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
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
MWRAs annual budget. A communitys I/I contribution relative
to all other communities in the system (but particularly Bostons
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