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<br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br />~ <br /> <br />Artificial Recharge of Ground Water in Colorado <br />A Statewide Assessment <br /> <br />Direct Injection <br />Direct injection differs from infiltration systems by recharging water directly into the saturated <br />zone of the confined or unconfined aquifer. Direct injection is accomplished through a well in <br />situations where the target aquifer is deep, confined, or contains impermeable layers. Injection <br />welI design styles vary with hydrogeological conditions and operation modes. Operational <br />modes also vary depending on project objectives. Wells may be used solely as injection wells <br />with the water extracted at remote locations, or the wells can serve for both injection and <br />extraction in an aquifer storage and recovery (ASR) application. The wells occupy very little <br />land surface area and can be compatible with nearly any type of existing land use. The <br />technology can also take advantage of existing water supply infrastructure, however, initial <br />design, installation, and O&M can be costly relative to infiltration recharge systems. Source <br />water must be of the highest quality and underground injection permitting is required. Since <br />there is no evaporation, losses are limited to the small quantities of water pumped during routine <br />well maintenance. <br /> <br />Injection well applications, shown in Figure IV -3 for an unconfined aquifer and IV -4 for a <br />confined aquifer, are described below. <br /> <br />. injection well- A well is completed in the saturated portion of an aquifer whether it be <br />unconfined or confined. Water is injected into the well casing through an injection pipe, <br />and the resulting head buildup causes the recharge water to flow out ofthe well screens <br />into the surrounding aquifer. <br /> <br />. ASR well- ASR wells function as dual-purpose wells in which recharge and recovery <br />from the aquifer occurs within a single well boring. Water is injected for storage to be <br />recovered at a later date, hence the term aquifer storage and recovery (ASR) well. <br />Injection may be through a separate injection pipe, or through the pump column equipped <br />with a special down-hole flow control valve. Installed well pumps not only enable <br />recovery of stored water, but also alIow periodic cycling to redevelop the wells, thus <br />maintaining their injection capacity. ASR wells have proven to be cost-effective, and can <br />be readily implemented within existing water utility facilities using well fields. <br /> <br />. Radial well- This is a large-diameter, cased borehole installed into the saturated zone of <br />an aquifer with screened pipes extending horizontally away from the casing some <br />distance into the aquifer. These installations potentially increase the surface area open to <br />the aquifer as well as the radius of influence of a well allowing higher injection or <br />extraction rates than a traditional well. <br /> <br />. Horizontal/directional well- This technology is relatively unproven for water supply <br />applications. A well is installed such that it approaches a horizontal orientation at depth. <br />The technology allows for longer screened intervals and, in theory, higher well yields <br />than a traditional vertical well installation, particularly in thinly bedded aquifers. <br /> <br />19 <br />