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Mr.M. Scott Mansholt—CEMC Second Quarter 2007 Groundwater Monitoring and Sampling Report July 26,2007 US Can-Welty Road Page 2 of 6 northeast of the site across Highway 33 and has stored and distributed bulk liquid and dry fertilizers since 1969. In addition, a former gas station is 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. Quarterly groundwater monitoring and sampling began on April 2005 at the request of the RWQCB. On April 30,2007,depth to groundwater was measured in wells MW-1,MW-2,MW-3, MW-4,MW-5, and WFSMW-1 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. A map showing the April 30,2007 potentiometric surface,using data from both the site and the Vernalis Pump Station site, is presented on Figure 3. Field data sheets are included as Attachment A. The groundwater monitoring data collected from the site on April 30,2007, is summarized below. • Site Wells in the Program: MW-1, MW-2,MW-3,MW-4,MW-5 and WFSMW-1. All six wells are flush mounted at the ground surface. • Depth to Groundwater at Site: Ranged from 31.81 feet below top of casing(btoc) (MW-5)to 35.64 feet btoc(MW-4). Based on all depth-to-groundwater measurements collected to date,the average depth to groundwater at the site is 34.07 feet btoc. • Calculated Groundwater Elevation: Ranged from 71.48 feet(MW-1)to 71.94 feet (WFSMW-1)above mean sea level(MSL). Based on all groundwater elevation measurements collected to date,the average groundwater elevation at the site is 71.48 feet above MSL. • Approximate Groundwater Flow Direction/Gradient: East at 0.001 feet per foot(ft/ft). Data from both the 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 On April 30,2007, following depth-to-groundwater measurements,wells MW-5 and WFSMW-1 were purged using the regulatory-approved, low-flow minimal drawdown method. 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 criteria is presented on field data sheets), groundwater samples were collected. Wells MW-3 and MW-4 were not sampled due to insufficient groundwater recovery for sample collection. Laboratory-provided bottles were used to preserve the samples. The bottles were labeled, sealed, and placed immediately into an ice-cooled chest for delivery to Lancaster Laboratories, Inc. (Lancaster)under SAIC chain-of-custody protocol. Lancaster is a California-certified laboratory(ELAP#2116). Samples were not collected from wells MW-1 and MW-2 due to the presence of SPO in those wells. Field data sheets are included as Attachment A.