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<br />• A minimum 3:1 setback should be maintained from the edge of the shoulder or embankment of <br />any of the public roads around the site perimeter such as Highway 36, Hygiene Road, and 61" <br />Street <br />• A minimum setback from the edge of the pit to the high water elevation of Foothills Reservoir <br />must be maintained at 200 feet unless the applicant provides a more sophisticated stability <br />analysis including an analysis of seepage and pore water pressure to demonstrate that a lesser <br />setback would be stable. From [he maps provided, it does not appear that maintenance of a 200- <br />foot setback from the reservoir will cause the Operator a hardship. <br />• Maintenance of a 3:1 mining setback from the water conveyance ditches on site will be adequate <br />to protect the ditches from any structural instability. However, dewatering and excavation at a <br />horizontal distance three times the excavation depth from a flowing ditch may increase seepage <br />loss from the ditch. The Rocky Mountain Consultants letter included in Exhibit G to the <br />application discusses possible mitigation for increased seepage from ditches, but no concise <br />mitigation plan is provided. <br />• Map Exhibit C-1 shows a number of underground utilities without specifying the type of utility <br />present. The applicant must specify if the buried utilities include any gas pipelines, sewer lines, <br />or critical water supply pipelines as these types of utilities would require specific protection in <br />addition to the proposed 3:1 setback. Typically, the Division would require installation and <br />monitoring of strain gauges on pipelines prior to and during mining within 200 feet. <br />45. [t is recommended that the applicant be directed to provide a concise mining setback and structural <br />protection plan for this project. The plan should specify which structures, including but not limited <br />to buildings, ditches, drains, utilities, roads, and fences, that are not 100 percent owned by Western <br />Mobile will be removed or relocated during the operation of the pit and should provide written <br />agreements for the removal or relocation of the structures. The plan should describe how the 3:I <br />setback distances to structures will be determined. For example, the setback to roads should be to <br />the edge of the shoulder or embankment. The setback to ditches should be to the top of the ditch <br />bank. The plan should specify that underground utilities will be located and mazked before mining <br />encroaches within 105 feet of the right-of--way line or should maintain the 3:1 setback to the right-of- <br />way. A specific statement should be provided on the setback to the Foothills Reservoir. A plan for <br />strain monitoring should be provided if there aze any critical buried utilities within 200 feet of the <br />proposed mining perimeter. <br />Other Issues <br />46. The Division received a letter from the Department of the Army, Corps of Engineers regarding the <br />Lyons Pit Permit Amendment. Attached is a copy of the letter. <br />47. The Division has received one objection to the amendment from the St. Vrain Valley Community <br />Watchdogs on August 15, 1999. The Division forwarded the letter to the applicant and Michael Hart <br />of Hart Environmental on August 24, 1999. Western Mobile Boulder responded to the comments on <br />August 30, 1999. <br />9 <br />