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Chevron -2- Alden 2 - Alden Park Tracy, San Joaquin County 26 May 2021 The samples collected from wells MW -7 and MW -21 were analyzed for TPHd following silica gel cleanup (SGC) sample preparation since the samples from both wells exceeded the reporting limit for TPHd. Both the primary and duplicate samples collected from well MW -21 were detected at concentrations of 160 pg/L for TPHd following SGC. The sample collected from MW -7 did not exceed the reporting limit of 50 pg/L following SGC. • The reductions in TPHd concentrations in samples following SGC indicate that natural attenuation is likely occurring in the groundwater beneath the Site. • Floating petroleum product is removed from eight wells using vacuum extraction and/or absorbent socks on a quarterly basis. • The SPH thicknesses reported for the December 2018 and September 2019 SPH monitoring events ranged from 0.01 to 6.78 feet • Approximately 58 gallons of petroleum product was removed between May 2020 and February 2021. Since product removal was initiated in April 1997, approximately 1,926 gallons have been removed. Arcadis recommendations: Continue quarterly SPH recovery at monitoring wells exhibiting measurable SPH using a vacuum truck and/or absorbent socks, from wells MW -1, MW -3, MW -5, MW -6, MW -15, MW -16, MW -18, and MW -20. Continue annual groundwater monitoring and sampling of monitoring wells where SPH or a hydrocarbon sheen is not detected using HydraSleeves or another no - purge sampling device, from wells MW -4, MW -7 through MW -10, and MW -21. Submit groundwater samples for analysis of TPHd. Groundwater samples reported to have TPHd concentrations greater than the reporting limit will also be submitted for TPHd analysis following SGC. Comments According to information in the Report, SPH thicknesses in the wells were last reported in September 2019. Arcadis states in the Report that the next SPH thickness monitoring event is tentatively scheduled for September 2022. The MRP requires product thickness to be reported annually for Site wells and failure to report the data is considered a violation. Product thickness for 2021 needs to be measured and submitted for review. Removal of floating petroleum product should continue on a quarterly basis. Annual groundwater monitoring and sampling of all monitoring wells should continue in accordance with the MRP. Staff concurs with the recommendations in the Report, with the comments noted above. By 15 September 2021, please submit the results of the product thickness measurements. By 1 May 2022, please submit the 2022 annual groundwater monitoring report.