Groundwater As a Loading Mechanism in Two Tidal Estuaries, Gowanus Canal and Newtown Creek, New York, New York

Sediment site investigation often focus on point source discharges and internal redistribution mechanisms such as prop wash and erosion as primary contaminant loading mechanisms in tidal estuaries.  Groundwater loading was assessed at the Gowanus Canal and the Newtown Creek Superfund sites by NYCDEP and the results compared to other studied loading mechanisms such as Combined Sewer Overflows (CSOs) and ebullition facilitated NAPL migration.  The results show that groundwater is an important mechanism that contributes significant loads of contaminants to the system.  Groundwater’s contaminant loads dwarf loads contributed by CSOs, however the groundwater loads are not as large as those contributed by ebullition facilitated NAPL migration (where it was quantified in Newtown Creek).  Evidence of groundwater’s contaminant contribution was established by comparing mass fractions of polycyclic aromatic hydrocarbons (PAHs) in groundwater, surface water, CSOs and sediment in Gowanus Canal, which showed a direct correlation between groundwater and surface water total PAH make up, while CSOs were found to have a significantly different PAH make up.  These analyses show that groundwater loading and ebullition assisted NAPL migration must be understood to have a comprehensive conceptual site model.