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Mr. Carol Campagna -2 - 10 February2090 <br /> •Shell Stockton Terminal . <br /> months to obtain the air discharge permit, six to nine months for PG&E to install a new or <br /> upgraded electrical service for the Site, and as much as six months to install and construct the <br /> AS/SVE wells and remediation system. Startup may occur about one month after construction <br /> is complete. Shell will conduct bi-monthly parameter collection and monthly vapor sampling. <br /> Samples will be submitted for analysis by EPA Method 8260B for TPHg, benzene, toluene, <br /> ethylbenzene and xylenes (collectively BTEX) and methyl tertiary butyl ether (MTBE). <br /> Groundwater monitoring at the Site is conducted pursuant to Monitoring and Reporting <br /> Program (MRP) No. R5-2005-0810. The Annual Report summarizes groundwater conditions <br /> observed at the Site in August and November 2009. Depth to groundwater averaged about <br /> 12 feet bgs and generally flowed to the south-southwest at a gradient of about 0.002 feet/foot <br /> with some variability. The vertical gradient was upward in August and downward in November. <br /> With the exception of the upward gradient, the observations were fairly consistent with <br /> previous observations. <br /> No separate phase hydrocarbons (SPH) were observed in monitoring wells during 2009. <br /> During the second half of 2009, maximum concentrations of TPHg, TPHd, and benzene were <br /> observed in SA2 well MW-10 at 31,000 micrograms per liter (tag/L), 5,300 pg/L, and <br /> 12,000 pg/L, respectively. SA1 well MW-1 contained the highest concentrations of MTBE and <br /> TBA at 18,000 pg/L and 10,000 pg/L, respectively. <br /> Groundwater remediation at the Site is currently being performed by operating a groundwater <br /> extraction (GWE) system which pumps water from MW-1. The GWE has been operated since <br /> April 2006. During the second half of 2009, the GWE treated about 39,050 gallons of water at <br /> an extraction rate of 0.16 gallons per minute and removed about 7.1 pounds (Ibs) of TPHg, <br /> 0.9 lbs of benzene, and 6.0 lbs of MTBE. <br /> Our comments are presented below. <br /> 1. Page 2 of the Revised RAP states that once the system is no longer removing hydrocarbon <br /> mass or contributing to declining hydrocarbon concentrations, active remediation will cease <br /> and no further active remediation will be required. We do not necessarily concur that no <br /> further active remediation will be required at that time. The ultimate remedial objective for <br /> the site is to achieve the background water quality objectives. The Central Valley Water <br /> Board staff will work with Shell to ensure that the current remedial system is optimized and <br /> operates to its full capacity. When operation of this AS/SVE system is no longer practical or <br /> effective, its use can be discontinued. However, as previously discussed, if Site use <br /> changes or more efficient remedial technologies become available, Shell will be required to <br /> continue efforts to achieve background water quality, if possible, through active <br /> remediation. <br /> 2. The remedial system design places AS wells in relatively close proximity to SVE wells. We <br /> are concerned that this arrangement could result in the extraction of soil vapors that are <br /> diluted by sparged ambient air. If this starts to occur, Shell should consider offsetting the <br /> sparging operation from the time extraction is occurring to extract vapors that do not <br /> originate directly from the AS wells. <br /> 3. The sampling plan does not include laboratory analysis for TPHd in soil vapors despite its <br /> well documented occurrence at elevated concentrations in soil and groundwater. The <br />