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pH <br />Chloride <br />Sulfate <br />Dissolved <br />Solids <br />Selenium <br />Thallium <br />6.5 -8.5 <br />250 mg /L <br />250 mg /L <br />mg/L <br />0.05 mg /L <br />0.002 mg /L <br />Response: <br />CEMEX agrees to continue sampling all analytes that have "applicable <br />standards ". CEMEX has engaged in a search of applicable standards for a variety <br />of CDPHE sources and the Clean Water Act § 303(d) List. CEMEX would like to <br />discontinue analysis for those analytes that have no applicable standards. We <br />have conducted a comprehensive search for applicable standards for the analytes <br />that have been historically analyzed in the ongoing sampling program (See <br />Reference List). No applicable standards were found for calcium, magnesium, <br />potassium, and sodium. Therefore, CEMEX proposes to continue sampling <br />chloride, sulfate, total dissolved solids, selenium, and thallium, and discontinue <br />calcium, magnesium, potassium, and sodium. <br />CEMEX's search of published standards logically applies to the St.Vrain <br />alluvium and would be applied to the CEM -004 monitoring well. The shallow St. <br />Vrain alluvial aquifer is — 40 feet below ground surface to the northwest of C -Pit. <br />CEMEX proposes ground water standards that are based on the drinking water <br />standards in CDPHE WQCC 5CCR 1002 -41 Regulation No. 41 shown in the <br />table below. <br />While it is clear that there are applicable standards in the St Vrain alluvium, it is <br />difficult to assign an appropriate suite of standards for water that maybe produced <br />(if any) in the Niobrara Formation within the Fort Hays Limestone and Smokey <br />Hill geologic units, where C -Pit is located. The first usable bedrock aquifer in <br />this area is 500 to 700 feet below the Fort Hays geologic unit in the Dakota <br />Sandstone. According to Banks and Gesso (1999) "The only usable ground water <br />sources in this area are in the alluvial deposits of the St. Vrain Creek and the <br />Dakota Sandstone ". It is very unlikely that water would accumulate in the Fort <br />Hays Limestone and Smokey Hill Shale units given the low permeability and <br />tightness of the bedrock (URS, 2004). Further evidence supporting the lack of <br />water in Niobrara formation comes from observations at the Dowe Flats Quarry <br />across Highway 66 from the Cement Plant. CEMEX is mining through the Fort <br />Page 2 of 6 <br />