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<br />Memo to Berhan Keffelew <br />CRESSON AM#7 Geotechnical Findings <br />page 3 <br /> <br />standard frequency testing determined either non-compliance with the specified permeability <br />limit (1.0 x l0" cnm/sec) or approaches that limit. CCRV has conunitted to conducting an extra <br />pernmeability test on a sanmple collected witlmin a ten foot radius of the first sample, if the original <br />result is higher than 9.0 x ]0' cnm/sec. This extra "10-foot radius" permeability test must meet <br />the specifications of < 1.0 x ] 0'° cnm/sec. Further, if a test on any x,000 cubic yard [es[ interval <br />tails (i.e., shows a permeability of >_ 1.0 x ]06 cm/sec, CC&V will conduct 4 additional tests <br />evenly spaced over the surface area of the 5,000 cubic yard testin, interval (e.g., in each of the <br />four quadrants). Each of these four tests must meet specifications (< LO x ] 0-6 cm/sec) and <br />testing tnus[ be re-performed on soil liner fill amended in the area of any failed [est. If any of the <br />four additional tests fail, the entire sequence will be repeated. <br />Squaw Gulch Overburden Storage Areas <br />CC&V submitted the required stability analyses for expanded overburden storage facilities in <br />Squaw Gulch. Upon initial review, the Division indicated tlmat the projected factors of safety of <br />several of the analyzed cross sections appeared to be inadequate to satisfy Division policy under <br />either pseudo-static or static conditions. However, Golder Associates had completed the pseudo- <br />static analyses assuming the previously approved seismic Peak Ground Acceleration (PGA) of <br />0.148. The Division subsequently found that a revised PGA of 0.08g would be appropriate for <br />application to pseudo-static analysis of the overburden storage areas. Upon recalculation, the <br />pseudo-static Factor of Safety (FOS) were found to be acceptable. <br />CC&V disagreed with the Division's policy choice regarding our preferred static and pseudo- <br />static slope safety factors for operational and reclaimed slope configurations. CC&V requested <br />that the Division modify its policy in this instance based upon several justifications. CC&V <br />observed that because the CRESSON overburden storage areas are not placed within <br />containment structures such as lined pads that lower factors of safety are warranted and <br />acceptable. Further, CC&V obseted that experience at the site using the same design criteria <br />demonstrate [he propriety of the design and constructiotm techniques. Finally, Golder Associates <br />has demonstrated [hat tlme Division's policy factor of safety requirements have been met in every <br />instance analyzed except for cross-section C-C' ttuough the Lower Squaw Gulch Overburden <br />Storage area, for which a static slope safety factor of 1.4 has been determined. <br />In consideration of CC&V's request and its justification presented in response to the Division's <br />adequacy concerns, the Division is persuaded to grant a variance in this one instance. In <br />accordance with Rule 6.5, "GEOTECHNICAL STABILITY EXHIBIT", subsection (3), the <br />Office finds, based upon the high degree of certainty of soil and rock determinations utilized in <br />the stability analyses, the relatively low risk to property and human safety represented by a <br />failure of this storage area, and the recent slope performance experience at this site, that a <br />