DEVELOPMENT OF GIS-BASED SUSTAINABLE GROUND WATER RESOURCES EVALUATION OF THE UPPER AND MIDDLE ROARING FORK AREA, PITKIN COUNTY, COLORADO

A GIS-based step-wise ground water resources evaluation procedure was created for use as decision/land use management tools by Pitkin County. The procedure, supported by two GIS maps and supporting data bases, guides the site-specific analysis with respect to: 1) ground water resources availability in terms of sufficient quantities for the purpose of its usage, and its economical exploitability; 2) long term sustainability of the utilization of the resources for water supply; and 3) the vulnerability of the resources to contamination.

The GIS maps and data bases developed for this project are limited to the area subject to previous studies conducted for Pitkin County by HSA (study area), specifically, (1) Middle Roaring Fork study area or MRF (Kolm and Gillson, 2004); and (2) Upper Roaring Fork study area or URF, comprising of the Upper Roaring Fork watershed including the North Star preserve (Kolm and others, 2000; Hickey and others, 2000). The data bases developed for this project include original GIS layers from the aforementioned studies, as well as GIS layers and data bases from Pitkin County, Colorado Division of Water Resources/Colorado Water Conservation Board, Natural Resources Conservation Survey (USDA), and U.S. Geological Survey.

Three case history examples are presented to illustrate the analysis procedure, using the GIS maps and data bases provided in this report, two in the MRF area and one in the URF area. The two MRF sites illustrate the variability of drinking water supplies, both in availability and sustainability, for sites located near to each other. The URF site illustrates that drinking water supplies in areas with sediment-bedrock connectivity are readily available and sustainable. All three sites are vulnerable to ground water pollution due to the absence of protective low-permeability hydrogeologic units between the ground surface and the aquifer units.