ONSITE WASTEWATER SYSTEM PHOSPHATE CONTRIBUTIONS TO WATER RESOURCES IN PIEDMONT WATERSHEDS

Major watersheds in North Carolina including Falls Lake, Jordan Lake, and the Tar-Pamlico River are impaired because of elevated phosphorus and/or nitrogen loading from point and non-point sources of pollution. Studies conducted in the coastal plain of North Carolina have indicated that onsite wastewater systems (OWS) may be a significant exporter of nutrients to groundwater and surface water. However, there is a lack of published research regarding OWS nutrient contributions to water resources in piedmont settings, where the geology and soils are much different than in coastal plain regions. Most of North Carolina’s population lives in the piedmont region, and a high percentage of piedmont residents utilize OWS, therefore it is important we have an understanding of how OWS function with regards to nutrient treatment. East Carolina University in cooperation with the NC Department of Health and Human Services, and Durham County Department of Public Health are engaged in a study to gather that information. The current study includes 5 sites in the central piedmont region of North Carolina with soils that formed from Carolina Slate Belt, Triassic Basin, and Felsic Crystalline parent materials. At these 5 sites, over 30 piezometers were installed to monitor groundwater adjacent to and down-gradient from OWS. Preliminary data indicate that ground water phosphate concentrations are low (typically < 0.01 mg/L) adjacent to the conventional style drain fields that have greater than 1 m depth to groundwater. However, the surfacing overflow from a malfunctioning OWS (0.37 mg/L) and the discharge from a sand filter system (mean 2.51 mg/L), both contained elevated concentrations of phosphate phosphorus. Because there is a high density of sand filter style OWS in the Lick Creek and Little Lick Creek Watersheds which drain to the nutrient sensitive Falls Lake, we will continue to monitor nutrient concentrations to determine the influence that sand filter style, and malfunctioning OWS have on water quality.