The original sanitary sewer collection system was constructed in 1901. The original pipe material used was primarily vitrified clay, although cast iron was used for crossing under streams and railroads, and brick was used for the Brookdale Interceptor which runs between East Street and Maverick Street through the Brookdale Cemetery. Manholes were also constructed using brick and mortar. These same materials were used as the system expanded up until the 1980’s when polyvinyl chloride (PVC) became the standard pipe material and precast concrete became the standard manhole material. Other pipe materials used in the system include ductile iron, asbestos cement, reinforced concrete, and high density polyethylene (HDPE) pipe.
Until 2005 when the first sewer pump station was constructed the entire system was served by gravity pipes ranging in size from 6 inches in diameter to 24 inches. The range of diameters in Dedham is relatively small given the size of the system due to the fact that there are several MWRA interceptor sewer lines running through Dedham which the sewer system connects to in eighteen (18) locations. The quantity of sewage is measured by the MWRA at these connections by meters and the data is used to calculate the annual MWRA flow assessment, which is the basis for the sewer rate.
The Town of Dedham sanitary sewer system is comprised of 471,755 linear feet (89.3 miles) of sewer main and 2,604 sewer manholes. The lateral service connections which service individual homes and businesses are privately owned and maintained.
On an average day 4.46* million gallons of sewage per day (MGD) travels through the sanitary sewer system and into the MWRA system for treatment at Dear Island. Unfortunately, based on the latest flow component estimates, only 1.80* MGD of that flow is actually from toilets, sinks, and industrial processes. The remaining 2.66* MGD of flow is comprised of clean groundwater and surface water which enters the sanitary sewer system through cracks, holes, roof downspouts, and illegal plumbing connections. This unwanted extra clean water is known is Inflow and Infiltration (I/I).
*Based on most recent I/I data provided by the MWRA