Artifical Recharge of Ground Water in Colorado

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