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<br /> ' Project 113-13-05, Work Plan Page 3
<br /> A,pump test was done by Parker Environmental Services at the site October 15-16, -`
<br /> 1991, and,it showed that all four monitoring wells are in the same aquifer., ,
<br /> A groundwater'sample was obtained from-MW-4 on January 10,.1992. Groundwater,, r
<br /> deptKprior to,removal was 24.65 feet, and the well bottom was measured at a depth
<br /> of 37.77 feet. Approximately ten gallons,was removed by bailer and placed-in 5=
<br /> ` gallon buckets, which were stored on-site in;the fenced loading area. After bailing,
<br /> groundwater depth_was 27 75 feet. The sample was non-detect for TPH-g and BTEX.
<br /> 4 On May 19, 1992, four bonngs were advanced to determine if residual soil'
<br /> contamination remained in the side walls of the excavation of the ,former tank pit.
<br /> Eight soil samples were obtained from four borings around the former location of the
<br /> underground tanks and gas island. The samples were analyzed at a State Certified
<br /> environmental lab for TPH as gasoline with BTEX: One,"sample from 2,feet 'depth at '
<br /> B-1 contained TPH as gasoline at 2.5 ppm, with toluene, ethylbenzene and xylenes all
<br /> detected°less than T ppm The source of this contamination was`concluded to'be s`
<br /> surface spills leaching through the`asphalt. Benzene was not detected. All other soil
<br /> samples,were non-detect fon' TPH-g and'BTEX.
<br /> A groundwater sample was procured from MW-4, which has historically been down- '
<br /> gradient from the former tank location. The sample was non-detect for TPH-g and
<br /> BTEX.
<br /> Quarter'y, monitoring was performed by Parker Environmental Services during
<br /> 1993. In March; 1993, during the first quarter of monitoring, xylenes were measured `
<br /> at 12, 1.1; and 0.96 ppb in three of the wells (MW-1, MW-2, and MW-3). Toluene,_' -
<br /> was present (1.2 ppb) in MW-4 All 4 wells were ND for 1,2-dibromoethane (ethylene
<br /> dibromkde) and for lead.
<br /> All wells were ND for both TPH-g and BTEX in July, September, and December, _
<br /> 1993, and in April and July, 1994. Groundwater levels ranged from about 21 feet BGS
<br /> to about 28 feet BGS over that period. Monitoring was not performed in October,
<br /> 1994,because of the low water table `
<br /> Monitoring resumed in January, 1995. Wells MW-1, MW-3 and MW-4 were found to be
<br /> free of the chemicals of interest at or above the analytical method detection limits MW-2
<br /> contained 1 3 ppb benzene, 0.91 ppb toluene, 0 79 ppb xylenes, and was ND for TPH as
<br /> gasoline and ethylbenzene April 1995 sampling and analysis showed trace amounts of
<br /> BTEX in MW-4. Water levels had risen up to about 12 feet above MSL.
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<br /> In July, 1995, all samples were non-detect for TPH-g and BTEX
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<br /> A Site Chronology and Case Closure Report were submitted to San Joaquin County
<br /> on December 22, 1995
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<br /> Parker Environmental Services, 190 East 7th Street, Pittsburg, CA 94565-2317 �
<br /> Phone (415) 439-1024 Fax (415) 439-2566
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