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' Mr Jay Jahangiri �eannsa-rRix ' Port of Stockton February 5, 2002 Page 4 total xylenes at 58 pg/t, and TPH-g at 6,900 pg/Q The analytical results of the groundwater ' sample collected from 41 feet bgs in boring B3-6 were non-detect for BTEX and TPH-g CONCLUSIONS AND RECOMMENDATIONS IThe analytical results of the soil and groundwater samples collected during this assessment indicate that soil and groundwater affected by PHCs appears to extend from south of UST Site No 3 (B3-6) to the east (B3-5) The full lateral extent of PHC-affected groundwater is not known to the east and south of the site Analytical results indicate that PHCs were not detected in the soil samples collected from the 40-foot zone in any of the borings The vertical extent of affected groundwater appears to be limited to the upper portion of the water column There is no impact to groundwater or soil at 41 feet bgs in B3-6 and no impact to soil at 40 feet bgs in B3-5 The TPH-g and BTEX detections in groundwater at 40 feet bgs in B3-5 were substantially less than in the 20-foot zone (3 to 4 orders of magnitude), these relatively low levels of PHCs are likely due to cross-contamination of the sampling tool from the impacted 20-foot zone The PID readings from 28 to 40 feet were zero and no product odor was apparent below 32 feet The work plan for this assessment also included installing one groundwater monitoring well, the location of which would be based on the results of the Geoprobe investigation This well has not been installed The location of the new groundwater monitonng well will be selected pending additional lateral and vertical assessment of PHC-affected groundwater Based on the findings of the Geoprobe investigation, the lateral and vertical extent of PHC impact has been defined to the northwest and northeast of UST Site No 3 (boring B3-7 and I B3-4, respectively) We recommend that exploration continue to the east and southwest (Figure 3) Geomatnx's September 11, 2001 work plan should be used, with the addition of several new Geoprobe locations as described below We recommend collecting grab ground- water samples from the 20-foot interval and analyzing the samples for BTEX and TPH-g If field screening of soil and groundwater at 20 feet bgs indicates PHC impact, then an additional groundwater sample will be collected at 40 feet bgs Soil samples will also be collected at I5-foot intervals starting at 10 feet bgs The soils will be logged and screened using a PID The goal of the additional assessment is to establish the extent of impact from the former UST Site No 3 Figure 3 shows six potential Geoprobe Iocations Four of the potential Geoprobe locations are spaced every 100 feet east of UST Site No 3, two others are spaced every 100 feet southwest of the UST site These locations will be marked on the ground for utility clearance, but will only be drilled as needed based on field screening and/or analytical results We propose to drill the Geoprobe locations sequentially, moving closer to or further from the former UST site depending on observed impact or analytical results A location for the groundwater monitoring well will be selected based on the extent of impact I TPO]EM6437 000%6437 stte3 LatVert Results doc w