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2018 ANNUAL GROUNDWATER MONITORING REPORT FORMER KEARNEY—KPF FACILITY-STOCKTON,CALIFORNIA MDL in a few shallow wells outside the Trigger Boundary. In the deep zone, concentrations of 1,4-dioxane remain below the detection limit. While the treatment system was not operating for the rebound study, concentrations of PCE, 1,1-DCE, and 1,4-dioxane in shallow zone well TP-1A fluctuated to levels higher than the lows achieved prior to stopping extraction. Once the treatment system was restarted in January 2015, concentrations of PCE and 1,1- DCE decreased to levels similar to or less than those observed before the treatment system was shut down in 2012. As of October 2018, most concentrations have decreased or remained the same since the treatment system was restarted in January 2015 and since pulsing of the treatment system began in January 2018. 4.3 Discussion of Remediation Progress The ongoing quarterly water level monitoring that has occurred since 1992 has demonstrated that groundwater extraction from wells in the intermediate zone at the site established and effectively maintained hydraulic gradients that contained migration of the constituent plumes. Further,the extraction system has reduced contaminant mass by orders of magnitude by drawing contaminated groundwater from the shallow zone downward into the similarly contaminated intermediate zone for subsequent capture by intermediate zone wells and destruction in the on-site treatment system.Accordingly,water quality hydrographs for the shallow zone and intermediate zone wells indicate that substantial remediation progress has been made, with all wells currently achieving or very nearly approaching the CLs(Appendix G and Appendix H, Water Quality Hydrographs, Zone vs. Constituents). In early 2012, after review of the data and evaluation of treatment system costs, Kearney proposed and DTSC approved a rebound study that entailed shutting down the extraction system but continuing to monitor to assess whether concentrations would rebound in the sustained absence of pumping. In addition, Kearney and DTSC agreed on additional, more frequent sampling of certain wells to test for plume expansion or migration during the study.The sampling would place particular focus on the deep zone, which is a drinking water source and in which there has been no detection of COCs for many years. The treatment system was shut down between March 2012 and January 2015. During that time, there was no reappearance of COCs in the deep zone. There was also no indication of plume expansion or migration in the intermediate zone. As discussed previously, CDCs increased in a few shallow zone wells. The treatment system was operated full time between February 2015 and December 2017. Because concentrations of most CDCs at the site are very low and have been for some time, Kearney proposed operating the treatment system in a pulsing mode to increase the efficiency of mass removal.This was approved in the permit with the understanding that the "on" pulses of the treatment system will be as long as the "off' pulses and that the treatment system will not be off for more than 3 months at a time. Because groundwater sampling occurred in Q2 and Q4 of 2018,and there are certain extraction wells that are part of the monitoring program, Kearney turned the system off in Q1 and Q3. The discussion below more fully characterizes the positive remediation progress at this site, with specific details regarding COCs that are detected in the shallow and intermediate zone wells. The deep zone is not discussed further, because concentrations have consistently remained below the CLs at undetectable levels for many years. D U D E K 10886-1 15 March 2019