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_� . MEMORANDUM'S- Cal/EPA
<br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL
<br /> BOARD `
<br /> T
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<br /> � CENTRAL VALLEY ALLEY REG10N
<br /> (916)255-3000 CALNET 8-494-3000 • FAX(916)255-3015 Pete Wilson,Governor i
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<br /> TO: Gordon L. Boggs E gg FROM: Patricia;'A. Anderson
<br /> DATE: 10 November 1997 SIGNATUF }
<br /> SUBJECT: REVIEW FOR NO FURTHER ACTION,FORMERSAN JOAQUIN CITY RESORT,30836
<br /> AIRPORT WAY,TRACY, SAN JOAQUIN COUNTY
<br /> This site operated as a gasoline service station from the 1960's to the late 1980's. Two 10,000-gallon gasoline
<br /> Il tanks,the associated product delivery lines, and dispenser,island were iemoved in October 1989. Soil samples
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<br /> collected from the-fank excavation near the east pipe, had 1,200 mg/kg total petroleum hydrocarbons as gasoline v
<br /> (TPH-g), 1,000 mg/kg benzene(B), 1,800 mg/kg toluene(T), 20,000 mg/kg ethylbenzene(E), and
<br /> 115,000 mg/kg xylene(X). Xylene was detected at 0.5 mg/kg beneath tank 1.1, No hydrocarbon contamination
<br /> was detected beneath tank 2.
<br /> From December 1989 to April 1990 c I i
<br /> ontaminated soil from the
<br /> P UST area was excavated to round water at
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<br /> 23 feet below ground surface(ft bgs). The highest concentrations of contamination occurred in the western and
<br />! southwestern areas of the excavation along Kasson Road. The excavation extended to Kasson Road and the store
<br /> building on-site. Soil samples,collected from the final excavation, h4nondetect(ND)to 110 mg/kg TPH-g,
<br /> ND to 250 mg/kg benzene,ND to 440 mg/kg toluene, 0.3 to 3850 mg/kg ethylbenzene, 1070 to 3700 mg/kg.
<br /> xylene. Soil samples,collected from borings throughout the site show that soil contamination extends from the
<br /> source in a north and south to west direction. The highest remaining concentration of contaminated soil exists
<br /> beneath the building at 20 feet below ground surface(ft bgs). Soil samples from this area had 810 mg/kg TPH-g, h
<br /> 9.4 mg/kg benzene, 1.7 mg/kg toluene, 23 mg/kg ethylbenzene, 60 mg/kg xylene, and 5.5 mg/kg MTBE
<br /> (detection limit 5.0 mg/kg).
<br /> t Approximately 2,500 yd3 of hydrocarbon impacted soil was removedfr{m the;UST area. This soil was aerated
<br /> on-site to nondetect.
<br /> The sail contamination at this site appears to have migrated in a northern and southern to western direction from.
<br /> __,the_source,of the contamination:Because soil contamination extends to,25 ft'bgs at P-1 aiid'ground water was
<br /> encountered in the excavation at 23 ft bgs, it appears the hydrocarbon contamination extended to ground water,
<br />` where it spread in all directions with a preference towards the south andl west due to possibly a low ground water
<br /> gradient. The Closure Report states that ground water occurs at 20 ft bgs and that regional ground water flow is
<br /> westerly,which explains the spread of contamination towards the west. The regional site map shows an unnamed
<br /> stream north of the site that is a tributary to the San Joaquin River. This stream may seasonally recharge the
<br /> aquifer and influence the direction of ground water flow towards the south, which explains the spread of
<br /> contamination towards the south and southwest. The spread of contamination towards the north may be due to
<br /> influence from the nearby domestic well or seasonal ground water discharge into the stream north of the site.
<br /> However, the direction of ground water flow at this site is unknown and',can only be speculated based on the i
<br /> indirect evidence of the distribution of hydrocarbon contamination in the soil.
<br /> Ground water samples, collected north of the source of contamination at 25 ft bgs were nondetect for petroleum
<br /> contamination. However,the soil contamination in the area of these water samples was i 1 to 21 mg/kg TPH-g,
<br /> nondetect for benzene and MTBE, and 0.058 to 0.119 for TEX. The lack of hydrocarbon contamination in
<br /> Our mission is to preserve and enhance the quality of California's water resources,and
<br /> Recycled Paper
<br /> ensure their proper allocation and efficient use for the benefit of present andfuture generations.
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