Laserfiche WebLink
<140//-Pa <br />TETRA TECH <br />July 26, 2011 <br />Ms. Kristen Fienberg <br />Lggal Department <br />vrowerCo <br />RE: Response to TowerCo's Iverson Mine Stability Analysis Questions <br />Dear Kristen: <br />As requested, we are following up to respond to the questions you posed in your email to us dated <br />July 25, 2011. Below is a listing of each of your comments followed by our response in italics. <br />1. We did receive a response from Lafarge in February (also attached), which included an <br />updated Stability Analysis Report and cover letter from Tetra Tech dated February 7, 2011 <br />( "TT Letter "), which purports to address the concerns raised by TowerCo in our response <br />letter, but the response was wholly inadequate and did not address 90% of our concerns. <br />To be more specific, Paragraph 3 of the TT Letter states that original report was <br />prepared to "satisfy Division of Reclamation, Mining and Safety (DRMS) standards <br />which require us to use conservative parameters "; however, Paragraph 4 of the TT <br />Letter states "we adjusted the stability analysis model to use more realistic parameters ". <br />I'm unclear as to whether we should now assume that the new Stability Analysis <br />Report is out of compliance with DRMS standards? <br />The Stability Analysis Report approved by the DRMS is not out of compliance with DRMS <br />Standards, otherwise the DRMS would not have been able to approve it. <br />2. Paragraph 4 of the TT Letter also states "the bedrock strength was adjusted to correspond to <br />a more realistic strength "; however, no basis is provided to substantiate these parameters. If <br />these new parameters were the result of a soils /rock exploration report, we should be <br />provided with a copy. If not, we should be informed as to how these adjustments <br />were justified. <br />Our analysis was based on the attached borelogs for the site and our engineering geologists' <br />extensive experience with similar materials throughout the area. <br />3. Paragraph 4 further states "the mining cell depth was adjusted to its actual proposed <br />depth of 19' near the TowerCo tower, and a more realistic slope of .75:1 <br />(Horizontal:Vertical) at the mine's high wall was used ". TowerCo will require a site plan <br />and topographic drawing(s) showing the final mine depth and slope similar for <br />illustration and our consideration. <br />Attached is a copy of the DRMS approved Mining Plan for Iverson Mine. <br />4. Paragraph 5 states: "the factor of safety information [TowerCo] reference is unrelated to the <br />Stability Analysis report that we prepared ". Again, as the site owner, it is not in TowerCo's <br />interest to accept limits lower than minimum code requirements for the mine wall compared <br />with tower foundation. <br />1900 S. Sunset Street, Suite 1 -F Longmont, CO 80501 <br />Tel: 303.772.5282 Fax: 303.772.7039 <br />www.tetratech.com <br />