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G�olagkal Tecknusl Page 6 Site Conceptual Model Report Marcs Property Project No 7012 August 23,2004 ' 2.5 Contaminant Distribution ' 2.5.1 Vadose Zone ' Figures 4 &. 6 illustrate the soil and groundwater contaminant distribution as superimposed on cross sections A - A' and B — B' The groundwater data from the June 7, 2004, monitoring event are presented in the diagrams adjacent to the respective well's screened interval ' In Figure 4, a column of soil contamination is present under the former UST ' excavation/dispenser area In the vicinity of MW-6/MW-106, no soil contamination was detected and Wm Hunter & Associates stated no contamination was present in MW--3 Tins suggests that the contanunation migrated downward to impact the groundwater without less ' permeable soil layers causing lateral dispersion higher in the column In Figure 6, a similar situation is present The contaminated soil column under the UST excavation/dispenser area appears to extend toward MW-5 @ 34 feet bgs The field geologist noted a strong HC odor at 40 feet b and a free product interface at 45 5 feet bgs in boring MW-7 The soil concentration of 9, 0 mg/kg TPH-D @ 45 feet bgs does correlate with the free product noted at this depth It is likely that the geologist had encountered non-aqueous phase liquids (NAPLs) entrained in the silty soil TPH-D was detected in soil at 55 feet at a concentration of 12,200 mg/kg, then attenuating to 331 mg/kg at 70 feet bgs Once reaching the groundwater table the diesel contamination spread laterally with the rise and fall of the groundwater table ' 2.5.2 Groundwater As stated above, Figures 4 and 6 illustrate the June 7, 2004, monitoring event groundwater ' contaminant distribution as superimposed on cross sections A - A' and B — B' The groundwater data are presented in the diagrams adjacent to the respective well's screened interval ' The TPH-D distribution in the shallow wells is illustrated in Figure 9. Well MW-5 continues to contain the highest concentrations of detected contaminants It has not been down gradient ' of the former UST location for the momtonng events completed by GTI to date The reason for this anomaly is not known, but could be related to geologic units that slope to the west None of the deep wells contained laboratory contaminants concentrations above the ' laboratory reporting limits and therefore a contour map was not developed 2.6 Contaminant Mass Estimate Calculations ' The total mass of diesel petroleum hydrocarbons released at the site is unknown In order to determine the fate and transport of the contamination and hence the future risk these compounds may pose to human health, an estimate of contaminant mass is necessary 1