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Mr.Mike Oliphant—CEMC Soil and Groundwater Investigation Report March 29,2013 Ahern Road—Vernalis Page 5 of 6 CONCLUSIONS AND RECOMMENDATIONS SAIC evaluated the results of this investigation and concludes the following regarding the nature and extent of affected soil and groundwater at the Site: • Crude-oil affected soil and groundwater were encountered in borings advanced within the Highway 33 ROW. BTEX compounds were not detected in soil or groundwater samples within the ROW, but concentrations of TPHc, TPHd, and several PAHs exceeded screening levels. • A depth-discrete groundwater sample screened at 84 feet bgs in SB-2contained TPHd at a concentration of 250 µg/L. The WQO and ESL for TPHd is 100 pg/L, which indicates that the vertical extent of affected groundwater is not likely to extend substantially below the maximum depth achieved at the Site. • Ethylbenzene and xylenes were detected in the groundwater sample collected from SB-4 with xylenes concentrations exceeding the ESL and WQO. These compounds are not typically found in groundwater samples collected at HPP-BTR sites. Neither compound was detected in the soil samples from other Site soil borings. The detections of ethylbenzene and xylenes are not likely the result of former HPP-BTR operations. • TPHd was detected in groundwater from boring SB-6 at a concentration of 660 µg/L, exceeding the screening level. • Borings SB-7 through SB-9 were advanced down gradient of the other soil borings at the Site,with no compounds detected above conservative screening levels. Based on analytical results, the extent of affected soil and groundwater has been delineated in the down gradient direction. • The lateral and vertical extent of affected soil and groundwater has been effectively delineated at the Site. As discussed in the Revised Soil and Groundwater Investigation Work Plan,to additional borings along the Highway 33 ROW to the northwest of SB-3 are not recommended. Development plans in the short or intermediate term are unlikely due to statements in the San Joaquin County General Plan and Williamson Land Act restrictions. No further investigation is recommended for the Site. • SAIC recommends preparation of a human health risk assessment incorporating data collected during this investigation as well as data from the off-site US Can— Welty Road investigation. 10.SAIC,2011. Revised Soil and Groundwater Investigation Work Plan,Ahern Road—Vernalis, Vernalis,San Joaquin County, California. November.