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' POmbo Ranch Facility August 17,2004 Subsurface Investigation Report& Second Quarter Groundwater Monitoring standards were used to monitor thesep arameters. At least 5 well volumes were evacuated from each well, and more, if necessary, until the above parameters ' stabilized. The wells or other sampling points were sampled in order of the least to the most contaminated, as best known or estimated. The samples were carefully poured from a Teflon bailer into clean glass vials with Teflon-lined ' screw caps. Care was taken to ensure that no air space existed in the vials by inverting to check for bubbles and re-sampling if necessary. ' The groundwater samples were analyzed or extracted within 14 days according to their EPA methods. The samples were analyzed for Total Petroleum Hydrocarbons (gasoline), BTX&E (Benzene, Toluene, Xylene, and Ethyl ' Benzene) and MTBE by EPA Method 8020. Analysis was conducted by GeoAnalytical Laboratories; a state certified analytical laboratory. 3.0I S TE CONDITIONS ' 3.1 Site Geology & Groundwater Occurrence ' The Pombo Ranch is located on the southwestern edge of the San Joaquin Delta. The shallow unconsolidated sediments present at Pombo Ranch are composed fine-grained overbank and coarse grained channel deposits sourced from Cretaceous and Tertiary rocks exposed in the Coast Range Mountains to the 10 southwest. The soils at Pombo Ranch are mapped by the US Soil Conservation Service as being composed of the Capay Series Soils, which are interpreted as forming in alluvial fans and interfan basins from a mixed rock source. Soils of the Capay Series are typically fine grained and montmorillonitic in nature. Soil boring logs are presented in Appendix B. ' Sediments at The Pombo Ranch site are composed of tan silty plastic clays and tan very fine grained, well sorted, silty sands. A thin shallow sandy unit is present within the upper silty clay in borings B4, B3/9, B10, B11, MW1, and MW3. This ' sandy unit appears to be confined to semi-confined beneath the overlying silty clay in borings B3/9, B 10, and B 11. The shallow sandy unit is not present in borings to the east and south of the former underground storage tank. A coarse ' sand to pebble gravel was encountered at 5 feet in boring B 12. The sand unit is underlain by wide spread clay layer in the western portions of the site. Hydrogeologic cross sections are shown in figures 8 and 9. Unconfined groundwater was measured at depths of 10.6 to 11.3 feet below grade on May 14, 2004. Groundwater elevation rose between 1 to 1.2 feet since the January 19, 2004 monitoring event. Groundwater flow on May 14, 2004 was to the Northeast and southwest with a very shallow gradient. A faint groundwater high is present at MW4 with very slight flow to the northeast — southwest away