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Tim Cazier
<br />November 13, 2012
<br />Page 2
<br />*Exceeds DRMS NPL
<br />*Exceeds DRMS NPL
<br />* *Outlier (confirmed by June 2012 measurements)
<br />GCC
<br />Rio Grande
<br />Pueblo Plant
<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, June 2012 and September 2012 sampling
<br />events are likely due to seasonal low groundwater levels following a dry Summer, Fall and Winter (rainfall
<br />in Pueblo was 25% below normal for 2011). These conditions tend to concentrate dissolved chemical
<br />species, raising the level of TDS in the samples. Previously, Contour observed that MW -003 appeared to
<br />be the most impacted by the dry conditions of 2011. This observation is supported by the fact that MW-
<br />003 was dry during the September 2012 sampling event and a sample could not be recovered.
<br />GCC maintains that it is not likely that the increases in TDS that are reflected in the last four 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 />NPL
<br />NPL
<br />MW -003
<br />April
<br />2011
<br />October
<br />2011
<br />March
<br />2012
<br />June
<br />2012
<br />September
<br />2012
<br />Sulfate, ulfa /le'
<br />n
<br />1950
<br />1160
<br />1610
<br />1860
<br />2490*
<br />Not
<br />sampled
<br />TDS, mg/1
<br />2630
<br />2190
<br />3060*
<br />3650*
<br />4700*
<br />Well dry
<br />R -226, PiC /I
<br />23.5
<br />2.3
<br />1.3
<br />3.5
<br />1
<br />Not
<br />sampled
<br />R -228, PiC /I
<br />12.3
<br />0.3
<br />0.8
<br />1
<br />0.2
<br />Not
<br />sampled
<br />Tim Cazier
<br />November 13, 2012
<br />Page 2
<br />*Exceeds DRMS NPL
<br />*Exceeds DRMS NPL
<br />* *Outlier (confirmed by June 2012 measurements)
<br />GCC
<br />Rio Grande
<br />Pueblo Plant
<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, June 2012 and September 2012 sampling
<br />events are likely due to seasonal low groundwater levels following a dry Summer, Fall and Winter (rainfall
<br />in Pueblo was 25% below normal for 2011). These conditions tend to concentrate dissolved chemical
<br />species, raising the level of TDS in the samples. Previously, Contour observed that MW -003 appeared to
<br />be the most impacted by the dry conditions of 2011. This observation is supported by the fact that MW-
<br />003 was dry during the September 2012 sampling event and a sample could not be recovered.
<br />GCC maintains that it is not likely that the increases in TDS that are reflected in the last four 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 />DRMS
<br />NPL
<br />MW -004
<br />April
<br />2011
<br />October
<br />2011
<br />March
<br />2012
<br />June
<br />2012
<br />September
<br />2012
<br />mg/1
<br />1950
<br />990
<br />1410
<br />1640
<br />1400
<br />sampled
<br />TDS, mg /I
<br />2630
<br />1850
<br />2640*
<br />3040*
<br />2480
<br />2,690*
<br />R -226, PiC /I
<br />23.5
<br />2.5
<br />3.8
<br />3
<br />2
<br />Not
<br />sampled
<br />R -228, PiC /I
<br />12.3
<br />3.6
<br />1.2
<br />13.0 **
<br />2
<br />Not
<br />sampled
<br />Tim Cazier
<br />November 13, 2012
<br />Page 2
<br />*Exceeds DRMS NPL
<br />*Exceeds DRMS NPL
<br />* *Outlier (confirmed by June 2012 measurements)
<br />GCC
<br />Rio Grande
<br />Pueblo Plant
<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, June 2012 and September 2012 sampling
<br />events are likely due to seasonal low groundwater levels following a dry Summer, Fall and Winter (rainfall
<br />in Pueblo was 25% below normal for 2011). These conditions tend to concentrate dissolved chemical
<br />species, raising the level of TDS in the samples. Previously, Contour observed that MW -003 appeared to
<br />be the most impacted by the dry conditions of 2011. This observation is supported by the fact that MW-
<br />003 was dry during the September 2012 sampling event and a sample could not be recovered.
<br />GCC maintains that it is not likely that the increases in TDS that are reflected in the last four 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 />
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