Engineering Design

The design for the Site cleanup includes the following elements:

  • Sediments with coal tar residues and elevated PAH concentrations will be removed by mechanical dredging. The dredging will extend across approximately 7 acres of the harbor, including portions of the navigation channel and the water on the Coast Guard Station, Solomon Jacobs Park, and National Grid and Maritime Gloucester properties. The dredged materials will be moved by barge to an approved treatment and disposal facility for eventual recycling.
  • To dredge the areas near the seawalls, structures such as piers and floating docks will be temporarily removed and will be replaced after dredging. A stability wedge consisting of concrete will be built at the base of the Coast Guard seawall to provide additional support to the wall and meet current design standards.
  • After dredging, a porewater cap will be built in the harbor next to the Coast Guard, Solomon Jacobs Park, and National Grid seawalls. This cap will treat the MGP compounds in the porewater beneath the harbor. The cap will not affect the navigation channel, or the use of the harbor by the adjacent property owners or the public.
  • In the upland areas, soil with elevated coal tar residues will be excavated from behind some of the park and National Grid seawalls and transported off Site for proper treatment and disposal. To remediate this material, the seawalls will be taken down, and after remediation, new seawalls will be built along the front of the park, along the access ramp to the public landing and in front of the National Grid building. The new seawalls will be aligned to better meet the needs of the Gloucester Harbormaster, and will match the appearance of the historical granite walls found along the Gloucester waterfront. The land in front of the National Grid building will provide waterfront access to the Gloucester Harbormaster and members of the public.
  • Further inland in the park, soil with elevated concentrations of hydrocarbons beneath the surface will be excavated until crews reach groundwater. The soil will be transported off Site for proper treatment and disposal, and the area will be capped with clean soil to limit future contact with deeper soil.
  • An automated pumping system will be installed at the Coast Guard, park, and National Grid properties to remove the dense non-aqueous phase liquid (DNAPL) present at 40 to 60 feet below ground surface. The system will pump DNAPL to an above-ground temporary storage unit, from which it will be periodically removed and transported to an appropriate off-Site disposal facility.
  • Deed restrictions will be filed for certain areas of the Site so that, among other things, the engineered barrier and porewater cap are monitored and maintained, future excavation or construction activities are conducted in a safe manner, and soil removed from the Site in the future is managed in accordance with applicable environmental regulations.

extra - Park from above

 

Over the course of this project, National Grid’s contractors will control odors to the extent practicable by limiting the size of the area disturbed, using foam and other engineered controls to limit potential odors, and stopping work if necessary.

A traffic control plan will be used to manage traffic in and around the remediation activity, including trucks traveling to and from the Site. This program will include route planning for trucks and other vehicles, and coordination with local authorities, agencies, and the surrounding community on transportation safety issues.

A Closer Look at the Site

Design - Proposed remediation
Design - Nearshore remediation
Design - Proposed remediation