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EXHIBIT A-1 <br /> CT2015-72 (C154210) <br /> STATEMENT OF WORK <br /> (Amended August 2015) <br /> BACKGROUND <br /> The San Luis Valley Irrigation District(the District)owns and operates the Rio Grande Dam and Reservoir <br /> on the Rio Grande in southwest Colorado. The dam is an 111-foot high earth and rock fill embankment with <br /> a crest elevation of 9470 feet. Key features of the project include the dam with a crest length of <br /> approximately 450 feet, an un-gated spillway at the right abutment of the dam,and a low level outlet that <br /> includes an 11-foot high by 15-foot wide tunnel with a.multiple sluice gate control structure near the middle <br /> of the tunnel. The reservoir is approximately six miles in length and 0.25 miles in width,oriented in a <br /> roughly northwest-southeast direction and has a capacity of 52,192 acre-feet. <br /> A comprehensive study for rehabilitation and/or enlargement of the dam and reservoir was conducted by <br /> Deere&Ault Consultants,Inc. (D&A)and CDM in 2007 and 2008("Rio Grande Multi-Use Rehabilitation <br /> and Enlargement Study,"CDM,2008). That study estimated costs of$19.2 million for rehabilitation and <br /> $33.2 million for enlargement. <br /> Construction of the dam began around 1908 with completion in 1914. The dam was constructed in a narrow <br /> valley between a massive volcanic formation known as Fish Canyon Tuff(at the right abutment)and a large <br /> rock slide that is a mixture of clays,sands,gravels,and large blocks of tuff(at the left abutment). The highly <br /> permeable rock slide material at the left abutment has been problematic since the first filling of the reservoir <br /> where seepage of the order of 1,500 gpm has been measured in the left abutment,with a total combined <br /> seepage of 2,500 gpm downstream of the dam. The seepage flow is responsive to reservoir elevation with <br /> flows increasing significantly at higher reservoir elevations(at gage 60 and above). <br /> The low level outlet was originally constructed with 10 sluice gates,made up of five control gates and five <br /> upstream guard gates. The gates frames used a combination of concrete and steel framing to support the <br /> gates. When first operated,the gate structure experienced significant vibrations such that failure of the gates <br /> appeared likely. The response was to fill two of the three gate chambers with concrete and extend the <br /> concrete downstream of the gates for a length of 5 feet to create a more rigid structure. This initial repair <br /> was completed in 1915 and was apparently left unchanged until 1982. Between 1982 and 1999,a series of <br /> repairs were made to the control gates, including replacing the three active gates and reinforcing the framing <br /> around the gates. After the last repairs were made in 1999,the flows from the low level outlet have been <br /> restricted to approximately 1,200 cfs. Flows significantly greater than 1,200 cfs cause excessive vibrations <br /> in the gates,gate stems,and steel reinforcing downstream of the gates. <br /> The dam was originally constructed with an unlined spillway at the right abutment. The spillway has been <br /> modified since its original construction by lengthening the crest of the spillway and lining the spillway deck <br /> and walls with concrete. A recent analysis on the spillway,performed by CDM in 2008, suggests that the <br /> spillway training walls are insufficient in height to pass the required 6,600 cfs design flow. The training wall <br /> height deficiencies exist at the entrance of the structure and continue throughout its length. The greatest <br /> concern with the spillway training wall heights exists on the left side. Any overflow of the left training walls <br /> has the potential to threaten the right abutment of the main dam. Based on the 2008 study,this appears to <br /> happen at flows below the design flow of 6,600 cfs. <br /> - 1 - <br />