THE CHLORIDE HYDROGEOCHEMISTRY OF SENECA LAKE, NY, USA

Seneca Lake has larger chloride and sodium concentrations (125 and 80 ppm) than the neighboring Finger Lakes in central New York (25 and 18 ppm). The current inputs from fluvial and salt mine waste sources are insufficient to attain the measured lake concentrations assuming steady-state, mass-balance arguments. Thus, previous workers hypothesized that additional Cl & Na entered the lake from the lake floor (Wing et al., 1995; Halfman et al., 2006). The deep bedrock floor under the lake provided a potential groundwater connection between the lake and underlying Silurian Salina Formation (rock salts).

Water samples and CTD profiles have been periodically collected from at least 2 sites in Seneca and the other 7 easternmost Finger Lakes, and the major streams flowing into Seneca Lake over the past decade. Samples were filtered (0.45 µm), and filtrate analyzed for major ions by IC. This data were augmented with historical Cl concentration data unearthed from archived municipal water quality reports and other data. It reveals that Cl concentrations have significantly changed over time, and thus, the chloride steady state assumption is incorrect.

The historical trends in Cl concentration divide the lakes into two groups. (1) Hemlock, Canadice & Skaneateles Lakes, revealed small Cl concentrations in the early 1900s (2 to 5 ppm) increasing stepwise in the 1960s and again in 1990s to today (20 to 30 ppm). The patterns mimicked those detected in other waterways influenced by increasing use of road de-icing salts. (2) Seneca and Cayuga Lakes revealed larger and steadily increasing Cl concentrations (40 to 110 ppm) in the early 1900s, a distinct peak in Cl concentrations (180 ppm) from 1965 to 1975, and then decreasing Cl concentrations to today (120 ppm). Modeling Seneca’s Cl inputs suggests that the estimated fluvial and mine waste fluxes still require another source to balance the early 1900s Cl budgets, probably from pre-1970s enhanced mine waste discharge. Mine “issues” leaked up to a million tons of salt into Cayuga and Seneca Lakes to attain the 1970s peak concentrations. Since then, chloride has been naturally flushing out of the lakes, and present day modeled inputs are similar to known stream, mine and diffusive inputs.