2007-08-10_REVISION - M2001107 (4)

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~ Geocechnical Engineering Rap~rt Gravel Evaluation Northwest of Weld County Roads 18 and 25 Weld County, Colorado Terracon Project No. 21035117 Terracon SUBSURFACE CONDtTION5 ' Soil and Bedrock Conditions ' As presented on the Logs of Boring, surface soils to depths of 6 to 7 feet consisted of overburden materials. The upper 6 inches of the overburden consisted of topsoil. The underlying overburden ' consists of silty sand, lean clay soils with varying amounts of silt and sand, and fine-grained poorly graded sands with silt. A layer of well graded sand v~ith gravel varying in thickness from 20 to 22 feet was encountered below the overburden. Bedrock underlies the sand and gravel at depths of 26 to 28 feet below the surface. The bedrock consists of claystone. Laboratory Test Results ~ Laboratory test results indicate that the sand and gravel are well graded and non plastic. Maximum t gravel sizes encountered ranged from 1 to t% inches. Groundwater Conditions Groundwater was encountered at approximate depths of 4 to 6 feet in the test borings at the time of -~ field exploration. These observations represent groundwater conditions at the time of the field exploration, and may not be indicative of other times, or at other locations. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions. Evaluation Based on the test borings drilled at the site by Terracon, approximately 1,775,353 cubic yards of sand and gravel is the estimated quantity at the site. Approxirpately 541,266 cubic yards of overburden would have to be removed to obtain the sand and gravel in this area. The above quantities are based on the average thickness of overburden and sand and gravel obtained from the test borings drilled by Terracon as outlined in our site plan, Appendix A, and on the area boundary based on the information provided by the client. Because of physical property boundaries such as roads and property lines, the quantity that can be removed is less than what is stated above. Based on the test borings, the average overburden thickness was approximately 6Y< feet and the average sand and gravel thickness was approximately 20% feet. This gives a ratio of sand and gravel to overburden of approximately 3.3 to ',. 3ased or: our visual observation during drilling and the I;mited laboratory tests run or. auger samples. the granular materials encountered consist of good quality aggregate suitable for use in construction materials. Cobbles or gravel larger than 1% inch in diameter were nct noted 4vithin the granular 3