Integrated Approaches to Reversing the Impacts of Nitrogen Eutrophication in Coastal Estuaries: Southeastern Massachusetts Case Studies

Background Federal and State regulatory agencies have implemented watershed-based nitrogen Total Maximum Daily Load (TMDL) limits for multiple coastal estuaries in Southeastern Massachusetts. Affected communities are developing strategies to restore these waterbodies in very different ways. Methodology Communities are exploring multiple options to reverse the impacts of nitrogen eutrophication in coastal estuaries. Traditional approaches rely primarily on centralized collection and enhanced nitrogen removal wastewater treatment. Innovative non-traditional technologies currently being piloted include shellfish aquaculture, permeable reactive barriers, tidal flushing improvements, and nitrogen reducing onsite septic system programs. Many communities are developing a hybrid approach where sewering is targeted for high density neighborhoods with non-traditional strategies being implemented in less densely developed areas. Results Communities with TMDLs have initiated watershed management plans (WMP) to outline strategies for watershed restoration. The communities of Oak Bluffs, MA and Chatham, MA each approached the watershed management planning process differently. Although their solutions were different, both communities faced a significant challenge- as a result of significant long term project costs — which has resulted in a robust public education effort. Case Study #1: Chatham's Septic to Sewer Strategy The Town of Chatham, MA has a severe nitrogen contamination problem. As shown in Figure 1, one third of the watersheds within the Town require 100% removal of wastewater nitrogen to meet the Town's TMDL goals. The solution to this problem was estimated to cost over $300 million for a community with a year-round population of just over 6,000. In order to solve this problem, the Town developed a phased implementation approach. This approach primarily consists of planned implementation of traditional sewering technologies with limited non-traditional technologies for targeted areas. In the first phase of the plan the Town's existing Water Pollution Control Facility was upgraded to a limit of technology nitrogen removal process and its flow capacity was increased (Figure 2). The Town has been implementing septic to sewer conversion projects that account for approximately 15-20% of its TMDL compliance requirements every three years (Figure 3). Now almost 40% complete with its TMDL compliance plan, over 700 properties have been removed to date from septic systems, providing a potential future nitrogen load reduction of about 3,000 kg/y for this initial part of a larger long-term implementation program. In addition, the Town has completed an inlet widening project (Figure 4) as well as implemented a fertilizer management plan, the only two non-traditional nitrogen reduction options that were feasible to help address the significant contamination issues in this town. Overall, the Town plans to achieve its nitrogen TMDL goals within a 20-year timeframe. Case Study #2: Oak Bluffs Hybrid Nitrogen Management Approach The Town of Oak Bluffs is a small community with a year-round population of less than 5,000 people. The majority of the Town lies within one of four nitrogen sensitive coastal watersheds (Figure 5). Every summer, the Town sees a substantial population increase from tourism, which has contributed to the nutrient impacts observed in the Town's water resources. The Town has a small centralized wastewater treatment system, with limited options for treated effluent recharge expansion, which has driven the Town to evaluate multiple non-traditional nitrogen management technologies as part of its comprehensive wastewater management plan (CWMP). In order to meet its nitrogen TMDL goals, the Town has developed a hybrid Recommended Plan, which integrates multiple nitrogen management strategies for each watershed including centralized sewering, an enhanced nitrogen removal on-site septic system program, inlet widening and permeable reactive barriers. The Recommended Plan includes the implementation of an adaptive management process to incorporate cost-effective pilot technologies into the plan once they demonstrate feasibility. The adaptive management process will involve ongoing water quality monitoring to track the results of implemented projects, and to adjust the plan going forward. Benefits and Next Steps The complex wastewater nitrogen contamination challenges in southeastern Massachusetts require significant investments to reverse years of environmental degradation. This problem is being addressed by the small communities in Southeastern Massachusetts with innovative solutions that seek to manage high costs by balancing traditional and non-traditional wastewater management solutions. The solutions outlined above are allowing for the recovery of degraded coastal waterways using fiscal sustainable approaches.