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The Otl aquifer is moderately permeable as indicated by an auger hole test on <br />alluvial well TR3. Exhibit 2.5-24 shows the data from the test in which the water <br />standing in the well was rapidly evacuated and the rate of recovery measured. <br />Standard auger-hole theory was used to estimate the permeability at 0.34 ft/hr. <br />Fan and terrace mapping for Oak Creek is shown on Exhibits 2.5-21 and 2.5- <br />22. The Oak Creek valley had undergone significant modification by man's activities. <br />At present, no alluvial fans could be recognized. Two levels of terraces (Otl and <br />Ott) were mapped. The Otl terrace is low lying and constitutes the modern flood <br />plain of Oak Creek. It is, to a large extent, confined by highway and railroad fills. <br />The surface of the Otl consists of predominently fine overbank deposits supporting <br />hydrophytic vegetation. Ground water contained in these deposits is directly <br />connected to Oak Creek. <br />Terrace deposits above the Otl are sparse, a fact which tends to support the <br />hypotheses that the Yampa River flowed through the Oak Creek Valley until <br />relocating to its present course. Three higher terrace deposits were mapped and <br />designated as Qt2. These terraces are located on the easl side of the valley <br />approximately 20 feet above the Otl terrace: The Ott terraces are composite <br />terraces and have been sculpted from the Iles~ormation. They are veneered with <br />• 4 to 6 feet of alluvium that show no indication of containing significant groundwater. <br />Ovality of Alluvial Waters -Four monitoring wells have been established <br />in the Otl terrace along Trout Creek. These are designated TRI through TR4 and <br />their locations are shown in Exhibit 2.5-2. Monitoring wells OK I and OK2 are <br />completed in the Otl terrace on Oak Creek aT locations shown on Exhibit 2.5-2. <br />Sample logs and completion details of these seven monitoring wells are contained in <br />Section 2.5.5. The alluvial wells were sampled monthly. <br />Tables 2.5-16a, 2.5-16b and 2.5-17 summarize the water quality data from the <br />alluvial wells on the two streams. On Trout Creek (Table 2.5-16) a large difference <br />between the mean concentration of dissolved solids in the upstream alluvial wells <br />(TRI and TR2) and that in the downstream alluvial wells (TR3 and TR4) is observed. <br />This difference is not related, apparently, to which side of the stream the well is <br />located on. For instance TRI is between The mine and the stream, but TR2 is on <br />the west side of the stream. Monitor well TRI is located adjacent to an old <br />underground mine and just down gradient from a rather large swampy area where <br />underflow from the Little Trout Creek watershed surfaces before entering Trout <br />Creek. Springs seep from The Ott terrace immediately west of TR2 and these <br />seepage waters enter the Otl terrace both upstream and downstream of TR2. <br />Revised 7-81 2.5-67 <br />