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<br /> <br />Infrastructure, such as roads, <br />buildings, airports, and dams, is built <br />and maintained by use of large quanti- <br />ties of natural resources such as <br />aggregate (sand and gravel), energy, <br />and water. As urban areas expand, <br />local sources of these resources are <br />becoming inaccessible (gravel cannot <br />be mined from under a subdivision, <br />for example), or the cost of recovery <br />of the resource becomes prohibitive <br />(oil and gas drilling in urban areas <br />is costly), or the resources may <br /> <br />BEDROCK AQUIFERS <br /> <br />become unfit for some use (pollution <br />of ground water may preciude its <br />use as a water supply), Governmental <br />land-use decisions and environmental <br />mandates can further preciude devel- <br />opment of natural resources, If infra- <br />structure resources are to remain <br />economically available, current <br />resource information must be avail- <br />able for use in well-reasoned deci- <br />sions about future land use, Ground <br />water is an infrastructure resource <br />that is present in shallow aquifers <br /> <br />and deeper bedrock aquifers that <br />underlie much of the 2,450-square- <br />mile demonstration area of the <br />Colorado Front Range Infrastructure <br />Resources Project. In 1996, mapping <br />of the area's ground-water resources <br />was undertaken as a V,S. Geological <br />Survey project in cooperation <br />with the Colorado Department of <br />Natural Resources, Division of <br />Water Resources, and the Colorado <br />Water Conservation Board, <br /> <br /> <br />EXPLANATION <br />GEOHYDROLOGIC UNITS <br /> <br />_ Laramie Formation <br />BLaramie-Fo:r;Hillsaquifer <br />_PicrreShale <br />_ Subcrop-Alluvium <br />overlies Laraniie-Fox <br />Hills aquifer <br />-4500-ALTITUDE OF BASE OF <br />LARAMIE-FOX HIlLS <br />AQUIFER-Interval 100 <br />feet. Datum is sealevel. <br /> <br />o 1 2 3MILES <br />1"1'" I <br />o 1 2 3 4 KILOMETERS <br /> <br />Figure 1. The broad outcrop of the Laramie-Fox Hills <br />aquifer extends northwest and southwest of Greeley. <br />The bedrock aquifer subcrops under the shallow aquifer <br />alon9 the Cache La Poudre River Valley (Robson, <br />Van Slyke, and Graham, 1998, HA-742), <br /> <br />Ground water in the demonstration <br />area is present in shallow aquifers <br />primarily located along larger stream <br />'valleys and in deeper bedrock aquifers <br /> <br />that extend eastward from the Front <br />Range through thousands of square <br />miles, Water in the shallow aquifers <br />commonly is pumped for irrigation <br /> <br />of crops because of low pumping <br />costs, large well yields, and water <br />quality that is well suited for irriga- <br />tion. Water in the bedrock aquifers <br />commonly is pumped for domestic, <br />municipal, and commercial uses <br />because higher pumping costs and <br />lower well yields can be tolerated, and <br />water quality is well suited for drinking, <br />Thus, land-use decisions that can affect <br />access to the aquifers or recharge to the <br />aquifers can affect irrigation supplies <br />andlor human water supplies, <br /> <br />Mapping of the outcrop and <br />subcrop of the bedrock aquifers along <br />the western margin of the Denver <br />Basin was undertaken to better define <br />the western extent of the bedrock aqui- <br />fers, their outcrop recharge areas, and <br />potential areas of subcrop water flow <br />between shallow and bedrock aquifers <br />(Robson, Van Slyke, and Graham, <br />1998). <br /> <br />The bedrock aquITffs are com- <br />posed of beds of permeable sandstone <br />that dip eastward into the subsurface. <br /> <br />u.s. Department of the Interior <br />U.S. Geological Survey <br /> <br />USGS Fact Sheet 113-98 <br />October 1998 <br />