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Waterloo Food & Fuel - 2 - 4 August 2021 3032 Waterloo Road Stockton, San Joaquin County being set at different depths. However, Apex believes that the remaining well network is sufficient to properly monitor the Site plume. In the UST Report, Apex states that review of the Site fueling facility operational fuel logs and recent UST system leak testing indicate no leaks in the current UST system. This review and testing was prompted by the appearance of free product in Site well EW-1 in September 2020. At that time, the sample collected from EW-1 contained 55,000 micrograms per liter (ug/L) total petroleum hydrocarbons as gasoline (TPHg), 6,700,000 ug/L TPH as diesel (TPHd), 470 ug/L benzene, and 1,300 ug/L naphthalene. In the UST Report, Apex also states that the fuel fingerprint analysis from the sample of free product collected from Site well EW-1 "identified chemical components...that would be expected from a sample of free product", but makes no conclusions as to whether the results are indicative of weathered or unweathered fuel. In the UST Report, Apex speculates that an inexperienced fuel delivery truck driver may have accidentally put diesel fuel into EW-1 instead of the Site UST fill port, though provides no evidence to back up this assertion. Due to the localized nature of the elevated diesel impact, Apex proposes to remove free product via batch extraction, and clarified the proposed batch extraction in an email communication on 3 August 2021. Apex proposes to perform three rounds of batch extraction over three consecutive quarters between semi-annual groundwater sampling events, with each round consisting of approximately 300 gallons extracted from each of the extraction wells EW-1 through EW-3 (total 900 gallons extracted per round). Apex will monitor pre- and post-extraction groundwater and free product levels, volume of water and free product removed, and duration of event. The EW wells will be sampled as part of the semi-annual sampling events before and after the batch extractions, with analysis to be consistent with standard semi-annual event analysis. AGI proposed a Site assessment scope of work in a 9 January 2019 workplan, and revised the proposed locations of the soil gas wells in a revised Site map submitted via email on 25 January 2019, both of which are on GeoTracker. Central Valley Water Board staff concurred with the assessment scope of work in a 28 January 2019 directive letter. However, this scope of work was not completed due to the consultant transition from AGI to Apex, and Apex requested that the assessment scope of work be deferred until after the fuel records review and UST leak testing were completed. In the UST Report Apex proposes to complete the approved scope of work. Central Valley Water Board staff partially concurs with Apex's proposals and requests the following: