2010-06-08_INSPECTION - M1977424

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Page 2 June 4, 2010 transducer installed in the vault. WWL reported the results of monitoring observations to the DRMS, BLM and CDPHE via email. The record of these email transmissions is provided in Attachment A. The weekly inspections of the pond detection system and electronic pressure transducer data from the detection vault showed that flow into the vault from the detection system pipes ceased on February 19'h, 2010. It is estimated that a total of 8,000 gallons of water was pumped from the vault into the pond. As stated in the notification letter, the key corrective action proposed by WWL was to conduct a thorough inspection of the liner. Because flow into the vault ceased, it was suspected that the liner leak was near or on the slope of the liner and that such a leak would have introduced a transient volume of water to the leak collection system during the 2009 high water period for the pond. The fact that water was no longer entering the vault indicated that water at current levels, which inundated approximately 95 percent of the bottom of the pond with 6 to 12 inches of water, was not contributing to leakage through the liner. As outlined by WWL in the notification letter, WWL conducted several inspections of the liner slope and portions of the pond bottom prior to liner repairs. Each survey was progressively more thorough than the previous survey and all observed holes or cracks were marked for repair. The surveys resulted in the delineation of 6 holes or cracks in the lower portion of the liner slope. One such hole was a two- inch cut that appeared adjacent to a liner joint weld in the northeast corner of the pond. This corner is slightly elevated and was above the water line at the time of the survey, but the corner would normally be submerged during high water periods (spring runoff and high rainfall in August). Three holes in the liner were apparently due to impact events of an unknown origin that caused very small (less thanY2- inch long) puncture-like openings. The other two cracks located at low-elevations on the liner were due to old welds that had broken open near the gauging station and spillway. Virtually all other cracks were well above the normal high water line and were associated with former old welds that had reopened; some of these were near the anchored portion of the liner. All observed holes or cracks were repaired by a professional liner repair contractor, H&H Environmental, Inc., on April 14, 2010. During the repair work, the liner contractor specifically mentioned that the liner was in good condition. The DRMS Inspection Report states that the required corrective action is "to replace the HDPE liner within 180 days of this inspection report, which is September 28, 2010." The report also states that "Other options that will minimize disturbance to the hydrologic balance will also be considered by DRMS." OOSI recognizes that the existing HDPE pond liner, installed in 1984, is beyond its typical life expectancy of 20 years. As you are aware, OOSI submitted Amendment No. 1- Water Transmission Pipeline and Evaporation Pond, in August 2006, and DRMS approved OOSI's request for a 10-year extension of the reclamation period beginning August 5, 2008. It is our understanding that it is the preferred goal of DRMS that OOSI reclaim the Evaporation Pond and that manage the retort water discharge by other methods. OOSI is currently monitoring the quality of the retort water that discharges into the Evaporation Pond, and investigating other means to treat or manage the retort water discharge. Constituents that are particularly problematic are the relatively non-reactive elements of boron, potassium, sodium, and the compound of sulfate. As an alternative to replacing the HDPE liner at this time, OOSI proposes to continue monitoring of the Evaporation Pond leak detection system and the liner repairs made in April. If the hypothesis of a liner leak being located at the toe of the liner is correct and the liner repairs are successful, no further leakage TMarshaII052410.doc