2/16/2012 SEWER COMMISSION Minutes

Home Browse Search

Massachusetts Estuary Project(PIEP) Linked Watershed Embayment Model Peer Review relevant technical support documents prepared by MEP(Howes et al.2005 and 2006). Those values are the driving force behind the actions that meet the TMDL load reductions to ensure that the threshold nitrogen concentrations are not exceeded once management practices are in place. The TMDL load allocation is essentially a pollutant budget that identifies the load reduction,and cap, necessary to attain water quality standards. For the estuaries reviewed,the regulated wasteload allocations(WLA) are minimal,so the focus is necessarily on unregulated nonpoint sources,primarily septic systems(See Table 3 in Commonwealth of Massachusetts,2006 and 2007, for Boumes and Pleasant Bay categorical nitrogen loads,respectively). The Panel's technical analysis has determined that the loading estimates are scientifically defensible and,therefore,appropriate for TMDL development and management planning purposes. Key Issue 2-Adaptive Management As described above,the EPA FACA tacitly endorsed a phased or an adaptive approach to address uncertainty and to ensure immediate management progress consistent with the level of scientific understanding, and the ability to manage pollutant sources. This approach is most relevant to the load allocations for nonpoint sources,which provide pollutant quantification and management challenges that generally exceed those for regulated point sources. Because the Cape Cod sources are almost exclusively nonpoint in nature, especially on-site subsurface disposal systems(OSDS) or"septic"systems, successful attaimnent of the TMDL cannot rely on emphasizing regulated point sources in the wasteload allocation. The nitrogen source distribution imbalance towards nonpoint sources will undoubtedly make attainment of the TMDL more challenging,and perhaps more costly. However,it may provide a better framework for phased implementation that could support a structured adaptive management approach. As recomrnended above in the Panel's review of the science,an adaptive management approach will help reduce scientific uncertainty and help adjust management actions so they may be more cost-effective within the iterative framework of adaptive management(Figures 1 and 2) (Williams et al.2009).The Cape Cod Commission and the member municipalities have explored adaptive management approaches relative to phased implementation plans(Cape Cod Conunission,2009, GHD,Inc. 2011). The Bourns TMDL identifies OSDSs as the dominant source of nitrogen loading to each of the five sub- embayments,ranging fiom 76%to 87%of the Present Watershed Load(Corn monwealth of Massachusetts,2006,Howes et al. 2005). The TMDL reductions of the controllable loads range from 55%to 87%(See Table 4 in Commonwealth of Massachusetts,2006),which means that OSDSs must be aggressively managed if the TMDLs for the Bourns Systems are to be attained. This direction is confirmed in CWMPs(e.g., Stearns &Wheler,2009)being developed by the municipalities that share the watersheds,which also provide the"reasonable assurance"that action will be taken to implement the TMDL: For the 16 Pleasant Bay sub-embayments,OSDS nitrogen loads ranged from 51%to 83% of the Present Watershed Load(Commonwealth of Massachusetts,2007,Howes et al. 2006). TMDL reductions of the controllable load ranged from 25%to 83%(See Table 4 in Commmonwealth of Massachusetts,2007). While this broader range reflects a wider variety of conditions in the watersheds of Pleasant Bay compared to Bourns,since OSDSs are again the dominant source, aggressive management will be required and will be detailed in CWMPs developed for the Pleasant Bay System as well. This Panel's assessment supports the science behind the goal setting,but there is uncertainty as to whether the TMDL will fully restore the estuaries' designated uses,especially for sensitive eelgrass meadows (see Section 5.3 above). However,it seems likely that management will have to at least meet the thresholds identified in the TMDLs,and that continued monitoring and assessment are necessary to reduce uncertainty. This sets the stage for an effective adaptive management approach since the towns are allowed flexibility by the MDEP and the EPA to phase implementation,monitor the results,and chart progress with respect to predicted enviromnental outcomes. In particular,tracking of benchmark nitrogen December 30,2011 �26