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<br /> USTs which reportedly stored gasoline, diesel, and 1,1,1-trichloroethane(TCA) were Identified as
<br /> Tanks No. 1 to 6 and 8 and were previously removed and petroleum hydrocarbon contamination was -�
<br /> documented during their removal in soil and groundwater(T&R, 2005, Figure 2). During March and April
<br /> 2004, during remedial excavations at the Site, a previously unknown UST that stored gasoline was also
<br /> discovered (T&R, 2005). Removal of the USTs and over-excavation of soil was performed with regulatory
<br /> oversight by the SJCEHD. -J
<br /> Groundwater monitoring at the site was previously performed by Advanced GeoEnvironmental, Inc., y
<br /> Stockton, California (AGE) under the oversight of the SJCEHD using fifteen groundwater monitoring wells
<br /> (fourteen on-site and one off-site). During December 2003, TIRR submitted a well destruction work plan
<br /> to the SJCEHD (T&R 2003), which was accepted on 12 January 2004(SJCEHD 2004). Between 1 March
<br /> 2004 and 26 March 2004, all on-site wells and one off-site well were destroyed according to the
<br /> procedures described in the work plan (T&R, 2004a). The on-Site wells included fifteen monitoring wells
<br /> and two extraction wells(which had been installed but not used)and one off-Site well. The well
<br /> destruction is documented elsewhere(T&R, 2005).
<br /> Prior to well destruction, AGE performed groundwater monitoring in fifteen groundwater monitoring wells
<br /> in May, 2002, with limited groundwater sampling also performed in November 2002(AGE, 2002). The
<br /> locations of these groundwater monitoring wells(former wells MW-1, MW-2, MW-4, MW-5, MW-8, mw-
<br /> 11, MW-12, MW-13, MW-18, MW-19A, MW-19B, MW-20A, MW-20B, MW-21A and MW-218)are shown on
<br /> Figure 3. Former well MW-21A was located near former UST-8 and had the greatest concentrations, with
<br /> a Total Petroleum Hydrocarbon (TPH)as gasoline (TPHg),TPH as diesel (TPHd), TPH as motor oil
<br /> (TPHmo)and Benzene, Toluene, Ethyl-benzene, and Xylenes(BTDK) concentrations of 7,300, 8,100, 930,
<br /> 130, 1.7, 160 and 3.8 µg/L, respectively, on 16 May 2002 (AGE, 2002). Former well MW-21B, also
<br /> located near former UST-8 had the greatest deeper concentrations with TPHg, TPHd, ethylbenze and
<br /> xylene concentrations of 750, 260, 0.75 and 4.5 µg/L respectively on 16 May 2002. Other former wells
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<br /> (MW-1, MW-2, MW-4, MW-5, MW-8, MW-11, MW-12, MW-13, MW-19A, MW-19B, MW-20A, and MW-20B)
<br /> did not have detections for TPHg. Former well MW-20A had a detection of 110 pg/L for TPHd (AGE,
<br /> 2002) as of May 2002.
<br /> Treadwell&Rollo prepared a 2004 Remedial Design and Implementation Plan (RDIP)for the Event J
<br /> Center that was approved by the DTSC(T&R 2004). The RDIP proposed to excavate soil at the Site
<br /> where it exceeded the commercial cleanup criteria established for the Event Center. During the March
<br /> and April 2004, soil excavations were conducted at the Site, and a previously unidentified UST was
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