DEVELOPMENT AND LONG-TERM FATE OF A CAPPED DISPOSAL MOUND AT AN OPEN WATER DREDGED MATERIAL DISPOSAL SITE

摘要

New London Harbor is a major commercial,recreational,and military port in New England.Infrastructure improvement projects within the harbor have often been driven by the changing draft requirements of military vessels operating out of the US Navy Submarine Base in Groton,Connecticut.Sediments removed as part of deepening projects are transported to the New London Disposal Site(NLDS)in eastern Long Island Sound and deposited on the seafloor. In 1995,the US Navy selected the Groton Submarine Base in the Thames River, Connecticut as the homeport for the new Seawolf class submarines.In order to accommodate these larger vessels,improvement dredging was required within both the federal navigational channel and multiple submarine berths.Pre-dredging characterization of the project sediments detected polycyclic aromatic hydrocarbon (PAH)and trace metal(Cu,Cr,and Zn)contamination in a portion of the dredging area. During the 1995-96 disposal season,an estimated volume of 305,000 m 3 of sediment classified as unacceptably-contaminated dredged material(UDM)was removed from berthing areas and placed in the northwestern quadrant of NLDS to form a discrete deposit on the seafloor.The navigational channel was then dredged,providing approximately 556,000 m 3 of capping dredged material(CDM)that was transported to NLDS and strategically placed on the seafloor to completely overlay and isolate the UDM from the marine environment.Once complete,the newest bottom feature on the NLDS seafloor was named the“Seawolf Mound”. Capping projects of this size generally require a comprehensive disposal site monitoring program to ensure adequate distribution and thickness of CDM over the UDM deposit.During the 1995-96 disposal season,detailed surveys were performed over the Seawolf Mound at the Baseline,Precap,and Postcap stages of development. In addition,follow-on surveys in 1997,1998,and 2000 employing precision bathymetry,sediment-profile photography,benthic community assessment,and sediment coring have been completed to monitor the physical and chemical composition of the deposited sediments to verify cap integrity,as well as assess benthic recolonization over the capped mound.This paper will present the time-series of results compiled from 1995 through 2000 that documents the initial development and mid-to long-term fate of the Seawolf Mound at NLDS.