Portland Disposal Site

Portland Disposal siteThe Portland Disposal Site (PDS) is one of three regional dredged material disposal sites located in the waters of Maine. It covers a 1 nmi2 (3.4 km2) area of seafloor centered at 43° 34.111' N, 70° 01.9386' W (NAD 83), approximately 7.1 nmi (13.2 km) east of Dyer Point, Cape Elizabeth, Maine. PDS is characterized by a rough, irregular bottom topography, with areas of soft sediment accumulation in the basins among bedrock outcrops. Sediments deposited at PDS have originated from dredging projects in Portland Harbor, Fore River, and many of the smaller rivers and harbors within the Casco Bay region. A total of 2,732,168 yd3 has been disposed of at this site since 1982. In recent years, there has been significant DAMOS monitoring activity at this site, as part of a comprehensive subaqueous capping feasibility study. The depositional environment of PDS, especially within the deeper fine-grained basins, indicates that volumes of dredged material can be placed without significant subsequent movement beyond the disposal site boundaries. Dredged material disposal operations specifically target these natural basins to form mounds of sediment on the seafloor. The various bedrock ridges surrounding the depositional areas provide a measure of protection from wave energy and thus act to contain the deposited dredged material. The steep sides of the depressions or hollows disrupt any near bottom orbital currents generated by passing storm waves, minimizing resuspension over the surface of the sediment deposit. In addition, the rock walls of the natural seafloor features prevent the lateral spread of non-cohesive sediment on the seafloor as a dredged material mound is developed over time.

Relevant DAMOS Reports