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Mr. Timm Comer <br />Manager. Environmental Resources ame& <br />Proposed SLF Specification Changes <br />July 20, 2010 <br />Given the observed trends in Figures 2 and 3, it is important to note that all permeability testing <br />is done at the MDD and OMC for the SLF sample (based on the frequency of sampling and <br />testing set forth in Amendment No. 9). When the SLF is sampled, it tested for grain size, <br />atterberg limits, compaction (moisture-density) and hydraulic conductivity (at the MDD and OMC <br />determined from the compaction test. When the SLF is placed, it is tested in-situ for MDD and <br />OMC, to make sure the SLF is compacted to the proper level to meet the hydraulic conductivity <br />specification. <br />The current Technical Specifications require in-situ testing of the SLF permeability, one test for <br />every 5,000 cubic yards (Table 2, Section 1400.1). In the Implementation of this specification, <br />SLF is placed and compacted, tested for density and thickness, then a sample is take for <br />permeability testing. Until the SLF permeability can be tested and verified, the area cannot be <br />covered with geomembrane and is exposed to the environment. The time required to complete <br />the permeability test varies between 1 to 2 weeks (AMEC does the testing on-site to minimize <br />the required testing time). During this period of time, the SLF is exposed to several drying and <br />wetting cycles and, in the monsoon season, heavy downpours. These conditions can damage <br />the SLF, requiring reworking and moisture conditioning, and in some cases complete <br />replacement. While reworking the SLF is done at CC&V, the quality of the re-worked SLF (even <br />though it meets the specifications), is not as good as fresh SLF. <br />In order to preserve the high quality of fresh SLF, AMEC proposes changing the requirement for <br />in-situ permeability testing of the SLF to testing the SLF stockpiles at a rate of one test per <br />4,000 cubic yards (Proctor compaction, particle size, and atterberg limits would also be <br />completed in the stockpile at one test per 4,000 cubic yards). Density and thickness testing <br />would still be done in-situ at a rate of one test per 5,000 cubic yards placed. Testing of the <br />stockpiles will allow the SLF permeability to be checked prior to placement. Once the SLF is <br />placed and compacted (density and thickness tests completed and passed), it can be covered <br />by geomembrane liner. This will preserve the quality of the SLF and prevent damage that can <br />occur after placement. Increased testing rate in the stockpiles will allow AMEC to monitor any <br />changes in the SLF character prior to placement in the VLF, the in-situ density testing will verify <br />proper compaction. <br />AMEC believes these proposed changes to the SLF specification will not affect the performance <br />or solution containment of the VLF. <br />If you have any questions or comments, please contact me at (303) 433-0262. <br />Sincerely, <br />AMEC Earth & Environmental, Inc. <br />John F. Lupo, Ph.D., P.E. <br />Principal Engineer <br />MACINTOSH HD:USERS:.ILUPO:D000MENTS:CC&V:SLF LETTER:SLF spec IeRerdoc 5