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Meeting Notes May 13, 2020 Subject/Client: Tosco/Unocal #05643 1502 El Dorado St, Stockton Ref. No. 11193145 Central Valley RWQCB Case #391068 From: Morgan Hargrave Tel: (530) 387-5712 Venue/Date/Time: Teleconference Copies To: Central Valley Regional Water Quality Control Board Attendees: Vera Fischer / Christopher Flower Ryan Bast / Morgan Hargrave On May 13, 2020, GHD hosted a teleconference meeting to discuss current site conditions and the path to case closure. Attendees included Vera Fischer and Christopher Flower from the Central Valley Regional Water Quality Control Board (CVRWQCB), and Ryan Bast and Morgan Hargrave from GHD. Topics discussed during the meeting are summarized below. MW-24 Analytical Results New B' Zone monitoring well MW-24 was installed to the east of the site to provide additional delineation to define the extent of the release to water quality objectives (WQ0s) in the 13' Zone. Concentrations of TPHg (870 pg/L), benzene (78 pg/L), MTBE (43 pg/L), and 1,2-DCA (4.8 pg/L) were detected above WQ0s, indicating the B' Zone plume may not be defined. Further sampling events are required to confirm the initial concentrations. 1,2-DCA Concentrations and Delineation In a letter dated March 26, 2020, CVRWQCB staff requested that 1,2-DCA plume maps be included in future groundwater monitoring and sampling reports. 1,2-DCA plume maps were included in GHD's April 16, 2020 First Semi-Annual 2020 Groundwater Monitoring Report. The plume maps indicate that additional wells are required to the north and northeast of the site to provide additional plume delineation to define the extent of the release above WQ0s in the B and C Zones. One B Zone well should be sited along or within Sperry Avenue, east-northeast of well MW-14. GHD 4080 Plaza Goldorado Circle Suite B Cameron Park California 95682 USA T 530 677 5515 W www.ghd.com