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SITE CONCEPTUAL MODEL Prepared by Cambria Environmental Technology, Inc " 11fi0 West Yosemite Avenue ` 97422510 Manteca,California San Joaquin County Environmental Health Department 1 1 Identify/Describe Release Unknown The highest levels of gasoline constituents in sod have been Source and Volume(if known) detected near the former dispensers in the north-central portion of the site 1 2 Discuss Steps Taken to Stop No direct repairs or action was taken to stop the release as there was n Release specifically identified equipment failure The USTswere removed from the site during 1983 Impacted soil and groundwater Vi�vered during the August 2001 site investigation 21 Current Site Use/Status The site is currently occupied by retail stores 2 2 Soil Definition Status The vertical and lateral extent of gasoline constituents In sod has been defined to the extent possible based on site physical constraints and access limitations No total petroleum hydrocarbons as gasoline (TPHg) an benzene, toluene, eth benzene, and xylenes(BTEX) have been detected in soil from bonngs B-4 ftough B-7, or from well borings MW-2 through MW-5 No petroleum hydrocarbons have been detected in sod below 30 feet below grade (fbg) MTBE has not been detected in sod samples collected at the o�0 site Sal tables and maps are included in Attachment 1 rN 2 3 Separate-Phase Hydrocarbon Separate-phase hydrocarbons have never been detected beneath the site IC� Definition Status 2 Groundwater Definition Status TPHg and BTEX are not typically detected In groundwater from wells MW-2, (BTEX) MW-4, and MW-5, and these wells provide lateral definition of petroleum hydrocarbons detected in wells MW-1 and MW-3 Groundwater analytical results are included in Attachment 2 M W 4 d a 4� X41; 2 5 BTEX Plume Stability and TPHg and BTEX concentrations in wells MW-1 and MW-3 are stable Non- Concentration Trends detect results in wells MW-2,MW-4,and MW-5 indicate the plume is not migrating Groundwater analytical results are Included in Attachment 2 2 6 Groundwater Definition Status No MTBE has been detected in site monitoring wells since installation in IgE) 2004 Groundwater analytical results are included in Attachment 2 2 7 MTBE Plume Stability and As noted above,MTBE has not been detected in site wells,and there is no Concentration Trends MTBE plume 2 8 Groundwater Flow Direction, Depth to water beneath the subject site has ranged from 15 8 to 22 9 fbg in Depth Trends and Gradient the monitoring wells, and groundwater elevations have ranged from 5 2 t Trends 121 feet above mean sea level The groundwater flow direction is variable across the site with groundwater gradient ranging from 0 002 to 0 015 2 9 Stratigraphy and Hydrogeology The site is underlain altemating layers of silts, silty sands, and sands with varying thicknesses The predominant soil type beneath the site is coarse- grained soils (sands and silty sands) There are several fine-grained layers (silt) beneath the site that do not appear to be laterally continuous Boring logs are included in Attachment 3, and a site cross section is included in Attachment 4 1660 Page 1 of 3 Date 12/1/2005