Taking Action to Improve Sassaquin Pond with a Watershed-Based Plan

This is the cleanest I've seen the pond in years!' remarked a passing jogger to the field crew preparing the boat for sample collection. This was one of many such statements received by CDM Smith staff during routine sampling of Sassaquin Pond in New Bedford, MA during the 2022 and 2023 field seasons following the implementation of water quality improvements by the City of New Bedford. This 38-acre 'kettlehole' pond is typical of those left throughout New England by an ice age during a former millennium. The groundwater- and surface runoff-fed pond now sits in a residential neighborhood, providing the surrounding area with aesthetic benefits but also periodic water quality concerns as a result of point and nonpoint source pollution from the residential area around the pond. This presentation will highlight the multi-pronged approach used to address water quality issues in Sassaquin Pond, from planning to implementation. This work presents a valuable case study in pond water quality planning and implementation, which will be useful for pond managers and the public alike. Background: The City of New Bedford has been working to improve the water quality in Sassaquin Pond since the 1970s. Actions taken include the installation of a sanitary sewer system in 1974 and 1975 to reduce nutrient and bacteria loads from septic systems, and the installation of structural stormwater best management practices (BMPs) to address total suspended solids and phosphorous loading in stormwater. Despite previous efforts, Sassaquin Pond remains on the 2022 303(d) Massachusetts Integrated List of Waters with impairments for Curly-leaf Pondweed, algae, fecal coliform, harmful algal blooms, and odor. Cyanobacteria blooms, such as those that occurred in 2012 and 2020, have been a particular cause for public concern. Previous studies of Sassaquin Pond have identified excess phosphorus from internal (pond sediments) and external (stormwater runoff) sources as the cause of these periodic algal blooms. Planning: CDM Smith worked closely with the City of New Bedford's Department of Public Infrastructure and the Sassaquin Pond Betterment Alliance to develop a Watershed-based Plan. This plan uses the latest field data in conjunction with information from previously completed studies to provide the City and the Sassaquin Pond Betterment Alliance with a roadmap of projects that can be implemented in a prioritized approach to improve water quality in Sassaquin Pond. The plan includes 30 recommendations for short- and long-term actions to reduce nutrient and bacteria loads to the pond. These include both structural and non-structural solutions with varying costs of implementation. As projects are implemented, progress toward water quality goals is evaluated via the monthly pond sampling program. Implementation: In the first two years since the completion of the work plan, the City of New Bedford has taken action to implement several of the plan's recommendations. These include: -Monthly pond sampling during the growing season (April to November) for 2022 and 2023, -Addition of a chemical coagulant (alum) to strip phosphorus from the water column and bind phosphorus in sediments to reduce internal loading, -Curb and sidewalk construction to reduce erosion in the watershed, -Prioritized catch basin inspections and cleaning, -Robust street sweeping, -Treatment of invasive species (Phragmites), and -The installation of green infrastructure along the pond's banks. These actions have resulted in improved water clarity, quality, and habitat. Additional structural improvements have been proposed, including re-routing some stormwater away from the pond's watershed to reduce total bacteria and nutrient loading, construction of additional shoreline green infrastructure to intercept and treat stormwater before it enters the pond, installation of more trash receptacles and pet waste collection areas, and the installation of new catch basin hoods for control of floatable debris. These projects are currently in the design phase, with construction planned in 2024. Additional field programs are also planned for 2024 including a bathymetric survey, an investigation of underwater springs, and a program to inspect and remove directly connected impervious area (DCIA) within the watershed. Results and Next Steps: This presentation will present creative and multi-faceted approaches to improving the quality of an urban pond, the lessons of which may be applied broadly to other surface water systems. The results of the routine pond monitoring provide quantitative evidence of the program's success so far. Overall, data collected from April to November of 2022 show pond water quality was significantly improved relative to historical conditions. The alum treatment helped improve water clarity. Massachusetts water quality criterion for dissolved oxygen was met in the pond, as were the guidance levels for Aquatic Life Use based on low levels of nutrients and chlorophyll. Wet weather monitoring at the three largest outfalls showed high levels of phosphorus and bacteria were discharged to the pond. Several of the actions planned for coming years are anticipated to reduce these levels.