Storm Drain 5 (SD-5) Groundwater Plume

December 1996

Storm Drain 5 (SD-5) Ground-Water Plume

Source of Ground-Water Plume:

A plume can result when fuels or solvents are spilled or dumped on the ground. As these materials filter through the sandy Cape Cod soil, they encounter ground water where the soil is saturated with water. As the ground water moves, it carries the fuels or solvents with it, creating a body of contaminated water, also known as a plume.

The source of the ground-water plume is the Storm Drain 5 (SD-5) site, which historically received runoff from various military and industrial activities on the MMR.

Plume Dimensions:

Approximately 10,000 feet long
Approximately 1,750 feet wide
Vertical thickness varies from 20 - 100 feet
50 - 130 feet below the ground surface

Primary Contaminants:

The primary contaminants of SD-5 are 1,2 dichloroethylene, tetrachloroethylene, and trichloroethylene (TCE), three chlorinated solvents used formerly at the MMR. Solvents are liquids used to dissolve or disperse another substance such as oil.

Proposed Containment Plan:

SD-5 North - An extraction/treatment/reinjection (ETR) remedial system is planned to contain the northern part of the SD-5 ground-water plume. The system will consist of 14 extraction and 14 reinjection wells installed off-base near the MMR border and an on-base treatment plant for the extracted water. The ETR system will draw the water out of the ground and remove the contamination by running the water through activated carbon canisters. The carbon adsorbs, or holds on to, the contaminants, and clean water is returned to the ground. The carbon canisters are recycled off-site periodically. Construction is expected to begin in March 1997, with system start-up estimated for August 1997.

SD-5 South - As recommended by the Technical Review and Evaluation Team, an ETR containment system is not planned for the southern portion of the SD-5 ground-water plume. The effectiveness of an ETR system is uncertain for this geological area because the plume is located near Ashumet and Johns Ponds, and the hydrogeology between the ponds is extremely complex. Instead, SD-5 South is scheduled for pilot testing of recirculating wells, a technology that cleans ground water inside wells without pumping the water to the surface. Gas bubbles pumped through the ground water collect the contaminants as a vapor. The vapor is then retrieved and treated above ground. The ground water is recirculated through the wells and becomes cleaner with each pass through the system. The system is scheduled to be on-line March 1997.