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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Artificial Recharge of Ground Water in Colorado <br />A Statewide Assessment <br /> <br />Subsurface Infiltration <br />Subsurface infiltration is the application of water below ground surface for infiltration to the <br />underlying unconfined aquifer. Subsurface infiltration recharge systems are utilized for <br />unconfined aquifers where surface conditions, such as impermeable layers or incompatible land <br />uses, preclude surface infiltration. These technologies reduce evaporation losses and can coexist <br />with other land uses such as parking lots or recreational fields; however, they are more limited in <br />size. The costs for installation and O&M can be much higher than for surface infiltration <br />systems because these systems require more sophisticated design and installation procedures and <br />have limited access for maintenance. <br /> <br />The general types of subsurface infiltration structures, illustrated in Figure IV -2, are described <br />below: <br />. Infiltration trenches -Excavated ditches are equipped with a perforated pipe embedded in <br />gravel. Trenches are excavated through impermeable soils into the top of the aquifer. <br />The land surface can be covered and contoured to accommodate other land uses such as <br />play fields, parking lots, etc. <br /> <br />. Infiltration galleries - Similar to infiltration trenches, but these consist of arrays of <br />multiple pipes. <br /> <br />. Dry wells -Wells that are installed above the water table in the unsaturated zone of the <br />aquifer. These are often used where water levels are deep and shallow wells reduce costs <br />as compared to completing a recharge well into the saturated zone of the aquifer. <br /> <br />. Infiltration shafts - Excavations are made through impermeable layers into the <br />unsaturated zone of the aquifer. These are larger diameter than a dry well and may be <br />cased or lined to maintain hole stability. <br /> <br />. Infiltration pits - Made similarly to an infiltration shaft but has a larger diameter. This <br />method could be classified as surface infiltration except that the application is generally <br />used to penetrate through soils oflower permeability. <br /> <br />18 <br />