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C~ Memo to Larry Oehler 6 October 24, 1993 flaw exists, or develops in the liner. Such a flaw could be the result of an installation blunder that was not detected through the QA/4C program, tearing of the liner during ground motion caused by an earthquake, or by a number of other mechanisms. I would recommend that the operator be required to achieve the worst case permeability for Type 2 material referenced in the design documents throughout Phase II of the facility. Preliminary testing indicates that none of the drainage layer material placed to date will meet this permeability criterion; the operator may find it necessary to import drainage blanket material from off- site, not only to complete the liner cover operation, but also to replace the liner cover already installed. Demonstration that minimum hydraulic conductivities of 5 x 10_4 cm/sec have been achieved within the drainage layer should take the form of one laboratory scale permeability test per acre of installed liner. Failing tests may be indicative of a need to increase the testing frequency. Another concern with construction of the Phase II ling, is with the long term exposure of the liner cover/drainage layer material to the elements. Harry Posey noted during a site visit during the spring of 1992 that geomembrane was exposed in several locations where liner cover had eroded or sloughed off (memo frmm posey to Humphries dated 4J24/92). At that time, Mr. Ron Zumwalt of BMRI stated that the exposed liner would simply be covered over by tailing, with no repair to the missing liner cover. My conversations with mine site personnel since that time indicate that proper liner cover maintenance has now been made a priority. Liner cover maintenance should be an on-going inspection topic for the Division. This should include inspection to assure that no plants with any significant root development are allowed to volunteer and grow on the liner cover. Rooting plants have been known to puncture synthetic liners. The Division staff that completed the original design review for the tailing impoundment recommended approval of a facility that incorporated a number of redundant design features to assure minimal environmental impact or loss of containment. Among the notable features touted as achievable in the original design documents are: 1. A high quality composite liner. 2. A drainage layer that would minimize head on the liner. This would reduce seepage to an inconsequential level through the small flaws that can be anticipated in any synthetic liner installation, and would also minimize seepage in the case of an unanticipated flaw or rupture of significant dimension.