ARCHIVED REPORTS_SECOND SEMIANNUAL 2018 GROUNDWATER MONITORING REPORT

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JACOBS® Second Semiannual and 2018 Annual Groundwater Monitoring Report • Compounds detected in shallow groundwater during the second semiannual period for 2018 include the following: . • TPH-g was detected in shallow groundwater at wells N-7, N-8, N-15, N-16, N-17, and RW-1. Reported concentrations of TPH-g in these wells ranged from 0.93 milligrams per liter(mg/L) at well N-8 to 3.7 mg/L at well RW-1. • TPH-d was detected in shallow groundwater at wells N-7, N-16, N-17, M-10, and RW-1. Reported concentrations of TPH-d in these wells ranged from 0.54 K mg/L at well N-16 to 5.1 K mg/L for the duplicate sample at well N-7. The"K" flag indicates the diesel-range organics (DRO) concentration may include contributions from lighter-end hydrocarbons that elute in the DRO range. . • BTEX compounds were detected in shallow groundwater at wells N-7, N-8, N-15, N-17, 0-1, and RW-1. Reported concentrations of benzene in these wells ranged from 1.4 micrograms per liter(Ng/L) in wells N-8 and 0-1 to 840 pg/L at well N-7. Deeper Groundwater . No TPH-g, TPH-d, or BTEX compounds were detected in samples from deeper well N-24. This is consistent with data reported during previous sampling events. . 2.2 Status of Remediation and Other Completed Activities This section presents the status of remediation and other completed activities for the second semiannual period for 2018 (April through September 2018). 2.2.1 Remediation Activities The following remediation activities were performed: • Phytoremediation. Maintained the phytoremediation system as described in the Cleanup Plan Using • Phytoremediation for the Source Area (CH2M, 2004). • MNA. Continued semiannual groundwater monitoring and reporting in accordance with MRP No. R5-2018-0806. Groundwater concentrations for TPH-g, TPH-d, and BTEX constituents continue to be stable to decreasing on a sitewide and seasonal basis. 2.3 Planned Upcoming Semiannual Activities The following activities are planned for the first semiannual period for 2019 (October 2018 through • March 2019): • Continue semiannual groundwater monitoring and reporting in accordance with MRP No. R5-2018-0806. • • Continue maintenance of the phytoremediation system as described in the Cleanup Plan Using Phytoremediation for the Source Area (CH2M, 2004). • Perform the annual tree monitoring event and submit the annual tree monitoring report as described • in the Cleanup Plan Using Phytoremediation for the Source Area (CH2M, 2004). 4 AX1015181035SCO • •