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<br />Artificial Recharge of Ground Water in Colorado <br />A Statewide Assessment <br /> <br />. Reducing subsidence - Restoration of ground-water levels can reduce or mitigate <br />subsidence that occurs due to water-level declines. Declining water levels can cause <br />compaction within the aquifer and subsequent land subsidence at the surface. <br /> <br />. Mitigating saltwater intrusion - Injection of fresh water is commonly used to halt the <br />advance of a saltwater intrusion front. Where saline or brackish water is present in a <br />fresh water aquifer, withdrawal of fresh water through production wells can cause the <br />saline water to encroach into the fresh water zone ofthat aquifer. <br /> <br />Protection of the Environment <br />As a water management tool, AR can also be used to benefit sensitive environments or mitigate <br />environmental contamination as follows: <br /> <br />. Protect endangered species habitat - AR projects within tributary alluvial aquifers <br />provide for recharge return flows that may be timed to augment stream flow during <br />low-flow months, thereby maintaining minimum water levels to protect aquatic and <br />terrestrial ecosystems. <br /> <br />. Maintain wetland hydrology - Maintenance of water levels through AR can help <br />protect sensitive wetlands. Ground-water conditions are an integral factor in <br />wetland viability and AR can be used to increase ground-water discharge rates to a <br />wetland. AR can also help maintain a supply of water to a wetland throughout the <br />season necessary to sustain plant and animal communities vital to the system. <br /> <br />. Control migration of ground-water contamination - Injection or recovery wells may <br />be used to maintain hydraulic control in an aquifer threatened by movement of <br />contamination plumes. <br /> <br />IV. Technologies for Artificial Recharge <br /> <br />AR technologies vary considerably, and their application depends on the hydrogeologic setting <br />of the target aquifer and the objectives of the particular application. Hydrogeologic <br />characteristics critical to determining an appropriate technology include (1) depth to the top of <br />the aquifer; (2) depth to water; (3) the stratigraphic layering above and within the aquifer; and (4) <br />the areal extent of the aquifer. These characteristics determine whether surface or subsurface <br />techniques can be implemented. Other considerations influencing the choice of available <br />technologies include surface topography and land uses. Aspects of the project objectives <br />pertinent to selecting a technology include (I) the volume of water to be recharged, (2) the <br />anticipated rate of recharge, (3) the ultimate fate of the water, and (4) the nature of the source <br />water. <br /> <br />The technologies are broadly grouped according to whether water is recharged at the surface or <br />underground and then by whether water is recharged into the unsaturated zone (vadose zone) or <br />directly into the saturated zone of the aquifer. Recharge facilities at the surface can be very <br />simple and can require minimal effort and cost to install and maintain. Conversely, recharge <br />facilities underground usually require more sophisticated design and can be more costly. The <br />following are brief descriptions of the technologies currently being used in AR projects. <br /> <br />14 <br />