11/17/2009 SEWER COMMISSION Minutes

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• Scenario 5—S&W: Centralized approach: 2 new WWTFs(one in Mashpee,one in Sandwich)with 3 ppm TN effluent and 5 effluent discharge sites; conversion of existing private WWTFs in Mashpee(except New Seabury) to pumping stations connected to the primary Mashpee WWTF In July 2008,MEP Technical Team reported to the Sewer Commission, S&W and LAI on the April 2008 scenario data. Technical Team analysis found significant differences between the land use/water use databases and the presented nitrogen loads from both firms. These differences created difficulties, not only in using the MEP models,but also in comparing the results between scenarios from the two firms. In order to resolve these differences, SMAST indicated that a single unified database was required to properly configure the scenarios to support the modeling effort by the MEP Technical Team. Following discussions with all parties, it was agreed that SMAST would create the required unified database. In November 2008, MEP Technical Team reported to the Sewer Commission that in the course of reconstructing the database, differences in the underlying database were found to be more extensive than just the land-use and build-out classifications and included mis-assignment of parcels to subwatersheds. In February 2009, a supplemental agreement between SMAST and Sewer Commission was approved to correct the databases and create a cleaned up,unified database. Cape Cod Commission agreed to provide GIS services in support of this effort. In July 2009, the updated unified database was transferred to S&W and LAI for review. By late October 2009,the wastewater flows and effluent treatment nitrogen concentrations determined by SMAST for both S&W and LAI scenarios had been approved by their respective firms. The resulting nitrogen loads were used by the MEP Technical Team to complete the scenario runs that are discussed in this memo. Unified Database Ni en Loads As mentioned, the updated unified database for the Popponesset Bay and East Waquoit Bay watersheds includes updates to the build-out estimates for Mashpee, Falmouth,and Barnstable land uses. The Sandwich estimates are the same as those used in the original MEP analyses of these systems. The included Mashpee parcel analysis update includes comments about development potential of most non-residential properties. . One notable change in the updated unified database that impacts nitrogen loads is an assumption by S&W that all newly developed or residential properties using private wells in either watershed are assumed to have a water use of 140 gallons per day(gpd). This is 9% lower than the 154 gpd used in the MEP analyses. The MEP water use is based on the average water use of all single family residences in Mashpee. Since the updated unified database changed the number of parcels from the original MEP build- out estimate,revised nitrogen loads from residential lawns,roof areas, and driveway areas, revised counts of residential parcels at build-out were developed using the updated unified database. Road, cranberry bog,and golf course areas were not changed from MEP calculations. All these loads from these sources are consistent across all five Sewer Commission scenarios.