ARCHIVED REPORTS -GROUNDWATER MONITORING REPORTS

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Ms Lon Duncan April 4, 2000 . Page 5 of 6 samples collected at 15 feet and 20 feet from boring SB5 • TPHg, TPHd, BTEX and VOCs detected in the groundwater ranged from at or near non-detectable to moderate levels in borings SB4 through SB8 TRPH and oxygenate additives were at not detected • Lead detected in the soil appears to be representative of background levels at the site Groundwater results appear to be suspect. Groundwater from borings with higher levels of organic contamination (primarily TRPH and TPHg) have lower concentrations of lead, and borings with lower levels of organic contamination have higher levels of lead The opposite should be true Conclusions • Soil in the immediate vicinity of the former UST has been significantly impacted by petroleum hydrocarbons,solvent related VOCs, and lead • The vertical extent of soil contamination has been defined No contaminants were detected below 31 feet bgs • The lateral extent of soil contamination has been defined to the north, south and east, and appears to be limited to the west. Impacted soil at the site appears to extend no more than 20 feet north, 20 feet west,or 10 feet southwest of the former UST location • Significant impact to shallow groundwater has occurred, however, contaminant concentrations appear to diminish appreciably within relatively close proxnnvty to the former UST • The extent of groundwater contamination has not been completely defined However, analytical results infer that the contaminant plume is localized, and is essentially bounded to the north by bongs SB7 and SB8 approximately 35 feet north of the former UST • Based upon San Joaquin County groundwater flow maps and recent analytical data it appears that groundwater flow at the site is generally in a northeasterly direction However, capillary zone soil contamination present in only borings SB 1 and SB6 suggests a northerly flow RECOMMENDATIONS Based upon field and analytical data collected during this investigation, Ground Zero recommends the following I Install four groundwater monitoring wells in the vicinity of the former UST excavation for the purpose of collecting confirmation groundwater samples and determine the local groundwater gradient and flow direction Due to limited access inside the buildings, the wells would necessarily be installed with a limited access ng or using small diameter monitoring wells installed with a direct push drilling rig Figure 5 presents suggested locations of proposed groundwater monitoring wells groundzelgabbardladd_bonng_rpt doc