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Additional Soil and Ground"t er Investigation Work Plan -° CCT Stockton Rail Yard, 1645 Cherokee Lane, Stockton,CA October 4, 2007 Page 5 from these wells was TPH-d, at a maximum concentration of loo µg/l in a samples collected from wells MW-1 and MW-3 on September 1, 2000. By the end of 2001, groundwater levels had declined and there was an insufficient volume of groundwater available to collect groundwater samples. These wells were destroyed in June 2005 in preparation for soil excavation activities. The locations of these destroyed wells are included on Figure 3. Based on data presented in the RAR, a grab groundwater sample (W-1)was collected from the excavation on July 13, 2005. At the direction of a representative from the SJCEHD, a grab sample was collected'of the water that had accumulated within the bottom of the open excavation. This grab sample was collected from water that had percolated into the bottom of the open excavation within the immediate vicinity of impacted soils being staged for removal. TPH-d was detected in sample W-1 at a concentration of 4,46o pg/l. However, all other analytical results from sample W-1 were below their respective laboratory reporting limits. Following completion of the excavation activities, and prior to backfilling, the accumulated water within the excavation was pumped out into a Baker tank for subsequent characterization and disposal. A grab water sample from the open excavation (W-1) collected prior to the pump out does not likely represent actual groundwater conditions. The elevated concentration of TPH-d in sample W-1 was likely a result of mixing with impacted soils within the excavation that were being staged for removal. Historical groundwater monitoring data from the site monitoring wells (Table 1) are inconsistent with the results for grab water sample W-1. 5.0 SITE ASSESSMENT ACTIVITIES Based on a review of data collected at the site,TRC proposes to advance four(4) onsite borings for the purpose of collecting soil and grab groundwater samples (Figure 5) to further assess the extent of hydrocarbon impacted soil and groundwater. 5.1 Pre-Field Activities Prior to commencing soil boring activities, drilling permits will be acquired from SJCEHD. Underground Service Alert(USA)will be notified at least two days prior to field activities to mark underground utilities at the proposed boring locations and around the property boundaries. In addition, a private utility locator will be contracted to confirm the absence of buried utilities at each proposed boring/well location. Prior to advancing each boring, a pilot hole will be cleared with an air knife to approximately 5 fbg to verify the absence of buried utilities. A site and job specific health and safety plan that promotes personnel safety and preparedness during the planned activities will be developed prior to mobilization and a copy will be available onsite during the field activities. On the morning of the day that the field activities are to commence, a "tailgate"meeting will be conducted with all exclusion zone workers to discuss the health and safety issues and concerns related to the specific work. 5.2 Soil and Groundwater Sampling Soil borings will be installed to determine the extent of impacted soil that still remains in place at the site and groundwater samples will be collected from the borings to determine the lateral distribution of dissolved-phase hydrocarbons in groundwater.