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 Water Quality of Effluents From Three Different Onsite Wastewater Treatment Systems
Samuel L. Rodriguez, Bryan W. Brooks, Pablo A. Davila, Ron Suchecki and Joe C. Yelderman Jr.
Item Number: NRL2006AC-23
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Anthropogenic impacts to aquatic systems by on-site wastewater is a topic of increasing concern. More than a trillion gallons of wastewater pass through on-site sewage facilities (OSSFs) each year. This makes decentralized OSSFs one of largest sources of effluent discharge to groundwater and surface water resources. OSSF impacts to aquatic life may be greater than many surveys indicate because studies usually do not include systems that might be contaminating surface water or groundwater in ways that are only detectable through on-site subsurface monitoring. After effluent is discharged from an OSSF, the fate and transport of wastewater constituents are determined by soil characteristics and groundwater in the drainfield; potential groundwater contamination can remain significant, especially in systems installed near the water table or a surface water body. Whole effluent toxicity (WET) test mehtodologies are widely used to assess potential adverse effects of centralized wastewater discharges on aquatic life. These WET tests represent one of the critical components of the U.S. Environmental Protection Agency’s Water Quality Based Approach to control discharge of toxic materials in toxic amounts to aquatic systems, because test organism responses integrate chemical, biological and physical aspects of effluent dischargess, whereas chemical analyses simply focus on select parameters. This study provides a novel assessment of freshwater toxicity of effluents from different OSSF treatment technologies (septic, aerobic and wetland) and a centralized activated sludge municipal facility, and relates bioassay results to other parameters routinely used to assess water quality. Results suggested that septic system failures close to surface or subsurface water bodies may have deleterious effects on aquatic organisms. Decentralized advanced aerobic treatment systems produced effluent that if introduced to aquatic systems would generally not be toxic, particularly if these aerobic effluents received dilution at a similar magnitude to centralized municipal effluent discharges. The approach used in this paper may serve as a model for evaluations of other OSSF technologies and will support future research of new wastewater treatment and assessment methodologies.