Onsite Wastewater System Phosphate Contributions to Water Resources in the Piedmont of North Carolina

Abstract

Major watersheds in North Carolina including portions of the Cape Fear, Neuse, and the Tar-Pamlico Rivers are impaired because of elevated phosphorus (P) 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 major contributor 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 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 was engaged in a study to gather that information. The study included 5 sites in the central piedmont region of North Carolina where over 30 piezometers were installed to monitor groundwater adjacent to and downgradient from OWS. Data indicated that ground water phosphate (PO4-P) concentrations were low (typically [less than] 0.01 mg/L) adjacent to the conventional style drainfields that have greater than 1 m depth to groundwater. However, the surfacing overflow from malfunctioning OWS (mean 0.37 mg/L) and the discharge from sand filter systems (mean 1.08 mg/L), both contained elevated concentrations of phosphate. Consequently, surface discharge sand filters systems were contributing higher concentrations of PO4-P to surface waters than conventional style OWS. This study will provide important information regarding the management of OWS that are contributing to phosphate loading to nutrient sensitive watersheds in the Piedmont of North Carolina.