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' C�ologualTec6inuslnc Page 12 Site Conceptual Model Report Project No 724 2 May 2,2046 ' petroleum hydrocarbons will generally be adsorbed to soil particles Groundwater plume dimensions are defined by quarterly sampling of the monitoring wells at the site It is extremely difficult to characterize the mass of soil gas at a site and it is generally not done ' GTI did not attempt to calculate the mass of TPH-G in soil due to a lack of data points as stated in section 2 5 1 above GTI has attempted to calculate the mass of TPH-G in groundwater at the site The discussions of how the plume dimensions were modeled are included below Appropriate figures are included to aid in the demonstration of plume dimensions 2.6.1 Soil Plume ' The extent and orientation of the soil plume cannot be determined due to the low levels present and lack of data points However, it appears that the soil plume is defined by ❑ MW-3 and MW-5 to the north and northwest ' ❑ MW-2,MW-6/106 and MW-71107 to the east o MW-1 to the south ❑ MW-4 is interpreted to be on the edge of the soil plume on the west under Grant Street None of the borings placed off site to the east of the Morita Bros property contained field evidence of contamination above the water table 2.6.2 Groundwater Plume The February 24, 2006 groundwater monitoring event and January 2006 CPT borehole data ' were used to define the groundwater TPH-G plume g Figure 13 illustrates the TPH-G concentration in the intermediate wells for the February 24, 2006 monitoring event and January 2006 CPT data The core of the plume is centered ' on well MW-108 (It is noted that the CPT data was obtained utilizing direct push methods and the water may be mixed vertically within the borehole GTI assigned the CPT-1 & CPT-2 sample points @ 70' bgs to the intermediate level due to the equivalent levels of TPH-G and proximity to the well MW-108208 well pair) Well MW-3 is shown outside of the plume boundary of 60 ug/1 TPH-G to distinguish it from a wider, co- mingled plume to be discussed in greater detail below ' ❑ Figure 14 shows the groundwater plume in cross section Plume is shown as submersed due to the groundwater elevation changes as noted above and the lack of contaminants in the shallow wells The plume is given a vertical height of 20 feet based on the screened ' intervals of the deeper wells which are historically non-detect ❑ CAD software was used to determine the volume within each contour line in Figure 13 This data was then used in the contaminant mass calculations ' 2.6.3 Soil Contaminant Mass Estimate Calculations The soil mass was not calculated but trace to low levels of BTEX & TPH-G in the groundwater plume suggest residual mass is present at minor levels