ARCHIVED REPORTS_SECOND SEMIANNUAL AND 2011 ANNUAL GROUNDWATER MONITORING REPORT

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L2.RESULTS FOR SECOND SEMIANNUAL PERIOD 2011 Shallow Groundwater Laboratory analytical results of shallow groundwater samples are consistent with data L reported during previous quarters,as shown in the time-series concentration charts in Appendix D. The data indicate that the lateral extent of petroleum-affected shallow groundwater is stable.The lateral extent of petroleum-affected groundwater is defined by ` wells M-1,M-8,M-10,N-18,N-19,and N-20(petroleum hydrocarbons were not present �• above the laboratory reporting limits in these wells,except for anomalous detections in well N-18,which are not believed to be site-related). Compounds detected in shallow L groundwater during the second semiannual period 2011 include the following: • TPHg was detected in shallow groundwater at wells N-7,N-8,N-15,N-16,N-17,N-18, 0-1 and RW-1. Reported concentrations of TPHg in these wells ranged from L 0.66 milligrams per liter(mg/L) at well N-18 to 36 mg/L at well N-7 (DUP). • TPHd was detected in shallow groundwater at wells N-7,N-16,N-17,M-10, and RW-1. Reported concentrations of TPHd in these wells ranged from 0.84 mg/L at well M-10 to 11 mg/L at well N-7(DUP). L • BTEX compounds were detected in shallow groundwater at wells N-7,N-8,N-15,N-16, N-17,N-18,0-1,and RW-1. Reported concentrations of benzene in these wells ranged Lfrom 7.6 micrograms per liter (µg/L) at well 0-1 to 8,900 µg/L at well N-7. The detection of benzene in well N-18 appears anomalous because TPH and BTEX constituents have not been detected historically in this well. In addition, detections may be attributed to offsite sources,which include farm buildings in the immediate vicinity of this well. I Deeper Groundwater No TPHg,TPHd, or BTEX compounds were detected in samples from deeper well N-24, except for anomalous detections of TPHd (0.53 mg/L,which is slightly above the reporting limit of 0.50 mg/L) and benzene (2.7µg/L),from the second semiannual event in 2011. This is consistent with recent data reported during previous quarters,which have been below detection limits except for anomalous detections. �- 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 2011 (April through September 2011). 2.2.1 Remediation Activities i' The following remediation activities were performed. i . Phytoremediation.Maintained the phytoremediation system as described in the Cleanup L Plan Using Phytoremediation for the Source Area (CH2M HILL, 2004). • Monitored Natural Attenuation. Continued quarterly groundwater monitoring and Lreporting in accordance with MRP No. R5-2007-0831.Groundwater concentrations for TPHg,TPHd,and BTEX constituents continue to be stable to decreasing on a sitewide and seasonal basis. ES102411163308SCOILW3521.DOCXfl12970D03 25