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2015 Annual Correctie Action Evaluation Report Austin Road Unit. Forward Landfill – Manteca California Page 2 concentrations at individual corrective action monitoring wells. An exceedance of a TVOC concentration TL would be suggestive of potential increasing VOC concentrations at that particular well. The TVOC mass TL and individual well TVOC concentration TLs are summarized on Table 1. In order to evaluate the effectiveness of corrective action at the ARU, this report evaluates groundwater monitoring results from the past four quarters-4hird quarter 2014, fourth quarter 2014, first quarter 2015, and second quarter 2015—based on the criteria listed above. Previous Annual Corrective Action Evaluation Reports submitted in 2002 through 2014 have confirmed the ongoing effectiveness of the ARU's corrective action measures. Tables 2 through 5 present a summary of the VOC groundwater monitoring results from the past four quarters, including the TVOC concentration for each well. Estimated (trace) detections of VOCs between the laboratory reporting limit (RL) and method detection limit (MDL) are presented on Tables 2 through 5, but such trace detections are not included in the calculation of TVOC concentrations. In the third quarter (August) 2014, domestic supply well 8106-A exhibited a detection of acetone at a concentration of 750 ug/L. This detection was not confirmed during the subsequent monitoring event in the fourth quarter (November) 2014. Although acetone was not detected in a field blank, trip blank, or laboratory method blank associated with 8106-A in August 2014, acetone is an established laboratory contaminant that has previously been observed in ARU groundwater samples. For example, acetone was detected in AMW-12 in May 2012 and was also detected in a lab method blank and field blank. Given that the detection was not confirmed and that acetone is an established lab contaminant, the August 2014 acetone detection at 8106-A was not included in the TVOC calculation for that event at that well In an August 19, 2005 letter, the RWQCB specified that future Annual Corrective Action Evaluation Reports shall include: • A discussion of the landfill cover, including any performance issues from the previous year, • A summary and discussion of the previous year's monitoring data from the facility's landfill gas monitoring system and landfill gas extraction system; • A comparison of the previous year's groundwater monitoring results to computer simulations originally presented in the August 6, 2001 Revised Engineering Feasibility Study; and • A discussion of the overall corrective action progress, including any proposed enhancements to the program. The RWQCB later incorporated these requirements into Section B.5 of the M&RP. These requirements are addressed in Sections 4, 5, 6, and 7, respectively, of this report. 1.0 TVOC Mass Isoconcentration maps of groundwater TVOC concentrations for the past four quarters—third quarter 2014, fourth quarter 2014, first quarter 2015, and second quarter 2015—are presented in Figures 1 through 4. Consistent with the Evaluation Procedures Report, these maps utilize a contour interval of 25 ug/L and do not include contouring for concentrations less than 1 ug/L. For each quarter, the TVOC mass was estimated using the following procedures: • The TVOC mass between each pair of isoconcentration contours was first estimated by multiplying the average TVOC concentration between those contours by the assumed aquifer HEIST & ASSOCIATES, INC