DISSOLVED METALS AND ASSOCIATED CONSTITUENTS IN ABANDONED COAL-MINE DISCHARGES, PENNSYLVANIA, 1999

Dissolved metals and associated constituents in 140 discharges from abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania were measured in 1999. “Clean-sampling” procedures in the field and various analytical methods in the laboratory, including inductively coupled plasma emission mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and ion chromatography (IC), were used to measure a total of 84 constituents. Flow ranged from 0.028 to 2,210 L/s. The pH ranged from 2.7 to 7.3; most samples were acidic (pH 2.5 to 4) or near neutral (pH 6 to 7). Specific conductance ranged from 0.131 to 3.980 mS/cm and was not correlated with pH. Alkalinity ranged from 0 (50 samples with pH <4.4) to 510 mg/L as CaCO₃. Concentration ranges, in mg/L, of dissolved SO₄ (34 to 2,000), Fe (0.046 to 512), Mn (0.019 to 74), and Al (0.007 to 108) were wide and varied in magnitude. Concentrations of dissolved O₂ typically were low (<2) throughout the range of pH, consistent with the predominance of Fe^II and Mn^II species. Dissolved Fe was not correlated with pH; alkalinity was positively correlated with pH; Al was negatively correlated with pH; SO₄ and Mn had negative, but weak correlations with pH.

Predominant trace metals, in order of median concentration (range in ug/L), were Zn (0.6 to 10,000), Ni (2.6 to 3,200), Co (0.27 to 3,100), Ti (0.65 to 28), Cu (0.4 to 190), Cr (<0.5 to 72), Pb (<0.05 to 11), and Cd (<0.01 to 16). Predominant rare-earth elements, in order of median concentrations (range in ug/L), were Y (0.11 to 530), Ce (0.01 to 370), Sc (1.0 to 36), Nd (0.006 to 260), La (0.005 to 140), Gd (0.005 to 110), Dy (0.002 to 99), and Sm (<0.005 to 79). Concentrations of most trace metals and rare earths were negatively correlated with pH, consistent with sorption control. In contrast, As (<0.03 to 64 ug/L) was positively correlated with pH and negatively correlated with dissolved O₂. These associations could indicate As mobilization by desorption from, or reduction of, hydrous ferric oxides under neutralizing conditions. All 140 samples exceeded USEPA continuous-concentration criteria for Al, Fe, Co, Ni, and/or Zn for protection of freshwater organisms. Ten percent of the samples exceeded USEPA drinking-water standards for As, and 33 percent exceeded those for Be.