SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Former Unocal #0187 6 Page 2 437 E. Miner Avenue October 23, 2008 Stockton, CA hollow stem auger drilling, but details on the size of the augers and the sampling equipment to be used for continuous collection of samples is not clarified. The Work Plan states that the deep probes will have sand placed three inches below the screen around the screen and three inches above the screen, one foot of dry bentonite will be placed above the sand and the remainder of the borehole will be filled with hydrated granular bentonite. Please be advised that a bentonite grout must be placed above the dry bentonite not just hydrated bentonite granules. The soil vapor study portion of the Work Plan is not approved as adequate and necessary. Technical justification for not using the existing vapor probes and for installation and placement of the proposed vapor probes must be provided. The other comments above must also be addressed. The Work Plan proposes to redevelop U-17 by using a surge block and purging ten well volumes of water from the well. This portion of the Work Plan is approved and should be performed as soon as possible. In an EHD letter dated November 9, 2006, Chevron was informed that an evaluation of the remaining soil contamination leaching into the groundwater had to be performed. The previous soil vapor probe investigation was conducted in October and November of 2006 and the report of that work was not submitted until July 2007. On August 13, 2007, the EHD met with Chevron to discuss this site and EHD wrote a summary letter of the meeting dated October 25, 2007, which included the following statement "A proposal for further evaluation of potential soil vapor intrusion and leaching of contaminants from the soil to groundwater is still required. Evaluation of feasible alternatives to remediate the concentrations of contaminants in the groundwater in the area of U3 is also required. These proposals should be submitted to EHD by December 10, 2007." In December 2007, a Membrane Interface Probe (MIP) and Cone Penetrometer Testing (CPT) work plan was submitted which stated that "Once the locations and depth of the remaining petroleum hydrocarbons are identified, remediation methods will be evaluated to reduce the residual concentrations to a level where monitored natural attenuation can be used to achieve water quality objectives in a reasonable time frame." The MIP and CPT investigation was completed in March 2008 but the report of the work was not submitted until July 2008. In a letter dated August 22, 2008, the EHD commented on the MIP and CPT investigation report and directed Chevron to submit a plan for conducting a soil vapor study, testing other remedial alternatives and restoring U-17. Instead Chevron submitted a plan for a soil vapor study, restoration of U-17 and a request for postponing remedial technology evaluation. The soil and groundwater in the southeast area of this site must be actively remediated so that site clean up will be completed within a reasonable time (estimated to be about 10 years). Chevron is not in compliance with EHD directives. A work plan that includes technical justification for not using the existing vapor probes, for installation and placement of the proposed vapor probes, addresses the -0ther-EHD comments on-the-October 10;-2008 Work Plan and proposes feasibility testing of remedial options must be submitted to the EHD within 30 days of the date of this letter.