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Colorado Division of Reclamation Mining and Safety January 6, 2011 <br />Mr. Eric Scott 5 103-81640 <br />activities began after July 30, the water levels in several of the wells never did recover to the July 30 <br />levels. <br />During the September 2010 monitoring event, samples from the four monitoring wells were analyzed for <br />the constituents listed in Table 3, which matches the abbreviated historic analyte list (i.e., sampling <br />events after September 9, 1999). The analytical results are also presented in Table 3. The analytical <br />laboratory reports from the September 2010 monitoring event are provided in Attachment C and <br />concentration versus time (time series) plots are presented in Attachment D. <br />The analytical data from the September 2010 monitoring event were checked for completeness and <br />reasonableness by Golder upon receipt from ACZ. A summary of the data checks is provided below. <br />¦ Samples were received by the analytical laboratory at appropriate temperatures <br />(4 degrees Celsius, +/- 2 degrees). <br />¦ All required analyses were conducted by the laboratory. <br />¦ All analyses were conducted within the recommended hold time with the exception of lab <br />pH, which should be measured at the time of sample collection. However, the lab <br />measured pH values are similar to the pH measured in the field using a portable pH <br />meter. <br />¦ Cation-Anion balances for all samples are within an acceptable range (2.4 percent or <br />less). <br />¦ Measured and calculated total dissolved solids (TDS) concentrations for each sample are <br />within 10 percent of one another. <br />¦ Few constituents were detected in the field blank sample and the concentrations of these <br />detections were either estimated at concentrations between the. method detection limit <br />(MDL) and the practical quantitation limit (PQL), or were significantly lower than the <br />groundwater sample concentrations. <br />¦ A majority of the MW-4 duplicate results are within 10 percent or less of the original <br />MW-4 sample concentrations. <br />Based on these checks, the September 2010 analytical results are, in general, considered valid. <br />However, several constituents were slightly above their historical range of concentrations prompting <br />Golder to request additional data checks by the lab. The lab did not find any errors or make any <br />corrections as a result of these additional checks. <br />4.0 COMPARISON OF RESULTS TO BENCHMARKS <br />Benchmarks levels were established for each constituent in the three downgradient wells based on the <br />methods described in the Groundwater Sampling and Analysis Plan for the Boettcher Limestone Quarry <br />in La Porte, Colorado (Golder 2010a). In summary, benchmarks were determined either from: <br />1. Regulatory standards listed in the CDPHE Regulation 41, Basic Standards for <br />Groundwater Tables 1 through 4 (Regulations); <br />2. Upgradient concentrations; and/or <br />3. Intra-well statistical methods performed on background concentrations from April 1999 <br />through July 2000. <br />A more detailed description of the methods used for determining benchmark levels is presented in <br />Attachment E. <br />The benchmark levels were compared to the September 2010 analytical results (Table 4) to evaluate if <br />there is evidence of potential impact on groundwater chemistry by CKD disposal. A summary of these <br />' <br />Golder <br />iA10\81640\0400\9wreP_ fnl_061'an11\10381640holcim 9wreP_fn1-Itr061'an11.docx Associates