the flooded mine. The flushing included a rapid decline in concentrations, and large variations in water chemistry. Chemical concentrations declined more rapidly in the flooded mine-pool, to about 20 to 30% of the initial values for Fe and SO4 -2 . In contrast, after initial flushing, water from the unflooded mine had Fe, SO4 -2 , and aluminum (Al) concentrations of 50 to 75% of original discharge quality. Each mine-pool is now in a maturation process with continuing declines in chemical concentrations, less variation in composition, and increasing metals attenuation in the mine-pool aquifer. The flooded mine-pool turned net alkaline after pumping about 21 pool volumes. After 35 years, Fe and SO4 are 5 to 10% of initial composition. Equilibrium calculations show that Fe may be controlled by poorly crystalline oxyhydroxides. Mine-pool oxidation reduction potential (ORP) is < +250 mv. The free draining mine still has pH < 3 after discharging about 25 pool volumes. Iron and SO4 concentrations are still 25 to 40% of original composition and Al is unchanged since the initial flush. Equilibrium calculations show that Fe may be controlled by oxyhydroxides or K-jarosite. Mine-pool ORP is +500 to 700 mv. Al is near apparent equilibrium with jurbanite. Declining Fe to SO4 -2 ratios in both mine-pools indicate that 60 to 80% of Fe dissolved from pyrite is being attenuated in-situ, probably by precipitation, exchange or adsorption. Flooding has suppressed, but not eliminated pyrite oxidation in one mine- pool. The free draining mine water chemistry is still controlled by sulfide oxidation. Both mine-pools may contain dissolved Fe from continuing mineral dissolution in the mine-pool aquifer indefinitely.
[1]
J. Hawkins,et al.
HYDROLOGIC CHARACTERIZATION OF A LARGE UNDERGROUND MINE POOL IN CENTRAL PENNSYLVANIA 1
,
2005
.
[2]
J. Hawkins,et al.
WATER QUALITY TRENDS IN A FLOODED 35 YEAR OLD MINE- POOL 1
,
2005
.
[3]
C. Cravotta,et al.
ACIDITY AND ALKALINITY IN MINE DRAINAGE: THEORETICAL CONSIDERATIONS
,
2004
.
[4]
M. L. Hughes,et al.
Long-term water quality trends at a sealed, partially flooded underground mine
,
2001
.
[5]
Paul L. Younger,et al.
Predicting temporal changes in total iron concentrations in groundwaters flowing from abandoned deep mines: a first approximation
,
2000
.
[6]
P. Younger,et al.
Long-term changes in the quality of polluted minewater discharges from abandoned underground coal workings in Scotland
,
1999,
Quarterly Journal of Engineering Geology.
[7]
P. L. Young.
The longevity of minewater pollution: a basis for decision-making.
,
1997
.
[8]
Mark A. Williamson,et al.
The kinetics and electrochemical rate-determining step of aqueous pyrite oxidation
,
1994
.
[9]
D. Nordstrom.
The effect of sulfate on aluminum concentrations in natural waters: some stability relations in the system Al2O3-SO3-H2O at 298 K
,
1982
.
[10]
D. L. Parkhurst,et al.
User's guide to PHREEQC (Version 2)-a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations
,
1999
.
[11]
James D. Robertson,et al.
SUBAQUEOUS DISPOSAL OF REACTIVE MINE WASTE: AN OVERVIEW AND UPDATE OF CASE STUDIES - MEND/CANADA
,
1994
.
[12]
R. Hammack,et al.
THE EFFECT OF OXYGEN ON PYRITE OXIDATION
,
1990
.
[13]
R. Sayers,et al.
Effect of sealing on acidity of mine drainage
,
1930
.