SITE INFORMATION AND CORRESPONDENCE FILE 1

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J 139 South Center Page 3 The request to reduce monitoring will be evaluated following the installation of the.proposed downgradient well and further hydrologic characterization. Significant groundwater contamination was detected in the samples collected on February 27, 1997. Also,the groundwater level has risen approximately 6 feet since the November 1996 sampling event and is approximately 10 feet above the screened intervals of most monitoring wells. PHS/EHD does not agree with your rational for reducing to semi-annual sampling of monitoring wells, MW1,MW2,MWS,and MW7,because the plume is adequately defined and that contaminant migrational velocity is less than 3 feet/year. In your February 28, 1997 correspondence,you stated that the dissolved plume is stable and not migrating,while in your April 28, 1997 correspondence,you stated that the plume may be increasing and that the downgradient extent of the contamination is not known. Please note that the extent.of groundwater and soil contamination is not known and PHS/EHD is unsure how a migrational velocity of less than 3 feet per year was determined. PHS/EHD does not agree with your rational for discontinuing monitoring of MW3,MW4, and MW6. Until the screened intervals of the wells which Chevron proposed to discontinue monitoring became submerged significant groundwater contamination was evidenced,for example MW6 which is located cross gradient, evidenced groundwater contamination of up to 2,300 ppb TPH-gas and 130 ppb benzene. PHS/EHD does agree that MW3 and MW4 which are upgradient have generally been non-detect, but given Chevron's attempts to evaluate the biodegration potential of the site,these wells should continue to be monitored and sampled quarterly. You should also be aware,that Chevron has not demonstrated compliance with PHS/EHD's directives and the ability of Chevron to receive reimbursement from the Underground Storage Tank Cleanup Fund is in jeopardy. If you have any questions or wish to schedule field activities,please contact me at(209)468-0337. Donna Heran,REHS,Director Environmental Health Division Cn Mary Meays, Senior REHS Margaret Lagorio,REHS Site Mitigation Unit Supervisor cc: Elizabeth Thayer, Central Valley Regional Water Quality Control Board cc: David Irey, San Joaquin County Deputy District Attorney . cc: Roger Hoffmore, Pacific Environmental cc: Tom Portele,Greyhound Lines,PO Box 660362 Dallas TX 75266-0362