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SEP 21200S EXHIBIT G <br />Division of Reclamation, <br />Water Information Mining and Safety <br />Weld County owns and operates the Hokestra Pit for extraction of aggregate resources (DMG <br />Permit No. M-80-149). The Hokestra Pit is located in Weld County just northeast of the City of <br />Longmont, east of the frontage road for Interstate 25 adjacent to the Weld County Service <br />Center. More specifically the pit is located in the NW 1/< of Section 2, Township 2 North and the <br />SE '/< of the SW '/< of Section 34, Township 3 North, Range 68 West, 6a' P.M, Weld County, <br />Colorado. This operation is south of the St. Vrain River and approximately 1.5 miles <br />downstream of the confluence with Boulder Creek and will impact the St. Vrain River in the <br />form of groundwater depletions due to evaporation and water uses associated with mining. The <br />impacts to the St. Vrain can be mitigated without injury to the vested senior water rights. Mining <br />at the Hokestra site will last another 20 yeazs. <br />The reclamation plan will leave lined reservoirs that are not hydraulically connected to the <br />alluvial aquifer. Once reclamation is complete, the lined reservoirs will have a total surface azea <br />of approximately 72.5 acres. A substitute water supply plan (SWSP) pursuant to C.R.S. 37-90- <br />137, has been filed with and approved by the State Engineer's Office (SEO) for replacement of <br />the depletions during the mining phase. This site is not mined continuously and is only <br />dewatered when mining occurs to allow for dry-mining. However, to be conservative we are <br />calculating the maximum potential evaporation that would be associated if no dewatering occurs. <br />Water Requirements <br />Water use at the site will include evaporation from exposed groundwater and water retained in <br />material removed from the site. The mining operation will extract sand and gravel deposits from <br />the St. Vrain alluvium that is approximately 20-30 feet deep and will influence the groundwater <br />systems hydraulically connected to the St. Vrain. The depth to groundwater is approximately 5 <br />to 10 feet below the surface. Due to groundwater inflow to the river from upland precipitation <br />and irrigation return flows to the south, the river generally gains flow in this reach. There is also <br />an un-named drainage to just east of the site that provides intermittent flow to the river and <br />contributes to the groundwater in the area. <br />Evaporative losses are dependent on the exposed surface azea, which may vary throughout the <br />mining operation. The estimated area for mining is shown on Exhibit G-1 as a 39.4 acre basin on <br />the west side, with another 23 acre basin and a 10.1 acre basin along the east side. There aze 9.9 <br />acres that were exposed before December 31, 1980 that have been associated with this area. <br />Therefore, by exempting the pre-81 acreage, the total exposed surface area that will require <br />replacement is 62.6 acres. <br />The gross annual evaporation for the site is 40 inches, which was taken from the NOAA <br />Technical Report NWS 33, Evaporation Atlas for the Contiguous 48 United States. Monthly <br />evaporation percentages, as suggested by the SEO were used to calculate monthly evaporation. <br />The Climatolog~of the United State No. 81 provided the estimated annual precipitation. The <br />Weld County Hokestra Pit <br />DMG ]12 Pesmit Amendment <br />Page 9 <br />