Dam removal is gaining widespread consideration as a stream restoration technique in the US. These barriers can be removed for several reasons including fish passage, economic concerns, and/or regulatory compliance. This Yale Sea Grant project, as part of an overall feasibility study for the proposed removal of a small dam on Raymond Brook, is an evaluation of the sediment quality behind the existing dam and its potential heavy metal pollution down stream following removal

Raymond Brook is a high energy headwater stream which lies in the Northeastern section of the Salmon River watershed near Hebron, CT. It flows adjacent to the Salmon River State Forest, Raymond Brook Marsh Wildlife Preserve and in close proximity to over 1,000 acres of other protected land. The Salmon River is a tributary of the Lower Connecticut River which drains into Long Island Sound. This central Connecticut watershed is largely undeveloped. For this reason, the Salmon River has been targeted as a major component of the national Atlantic salmon restoration effort coordinated by the Connecticut River Atlantic Salmon Commission.

Raymond Brook Dam, which is proposed for removal, was constructed to create a pond for a children’s camp located on the premises. The dam is small, only 3-4 feet tall and 12 feet wide with an impounded area of 0.5 acres. The proposed project would remove Raymond Brook Dam in its entirety. It is important to consider the concentration of pollutants associated with impounded sediments because dam removal and its related restoration activities may suspend some of the fine sediment and transport any associated pollutants downstream. Project partners (Connecticut River Watershed Council, The Nature Conservancy, American Rivers, and the Inland Fisheries Division of Connecticut DEP) will use this analysis in their decision-making as they proceed with the dam removal process.

Sediment probing indicated that Raymond Brook contains areas of rapid flow and one of a slower nature. This affects the type and size of sediment deposited on the stream bed, which directly affects the type of pollutant expected. Samples were analyzed for twelve heavy metal pollutants regulated in Connecticut: antimony, arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, silver, vanadium and zinc. All of the metals of interest, with the exception of mercury, were found to be within state allowable limits. Mercury was detected at an elevated rate, but this data may be unreliable due to a possible sampling error. This unknown mercury content is negligible, because this sample was collected in an area of the pond that will not be excavated. Therefore no sediment is expected to be mobilized. In addition, as part of removal this area will be allowed to grow into aquatic vegetation, keeping the sediment immobilized and serving as a mitigation effort.

Based on these preliminary sediment analyses, it is unlikely that the Raymond Brook Dam Removal project will impact the downstream aquatic habitat with trace metals.