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>> Mr Jeff Wong Page 8 of 10 . (ELAP # 1149) in Folsom, CA The vapor samples were analyzed for total petroleum hydrocarbons (C5+) as gasoline (TPHg), C2-C4 hydrocarbons referenced to gasoline and for benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method TO-3 Reported TPHg (C5+) concentrations ranged from 220,000 to 240,000 micrograms per liter (ug/L) in well MW1 and from 65,000 to 66,000 ug/L in well VW1 Benzene was detected at 6,300 ug/L in MW1 and 2,400 ug/L in VW1 MTBE was detected at 3,800 ug/L in MWl and 1,700 ug/L in VW1 Vapor analytical results are summarized in Table 6 Copies of the chain-of-custody record and laboratory reports are included in Attachment E Projected Gasoline Removal Rates The VET was conducted to determine if soil vapor extraction would be an effective method to remediate vadose soil contamination and reduce or eliminate free-phase gasoline hydrocarbons associated with a former gasoline UST Analytical data from soil samples in and around the former UST pit suggest that very little affected soil remains in the vadose zone Most of the impacted soil lies within the capillary fringe and saturated zones The water table beneath the site currently exists at a depth of approximately 65-67 feet bgs However, vapor extraction may be effective in reducing free- phase gasoline that may remain on the water table, and may accelerate the reduction of dissolved gasoline constituents Based on the test results, the effective radii of influence for the wells is estimated to be approximately 35-50 feet, which would provide adequate coverage of the source area as well as some coverage of the area immediately downgradient (east and northeast) of the source area The projected flow rate at startup of a vapor extraction system (VES) would be approximately 25 to 30 cfm from well VW1 and approximately 15 to 20 cfm from well MW1, if used Assuming an average gasoline vapor concentration (C5+) of approximately 65,000 ug/L from VW1 and 200,000 ug/L from MW1, this corresponds to an initial gasoline extraction rate of approximately 450-600 pounds per day The initial recovery rate would not be sustainable, however, due to substantial decreases in vapor concentrations that typically occur within the first few months of VES operation Initial hydrocarbon removal rate calculations are included in Attachment E SUMMARY Three A Zone wells (MW10 through MW12), one B Zone well (MW14B), and one C Zone well (MW13C) were installed at the site to further investigate the lateral and vertical extent of groundwater contamination Soil encountered during drilling consisted primarily of silts and clays with laterally continuous beds of sand at various depths The shallow water table was encountered at a depth of approximately 67-70 feet bgs, within generally fine-grained soil Deeper potential water-bearing (sandy) zones were encountered from approximately 105-134 feet bgs and 185-220 feet bgs A relatively thick silt/clay bed was encountered in well MW13C from approximately 139 to 185 feet bgs Groundwater flow direction • in the shallow aquifer was generally to the northeast G 1GROLNDZEITULESURG\ReportslHSA_Mud wells Report 2 doc