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WATERSHED-SCALE TRANSPORT MODELING OF ONSITE WASTEWATER POLLUTANTS IN THE BLUE RIVER DRAINAGE BASIN
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15756)Authors: P.J. Lemonds, J.E. McCray
Keywords: Watersheds, Hydrology, Water Quality, Wastewater, Onsite Systems
Lake Dillon (or Dillon Reservoir) in the Blue River Watershed, Colorado, is a primary drinkingwater reservoir for Denver, Colorado. Eutrophication of the lake is a concern, primarily from phosphorus (P) loading. Local officials have attributed the P loading to onsite wastewater systems (OWS). The watershed model, SWAT, is used to construct a hydrologic and transport model of the Blue River watershed to better understand the potential influence of various point and nonpoint sources of P in the watershed. The watershed model was calibrated to measured flow rates and the models performance with respect to pollutant transport was evaluated by comparing results to measured P concentrations. The hydrogeologic model results are most sensitive to the physical parameters associated with snowmelt, as well as orographic effects on precipitation and evapotranspiration. However, uncertainties in chemical-transport parameters preclude a rigorous assignment of relative contributions of various P sources. Rather, the effort has elucidated what P transport parameters that are most crucial to accurate simulations for this watershed. The model was most sensitive to the P sorption coefficient, the P availability index, and the P enrichment ratio (a measure of P in runoff sediments compared to immobile sediments). Modeling results indicate that OWS are likely not the most significant sources of P to Lake Dillon.
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