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Second Semi-Annual 2021 Groundwater Monitoring, Batch Extraction Results Report & Supplemental Site Investigation Waterloo Food and Fuel 3032 East Waterloo Road, Stockton, California Page 9 RECOMMENDATIONS Apex has completed the required monitoring per CVRWQCB as requested in the August 2021 letter (Appendix A). An assessment of the condition of each of the groundwater monitoring wells found that the CMT wells are by in large degrading. The degradation in this instance is indicated by a loss in the vertical angle of several of the chambers of some of the CMT wells. This loss of vertical angle is making it more difficult, and in some cases not possible to obtain water/liquid level and collect samples. However, after a review of the groundwater, elevation data collected from the monitoring wells associated with the Site, along with an assessment of the condition of the wells, Apex concludes that the well network is continuing to function in a manner that provides for an effective monitoring program. This assertion is made after review of the groundwater elevation data from the remaining wells and the zones they represent (shallow zone, mid zone, and deep zone). There are multiple functioning wells remaining that are screened in each of the three zones. Apex recommends no changes in the current groundwater monitoring network currently. If multi-levels of groundwater monitoring are going to persist, some of the CMT wells may have to be replaced as the channels continue to degrade. Historically, TPHd has not been analyzed in the groundwater monitoring events associated with the Site. TPHd appears to be generally concentrated in the vicinity of the USTs and EW-1 and EW-2. Apex has implemented the portion of the AdvancedGeo Environmental, Inc., Additional Site Assessment Workplan, dated January 9, 2019 as directed by the CVRWQCB August 2021 letter (Appendix A). The results of the seven soil borings indicated that the release indicated by the historical piping samples is no longer present at detectable concentrations. None of the 14 samples collected as part of the Workplan implemention revealed concentrations of constituents of concern exceeding the laboratory detection limits. Based on these findings, soil samples will support a future Low Threat Closure Request. The next semi-annual groundwater monitoring event for this Site will be performed in the first quarter 2022 after the final two batch extraction events. Based on a review of the groundwater quality data review at the end of the first quarter 2022, Apex anticipates that a Low Threat Closure Request will be submitted in Spring 2022.