SITE INFORMATION AND CORRESPONDENCE_2001-2018

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Ms. CarolCampagna -2 - Shell 2 _Shell Stockton Terminal 27 March 2009 under a site-specific WDR. If determined feasible, CRA anticipates approval of a site-specific WDR would take nine months to one year. As requested in the RAP, the Report also presents a brief work plan for implementing an air sparge/soil vapor extraction (AS/SVE) pilot test. The AS/SVE pilot test is based on site data, generated during the DPE pilot test, which Shell has interpreted as evidence that the soil formation is more permeable than previously thought. Shell is proposing to first collect vapor samples to establish existing conditions and then performing a two-day pilot test. Existing wells OW-02 and MW-22 will be utilized as air sparge and vapor extraction wells, respectively. MW-20, OW-3, OW-7 and OW-8 will be used as observation wells. All vapor samples collected will be analyzed for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylene (BTEX), and methyl tertiary butyl ether (MTBE) by EPA Method 82608. The 2 February 2009 Groundwater Monitoring and Remediation Report, 2008 Semi-Annual Report - 3rd and 4«' Quarters (Annual Report) summarizes groundwater conditions observed at the site during 2008. The prevailing horizontal and vertical groundwater gradients are southwesterly and downward, respectively. No separate phase hydrocarbons (SPH) were observed in monitoring wells during the second half of 2008. Maximum concentrations of TPHg and TPH as diesel (TPHd) were observed in SA1 wells MW-1 and MW-16, respectively. MW-1 contained 30,000 micrograms per liter (Ng/L) of TPHg, and MW-16 contained 6,800 pg/L of TPHd. MW-24 and MW-1 contained the highest concentrations of benzene and MTBE at 3,900 pg/L and 17,000 pg/L, respectively. MW-1 contained the highest concentration of tertiary butyl alcohol (TBA) at 8,800 pg/L. SA1 has historically contained the highest concentrations of dissolved petroleum hydrocarbons. Our comments are presented below. 1. We concur with Shell's proposal to conduct sampling to determine baseline groundwater concentrations to evaluate the potential for land disposal and re-injection. The California Code of Regulations, Title 27, section 20415(e)(10) contains statistical procedures recommended for establishing baseline concentrations. Facilities disposing of treated wastewater to land are required to use data from at least 12 consecutive groundwater monitoring events to determine background concentrations. However, it may be possible to begin discharging before completing all 12 events with a provision to continue background sampling and revise background concentrations each quarter with new data. As stated in our 16 January 2009 email, if Shell chooses the re-injection option, higher discharge limits can be allowed when discharging back into polluted groundwater. The actual limits would be the subject of negotiations between Shell and Board staff. However, Regional Board staff are concerned about potential for the re-injection to cause mounding, which could exacerbate plume migration. By 30 April 2009, Shell needs to submit a work plan to monitor for baseline concentrations, in order to evaluate the land disposal options. 2. Comment No. 5 of our 14 September 2007 letter states: We concur with Shell's proposal to discharge the treated DPE effluent to the vacant lot north of the facility, if Shell enrolls in Order No. R5-2003-0044 and meets all the requirements of that Order. We agree that implementation of this disposal method will depend[on]the results of infiltration testing to determine capacity of the soil in this area. However, we are concerned about break- .