ARCHIVED REPORTS_SECOND 2008 SEMI-ANNUAL GROUNDWATER MONITORING AND SAMPLING REPORT

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' M.Scott Mansholt—CEMC Second Semi-Annual 2008 Groundwater Monitoring and Sampling Report September 26,2008 Vernalis Pump Station Page 2 of 7 surface(bgs)in 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 the Richmond Refinery. 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)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 at the site in 1998 and wells were monitored on an irregular basis until July 2005, when quarterly groundwater monitoring and sampling began. Semi-annual and quarterly monitoring began at on-site wells MW-1 through MW-5 and off-site wells MW-6 and MW-7, respectively, in August 2007. ' The second quarter 2008 monitoring and sampling for MW-6 and MW-7 was conducted on April 9, 2008, and the third quarter 2008 monitoring activities were conducted on July 16 and July 17, 2008. For both events, depth to groundwater was measured in the wells using a hydrocarbon/water interface probe. Cumulative depth-to-groundwater measurements, groundwater elevations,and separate-phase oil(SPO) thickness measurements are provided in Table 1. A map showing the July 2008 site potentiometric surface is shown on Figure 3. A map showing the April 2008 groundwater elevations is indicated on ' Figure 4; there were only two data points (MW-6 and MW-7), which provided insufficient data to calculate groundwater flow direction or gradient. Field data sheets are included as Attachment A. A summary of the second quarter monitoring results for MW-6 and MW-7, and third quarter 2008 monitoring results for wells MW-1 through MW-7 are as follows: • Site Wells in Program: MW-1 through MW-5 (off-site wells MW-6 and MW-7 were properly abandoned in August 2008). Well MW-5 is flush mounted with the ground surface, and the other four wells have above-ground stovepipe completions. Monitoring wells MW-1 through MW-3 and MW-5 are monitored on a semi-annual basis. Monitoring well MW-4 has not been sampled since May 2006 due to a damaged casing, and the RWQCB approved abandonment of this well. • Wells Containing SPO: Well MW-1 contains an oil-absorbing(oleophilic) sock due to historic ' observations of SPO. • Depth to Groundwater at Site: Depth to groundwater was 34.69 and 35.91 below top of casing (btoc), respectively, during the second quarter monitoring of MW-6 and MW-7. Depth to groundwater measurements were collected from MW-1 through MW-7 during the third quarter of 2008, and ranged from 34.66 feet btoc(MW-6)to 38.66 feet btoc (MW-1). The average depth to ' 1. Geological Technics,Inc., 1995. Preliminary Environmental Site Assessment: Vernalis Property,35500 Welty Road, Vernalis, California. February.