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• BTEX by EPA Method 8260B • MTBE, TBA, ETBE, DIPE, EDB, 1,2-DCA, TAME, ethanol, and naphthalene by EPA Method 8260B All soil samples will be analyzed on a standard turnaround time. 5.8 Decontamination Reusable downhole drilling and sampling equipment will be thoroughly decontaminated before each use. The decontamination station will include a self-contained wash bin, steam cleaner, and holding tank. All equipment will be decontaminated with a pressure washer and scrubbed with Alconox®detergent or equivalent. Decontamination water will be stored onsite in 55-gallon drums and managed as described in Section 5.9. 5.9 Investigation Derived Waste Disposal Soil cuttings, decontamination water, and groundwater generated during monitoring well installation will be segregated and placed in Department of Transportation (DOT)compliant 55-gallon drums, labeled, and stored in a designated area onsite. The drums will be sampled for waste characterization and transported to an approved facility for disposal following receipt of analytical results. 5.10 Monitoring Well Development and Survey After a minimum of 72-hours following monitoring well installation, the new wells will be developed using a combination of groundwater surging and extraction to dislodge fine sediment from the sand pack and remove sediment from the well casing to the extent practicable. Surging and extraction will continue until at least ten well casing volumes of groundwater are extracted and sediment in the extracted groundwater is negligible. The wells will be surveyed by a California state licensed surveyor. 5.11 Groundwater Sampling Following monitoring well installation, development, and surveying; the wells will be added to the existing groundwater monitoring and sampling schedule and sampled on a semi-annual basis. Monitoring wells will be sampled via EPA Low-Flow(minimal drawdown) methodology using a QED Bladder Pump or similar. Groundwater will be purged from monitoring wells at a rate of 100-500 milliliters per minute (mL/min) until stabilization is reached. Temperature, pH, specific conductance, oxidation-reduction potential, dissolved oxygen, and water level drawdown (water quality measurements)will be recorded every 3-5 minutes to determine stability. A purged well has reached stabilization when three consecutive sets of water quality measurements within defined parameters are recorded and drawdown is negligible. Once a monitoring well has been purged and stabilization is achieved, groundwater samples will be collected using polyethylene tubing to fill appropriate laboratory-supplied containers. Samples will be labeled, stored on ice at or below 4 degrees Celsius, and transported under chain-of-custody to the laboratory. 5.12 Schedule and Reporting GHD will implement the proposed work plan after receiving approval from the RWQCB, or within 60 days of work plan submittal. GHD will prepare and submit Department of Water Resources (DWR)Well Completion Reports (Form 188)to the DWR and will submit a well installation report summarizing site assessment activities to the RWQCB within 90 days of completing the fieldwork. The report will include all analytical laboratory reports, permits, and provide conclusions and recommendations. GHD I Phillips 66 112594700 1 Offsite Investigation Work Plan 5