Brooklyn, New York

Mass Loading Expert Regarding MGPs for the Gowanus Canal NPL Site Remedial Design Allocation

The Gowanus Canal is a 1.8-mile-long, man-made canal located in the Borough of Brooklyn in New York City.  Decades of industrial and commercial activities have resulted in the Canal becoming contaminated.  The selected in-Canal remedy for this site listed on the U.S. Environmental Protection Agency’s (EPA’s) National Priorities List (NPL) consists of (1) the dredging of soft sediments from the Canal floor; (2) in-situ stabilization of NAPL-impacted native sediments and construction of a multi-layer cap covering NAPL in the native sediments; (3) long-term monitoring and maintenance; and (4) implementation of institutional controls.

To support New York City’s position in the cost allocation process, First Environment prepared an expert report on the environmental practices and mass loading of three manufactured gas plants (MGPs) that operated along the Canal within a period spanning 90-some years from the 1860s to about the mid-1950s.  First, through detailed research into primary source documents, we presented an overview of MGP processes (coal gas, carbureted water gas and oil-gas) and characterized residuals management practices in terms of standard of care over the time frame. Simultaneously, we developed a conceptual mass loading model that served as the basis for a process-based calculation tool that quantified the mass loading of non-aqueous phase liquid (NAPL) and polycyclic aromatic hydrocarbons (PAHs) to the Canal.

Second, we drilled down into historical records specific to the MGPs along the Canal and supporting primary source documents to establish facts regarding the development and operations of the MGPs over their operational periods. We then used our general and specific findings to develop and refine a mass loading calculation tool based on annual gas production data, accepted production-to-waste ratios, historical practices, and evidence-based engineering assumptions as to chemical makeup, transport, and degradation. We were able to ground truth our calculations with actual findings from environmental investigations in the field at the MGPs and at other similar sites.

To further assist in the allocation process, First Environment also reviewed CERCLA 104(e) and Allocation Questionnaire responses submitted by PRPs as well as Nexus Packages prepared by a consultant for the MGP party covering all participants.  In addition, we prepared a report that provided an assessment of groundwater pathways for certain upland sites and calculated the current mass loading of dissolved PAHs through groundwater to the Canal. Lastly, First Environment assessed the MGP PRP’s allocation methodology to highlight various inadequacies and shortcomings and to support the City’s position.