Integrating Nitrogen Reducing On-Site Programs into Coastal Watershed Management Programs

Objective
The coastline of Southeastern Massachusetts (Study Area) is comprised of multiple coastal estuaries. Nutrient enrichment, primarily associated with population growth and watershed land use changes over the past sixty years, has exceeded these watersheds' nitrogen assimilative capacities resulting in severe water quality degradation. Documented ecosystem impacts include aesthetic degradation, disruption to benthic communities and loss of native eelgrass beds (Figure 1).

The Massachusetts Estuaries Project was established to evaluate nitrogen-impaired coastal estuaries and to establish nitrogen loading thresholds that can be used as management goals in each studied watershed. Using these thresholds, Federal and State regulatory agencies have implemented watershed-based nitrogen Total Maximum Daily Load (TMDL) limits for nitrogen-impacted estuaries. The watershed contributing to a coastal estuary in the Study Area is often extensive — for example, about half of the land on Cape Cod contributes to a nitrogen sensitive coastal estuary (Figure 2).

#Multiple communities are developing a hybrid approach to nitrogen management where traditional centralized wastewater collection and treatment is targeted for the highest density neighborhoods and decentralized strategies, such as nitrogen reducing on-site septic system programs, are being implemented in less densely developed areas. Using case studies in Southeastern Massachusetts, this presentation will focus on strategies that small communities are developing to increase the reliability of decentralized programs as a key nitrogen management strategy in watershed management planning.

Methodology
Historically, the majority of properties in the Study Area have been developed utilizing conventional on-site septic systems for wastewater treatment and recharge. These systems are designed for pathogen breakdown and do not target nutrient breakdown. The Massachusetts Estuaries Project (MEP) has demonstrated that these conventional septic systems are the largest source of controllable nitrogen to many of the degraded estuaries in Southeastern Massachusetts.

Research and development is currently being conducted to develop nitrogen-reducing on-site septic systems that can be utilized as a decentralized wastewater management strategy, particularly in low-density areas where centralized wastewater collection and treatment is not cost-effective. Currently several nitrogen-reducing on-site septic systems are being evaluated to determine whether these systems can consistently meet anticipated effluent nitrogen concentrations (at least sixty percent nitrogen breakdown compared to conventional systems). Many of these systems mimic a traditional wastewater treatment process — using a blower in the septic tank for aeration before directing flow through a de-nitrifying media (such as wood chips) for denitrification. Phosphorus removal performance is also being evaluated for systems upgradient of freshwater systems. Preliminary effluent nitrogen and phosphorus data from these systems and the regulatory pathways to establish anticipated effluent nitrogen concentrations for systems will be discussed in the presentation. Carbon footprint impacts of a centralized versus decentralized treatment system will also be reviewed.

Implementation of a nitrogen-reducing on-site septic system program requires systematic monitoring and reporting to demonstrate that systems installed as part of the program are consistently meeting anticipated nitrogen removal goals. Communities are developing strategies to implement a Responsible Management Entity (RME) to manage these programs. An RME is responsible for oversight, monitoring, reporting and enforcement of the program and could be fulfilled through a Town department or subcontracted to a third-party entity.

Regulatory mechanisms also need to be established outlining how existing conventional septic systems within a program area will be replaced with nitrogen-reducing systems through an anticipated planning period. Communities are exploring implementing a series of triggers for system replacements in local Board of Health regulations to regulate the conversion process or implementing a phased approach which targets systems closest to sensitive receptors in earlier stages of the program.

An adaptive management approach is integral to monitor progress and performance of the program and to allow for the program to be adjusted based on performance. The adaptive management program includes ongoing water quality monitoring to evaluate the impacts of the program on coastal estuary health and milestone evaluations to determine program success.

Benefits and Next Steps
The complex nitrogen eutrophication challenges in southeastern Massachusetts require significant investments to reverse years of environmental degradation. If implemented correctly, a nitrogen-reducing on-site septic system program can successfully be used as part of a fiscally sustainable watershed management program to restore degraded coastal waterways. This presentation will discuss considerations important in the planning process and regulatory mechanisms that are being developed to increase the reliability of these programs in nitrogen management planning and implementation.