PRELIMINARY CHARACTERIZATION OF THE GROUNDWATER SYSTEM IN THE BLUE RIVER WATERSHED, COLORADO, WITH APPLICATION TO ONSITE WASTEWATER POLLUTANTS

Watershed scale groundwater system characterization can be a challenge due to the scarcity of and the inherent uncertainties associated with, publicly available data; and the high costs associated with additional field scale investigations. In the Blue River Watershed of Summit County Colorado, we have seen that with limited supplemental field work and the proper manipulation of publicly available data; an evaluation of the physical parameters of the ground-water system, an analysis of the chemical constituents of the water, and regional trends of anthropogenic effects can be derived.

Evaluation within the Blue River Watershed of Summit County was focused on two site locations in the watershed: (1) Frisco Terrace, located near Lake Dillon; and (2) Blue River Estates, located along a tributary of the upper reaches of Blue River. Data analyzed for site characterization included: state engineer well logs, soil data from samples collected during the installation of 4 additional monitoring wells, 15 months of temporal chemical water quality data from those 4 wells, and surface water quality data collected by the USGS and CSM, during a nutrient impact analysis of the surface water of the Blue River Watershed. Initial physical evidence indicates groundwater surface water interactions. Particle analysis of soils collected during drilling were used to estimate hydraulic conductivity (K) and yielded a range of K from 10-1 to 10-2 cm/s, suggesting relatively fast possible chemical transport times. The preliminary chemical analysis indicates an increase of anthropogenic constituents such as TDS, Chloride, Nitrate, and Sulfate as monitoring-well locations progress from the unpopulated background site, through Blue River Estates, to the site at Frisco Terrace near Lake Dillon. Thus, ground water pollution from anthropogenic effects is possible, although not necessarily from wastewater. Historical mining activities also appear to influence the ground water quality.