Gowanus Canal Superfund Site. I: NAPL Mobility Testing of MGP-Impacted Sediments

Abstract

The Gowanus Canal superfund site is located in Brooklyn, New York. The site is impacted by nonaqueous phase liquid (NAPL) from historic manufactured gas plant (MGP) sites and other sources. One of the primary objectives for the selected remedy included eliminating the migration of NAPL into the canal. Accordingly, the amount of NAPL present in sediment samples was quantified and physical testing was conducted to determine a threshold amount of NAPL that could be potentially mobilized into the canal as a result of upwelling groundwater. Undisturbed core samples of native sediment were collected and analyzed for NAPL, water, and air pore fluid saturation (PFS) using the Dean-Stark extraction method, and the total petroleum hydrocarbon (TPH) content. Sediment samples were found to contain NAPL saturations ranging from nondetectable (<0.12%) to 52%. A relatively good correlation (R2=0.77) was observed between the Dean-Stark and TPH results when compared on an equivalent mass basis. The NAPL mobility was evaluated for induced groundwater fluxes ranging from average existing site conditions to a factor of 10 higher (13–130 cm/day). Consistent NAPL mobility was observed when the NAPL saturation exceeded 21%. However, when the NAPL saturation results were converted to TPH on a mass basis (milligrams of NAPL per kilogram of sediment), the results were a poor indicator of NAPL mobility.