SITE INFORMATION AND CORRESPONDENCE

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AReADIs Ms. Kristi Shelton November 12,2009 Soil borings advanced on-site during the same investigation indicated a maximum TPHg concentration of 31 mg/kg, and maximum BTEX concentrations of 1.5 mg/kg, 0.079 mg/kg, 1.3 mg/kg, and 3.6 mg/kg, respectively. All of these concentrations were detected in the sample collected from soil boring S3 at a depth of 12 feet bgs (see Table 2). With the exception of boring 83, all soil samples collected on-site i during the investigation indicated concentrations that were below the Regional Board's Environmental Screening Levels (ESLs)for shallow soil. Groundwater samples collected during the most recent monitoring event(June 2009) indicated two wells (MW-6 and MW-7) with groundwater concentrations that significantly exceed the Water Quality Objectives(WQOs)established for the Site. In their September 17, 2009 letter, the Regional Board references the following WQOs: TPHd (100 micrograms per liter [pg/L]), TPHg (5 pg/L), and naphthalene (17 pg/L). Based on Regional Board guidance documents, ARCADIS believes the WQO for TPHg is 100 pg/L, and not 5 pg/L as stated in the letter. Based on the June 2009 analytical results, TPHd (1,300 pg/L), TPHg (740 pg/L), and naphthalene (40 pg/L) concentrations in well MW-6 exceed WQOs. Well MW-7 indicated TPHd (300 pg/L) and TPHd (320 pg/L) concentrations that exceed WQOs. A summary of the analytical results for groundwater is presented in Table 3. In order to further assess potential soil impact adjacent to boring S3 and monitoring wells MW-6 and MW-7, Chevron EMC is proposing to collect soil samples in the vicinity of these locations according to the following scope: Proposed Scope of Work Task 1: Project Initiation • Update the site-specific Health and Safety" Plan (HASP). A copy of the HASP will be on-site during all field activities and will include Journey Management Plans (JMPs) and Job Safety Analyses (JSAs). Loss Prevention Observations (LPGs) will also be performed during the field ' activities. • Secure access agreement with Delta Blood Bank to advance four soil borings at the Site. Delta Blood Bank is the current title holder of the property. • Mark the proposed boring locations and notify Underground Service Alert to mark underground utilities located in the vicinity proposed borings. • Notify the Regional Board, Delta Blood Bank, and Chevron EMC of the scheduled field activities. Page: G:ICvmnomUEMChe 0&%Conal HollowlClosura Report AddendumICknumReport Addendum11.12.09.dw 3/5