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970 358 1111 LL~O X022 <br />Leaf Engineering, Inc. <br />' 2607 W.10`a Street <br />' Greeley, CO 80634 <br />Forrest Leaf, P,E. (970}351-0210 Phone <br />(97b)-392-0300 Fax <br />forrest teafQagwest.net <br />August 1, 2003 <br />Andy Zones <br />Lind, Lawrence & OmnhofF <br />1011 Eleventh Avenue <br />Greeley, CO 80631 <br />Ile: Coyle, AWC Heit Pit Aquifer Analysis: Job No: 10120' <br />I have reviewed the engineering documentation provided by Wright Water Engineers, Inc. (W WE). Below are my <br />tOmmeatS: <br />1. W WE and Calibra Consulting, LLC (CC) conducted a two dimensional groundwater model of tha alluvial <br />aquifer in the vicinity of the proposed Heit gravel mine. The applicant has proposed to construct a <br />bentonite slurry wall surrounding the entire gravel mine prior to the commencemrnt 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 Hydro/ogle Characterisrits of the Yalley- <br />Fill Aquifer in the Bright Reach ojehe South Platte River Palley, Colorado. While this report is suitable for <br />the general characterization of the direction of she regional groundwater flow and the regional aquifer <br />h~ansmissivity, it does not characterize the present day saturated thickness and conductivity, Howevcy <br />W WE and CC used the groundwater analysis ro predict the relative irapacr ro the local aquifer in the <br />vicinity of the gravel mine which is appropriate to quantify the potential for injury to area wells and ]and <br />uses.` <br />2. The results of the W WE and CC model ate consistent with similar two dimensional analyses that I have <br />conduced on slurry walls in the South Platte alluvium. I agree with the predicted change in local aquifer <br />levels surroundmg 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 we115D354-F relative to the 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 watt as <br />predicated by W WE and CC. While I agree with the predicted response, immediate mitigation measures <br />should be implemented prior to the construction of the slurry wall and the commencement of mining. <br />These should include: <br />a. Tbc relocation of well 50354-F further north of the well's present location. This relocation should <br />be selected based on AWC's needs and s technical demonstration by the applican['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 tight of ways as required for 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:uml\CoylcVones Heii Pt[ Aquifer Letterl.doc <br />