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1 Fuller Mobile Home Park ' 365 E. Louise Ave., Lathrop, California May 28, 1998 Phase II Site Characterization - Continued Page• 5 4.0 Soil Conditions ' The subsurface lnthology 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) Analyses of ' soil samples show BTEX, Gasoline & Diesel contamination in the samples extend from 12 5' to 17 5' below ground level (bgl) typically Bonng 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 I 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 mdncate good intrinsic values for remediation (Appendix D) A supporting factor to this are the analytical values of Diesel Hydrocarbon declining from 14,000,000 ug/kg found at Bonng B-3 at 12 5' in depth during the 1992 sampling • and the 310,000 ug/kg found at B-11 at 12 5' in depth in the 1998 sample These comparisons are used based on the proximity to the former UST location f