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t r Apparently suitable soils will be further characterized by: • Standard Proctor test(ASTM D698) • Saturated hydraulic conductivity(ASTM D5084) • Soil water characteristics curve (SWCC) (ASTM D6836), Methods A and D applicable to coarse grained soils. C. Preliminary calculations to determine likely thickness of ET cover,using the results of the above tests on suitable soils. • Confirming or adjusting the ET cover thickness once the likely thickness is established using for 5-year simulation. This simulation will use the five wettest consecutive winters measured over the last 50 years, if information is available. The above work will result in the criteria that will be used to compare an ET cover with a prescriptive cover. The County will then compare the cost of the ET cover to a typical engineered alternative closure (two-foot foundation layer, GCL as barrier layer, one-foot vegetative layer). If the cost of the ET cover is favorable and if the study demonstrates acceptability in accordance with RWQCB acceptance criteria, then the County will submit this evaluation for RWQCB review. 3. Landfill Gas (LFG) System LFG will be collected directly from the refuse of Module"I" because Module "I" is unlined: The final design features will be prepared by the consultants selected for the work. In general, the LFG system will be subject to the approval of a request for Authority to Construct submitted to the APCD by the County. Design criteria contemplated at this time are: A. Location of Collectors • Vertical wells will be installed on flat areas and adjacent to access roads where drill rig access is possible. Vertical wells will not be installed where Module 1 liner extension will be placed. •. Horizontal collectors will be installed under Module 1 liner extension,based on the use of an HDPE membrane or equivalent in the Module 1 liner extension design. B. Vertical Well Depth • Two-thirds of the depth of refuse fill in deep areas,not less than 65 feet deep • Under no circumstances deeper than 10 feet above the bottom of the refuse fill C. Vertical Well Spacing: Radius of influence assumed to be not less than three times the well depth; therefore, spacing between wells will be approximately six times well depth. Spacing of wells will be adjusted to conform to landfill configuration. Foothill Sanitary Landfill Site Improvement 3 Department of Public Works/Solid Waste Revised March 12,2004 County of San Joaquin