2011-05-12_PERMIT FILE - M2011028 (2)

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• I. SUMMARY AND CONCLUSIONS Borrow Area B will be the primary source for pervious embankment materials, coarse-grained soil cement aggregate, possibly concrete aggregate, and riprap for Ridges Basin Dam. The haul distance to the damsite varies from 1.5 to 2.5 miles. An existing borrow pit is located on the north side of the borrow area and approximately 250,000 to 500,000 cubic yards has been removed from this area. Investigations to date have consisted of 43 backhoe test pits, 4 rotary drill holes, 14 Odex drill holes, 4 large test trenches, and 10 full scale gradation samples. In addition, 14 sidewall exposures in the test trenches and existing open pit cut slopes were visually classified using the Unified Soil Classification System, and stick logs were developed. Field lab testing has consisted of standard physical properties (gradation analysis, soil consistency limits, specific gravity, absorption, etc.), laboratory compaction, index unit weights, inplace moisture content and density tests, and a limited number of percolation tests. In addition, selected samples from the 10 full scale samples were visually classified petrographically, tested for rock hardness, and 34 L.A. Abrasion tests were performed to estimate the rock quality of the aggregate at the Durango Projects Office materials laboratory. Two test trenches remain open for inspection. • Quaternary Glacial Outwash Terrace Deposits (Qt) will be the primary source for coarse-grained material from Borrow Area B. The terrace deposit is overlain by the Upper Eolian Clay (Qeo) which has an average thickness of about 9 feet. Approximately the upper 5-feet of the terrace deposit is generally weakly to moderately cemented with calcium carbonate. The terrace deposit is about 75 feet thick, two- thirds of which overlies another clay layer termed the Lower Eolian Clay (Qeol). The Lower Eolian Clay exists throughout the northern portion of the borrow area and ranges from 1 to 9 feet thick. The terrace deposits are underlain by bedrock of the Tertiary Animas Formation. Average gradations for the glacial outwash terrace deposit (Qt) consist of the following: Matphl:aa, SfZes, .....:.. 1984 Explorati:ons.(42 Test Pits) 1941 Explorations.(10 Large Samples) Minus 3-inch - gravel 65% 59% sand 25% 31% fines 10% 10% Oversize (Plus 3-inch) 3" to 5% to 10% Total = 22% by volume 14% Total = 22% by volume 5" 10% Total = 29% by weight 13% Total = 28% by weight 5" to 12" 5% 1% Plus 12" Est. by Vol. by Weight • Vueelninuche Construction Autfi x' P.O. Box AA - Towaoc, CO 81334 1 A"IMAS etAoAF_rL G12A\1W- C- ? (4 PaiT T ^ PA?e I ^ R