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<br />(Page 3) <br />MINE ZD # QR PROSPECTING ID # M-94-117 <br />INSPECTION DATE 10/7/98 <br />3. Install consolidation/settlement monitoring. <br /> <br />INSPECTOR'S INITIALS ACS <br />4. Install granular soil buttress as illustrated in sketch attached to this report. <br />5. When the rate of settlement decreases to an acceptable level, apply liner to dam and <br />buttz~ess, and tie into new liner at interim berm. The design engineer to supply, for <br />Division review and acceptance, a detail on how the liners will be overlapped and joined at <br />the interim berm. <br />The thickness of the granular soil buttress should be designed as follows. Assume that the <br />safety factor of the extant embankment raise is at unity. This is a valid assumption even <br />though the stability analysis for a failure along the tailing/HDPE interface using assumed <br />interfacial shear strengths yields lower safety factors, because the embankment raise has <br />been complete for three weeks and appears to be currently stable. Using a safety factor of <br />one, algebraically determine the interfacial shear strength, and using the shear strength so <br />determined, design a buttress with sufficient weight to increase the safety factor to 1.2. <br />A bu'=tress so designed would remain in place and have the liner system applied over it once <br />the I~rimary consolidation of the tailings under the buttress has been achieved. The Operator <br />maychoose to speed the tailing consolidation by installing a thicker buttress than required <br />for a safety factor of 1.2, then stripping the excess soil from the buttress after primary <br />consolidation. The Operator will provide a design based on the conceptual overview contained <br />in this report, and the design provided will be subject to Division review and approval. <br />The following additional observations were made during the course of this inspection: <br />1. The Operator was using a small front-end loader to transport scalped tailing to the back <br />(upstream end) of the pond, and dumping the tails at the edge of the lined area. The dumped <br />tailings would then slide down the liner to the bottom of the pond. The Operator must <br />exercise care and diligence to assure that no rocks are dumped into the pond with the <br />tailings as damage to the liner could result. The Operator must also assure that the tailing <br />slicing down the liner does not result in liner wrinkles that fold over. <br />2. The plan approved in technical revision TR-03 discusses installation of silt fence at the <br />toe of the emban)anent as needed. No silt fence has been installed up to this point. If the <br />doom stream face of the dam is not seeded prior to winter, silt fence will have to be <br />installed in order to be prepared for spring precipitation and snowmelt. The silt fence <br />would be required along the entire toe of the dam and must be properly installed by keying <br />and burying the fence into a trench. <br />cc: Carl Mount, DMG <br />I & E Contact Address <br />NAME Maxine Stewart <br />OPERATOR ITEC Environmental Colorado. Inc. <br />STREET 707 17th St., STE. 3120 <br />CITY/STATE/ZIP Denver. CO 80202 <br />[] CE <br />~ BL <br />[] FS <br />^ ~ <br />~ HMWMD (CH) <br />~ SE <br />~ WQCD (CH) <br />~ OTHER <br />