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Stantec Addendum Work Plan for Human Health Risk Assessment Former Tosco Bulk Terminal #10013 February 14, 2011 Soil Gas Probe Installation and Soil Gas Sampling and Analysis Three temporary soil gas probes will be installed (SG-1 through SG-3)and soil gas samples will be collected under the direction of a Stantec field representative at the locations shown on Figure 2. This work will be done in accordance with the DTSC protocol presented in Attachment 2. The soil gas probes will be driven to the target depth of five feet below ground surface using an electric rotary hammer or Strataprobe. After each probe is set to the target depth, the sampling line will be installed and capped with a vapor-tight valve, the valve will be closed, and the probe will be raised slightly to expose the vapor sampling port. Due to sampling from temporary soil gas probes and sending the samples into a fixed laboratory, the default three tubing volumes (based on field calculations depending on the diameter and length of the inert tubing) will be purged from each temporary soil gas probe prior to sampling using a 60 ml surgical syringe. Purging of the line will commence approximately 20 to 30 minutes after the probe is set to allow for equilibrium. Purge and sample rates for the proposed samples will be between 100 and 200 milliliters per minute(ml/min)to limit stripping and prevent ambient air intrusion. During sampling, a leak check gas (1,1- difluroethane)will be used to confirm that the sample train and probe rod is tight and leak free. Soil gas sampling will not be performed within 72 hours of a significant rainfall. Stantec will oversee the collection of soil gas samples in 1 liter Summa TM canisters and submit them under chain-of-custody documentation to a California state-certified laboratory (Air Toxics Ltd. located in Folsom, California)for chemical analysis. The vapor samples will be analyzed for TPHg, BTEX, VOCs, and fuel oxygenates including MTBE, TBA, di-isopropyl ether(DIPE), ethyl tertiary butyl ether(ETBE), tertiary-amyl methyl ether(TAME), ethanol, ethylene dibromide(EDB), and 1,2- dichlorethane (1,2-DCA), and 1,1-difluoroethane (leak check gas) using EPA Method TO-15. Laboratory detection levels will be set to accommodate the appropriate assessment of the residential land use RWQCB-San Francisco Bay Region (SFBR) Environmental Screening Levels (ESLs)and CalEPA California Human Health Screening Levels(CHHSLs). A duplicate sample will be collected and analyzed along with a laboratory provided trip blank to aid in quality control/quality assurance measures. Soil Gas Probe Borehole Abandonment Following the completion of sampling, the soil gas probes will be removed and the sampling points will be grouted from the total depth to ground surface using neat cement. Reporting The stand-alone report will include, tabulated analytical data comparing results with residential use RWQCB-SFBR ESLs and CalEPA CHHSLs, field notes, soil vapor laboratory analytical reports, chain-of-custody documentation,and conclusions. Once the required soil gas data is approved and verified, the data will be used for risk evaluation purposes related to the proposed HHRH. 3