STATE OF GROUND AND SURFACE WATER IN THE CENTRAL ROARING FORK VALLEY, PITKIN COUNTY, COLORADO-A HIERARCHICAL APPROACH USING GIS AND 3-DIMENSIONAL HYDROGEOLOGIC MODELING

Pitkin County, Colorado, located in the Southern Rocky Mountains, is rapidly undergoing land use changes from agriculture and open space to urban development. The purpose of this study is to undertake a watershed-based, hierarchical systems analysis (HSA) to develop an integrated hydrologic system conceptual model from Aspen to Basalt, Colorado. The approach is to: 1) Characterize the hydrogeology of the Central Roaring Fork Watershed area using multidisciplinary data, including climate, vegetation, surface water, topography, anthropogenic activities, soils and geomorphology, and geology; 2) Develop a hydrogeologic framework solid block model to visualize and analyze the Central Roaring Fork Watershed system; 3) Characterize the hydrologic system of the Central Roaring Fork Watershed with respect to both surface water and ground water subsystems; and 4) Use this knowledge and tools to develop site conceptual models of four typical sites within the regional scale context of the analysis to guide decisions on regulation, environmental remediation, and to project hydrologic system uncertainties. Four representative site-scale areas within the region were analyzed using HSA: 1) Brush Creek Valley Hillslope Subsystem near Snowmass Village; 2) West Roaring Fork Valley Hillslope Subsystem; 3) Disconnected Glacial Terrace East Roaring Fork Valley Hillslope Subsystem; and 4) Connected Glacial Terrace East Roaring Fork Valley Hillslope Subsystem.

A three-dimensional solid block model, constructed using Intergraph ERMA and GeoMedia software, was developed that shows the relationships and interconnectedness between the aquifers. The results are used to: 1) Locate sources of dispersed pollution for pollution prevention and regaining compliance (for example, ISDS regulation); 2) Evaluate cascading effects of point source and dispersed pollution on a system scale; 3) Target source, pathway, and fate of pollution within a system context; and 4) Target geotechnical problem areas that are caused by surface and ground water systems.