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<br />~1 <br />Groundwater in the area occurs in both the sedimentary rocks and in the alluvial <br /> aquifer of the St. Vrain Creek. Groundwater levels in the sedimentary strata are <br /> well below the bottom of C-Pit. Ponded water currently in C-Pit is from surface <br />' runoff, collected precipitation, Boulder Feeder Canal seepage, and runoff from <br /> the sprinkler system. Southdown drilled two water wells immediately east of the <br />' permit area and had to advance the holes 800 feet or more to encounter a <br />useable water supply. The exposed highwalls of C-Pit are dry except for <br /> seepage in response to rainfall or snowmelt, or from ditch seepage. The <br /> direction of groundwater flow in the sedimentary strata is to the east, primarily <br />' along bedding planes. <br /> The western highwall of C-Pit was dry this year, before the water began to flow in <br /> the Boulder Feeder Canal. About 3 days after the Canal started flowing, <br /> seepage appeared in the C-Pit highwall. This fact indicates that groundwater is <br /> not the source of these observed seeps. Figures 3A, 36 and 3C show a <br /> sequence of photographs of the western highwall of C-Pit before and after the <br /> Canal started flowing. <br />'' There is no apparent hydraulic connection between C-Pit and the alluvial aquifer. <br />The alluvial aquifer of St. Vrain Creek is in contact with the sedimentary strata <br />' east of C-Pit but not in contact with C-Pit itself. Groundwater in the alluvial <br />aquifer is typically 5-8 feet below ground surface and flows east-southeast, <br />generally towards St. Vrain Creek. <br />' <br /> Further evidence of the lack of potential for leachate generation from the <br /> disposed CKD is provided by an analysis of the pH of the dust control water and <br />' precipitation runoff that collects along the C-Pit highwall downgradient of the <br /> disposed CKD. The water that collects along the highwall is either in direct <br /> contract with CKD, or is dust control water or precipitation that fell on the CKD <br />' and drained to this low area. If the CKD were not hydrated in its disposed state, <br /> the runoff water could be expected to have a much higher pH than natural waters <br /> that may occur in the area. <br />' <br /> In order to determine the potential impact of the disposed CKD on area water <br /> quality, field pH measurements were made on April 7, 1999 at the edge of the <br />' water that had collected along the C-Pit hghwall. The pH measurements were <br /> taken in the water at approximate 100-foot intervals from the northeast to the <br /> southwest end of C-Pit. The water depth varied between about 6 inches to one <br /> foot at the measuring stations. The pH measurements ranged between 8.34 and <br /> 8.50 standard pH units. These pH values are similar to the 8.04 field pH <br /> measured at A-Pit. The results of the C-Pit pH survey suggest that the quality of <br />' water that contacts and runs off the disposed CKD is similar to the natural water <br /> quality in the area and that the disposed CKD does not pose a significant threat <br />' to groundwater quality. <br /> <br />' 13 <br />