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<br />Memo to Berhan Keffelew <br />Update -Underground Workings <br />page 3 <br />You also indicated that CC&VG proposes to proceed with the installation of the overlay <br />geogrid in the original locations, even though the location and existence of the suspected <br />underground workings cannot be verified or proven. I am concerned about this proposal. <br />Without completing an analytical evaluation of this proposal, I suspect that the indiscriminate <br />placement of geogrid could be deleterious. If a shaft were incorrectly located, CC&VG might <br />coincidentally install geogrid with the panel edge spanning a shaft opening. If this opening <br />were subsequently to collapse or consolidate, the edge effects of the geogrid could <br />accentuate differential movement and strain, rather than dissipate the distribution of strain <br />upwards towards the critical geomembrane liner. <br />In my opinion it is important that this issue be satisfactorily resolved before CC&VG <br />commences the installation of soil liner material. <br />cc: Bruce Humphreys <br />Jim Stevens <br />Al Sorenson <br />Jim Dillie <br />Doc: CRESUGRD.LTR <br />JP/1P <br />