The Wetlands at Long's Park: The City of Lancaster's Park Enhancement and Water Treatment Project

The City of Lancaster, PA, has constructed an innovative water quality improvement project in one of its public parks to capture and treat stormwater runoff as part of its Chesapeake Bay Pollutant Reduction Plan. Runoff quality improved by the project will result in reduced nitrogen, phosphorus, and sediment loading to the Little Conestoga Creek Watershed in the Lower Susquehanna River Basin, which will ultimately contribute to improved water quality in Chesapeake Bay. The project is located in Long's Park and is designed to complement the park as an aesthetic and recreational amenity. The Park is a popular 80-acre public recreational area owned and operated by the City of Lancaster that is used extensively by residents and tourists every year. Public use features of the park include a petting zoo, pavilions, ball fields, and the 3-acre Long's Pond. Warm weather activities include music and food festivals and events, which further attract large numbers of park visitors. Because of the popularity of Long's Park, the proposed project will be highly visible and will provide a unique opportunity for public educational outreach to park visitors and surrounding municipalities, private property owners, and other engineers and professionals in the field. The Long's Park water quality improvement project includes a proposed pump station to convey water from Long's Pond to a constructed natural treatment system (NTS) consisting of a treatment train that includes a forebay equipped with floating wetland islands (FWI), an iron-enhanced sand filter (IESF), and two constructed wetland marshes, with discharge to Long's Pond. NTS are engineered or modified ecosystems that use natural biological, physical, and chemical processes to improve water quality. As an increasingly popular approach to water management, NTS are sustained by renewable natural sources of energy such as solar radiation, wind, gravity, and energy storage in biological and chemical forms. With lower operating costs, less energy consumption, and fewer residuals produced than conventional active treatment, NTS provide cost-effective solutions for treatment of various types of water inflows including stormwater. The forebay was designed as an open basin to receive the first flush of stormwater inflows and achieve significant removal of particulate solids and associated pollutants. The FWIs function to improve basin hydraulics by enhancing dispersion and by supplementing solids and nutrient removal through settling, filtering, and uptake processes associated with the suspended root mat of the aquatic plants. In addition, the FWIs are expected to provide an attractive resting, nesting, and feeding habitat for waterfowl, wading birds, and aquatic wildlife such as frogs and turtles. The IESF receives the outflow from the forebay and will promote phosphate removal through iron oxidation. The vertical flow filter media bed consists of sand mixed with iron. As stormwater infiltrates through the media bed, the elemental iron rusts to form iron oxides that bind phosphate via surface adsorption. This media bed is also expected to provide enhanced nitrification of reduced nitrogen. Flow from the sand filter passes through two constructed marshes in sequence that include deep and shallow zones for enhanced solids retention, denitrification, phosphorus uptake, and ecological habitat including natural mosquito control. The marshes are expected to polish any residual iron possible from the sand filter and stormwater via filtration of particulates, denitrification, and additional phosphorus removal. Finally, an outflow pipe from the lower marsh was constructed to convey the outflow from the marshes to Long's Pond. Long's Pond receives treated stormwater and is expected to become less eutrophic through increased flushing. To provide enhanced flushing of Long's Pond, a new pump station pumps approximately 25 gpm from Long's Pond to the forebay. Concentrations of nutrients and algal biomass are expected to decrease. The Long's Park NTS is projected to reduce stormwater runoff total suspended solids (TSS) and nutrients. Based on the daily water balance model conducted for this system over the 24-year period of record (1997-2020), the annual average inflow the NTS receives is approximately 44,000 gallons per day. This total inflow includes stormwater runoff from approximately 7.7 acres of contributing drainage area and a continuous 25 gpm flowrate from Long's Pond. This flow was used to predict the water quality performance of the Long's Park water quality improvement project. The NTS's capacity to improve stormwater quality was evaluated using current approaches to modeling treatment wetland performance. Common stormwater constituents include nutrients, suspended solids, metals, bacteria, and organic compounds. Left untreated, these pollutants can result in the eutrophication of downstream water bodies and impairment of aquatic ecosystems. NTS are documented to be an effective means of removing stormwater-derived contaminants. The primary removal mechanisms of NTS include solids settling, metal adsorption and precipitation, microbial transformation to gaseous compounds, and plant uptake and burial. The water quality model results indicate that on an annual average basis, the treatment system will provide a reduction of 20 pounds of phosphorus, 100 pounds of nitrate, and 12,000 pounds of TSS. As shown in Table 1, these reductions results in a 50% reduction of TP, 32% reduction of TN, and 95% reduction of TSS. Public recreational use features are incorporated into the concept in the form of all-weather access trails to the NTS that wind around the site in addition to a boardwalk that will enable public access through the lower marsh. The configuration of the trail is designed to allow short and long walks through the site. Educational signs will be provided in the future to inform the public of the purpose of the project. Together, these facilities are expected to create a unique and engaging experience for park visitors. This presentation will cover all aspects of this project, from its initial conceptualization to its construction, which was completed in the summer of 2023. Water quality monitoring results, if available, will also be shared.