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 < 3, iron (Fe) concentrations of 200 to > 900 mg/L, and sulfate (SO 4-2) 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 SO 4-2. In contrast, after initial flushing, water from the unflooded mine had Fe, SO 4-2 , 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 SO 4 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 SO 4 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 SO 4-2 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 minepool. 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.