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Prior top lacement of the final cover, the header system will be removed. In order to minimize interruption of the system operation, the header will be removed in phases with each phase re -installed and made operational prior to removal of the next phase. Any affected wells will be disconnected prior to removal of the header. Headers can be re -installed if the integrity of the pipe remains intact and if it can be adjusted to a positive grade. Otherwise, the pipelines must be replaced. The main header system will remain on-line during the entire construction period. Any deep or shallow vertical gas collection wells in place at closure will be protected during the placement of the final cover since control of landfill gas must continue during cover construction. The top of the vertical or horizontal wells will be extended through the final cover and then reconnected to the lateral header line as before. Any damaged or non-functional vertical wells will be abandoned and new replacements installed to provide gas extraction coverage. Final cover material will be placed and compacted by hand around the wells or vaults to protect against damage by earthmoving equipment. The condensate will drain along the subheaders and main headers to collection sumps. When the headers are re -installed after final cover construction they will again gravity drain back to the collection sumps. 3.9 LANDFILL GAS MONITORING SYSTEM 27 CCR, Section 20925 requires that subsurface gas monitoring wells (probes) be installed as part of closure around the perimeter .of the landfill within the property limits but outside the limits of refuse with a spacing of approximately 1,000 feet. As discussed in Section 2.1 Lthe existing gas migration monitoring system consists of 18 probes located as shown on Drawing 13 of the )TD. As part of closure, the existing probes will be protected in place. 3.10 GROUNDWATER/SURFACE WATER MONITORING SYSTEM Groundwater monitoring programs are currently being implemented on a quarterly basis at the existing Forward and Austin Road Landfills, as discussed in Section 2.2. Figure 2 shows the location of the existing groundwater monitoring wells. This monitoring network may later be expanded during the active landfill life and will be maintained throughout the post -closure period. Forward Landfill PCPCMP 3-13 L:\Allied\2000.193\Reports\FinaIPCPCMP:FL-sec3: 8/20/01 BRYAN A. STIRRAT &. ASSOCIATES