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. . Resources Conservation Service and records on file with the Jefferson County Health Department. Infiltration rates also are affected by land use, which can be estimated from demographic information from the Jefferson County PI,mning Department. Individual well withdrawals can be estimated with State Engineer records, County demographic information, and on-site measurements. Stream discharge information can be estimated from previous discharge records and the installation of stream gages. Vegetation, cover can be estimated using available information from U.S. Fish and Wildlife, Colorado Division of Wildlife, and any available information from LANDSAT satellite photographs [and possibly from AVIRIS (Airborne Visible-Infrared Imaging Spectrometer) data from a recent flight over the area]. Septic system return flow can be estimated using the previously determined infiltration rate, County demographic information, and on-site infiltration measurements. All of the information collected for the study is being stored in a USGS database that can be accessed by Geographic Information System (GIS) software (ArclNFO and ArcVIEW). A portable Global Positioning System (GPS) will be used to locate existing wells and surface features to supply spatial data (latitude, longitude, and elevation) to the GIS software. The GIS system allows individuals to visualize the spatial and temporal variability of the ground-water system and its various components. The database and GIS data also will be compatible with the Internet to allow access by the various cooperating agencies and the public. E.2. Monitoring the ground water resource An important aspect of understanding a ground-water resource is reai-time data. The monitoring aspect of a ground-water study is similar to a statement from a checking account, providing information about the status of an account. Monitoring can include water-level measurements, stream-discharge measurements, precipitation measurements, and water-quality sampling. Information from a well planned monitoring program can reveal seasonal and year to year changes in ground-water storage and quality. Long- term monitoring can provide the County with an "early warning system" of impending problems such as potential health hazards and decreasing water supplies. The current ground-water surface in the study area are being determined by measuring ground-water levels from existing ground-water monitoring wells and household/domestic wells. Although additional wells are needed to provide sufficient coverage of the basin, water~levels are currently being measured by USGS personnel to develOp a database of the area. After the initial definition of the ground-water surface, the data can be - anaiyzed with geostatistics to determine a network of wells that will provide the most information with the least number of wells sampled (several full samplings may be required prior to reaching this point). Long- term monitoring will involve measuring these wells at least monthly or installing data-loggers on specific wells that could provide a continuous record of ground-water levels. To determine a major outflow of the ground-water system, a surface-water gage was installed on Turkey Creek, prior to its crossing of the junction of the crystalline bedrock of the Front Range and the uplifted sedimentary layers of the eastern plains (hogback). A continuous record of surface water leaving the Turkey Creek drainage provides important information about the water budget of the system. Historical surface-water discharge data is available for the Turkey Creek drainage and can be compared with new data. Long-term monitoring of Turkey Creek also can provide an early warning system of declines in ground-water resources. Average precipitation calculations will provide sufficient information for an initial water budget for the Turkey Creek drainage, but precipitation gages provide the additional refinement of providing 3