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2016 Corrective Action Evaluation Report - Austin Road Unit Forward Landfill In addition, the Forward Landfill 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. 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. Quarterly landfill gas sample results for ARU are provided in Appendix C. These results were provided by SCS Field Services (SCS). ARU perimeter gas monitoring probes were monitored quarterly for methane, carbon dioxide, oxygen, balance gas, and static pressure. Quarterly results are generally consistent from quarter to quarter at the ARU, and methane was not detected in any ARU perimeter monitoring probe above a concentration of 0.1% during the monitoring period. Given the consistency of the perimeter gas monitoring probe data over the past year and the lack of detectable methane above 0.1%, it can be concluded that the gas collection system continues to operate effectively. Forward continues to enhance the landfill gas extraction system including the installation of additional landfill gas extraction wells, the installation of a soil vapor extraction system and regular maintenance and adjustments of the LFG well field by SCS. 9 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 PCE, trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), 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 µg/L after nine years of recharge. Use of the recharge basin was initiated in May 2003, and the May 2016 results therefore correspond to approximately 13 years after initiation of the recharge basin. Accordingly, there are no projected isoconcentration maps available for comparison to current results. Consistent with past Annual Corrective Action Evaluation Reports, isoconcentration maps presented in Appendix D are for the four modeled VOCs using the second quarter monitoring Project No. 2016.0007 1 2016 Corrective Action Evaluation Report - Austin Road Unit 5 Forward Landfill