Ground water is a scarce and vulnerable resource. It is threatened by many factors - among others: Nutrients, pesticides and hazardous wastes. Ground water is the most important source of public water supply in Denmark, since surface water is used only in very long, dry periods. This occurs very seldom in Denmark. Therefore, protection of the groundwater is an important issue for the local, regional and central authorities. This paper will focus on the use of GIS for such purposes and will demonstrate a practical application of a GIS based ground water vulnerability study which was set up for the County of Copenhagen. This area covers the suburbs of Copenhagen, which is the most densely populated area in Denmark.
In 1991 the Missouri Department of Natural Resources began implementation of the Public Drinking Water Vulnerability Assessment Program. This program was designed to determine which public water supplies in Missouri are threatened by chemicals being tested under the Safe Drinking Water Act. The Center for Agricultural, Resource and Environmental Systems was contracted to examine the spatial relationship between water sources and potential sources of contamination. State and federal data bases were researched for 54 agricultural and industrial chemicals. This information was placed into a GIS and compared to Missouri's public drinking water sources. If the GIS indicates no potential sources of contamination for a chemical in an area which would affect the water state-wide analysis has resulted in the savings of over $13 million to the state of Missouri in 1994 and 1995.
The U.S. Geological Survey cooperates with Federal, State, and local water-management agencies to collect hydrologic data and make scientific studies that improve the knowledge and understanding of Nevada's water resources. The Spatial Applications Section of the U.S. Geological Survey, Nevada District is involved in the creation, analysis, and display of digital data to support such activities and studies. The section routinely incorporates state-of-the-art technologies such as geographic information systems (GIS), remote sensing, near-real-time data transmission, comprehensive relational data bases, and multidimensional digital models. Some of the activities and studies the Spatial Applications Section of the Nevada District was involved with in 1995 are: Ash Meadows Ground-Water Discharge Data Synthesis of Irrigation Drainage Areas Geographic Information System for Lake Tahoe Basin Ground Water Budget for Dayton Valley Ground-Water Conditions in and near Newlands Irrigation Project, Carson Desert Ground-Water Conditions, Desert Valley Humboldt Basin Mining Effects Intermittent Recharge in Eagle Valley Nevada Basin and Range National Water-Quality Assessment (NAWQA) Railroad Valley Evapotranspiration Truckee-Carson Program, River Basin Modeling and Monitoring Upper Carson GIS: Spatial Data Base for Water Rights Information Virgin River Geomorphic Study Walker River Assessment Water Resources Data Report (ADR), Water Year 1994 Water Resources Evaluation of Spanish Springs Valley
The geology of much of the Door Peninsula is characterized by a shallow soil layer underlain with limestone bedrock that has numerous sinkholes and fractures. It is also an agricultural area in which the spreading of manure over fields is a common practice. The purpose of this model is to determine the potential for runoff from these fields to reach the groundwater. The model inputs include several ArcInfo coverages that characterize the natural features important to groundwater contamination in the area. These are soil attenuation, fracture traces, closed depressions in the landscape, and miscellaneous geologic features such as sinkholes, crevices, quarries, and exposed bedrock. In addition, an ownership parcel coverage allows each parcel to be assigned a value based on its potential to contribute to groundwater pollution. This value is determined by the existence of the natural features listed above. Also, each barnyard in a parcel is assigned a value for animal units, which is an estimate of how much manure is produced there. All data was compiled at a scale of 1:24,000. Each parcel is assigned points for its average soil attenuation weighted by area, the number of fracture traces and geologic features present, the proportion of the parcel's area that falls within a closed depression, whether that depression has a definable principle outlet (sinkhole), and the number of animal units associated with its barnyard. Also, for a buffered area around each parcel, a lesser number of points is assigned for average soil attenuation and the number of fracture traces and geologic features present. The results are used to determine best management practices for manure spreading in each parcel within the watershed.