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Mr. James L. Barton P.G. Central Valley Regional Water Quality Control Board December 3, 2015 Page 2 was detected in the soil sample collected at a depth of 23 feet bgs from Boring B-41 at a concentration of 40 mg/kg. Groundwater samples were also collected from each boring at discrete depths. The samples were analyzed for TPHg by EPA Test Method 8260, TPHd by EPA Test Method 80158, and VOCs by EPA Test Method 8260. TPHg and TPHd were detected in the groundwater sample collected at a depth of 15 feet bgs from Boring B-41 at concentrations of 990 and 350,000 pg/L, respectively. TPHd was also detected in the groundwater samples collected at 45 and 57 feet bgs at concentrations of 160 and 190 pg/L, respectively. Boring B-39 was drilled at the property boundary with the Union Pacific Railroad approximately 100 feet southeast of Boring B-41. A sample was collected from the first water encountered at 24 feet bgs. Analytical results of this sample indicated the presence of TPHg and TPHd at concentrations of 430 pg/L and 63,000 pg/L respectively. Boring B-36, approximately 100 feet northwest of Boring B-41, did not have detectable concentrations of TPHg or TPHd at first groundwater. The remaining borings northeast(Boring B-37) and southwest(B-38) of Boring B- 41 detected TPHd at a maximum concentration of 130 pg/L and based on the groundwater sampling conducted around boring B-41, URS concluded that groundwater concentrations decreased significantly both laterally and vertically away from Boring B-41. Various VOCs (1,1-Dichloroethene, 1,1-Dichloroethane, sec-Butyl Benzene, and cis-1,2- Dichloroethene) were detected at low levels (up to 7.0 pg/L) in groundwater samples from three borings (B-37, B-39 and B-41; however, none of the VOCs detected exceeded California Environmental Screening Levels. Groundwater flow direction at the site and in the B-7 area has historically been to the southwest. SCOPE OF WORK The Water Board's September 23 and 25 letters indicated that Well MW-5 in Area B-7 was reported to have the highest onsite concentrations of TPHd and that there was no vertical delineation of TPHd in this area. Per these findings, Amec Foster Wheeler proposes the installation of four soil borings in Area B-7 as detailed on Figure 2. Boring location rationale are as follows: • Location south-southwest of Well MW-5 to assess downgradient extent of TPHd • Location in vicinity of boring B-6 where TPHd was detected in a previous grab groundwater sample at a concentration of 21,000 pg/L • Location in vicinity of boring B-7 where TPHd was detected in a previous grab groundwater sample at a concentration of 5,300,000 pg/L • Location south-southwest of Well MW-1 B to assess downgradient extent of TPHd Amec Foster Wheeler