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<br /> . Request For Closure,Fortner Unocal Station#0123,Tracy,CA
<br /> April 19,2001
<br /> 10) Reports/information.
<br /> L M Swift and Associates, Phase I Environmental Site Assessment, Report #93-11140, dated
<br /> March 10, 1994
<br /> Enviros, Inc,Phase I Environemmal Site Assessment, Report#E4/94150 01, dated December 16,
<br /> 1994
<br /> Pacific Environmental Group, Inc , Soil and Groundwater Investigation Report, dated November
<br /> 22, 1995
<br /> Pacific Environmental Group, Inc, Underground Fuel Tank Removal and Monitoring Well
<br /> Installation, Report#310-097 113, dated February 14, 1997
<br /> Pacific Environmental Group, Inc , Soil and Groundwater Investigation, Report #910-017 IA,
<br /> dated December 2, 1998 '
<br /> Gettler-Ryan Inc,Soil Boring Report, Report#240073 03-1, dated March 10,2000
<br /> Gettler-Ryan Inc, Monitoring Well Installation Report, Report#240073 05-1, dated February 17,
<br /> 2001
<br /> • MPDS Services, Inc , Groundwater Monitoring Reports, Quarterly from June 1995 through
<br /> March 1998
<br /> Gettler-Ryan Inc, Groundwater Monitoring Reports, Quarterly from June 1998 through March
<br /> 2001
<br /> 11) Best Available Technology(BAT)used or an explanation for not using BAT.
<br /> Engineered remediation of the soil or groundwater impact was not implemented at this site
<br /> Possible sources of additional impact(USTs)have been removed or properly abandoned in place,
<br /> and analytical data indicate that impact is of limited extent Historical groundwater analytical
<br /> data show that residual petroleum hydrocarbons are limited to an area around well U-4, and
<br /> concentrations have significantly diminished since sampling of that well began in March 1997,
<br /> indicating that natural attenuation has taken place since the source (USTs) in that area was
<br /> removed in 1996 Since downgradient wells U-6 through U-8 are non-detect for petroleum
<br /> hydrocarbons, natural attenuation is preventing the migration of petroleum hydrocarbons
<br /> 12) Reasons why"background"was/is unattainable using BAT.
<br /> Except of sporadic detections, concentrations of TPHd, TPHg, and BTEX have attained
<br /> background levels in all wells except U-4 Since sampling of well U-4 began in March 1997,
<br /> TPHg, TPHd, and benzene concentrations have diminished significantly since the removal of the
<br /> source (USTs) in 1996, showing that background levels will be attained by natural attenuation,
<br /> • and engineered remediation activities are not necessary
<br /> 240073 06 5
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