Background/Objectives: The Gowanus Canal (the Site) is located in Brooklyn, NY and sediment at the Site contains polycyclic aromatic hydrocarbons (PAHs) from nearby historical industrial activities and sewer discharges.
Non-aqueous phase liquid (NAPL) is also present beneath the sediment at the Site at a limited number of locations along the canal. The remedy to address PAH and NAPL at the Site may include areas where an active cap will be used to control potential migration of PAHs and NAPL from sediment into the water way. An initial set of treatability studies have been conducted to identify potential active cap amendments that could be used to control the potential migration of PAHs in the dissolved phase and to sequester NAPL that may be present in some specific locations at the Site. A second phase of treatability studies will be conducted using amendments identified during the initial testing in a test configuration that more closely simulates potential future cap designs in specific areas of the canal. This presentation will describe testing conducted to support the selection of amendments for a potential active cap at the Site based on their performance under site-specific conditions to adsorb site-specific target contaminants.
Approach/Activities: Treatability studies were conducted at Geosyntec's SiREM Laboratory to evaluate the capacity of activated carbon (AC) products to sorb the dissolved phase PAHs. AC will also sequester organic compounds other than PAHs but only PAHs and NAPL have been identified as contaminants of potential concern. Tests were completed using methods which were reviewed by the US EPA and leading technical experts in the field. AC experiments included a kinetics test, an AC capacity screening test (of 11 commercially available types of AC) and a more extensive isotherm test using the optimal types of AC identified. All AC tests used site-specific simulated pore water which was prepared by contacting groundwater and NAPL from the Site to create a high concentration scenario. Microcosms with simulated site pore water were continually agitated throughout the 8-day tests and were amended with varying amounts of AC. Treatability studies were also conducted to evaluate the sequestration of NAPL from the Site onto oleophilic clays. Two different types of NAPL sorption capacity tests (one centrifuge method and one using a microcosm containing NAPL and potential sediment cap material) were completed using site-specific NAPL and five types of oleophilc clay.
Results/Lessons Learned: The results of the testing demonstrated that significant reductions in the concentration of dissolved PAHs could be obtained with different types of AC. All types of AC were capable of reducing concentrations of PAH in simulated pore water but optimal types of granular AC (GAC) and powdered AC (PAC) for treating simulated site pore water were identified. Isotherm testing on selected GAC and PAC provided data to be used for design purposes in sediment cap modeling. Likewise, more than one type of oleophilic clay was found to be effective at sequestering the site-specific NAPL, although there were significant differences in the capacity of different types of oleophilic clays to sorb NAPL. The phase I treatability study experiments were successful at identifying potential AC and oleophilic clays to be used in column studies and ultimately for use in a