Community Sewer Assessments

MWRA bases community sewer assessments primarily on community shares of wastewater flow and population. On average, approximately 61% of FY02 sewer assessments are based on flow, and 38% are based on total and sewered population. A small portion reflects the cost of treating "high strength" flow from certain industries, which discharge into the MWRA system. High strength flow contains high concentrations of solids and oxygen consuming organisms.

MWRA uses three-year flow averaging to smooth fluctuations in assessments that would otherwise result from variations in annual rainfall and local sewer conditions.

Changes in community assessments reflect year-to-year changes in rainwater infiltration and inflow (I/I) into local sewers as well as increases in MWRA’s annual budget. A community’s I/I contribution relative to all other communities in the system (but particularly Boston’s I/I contribution) is a key factor in the differences among percentage changes in various community assessments. Local initiatives to reduce infiltration and inflow into sewer systems can help limit increases in community assessments. MWRA estimates show that infiltration and inflow as a percentage of total community flow ranges from 40% to 74%.

Sewer Flow Characteristics % by Community for 2002 (PDF)