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Boston Harbor and Massachusetts Bay
MWRA Environmental Quality Department

Contingency Plan

MWRA developed 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. When monitoring indicates that "Caution" or "Warning" threshold levels for certain environmental indicators are exceeded, these exceedance reports must be posted on this website.

MWRA has earned a Platinum 7 Peak Performance award from the National Association of Clean Water Agencies in recognition of the Deer Island Treatment Plant having  100% compliance with its National Pollutant discharge Elimination System permit for 7 consecutive years through 2013

Download Contingency Plan (PDF)

Contingency Plan Reports:

Contingency Plan Exceedance Reports

Contingency Plan Quarterly Report on Ambient Monitoring
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 Report on Effluent Monitoring
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. It compares all results to Contingency Plan thresholds.

A review of zooplankton communities in the Massachusetts Bay/Cape Cod Bay system
The MWRA must report on the results of special zooplankton studies and evaluate whether a scientifically valid zooplankton community threshold could be developed. (PDF 222 KB)

Project Plan for Nitrogen Monitoring in Deer Island Treatment Plan Waste Streams 
A plan to facilitate the selection of nitrogen removal technology. (PDF 3 MB)

Proposed Modifications to the Contingency Plan (November 2001)
Proposed Contingency Plan threshold modifications to dissolved oxygen concentration, dissolved oxygen saturation, and Alexandrium abundance.
(See previous modification request)

Dissolved oxygen background calculation method   
Explanation of statistical approach to calculation of dissolved oxygen "background conditions" in support of proposed Contingency Plan modifications.

Outfall Contingency Simulation: Treatment Plant Chlorination Upset and Red Tide  
Simulates the notification and decision-making processes that would occur in the event of unexpected problems at the treatment facility or in Massachusetts Bay.


Many of our reports are in PDF format, which requires Adobe Acrobat Reader®, a free program available from Adobe Systems. To request a paper copy of any report, please contact the MWRA Environmental Quality Department at 617-788-4601, or e-mail us at