Clean sampling and analysis procedures were used to quantify more than 70 inorganic constituents, including 35 potentially toxic or hazardous constituents, organic carbon, and other characteristics of untreated (influent) and treated (effluent) coal-mine discharges (CMD) at 38 permitted coal-mining or coal-processing facilities in the bituminous coalfield and 4 facilities in the anthracite coalfield of Pennsylvania. Of the 42 facilities sampled during 2011, 26 were surface mines, 11 were underground mines, and 5 were coal refuse disposal operations. Treatment of CMD with caustic soda (NaOH), lime (CaO or Ca(OH)2), flocculent, or limestone was ongoing at 21%, 40%, 6%, and 4% of the facilities, respectively; no chemicals were added at the remaining facilities. All facilities with CMD treatment incorporated structures for active or passive aeration and settling of metal-rich precipitate.
The untreated influent samples had wide ranges of pH (2.8–7.6), hot acidity (−600 to 8000 mg/L as CaCO3), specific conductance (SC; 253–13,000 μS/cm), total dissolved solids (TDS; 168–18,100 mg/L), and associated dissolved ( 0.05) included flow rate, SC, osmotic pressure, hardness, alkalinity, total organic carbon (TOC), K, Cl, NO3, PO4, Sb, Sr, Br, Se, Mo, and V. Although temperature, dissolved oxygen, pH, Ca, and Na were greater in the effluent than the influent, most constituents decreased as a result of treatment, including TDS, acidity, SO4, Al, Fe, Mn, Mg, As, Ba, Be, Cd, Cr, Co, Cu, F, Pb, Ni, NH3, Tl, Ti, U, Zn, Zr, total phenols, total inorganic carbon (TIC), biological oxygen demand (BOD), and chemical oxygen demand (COD). Nevertheless, some constituents that decreased, such as SO4, still did not meet reference criteria.
Findings from this study suggest that typical chemical or aerobic treatment of CMD to pH > 6 with removal of Fe to
