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ENVIRONMENTAL HEALTH DEPARTMENT <br />SAN JOAQUIN COUNTY <br />304 East Weber Avenue, Third Floor <br />Stockton, California 95202-2708 <br />Telephone: (209) 468-3420 <br />Fax: (209) 464-0138 <br />Website: www.sjgov.org/ehd/ <br />Donna K. Heran, R.E.H.S. <br />Director <br />Al Olsen, R.E.H.S. <br />Program Manager <br />Laurie A. Cotulla, R.E.H.S. <br />Program Manager <br />Unit Supervisors <br />Carl Borgman, R.E.H.S. <br />Mike Huggins, R.E.H.S., R.D.I. <br />Douglas W. Wilson, R.E.H.S. <br />Margaret Lagorio, R.E.H.S. <br />Robert McClellon, R.E.H.S. <br />Jeff Carruesco, R.E.H.S. <br />OCT 17 as <br />DONNA SARTINI-GARDNER RONALD JR & BONNIE BARBER <br />1206 W STRUCK 10411 SMALL RD <br />ORANGE CA 92667 MANTECA CA 95336 <br />RE: 26056 (26090) N. Thornton Road, APN 00115048 <br />Thornton, CA <br />San Joaquin County Environmental Health Department has reviewed our Local <br />Oversight Program file on the above referenced site that is contaminated from <br />unauthorized release(s) of petroleum stored in the former underground storage <br />tanks (UST's) located at the site. There is a San Joaquin County Service Area <br />(Thornton) municipal well approximately 120 feet from the location of the former <br />UST's. A monitoring well (MW4) was placed between the location of the former <br />UST's and the Thornton municipal well. MW4 is screened between 10 and 30 <br />feet below surface grade (bsg) and monitors first encountered groundwater. The <br />analytical results of the water sample collected from MW4 on July 31, 2005, <br />showed benzene at a concentration of 6.4 micrograms per liter (ugh!) and Total <br />Petroleum Hydrocarbons as gasoline (TPH-g) at a concentration of 2600 ug/I. <br />The maximum contaminant level for benzene in public drinking water is 1 ug/I. <br />Therefore, the contamination at the site continues to be a threat to the Thornton <br />municipal well. <br />Soil contamination was defined laterally and vertically to the north in November <br />1996 by samples from soil boring SB7. A grab groundwater sample was <br />collected at 28 feet bsg in SB7 and the analytical results show that contamination <br />was not detected. That groundwater data provided lateral definition of the <br />contaminant plume at that time, but vertical definition has never been completed <br />and there is no current lateral definition for the contamination. <br />Soil boring SB1 and monitoring well MW1 provided soil and shallow groundwater <br />contaminant definition to the east of the former UST location. Monitoring wells <br />MW2 and MW5 provided shallow groundwater definition west and south of the <br />former UST location. Although groundwater elevation readings indicate the <br />shallow groundwater flows southwesterly, contaminant concentrations indicate <br />the shallow groundwater flows toward the Thornton municipal well. <br />Since April 2002, groundwater samples have only been collected for analysis <br />from monitoring wells MW3 and MW4 and that has not been done quarterly.