The Impact of Onsite Wastewater Treatment Systems On the Nitrogen Load and Baseflow in Urbanizing Watersheds of Metropolitan Atlanta, Georgia.

Onsite wastewater treatment systems (OWTSs) are widely used in the Southeastern United States for municipal wastewater treatment. As urban and suburban populations increase, the use of OWTSs is expected to further increase. This region heavily depends on surface waters for its water supply, therefore, the impact of OWTSs on surface water quality and quantity must be investigated. Conventional OWTSs can be potential sources of N pollution for groundwater and streams that can cause human health concerns and stimulate algal growth resulting in eutrophication. The overall goal of this project is to determine the impact of OWTSs on the N load and the baseflow in urbanizing watersheds of Ocmulgee and Oconee River basins in Georgia. This paper presents preliminary results of the differences in the N load and baseflow as well as other water quality indicators such as temperature, pH, electrical conductivity (EC), dissolved oxygen, and chloride (Cl) in streams of watersheds impacted by high (HD) and low density (LD) OWTSs. Synoptic samples and discharge measurements of 24 watersheds were taken 3 times per year under baseflow conditions. Four watersheds were sampled continuously using automated water samplers. EC and Cl concentrations and yields were significantly higher in streams of watersheds impacted by HD OWTSs, which may indicate the presence of contaminants from OWTS effluent. Nitrate-N concentrations and yields and baseflow yields showed no significant difference, however regression analysis may show differences as a function of OWTS density. Further analysis is needed to accurately determine the impact of OWTSs on water quality and quantity at the watershed-scale. Results from this study will enable OWTS users, the OWTS industry, and local and state planners to make informed decisions on the installation and maintenance of OWTSs by providing data on their contribution to the N load and baseflow of surface waters in the region.