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Applegate <br />Group, inc. <br />Water Resource Advisors for the West <br />March 15, 2016 <br />Alex Schatz <br />Brannan Sand and Gravel, LLC <br />2500 Brannan Way <br />Denver, Colorado 80229 <br />RE: Brannan Pit 29 - French Drain Installation - Mining Permit No. M-1980-183 <br />Dear Mr. Schatz: <br />In response to groundwater mounding issues to the south of Pit 29, a French Drain system was <br />installed with the invert set at the historic groundwater elevations prior to slurry wall installation. <br />A copy of the approved plan and profile is attached for reference. The attached construction <br />observation report summarizes our observations during installation activities on December 7th <br />2015, indicating that the drain, surrounding bedding material and filter fabric were installed in <br />conformance with the approved plans. Please note that the words slotted and perforated were <br />used interchangeably although the pipe was perforated with circular holes as pictured in Figure <br />10 of the construction observation report. Also attached is the as -built survey performed by <br />Bayer & Associates, Inc. on March 11, 2016 showing the as -built invert elevations at the <br />manholes. <br />Table 1, below summarizes the as -built and design invert elevations for the drain. The critical <br />elevations called out in the original design are Manholes 1 and 3 which are located at the <br />southeast and southwest limits of the drainage system, respectively. The design elevations at <br />these critical points are based on a 1980 groundwater contour map (elevations adjusted from <br />NGVD 29 to NAVD 88) with the invert of the pipe set approximately 0.75 -ft below the reported <br />groundwater elevation of the map. The elevation at Manhole 1 is within 0.05' of the design, and <br />Manhole 3 is within 0.19' of the design invert elevations, both of which are approximately 0.5 -ft <br />to 1 -ft below historic groundwater elevations. <br />Table 1. As -Built vs. Design Invert Elevations for Perforated Pipe Drain <br />Manhole ID <br />Invert In <br />Invert Out <br />Design <br />As -Built <br />Difference <br />Design <br />As -Built <br />Difference <br />MH -1 <br />5009.0 <br />5008.95 <br />0.05 <br />MH -2 <br />5008.0 <br />5007.77 <br />0.23 <br />5008.0 <br />5007.74 <br />0.26 <br />MH -3 <br />5007.0 <br />5007.19 <br />0.19 <br />5006.8 <br />5006.97 <br />0.17 <br />MH -4 <br />5005.4 <br />5005.36 <br />0.04 <br />5005.4 <br />5005.32 <br />0.08 <br />MH -5 <br />5004.0 <br />5003.82 <br />0.16 <br />5003.8 <br />5003.78 <br />0.02 <br />Outfall <br />5003.00 <br />5002.57 <br />0.43 <br />7405 W. Highway 50, Suite 123 <br />Salida, CO 81201 <br />1490 W. 121st Avenue, Suite 100 <br />Denver, CO 80234 <br />303-452-6611 <br />www.applegategroup.com <br />823 Grand Avenue, Suite 120 <br />Glenwood Springs, CO 81601 <br />