2/16/2012 SEWER COMMISSION Minutes

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Massachusetts Estuary Project(MEP) _ _Linked Watershed Embayment Model Peer Review 6. CONCLUSIONS 6.1. Response to Charge Question 1 Charge Question 1 to the scientific peer review panel was: Is the MEP modeling approach scientifically defensible and functionally adequate to be relied upon in the development and implementation of appropriate nitrogen TMDLs for the estuaries and embayments of Cape Cod in support of the state's Comprehensive Wastewater Management Planning and EPA Clean Water Act requirements and in developing overall wastewater and nutrient managementplans for Cape Cod to meet the TMDLs? The Panel finds that the MEP modeling approach is scientifically credible. It is consistent with current understanding of existing conditions for Cape Cod estuaries,based on available data. The components in the approach are well-known and documented. Computation of watershed nitrogen loads is strongly data- driven and quantitatively linked to estuarine nitrogen concentrations. A fundamental principle in the development and application of environmental models to inforin management decisions is that there should be compatibility among the study questions and objectives, available data and resources, and level of model complexity. The Panel finds that the level of complexity in the components and linkages of the MEP modeling approach is simple,parsimonious and well balanced within this context. The Panel also finds that the MEP modeling approach is functionally adequate. This approach is specifically designed for groundwater dominated systems and explicitly considers nitrogen loads from septic systems,the dominant controllable watershed source of nitrogen for Cape Cod estuaries. The MEP modeling approach is appropriate and useful,within the overall decision support system,for evaluating alternative scenarios and inforining nutrient management plans, and is consistent with existing nationwide TMDL practices. 6.2. Response to Charge Question 2 Charge Question 2 to scientific peer review panel was: To what level of accuracy~rill the NIEP linked model predict the effect of alternative nitrogen load planning scenarios and/or the prospective water quality in the affected estuaries and embayments and what is the degree of uncertainty in those predictions relative to alternative planning methodologies available in the industry? In order to respond to this question,the Panel assembled a list of the various parameters that serve as inputs to the MEP linked model. For the calculation of nitrogen loads alone,we counted more than twenty. Moreover,each parameter has a greater or lesser effect on the linked model predictions depending on the character of the particular watershed to which it is being applied. For example,for Pleasant Bay with its large surface to watershed area ratio,direct atmospheric deposition to the Bay has a more significant effect than to bays with smaller surface to watershed area ratios. In those bays with smaller surface area, septic and lawn fertilizer loads are correspondingly more significant. v December 30,2011 �� (-28