AN UPDATE ON BOSTON'S PROJECT TO REMOVE SEWAGE FROM THE STORM DRAINAGE SYSTEM

The Stony Brook Illegal Connection Investigation is an integral part of the Boston Water and Sewer Commission's program to reduce sewage discharges to Boston's storm drainage system, the Charles River, and ultimately Boston Harbor. The project incorporates innovative techniques to identify wastewater in the storm drain system, which is tributary to the Stony Brook Conduit. The Stony Brook Conduit discharges to the Charles River from a drainage area of approximately 8,400 acres. The study area for this project encompasses approximately 6,000 acres served by separate sanitary sewer and storm drain systems; the remaining 2,400 acres are served by combined sewers.The project to remove illegal connections from the Stony Brook Conduit began in 1999 with a pilot study. Two of the sub-areas, representing about 8 percent of the overall study area, were selected to test the methodology developed by the Commission to locate and remove illegal connections. During the pilot project, all manholes were inspected during dry weather conditions, starting at the upstream end of each drainage path. Visual observation and field tests of water quality parameters (pH, conductivity, temperature, ammonia, and surfactants) were used to identify contamination. Where evidence of contamination was not found during inspections, sandbags were placed during dry weather for 48-hours to confirm the absence of contamination. After contaminated reaches were identified, dye tests were performed to identify the sources. The pilot study investigation identified 31 illegal connections, all but three of which were corrected within an average of 40 days from notification. The three remaining connections were complex situations requiring additional assessment and special repair techniques. Repair of the 28 illegal connections resulted in the elimination of more than an estimated 7,000-gpd of untreated wastewater discharge to the Stony Brook Conduit.Following the pilot project, the methodology was refined, significantly reducing the number of total drain manholes inspected and increasing the use of sandbags to focus investigations and reduce the number of dye tests. Over 1,430 manholes have been inspected as of April 19, 2002, with contamination identified at 450. Investigations were isolated to about 250 reaches of storm drain, prompting dye testing at more than 2,125 buildings. 278 illegal connections have been identified, and 159 have been repaired. Nine of the remaining illegal connections could not be repaired by conventional excavation and redirection. Special designs are underway for repair at these locations. Fieldwork is scheduled to be substantially complete by December 2002.