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SiTE CONCEPTUAL MODEL Prepared by Cambria Environmental Technology, Inc 210 Preferential Pathways Analysis No analysis has been performed Given the fact that groundwater Is typically deeper than 15 fbg at this site,and most underground utilities are buried less than 5 fbg, it is unlikely that underground utility trenches could act as preferential pathways 211 Other Pertinent Issues 1,2-DCA has been detected in groundwater samples collected from four of the site monitoring wells at concentrations as high as 4 7 parts per billion (ppb) 1,2-DCA concentrations appear to be stable Tertiary butyl alcohol(TBA)has been detected in groundwater samples collected from three of tho monitoring wells at the site TBA concentrations have been as high as; ppb We believe the TBA detected beneath the m., subject site is from an offstte source since oxygenated fuel was never sold at S�'31 this gas station The former service station ceased operation in 1983 or earlier Fuel oxygenates(including TBA)were not added to Shell gasoline until 1991,well after this site ceased operation Therefore it is not possible that the TBA originates from a release at the subject site •" 3 11 Remedial Actions Taken No active remediation has been conducted at the site 3 2 Area Remediated NA 3 3 Remediation Effectiveness NA 41 Designated Beneficial Water Existing and potential beneficial uses Include municipal and domestic water . Use supply, agricultural supply, industrial service supply, and industrial process su 1 CVRWQCB Basin Plan 4 21 Shallow Groundwater Use None identified 4 3 Deep Groundwater Use Water su 4 4 Well Survey Results A well survey conducted by Cambria in 2005 identified sixteen wells within 112-mile radius of the site Fifteen of the wells are located at least 1,200 fee from the site, but the location of one of the wells could not be determined door-to-door survey of properties within a 500-foot radius did not identify an wells 4 5 Likelihood of Impact to Wells I Based on their distances from the site,the identified wells are not likely to be impacted by site conditions 4 6 Likelihood of Impact to Surface A small lake within the Manteca Park Golf Course property is located 1,9N Water feet northwest of the site No other surface water bodies were obsery within 3h-mile of the site Due to the distance from the site,this surface water body is not likely to be impacted by the former Shell site iw 51 Site Conceptual Exposure Model The site Is currently occupied by retail stores The area surrounding the site (current and future uses) Is commercial Future use of the parcel is assumed to be similar to current use 5 2 Exposure Pathways Potential exposure pathways include onsite commercial occupant inhalation of vapors from impacted soil and groundwater, dermal exposure, particle inhalation, and ingestion of impacted soil by onsite construction workers, and ingestion of impacted groundwater offsite 5 3 Risk Assessment Status No formal risk assessment has been erformed for the site 5 4 Identified Human Exceedances None identified 1660 Page 2 of 3 Date 12/1/2005