Artifical Recharge of Ground Water in Colorado

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