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DEERE & AULT <br />November 12, 2014 <br />Mr. Edward Lanyon <br />Water Resources Administrator <br />City of Thornton <br />Infrastructure Maintenance Center <br />12450 Washington Street <br />Thornton, Colorado 80241 -2405 <br />Re: Hatchery Gravel Pit Slope Stability Analysis in Response to the City of Thornton <br />Objection; <br />D &A Job No. CG- 0247.015.00 <br />Dear Mr. Lanyon: <br />This letter presents Deere & Ault Consultants' (D &A) engineering analysis in response to a letter <br />of objection for the issuance of a Reclamation Permit filed by the City of Thornton (City) against <br />the Hatchery Pit. The proposed Hatchery Pit is located approximately 3.5 miles north of <br />Commerce City, Colorado, north of East 88th Avenue, west of I -76, and east of the South Platte <br />River. More specifically, the site is located in the Northeast Quarter of the Southwest Quarter of <br />Section 20, Township 67 West, Range 2 South of the 6th P.M. in unincorporated Adams County. <br />A vicinity map of the area is shown on Figure 1. Albert Frei and Sons is in the process of <br />evaluating the potential for the development of a gravel mine on the property. <br />OVERVIEW <br />The City submitted an objection letter, dated October 8, 2014, to the Division of Reclamation, <br />Mining Safety. The letter is attached for reference. The City operates North Dahlia Reservoir as <br />a major component of the City's raw water infrastructure. North Dahlia Dam (aka Tigers Dam) <br />is a jurisdictional dam with a soil - bentonite slurry wall liner beneath the dam. The Bull Seep <br />runs south to north along the toe of the dam west of the Hatchery Pit. The objection states that <br />the planned excavation location and depth of excavation for the slurry wall and mine are <br />unknown to the City. Based on this the City requested an engineering analysis to evaluate the <br />potential for the proposed excavation to cause negative impacts to North Dahlia Dam and <br />Reservoir. Albert Frei and Sons retained D &A to perform this engineering evaluate and respond <br />to the City's concerns. <br />ANALYSIS <br />D &A performed a slope stability analysis for the Hatchery Pit based on the proposed location of <br />a soil - bentonite slurry wall lined gravel mine east of the North Dahlia Dam. The City provided <br />as- constructed information for the North Dahlia Dam. With the as- constructed information for <br />the dam, existing site survey information and available geotechnical data, D &A developed a <br />600 S. Airport Road, Building A, Suite 205 <br />Longmont, CO 80503 <br />Phone: 303- 651 -1468 • Fax: 303 - 651 -1469 <br />