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6633 Pacific Ave., Stockton
<br /> Stockton, San Joaquin Courti,
<br /> continued under the regulatory lead of the San Joaquin County Environmental Health
<br /> Department (SJCEHD). In May 1991 the list of chlorinated solvents detected in groundwater
<br /> included 1,2-DCA , 26 ug/L; PCE, 850 ug/L; trichloroethylene (TCE), 13 ug./L; and chloroform,
<br /> 1 .4 ug/L, with no petroleum hydrocarbons detected. In June 1991, Chevron's consultant
<br /> stopped identifying the chlorinated solvents, and resumed reporting as TPHg, 630 ug/L. In
<br /> December 1991, maximum groundwater concentrations were TPHg, 680 ug/L; benzene,
<br /> 120 ug/L; toluene, 80 ug/L; ethylbenzene, 12 ug/L; and xylenes, 45 ug/L. By March 1992,
<br /> TPHg had increased to 1,400 ug/L, as benzene-toluene-ethylbenzene-xylenes (BTEX)
<br /> concentrations were declining. In July 1992, monitoring well MW-6 was installed, and MW-1
<br /> was abandoned. The records for installation of MW-7 were not found by Chevron, however a
<br /> workplan was submitted to SJCEHD on 30 June 1993 and quarterly monitoring for this well
<br /> began September 1993. By December 1993, MW-2 groundwater concentrations increased to
<br /> a maximum TPHg, 1200 ug/L; and benzene, 840 ug/L. By November 1994, maximum
<br /> benzene concentrations declined an order of magnitude as TPHg concentrations remained
<br /> elevated or increased. In September 1995, four of five soil borings were (SB-1 through SB-3
<br /> and SB-5) were sampled for soil (SB-4 experienced refusal three times at 4' bgs). Maximum
<br /> soil concentrations were TPHg, 56 mg/kg; toluene, 0.042 mg/kg; ethylbenzene, 0.13 mg/kg;
<br /> and xylenes, 0.031 mg/kg.
<br /> From December 1997 to January 1998, three repair hoists, two waste oil USTs (WOT-1 and
<br /> WOT-2) and associated piping were removed. Maximum confirmation soil concentrations
<br /> (WOT-1) were TPH as diesel (TPHd), 4,900 mg/kg; TPH as motor oil (TPHmo), 7,400 mg/kg;
<br /> and total BTEX, 8.4 mg/kg. Also detected in soil were chlorinated solvents
<br /> cis-1 ,2-dichloroethant (cis-1 ,2-DCE), 2.2 mg/kg and PCE, 1 .5 mg/kg. Monitoring well OW-1
<br /> (workplan submitted to SJCEHD on 10 July 1995 with no subsequent installation report) was
<br /> added to the quarterly monitoring in April 1998.
<br /> Additional groundwater monitoring wells (MW-8 through MW-10, MW-11 D (deep zone to 90'
<br /> bgs)), MVV-12 through MVV-14 were installed onsite and downgradient to the east across
<br /> Pacific Street between March and June 2001. Only xylenes. 0.018 mg/kg and methyl tert-butyl
<br /> ether (MtBE). 0.065 mg/kg were detected in soil during the wells installation In June 2001
<br /> maximum concentrations were TPHg, 130 ug/L and MtBE, 1,200 ug/L, with no BTEX detected
<br /> in groundwater. Well OW-1 was destroyed in March 2001 .
<br /> The 4 April 1995 Corrective Action Plan proposed monitored natural attenuation as the
<br /> remediation for the petroleum hydrocarbons in groundwater, due to commingling with the
<br /> chlorinated solvent plume. In June 1998, Lincoln Properties Ltd. (AKA Lincoln Center
<br /> Environmental Remediation Trust, or LCERT) installed two groundwater extraction wells
<br /> (GEW-007A and GEW-008A) along the east side of the Chevron station (downgradient from
<br /> the former USTs) and connected them to an off-site treatment facility on their property, for the
<br /> dry cleaners chlorinated solvent plume. The LCERT claims GEW-007A and GEW-008A
<br /> (currently running), and other GEW wells, also treated the Chevron petroleum hydrocarbons
<br /> plume, based on influent TPHg detections in their treatment system.
<br /> On 21 September 2004, the SJCEHD transferred lead agency status for the USTs case to the
<br /> Regional Water Board; claiming that one agency should provide direction for the commingled
<br /> dry cleaners and the USTs cases. After conducting a file review of the available data and
<br /> case file Regional Water Board staff in letters dated 22 February 2005, 14 April 2005. and
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