ARE HISTORICAL CHLORIDE DATA INCONSISTENT WITH SALINE GROUNDWATER INTRUSIONS IN SENECA LAKE, NEW YORK?

The Finger Lakes of western and central New York support a rapidly expanding tourist industry and provide fresh drinking water to neighboring communities including the cities of Rochester and Syracuse. Threatening both uses are elevated chloride and sodium concentrations in Seneca Lake (~130 & 80 ppm), and to a lesser degree Cayuga Lake (50 & 25 ppm), compared to the other Finger Lakes (~20 & 10 ppm, respectively). Previous researchers hypothesized that the elevated chloride and sodium concentrations result from an additional saline groundwater source to Seneca and, to a lesser degree, Cayuga Lake from the underlying Paleozoic rock-salt deposits due to their great depth. However, Jolly (2005) presented historical chloride concentrations of ~30 ppm in 1900 for Seneca and Cayuga Lakes that question a geologically constant saline groundwater source. His historical data also revealed a steady increase in chloride concentrations from 1900 to modern values by 1970. We now hypothesize that the historical chloride data reflect increased contributions of road salt, salt mining activities in the region, and a mid-century pulse of saline groundwater.

Modern and historical major ion concentration data from the Finger Lakes are presented to investigate our hypothesis. Water samples were collected from nine of the eleven Finger Lakes since 2000. Since September of 2004, samples were collected weekly in Seneca Lake during the spring, summer and fall, monthly in the remaining lakes at both shoreline and mid-lake sites, and annually from sixteen streams in the Seneca Lake watershed. The samples were filtered and the filtrate analyzed by ion chromatograph for chloride, sulfate, calcium, magnesium, potassium, and sodium. The modern data cluster into three ion groups: (1) potassium is in equilibrium with stream inputs, (2) calcium and magnesium are depleted in the Finger Lakes relative to stream inputs due to the precipitation of calcite within the lake, and (3) chloride and sodium are enriched in Seneca and Cayuga Lakes relative to stream inputs. Historical data will be gathered from neighboring lakes using archived Health Department and Water Supply reports.