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Montgomery Wards/ Unocal Station #5098 - 3 - 12 April 2012
<br /> 5400 /5606 Pacific Avenue
<br /> Stockton, San Joaquin County
<br /> wells (MW-10 through MW-18, MW-10A, MW-14A, MW-15 R [replaced MW-15 in 2007],
<br /> MW-21S, MW-22S, MW-24S, MW-18D, MW-19D, MW-21D, ,MW-22D, MW-24D) and
<br /> remediation well AS-26 were installed at Unocal and offsite from 1989 through 2007.
<br /> Maximum Unocal soil investigation results in milligrams per kilogram (mg/kg) conducted
<br /> from 1985 to 1992 are summarized in Table 2a below.
<br /> Date TPHg B T E X Pb 1,2-DCA
<br /> 4-86 12,450 128 1,060 NA 5,280 NA 11.4
<br /> 5-87 9,500 44.5 500 NA 1320 NA 0.21
<br /> 9-88 740 52 54 39 130 11 1.0
<br /> 5-92 700 9.2 19 8.0 0.6 NA 1.5
<br /> Maximum Unocal groundwater investigation results in micrograms per Liter (ug/L) from
<br /> February 1989 to June 1999 are summarized in Table 2b below.
<br /> Date TPHg B T E X MTBE 1,2-DCA Oxygenat
<br /> es
<br /> 2-89 1,600 54 8.01 23 20 NA 440 NA
<br /> 6-92 23,000 2,300 2,000 840 1,700 NA 68 NA
<br /> 6-96 36,000 5,900 1,000 800 4,500 150 200 NA
<br /> 9-97 50,000 15,000 1,100 720 7.700 2,400 0.68 NA
<br /> 6-99 23,000 6,000 250 250 1,900 6 <0.5
<br /> Oxygenates=methanol,ethanol,tertiary butyl alcohol(TBA),di-isopropyl ether(DIPE),ethyl tert butyl ether(ETBE),and
<br /> tertiary amyl methyl ether(TAME) -
<br /> Combined Sites since 1999
<br /> On 24 November 1999, the SJCEHD concurred with Wards and Unocal that, based on
<br /> the historical groundwater monitoring, groundwater flow direction to the southwest, and
<br /> geologic evidence of interconnected zones in the shallow aquifer, the two groundwater
<br /> plumes were commingled under the Wards site and directed concurrent groundwater
<br /> monitoring for the two sites. On 21 August 2000, the San Joaquin Delta College
<br /> reported the Robinhood Irrigation Well (RIW), located across Pacific Avenue 200' to the
<br /> south-southwest of Wards, was taken out of service due to strong petroleum
<br /> hydrocarbons odors reported from sprinklers on campus. Both UST cases were
<br /> transferred to the Regional Board, and the Executive Officer issued Cleanup and
<br /> Abatement Order No. R5-00-707 to Wards, Unocal, and Stone Brothers (owners of the
<br /> former Wards property) on 11 September 2000. The RIW was properly abandoned in
<br /> 2001 and a new RIW was installed on campus 3,300' from the commingled plume.
<br /> Nested monitoring wells MW-21 S/D, MW-22S/D, and MW-24S/D were installed to
<br /> investigate the RIW impacts. Nine additional remediation wells (AS-14, AS-15, AS-17,
<br /> AS-18, AS-20 and AS-21, and VIEW 16, VEW-19, and VEW-22) were installed at Wards
<br /> in April 2008 during upgrades to the SVE/AS system (Figure 3). Three soil vapor wells
<br /> (SV-1 through SV-3) were installed in May 2010.
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