November 15, 2001

Re: Massachusetts Water Resources Authority, Permit Number MA0103284
Proposed Changes to Contingency Plan: Dissolved Oxygen and Alexandrium thresholds

Dear Mr. Haas and Ms. Murphy:

The Massachusetts Water Resources Authority ("MWRA") received the April 3, 2001 correspondence from United States Environmental Protection Agency ("EPA") and Massachusetts Department of Environmental Protection ("DEP") relating to MWRA’s October 13, 2000 request to modify certain parameters of the Contingency Plan. In accordance with EPA and DEP’s April 3, 2001 letter, MWRA submitted the Contingency Plan Revision 1, May 2001.

This letter serves as submission of revisions that were made on an interim basis in the May, 2001 revision to the Contingency Plan, to the Dissolved Oxygen and Nuisance Algae thresholds, as provided in Part I.8.c of the NPDES Discharge Permit:

The list of revisions MWRA is formally requesting by this correspondence is:

• Change the Caution Level threshold for the water column nearfield, nuisance algae Alexandrium tamarense to 100 cells/liter in any sample, as in Table 1-1 and Table 5-1 of the Contingency Plan Revision 1, May 2001.



• Add the phrase "unless background conditions are lower" to the Caution Level and Warning Level thresholds for water column nearfield bottom and Stellwagen bottom dissolved oxygen concentration and dissolved oxygen percent saturation, as in Table 1-1 and 5-1 of the Contingency Plan Revision 1, May 2001.

Both these modifications have been reviewed and approved by EPA, DEP and the Outfall Monitoring Science Advisory Panel ("OMSAP"). In October, 2000 MWRA had requested revisions to the Water Column Dissolved Oxygen Percent Saturation threshold, and the Water Column Nuisance Algae Alexandrium threshold. EPA and DEP (April 3, 2001) did not approve those requests, but did suggest the alternative thresholds described above for these parameters to be implemented on an interim basis. MWRA included those modifications to its thresholds as interim changes, in the May, 2001 revision of the Contingency Plan. This revision of the Contingency Plan was approved by EPA and DEP in correspondence dated June 29, 2001. As requested by EPA and DEP on June 29, 2001, MWRA submitted a statistical approach as recommended in Attachment A of EPA’s and DEP’s April 3, 2001 letter, to calculate the 5^th percentile of the background conditions for dissolved oxygen levels. In correspondence dated July 27, 2001 EPA and DEP approved this statistical approach. On October 16, 2001 MWRA presented the interim revisions to the Dissolved Oxygen and Alexandrium thresholds to OMSAP for review. Details of these threshold calculations are in the information briefing presented to OMSAP (Attachment A to this letter). OMSAP voted to approve all these threshold revisions.

MWRA appreciates the consideration EPA and DEP have given to MWRA’s Contingency Plan Modification requests. MWRA shares EPA and DEP’s view that the plan, as a "living document," needs to be reviewed and improved or revised based on current scientific understanding and will continue to work with the regulatory agencies to develop such a plan.

Sincerely,

Michael J. Hornbrook
Chief Operating Officer

Cc: