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1MAfLAC� iF INC. i <br /> s, ~T <br /> WA 40. 1631.01 <br /> 5 <br /> May 24, 1991 <br /> Page 2 <br /> Lane and in all other directions by agricultural land. A microwave relay station is located on <br /> the site and rests on an elevated buildiog pad approximately ten feet above original grade <br /> (Plate 2). <br /> The site is owned by Lawrence Stefans and was farm land until 1985 when the property was <br /> leased to US Sprint Corporation. After constructing the microwave relay facility in 1985, US <br /> Sprint relinquished their lease to McCaw Cellular Communication in November, 1990. McCaw <br /> Cellular Communication currently operates the facility. <br /> F' Previous Site Work <br /> P3 In 1985 US Sprint installed an 8,000-gallon underground diesel tank on the site to be used <br /> as a fuel source for the station's emergency generator. The tank was removed on November <br /> ° 9, 1988 by Post Tank Company under the supervision of a representative of the San Joaquin <br /> County Environmental Health Department. On November 15, 1988, GHH Engineering <br /> collected three soil samples 71, T2 and T3) from beneath the tank and concrete hold-down <br /> stab at a depth of approximately 13 feet below grade; two additional samples (P4 and P5; <br /> depths approximately three feet below grade) were collected at this time from beneath the <br /> i <br /> I,ss ea e r v t d non-detectable concentrations of <br /> product piping (Plate 3). Laboratory test resu a <br /> total petroleum hydrocarbons (TPH) and benzene, toluene,xylenes and eth, yt benzene (BTX&E) <br /> in all the samples with the exception of SamWe T3. Sample T3 revealed trace amounts of <br /> y <br /> toluene 00 mglcg)., xyFe i°es 456 mg/ic°g) and,'...,;allyl bepzeoe (11 cng&g). A copy of GHH <br /> Engineering's summary letter of January 9, 1989 is included as Appendix B. <br /> 1¢ <br /> Upon completion of laboratory testing, clean imported fill was used to backfill the tank <br /> excavation from the top of the concrete hold-down slab to grade. Pea gravel was placed into <br /> the product piping trench from approximately three feet to subgrade. The trench excavation <br /> was then capped with a two inch layer of asphalt. <br /> l <br /> Our firm conducted a subsurface soils investigation (Subsurface Soils Evaluation Report, <br /> January 22, 1991) on December 4, 1990. Four soil borings were drilled and samples <br /> collected from the bottom of the borings at the locations shown on Plate 4. Samples <br /> ' collected from Borings 131 and B2 were taken at a depth of 15 feet from directly below <br /> Samples T1 and T3 taken by GHH Engineering during the previous tank removal operation. <br /> Samples collected from Borings B3 and 84 were taken at a depth of five feet in the product <br /> t piping trench. Laboratory test results revealed non-detectable concentrations of BTX&E in all <br /> f <br /> <g <br />