SITE INFORMATION AND CORRESPONDENCE_2001-CURRENT

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Montgomery Wards / Unocal Station #5098 - 2 - 12 April 2012 5400 / 5606 Pacific Avenue Stockton, San Joaquin County Wards From 26 June 1986 through 2 June 1988, Wards removed two 10,000-gallon gasoline USTs, one 550-gallon waste oil UST and, two 1,000-gallon and two 500-gallon bulk oil USTs. Based on the soil confirmation sample results, the SJCEHD required Wards to conduct further investigation of the USTs. Wards advanced eleven soil borings near the USTs between 1988 and 1992. Total Petroleum Hydrocarbons (TPH) and chlorinated solvents were detected in two soil borings. In September 1991, twelve borings (PL-1 through PL-12) were advanced under the piping that was closed in place in 1986. Fifteen onsite monitoring wells (MW-1 through MW-9 [replaced by MW-9R in 2008], and MW-27 through MW-32) and forty five remediation wells (VEW-16 through VEW-22, VEW-1A through VEW-13A, VEW-1B through VEW-13B, and AS-14 through AS-26) were installed at Wards from 1993 through 2008 (Figure 2). Remediation by soil vapor extraction and air sparging (SVE/AS) began in November 1999, and continued intermittently until October 2009. Maximum Wards soil investigation results in milligrams per kilogram (mg/kg) conducted from 1986 to 1992 are summarized in Table 1 a below. Date TPHg B T E X MTBE Pb DCA 5-88 38 NA NA NA NA NA NA 36 5-91 5,400 0.57 250 170 860 NA NA 38.9 9-91 2,000 0.0144 0.95 0.65 9.55 NA NA NA 2-93 3,110 6.517 81.9 29.9 166 NA NA NA 1-95 670 0.6 5 6.1 43 NA NA NA TPHg=total petroleum hydrocarbons as gasoline B=benzene T-toluene E=ethylbenzene X=xylenes Pb= total lead MTBE=methyl tert butyl ether 1,2-dichloroethane(1,2-13CA), a gasoline lead scavenger NA=not analized Maximum Wards groundwater investigation results in micrograms per Liter (ug/L) conducted from March 1995 to March 1998 are summarized in Table 1b below. Date I TP H B T E X MTBE 1,2-DCA 3-95 1 100,000 I 15,000 I 20,000 1 2,500 12,000 «00 7. 3-98 55,800 6,630 990,8 2,170 9,890 Unocal In July 1985, Unocal removed two 10,000-gallon fuel USTs and one unknown quantity waste oil UST. Due to soil contamination reported from the USTs, the SJCEHD required an investigation. From 1985 through 1988, nineteen soil borings were advanced (seven were converted to soil vapor extraction wells). Fifteen monitoring wells (MW-1 through MW-15) and six groundwater recovery Wells (EW-1 through EW-6) were installed and all wells were later destroyed during the 1988 soil over-excavation to 35 feet below ground surface (' bgs) and site redevelopment from 1990 to 1991. Between September 1988 and December 1988, approximately 6,000 cubic yards (yd 3) of soil was initially excavated. Approximately 4,200 yd of soil was reused onsite as clean fill, 1,600 yd of soil was aerated and also reused onsite as fill, and 200 yd of contaminated soil was hauled offsite for disposal. Twenty one replacement monitoring