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2015 Annual Correctie Action Evaluation Report Austin Road Unit. Forward Landfill — Manteca California Paee 4 second quarter 2015. There were reportedly no notices of violation (NOVs) issued to the facility for cover -related issues from the third quarter 2014 through second quarter 2015. 5.0 Landfill Gas Monitoring Results The gas collection and control system at the Forward Landfill complex includes 194 extraction wells, a flare for thermal destruction (Flare A-2), a backup flare (Flare A-1), and a methane gas recovery facility that generates electricity. The Forward Landfill complex includes 27 perimeter landfill gas monitoring probes spaced 1,000 feet apart, pursuant to Title 27 of the CCR These probes include multi-level monitoring of shallow and deep intervals. Several of the probes also include monitoring of a medial interval. Combined, the perimeter monitoring system includes 77 individual monitoring points, plus additional temporary gas probes. Thirteen of the 27 permanent probes are located around the perimeter of the ARU: GP -13 through GP -25. These 13 probes comprise 39 of the complex's 77 individual monitoring points: Landfill gas sample results for the third quarter 2014 through second quarter 2015 at ARU are provided in Appendix C. These results were provided by SCS Field Services (SCS). ARU gas monitoring probes GP -13 through GP -25 are monitored quarterly for methane, carbon dioxide, oxygen, balance gas, and static pressure. Landfill gas results are generally consistent from quarter to quarter at the ARU. Methane was not detected in any of ARU monitoring probes above a concentration of 0.2% during the third quarter 2014, fourth quarter 2014, first quarter 2015, or second quarter 2015. Given the consistency of the gas monitoring probe data over the past year and the lack of detectable methane above 0.2%, it can be concluded that the gas collection system continues to operate effectively. Information supplied by the facility indicates that several enhancements to the landfill gas extraction system have been made in the past thirteen years. These include the installation of additional landfill gas extraction wells, plus the installation of a soil vapor extraction system and temporary gas probes along the western edge of the Forward Landfill. 6.0 Comparison of Current to Modeled Groundwater Quality The August 8, 2001 Revised Engineering Feasibility Study for Austin Road Landfill (hereafter, EFS) presented projected isoconcentration contour maps for select VOCs in groundwater based on computer modeling simulations. These simulations projected how the concentrations of individual VOCs could potentially change following the initiation of recharge within the artificial basin. The EFS presented projected maps corresponding to each year following the initiation of recharge, for up to nine years. The four VOCs that were modeled were tetrachloroethene, trichloroethene, cis-1,2-dichloroethene, and vinyl chloride. In past Annual Corrective Action Evaluation Reports, these projected isoconcentration maps were compared to maps based on contemporary data, collected from the same monitoring wells utilized in modeling. However, the EFS simulations projected that none of the modeled VOCs would be detected above 1 ug/L after nine years of recharge. Use of the recharge basin was initiated in May 2003, and the May 2015 results therefore correspond to approximately 12 years after initiation of the recharge basin. Accordingly, there are no projected isoconcentration maps available for comparison to current results. For reference purposes, this report presents current isoconcentmtion maps for the four modeled VOCs. These maps are based on second quarter (May/June) 2015 monitoring results and are presented in )�,IST & ASSOCIATES, INC