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Additional Soil and Groundwar5r Investigation Work Plan-Addendum CCT Stockton Rail Yard, 1645 Cherokee Lane,Stockton,California December 17, 2007 Page 2 As such, TRC has revised the plotted location of sample WWCSF-78 (Figure 4, Attachment 1) and adjusted the proposed boring location for one of the two borings previously proposed for the north side of the excavation boundary (Figure 5, Attachment 1). TRC has kept one of the previously proposed boring locations along the northeast side of the excavation boundary because this is reported to be in the downgradient direction. ONE GRAB GROUNDWATER SAMPLE ANALYSIS SJCEHD Comment Paragraph 4: SJC/EHD personnel went to the site...a grab groundwater sample was collected, but no documentation of, or laboratory analytical report for this sample was submitted with the CLS Report. TRC Response: After a thorough review of all electronic files provide to TRC by CCT and CLS, TRC was able to locate an analytical report that includes one water sample (GW-2) collected on September 2, 2005. Total petroleum hydrocarbons as gasoline were detected in sample GW-2 at a concentration of 510 micrograms per liter (µg/1). Total petroleum hydrocarbons as diesel were also detected in sample GW-2 at a concentration of 1,10o µg/1. In addition various volatile organic compounds and semi- volatile organic compounds were detected at low concentrations, below 50 µg/1. A copy of the analytical report is included in Attachment 2. SJC/EHD CONDITIONS SJCEHD Comment i, Paragraph 7: You understand and agree that the installation of groundwater monitoring wells may still be required. TRC Response: TRC understands that, pending the results of this investigation, groundwater monitoring wells may still be required. SJCEHD Comment 2, Paragraph 7: The proposed boring locations are to be moved for more appropriate collection of grab groundwater samples near the original source of the contamination from the former diesel underground storage tank(UST). TRC Response: TRC is proposing one additional boring location (for a total of 5 borings) in the middle of the excavation area, near the former location of the diesel UST. Due to the thick column of backfill that will be encountered in this proposed boring, no soil samples will be collected unless native soil is observed prior to encountering groundwater. This boring will be advanced primarily for the sole purpose of collecting a grab groundwater sample.