Onsite Wastewater System Nitrogen Loading to Groundwater in the Newport River Watershed, North Carolina

Abstract

The objectives of this research were to calculate the on-site wastewater system (OWS) nitrogen loading to groundwater in the Newport River watershed, North Carolina and determine if these loads were large enough to be included in watershed nutrient management plans along with other nutrient sources such as row-crop agriculture. Nitrogen loadings were calculated using hydrological and groundwater quality data beneath 16 OWS installed in three different soil groups, and watershed demographic and soil data. Over 30,000 people use OWS in the watershed with 76% of the systems installed in group I soils (sands), 11% in group II soils (sandy loams), and 13% in group III soils (sandy clay loams). OWS in group III soils had lower total dissolved nitrogen loading rates (0.04 kg/person/yr) to groundwater than systems in group I (1.41 kg/person/yr) and II soils (0.33 kg/person/yr). The total dissolved nitrogen loading rates from OWS to groundwater, assuming 20 people/ha in group II and I soils (6.5 to 28.1 kg/ha/yr), were significant, but less than potential agricultural contributions to groundwater (37.5 kg/ha/yr) for the area. OWS are significant sources of shallow groundwater nitrogen loading in coastal watersheds with sandy soils, and these contributions should be considered in regulatory efforts to reduce nutrient pollution