ARCHIVED REPORTS_3RD QUARTER 2010 SITE STATUS REMEDIAL SUMMARY AND GROUNDWATER MONITORING REPORT

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Stantec ' L& M OPERABLE UNIT-THIRD QUARTER 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling ' October 27, 2010 south in the L&M OU during 3Q10. Benzene in B-Zone groundwater is delineated during 3Q10 except for a small section to the north of the site. TBA had no detections above the MDL, therefore is considered delineated in B-Zone groundwater during the 3Q10. ' Dissolved TPHg in C-Zone groundwater is delineated to the west and partially to the north during the 3Q10. Dissolved TPHd and MtBE in C-Zone groundwater are delineated to the south, west, and to the north. TBA is delineated to the south and west only. Dissolved TPHo in ' C-Zone groundwater is delineated to the east and west only during the 3Q10. Benzene is located in two separate sections of the site (central and south).in C-Zone groundwater. Benzene is delineated in the central section of the site and delineated to the northwest and tnorth only in the southern section of the site (Figures 18 through 23). Dissolved TPHg and benzene in D-Zone groundwater are delineated to the west and partially to the south during the 3Q10. Dissolved TPHd in D-Zone groundwater is delineated to the south, east, and west during the 3Q10. Dissolved TPHo in D-Zone groundwater is delineated to the east and partially to the north during the 3Q10. MtBE in D-Zone groundwater is delineated. ' TBA in D-Zone groundwater is delineated to the south and west (Figures 25 through 30). The extent of petroleum-affected deeper (B-, C-, and D-Zones) groundwater has not been ' investigated by the RDA at the LOU and MOU to the east. 2.8 ARSENIC ' During the third quarter 2010, arsenic concentrations ranged from 0.011 mg/L (MW-21) to 0.24 mg/L (MW-18) in A-Zone wells, from 0.0081 mg/L (MW-35) to 0.086 mg/L (MW-59) in ' B-Zone wells, from 0.0070 mg/L (MW-61) to 0.031 (MW-54) in C-Zone wells, and from 0.020 (MW-71 and MW-74) to 0.040 (MW-55) in D-Zone wells. Arsenic concentrations over the past three years appear to be relatively consistent. Graphs depicting arsenic trends in selected ' A-Zone and B-Zone wells within the petroleum hydrocarbon plume (shallow wells MW-9,MW-32, 2AMW-13, DPE-9 and deep zone well MW-17) and shallow and deep well pairs along the perimeter of the dissolved plume (MW-34/MW-35, MW-25/MW-26, and MW-27/MW-28) are included in Appendix G. ' 2.9 PURGE WATER STORAGE AND DISPOSAL Between July 19 and 22, 2010, approximately 500 gallons of purge water was transferred to the ' on-site remediation system to be treated and discharged to the sanitary sewer under the waste water discharge permit for West Weber Avenue and North Lincoln Street, Stockton, CA. Field data sheets for calculating purge volume are included in Appendix C. ' Ifflde ter\lw SWr ton(ParW 2A.0415)\Reports\OMR2010\3010\3O10QSSRORSROMR Stoc lon_FINALAm 2.26