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.. ~ . HELTON 8 WILLIAMSEN, P.C. CONSULTING ENGINEERS IN WATER RESOURCES e 38e INVERNESS DRIVE SOUTH, SUITE 144 ENGLEWOOD, COLORADO 80112 PHONE (307) 792-2161 FAX (3071 792-2165 March 16, 2000 Mr. Hal D. Simpson, State Engineer Colorado Division of Water Resources 1313 Sherman Street. Room 818 Denver, Colorado 80203 Subject: Substitute Water Supply Plan Renewal - eent County Ready-Mix Dear Mr. Simpson: This letter requests the renewal of a substitute water supply plan for Bent County Ready- Mix for operation of the gravel pit near Las Animas. This plan is similar to the plan approved by you on March 4. 1999 that is valid through March 31, 2000. The gravel pit Is located in the NW'/.NE'/. of sec. 8, T. 23 S., R. 52 W. in Bent County. This location is approximately 0.6 mile south of the Arkansas River and 1.3 miles west of the city of Las Animas. Mining operations began in 1975 and have exposed a water surface area of approximately 4 acres. According to aerial photography available from the Soil Conservation Service, at least 2 acres of the water surface was exposed prior to December 31. 1980. Bent County Ready-Mix plans to mine roughly 2,000 tons of sand and gravel per year, and it is planned that the pit area will expand to 4.3 acres this year. Water Uses Water uses at the gravel pit include surface water evaporation and moisture retained within the mined aggregate, The mining operation is Considered a "dry operation", which means that no water is used at the mine site for aggregate washing or dust suppression. The evaporation losses from the surface water exposed after December 31. 1980 were calculated using the general criteria for substitute water supply plans for gravel pits provided by the Office of the State Engineer. The gross evaporation rate was estimated at 57 inches or 4.75 feet annually by interpolation of isopleths on National Oceanic and Atmospheric Administration's (NOAA) Technical Report NWS33 (Map 3). The derivation of monthly net lake evaporation is shown in Table 1. The gross evaporation was distributed according to the monthly percentages within the general criteria for substitute water supply plans for gravel pits. Effective precipitation at the gravel pit was estimated at 7p percent of the average monthly precipitation measured at NOAA's weather station in Las Animas during the period of 1980-94. The net lake evaporation rate estimated for the gravel pit is 48.12 inches or 4.01 feet annually. Water lost in stockpiling was estimated at 4 percent of the projected aggregate removal. This percentage is based on criteria set forth within the guidelines provided by the Office of the State Engineer for gravel pit substitute water supply plans A protection of 80 tons or 0.06 acre- foot of water will be consumed in 12 months within the removed aggregate. ZO'd .'.d `uaswe~LLl-M 'S uo'ILaH VLi=Oi 00-ii-~dV