Project Summary:

The Air Force is committed to improve the ecological health of an off-base pond being impacted by a sewage plume as part of its overall environmental cleanup program.  A P rich groundwater plume that originates from a former MMR wastewater treatment plant, discharges to a state-owned glacially formed kettle hole pond.  The plant operated for more than 50 years leaving a large mass of P sorbed to sandy soils upgradient of the pond.  This mass of P has been found to desorb very slowly from the aquifer in an anoxic setting formed by microbial degradation of other sewage related compounds.  Current P loading is estimated to be 100-200 kg/yr and is expected to completely discharge to the pond through a very small zone of its bottom sediments in 20 to 30 years.  Continued P discharge to the pond is expected to produce an increased frequency of blue-green algae blooms.   The installation of a geochemical barrier in the P discharge zone (footprint) is expected to significantly reduce P loading to the pond, thereby enhancing its overall ecological health.  The geochemical barrier project was a final step in P remediation for the pond following closure of the plant in 1995 and a hypolimnetic alum treatment in 2001. 

AFCEE installed the geochemical barrier in the top three feet of pond sediments along 300 feet of the northwest shoreline of Ashumet Pond and it extended 40 feet out into the pond.  The project was installed in August and September of 2004.   The project consisted of excavating approximately three feet of pond sediments, mixing the sediments with zero-valent iron (ZVI) and then placing the mixture back in the excavated areas.  The surface was then contoured to match the original shoreline elevations.   Permits for this project were obtained from the Falmouth Conservation Commission, the U.S. Army Corps of Engineers and the Massachusetts Department of Environmental Protection. 

Scientists from the U.S. Geological Survey (USGS) explained the results of preliminary monitoring work conducted in September and November at the December 8, 2004 meeting of the Plume Cleanup Team (PCT).  Two rounds of post-installation sampling have been performed and more data collection over the next several years will allow for a more detailed evaluation of barrier performance.  Preliminary data collected just after barrier installation and in November 2004 suggests substantial removal of P from the plume. 

Much research and discussion was done cooperatively with scientists, permitting agencies and the local community to develop an effective science-based strategy that was both permitable and publicly acceptable.  Numerous public meetings, Ashumet Pond Nutrients Advisory Group (APNAG) and PCT meetings, were held by the Air Force in each step of the research process to keep the local community informed.   This approach allowed the Air Force contractors to provide scientific information in small digestible pieces that could easily be understood in an evening meeting.  The USGS and Air Force contractors will continue monitoring barrier performance, the movement and eventual dissipation of the P groundwater plume, discharge zone concentrations and pond water quality.  Results of this work will continue to be presented at PCT meetings and posted on this website.   An update of the construction and monitoring of the iron barrier will be presented at an APNAG meeting in Spring 2005. 

Reports:

Notice Of Intent Application for the Ashumet Pond Geochemical Barrier, 2004 - NOI for Ashumet Pond Barrier.pdf
Ashumet Pond Phosphorus Inactivation Report, February 2002 - Ashumet Final Report.pdf

USGS Presentation, December 2004 - Monitoring Discharge of the Phosphorus Plume to Ashumet Pond

Ashumet Pond Nutrients Advisory Group - APNAG