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CONCLUSIONS <br />Results of the second half, 2010, groundwater sampling performed at the GCC Rio Grande <br />Cement Plant during October 2010 are presented herein. All analyses required were <br />performed as requested. <br />Results for several dissolved metals were found to be non-detect for all wells. These metals <br />include: aluminum, beryllium, chromium, cobalt, nickel, silver, vanadium, zinc, antimony, <br />arsenic, cadmium, lead, thallium, and mercury. Most of these metals have also been <br />reported as non-detect in the previous quarterly sampling events. If these constituents <br />continue to be non-detected in future samplings events, or if these have not been <br />historically detected, GCC Rio Grande may petition to have these constituents removed <br />from the routine monitoring program. <br />Selenium was the only metal to exceed a primary drinking water standard. This occurred at <br />well MW004. Selenium has exceeded the drinking water standard at well MWO04 for each <br />of the monitoring events performed at the site to date. Elevated selenium in the vicinity of <br />the St. Charles River and other areas is documented to be naturally occurring with sources <br />in unit of the Pierre Shale, the Niobrara Formation and from soils formed from those <br />bedrock units. Secondary water quality standards were exceeded for dissolved manganese <br />and for sulfate. These constituents may have negative aesthetic impacts on water used for <br />domestic purposes. <br />Elevated radiochemical activities for gross alpha and radium 226/228 are likely associated <br />with naturally occurring conditions in the St. Charles River alluvium. There is no <br />indication that the elevated radiochemical activities have any association with cement plant <br />activities. <br />6