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Cucharas Feasibility Study| Introduction 5 original construction of the dam and those completed in 1986 by GEI Consultants. Following is a summary of the findings contained in those reports. Prior to construction of the dam in 1909, five test holes were drilled in the canyon floor. Four holes in the 200‐foot wide river channel section and one hole 35 feet above the river channel on the right abutment. These borings indicated that the foundation consists of 20 to 40 feet of sandy soils and boulders over shale bedrock in the channel section and approximately 30 feet of clayey soils and boulders over bedrock on the right abutment. A geotechnical field exploration was also performed in 1986 by GEI during a safety evaluation of Cucharas Dam. The investigation consisted of drilling five test borings into the dam and at the downstream toe of the dam, including five observation wells. Three bore holes located along the downstream toe were advanced to an approximate depth of 25 feet and two bore holes located on the crest of the dam were advanced to an approximated depth of 140 feet. The foundation soils at the toe of the dam and under the dam consisted of 10 – 17 feet of silty sand, silty gravelly sand and silty sand and gravel overlaying 0 – 4 feet of clayey gravels. The silty sand layer was composed of mostly fine to medium sand, with approximately 10 to 50 low plasticity fines and 0 to 20 percent gravels up to 1‐inch maximum size. The clay gravel was composed of ½ ‐ 1‐inch gravels with a 30 percent widely graded sand with about 30% medium plasticity fines. Standard Penetration Tests (SPT) ranged from 7 blows/ft to 50 blows/3 inches and averaged 23 blows/ft. Bedrock was encountered at depths of 17 to 20 feet along the toe of the dam and consisted of hard to very hard claystone and shale with interbedded sandstone layers. Borings were advanced approximately 5 feet into bedrock. Some additional geotechnical testing and analyses was performed by GEI in 2010 as well. Several test pits and some exploratory boreholes were done. The test pits looked at potential sources of material for dam building. The boreholes logged underlying geology and also did some packer testing. The underlying foundation rock for the dam did not present any unusual or extraordinary conditions that would preclude the rehabilitation or construction of a dam. The materials in the embankment can be divided into two types: 1) Mixed earth fill/rock fill in the upper section of the dam and 2) Sound rock fill in the lower section of the dam. The mixed earth fill/rock fill materials were generally the consistency of a loose to medium dense sand with relatively low SPT blow counts, less than 10 per foot. The sound rock fill consisted primarily of cobble and boulder size materials. It was estimated that more than 90% of the sound rock fill is composed of sandstone. Other rock types, including claystone, limestone and conglomerates were encountered, but comprised less than 10% of the recovered samples. The overall quality of the sound rock fill zone considered to be average to good with respect to strength and durability. Additional studies completed by GEI in 2010 verified the geologic data above and did not reveal any new concerns or fatal flaws that would preclude the construction of a new dam or the rehabilitation of the old dam.