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STATE OF CALIFORNIA -Environmdntal Proted* i Agency %"Noe PETE WILSON, Governor <br /> 40ALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A s - <br /> 4 <br /> Sacramento, CA 95827-3098 �.� ,,�•n �,�„� ,; 31 , <br /> PHONE: (916) 255-3000 <br /> FAX: (916) 255-3015 <br /> 1 March 1994 <br /> Charles Iker <br /> Ford New Holland <br /> P.O. Box 6219 <br /> Stockton CA 95206 <br /> CONCURRENCE WITH CLOSURE OF FORD NEW HOLLAND, 2150 WEST CHARTER WAY, <br /> STOCKTON, SAN JOAQUIN COUNTY <br /> According to your 13 October 1988 Preliminary Report, two underground storage tanks, one 1000-gallon <br /> diesel and one 3000-gallon regular gasoline, were removed from this site on 20 November 1987. San Joaquin <br /> County Public Health Services reports that no holes were observed in either tank. Analysis of soil and water <br /> samples (standing water was found in the tank pit at 11 feet below ground surface) taken from the pit revealed <br /> petroleum products contamination. <br /> According to your 6 January 1989 Site Assessment Report, soil found at this site is "...slightly moist sandy silt <br /> to a depth of approximately nine to ten feet below grade, underlain by a saturated sand to a depth of <br /> approximately sixteen feet." Ground water at the site can be from three to twelve feet below ground surface <br /> (BGS), and the ground water gradient can fluctuate between northerly and southeasterly, with a magnitude of <br /> approximately 0.04 feet per foot. The fluctuation in ground water level and direction is due to the nearby <br /> agricultural use of the shallow aquifer. <br /> According to your June 1990 Site Remediation Report, the tank pit was overexcavated on 21 February 1990. <br /> The pit was enlarged in all directions except towards the east wall, which showed seven parts per million <br /> (ppm) total petroleum hydrocarbons as gasoline (TPH-G). Approximately 161 cubic yards of soil were <br /> removed from the pit and taken off-site. Verification soil samples were taken to ensure that most of the <br /> contaminated soil was removed. Analysis results of these samples revealed levels of BTEX, TPH-G, and <br /> TPH-D below laboratory detectable limits. The pit was backfilled to three and half feet BGS with clean, <br /> imported pea gravel. The top of the pit was filled with stockpiled soil from the tank removal and <br /> overexcavation, which contained up to two ppm TPH-G. <br /> Four ground water monitoring wells (MW) were installed on the site in November 1988, and a fifth well was <br /> installed in September 1991, southeast of the tank. The soil samples from the borings showed no sign of <br /> contamination. All wells were sampled periodically starting in November of 1988. Table I shows sampling <br /> results for MW4 obtained from your 17 August 1992 Results of Second Quarter 1992 Well Sampling. <br /> According to Table I, in September 1990, ground water was found at 4.6 feet BGS and sampling results <br /> indicate high concentrations of contaminants. Since that date, the ground water level has dropped to over 11 <br /> feet BGS and sampling results have show non-detectable levels of contaminants. Results from the last three <br /> sampling events for all monitoring wells (January, April, and July 1992) have revealed levels of BTEX and <br /> TPH-G below laboratory detectable limits. <br />