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I I I I I I I I EXECUTIVE SUMMARY The Woods Lake Dam was investigated by SMITH GEOTECHNICAL at the request of the Woods Lake Mutual Water and Irrigation Company, The dam has not been restricted by the State Engineer, however, they have notified the Owner the spillway is inadequate. The dam embankment was investigated by drilling four exploratory holes and conducting laboratory tests on the soil samples retrieved, The main dam and saddle dam were also surveyed to provide the dam crest elevations and cross section information on the embankments. No engineering stability or hydrologic studies were conducted on the dam at this time. The significant findings of our investigation include the following, I, The embankment dam is predominantly silty sand of low density. Standard Penetration Test values ranged from I bpf to 7 bpf. 2. The saddle dam is approximately 1.5,feet lower than the main dam which provides a freeboard of only 2.5,feet. I 3. The phreatic surface of the dam is very high with water levels in the borings that were only 2-foot to 3,foot lower than the reservoir water level. I 4, The existing emergency spillway located on the right abutment of the dam can be widened to about ISO-feet from its current width of 40,feet. Based on the analysis conducted by the State Engineer, the spillway width required may be in the ISO foot range, I I I I I The cost estimates to rehabilitate the dam range from $71,000 to install a new emergency spillway and raise the saddle dam crest to $231.500 for a complete rehabilitation, The lower cost alternative will solve the immediate need to satisfy the State Engineer's concerns over the spillway but does not address the long term needs of the dam structures, The full rehabilitation alternative provides a structure with a new outlet, toe drains and spillway and will provide a viable structure for the next 75 to 100 years. The best alternative from an engineering point of view would be the full rehabilitation. From an economic point of view the Company may want to phase the repair work to minimize the impact on assessments. The outlet is believed to be serviceable for at least the next five to ten years and in our opinion does not have to be replaced immediately. This is somewhat dependent however on the condition of'the outlet upstream of the gate tower which has not been inspected. Based on our experience it is better to mobilize a contractor and fix all the problems at once. This is always the least expensive alternative overall and is much easier on the Company to enter into the financing, planning, engineering, and construction once rather than several times. I I I The final decision however can only be determined by the Company. The financial status of the Company, the need for the water, the philosophy as to liability and other such aspects play into the final decision. These can only be answered by the Company to meet it future goals for the reservoir. I