Water-quality trends for a stream draining the Southern Anthracite Field, Pennsylvania

Abstract

Stream flow, chemical and biological data for the northern part of Swatara Creek, which drains a 112 km 2 area in the Southern Anthracite Field of eastern Pennsylvania, indicate progressive improvement in water quality since 1959, after which most mines in the watershed had been flooded. Drainage from the flooded mines contributes substantially to base flow in Swatara Creek. Beginning in 1995, a variety of treatment systems and surface reclamation were implemented at some of the abandoned mines. At Ravine, Pa., immediately downstream of the mined area, median SO 4 concentration declined from about 150 mg l −1 in 1959 to 75 mg l −1 in 1999 while pH increased from acidic to near-neutral values (medians: c. pH 4 before 1975; c. pH 6 after 1975). Fish populations rebounded from non-existent during 1959–1990 to 21 species identified in 1999. Nevertheless, recent monitoring indicates (1) episodic acidification and elevated concentrations and transport of Fe, Al, Mn, and trace metals during storm flow; (2) elevated concentrations of Fe, Mn, Co, Cu, Pb, Ni, and Zn in streambed sediments relative to unmined areas and to toxicity guidelines for aquatic invertebrates and fish; and (3) elevated concentrations of metals in fish tissue, notably Zn. The metals are ubiquitous in the fine fraction (<0.063 mm) of bed sediment in mining-affected tributaries and the main stem of Swatara Creek. As a result of scour and transport of streambed deposits, concentrations of suspended solids and total metals in the water column are correlated, and those for storm flow typically exceed base flow. Nevertheless, the metals concentrations are poorly correlated with stream flow because concentrations of suspended solids and total metals typically peak prior to peak stream stage. In contrast, SO 4 , specific conductance and pH are inversely correlated with stream flow as a result of dilution of poorly buffered stream water with weakly acidic storm runoff derived mainly from low-pH rainfall. Declines in pH to values approaching 5.0 during storm flow events or declines in redox potential during burial of sediment could result in the remobilization of metals associated with suspended solids and streambed deposits.

Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones

“…Brennan and Lindsay [58] found that a more prolonged and intensive reduction period was required for the reduction of crystalline oxides (hematite) compared to nearly amorphous iron (hydr)oxides. Younger, freshly precipitated iron has a large (>200 m 2 /g) [38,39,59] and complex surface area [60,61]. Grain size is also a major control on the potential for reduction.…”

Abandoned Mine Drainage in the Swatara Creek Basin, Southern Anthracite Coalfield, Pennsylvania, USA: 2. Performance of Treatment Systems

“…During 1996-1998, streamwater of Swatara Creek at Newtown and Ravine ( Fig. 1) ranged from mildly acidic to near-neutral (net acidity -20 to 10 mg/L CaCO 3 ; pH 4.5-8.0) with moderate concentrations of dissolved solids (SC 60-400 lS/cm) that varied as a function of stream flow (Cravotta and Bilger 2001;Cravotta and Weitzel 2001). Higher values of pH, SC, and SO 4 were associated with base-flow conditions sustained by near-neutral groundwater and net-alkaline AMD in the upper part of the watershed, such as the Tracy Airshaft and Colket discharges (Fig.…”

Effects of historical coal mining and drainage from abandoned mines on streamflow and water quality in Bear Creek, Dauphin County, Pennsylvania — March 1999–December 2002

“…Increased transport of iron, the principal pollutant in mine drainage entering Bear Creek, can occur in streams that rapidly respond to storm events through scour of streambed sediments and episodic acidification (Cravotta and Bilger, 2001). Iron and trace metals generally are associated with fine streambed sediments (<0.063-mm size particles), those that are most likely to be entrained and transported during rapid increases in flow.…”

“…16), it remained near-neutral (minimum pH = 6.1; table 5) making the dissolution of relatively insoluble Fe(OH) 3 unlikely over the range of measured pH values. Nonetheless, there are processes facilitated by decreases in pH and (or) redox potential of streambed sediments or the water column that may increase the concentrations of dissolved metals (Cravotta and Bilger, 2001). …”