SITE INFORMATION AND CORRESPONDENCE_2001-CURRENT

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Montgomery Wards / Unocal Station #5098 -4 - 12 April 2012 5400 / 5606 Pacific Avenue Stockton, San Joaquin County Maximum final soil investigation results in milligrams per kilogram (mg/kg) since November 1999 are summarized in Table 3a below. Date I TPHg B I T E X Pb MTBETBA 1,2-DCA 4-08 1 3,700 1 10 1 82 76 430 7.17 NA NA NA soil sampled at 50'bgs at AS-20,declined to below ESLs at 80'bgs Maximum groundwater investigation results in micrograms per Liter (ug/L) since December 1999 to end of groundwater monitoring in August 2010 are summarized in Table 3b below. Date TPHg B T E X MTBE 1,2- 1 Oxygenates Naphthalene DCA 12-99 38,100 5,000 4,050 652 12,420 150 4.1 NA 665 10-09 3,400 62 37 52 210 <0.5 <0.5 <0.5 <1 2-10 2,100 4 5 31 25 <0.5 <0.5 <0.5 <1 8110 500 56 15 16 44 <0.5 <0.5 <0.5 4 The SVE/AS remediation system was shut down for groundwater rebound testing in September 2009, then restarted after sampling showed rebound in October 2009, and finally shut down in December 2009 for a second rebound test. A third round of rebound testing in August 2010 confirmed no significant rebound was occurring in groundwater, and site closure was requested by Chevron. SVE/AS removed 97% of the estimated pre-remedial mass of petroleum hydrocarbons (see Residual Mass Calculation below) at Wards. The mass removed by Unocal was not presented in the available documents. Risk Assessment Soil gas surveys were conducted in May 2010, September 2010, and October 2010. The May 2010 and September 2010 soil vapor results failed the San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs) and the California Human Health Screening Levels (CHHSLs) for TPHg and benzene, for residential property concerns, and were compromised by high levels of tracer gas (May 2010), a lab failure to analyze for tracer gas (September 2010), and failure to reach target vacuum levels for both soil vapor events. The October 2010 event did not report any problems with the soil vapor samples. A Johnson and Ettinger Model Human Health Risk Assessment (TIER 2) was conducted on all three of the soil vapor data sets. The TIER 2 determined that residual petroleum hydrocarbons in soil vapor did not pose a threat to human health or the environment (below 1x10-5 cancer risk and below 1.0 hazard quotient), indicating that soil and groundwater are not contributing to risk from vapor intrusion. Prior to remediation by SVE/AS in 2000, residual soil contamination failed the ESLs at 15 feet below ground surface (' bgs) for gross contamination and direct exposure, with TPHg (1,580 mg/kg) and direct exposure with