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GROUND ZERO ANALYSIS, INC. <br /> 1714 Main Street <br /> Finalon, California 95320-1927 <br /> Telephone: (209) 838-9888 <br /> Facsnnde: (209) 838-98M <br /> ' October 2, 1998 <br /> Mr Ron Rowe <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> ' 304 East Weber Avenue, 3rd Floor <br /> Stockton, CA 95202 <br /> ' Subject Third Quarter 1998 Report, KnowleslRoek Property, 102 South Wilson Way, <br /> Stockton, California (Figure 1) <br /> Dear Mr Rowe <br /> yGround Zero Analysis, Inc (Ground Zero) has prepared this report to summarize activities <br /> during the third quarter 1998 at the subject site Groundwater related activities included <br /> ' monitoring groundwater elevations, purging and sampling groundwater, and analyzing samples <br /> for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, total <br /> xylenes (BTEX). Additionally, after approval by San Joaquin County Public Health Services <br /> ' Environmental Health Division (PHSIEHD), samples from wells MW1, MW3, MW4, MW11, <br /> MW 12, and MW 13 were analyzed for oxygenates [methyl tert-butyl ether (MTBE), ethyl tert- <br /> butyl ether (ETBE), di-isopropyl ether (RIPE), tertiary amyl methyl ether (TAME), and tertiary <br /> butyl alcohol/tert-butanol (TBA)] using EPA method 8260 <br /> Also during the third quarter 1998, the vapor extraction system (VES), which began full time <br /> operation on November 19, 1997, operated for 612 hours, removing an estimated 1,600 pounds <br /> of hydrocarbons from the subsurface As of September 14, 1998, the system had operated for <br /> a total of 3,965 hours and had removed an estimated total of 9,500 pounds of hydrocarbons <br /> ' GROUNDWATER ACTIVITIES <br /> Groundwater Monitoring and Sampling <br /> Groundwater monitoring was conducted on August 11, 1998 The depth to groundwater was <br /> measured in each well and subtracted from the wellhead elevation to determine groundwater <br /> ' elevation. Water levels rose an average of 2.03 feet since last monitored on May 5, 1998. <br /> Groundwater flow was generally easterly with a gradient ranging from 0 003 to 0.015 feet per <br /> foot. A groundwater gradient map generated using the August 11, 1998 monitoring data is <br /> r_ _ <br />