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USEPA/USGS Research on CECs in Septic Systems
Citation:
Glassmeyer, S. USEPA/USGS Research on CECs in Septic Systems. OKI Groundwater Workgroup, Cincinnati, OH, March 15, 2023.
Impact/Purpose:
Contaminants of emerging concern (CECs) are present in household wastewater. This presentation covers analysis of groundwater in a community with on-site septic systems, and a second project evaluating removal in innovative/alternative septic systems installed at a test facility. Some CECs are found in groundwater at concentrations that are equivalent to that found in wastewater effluents. The preliminary results from the test facility indicate show differences in removal that is both compound and treatment dependant. This data can be used by local governments making decisions on what septic systems should be installed in their areas.
Description:
Groundwater is susceptible to elevated nitrogen concentration and co-pollutants from a variety of sources, including onsite wastewater treatment systems. For example, conventional onsite septic systems can release high levels of both nutrients (e.g., nitrogen and phosphorus) and contaminants of emerging concern (CECs) to groundwater and, in turn, into nearby receiving surface waters. In some areas, centralized wastewater treatment is not practically possible due to cost, lack of political will, or physical limitations; as such, septic systems should no longer be considered a temporary measure in advance of sewers but rather a permanent part of residential wastewater treatment infrastructure. Some coastal communities have been evaluating the removal of conventional septic systems and the installation of innovative/alternative (I/A) septic systems to reduce nutrient loads. Communities can select from various proprietary and non-proprietary I/A systems, each with its specific benefits and limitations. Enhanced I/A systems that include a lignocellulosic carbon source have been demonstrated to efficiently remove nitrogen from effluent along with some CECs. The removal of CECs during I/A treatment may be a co-benefit of installing these systems for residential wastewater treatment. Conversely, if some critical CECs are not removed (or only minimally removed) by the I/A treatment, communities may choose to opt for sewers instead of installing I/A septic systems. This project examines the removal from effluent of over 280 chemical and microbial CECs by conventional and I/A septic systems. Two conventional treatments were sampled: 1) a standard pipe-in-stone trench with 1.3 m of vadose zone and 2) a drip disposal system where the septic tank wastewater disposal is in the active bio-zone (root zone) underneath the turf with percolate collected at a 0.6 m depth. Effluent was collected from 4 points in 3 different I/A systems: 1) a saturated wood layer system; 2) a denitrifying system with an aeration chamber and denitrification chamber; and a second denitrifying system with collection points after both the 3) nitrifying bed and 4) wood chip bioreactor. This study will fill a critical information gap about the impact and/or mitigatory effect I/A systems have on ground and surface water quality as a diffuse source of CEC pollution. In addition, it will provide important contributions to the growing body of literature on the performance of I/A septic systems.