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Tim Cazier <br />August 3, 2012 <br />Page 2 <br />"Exceeds DRMS NPL <br />*"Outlier (confirmed by June 2012 measurements) <br />GCC <br />Nlo Grande <br />Pueblo I'lant <br />The attached Report, which was prepared by Contour Consulting Engineering (Contour), explains that the <br />TDS results obtained during the October 2011, March 2012 and June 2012 sampling events are likely <br />due to seasonal low groundwater levels following a dry Summer, Fall and Winter (rainfall in Pueblo was <br />25% below normal for 2011). These conditions tend to concentrate dissolved chemical species, raising <br />the level of TDS in the samples. Contour observed that MW -003 appeared to be the most impacted by <br />the dry conditions of 2011 and believes that this has not yet recovered from the dry conditions. This <br />conclusion is supported by the corresponding increases in sulfate in MW -003. <br />GCC maintains that it is not likely that the increases in TDS that are reflected in the last three sampling <br />events are the result of contamination from the GCC facility. As a result of the prolonged dry conditions <br />and lowered water levels, it is unlikely that continuous saturated conditions exist between the plant and <br />the compliance wells. <br />Therefore, GCC believes that, given the current dry conditions, there is no justification to continue <br />quarterly sampling all three monitoring wells. At a minimum, quarterly sampling for TDS in only MW -003 <br />should continue to be required <br />Please contact me if you have questions about this report. <br />%Sincerely, <br />1 / <br />Barbara T. Hodgsorti'__/ <br />Environmental Manager <br />(719) 647 -6829 <br />bhodgson @gcc.com <br />MW-004 <br />DRMS <br />NPL <br />April <br />October <br />March <br />June <br />2011 <br />2011 <br />2012 <br />2012 <br />Sulfate, <br />mgll <br />1950 <br />990 <br />1410 <br />1640 <br />1400 <br />TDS, mgll <br />2630 <br />1850 <br />2640" <br />3040" <br />2480 <br />R -226, PiC /I <br />23.5 <br />2.5 <br />3.8 <br />3 <br />2 <br />R -228, PiC/l <br />12.3 <br />3.6 <br />1.2 <br />13.0 "" <br />2 <br />"Exceeds DRMS NPL <br />*"Outlier (confirmed by June 2012 measurements) <br />GCC <br />Nlo Grande <br />Pueblo I'lant <br />The attached Report, which was prepared by Contour Consulting Engineering (Contour), explains that the <br />TDS results obtained during the October 2011, March 2012 and June 2012 sampling events are likely <br />due to seasonal low groundwater levels following a dry Summer, Fall and Winter (rainfall in Pueblo was <br />25% below normal for 2011). These conditions tend to concentrate dissolved chemical species, raising <br />the level of TDS in the samples. Contour observed that MW -003 appeared to be the most impacted by <br />the dry conditions of 2011 and believes that this has not yet recovered from the dry conditions. This <br />conclusion is supported by the corresponding increases in sulfate in MW -003. <br />GCC maintains that it is not likely that the increases in TDS that are reflected in the last three sampling <br />events are the result of contamination from the GCC facility. As a result of the prolonged dry conditions <br />and lowered water levels, it is unlikely that continuous saturated conditions exist between the plant and <br />the compliance wells. <br />Therefore, GCC believes that, given the current dry conditions, there is no justification to continue <br />quarterly sampling all three monitoring wells. At a minimum, quarterly sampling for TDS in only MW -003 <br />should continue to be required <br />Please contact me if you have questions about this report. <br />%Sincerely, <br />1 / <br />Barbara T. Hodgsorti'__/ <br />Environmental Manager <br />(719) 647 -6829 <br />bhodgson @gcc.com <br />