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Mr. Peter Hays <br />Re: SerFer Pit, Adequacy Letter Respo e <br />July 9, 2008 <br />Page -4 of 7 <br />Rule 6.4.7 Exhibit G - Water. Information _ <br />9. The Applicant states that the entire mine site lies within the 100-year flood plain of the <br />Cache la Poudre River. In the. event of a significant flood event (10-year flood or greater) <br />it is likely that the existing pit will be captures by the Cache la Poudre River.. Whenever <br />mining will occur within feet of the river channel; a flood analysis and flood control plan must be,evaluated 1460 <br />d submitted. <br />The flood lain study is included as Exhibit G.9. <br />•10. Rule 6.4.7(1') requires the applicant to directly state if surface water or ground water will <br />be affected-by the mining, operations: The applicant noted registered wells within 600 feet <br />of the affected land based on information obtained by the OSE. However, aground water <br />study may reveal wells outside the 600 foot radius that may be impacted. If so, these will <br />need to be addressed a?d exhibits amended. In accordance. with Rule 6.4,3(2)(b) the <br />Division requests that they applicant identify and characterize the aquifer t be mined in dt <br />through. The Division also requests that- the applicant define or predict the cone of <br />depression or;shadow and mounded effect expected for any areas to be dewatered and dry <br />mined or as_a result of installation of the compacted clay liner. The cone of depression <br />and assessment of other effects should define at a minimum, the, horizontal and vertical <br />extent- of expected impacts. If . during the assessment, the applicant determines that a <br />drawdown, shadow or mounding effect will occur offsite. that. may impact a current,:, <br />groundwater use, the applicant must. explain any mitigation measures to be implemented <br />and trigger points that would- put -mitigation measures into, effect: Typically,,, a trigger <br />point of a 2 feet change* f historic ground water levels is acceptable. <br />The -groundwater (study is included as Exhibit G.10. <br />I •, <br />11. The applicant needs ? o describe - how . the drawdown of the. pits and-' any <br />shadowing/mounding effects will impact the structural integrity of the surrounding wells, - <br />surface water drainages, activities which rely on ground water in the vicinity of the site, <br />and-vegetation on or near) the site (including the cottonwood trees in the riparian area near <br />the Cache Ia_Poudre---River and the wetlands adjacent-to the pits). The applicantmust also <br />describe any mitigation measures to be implemented and trigger points that would put <br />mitigation measures into effect. <br />The mitigation plan is included in Exhibit G.10. <br />12., Based upon the -possible potential- for ground:. Water impacts from dewatering and lining <br />the pit, monitoring wells should -be considered and installed to ensure compliance with <br />Rule 3.1.6(1) of the Construction Material Rules and Regulations which require that . <br />"disturbance to the prevailing hydrologic balance of the affected land . and to the <br />surrounding area and -to the quantity -and quality of. water in surface and ground water <br />systems both during and after the. mining operation and during reclamation shall be <br />; <br />minimized...". In particular, the. Division. recommends monitoring wells, be selected or,