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ARCADIS <br />3. Results <br />3.1 Groundwater Elevations and Flow Characteristics <br />Measured depth to groundwater data (Table 1) were used to develop groundwater <br />elevation contours (Figure 2). The water table is encountered in the Codell Sandstone <br />Member of the Carlile Formation (RGI 1999), which underlies the quarried rock. All of <br />the monitoring wells are screened in the Codell Sandstone. The groundwater flow <br />pattern is similar to what has been observed in the past. <br />Groundwater generally flows south toward the Arkansas River, which is the major <br />groundwater discharge zone in the area, as reported by previous investigators (i.e., <br />BBL 2002, RGI 1999). One new groundwater monitoring well (MW -13) was installed on <br />April 3, 2009, and the water level in this well appears to conform to the general <br />groundwater direction, as measured in the other site groundwater monitoring wells. <br />Based upon an average measured horizontal groundwater gradient of 0.02 feet per <br />foot (ft/ft), a reported Codell Sandstone hydraulic conductivity of approximately 4.5x10 <br />centimeters per second (cm /sec; RGI 1999), and a range of effective porosities for <br />sandstone of five to 30 percent (Freeze and Cherry 1979), the resulting groundwater <br />velocity is 0.3 to 1.9 feet per year (ft/yr). This range is similar to previously reported <br />values by RGI (1999) and previous groundwater monitoring reports for this site <br />prepared by ARCADIS. <br />3.2 Analytical Results <br />Laboratory analyses of the groundwater samples were conducted at ACZ's Steamboat <br />Springs, Colorado facility. Results of the laboratory analyses are provided in Table 2. <br />The Laboratory Analytical Results Report is provided as Appendix D. Historical <br />groundwater quality data are provided in Appendix E (updated with results through <br />2012). <br />3.2.1 2012 Results <br />Per the requirements of the DRMS- approved GMP, because sodium and iron <br />concentrations exceeded their NPLs by more than 10 percent (14 and 206 percent <br />respectively) in monitoring well MW -7 during the March 2012 sampling <br />event,(ARCADIS, 2012),sampling of this well was required in September 2012. The <br />results of the semi - annual sampling of MW -7 were documented in the letter to Holcim <br />2013 Groundwater <br />Monitoring Report <br />Florence, Colorado <br />H <br />