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GROUND ZERO ANALYSES, INC. <br /> r <br /> 1714 Mani Street <br /> Fscalon, Caldbrnm 95320 <br /> Telephone: (209) 838-9888 <br /> Fwsunde• (249) 838-9883 <br /> April 20, 1998 <br /> Mr Ron Rowe <br /> San Joaquin County-Public Health Services <br /> Environmental Health Division <br /> 445 North San Joaquin Street <br /> P 0 Box 388 <br /> Stockton, CA 95201-0388 <br /> Subject First Quarter 1998 Report, Knowles/Roek Property, 102 South Wilson Way, <br /> Stockton, California <br /> Dear Mr Rowe <br /> Ground Zero Analysis, Inc (Ground Zero) has prepared this report to summarize activities <br /> during the first quarter 1998 at the subject site (Figure 1) Groundwater related activities <br /> included monitoring groundwater elevations, purging and sampling groundwater, and analyzing <br /> samples for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, <br /> total xylenes (BTEX), and oxygenates--methyl tert-butyl ether (MTBE), ethyl tent-butyl ether <br /> (ETBE), di-isopropyl ether (DIPE), tertiary amyl methyl ether (TAME), and tertiary butyl <br /> alcohol/tert-butanol (TBA) Also during the first quarter 1998, the vapor extraction system <br /> (VES), which began full time operation on November 19, 1997, shut down on January 29, 1998 <br /> as a result of a malfunctioning air flow sensor switch Attempts to restart the system and isolate <br /> the problem in February were unsuccessful The sensor malfunction apparently was a result of <br /> moisture and the system was restarted and placed back in full time operation on March 10. The <br /> system operated for a total of 908 hours during the quarter <br /> GROUNDWAIER ACTIVITIES <br /> Groundwater Monitoring and Sampling <br /> Groundwater monitoring was conducted on February 25, 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 69 feet since last monitored on November 18, <br /> 1997 Groundwater flow was generally east-southeasterly with an average gradient of 0 007 feet <br /> roek\gmr11 qm 1998 <br />