Onsite Wastewater System Effects on Groundwater Quality

Abstract

ABSTRACT

Hales, Donnarie. Masters of Environmental Assessment. Onsite Wastewater System Effects on Groundwater Quality.

More than 40,000 onsite wastewater systems (OSWWS), also known as septic systems, are installed in North Carolina each year, with residents depending on the systems for treatment and disposal of wastewater effluent. The transfer of wastewater from septic systems through the soil profile can pose public and environmental health risks if the system is not efficiently treating the effluent. The potential for groundwater and surface water contamination related to OSWWS can be dependent on soil types and groundwater depth. A groundwater-monitoring network located adjacent to the septic system of a school located in the coastal plain of North Carolina was used during this study to observe the pH, nitrate, ammonium, dissolved oxygen, and electric conductivity levels in the OSWWS drain field to determine the treatment provided by the OSWWS. Samples were also collected from the holding tank to compare the nutrient reduction from the tank to the drain field. A background well located up gradient of the OSWWS was also monitored to observe the groundwater quality on site distanced from the OSWWS. Current water quality regulatory efforts focus on nutrient loading from stormwater and agricultural runoff, as well as municipal wastewater treatment discharge, without addressing the billions of gallons of nutrient rich water being released into the ground by septic systems. While the study revealed a decrease in nutrients from the holding tank to the drain field for this individual site, the results substantiate that potential pollutant contributions from septic systems should be included in water quality regulatory efforts.