February 15, 2011 - small non-hydro dam removal

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.

November 10, 2010 - dam removal on Martha's Vineyard

This summer I was fortunate to spend a week on the island of Martha's Vineyard in Massachusetts.  I learned about the island's energy resources, including solar and wind on Martha's Vineyard.

Photo: wind power near the islands: Falmouth, Massachusetts.

Following up on my recent looks at dam removal, today I'm looking at some possible dam removal activity on Martha's Vineyard.  It's what you might term a large-sized island: 87.48 square miles (231.75 km²), making it the third-largest island on the east coast of the US, and the largest island on the east coast not tied to land by a bridge or tunnel.  Population-wise, the year-round population of about 15,000 residents is augmented by tourists and seasonal residents, peaking at up to 75,000 people in summer.  Still, it's a manageable size, with all points of the island relatively accessible to visitors.

It's the relatively moderate size of Martha's Vineyard that made me surprised to learn that the island is home to at least 3,000 dams.  That's about 13 dams per square kilometer, or 34 dams per square mile.  The vast majority of these dams were built in the last 200 years to provide power, water, or both to mills -- almost all of which are no longer in operation.  With no maintenance, and no ongoing operations like hydropower production, many of these dams have become overgrown, forgotten, and in poor condition.

In response to a near-disaster in 2005 when rain-induced flooding nearly broke an old dam in a densely-populated area, the Commonwealth of Massachusetts enacted new dam safety and liability laws.  These changes made it more clear that whoever owns a dam is responsible for its safety -- and for the consequences of its failure.  Many property owners did not even realize that they owned aging dams when they purchased former industrial sites, like the Briggsville Dam in Clarksburg whose owner was surprised to find itself responsible for costly repairs or removal.

When costly repairs are required to maintain state and federal licenses and certifications, dam removal is one option.  Some dams on the Vineyard still provide valuable services, like flood control or providing water supply to residents and businesses.  Others, like the Mill Pond dam in West Tisbury, impound water for scenic and recreational purposes.  Still others remain in streams, holding back small ponds, in unknown condition.  Some may be candidates for removal, while others may be candidates for powering up as small hydro-electric sites.  As an island interested in sustainability, as well as reliability, it will be interesting to see which Martha's Vineyard dams are removed, and which will be restored.