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standard is listed. Any exceedances to the basic standards are shown as shaded cells in <br />Table 1. The only dissolved metal detection to exceed a primary drinking water standard is <br />that for selenium in alluvial well sample MW004. This selenium detection corroborates <br />similar results from the previous 2008, 2009, and 2010 events. Elevated selenium <br />concentrations associated with certain shallow sedimentary rock units in the Pueblo area <br />have been well documented, and include the St. Charles River alluvium (April 2007, GEI <br />Consultants, Inc, Aquatic Biological Monitoring and Selenium Investigation of the <br />Arkansas River, Fountain Creek, Wildhorse Creek, and the, St. Charles River). <br />Secondary standards for manganese are exceeded in alluvial wells MW002 and MW003. <br />Secondary standards are typically associated with aesthetic impacts to water quality, <br />including taste, staining potential, and potential for fouling. <br />General Chemistry <br />Results of the general chemistry results are presented in Table 1. The anion and cation <br />balance was poor for well MW002, with a percent differences greater than 10 percent. <br />Historically, the laboratory has attributed poor ion balance to the relatively elevated <br />bicarbonate concentration, which is calculated from the total fraction, relative to cations, <br />which are calculated from the dissolved fraction. No action is taken with respect to data <br />quality due to the poor ion balance in the groundwater samples. <br />General chemistry parameters do not have primary health based standards. Fluoride (2.0 <br />mg/L), chloride (250 mg/L), and sulfate (250 mg/L) have secondary or agricultural <br />standards. The sulfate concentrations in all three of the alluvial wells sampled have <br />exceeded the 250 mg/L secondary domestic drinking water standard in each of the sampling <br />events. Excess sulfate in drinking water may have negative aesthetic impacts such as <br />laxative effects. <br />Well MW004 has historically recorded the highest sulfate, TDS, and nitrate concentrations. <br />However, in the last three events, none of the general chemistry parameters are significantly <br />elevated in one well over the others, and no trends are evident. <br />Radiochemistry <br />Results of the radiochemistry analyses show that gross alpha activities exceed the Colorado <br />groundwater standard of 15 picoCuries/Liter ( pCi/L) in wells MW002, MW003, MW004, <br />and DUP -01 (MW002 duplicate sample). The 15 pCi/L standard excludes activities due to <br />radon and uranium. Radon and uranium activities were not measured, and the gross alpha <br />contribution from these two sources cannot be evaluated at this time. Gross alpha activities <br />have exceeded the standard in well MW004 in all previous sampling events. Gross alpha <br />activities have exceeded the standard at wells MW002 and MW003 in each of the <br />monitoring events since 2008. <br />3 <br />