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Mr.M. Scott Mansholt—CEMC 2008 Annual Groundwater Monitoring and Sampling Report April 16,2008 US Can-Welty Road Page 2 of 6 from the early 1900s until it was decommissioned in the 1970s. The TAOC pipeline was used to transport heated crude oil from the Central Valley to the San Francisco Bay Area. Kinder Morgan Energy Partners,L. P. currently operates a pipeline located between the site and Highway 33 that transports gasoline,jet fuel, and diesel. Western Farm Service(WFS)is located directly northeast of the site across Highway 33 and has stored and distributed bulk liquid and dry fertilizers since 1969. A former gas station is also located northeast of the site. GROUNDWATER MONITORING AND SAMPLING MONITORING Groundwater monitoring and sampling began at the site in 1999 when wells were monitored and sampled on an irregular basis. At the request of the RWQCB, quarterly groundwater monitoring and sampling began in April 2005 and,based on historical groundwater quality results,was reduced from quarterly events to an annual event in August 2007. Depth to groundwater was measured in wells MW-1,MW-2,MW-3, and MW-4 on January 28,2007,using a hydrocarbon/water interface probe. These measurements as well as historical depth-to- groundwater measurements, groundwater elevations, and product thickness are presented in Table 1. Groundwater monitoring data from the adjacent Vernalis Pump Station site are also included in Table 1 for reference and completeness. Maps showing the January 2008 and July 2007 potentiometric surfaces,using data from both the US Can-Welty Road site and the Vernalis Pump Station site, are presented on Figures 3 and 4,respectively. Field data sheets are included as Attachment A. The groundwater monitoring data collected from the site in January 2008 is summarized below. • Site Wells in the Program: MW-1,MW-2,MW-3 and MW-4. WFSMW-1 was removed from the program at the request of the RWQCB in August 2007 and MW-5 could not be sampled due to site access limitations. All six wells are flush mounted at the ground surface. • Depth to Groundwater at Site: Ranged from 33.54 feet below top of casing(btoc) in MW-2 to 35.85 feet btoc in MW-4. Depth-to-groundwater measurements collected to date indicate that the average depth to groundwater at the site is 34.07 feet btoc. • Calculated Groundwater Elevation: Ranged from 71.16 feet above mean sea level (MSL)in MW-I to 71.47 feet above MSL in MW-2. Groundwater elevation measurements collected to date indicate that the average groundwater elevation at the site is 71.53 feet above MSL. • Approximate Groundwater Flow Direction/Gradient: East at 0.001 feet per foot (ft/ft). Data from both the US Can-Welty Road site and the Vernalis Pump Station site were used in calculating the groundwater flow gradient. Wells that were found to contain separate-phase oil (SPO)were not used in the groundwater flow-gradient calculations. SAMPLING Between January 28 and January 30,2008, following depth-to-groundwater measurements,wells MW-3 and MW-4 were purged using the three well casing-volume purge method due to a slow recharge rate.