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PUBLIC HEALTH SERVICES <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION ": ° A <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor - Stockton, CA 95202 <br /> 209/468-3420 FILE a <br /> � ' <br /> CARL KNOWLES JUL 0 8 1999 <br /> 1140 W HAIRIER LN <br /> STOCKTON CA 95209 <br /> RE. 1140 W HAMMER LANE SITE CODE. 1124 <br /> STOCKTON CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHD/EHD) is the lead <br /> agency providing the oversight of the investigation and cleanup of releases from underground <br /> storage tanks (UST) within San Joaquin County. PHS/EHD has a contract with California State <br /> Water Resources Control Board to conduct an underground storage tank corrective action <br /> program. The above referenced site was placed in the PHS/EHD Local Oversight Program (LOP) <br /> in March 1987 <br /> PHS/EHD staff met with you, your consultant Ground Zero Analysis, Inc., John Lane, and your <br /> attorney, Patrick Riddle, on January 29, 1998. At that meeting, we discussed site history which <br /> included: UST closure. soil remediation, results from the groundwater and soil investigation, and <br /> additional sampling required in the source area of MW#5. <br /> On June 26. 1998, this office approved the Work Plan submitted by Ground Zero and permits <br /> were issued for soil and groundwater sampling in the area of MW#5. The work began on June 29 <br /> and was completed on July 15, 1998. <br /> A report dated August 25, 1998, containing the findings from 3 on site borings has been reviewed <br /> by PHS/EHD. Soil and groundwater contamination to 98.5 feet below ground surface was <br /> evidenced in S-061a. Soil concentrations of 0.0078 parts per million (ppm) Benzene and <br /> groundwater concentrations of 27 ppm Benzene were detected in samples collected at 98.5 feet <br /> below ground surface. Due to these high concentrations and the vertical extent of the <br /> contamination discovered, additional definition will be required. In order to characterize the full <br /> extent of the plume, an investigation including soil and groundwater sampling must be performed <br /> in the vicinity of MW#5. To date, no investigation has been performed to the north of MW#5. a <br /> P - � <br /> PHS/EHD has also completed review of all Quarterly Monitoring reports including the most recent <br /> May 6, 1999 submittal prepared by Ground Zero Analysis, Inc. Depth to groundwater has <br /> decreased considerably during the course of the investigation with little change in gradient. Due <br /> to the rise in groundwater, only MW#3 is now screened properly. Gasoline contaminant <br /> concentrations in the groundwater continue to decline in the on site monitoring wells, with the <br /> exception of MW#5 (10,000 ppb Benzene). Contaminants have not been detected in the <br /> groundwater from the off site/down gradient MW#8. <br /> Since samples from MW5 have evidenced the highest gasoline concentrations throughout the site <br /> remediation and investigation, the contamination may be localized, but is not fully defined. <br /> Additional soil and groundwater data in the area of MW5 will be required to further delineate the <br /> lateral and vertical extent of contamination. <br /> A Division of San Joaquin County Health Care Services <br />