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<br />Final Draft - Preferred Storage Options Plan <br />Southeastern Colorado Water Conservancy District <br />June 8, 2000 <br /> <br /> Reservoir Capacity (at) <br /> Major Cost Item 10,000 30,000 51,000 <br />. General Conditions 2.7 7.7 10.3 <br />. Dam Construction 10.7 41A 58.6 <br />. Facilities Modification 7.0 9.6 10A <br /> Construction and Mitigation <br />. Permitting and NEPA 1.6 4.7 6.3 <br />. Legal, Administrative and 3.1 8.8 11.9 <br /> En9ineering Costs <br />. Land Acquisition OA 0.7 0.7 <br />. Total Project Cost $25.5M $72.9M $98.2M <br /> Unit Cost (per at) $2,550 $2,430 $1,930 <br /> <br />Gravel Lakes Storage <br /> <br />Technical Issues. The develooment or conversion of sand and {!favel mine nits into wW~r <br />.. V.l - -- ~~ <br />storage facilities is gaining popularity along Colorado's Front Range, particularly along <br />the South Platte River and its larger tributaries. These facilities often are used in <br />exchange plans, wherein municipal return flows are stored and released in exchange for <br />water diverted from upstream sources. <br /> <br />The Colorado State Engineer has promulgated strict rules on allowable leakage into these <br />reservoirs so that adjacent groundwater levels and associated water rights are not <br />impacted. Unless leakage criteria are met, operation of the gravel lakes storage will be <br />subject to the same augmentation requirements as alluvial wells. To meet the strict <br />leakage criteria, the lakes must be lined, either with an impervious earth liner or a soil- <br />bentonite slurry wall around the pit. The slurry walls usually are keyed into underlying <br />bedrock to cut off seepage. <br /> <br />Gravel lakes range in size from a few acres to over 100 acres in surface area. The lakes <br />usually are 20 to 30 feet deep, creating storage capacities of 500 to 2,000 af. Storage is <br />filled by gravity inlet channels or by pumping. The lakes are drained by deep gravity <br />outlets or by pumping. <br /> <br />Gravel lakes can be developed after mining is completed or concurrent with mining <br />operations. For previously mined pits, the slurry wall method is applied. For <br />development during mining, either lining method can be used with method selection <br /> <br />~ GEl Consultants, Inc. <br /> <br />3-16 <br /> <br />J:\PROJECTS\99061\Repons\Prefmed SOP Final wpd <br />