WATER- SEDIMENT INTERACTIONS IN AN ACIDIC PIT LAKE, ANTHRACITE DISTRICT, EASTERN PENNSYLVANIA

Historic surface mining of anthracite in eastern Pennsylvania has left a legacy of abandoned mine sites. Some of these mines extended below the pre-mining water table and flooded with water following mine closure to become pit lakes. Several of these pit lakes exhibit poor water quality resulting from low pH and high trace metal concentrations, presenting a potential environmental concern. The purpose of this study is to gain an understanding of the relationship between the aqueous geochemistry and the mineralogy of sediments precipitating from lake water in pit lakes within the Upper Lehigh Watershed near Freeland, PA. The Pond Creek abandoned mine site contains a chain of over six of pit lakes that range in pH from 4.33 to 3.65. Preliminary water quality data show elevated levels of Fe (3.21 mg/L), Mn (0.66 mg/L), and Al (2.22 mg/L) within surface and ground water. Temperature profiles show that at least one of these lakes is stratified during summer months. Concentrations of Fe, Zn, Co, Ni, and Al increase from the lake surface to a depth of 5 m, and decrease from a depth of 5 m to the bottom of the lake (25 m). These trends may be the result of mineral precipitation in the metalimnion and hypolimnion. Preliminary qualitative X-ray fluorescence (XRF) analysis on lake sediments collected at a depth of 2 m showed an average composition of Si (58 wt%), Al (17 wt%), Fe (14 wt%), and K (9 wt%), whereas sediments collected at a depth of 25 m showed Si (47 wt%), Fe (25 wt%), Al (20 wt%), and K (7 wt%). The 10 wt% increase in Fe concentration between shallow and deep sediments may indicate the precipitation of Fe-hydroxides at depth. Quantitative XRF and X-ray diffraction analysis of lake sediments will provide a better understanding of the geochemical reactions occurring at the sediment-water interface. It is hoped that the findings of this study will lead to an improved remediation strategy for the site.