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C-PIT Hydrogeologic Investigations <br />Technical Revision No. 8 <br />2: Site Analysis and Field Activities Mining Permit M-1977-208 <br />one-point measurement (at 40 percent of the depth of flow) was performed to determine average velocities. <br />Flow rates were calculated and summed for each interval of the canal across the transects. <br />The NCWCD website reported that at the time of the Brown and Caldwell gauging, the Elow rate at the 10- <br />foot flume located on the canal upstream of C-Pit and immediately east of Highway 36 (Foothills Parkway) <br />was 89 cfs. See http://www.ncwcd.org/datareports/flowdata.asp?sid=4021. <br />2.2.3 Field Observations <br />Brown and Caldwell personnel visually inspected the western highwall of C-Pit on May 3, 2007, July 19, 2007, <br />and August 22, 2007. This section also summarizes other observations made during multiple site visits in the <br />Spring and Summer of 2007. <br />May 3, 2007 <br />At the time of the May 3 inspection, the Boulder Feeder Canal had been flowing at the relatively low flow rate <br />of less than ]0 cfs since commencing to flow for the 2007 irrigation season around April 10, 2007. The <br />Swede Ditch had been flowing since mid-April, and was reported to be running at 16 to 25 cfs around May 3. <br />The upper three to eight feet of the western C-Pit highwall is composed of silty clay soils that transition to a <br />weathered shale unit (Smokey Hill Shale) which overlies the Fort Hays Limestone. The shale underlying the <br />uppermost unconsolidated material is highly fractured and jointed, with the fractures delaminated and open. <br />Wet, muddy fracture zones were evident at multiple locations, some in the middle of the highwall and others <br />near the base, indicating seepage through the limestone and shale and possibly the shale-limestone contact. <br />A few of these zones transmitted dripping water. White deposits that appear to be the residue of evaporated <br />seepage were evident throughout the exposed section, some of which may be carbonate evaporates from the <br />unmined limestone. The presence of what appears to be permanently vegetated areas, both on the highwall <br />in some locations and consistently along the toe of the highwall where it meets the partially filled floor of C- <br />Pit, indicated the sufficiently regular presence of water to sustain vegetation. See Photos No. 8 through 10 in <br />Appendix C. <br />July 19, 2007 <br />By July 19, 2007, the Boulder Feeder Canal had been running in the 90-110 cfs range for over three weeks. <br />Field gauging measurements made that day along the canal reach west of C-Pit indicated an average flow of <br />87.2 cfs. The Swede Ditch, which was reported to have been running nearly Cull at 25-30 cfs since <br />April/May, had been shut off several days prior to July 19 due to reduced flows in St. Vrain Creek and limited <br />junior downstream water rights. Observation confirmed that the Swede Ditch had very little to no flow on <br />July 19. <br />Inspection of the western highwall of C-Pit on July 19 revealed wet, muddy fracture zones at multiple <br />locations, some located in the middle of the highwall and others near the base. A few of these zones <br />transmitted dripping, or even lightly flowing water. What appears to be permanent vegetation continues to <br />grow at these locations. See Photo No. 11 through 13 in Appendix C. <br />August 22, 2007 <br />The NCWCD website indicates that during the week of August 12, the Canal flow rate had increased from <br />below 80 CFS to over 100 CFS. On August 15, 2006 a peak of 160 CFS was briefly reached before receding <br />to between 90 and 100 CFS. Afield inspection on August 22, 2007 confirmed that Canal seepage losses were <br />2-5 <br />Use o(con~ents on phis sheet is subject io the Iimi~aUOns spem~ietl at the end of ~hls document <br />\1BCDEN021pro1ecislDatalGEN\Cemex\TR-B\RepoNngICEME% Repor108-31-07 doc <br />