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Mr.M. Scott Mansholt—CEMC Third Quarter 2006 Groundwater Monitoring and Sampling Report October 25,2006 Vernalis Pump Station Page 3 of 5 Technical Approach to Site Evaluation and Decision-Making for the Historical Pipeline Portfolio (herein referred to as the CTA), diesel products are not associated with the Historical Pipeline Portfolio (HPP) sites and typically are not present at these sites.3 However,WQOs are applied to "diesel-range hydrocarbons"(extractable TPH, C10—C25)found in groundwater samples from HPP sites because no WQOs are established for crude oil/Bunker C fuel oil, and historical data indicates that diesel-range hydrocarbons are often detected at sites affected by crude oil/Bunker C fuel oil. Per the CTA, groundwater samples are quantified against a diesel standard so that the comparison to the WQOs is as direct as possible. Based on the previous soil and groundwater investigations,petroleum-affected soil and groundwater have been delineated vertically to a maximum depth of approximately 80 feet bgs. The RWQCB approved the delineation results in their letter dated March 19,2004. Based on the 2005 site investigation, it appears that affected soil is laterally delineated north-northwest,north- northeast, south-southwest, and south-southeast of the former boiler house and pump house, and affected groundwater is delineated northwest and west of the former pump house and boiler house. Groundwater monitoring wells MW-5,MW-6, and MW-7 were installed during the May 2005 investigation. A report of this investigation was prepared and submitted to the RWQCB in August 2006. A sheen of separate-phase oil(SPO)was observed in well MW-1. TPH as diesel- range organics(TPHd)have been consistently detected in one well,MW-7, at concentrations ranging from 240 to 710 micrograms per liter(µg/L). No TPH as gasoline-range organics (TPHg)or benzene,toluene, ethylbenzene, and total xylenes(BTEX)have been detected in the groundwater from the site wells. Low levels of polynuclear aromatic hydrocarbons(PAHs)have been detected in groundwater from MW-2,MW-3,MW-5,MW-6, and MW-7. GROUNDWATER MONITORING AND SAMPLING MONITORING On August 10, 2006, depth to groundwater was measured in wells MW-2,MW-3,MW-4,MW-6, and MW-7 using a hydrocarbon/water interface probe. Depth to groundwater was not measured in MW-1 because of the presence of a petroleum-absorbing(oleophilic) sock and MW-5 because it was not accessible during the monitoring event. Depth to groundwater in these wells ranged from 33.87 feet below top of casing(btoc)in MW-6 to 37.75 feet btoc in MW-4. Calculated groundwater elevations ranged from 70.85 feet(MW-7)to 71.52 feet(MW-4) above mean sea level. The approximate groundwater flow direction beneath the site is to the east at a calculated gradient of approximately 0.001 ft/ft. Cumulative depth-to-groundwater measurements, groundwater elevations, and SPO thickness measurements are presented in Table 1. A map showing the potentiometric surface is presented on Figure 3. Field data sheets are included as Attachment A. SAMPLING Following depth-to-groundwater measurements,wells MW-6 and MW-7 were purged using the regulatory approved low-flow minimal drawdown method. Wells MW-2,MW-3, and MW-4 were not sampled because the water volume in the wells was insufficient for sample collection. MW-5 was not accessible during sample collection and was not sampled. A low-flow submersible pump with dedicated polyethylene tubing was used. During the purge process,pH, specific conductance,temperature, oxygen-reduction potential,turbidity,and dissolved oxygen water-quality parameters were recorded. After water-quality parameters stabilized(stabilization 3. Geomatrix Consultants,Inc.,2005. Technical Approach to Site Evaluation and Decision-Making,Historical Pipeline Portfolio,Central Valley Region. February.