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Boston Harbor and Massachusetts Bay
Massachusetts Water Resources Authority


Contingency Plan

Included in MWRA's NPDES discharge permit is a Contingency Plan to ensure that discharge from the Bay outfall does not result in adverse impacts. The Plan identifies thresholds that can suggest that effluent quality or conditions in the Bay may be changing.

The Outfall Contingency Simulation report simulates the notification and decision-making processes that would occur in the event of unexpected problems at the Deer Island Treatment Plant or in Massachusetts Bay.

When monitoring indicates that "Caution" or "Warning" threshold levels for certain environmental indicators are exceeded, Contingency Plan Exceedance Reports are sent to regulators and posted on this website.

Contingency Plan Quarterly Reports on Ambient Monitoring (PDF)
Data on mussel contamination, dissolved oxygen, and algae at sampling locations in Massachusetts Bay, compared with threshold limits in the Contingency Plan.

Contingency Plan Quarterly Reports on Effluent Monitoring (PDF)
Summary of data on pH, fecal coliform, toxicity, oil and grease, and nitrogen in Deer Island Treatment Plant effluent (treated wastewater) compared with threshold limits in the Contingency Plan.

Outfall Monitoring Overview 
The annual Outfall Monitoring Overview presents monitoring program results for effluent and field data from the previous year. All results are compared to Contingency Plan thresholds.

Contingency Plan Exceedances

MWRA's NPDES discharge permit requires MWRA to report Contingency Plan exceedances to regulatory agencies and the public. These notices are triggered by unusual results of effluent or ambient monitoring. Effluent monitoring takes place in the treatment plant, while ambient monitoring examines the environment surrounding the outfall in Massachusetts Bay.

Contingency Plan Modifications

Under MWRA's NPDES discharge permit, Contingency Plan interim modifications can be made at any time and do not require a modification to the permit. The Contingency Plan was intended to be a living document, with a modification process outlined by the U.S. Environmental Protection Agency.