SITE INFORMATION AND CORRESPONDENCE

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Joe Lentini • • Former Pipelines, Tracy 2 5 November 2010 The Update provided the property owner of the Site, Golden State Developers, with a brief summation and drilling schedule for the proposed 11 shallow and four deep well installations. The Residential Well Report states that domestic supply wells No. 1 (24080 Hansen Rd), No. 2 (24380 Hansen Rd), No. 3 (24322 Hansen Rd), No. 5 (24184 Hansen Rd) and No. 6 (23928 Hansen Rd) were sampled on 15 June 2010. The samples were submitted for laboratory analysis for TPH as diesel (TPHd), TPH as crude (TPHc), and benzene, toluene, ethylbenzene, and xylenes (collectively BTEX). Laboratory analytical results showed that these wells were all non-detect (ND) for all constituents tested. Therefore, consistent with the 8 March 2010 Work Plan, no additional sampling will be conducted in these wells. The Investigation Report describes the results of the drilling, soil sampling, monitoring well installation, and groundwater sampling of 13 well borings (MW-1 through MW-4, MW-5A, MW-56, MW-5C, and MW-6 through MW-11) installed along the northwest alignment of the pipeline between 12 July and 23 August 2010. All wells except MW-513 and MW-5C are designated as shallow wells and installed at a maximum depth of 50 feet bgs. MW-5B and MW-5C are deeper wells with total depths of 115 and 180 feet bgs, respectively. The original locations and sampling plan for the monitoring wells were presented in the 15 October 2009 Monitoring Well Installation Work Plan (Work Plan) which proposed to (1) collect depth discrete grab groundwater samples and install a sentinel well cluster between the Trench 1 area and the domestic supply wells to the north, (2) install three shallow wells at the Trench 2 area, (3) install three wells in the Trench 3 area, including a cluster near boring B-69, and (4) install three shallow wells in the Trench 4 area. Shell's 21 January 2010 Work Plan Addendum modified the sampling and well locations. The Addendum proposed to relocate the MW-5 wells, eliminate a shallow boring from the Trench 3 area, collect additional soil and groundwater samples, and extend the deepest well to 172 feet bgs. Central Valley Water Board staff conducted a site visit on 14 July 2010 and observed the well casing installation of MW-9 through a hollow-stem auger. The drillers stated that heaving sands were encountered in several boreholes. The boring logs in Appendix C of the Investigation Report show that the upper 50 feet of soil generally consists of silt to about 35 feet bgs, which contains a 5-foot thick sand layer at about 15 feet bgs. A bifurcated sand aquifer of variable thickness is encountered at depths ranging from 35 to 48 feet bgs. Shell screened the shallow wells across this sand aquifer. Depth to groundwater varied from about 35 to about 40 feet bgs in this shallow zone. Using the groundwater levels measured in the shallow wells, Shell calculated that that groundwater flow is to the northwest at a gradient of about 0.0006 feet per foot. Laboratory analytical results show that TPHc and TPHd are present in soil samples collected from MW-1, MW-2, MW-4 and MW-5 at depths ranging from five to 45 feet bgs. Maximum contaminant concentrations were observed in the soil samples collected from 30 feet bgs in MW-2. TPHc and TPHd were detected at 79,000 and 41,000 milligrams per kilogram (mg/kg), respectively. Based on the