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Soil and Groundwater investigation Report ARCO FacilityNo 6100 Tracy,California Page 7 MTBE, TBA, DIPE, TAME, ETBE and ethanol were not detected in any of the samples analyzed Methanol was detected at concentrations ranging from less than 2 mg/kg to 10 3 mg/kg Ethylene dibromide and 1,2 DCA were detected in the sample collected from I I I feet bgs at concentrations of 0 436 mg/kg and 0 194 mg/kg, respectively Samples collected from 152 feet and 202 feet bgs were calculated to have permeability values of 6 5 x 10-7centimetersper second (cm/s) and 2 4 x 10"6 cm/s, respectively The laboratory report for the permeability tests is included in Appendix C Product Removal An estimated 6 gallons of product have been removed from the well between October 3 and November 7, 2000 Field data sheets from the weekly monitoring of the skimmer are included in Appendix B Use of the free product skimmer will continue as warranted The monitoring frequency will be adjusted according to the rate of product recovery Summary of Findings The following summarizes the results of the investigation • The soil beneath the site is primarily silt and clayey silt with a zone of silty sand and sandy silt present from approximately 60 to 106 feet bgs, • Permeability rates on soil type logged from approximately 120 feet bgs to the total depth of the boring are low (2 4E-06 and 6 5E-07 cm/sec), • Depth to water measurements in the vapor extraction wells and monitoring well MW-1 indicate that groundwater occurrence beneath the site is highly variable and localized, • Petroleum hydrocarbons detected in soil samples collected from the boring appear to be predominantly at depths between approximately 105 to 125 feet bgs, • The highest concentrations of petroleum hydrocarbons were detected in the sample collected from 111 feet bgs (4,400 and 22 3 mg/kg TPHG and benzene, respectively), • MTBE and other oxygenates were not detected in any of the samples analyzed, • Free product is present in monitoring well MW-1 and slowly recharges when product is removed LIMITATIONS This report was prepared in general accordance with accepted standards of care that existed at the time this work was performed No other warranty, expressed or implied, is made Conclusions and recommendations are based on field observations and data . obtained form this work and previous investigations It should be recognized that definition and evaluation of geologic conditions is a difficult and inexact art Judgments