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6.0 DISCUSSION The intent of this investigation was to, replace the groundwater monitoring wells that are dry, begin a quarterly groundwater monitoring program on the newly installed groundwater wells, to assess the groundwater flow direction and hydraulic gradient and to determine the ' appropriateness of using vapor extraction technology to remediate TPH from the vadose and capillary zones ' No significant concentrations of TPH (gasoline or diesel) were found in soil borings drilled by Park with the exception of MW-3-P at 30 feet bgs (380 ppm as gasoline and 70 ppm as diesel) Soil boring B-1 was drilled by Applied Geosystems approximately 5 feet from Park's MW-3-P. The 30 foot soil sample analyzed by Applied Geosystems indicated a concentration significantly less (16 68 ppm total volatile hydrocarbons and 30 ppm total extractable hydrocarbons) than that ' of Park's soil boring The data suggests that the significant concentrations of petroleum hydrocarbons are not that widespread below the site The relatively low BTEX concentrations and analytical chromatograms suggest the petroleum hydrocarbons detected are significantly aged Groundwater test results from MW-2-P and MW-3-P indicated that TPH as gasoline and BTEX ' were present in low concentrations in the groundwater bevels of TPH ranged from not-detected in MW-1-P to 0 670 mg/l in MW-3-P as gasoline Benzene was only detected in MW-2-P at a concentration of 0 0033 mg/1 Lead was detected in MW-3-P at a concentration of 0 0011 mg/1 which is well below the 0 05 mg/l State of California, Department of Health Services, Drinking Water Standard Groundwater measurements indicate the direction of flow is to the northeast at a gradient of about 0 3 feet per 100 feet 1 At this time, there is limited data indicating the source of the petroleum hydrocarbons. No soil sample results from this or previous investigations reviewed by Park indicated detectable ' petroleum hydrocarbons continuously from the surface to the groundwater Soil analytical data collected during this investigation and in previous investigative reports do not provide conclusive evidence that the soils from below the USA tanks or soils located in the vicinity of the site have ' contributed to the petroleum hydrocarbon compounds found in the groundwater Figures 7 and 8 in Appendix A provide a graphical presentation (cross-sections) of TPH concentrations in the ' soil beneath the site A vapor extraction treatability test was conducted on six of the seven wells (MW-1-P; MW-2-P, ' MW-3-P, MW-1, MW-2, VEW-1-P) on the site Well S-1 was not monitored during this test Vapor concentrations of TPH as gasoline ranged from 790 ppmv in VEW-1-P (Total depth of 20 feet) to 24,000 ppmv in MW-2 ('Total depth of 70 feet) BTEX concentrations ranged from ' 0 34 ppmv in MW-2-P as total xylenes to 200 ppmv as benzene in MW-2. B iizsii iurr 15 1