2003-03-24_REVISION - M2001085 (4)

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AM4/ DRAFT March 24, 2003 Mr. Tony Waldron Colorado Division of Minerals and Geology 1313 Sherman St., Room 215 Denver, Colorado 80203 Subject: Response to Adequacy Review Adams County RV Park, LLC, dba 124`h Estates Partners, File No. M-2001-085 124`h Estates Sand & Gravel Mine, Amendment Application No. 1 Dear Tony, Following is the Applicant's response to the Division's adequacy review comments of March 19, 2003. Responses are presented in the same order/format as the comments were received. 1) The maps need to be revised to show the entire permitted area on one sheet. The details of the mining and reclamation for the originally permitted areas can be referenced but the entire affected/permitted area should be identified on one map. The mining plan map also needs to be revised to show the location of the visual berms that are being added via negotiations with Adams County. Enclosed are revised copies of Sheets 1 and 2 of Exhibit C-1, Pre-Mine Plan Map; Exhibit C- 2, Mine Plan Map; and Exhibit F, Reclamation Plan Map. 2) How is this mining plan impacting the regional hydrology of the area and what is the operator doing to minimize the impacts to the prevailing hydrologic balance? Although our office has not received any objections to this application, we were copied on a letter of concern to Adams County about down-gradient well impacts. Since there are a number of wells within 600 feet of the site, please explain the potential impacts and proposed mitigation for these wells. The Applicant's mining plan includes the installation to bedrock of an impermeable, bentonite slurry wall around the perimeter of the mine, before any mining takes place below the water table. This step in the mining process will isolate the mine from surrounding groundwater before significant mining takes place and will be undertaken for the specific purpose of eliminating possible impacts to local water wells during mining. The slurry wall will be installed in accordance with guidelines of the State Engineer's Office, which stated in its referral comments of January 22, 2003, "If a slurry wall that meets the State Engineer's Office lining requirements is constructed prior to mining, and ground water is not consumed by the operation, our office does not anticipate any water rights issues." The letter of January 22, 2003 from the Office of the State Engineer is attached to this Response to Adequacy Review. Following mining, the bentonite slurry wall will be capped with clay to create a fully lined, isolated, water storage reservoir. The reservoir's effect on groundwater will be like that of a rock in a. very slow moving stream. Ground water will back up and rise slightly on the upstream side of the reservoir; and there can be a slight decrease in ground water elevation on the downstream side. This phenomenon is sometimes called a mound and shadow effect. Because of the highly permeable soils that are present in this area of the historic South Platte River channel, however, the shadow (downstream) effect will be minimal (one foot or less) and will not likely be detectable at 50 to 100 feet from the outside edge of the reservoir. Records of the State Engineer indicate that there may be twenty four registered wells within 600 feet of the proposed mining site. Well information was summarized in Exhibit G of the application materials. Of these twenty four wells, fourteen are deep wells finished in a confined bedrock aquifer. The approximate location and depth of one well (Permit No. 60905) is unknown, although records of the State Engineer indicate that it is located south of 1201h Avenue and upgradient of the proposed mining area. (Groundwater in the area of the site flows in a north/north-westerly direction towards the South Platte River.) Of the ten wells that are finished in shallow groundwater, two (Permit Nos. 99012A and 11020R) are south of 120th Avenue and upgradient. Two (Permit Nos. 10898R and 2437) are located significantly east of the mining area, upgradient, and likely more than 600 feet away. One (Permit No. 10899R) is owned by the Applicant and is inactive.