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Underground Storage Tank Delineation Sampling Using Cone Penetration Testing With An Ultra-Violet Optical Screening Tool Report 216 N.California Street Page 6 of 7 borings at each location, see Figure 3, Appendix A. Qualitative analysis of the data, in terms of date of sampling and analysis, or spatial trends, support the use of the data for the intended use, to define the vertical and lateral extent of hydrocarbon contamination on this Site. 4.0 DATA ANALYSIS UVOST data indicates that hydrocarbons were present at the locations of CPT1, CPT2 and CPT3. UVOST data indicates that the majority of hydrocarbons is present near the current groundwater level, and may form a sorbed phase (soil) diesel plume. The plume thins and becomes shallower with greater lateral distance from the source. Laboratory analysis of soil samples collected at depths 72, 80, and 100 feet below the surface in CPT1 had been impacted by hydrocarbons quantified as diesel and small concentrations of ethyl benzene and xylenes, but at concentrations that are 300 times lower than the sample collected at 60 feet below ground surface. A similar spatial trend was indicated by the laboratory data for the groundwater samples and may form an aqueous phase(dissolved) diesel plume. Groundwater collected at a depth of 61 feet at CPT1 had a laboratory reported diesel concentration of 3,600 pg/L while a ground water sample collected two feet away laterally and at a depth of 75 feet, 14 feet deeper, did not have a diesel concentration that was at or above the laboratory reported detection limit of 50 pg/l, or about 70 times lower and better than CRWQCB water quality goals. Soil and groundwater samples that were collected at close depth intervals indicate a strong correlation between diesel concentrations in soil and diesel concentrations in groundwater. Soil sample CPT1-60 had a diesel concentration of 3,500 mg/kg and groundwater sample CPT1-61 had a diesel concentration of .. 3,600 pg/L. Soil sample CPT1-72 had a diesel concentration of 230 mg/kg and groundwater sample CPT1-75 had a diesel concentration of less than 50 pg/L. Soil sample CPT2-35 had a diesel concentration of 4,600 mg/kg and groundwater sample CPT2-41 had a diesel concentration of 5,800 pg/L. The three pairs of data indicate that groundwater concentrations are approximately one-thousandth of the soil concentrations. 5.0 DISCUSSION AND CONCLUSIONS Soil and groundwater grab samples combined with the use of CPT and UVOST systems have provided _ sufficient data to develop a preliminary site conceptual model (see Figure 5, Appendix A). Spatial trends interpreted from available data indicate that heating oil, quantified as diesel, was released from the vicinity of the storage tank, transported downward due to gravity, and adsorbed to fine grain soils. The _ body of diesel thins with distance laterally from the source, and attenuates to lower concentrations both laterally and vertically. The weak correlation of UVOST data and laboratory data may indicate that the distribution of hydrocarbon concentrations within the plume is heterogeneous. Based on the limited data collected during this investigation, UVOST may be useful for defining diesel contamination in soil at concentrations greater than 1,00 mg/kg. The highest sorbed phase diesel concentration reported in laboratory analytical data based on soil samples collected during this phase of the investigation was 4,600 mg/kg in sample CPT2-35. The liquid phase or sorbed phase diesel intersected the water table at some time in the past and interacted to form an aqueous phase diesel plume that is collocated with the sorbed phase plume. Aqueous phase hydrocarbons may be transported at greater velocities, or distances through coarser grained materials, including sands or historic stream channels that have been present at the location of the Site, see Figure 6, Appendix A. The full lateral and vertical extent of the sorbed phase and aqueous phase diesel plume has not been •• demonstrated,based upon data collected during this phase of the investigation. Laboratory analytical data indicates that lower concentrations of diesel were present in soil samples collected from CPT1 at depths 4M i4) CONDOR