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BRIERLEY <br /> ASSOCIATES <br /> Creating Space Underground <br /> March 18, 2017 <br /> 516051-000 <br /> Transit Mix Concrete <br /> 444 E. Costilla <br /> Colorado Springs, CO 80903 <br /> Attention: Brandon Heser, PE <br /> Aggregates Engineer <br /> Subject: Stability Assessment <br /> Daniels Sand Existing Wash Fines Pond <br /> Colorado Springs, CO <br /> Mr. Heser, <br /> The Daniels Sand existing wash fines pit is approximately 11 acres with a storage volume <br /> estimated at approximately 300 acre-feet. The existing pond was built approximately 10 years <br /> ago however has only been operational for the last 4 or 5 years. The Colorado Division of <br /> Reclamation, Mining, and Safety (DRMS) performed an inspection on December 7, 2016 and <br /> Brierley has reviewed the inspection report. <br /> DRMS observed "sparse vegetation, erosion rilling and portions of over steepened slope on the <br /> southwest embankment outer face of the current wash pond reducing the erosional stability and <br /> potentially the geotechnical stability of the embankment". <br /> DRMS required additional material to be placed on the outside face of the southwest <br /> embankment to achieve a flatter slope. We understand that Transit Mix has performed this <br /> grading and placed the fill in thin lifts, compacting each lift. Transit Mix reported that the slope is <br /> slightly steeper than 3H:1 V and Brierley's field engineer estimate a slope steepness of <br /> approximately 2.5H:1 V Transit Mix will establish a vegetative cover to reduce erosion potential. <br /> Because Transit Mix has completed this work, DRMS is not requiring geotechnical stability <br /> analysis at this time. Rather, DRMS accepted Transit Mix's commitment to install a piezometer <br /> in the southwest embankment. Brierley performed a geotechnical boring and installed the <br /> piezometer. The boring revealed about 20 ft of sandy fill material underlain by the native Sand. <br /> At the time of drilling groundwater was measure to be about 36 ft deep. Transit Mix has <br /> measured the piezometer on a few occasions and no water was encountered, indicating the <br /> groundwater is at or deeper than 36 ft (the total depth of the piezometer). <br /> Based on the factors listed below, it is our opinion that the 2.5:1 slope is stable and that no <br /> further analysis is necessary: <br /> • Prior to flattening the slope, there was no evidence of deep-seated slope instability <br /> • Flattening the slope has improved the slope stability by increasing resistance to sliding <br /> • The groundwater level is well below the base of the embankment and is not a factor in <br /> slope stability <br /> • Over the next several months, the free water in the wash fines pit will be removed, <br /> thereby decreasing the loads on the embankment <br /> 990 S.Broadway,Ste.222, Denver,CO 80209 1303.703.1405 1 www.BrierleyAssociates.com <br />