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Linda S Thompson <br /> Project Manager <br /> n ' Room P4-3038 <br /> 7131293-2867 <br /> Remediation Technology Conoco Inc <br /> Pax 713/293-3305 P O Box 2197 <br /> Houston, TX 77252-2197 <br /> February 6, 1996 <br /> Mr Harlin Knoll <br /> San Joaquin County PHS/EHD <br /> P 0 Box 2009 <br /> Stockton, California 95201 RECEIVED <br /> RE. Remediation System Shutdown <br /> Former Econo Gas Station F E B 121996 <br /> 4325 East Washington Street <br /> Stockton, California ENVIRONMENTAL HEALTH <br /> PERMIT/ SERVICES <br /> Dear Mr Knoll <br /> As we discussed during our telephone conversation this morning, the remediation system <br /> at the above referenced site will be shut down until further notice The annual <br /> groundwater monitoring will continue In addition, one of the two downgradient <br /> monitoring wells(MW-29 and MW-30)will be sampled quarterly, alternating from one well <br /> to the other (see attached Groundwater Gradient Map) <br /> Since the remediation system began operation in August 1989, approximately 106,000 <br /> pounds (17,000 gallons) of gasoline have been removed and treated Concentrations of <br /> total petroleum hydrocarbons as gasoline (TPHg) In the soil vapor have decreased from <br /> a high of 33,000 mg/m3 to approximately 200 mg/m3 (see attached Summary of Air <br /> Monitoring Analytical Results) Groundwater has contained no detectable concentrations <br /> of TPHg or benzene, toluene, ethylbenzene and xylenes (BTEX) since May 1993 <br /> Groundwater elevations have fluctuated significantly since assessment began in 1985 <br /> Data indicate that groundwater was 45 to 50 feet below ground surface (bgs) in 1985 <br /> then dropped to 80 to 85 feet bgs in late 1992 1995 data indicate that the groundwater <br /> level has risen to approximately 72 feet bgs <br /> We will observe the quarterly groundwater data for six to twelve months following the <br /> system shutdown Pending the outcome of the anticipated regulatory changes, this site <br /> may be a candidate for closure If you have any questions, please contact me at (713) <br /> 293-2867 <br /> Sincerely, <br /> Linda S Thompson <br /> Project Manager <br />