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Mr Jeffrey Wong <br /> C A M B R I A February 23, 2006 <br /> Item Evaluation Criteria Comments/Discussion <br /> 112 mile southwest of the site The well was installed <br /> in 1988 and is screened from 150 to 310 fbg and <br /> sealed from the surface to 50 fbg No other wells <br /> were identified within a half-mile radius of the site <br /> 4 3 Likelihood of Impact to Wells Impact due to site activities is unlikely due to the <br /> distance of the domestic well from the subject site <br /> 4 4 Likelihood of Impact to Surface No surface water bodies were identified within a <br /> Water half-mile radius of the site The Mokelumne River <br /> and industrial waste ponds are located just over 112 <br /> mile north of the site Impact of surface waters due <br /> to site activities is unlikely due to groundwater depth <br /> and distance from the subject site to surface water <br /> 5 Risk Assessment <br /> 5 1 Site Conceptual Exposure Model The site is currently an active fuel station The area <br /> (current and future uses) surrounding the site is commercial and industrial <br /> Future use of the parcel is assumed to be similar to <br /> current use <br /> 5 2 Exposure Pathways Potential exposure pathways include on-site <br /> commercial occupant inhalation of vapors from <br /> impacted soil, dermal exposure, particle inhalation, <br /> and ingestion of impacted soil by on-site construction <br /> workers, and ingestion of impacted groundwater off <br /> site <br /> 5 3 Risk Assessment Status No formal risk assessment has been performed for <br /> the site <br /> 5 4 Identified Human Exceedances NA <br /> 5 5 Identified Ecological NA <br /> Exceedances <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Shell advanced boring SB-6 to further assess the presence of MTBE in soil near the USTs The <br /> boring is located adjacent to borings; GP-1 and S13-1 and SVE well SVE-2 MTBE was detected <br /> at concentrations of I 1 ppm at 34 fbg, 0 47 ppm at 39 fbg, and 0 85 ppm at 54 fbg No MTBE <br /> was detected in samples collected at 24 and 29 fbg in this boring As requested by SJCEHD, <br /> Shell attempted to target silty soils Samples SB-6-24, SB-6-34, and SB-6-39 were collected in <br /> silts No silts were encountered below that depth to the total explored depth of 65 fbg (depth to <br /> groundwater was approximately 59 fbg) - <br /> Boring SB-1 (advanced in January 1999) contained the highest MTBE concentrations detected in <br /> soil at this site 92 9 ppm at 25 fbg, 15 0 ppm at 35 fbg, and 2 30 at 40 5 fbg Concentrations at <br /> 12 <br />