12/20/2012 SEWER COMMISSION Minutes

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Among the 11 sites where the bulk of the study area wastewater flow is discharged are: Willowbend, Keeter, Transfer Station, and Back Roads. The Keeter site, which receives 0.34 MGD, is located in the Rock Landing subwatershed, but borders on the Ockway Bay and Great River subwatersheds. After discussing this with GHD staff, it was decided to assign 50% of the load to Rock Landing, and 25% each to Ockway Bay and Great River. Similarly, project and GHD staff discussed and assigned the 13,908 gallons per day (gpd) @ 3 mg/L TN from the permeable reactive barriers at Pirates Cove based on the estimated watershed divide on the peninsula where Pirates Cove is located. Option I for Popponesset Bay and East Waquoit Bay Option 1C is based on projected build-out watershed nitrogen loads and treats and discharges most of Mashpee's wastewater within the two estuary watersheds and discharges the majority of the treated effluent from Falmouth, Sandwich, and Barnstable sections of the study area outside of the watersheds. This option keeps 74% of the total study area wastewater flow(2.0 MGD)within the estuary watersheds: 18% (0.48 MGD)remains on standard septic systems, 1%utilize cluster denitrifying septic systems @ 19 mg/L TN, and the remainder of flows are treated to 3 mg/L TN and are discharged at ten(10) sites within the estuary watersheds (Figure 5). Site discharges to the multiple discharge sites (i.e., Keeter, Pirates Cove,Willowbend,and Back Roads)are assigned on the same basis as in Option 1B. SCENARIO RESULTS: Popponesset Bay Scenario Results Comparison to Threshold Nitrogen Concentrations: Using the MEP linked model for Popponesset Bay,project staff compared the overall scenario nitrogen loads for each of the Options developed by the Sewer Commission and GHD to the threshold/TMDL loads approved by MassDEP and USEPA.'Based on this comparison,all three options meet the threshold values/TMDLs at the sentinel station for restoration of eelgrass in Popponesset Bay(Table 3). In addition,all three options do meet the water column TN concentrations within each of the three tributary sub-embayments that would be restorative of infaunal habitat. Among three Options,Option 1 C results in the TN concentrations closest to the TMDL thresholds(i.e. has the highest concentrations),while Options IA and 113 are removing more watershed nitrogen load than necessary. It should be noted that all of these scenarios included removal of wastewater from the study area for discharge outside of the watershed and that no other alternative nitrogen reduction strategies other than improved wastewater treatment were incorporated. Eastern Waquoit Bay Scenario Results: Comparison to Threshold Nitrogen Concentrations: Using the MEP linked model for Waquoit Bay,project staff compared the overall scenario nitrogen loads for each of the Options developed by the Sewer Commission and GHD to the threshold concentrations in the Eastern Waquoit Bay MEP Report.$Based on this comparison, all three options do not meet the threshold values at the sentinel station for restoration of eelgrass in Jehu Pond or Hamblin Pond(Table 4). All three options do meet the water column TN concentration that would be restorative of infaunal habitat in the Quashnet River. The previous round of scenarios for Eastern Waquoit were based on the Eastern Waquoit MEP Linked model,which only included the eastern portions of the overall Waquoit Bay watershed(see Figure 1) and a water quality model that was based on three years (2001-2003) of water quality data. The whole 7 Approval of Popponesset Bay System Total Maximum Daily Loads For Total Nitrogen. January 22,2008 letter from Stephen S.Perkins,Director,Office of Ecosystem Protection,USEPA,Region 1 to Laurie Burt, Commissioner,Massachusetts Department of Environmental Protection. 8 TMDLs were approved for Quashnet River,Hamblin Pond,Little River,Jelin Pond,and Great River in the Waquoit Bay System on November 7,2007,but the approval letter only references nitrogen loading rates(in kg/day) rather than concentrations. Concentrations are used here.