SITE INFORMATION AND CORRESPONDENCE

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Mr.M. Scott Mansholt—CEMC First Semi-Annual 2007 Groundwater Monitoring and Sampling Report October 29,2007 Vernalis Pump Station Page 2 of 5 gasoline,jet fuel,and diesel. The KM pipeline is located along and outside of the northeastern site boundary within the UPRR right of way(ROW). A 1995 Environmental Site Assessment determined that the KM product pipeline was installed approximately 4 to 5 feet below ground surface(bgs)during 1985,was constructed of 0.25 inch-thick wrapped steel,and was under the control of a subsidiary of Southern Pacific Pipeline Company. ' Standard Oil(predecessor of Chevron)operated the Vernalis Pump Station from 1902 to 1935 as part of the former OVP system that transported heated heavy petroleum(crude oil) from San Joaquin Valley oil fields in Bakersfield to a refinery in Richmond, California. The OVP was located along the northeastern side of the site and parallel to the existing UPRR tracks and Highway 33. Site features included a boiler house, a pump house, a sump, an incinerator, a rubbish pit, cottages, and three bulk-storage tanks with secondary containment structures. These surface structures were located on the Arcos property. The property located immediately southeast of the Arcos property was a former Tidewater Associated Oil Company(TAOC; predecessor to Texaco and now Chevron)pump station(TAOC Ohm Pump Station). The 1995 Environmental Site Assessment indicated that the former Vernalis Pump Station was owned by Vernalis Enviropur-West, and was used for bulk storage of petroleum and oil products.' GROUNDWATER MONITORING AND SAMPLING MONITORING Groundwater monitoring and sampling began in 1998 and wells were monitored on an irregular basis until July 2005,when quarterly groundwater monitoring and sampling began. The first semi-annual 2007 monitoring activities were conducted on August 6, 2007,when depth to groundwater was measured in wells MW-1 though MW-7 using a hydrocarbon/water interface probe. Cumulative depth-to-groundwater measurements, groundwater elevations, and separate- phase oil(SPO)thickness measurements are presented in Table 1. A map showing the August 2007 site potentiometric surface is presented on Figure 3. A map showing the August 2006 site potentiometric surface is presented on Figure 4 for comparison. Field data sheets are included as Attachment A. A summary of the first semi-annual 2007 monitoring results are presented as follows: • Site Wells in Program: MW-1 through MW-7. Well MW-5 is flush mounted with the ground surface and the other six wells have above-ground, stovepipe completions. • Wells Containing SPO: Well MW-1 containing an oleophilic sock due to historic observations of SPO. • Depth to Groundwater at Site: Ranged from 33.23 feet below top of casing(btoc) (MW-6)to 37.32 feet btoc (MW-1). The average depth to groundwater at the site is 36.47 feet btoc based on all depth-to-groundwater measurements collected to date from these wells. • Calculated Groundwater Elevation: Ranged from 69.06 feet(MW-1)to 72.24 feet (MW-3)above mean sea level(AMSL). The average groundwater elevation at the site is 71.05 feet above MSL based on all groundwater elevation measurements collected to date from these wells. 1. Geological Technics,Inc., 1995. Preliminary Environmental Site Assessment: Vernalis Property,35500 Welty Road, Vernalis, California. February.