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CNAPTERTHREE Affected Environment <br />Resources State Engineer's office. A summary of the well seazch for the three azeas as well as <br />location maps for the wells aze presented in Appendix C. The well summary includes the <br />township, range and section of each well, the owner of the well, the well use, and, if available, <br />the geologic aquifer, well yield, well depth, and water level. Well use included the following <br />categories: municipal, domestic, crop irrigation, livestock, industrial, commercial, and <br />monitoring wells. In addition, wells were also classified as "other" if the use of the well was <br />unknown or unavailable to the State Engineer's Office. The purpose for conducting the well <br />seazch was to identify types of groundwater use in the project azea and to geographically locate <br />these uses. <br />3.4.2 Project Area Hydrogeology <br />Hydrogeologic chazacteristics of the Piceance Site, pipeline comdor and Pazachute Site aze <br />discussed in this section. <br />3.4.2.1 Piceance Site <br />Three aquifers occur within three principal geologic sequences at the Piceance Site: the neaz- <br />surface alluvial aquifer beneath the streams (Alluvial Aquifer); the Upper Aquifer, which <br />includes the saturated part of the Uinta Formation and the upper part of the Pazachute Creek <br />Member above the Mahogany Zone; and the Lower Aquifer, which includes the lower part of the <br />Parachute Creek Member from the Mahogany Zone down to the top of the Saline Zone <br />(Dissolution Surface). The Mahogany Zone is considered a leaky, semi-confining layer, while <br />~~ ~ the Saline Zone is a confining layer. Monitoring wells installed by American Soda aze shown on <br />p° <}*• a Figure 2-10. Information from the wells was used to characterize baseline hydrogeologic <br />,~ <br />~~,.•°i•' conditions described below. <br />lV <br />Alluvial Aquifers <br />Local alluvial aquifers neaz the Piceance Site aze restricted to the broad, low-lying Piceance <br />Creek valley and tributary drainages. These shallow aquifers aze primarily confined to <br />Quaternary alluvium valley fill consisting of sand, gravel, silt, and clay weathered from the <br />Tertiary Uinta Formation sandstones and mazlstones. The alluvial material is generally <br />permeable; however, clay lenses may create azeas of low permeability or even impermeable <br />intervals. Alluvium thickness at the Piceance Site, estimated at 95 feet, is based on information <br />from American Soda's alluvial aquifer monitoring we1121-2, which is located in the alluvium of <br />a tributary drainage to Piceance Creek. The depth to groundwater in we1121-2 is approximately <br />70 feet bgs, indicating a saturated thickness of about 25 feet. Groundwater flow within the Z <br />alluvial aquifers is controlled by topographic slopes and stream flow directions. Therefore, <br />groundwater flow in alluvium at well 21-2 is expected to be to the east. <br />Alluvial groundwater at the Piceance Site is classified as a sodium bicarbonate type. TT)S <br />concentration meastued in a sample collected while drilling alluvial monitoring well 21-2 was <br />1,540 mg/l. This TDS value falls within the range observed over the entire basin of 470 mg/1 to <br />6,720 mg/1(Weeks and Welder 1974). In general, the water quality of the Alluvial Aquifer is <br />more similaz to that of the Upper Aquifer than to that of the Lower Aquifer. <br />3-18 Groundwater <br />