Laserfiche WebLink
Sewer Commission Wastewater Scenarios-Chart <br /> Mr. Eichner presented charts representing surface water nitrogen loads of Mashpee, Santuit and <br /> Quaker Run Rivers as well as the direct groundwater chart for Popponesset Bay, Popponesset Creek, <br /> Pinquickset Cove, Ockway Bay,Mashpee River and Shoestring Bay. Mr. Eichner reported that the <br /> MEP build out(orange) and MEP threshold scenario (light blue)were provided as a point of <br /> comparison because it indicates what is needed to meet the threshold concentrations. <br /> Scenario Results <br /> Mr. Eichner indicated that once the nitrogen loads of the watershed are resolved,they are then brought <br /> into the water quality model in order to identify the targets of 1)the eelgrass regulatory TMDL (total <br /> maximum daily load)of 0.38 adopted by the EPA, and 2)the restoration of infaunal habitat of 0.4-0.5 <br /> ppm TN. The bold figures within each of the scenarios represent figures that meet the MEP <br /> thresholds. All scenarios meet the infaunal habitat for Shoestring Bay and Ockway Bay. Scenario 3 <br /> meets all of the infaunal and TMDL. Mr. Eichner added the importance of the differences among the <br /> scenarios and the differences of the assumptions used;which is discussed further in the memo <br /> forwarded to the Sewer Commission. <br /> Additional Issues to Consider <br /> Mr. Eichner noted that there are additional issues to consider, such as the use of alternative septic <br /> systems as is recommended in Scenario 3. Twelve types of alternative septic systems have been <br /> approved by the Massachusetts DEP with provisional permits and are assigned 19 ppm TN effluent for <br /> residential use and 25 ppm TN effluent for commercial use. Scenarios 2 and 5 do not utilize <br /> alternative septic systems. Scenario 1 uses 380 I/A systems and Scenario 4 uses 130. Mr. Eichner <br /> reported that the wastewater treatment plants require groundwater discharge permits issued by the <br /> DEP,which have a limit of 10 ppm TN effluent. Mr. Eichner stated that the existing plants are <br /> producing 2.4-9 TN effluent,which is a large range, and the final goal is to meet the TMDL. <br /> Additionally, anything above 1 million gallons at traditional municipal treatment plants has been <br /> permitted by the DEP for 3 ppm TN. Mr. Eichner suggested that the town will need to balance what <br /> will work best in the regulatory environment and what can be achieved in reducing the nitrogen load. <br /> Questions &Discussion <br /> What is the concentration of nitrogen in Nantucket Sound? Same as the last version of the model, <br /> but Mr. Eichner did not confirm the figure definitively. <br /> Is a cost comparison of the 5 scenarios available? Mr. Fudala responded that rough cost estimates <br /> were available in the original drafts of the scenarios but the Commission is looking to review results at <br /> this point. <br /> Why is 10 used as a basis for the MEP (light blue) models instead of the actual performance <br /> figures of the existing treatment plants? Lower numbers have resulted for the Stearns&Wheler <br /> scenarios. Jeff Gregg, of Stearns & Wheler, responded that the treatment plant flows are significantly <br /> less than the future and they opted to use more conservative numbers as approved by the State, <br /> particularly for Scenario 1. Chairman Fudala reported that the Planning Board has been monitoring the <br /> plants on a monthly basis and the results are all consistently below 10. <br /> Scenario 3 maintained all of the existing plants and added 16 clusters. What number was used <br /> for the performance of existing plants? 3.75 TN effluent was used for all scenarios. The Chair <br /> expressed concern that different numbers were used for different scenarios for the same plants and <br /> 3 <br />