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Mr. Kevin Basso -2 - 14 August 2002 Ar actually released from the Unit will likely contain a concentration somewhere between the,two end members. 2. The anticipated liner leakage volume on page 11 and 12 of Appendix A is calculated with the following assumptions: four, 1-cm2 holes in the HDPE per acre of landfill; 12 inch head; CCL hydraulic conductivity= 10-7 cm/sec; CCL thickness =2 feet; and saturated flow. Note there is a calculation error in the results as presented and staff recalculated the anticipated leakage volume as 0.0017 ft3/acre/day or 0.0127 gallons/acre/day from the same assumptions. Leachate leakage volume calculations are based on assumptions, some are conservative such as: one foot of sustained head and saturated conditions; others may be optimistic. Actual performance of an installed landfill liner may be somewhat better or much worse in the case of a rip or tear in the HDPE component of the liner. 3. For the Board to approve single composite liners for use at your site, Forward needs to reasonably conclude from the revised expected leachate concentration analysis (issue 1 above) and the leachate leakage volume calculations (issue 2 above) that measurable pollution will not be released to the environment by their landfill design and operations. Sufficient compelling analysis must be submitted that in this specific case a single composite liner meets the intent of the performance standard. 4. The key assumed parameter in the liner leakage analysis is the four, 1-cm2 holes per acre in HDPE liner. Use of this assumption follows the USEPA's HELP3 model and is the apparent industry standard for landfill construction. The four, 1-cm2 holes per acre standard appears to be someone's best guess and assumes nearly perfect construction quality. In order to confirm that the necessary level of construction quality is achieved, Forward Inc. should revise their CQA plans for all future units to include a liner leak test over the entire base liner to be performed after installation of the gravel drainage layer and the operations layer. This will be a final opportunity to detect and repair any rips, tears, or other holes in the HDPE that might have occurred during manufacture, construction or installation of the cover layers. Forward should implement the enhanced CQA procedures proposed in the demonstration during installation of the operations layer on the side slopes. 5. Gas phase transport is an important part of contamination transport at landfills that have releases in the Central Valley. Existing groundwater contamination at the Austin Road facility is predominately associated with landfill gas. Forward Inc. will implement improvements to the existing landfill gas extraction(LFG) system at Austin Road as part of an improved remediation plan. Forward Inc. should include expansion of the LFG system to cover the new cell as part of the construction plan for any future units. 6. Forward Inc. proposes to use a single composite liner that consists of on the base: a prepared subgrade, two feet of compacted clay, 60 mil HDPE, one-foot gravel drainage layer, filter fabric, one-foot operations layer, and a first waste layer composed of selected waste. Landfill sideslopes will be composed of a prepared subgrade, two-feet of compacted clay or GCL, 60 mil HDPE, geocomposite drainage net, and one-foot operations layer. Forward proposes to install a double composite liner tinder landfill sumps, conduct an electric leak test over the sump, conduct CQA inspections during placement of the operations layer and first lift of refuse, and use selected material in the operations layer.