A 2014 UPDATE ON THE CHLORIDE HYDROGEOCHEMISTRY IN SENECA LAKE, NEW YORK. John Halfman Department of Geoscience, Environmental Studies Program, Finger Lakes Institute Hobart & William Smith Colleges Geneva, NY 14456
[email protected] 12/10/2014 Introduction: Seneca Lake is the largest of the 11, elongated, north-south trending, Finger Lakes in central and western New York State (Fig. 1). It has a volume, surface area, watershed area, and maximum depth of 15.5 km3, 175 km2, 1,621 km2 (including Keuka watershed), and 188 m, respectively (Mullins et al., 1996). The lake basins were formed by glacial meltwaters eroding and deepening former stream valleys underneath the retreating Pleistocene Ice Sheet cutting into the Paleozoic sedimentary rocks approximately 10,000 years ago. Each basin was subsequently filled with a thick deposit of glacial tills and a thin veneer of pro-glacial lake clays. Basins not completely filled with sediment (e.g., Tully Valley), were subsequently filled with water and slowly accumulating postglacial muds. Seneca Lake is classified as a Class AA water resource by the New York State Department of Environmental Conservation (NYS DEC), except for a few locations along the shore (http://www.dec.ny.gov/regs/4592.html, Halfman et al., 2012). It supplies drinking water to approximately 100,000 people in the surrounding communities. Berg (1963) and Schaffner and Oglesby (1978) noted that chloride concentrations were significantly larger in Seneca Lake, and to a lesser extent in Cayuga Lake, than the other Finger Lakes. Wing et al. (1995) argued that the elevated chloride concentrations required an extra source of chloride beyond the measured fluvial fluxes to the lake.