Remediating a Working Waterfront, Gloucester, MA

From 1854 until 1952, the former Gloucester Gas Light Company (GGLC) operated a facility along the Gloucester, Massachusetts, waterfront to convert coal and oil into manufactured gas. The former manufactured gas plant (MGP) has since been re-developed consisting of a working waterfront with properties owned and operated by seven different entities, including the federal government, a local municipality city park and harbormaster facilities, a utility company, a non- profit marine museum, a harbor-side restaurant, and commercial fisheries-related operations. In 2010, site investigations and data were collected across the site which identified compounds from the former MGP site present below the upland ground surface and within Gloucester’s Inner Harbor. Subsequent to completion of the site investigation programs, a remedial action plan (RAP) resulted in the selection of a regulatory approved remedial alternative. In 2015, a $30 million two-season construction project was begun to implement the remedial alternative. This paper presents the basis of design and descriptions of the design and construction process for a complex remediation project in a working urban marine environment. Key design considerations include isolation or removal of MGP-impacted soil and sediment via the construction of engineered barriers within the tidal zone, overcoming geotechnical subsurface and tidal challenges, addressing unstable historical waterfront seawalls, and minimizing impacts to ongoing commercial and government waterfront operations. The engineered barriers constructed along the waterfront included a geosynthetic wrapped-face wall fronted by a granite block seawall with a groundwater treatment chimney between the two walls and an adjacent impermeable pile supported concrete seawall with a subsurface sheetpile wall as a vertical barrier to NAPL migration through/below the seawall. These seawalls were designed to replace the unstable granite block walls and to meet historical commission requirements for consistency with the existing wharves in the harbor.