SITE INFORMATION AND CORRESPONDENCE

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Joe Lentini - 2 - 5 November 2010 Shell Mountain House groundwater ranged from about 28 to 35 feet bgs. Groundwater flow generally was toward the northwest in Neighborhood B and to the northeast in Neighborhoods C and D. Gradients ranged from 0.002 to 0.02. Groundwater samples were submitted for laboratory analysis of total petroleum hydrocarbons as diesel (TPHd), TPH as crude (TPHc), BTEX, and naphthalene. Consistent with results observed in previous quarters, no TPHc, TPHd, BTEX or naphthalene was detected in any of the groundwater samples obtained from Neighborhoods B, C or D. Overall, the third quarter groundwater monitoring results were consistent with results observed in previous quarters. Our comments are presented below. 1. The analytical laboratory testing that detected the helium tracer gas at 28,200 pg/m3 (28.2 pg/L) was performed at a detection limit (DL) that greatly exceeded the DTSC's suggested DL of 10 pg/L' for this compound. Although the presence of the leak potentially presents some doubt as to whether BTEX in SVP-1 is actually non-detect (ND), resampling is not warranted. The results of soil vapor sampling conducted in December 2006 in the area of SPV-1 and in other excavation areas detected benzene in soil gas as high as 570 pg/m3. Johnson & Ettinger (J&E) modeling of the highest benzene concentrations in these areas showed that the soil gas posed no incremental cancer risk from intrusion into indoor air in excess of the one-in-a-million de minimis standard. The totality of the results indicate that the residual concentrations of petroleum hydrocarbon contamination in soil gas in Area 5 warrant no further action (NFA). 2. With the exception of a few detections of TPHd that were below the water quality objective of 100 pg/L, the monitoring results over the past five quarters have been ND for petroleum hydrocarbons. These results indicate that it is appropriate for Shell to request an NFA determination for this Site. As discussed in previous correspondence, Shell anticipated that it would submit an NFA request. Please submit the request by 10 January 2011. Staff will review that report to determine if NFA is appropriate and make recommendations for attaining site closure. 3. A review of the State Water Resource Control Board's (State Water Board's) GeoTracker database indicates that electronic data deliverables (EDFs) from 2008, 2009 and before 2007 have not been submitted. The x, y, z well survey data are also absent. The GeoTracker Global Identification number for this site is SL06077772408. Be advised that submission of site data to the GeoTracker database was required starting in September 2001. Submission to the State Water Board's GeoTracker database is required by Title 23 and Title 27 the California Code of Regulations. All documents, including work plans, correspondence, quarterly monitoring reports, investigation/cleanup reports, etc., and all analytical and site data must be electronically uploaded to the GeoTracker database and is due at the time the paper copy is submitted to this office. Until you receive further direction from Central Valley Water Board staff, you will be required to submit paper copies of all reports and correspondence. For specific information about EDF submittals, you may call the GeoTracker help-desk at (916) 327-3918 or log on to the State Water Board's GeoTracker web site at: http://www.geotracker.swrcb.ca.gov, and click on the Electronic Advisory—Active Soil Gas Investigations, Department of Toxic Substances Control/California Regional Water Quality Control Board Los Angeles Region, 28 January 2003