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

The Massachusetts Water Resources Authority (MWRA) completed its Long-Term Control Plan for CSO control (LTCP) in 1997. The plan used a watershed approach to assess the impacts of CSO in the context of other sources of pollution in the watershed, including stormwater and upstream flow. The recommended plan proposed to eliminate CSO to critical use areas, and cost-effectively minimize CSO in non-critical use areas. Regulatory acceptance of the plan was contingent upon changing existing water quality standards in areas where CSO would remain. At the time that the LTCP was being developed, the state water quality standards were being revised to establish a category under which minimized CSO discharges could remain, provided that certain specific conditions were met. Based on the MWRA's LTCP, the United States Environmental Protection Agency and the Massachusetts Department of Environmental Protection agreed to revise the water quality standards for certain waters within Boston Harbor, but the two agencies did not agree on the methodology for meeting the criterion for “substantial and widespread social and economic impact”. For the Charles River, a twoyear water quality variance was granted to allow further study of the impacts of non-CSO sources of pollution, as well as for additional CSO control alternatives, prior to a final determination of the water quality standard. To date, certain conditions of the variance have been completed, while others are on-going. Key on-going variance activities include: an assessment of providing additional CSO storage; a performance evaluation of the MWRA's Cottage Farm CSO Facility, which discharges to the Charles River; development of a more detailed stormwater runoff model for areas tributary to the Charles River; and upgrading the receiving water model for the Charles River.