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2010 Groundwater <br />• <br />ARCADIS Monitoring Report <br />Florence, Colorado <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. <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 (e.g., <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 a measured horizontal groundwater gradient of 0.0191 feet per foot (ft/ft), <br />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 5 to 30 percent (Freeze and Cherry 1979), the resulting groundwater <br />velocity is 0.296 to 1.776 feet/year. This range is similar to previously reported values <br />(RGI 1999). <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 C. Historical <br />groundwater quality data are provided in Appendix D. <br />Concentrations of metals and other constituents measured in groundwater at well MW- <br />7 were compared to the compliance standards proposed in the GMP presented to the <br />DRMS in February 2009. Sodium exceeded the DRMS-approved compliance standard <br />of 226 milligrams per liter (mg/L) at well MW-7. No other analytes measured at MW-7 <br />exceeded the compliance standards. <br />Per the requirements of the DRMS-approved GMP, if the results of two or more of the <br />selected analytes used for compliance (TDS, sulfate, potassium, sodium, iron, and <br />manganese) exceed their respective compliance values by more than 10% in <br />monitoring well MW-7, Holcim is required to modify the sampling frequency from <br />t <br />GACOMMOM25511110 Final Reports and Pmwntations\tAamh 2010\Text\H016m March 2010 Final GW Monitoringd- 7