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Leaf Engineering, Inc. <br />2607 W. 10`h Street <br />Forrest Leaf, P.E. <br />Greeley, CO 80634 <br />Andy Jones <br />Lind, Lawrence & Ottenhoff <br />1011 Eleventh Avenue <br />Greeley, CO 80631 <br />August 1, 2003 <br />Re: Coyle, AW C Heit Pit Aquifer Analysis: Job No. 10120 <br />(970)-351-0210 Phone <br />(970)-392-0300 Fax <br />Correst_leaf@qw es [.net <br />I have reviewed the engineering documentation provided by Wright Water Engineers, Inc. (WWE). Below are my <br />comments: <br />1. W WE and Calibra Consulting, LLC (CC) conducted a two dimensional groundwater mode] of the alluvial <br />aquifer in the vicinity of the proposed Heit gravel mine. The applicant has proposed to constmct a <br />bentonite slurry wall surrounding the entire gravel mine prior to the commencement of gravel mining and <br />the exposure to groundwater. W WE and CC used regional aquifer properties and regional groundwater <br />gradients from 1972 as published in the USGS Open File Report Hydrologic Chnracteristics of the Vnlley- <br />Fill Aquifer in the Bright Reach of the Soteth Platte River Ynlle}~. Colorado. While this report is suitable for <br />the general characterization of the direction of the regional groundwater flow and the regional aquifer <br />transmissivity, it does not characterize the present day saturated thickness and conductivity. However, <br />WWE and CC used the groundwater analysis to predict the relative impact to the local aquifer hr the <br />vicinity of the gravel mine which is appropriate to quantify the potential for injury to area wells and land <br />uses. <br />2. The results of the WWE and CC modal are consistent with similar two dimensional analyses that I have <br />conduced on slung walls in the South Platte alluvium. I agree with the predicted change in local aquifer <br />levels surrounding the slurry wall. <br />3. The applicant indicated that well 50354-F, owned by Aquatic Wetlands Company (AWC) is not adversely <br />impacted by the construction of the slurry wall but has not provided any technical justification qualifying <br />this assumption. In my opinion, the location of well 50354-F relative to [he proposed slurry wall will likely <br />result in a decrease in the production rate of the subject well. <br />4. The slurry wall will cause a decrease in the local water level on the north and east side of the slurry wallas <br />predicated by W WE and CC. While I agree with the predicted response, immediate mitigation measures <br />should be implemented prior [o the constmction of the slurry wall and the commencement of mining. <br />These should include: <br />a. The relocation of we1150354-F further north of the well's present location. This relocation should <br />be selected based on AWC's needs and a technical demonstration by the applicant's engineers that <br />the new location will result in the same production rate as presently exists prior to the construction <br />of the slurry wall. The applicant should agree to obtaining all necessary permits and water rights, <br />piping and right of ways as required far the relocation. <br />b. The applicant should agree to provide immediate mitigation measures to mitigate the decline of <br />water levels north and east of the slurry wall to avoid injury to AWC's nursery stock. <br />- Water Rights • Hydrology • Hydraulics • Water Quality <br />E:1Lea~CoyleVones Heit Pit Aquifer Lenerl.doc <br />1 EXHIBIT <br />8 B <br />