February 15, 2011 - small non-hydro dam removal

Tuesday, February 15, 2011

From the dam removal department:

Picture a small dam stretching about 50 feet across a stream.  The Gravesleigh Dam on Sackett Brook in Pittsfield, Massachusetts was built in the 1930s by Merle Dixon Graves, a native of Bowdoinham, Maine who served in the Massachusetts House of Representatives from 1921-1924 and who owned Gravesleigh, an estate surrounding the brook just above its confluence with the Housatonic River.  Merle Graves had the dam built to create a small pond for his estate.  Over the years, the pond filled with silt, and much of the Gravesleigh estate became Massachusetts Audubon Society's Canoe Meadows Wildlife Sanctuary.

Now, Massachusetts Audubon is interested in removing the dam for reasons including improving water quality, restoring riparian wildlife habitat, and creating educational opportunities to learn about watershed health and science.  Moreover, as part of a deal to allow the Pittsfield Municipal Airport to expand, the dam site has been identified as able to offset some of the habitat lost at the airport as a condition for state water quality certification.  With the impoundment silted in, and no renewable power production at the site, these benefits may make the Gravesleigh Dam seem like a good candidate for dam removal.

The Housatonic Valley has a long history of industrial manufacturing, some of which resulted in PCB (polychlorinated biphenyl) contamination of the valley's soils and water.  According to EPA, "PCBs are probable human carcinogens and can also cause non-cancer health effects, such as reduced ability to fight infections, low birth weights, and learning problems."  If these chemical contaminants are trapped in the sediment impounded by the Gravesleigh Dam, the dam's removal could send the PCBs downriver into the Housatonic.  This is the same problem as found on Twelve Mile Creek in Clemson, South Carolina, where dam removal initiatives must be weighed against the risk of disturbing PCB-laden sediments.  In Pittsfield, dam removal could be paired with sediment remediation, but that would significantly add to the project's cost - already predicted to be $303,000 without sediment remediation.  This points to the importance of understanding what's trapped behind the dam.

Sampling of impounded sediments was undertaken last summer.  While most samples came back negative for PCB, one of the sediment samples did show PCB contamination.  This triggered another round of sediment testing last month.  The results of that testing have just come in, and suggest that sediment remediation will not be required for dam removal.

The Gravesleigh Dam's saga may soon be over.  In this case, chemical contaminants trapped behind the dam may not prove sufficient to prevent the dam's removal.   Each dam has its own story, and may have its own baggage that must be addressed if the dam is to be removed.  I'll keep you posted on the Sackett Brook story as it continues to flow.

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