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Little Thompson Water District - Proposed Dry Creek Reservoir September 13-14, 2005 Agenda Item 12a water treated by the plant is delivered directly from Carter Lake to the filter plant through a single supply, the St. Vrain Supply Canal. Consequently, the Districts are entirely dependent on availability of water from Carter Lake. In wet years, the Districts are unable to treat and store all of the water to which they are entitled, and consequently must take less than their water rights would allow. In dry years, the Districts can have a shortage of water that cannot be overcome by supply from Carter Lake, and consequently are forced to meet their current demands by augmenting with water from outside entities that may not be available in the future. In addition, any condition that would interrupt supply from Carter Lake such as maintenance to Carter Lake or the St. Vrain Supply Canal also would cause interruption in operation of the treatment plant. Currently, the only storage the Districts have, other than Carter Lake, is in their treated water storage tanks. These tanks can meet the needs of the Districts for only about eight hours. . . Following CWCB loan approval in November 2002, the permitting process and final design began in May 2003. Since the completion of the original CWCB Feasibility Study, the Districts have determined that it is necessary to construct the larger reservoir. Specifically, the Districts are interested in enhancing the Filter Plant operations, relative to the following needs: 1. Additional storage for current C-BT supplies so that water can be efficiently and immediately delivered to the plant in response to customer demands; 2. Carry-over storage for the Districts' existing C-BT water supply for use in future years and as drought protection; and 3. Reduced reliance on the C-BT water delivery infrastructure by providing an additional method of delivering existing raw water supplies to the Carter Lake Filter Plant. During design, several reasons influenced the decision to construct the larger reservoir: 1. As the original feasibility study was completed, the area was experiencing drought conditions and it became evident that if the Districts had to contend with a long-term . drought, the smaller reservoir may not be adequate. 2. Area landowners were concerned that the Districts might enlarge the dam in the future and want to purchase or condemn their remaining property. 3. The Districts believed that constructing the larger reservoir made sense from both a funding and timing perspective. 4. The embankment material to construct the larger dam would have been inundated by the smaller reservoir, hindering future enlargement. The reservoir would have to be drained or lowered for an extended period of time to accommodate the construction of the enlargement. The enlargement construction would hinder the Districts' ability to treat water. 5. The larger reservoir would prevent the Districts from being exposed to changing future permitting requirements. The purpose of the project is to provide raw water storage for the Carter Lake Filter Plant. The differences between the projects are related to the size of the facilities. Key differences include: 1. Increase in capacitv from 5,200 acre-feet to 8,850 acre-feet; increase in dam heiqht from 42 to 55 feet; and increase in dam crest lenQth from 2,610 to 4,820 feet; 2. Construction of a roller compacted concrete (RCC) and labyrinth combination spillwav near the center of the dam, instead of a spillway along the right abutment; 3. Increase in pump station capacitv from 5,000 gpm (7 MGD) to 6,300 gpm (9 MGD) to providing more flexibility, with an option for future expansion to 8,400 gpm (12 MGD); and 4. Acquisition of four additional total properties and two less partial properties (three of the partial property acquisitions became total acquisitions and one additional partial acquisition is required). The new project requires 9 total property acquisitions and 15 partial acquisitions. .' Page 2 of 6