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R604 :UPDATE 16 2-23-1993 <br /> BTEX in Ground Water (EPA method 602) : <br /> No BTEXs were detected in monitoring wells from the March 5, and <br /> �►` June 2, 1992 sampling. During the December 16, 1991 sampling <br /> round only MW1, MW2, and MW5, had BTEXs in very low <br /> concentrations. During the September 11, 1992 sampling, sample <br /> results from MW1 detected only benzene (1 .2 ug/L) and MW5 sample <br /> results indicated only the xylenes (4 . 1 ug/L) . The latest <br /> sampling results (December 7, 1992) showed only MW5 to contain <br /> ethylbenzene (1 .2 ug/L) and xylenes (35 ug/L) . MW5 is presently <br /> being utilized as a vapor extraction well . This pulling of the <br /> contaminants to the well consequently increased concentrations . <br /> MAXIMUM_ CONTAMINANT LEVELS FOR PRIMARY DRINKING WATER, TITLE 22 <br /> or DHS. <br /> BENZENE 1 ug/L TOLUENE 100 ug/L <br /> ETHYLBENZENE 680 ug/L Total XYLENES 1, 750 ug/L <br /> Vapor extraction has removed most BTEXs from the ground water as <br /> shown by sample results obtained from the monitoring wells since <br /> March 5, 1992 . Except for MW1, which contained 1 .2 ppb benzene <br /> on the September 11, 1992 sampling, the "Present California Water <br /> Quality Goals" have been met, see Table 1 . <br /> Fecal Coliform: <br /> From December, 1991 through February, 1992, monthly fecal <br /> coliform samples were collected from monitor wells MW3 , MW4 , MW5 <br /> and MW6 . Samples were again collected in June, 1992, from <br /> monitoring wells MW3 , MW4 and MW6 . During the September 11, 1992 <br /> sampling, MW3 and MW6 were dry; no fecal coliform samples were <br /> obtained. Table 2 shows the results of these samples . As of <br /> June, 1992 all these wells are below detection limits, <2 . 2 MPN, <br /> for fecal coliform. <br /> VAPOR EXTRACTION <br /> Vapor Recovery Results: <br /> The vapor extraction system was shut down on November 21, 1991 on <br /> completion of operation under Initial Variance #91-19 and 90 day <br /> Variance #91-20 . A total of 13 , 1.1.6 pounds of gasoline range <br /> hydrocarbons were removed from the soils and ground water beneath <br /> this site by that time. <br /> The vadose zone vapor recovery wells (P1, P3-Swarm and EX) <br /> contributed little to the total recovered hydrocarbons during <br /> this time period: P1 = 1 . 3 pounds, P3--Swarm = 561 .4 pounds and <br /> EX = 127 pounds . <br /> The system was restarted under the Authority to Construct Permit <br /> (AP 91-106) on March 31, 1992 . <br /> On July 21, 22, and 23, 1992, four new vadose zone vapor recovery <br /> wells were installed and manifolded to the recovery system. As <br /> page 2 <br />