Water Quality Variance for the Charles River: An On-Going Example of theProcess for Water Quality Standards Revisions for CSO-Impacted Waters

摘要

The Massachusetts Water Resources Authority (MWRA) completed its Long-TermrnControl Plan for CSO control (LTCP) in 1997. The plan used a watershed approach tornassess the impacts of CSO in the context of other sources of pollution in the watershed,rnincluding stormwater and upstream flow. The recommended plan proposed to eliminaternCSO to critical use areas, and cost-effectively minimize CSO in non-critical use areas.rnRegulatory acceptance of the plan was contingent upon changing existing water qualityrnstandards in areas where CSO would remain. At the time that the LTCP was beingrndeveloped, the state water quality standards were being revised to establish a categoryrnunder which minimized CSO discharges could remain, provided that certain specificrnconditions were met. Based on the MWRA’s LTCP, the United States EnvironmentalrnProtection Agency and the Massachusetts Department of Environmental Protectionrnagreed to revise the water quality standards for certain waters within Boston Harbor, butrnthe two agencies did not agree on the methodology for meeting the criterion forrn“substantial and widespread social and economic impact”. For the Charles River, a twoyearrnwater quality variance was granted to allow further study of the impacts of non-CSOrnsources of pollution, as well as for additional CSO control alternatives, prior to a finalrndetermination of the water quality standard. To date, certain conditions of the variancernhave been completed, while others are on-going. Key on-going variance activitiesrninclude: an assessment of providing additional CSO storage; a performance evaluation ofrnthe MWRA’s Cottage Farm CSO Facility, which discharges to the Charles River;rndevelopment of a more detailed stormwater runoff model for areas tributary to thernCharles River; and upgrading the receiving water model for the Charles River.