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III IIIIIIIIIIIII III 999 FtE(~EIVED JAIV 1 5 2002 January 14, 2002 Division cl Minerals and Geology Ms. Kate Pickford Environmental Protection Specialist FE-X: (303) 832-8106 Division of Minerals and Geology 1313 Sherman Street, Room 2 ] 5 Denver, CO 80203 Re: Permit No. M-1999-021 -Stegner Farms - Techni<:al Revision TR-003 Dear Kate: AGGREGATE INDUSTRIES In your letter of December 27, 2001, you requested that we indicate how information and data we propose to incorporate from the groundwater study and mapping that is being conducted at the above-referenced operation will be used to satisfy the purpose of the technical revision that we have submitted in response to the requirements of the Division's inspection report dated October 31, 2001, specifically: • To delineate the areal extent ojthe depressio.7 resulting from the presence of the slurry wall, and thus help !o establish an approximate boundary of the down gradient depression; and, • To indicate how the data the technical revision proposes to incorporate will be used to define the groundwater surface in the area north and west of the slurry wall, indicating the extent ojthe mounding effect imposed by the slurry wall." The study Aggregate Industries initiated proposes to attempt to determine vazious causes and the extent of their effects on groundwater level changes in the azea of the Stegner Farm slurry wall, as well as respond [o the Division's specific requests with regard to the slurry wall as noted above. According to Richard Henry, the Scientech, Inc. hydrogeologist conducting the study, these determinations will be made by: • Evaluating local precipitation, temperature, and evapotranspiration data for the Fort Collins area to assess the potential impact of c limate on regional groundwater levels prior to and since [he slurry wall was installed; • Evaluating pre- and post-slurry wall groundwater levels using monitoring well hydrographs to compaze pre- and post-slurry wall groundwater levels and trends. These hydrographs will also be used to determine st;asonal and other influences (e.g.,vrigation period, local dewatering, e[c.) on groundwater levels; Aggregate Industries West Central Region, Inc. 3605 South Teller Street Lakewood, CO 80235 Connie Nickle Davis, Suppon Sen ices P. O. Box 337231. Groeley. CO Bu633 970-336fi526 Fax: 970-378fi8`.6 Telephone: 303-985-1070 An Equal Opportunity Employer