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1 Pombo Ranch Facility May 2006 Site Closure Report 1 MW-105 was located further down gradient to avoid shallow soil contamination. The ' boring was drilled through at least 7 feet of relatively dry clay into a course sand and gravel layer. A soil sample was collected every 10 feet for laboratory analysis. The 10 foot deep sample contained traces of gasoline and ethyl benzene. Soil samples collected ' at depths of 20, 30, and 40 feet were reported as non-detected for the compounds analyzed. A shallow well, MW-5, was added to the scope of work and located next to MW-105. Soil samples were not collected from this boring since it was situated within five feet of MW-105. ' Laborat ry Soil Sam le Results (May 5, 2004 Sample I.D. Gasoline Benzene Toluene E-Benzene Xylenes Oxy's ' Mg/K µ /K /K IKpg/Kg EB-4-10' 12 <25 <25 188 52 ND MW-4-10' 405 <625 <625 7000 17300 ND MW-4-15' <1.0 <5.0 <5.0 1 <5.0 <5.0 ND MW-105-10' 2.2 <25 <25 25 <25 ND MW-105-20' <1.0 <5.0 <5.0 <5.0 <5.0 ND ' MW-105-30' <1.0 <5.0 <5.0 <5.0 <5.0 ND MW-105-40' <1.0 <5.0 <5.0 <5.0 1 <5.0 ND 1 Well records for all wells within a 2000-foot radius of the site were requested from the Department of Water Resources. Water Resources reported records of several wells in ' the northwest quarter of section 30 Township 2 South / Range 5 East but no wells records for wells within 2000 feet of the site. There were no well completion reports on file for the three domestic wells identified in the earlier receptor survey. The three domestic ' wells are shown on Figure 1. Construction details have not been recovered for the nearby wells and the wells are reported to have not been serviced for many years. 1.2 Conceptual Site Model 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 southwest. ' The soils at Pombo Ranch are mapped b the US Soil Conservation pp Y 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 134, B3/9, B10, B11, MW1, and MW3. This sandy unit 5