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' R_ O <br /> Ms. Mary Meays TAN <br /> June 7, 1995 (9347-0020) <br /> BACKGROUND <br /> The results of previous site assessmdnts and the removal of the(former) steel underground <br /> fuel-storage tanks were documented by Aegis Environmental, Inc. in reports dated June 18, 1990, <br /> and January 4, 1991. Ground water has been monitored and sampled on a quarterly basis since <br /> July 1990. The estimated ground water flow direction has been predominantly to the southeast. <br /> Separate-phase petroleum hydrocarbons have been observed only in well MW-3, but have not <br /> been observed since August 1993. Dissolved petroleum hydrocarbons in well MW-1 (northeast <br /> corner of the site) have dropped to concentrations below the laboratory detection limits. <br /> During late 1991 and early 1992, a 75-day vapor extraction test was performed on site by <br /> Aegis Environmental, Inc. During the test, vapors were extracted from wells VEW-I, VEW-2 <br /> and MW-3. Wells VEW-1 and VEW-2 were installed to address petroleum hydrocarbons in soil <br /> beneath the former steel tanks. <br /> PROPOSED WORK <br /> To achieve objectives 1 through 4 outlined above, Fugro proposes to perform the following: <br /> • Drill and sample three soil borings on site in the areas of investigation shown on <br /> Figure 2. <br /> • Collect ground water samples from each of the borings. <br /> The borings will be drilled in the numbered sequence shown on Figure 2. Historical <br /> ground water flow information indicates the southeast corner of the Shell site is downgradient <br /> of the former underground storage tanks. Investigation area #1 is a revision from the originally <br /> proposed off-site area of investigation east across Pacific Avenue, on the 6132/6138 Pacific <br /> Avenue, Marengo Property. <br /> The boring in area #2 is proposed to investigate whether petroleum hydrocarbon <br /> concentrations previously detected beneath the former steel underground storage tanks have <br /> attenuated. In 1990, concentrations of total petroleum hydrocarbons (TPH), as gasoline, up to <br /> 17,000 parts-per-million were indicated in soil samples collected from the borings for vapor <br /> extraction wells VEW-I and VEW-2. The boring proposed in area #3 will investigate soil and <br /> ground water upgradient from the former tanks. <br /> The soil borings will be advanced and sampled using a GeoProbe truck provided by <br /> Vironex of Foster City, California. The GeoProbe hydraulically drives a 1-1/4-inch diameter <br /> push rod assembly to the desired depth. Undisturbed soil samples are then collected for Feld <br /> screening and possible laboratory analysis. The GeoProbe does not generate soil cuttings and is <br /> much quicker at collecting soil and ground water samples than a conventional hollow-stem auger <br /> drill truck. <br /> 93470020.BWP -2- <br />