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<br />Artificial Recharge of Ground Water in Colorado <br />A Statewide Assessment <br /> <br />Modification of Natural Rechare;e <br />In addition to artificially recharging ground water with imported source water, natural recharge <br />from a local source can be increased by enhanced, induced, or incidental means. Figure II-I <br />illustrates these various types of recharge. The natural outflow of ground water through an <br />alluvial aquifer can also be modified to increase ground water in storage by installing ground- <br />water dams in an aquifer. <br /> <br />. Enhanced recharge is commonly done through vegetation management, where deep- <br />rooted water-loving vegetation is replaced by shallow-rooted water-conserving vegetation <br />or bare soil. Enhanced recharge can also be achieved by routing storm-water runoff from <br />urban areas to designed infiltrationJacilities. <br /> <br />. Induced recharge is created by pumping alluvial wells adjacent to streams and rivers. <br />Increased gradients produced by pumping enhance flow through the streambed and <br />banks. <br /> <br />. Incidental recharge -is the unintentional recharge of ground-water resources through <br />leaks from water and wastewater storage and distribution structures; sewage disposal by <br />septic-tank leach ficlds; and deep percolation from irrigation. The reduction in <br />evapotranspiration and increased runoff resulting from urbanization (more land surface <br />covered by impermeable materials) may also be considered incidental recharge where <br />that water flows to native surfaces or ephemeral streams. <br /> <br />. Ground-water dams are structures that intercept or obstruct the natural flow of ground <br />water in shallow alluvial aquifers. Ground-water dams are constructed by digging a <br />trench down to bedrock across a valley and backfilling with low permeability materials. <br /> <br />Undere;round Water Storae;e Options <br />Underground water storage options include natural or manmade voids in the subsurface, such as <br />abandoned mines or natural caverns. A critical aspect of underground water storage is being able <br />to maintain hydraulic control of the injected water. Nationally, coal mines are currently being <br />utilized for water storage with most of the active projects located in the Central Appalachia Coal <br />Basin. Successful water storage deployment in coal mines is very dependent upon the <br />hydrogeologic characteristics of the mine environment and surrounding host rock, and <br />geochemical interactions that influence water quality. The city of Arvada is currently utilizing <br />the abandoned mine workings at Leyden for underground water storage by direct injection. <br />Other abandoned coal mines along the Front Range may also be suitable for storage purposes. <br /> <br />Inactive underground metal mines throughout Colorado may also represent potential water <br />storage sites. Initial considerations in using inactive metal mines concern potential water quality <br />degradation due to chemical reactions with host rock. Hydraulic control is also a significant <br />consideration, as most metal-mining districts are in steep, mountainous terrain deeply dissected <br />by streams. Significant costs would be incurred to seal the mines to maintain hydraulic control <br />of injected water. <br /> <br />Like abandoned mines, natural cave systems consist of subsurface void space that may be <br />suitable for underground water storage. Colorado contains a few hundred caves scattered <br />throughout the mountainous western part of the state. Like mines, the ability to maintain <br /> <br />22 <br />