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W <br /> Working to Restore Nature <br /> 1710 Main Street October 13, 1992 <br /> Escalon, CA 95320 <br /> Phone (209)838-3507 <br /> FAX (209)838-3509 �� - ri C ro F r-« r. <br /> ± ' E w i {I <br /> Ms Mary Meays OCT 1 � 1��� <br /> San Joaquin County Public Health Services <br /> Environmental Health Division ENVIRONMENTAL HEALTH <br /> P O Box 2009 FIEF MIT/WIVICV.5 <br /> Stockton, CA 95201 <br /> RE Quarterly Monitoring Report, July through September 1992, Site Code 1864, <br /> 26056 Thornton Road, Thornton, CA <br /> Dear Ms Meays <br /> This letter report details RESNA Industries' (RESNA) groundwater monitoring activities during <br /> the third quarter of 1992 at the above referenced site (Figure 1) Activities during the quarter <br /> included monitoring of groundwater, sampling for dissolved hydrocarbons from the six <br /> monitoring wells on-site, and evaluating the petroleum hydrocarbon concentrations in the <br /> groundwater at the site <br /> BACKGROUND <br /> On September 6, 1989, three underground gasoline storage tanks were removed at the project <br /> site by Western Meter Service of Stockton, California Soil samples were collected beneath each <br /> tank and the associated piping The soil samples were analyzed for benzene, toluene, <br /> ethylbenzene, xylenes (BTEX), total petroleum hydrocarbons as gasoline (TPHG), tetra ethyl <br /> lead (TEL), and ethylene dibromide (EDB), by California Water Labs utilizing appropriate EPA <br /> and DHS methodologies Soil samples collected from beneath two of the tanks contained <br /> moderate to high levels of ethylbenzene and xylenes (1 2 to 70 parts per million [ppm]) as well <br /> as TPHG (470-830 pprn) <br /> The presence of elevated concentrations of petroleum hydrocarbons in the tank pit soil samples <br /> indicated further investigations would be required <br /> In a two phased approach beginning on November 1 , 1990, RESNA personnel advanced six soil <br /> borings (MW1-MW6) to depths ranging from 27 to 30 feet below grade at the project site to <br /> accomplish the following 1) Define the lateral and vertical extent of hydrocarbon impacted <br /> soils, 2) determine soil stratigraphy, and 3) install groundwater monitoring wells within the <br /> uppermost aquifer in order to assess groundwater duality The boring/well locations are plotted <br /> QR090992 FNL <br />