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Geotechnical Engineering Report <br />Gravel Evaluation - Saddlehorn Ranch Site <br />NE of Highways 257 and 60 -Milliken, Colorado <br />Terracon Project No. 21015136 Terracon <br />Evaluation <br />Based on the test borings drilled at the site by Terracon and the limited information provided by <br />Andesite, approximately 1,650,000 cubic yards of sand with gravel was encountered at the site. <br />Approximately 570,000 cubic yards of overburden will have to be removed to obtain the sand with <br />gravel. The above quantities are based on the average thickness of overburden and sand obtained <br />from the test borings drilled by Terracon and from the information provided by Andesite. Based on the <br />test borings, the average overburden thickness was approximately 7 feet and the average sand with <br />gravel thickness was approximately 21.5 feet. This gives a ratio of sand with gravel to overburden of <br />3.1 to 1. The average overburden thickness from the Andesite borings was approximately 5 feet and <br />the average sand with gravel thickness was approximately 14 feet resulting in a ratio of sand with <br />gravel to overburden of 2.7 to 1. The combined average of the two sets of data indicate an average <br />overburden of approximately 6 feet and a sand with gravel thickness of approximately 18 feet. This <br />gives an overall ratio of sand with gravel to overburden of 2.9 to 1. <br />Based on our visual observation during drilling and the limited laboratory tests run on auger samples, <br />the granular materials encountered consist of good quality aggregate suitable for use in construction <br />materials. However cobbles or grave! larger than 1 inch in diameter were not noted within the <br />granular stratum. In order to use this material for typical construction materials such as base course, <br />concrete, and asphalt aggregate, extensive screening may be required. This may generate large <br />amounts of reject sand material. The material may be used without processing for structural fill and <br />subbase material. To more accurately evaluate the quality of the granular material as well as the size <br />of the particles, additional test borings and test pits should be dug at the site and detailed laboratory <br />tests should be performed. <br />Since the sand with gravel is below groundwater, dewatering of the pit will be required to excavate the <br />sand with gravel, or a drag line will be needed to remove the overburden and aggregate. <br />Additionally, it is our understanding the site may be developed into a storage pond following the <br />completion of gravel excavation. Based on our observations of the siltstone/claystone bedrock <br />generally encountered beneath the sand and gravel, the siltstone/claystone bedrock materials appear <br />suitable for use as liner material along the side walls of the storage pond. However, lenses of <br />sandstone bedrock were encountered at the site which would not be considered suitable for lining of <br />the storage pond. Laboratory evaluation of the bedrock materials for use as a storage pond lining is <br />recommended prior to its use to determine the permeability and ensure the suitability of the material <br />for use as a liner. Based on visual observation, a range of permeability for the siltstone/claystone <br />bedrock encountered, if properly processed, are anticipated to be on the order of 10$ to 10~ cm/sec. <br />4 <br />