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Surface water 23 <br />Straight Gulch is an intermittent stream below sampling point USG. The upper reach of <br />Straight Gulch is in a narrow valley and the channel is incised 10 -15 ft into the valley fill. <br />The valley widens to the south. <br />In December 2004 through January 2005, flows at the upper Straight Gulch sampling <br />station (USG) ranged from 10 to 20 gpm. During the same period, flows at the lower <br />Straight Gulch sampling station (LSG) ranged from about 5 to 35 gpm. Flow increased <br />at both stations in February 2004 with the upper station estimated at 110 gpm and the <br />lower station at 225 gpm. Flow at both stations was about 100 gpm in March 2004 and <br />225 gpm in April 2004. <br />Monitoring locations <br />The locations of the Straight Gulch monitoring stations are shown on Figure 4.2. <br />Sampling point USG is immediately adjacent to valley fill well MS- 04 -01. Sampling point <br />LSG is immediately adjacent to valley fill well MS- 04 -02. <br />4.4 Stream water quality <br />Surface water quality samples were collected from the stream sampling locations <br />described above and listed in Table 4.1. Samples were collected monthly starting in <br />December 2004. At the time this report was prepared, data for the sampling events <br />were available from the start of the program through April 2005. <br />Analytical results from the stream monitoring locations are presented in Appendix 4.C. A <br />summary of analytical results is presented in Table 4.2. Table 4.2 also includes <br />Maximum Concentration Limits (MCLs) based on EPA primary water quality criteria, as <br />well as secondary drinking water quality criteria (US EPA, 2003). Although these criteria <br />are not specifically applicable, they provide a basis for comparison. All surface water <br />samples (except UCG) exceeded the secondary drinking water standard for TDS of <br />500 mg /l. The elevated TDS also led to exceedances of the MCL or secondary drinking <br />water standard for alkalinity and sodium. The inorganic chemistry of the major ions is <br />illustrated on a trilinear diagram (Figure 4.3). <br />2572 -R2 Colowyo Coal Company <br />Water Management Consultants <br />