AN UPDATE ON THE CHLORIDE HYDROGEOCHEMISTRY IN SENECA LAKE, NY

Seneca Lake has significantly larger chloride and sodium concentrations (125 and 80 ppm) than the neighboring Finger Lakes in central NY (mean 25 ± 0.7 and 18 ± 0.6 ppm). The modern-day fluvial and salt mine waste fluxes are insufficient to attain the measured lake concentrations based on steady-state, mass-balance arguments. Thus, previous workers hypothesized that the additional salt entered from the lake floor (Wing et al., 1995; Halfman et al., 2006) to balance the budget. The deep bedrock floor under the basin provided a groundwater connection between the lake and underlying Silurian Salina Formation (rock salts). This presentation updates the major ion hydrogeochemistry of Seneca and neighboring Finger Lakes.

Water has been periodically collected from at least 2 sites in the 8 easternmost Finger Lakes, and the major streams flowing into Seneca Lake over the past decade. Samples were filtered (0.45 mm), and filtrate analyzed for Cl^-, SO₄^2-, Na⁺, K⁺, Mg²⁺, Ca²⁺ by ion chromatograph. This data were augmented with historical Cl concentration data and salt mine waste discharge data, unearthed from archived water quality reports by municipal water providers and the EPA ICS web site. Cl concentrations have significantly changed over time. Thus, chloride is not at steady state in these lakes.

The historical chloride concentration trends divided 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 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 a groundwater source to balance the early 1900s Cl budgets. Mine “issues” leaked up to a million tons of salt into the lake to partially support the mid-century peak concentrations. Since the 1970s peak, groundwater inputs are no longer necessary to support the measured Cl concentrations.