Implementing A Water Quality Restoration Program Through An Adaptive Management Approach: Falmouth, MA Case Study

Introduction
The Town of Falmouth, Massachusetts has almost 70 miles of shoreline which forms fifteen coastal estuaries along Buzzards Bay and Vineyard Sound. Like many similar estuarine systems along the East Coast, nutrient enrichment, primarily associated with population growth and water-shed land use changes, has exceeded these watersheds' assimilative capacity and resulted in water quality degradation. Documented impacts include aesthetic degradation, disruption to benthic communities and loss of native eelgrass beds.
Background
The University of Massachusetts Dartmouth School of Marine Science and Technology (SMAST) has been operating a water quality monitoring program in Falmouth's southern estuaries since 1989. This data has documented declining water quality in Falmouth's coastal estuaries and was used as the basis of the multiple Total Maximum Daily Load (TMDL) nitrogen limits established by the Commonwealth of Massachusetts for Falmouth's watersheds. Figure 1 summarizes the nitrogen removal requirements for each coastal estuary in Falmouth needed to meet TMDL and watershed restoration goals. Figure 2 shows the estimated percent of septic system nitrogen that needs to be removed from each of Falmouth's South Coast Estuaries to meet TMDL goals.
Methodology
The Town of Falmouth has been tackling this daunting nitrogen management challenge on a watershed by watershed basis, starting with the Little Pond Watershed. As demonstrated in Figure 1, the Little Pond Watershed is one of the most severely impacted watersheds in Falmouth. The TWMP outlined the need to remove 100 percent of controllable nitrogen sources in Little Ponds lower watersheds. The watershed is one of the most densely developed areas in Falmouth, resulting in sewering being identified as the most cost effective option to manage nitrogen in the watershed. In 2014, the Town of Falmouth received approval of their first Targeted Watershed Management Plan (TWMP) for the Little Pond Watershed. An estimated eighty-eight percent of nitrogen inputs into Little Pond watershed were removed through sewer extensions to this peninsula in 2017.
The Town is concurrently evaluating the water quality impacts of sewering in this watershed (to remove septic nitrogen load) and assessing the feasibility of implementing non-sewering nitrogen management strategies to address the remaining twelve percent of nitrogen that needs to be removed from the watershed to achieve TMDL goals.
1. Evaluating Water Quality Impacts of Replacing Septic Systems with Sewering The Town is partnering with the United States Geological Survey (USGS) to use the Little Pond sewering project as a case study to evaluate the effects of septic to sewer conversion on groundwater quality in a densely-developed coastal neighborhood. In this study wastewater impacts are being tracked based on elevated levels of nitrates, boron, fluoride, contaminants of emerging concern, low pH and low dissolved oxygen concentrations. A monitoring network comprised of fifteen monitoring wells throughout the peninsula is being used to evaluate the flushing rate of the existing septic groundwater plume. This will provide a valuable comparison to initial estimates. Sampling was initially implemented in 2016, prior to sewer connections being available in this area and is continuing post-sewering. This presentation will discuss preliminary findings of this monitoring program.
2. Assessing the Feasibility of Non-Sewering Nitrogen Management Approaches As the Town continues its nitrogen management planning for less densely developed areas along its South Coast Estuaries, it has developed a TMDL Compliance Approach for each watershed that incorporates both sewering and non-sewering approaches. The Town is actively pursuing pilot and demonstration projects for the non-sewering approaches to assess their feasibility. Data collected in each demonstration project will be used to assess the feasibility of implementing these technologies in other coastal watersheds. Nitrogen reduction strategies being evaluated include permeable reactive barriers, fertilizer management; stormwater management; shellfish aquaculture for nitrogen polishing; inlet widening to enhance tidal flushing and the use of enhanced innovative and alternative on-site treatment systems. The Town is collaborating with SMAST to implement a baseline monitoring program for the coastal estuaries, which will be used to assess performance of both sewering and non-sewering alternatives. The Town is currently partnering with the Woods Hole Oceanographic Institute to install and monitor a pilot permeable reactive barrier in one of its nitrogen-impaired watersheds. The pilot utilizes injected emulsified vegetable oil to provide a carbon source in the soil to convert groundwater nitrates to nitrogen gas through denitrification. Data collected through the pilot is being used to evaluate optimal carbon loading rates and to validate the assumptions that a full-scale installation (120 feet in length and 20 feet depth) at this site would be capable of removing a nitrogen load equivalent to sewering 130 homes in the watershed.
The Town is also undertaking a 3-year pilot aquaculture project to evaluate potential nitrogen removal rates from oyster harvesting. The Town piloted a novel shellfish management process in the Eel River to propagate oysters at three locations through a partnership with private aquaculture growers. Eel River was selected based on site specific characteristics, including water depth, bottom type and its designation as an approved shellfish growing area. The private aquaculture growers are responsible for purchasing seed, growing and harvesting the oysters in the chosen locations. Additionally, the growers are required to report the harvest weight of harvested oysters and to provide samples to the Town for independent analysis of nitrogen content from the removed animals. The pilot project goals are to assess the feasibility of utilizing commercial growers to implement a water quality nitrogen polishing program and to verify initial assumptions on how much nitrogen is removed from the waterbody through aquaculture cultivation and harvest.
Results and Benefits
The Town of Falmouth has developed a planning strategy which utilizes baseline water quality monitoring data to assess environmental impacts of both sewering and non-sewering nitrogen management strategies. As the Town continues its watershed by watershed nitrogen management planning approach, non-traditional demonstration projects that prove to be feasible and cost effective will be added to the Plan through a Notice of Project Change in accordance with the (Massachusetts Environmental Policy Act) (MEPA) review and approval process. Utilizing non-sewering nitrogen management strategies in less densely developed portions of the Town is anticipated to result in a more cost-effective nitrogen management program and to provide the Plan with flexibility to incorporate newer technologies into the Plan as anticipated performance of these systems is assessed and documented through pilot testing.