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I <br />' 22 December 1998 <br /> AGE-NC Project No 95-0128 <br /> Page 7 of 8 <br />' • MTBE was detected at significant concentrations north of the site boundary on the <br /> McDonalds property and at lower concentrations northeast of the site boundary in the City <br /> of Stockton right-of-way Figure 4 depicts the distribution of MTBE concentrations detected <br /> fduring the last quarter <br /> • The deeper grab ground water sample collected from soil probe boring B13 is slightly more <br />' impacted than the shallower sample from the same boring, and contained MTBE and TBA <br /> which were not detected in the shallower samples <br />' • The east, south and west boundanes of the plume of dissolved MTBE is well constrained or <br /> can be reasonably approximated, but the northern,northwestern and northeastern boundaries <br /> are not delineated with the data currently available <br />' 9 At this point in time, the plume of hydrocarbon-impacted soil is reasonably well defined, <br /> although not tightly delineated on the north, the plume of dissolved peti oleum hydrocarbons <br /> as TPH-g is reasonably defined, and the plume of dissolved MTBE is defined on the east, <br />' south and west, but is not delineated toward the north <br /> 5.0. RECOMMENDATIONS <br />' Based on the results of this investigation, AGE recommends <br /> • Preparation of a Corrective Action Plan Addendum that will include an analysis of ground <br />' water remediation alternatives <br /> • Installation of a ground water monitoring well near the location of soil probe boring B 16 and <br />' an additional ground water momtonng well approximately 100 feet further north of B 16, in <br /> the sidewalk along Pacific Avenue, to monitor the dissolved MTBE plume <br />' • Installation of additional soil vapor extraction and/or in-situ air sparging wells concurrently <br /> with installation of the additional monitoring wells, in preparation for active remediation at <br /> the site <br /> r T-,t, of remed.,ation of sod --A rtrni.�nd,vito vn the Cita iinnn annrnl,al of the C A P a�nd <br /> b"' Y YY <br /> CAP addendum by the PHS-EHD <br /> • Continued monitoring of the ground water monitoring system, the next quarterly ground <br /> monitoring event should be scheduled for October 1998 All wells should be sampled during <br /> this monitoring event <br /> Advanced GeoEn%eronmen[al Inc <br />