ASSESSMENT OF REMEDIAL ALTERNATIVES FOR A GLACIAL-DRIFT AQUIFER IN THE ONONDAGA VALLEY, SYRACUSE NY: INSIGHTS FROM GEOCHEMICAL AND VARIABLE-DENSITY FLOW MODELS

Naturally occurring halite brine within glacial-drift deposits that fill the Onondaga Valley near Syracuse, N.Y., was pumped to produce salt during the 18th and 19th centuries, and later formed the basis of a chemical industry that lasted into the late 20th century. A continuing environmental legacy of this enterprise remains in the presence of saline waste-disposal beds on the shores of Onondaga Lake, which has been identified as one of the Nation's most contaminated lakes as a result of discharges from industrial, sewage, and stormwater sources. Discharge from the waste-disposal beds caused hypersaline conditions in the lake by the middle of the 20th century, resulting in chemical stratification of lake water and failure of spring turnover during a number of years. The salinity of the lake water decreased significantly following closure of the chemical plant, with chloride concentrations falling from 2,000 mg/L in 1980 to 500 mg/L by 2005.

Results from geochemical and variable-density flow models indicate that the halite brine formed about 16,700 years ago following the last glacial recession. The brine remains trapped beneath lacustrine sediments underlying Onondaga Lake, where it has persisted to the present. Variable-density flow simulations suggest that waste from the former chemical industry could have migrated along the periphery of the brine pool beneath the lake shore, despite the nearly flat hydraulic gradient. The age of the brine suggests that contaminants that have seeped into bedrock beneath adjacent industrial areas may remain trapped beneath the brine pool and overlying glacial till—although their ultimate fate is not known. Simulation results also indicate that the brine pool, currently being considered as a deicing source for local roads, is a finite reservoir. Finally, model simulations suggest that migration of saline water through the glacial drift from a former salt-solution mining operation 30 km to the south will not affect the salinity of Onondaga Lake.