ASSESSING CUMULATIVE EFFECTS OF NUTRIENTS FROM DECENTRALIZED WASTEWATER TREATMENT SYSTEMS

Nearly 30 years since the passage of the Clean Water Act, many of the nation’s surface waters remain above water quality standards. As the focus of water quality control shifts from solely point source control to also include nonpoint source control, environmental regulation is transferring from command and control to more performance-based methods through implementation of a watershed approach and enforcement of Total Maximum Daily Loads (TMDLs). Considering nearly 25% of the U.S. population is served by decentralized soil-based wastewater treatment systems (SBWTS) while 37% of new homes are being constructed with SBWTS, the potential for these decentralized systems to contribute nonpoint source contamination to surface waters is growing. The purpose of this research is to evaluate the available knowledge of nutrient fate and transport from SBWTS on a site scale in order to quantify the cumulative effects of SBWTS on a watershed scale. Based on this assessment, preliminary recommendations will be made for a module to incorporate SBWTS into the Watershed Analysis Risk Management Framework (WARMF) model, a decision support system that provides local watershed stakeholders a roadmap for reaching a consensus on TMDLs and a watershed management plan. This research is being performed as part of a larger collaborative effort over the next two years to develop and test a methodology for assessing the water quality impacts of SBWTS including individual and cumulative effects on local water supply wells as well as downstream receiving waters.