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s North County Sanitary Landfill -5— Module 5— Module 4-Liner Performance Demonstration San Joaquin County constituents of concern as established in the Water Quality Protection Standard as discussed in Section 1.3 comments. The Report mentions that a limited sensitivity analysis was performed on selected input parameters.. However, the details of this analysis are not presented. The only detail provided is the outcome of increasing the leakage rate from 0.2 gal/ac-day to 2.0 gal/ac-day, in which it was reported that`,`all seven modeled constituents remained well below MCLS." The definition of degradation is any statistical or nonstatistical increase above the WQPS (that is, two or more constituents detected above the MDL or one or more constituent detected above the PQL in the case of non-naturally occurring organics, as per the Standard Provisions). The outcome of the sensitivity analysis for this particular input parameter is therefore evidence of a release. Please perform a sensitivity analysis on all input parameters and provide a detailed explanation of the analysis and impact of the results. Appendix A — Table A-1 Table A-1 shows computed leakage rates for composite liner designs. The alternative GCL liner was computed with"poor" and"good contact,"but the prescriptive liner was only computed with"poor contact." Please provide an analysis of the prescriptive liner with"good contact" for comparison. Appendix D— VLEACH Modeling Table 2 - Please provide an explanation of what these parameters were based on? The foc percentage appears to be high for soils on the eastern side of the San Joaquin Valley based on samples taken at other sites. Please provide the rationale for using the organic carbon fraction of 0.05%. We recommend the County measure the true organic carbon content of the representative soil underlying the site (i.e. at the proposed depth of the base of the landfill). The polygon are of 100 sq. feet should be reduced to one square foot to represent more closely preferred pathways. A sensitivity analysis should be performed on each of these parameters. Appendix E Table 1 —Please include other alternatives for cost comparisons, such as a bottom liner with a double composite system and a pan-lysimeter under drainage systems in the landfill. This would give several other options for liner system cost calculations that could be included in a liner design. In studies done by USEPA it has demonstrated that approximately half of all composite liner leak to some extent. The majority of these problems appear to be either the liner being compromised during construction or poor design. To reduce the risk of holes or rips during construction, as proposed above, some type of electrical testing would be appropriate over the entire liner. In addition, at many landfills the impacts to groundwater appear to be in the gas phase transporting volatile organics compounds to groundwater. It appears prudent to construct and operate a gas collection and control system as the landfill is being filled. With an extensive electrical testing of the liner system, a landfill gas extraction system and addressing our comments in this letter, staff believe we can support a single composite liner to the Board.