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i Fuller Mobile Home Park 36S E. Louise Ave., Lathrop, California May 28, 1998 Phase H Site Characterization- Continued Page: 5 • I 4.0 Soil Conditions The subsurface hthology of the Fuller Mobile Home Park site in Lathrop, California, is characterized generally by silty, clayey sands with thin interbedded silts and clays This is typical of the valley fill deposits in the region However, this area of investigation finds soils characterized as clay with sands, gray in color, moist with medium plasticity in bonngs B-7 thru B-11 B-12 follows the general classification (Appendix C) It is this ' distinct difference in soils characteristic in the general proximity of monitoring well MW-3 which attributes to the intermittent detection of contaminates in the groundwater Analyses of soil samples show BTEN Gasoline & Diesel contamination in the samples ' extend from 12 5' to 17 5' below ground level (bgl) typically Boring B-7 to the south finds Diesel contamination extending to a depth of 22 5' bgl Boring B-12 identified MTBE ranging from 2 7 to 2 8 ug/kg at 27 5' and 32 5' at the eastern boundary approximately 11 feet into the neighboring property • Lithologic cross-sections were constructed from data from all borings (Figures 5, 6, 7 & ' 8) Contamination cross-sections were constructed from analytical data from all borings (Figures 9, 10, 11 & 12) Soil Samples from B-5 & 6 and MW-4, 5, 6 & 7 were all ND (Table 1 & Appendix A) From these cross-sections the lateral and vertical extent of soil contamination has been defined (Figure 13) 5.0 Biological Assay Data & Dissolved Oxygen ' At the request of Mr James Digorgio of the State Water Regional Board a Hydrocarbon Degrading Bacteria Enumeration Assay was conducted on samples collected from the contaminated soils zone Samples submitted for Assay were B-7 at 12 5' bgl, B-9 at 12 5' ' bgl and B-11 at 12 5' bgl The Biological Hydrocarbon Degrading Assay identified both long and short chained ' hydrocarbon degraders The Colony Forming Units (CFU) per gram of sample ranged from 3 9 x 102 CFU in B-7 to 2 4 x 102 CFU in sample B-9 This indicates greatly elevated levels of hydrocarbon degrading bacteria in the contaminated soils mass In a ' discussion with Dr Sean P Bushart, Ph D with Cyto Culture International, Inc , he stated that the levels of dissolved oxygen identified in MW-3 at 2 2 mg/L and MW-6 at 4 0 mg/L in conjunction with the actual values of Hydrocarbon Degrading Bacterial Colony ' Forming Umts/gram present does indicate good intrinsic values for remediation (Appendix M D) A supporting factor to this are the analytical values of Diesel Hydrocarbon declining ' from 14,000,000 ug/kg found at boring B-3 at 12 5' in depth during the 1992 sampling