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MASS BALANCE MODELING AND WATER QUALITY MONITORING FOR IMPACT ASSESSMENT OF DEVELOPMENT WITH ONSITE WASTEWATER SYSTEMS COMPARED TO THAT WITH CENTRALIZED TREATMENT PLANTS

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  701P0104,  . (doi: 10.13031/2013.15771)
Authors:   Jennifer L. Bagdol, Robert L. Siegrist, and Kathryn S. Lowe
Keywords:   Dillon Reservoir, Summit County, Blue River, Onsite Wastewater Systems, Water Quality Monitoring

In many locations throughout the U.S. there is a need to understand the water quality effects of lower density suburban development served by onsite wastewater systems with dispersed effluent release to the environment, as compared to the effects attributed to higher density urbanized development and centralized treatment plants with point source effluent discharges. In the Dillon Reservoir watershed in Summit County, Colorado, there is a mix of urbanized development with centralized wastewater treatment plants (CWTP) along with suburban and rural development served by onsite wastewater systems. Water quality management and land use planning in the area requires proper understanding of the relative effects of current and future wastewater management strategies on water quality characteristics. Water quality is extremely important in the Dillon Reservoir watershed as the Blue River is the source of drinking water for the City of Breckenridge and the Reservoir supplies 25% of the drinking water for the city of Denver. In addition, the Blue River and Dillon Reservoir support varied and important recreational activities (e.g., fishing, skiing, kayaking) that are reliant upon good water quality. A research project was recently completed by the Colorado School of Mines, Electric Power Research Institute, Systech Engineering, the U.S. Geological Survey, and the Summit County Environmental Health Department to quantify the site-scale processes and watershed-scale cumulative effects of decentralized wastewater systems. As part of this larger project, a water quality monitoring program was carried out in the Dillon Reservoir watershed to assess the relative impacts of suburban development with onsite wastewater systems (OWS) compared to urbanized development with CWTP. In this research, mass balance calculations were initially made to estimate the range of potential effects from OWS and to refine a water quality monitoring program, including determination of the analytical methods and detection limits required to quantify if any effects were present. This was followed by one year of water quality monitoring at up to 20 locations in the watershed. At each location on a monthly frequency, stream flow was determined and samples were collected and analyzed for a suite of physical, chemical, and microbial parameters. Mass discharge rates were calculated and an urbanizing land use gradient was revealed, with equal or lesser water quality effects from the rural-suburban areas with OWS compared to equal or greater water quality effects attributable to urbanized areas with CWTP. This paper will present the methods and results of this impact assessment in the Dillon Reservoir watershed and make recommendations for application of the study approach in other development regions.

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