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Pomba Property Corrective Action Plan ' Page: 4 confined to semi-confined, sandy unit (upper sand). Gasoline, volatile aromatic hydrocarbons, and MTBE were detecte&the upper sand in boring B3 at 10 feet. 1 Gasoline and volatile aromatic hydrocarbons were detected in the laboratory sample collected from boring B-11 in the upper sand discussed above. MTBE contamination was not detected in boring B 11. Soil contamination has not been ' recognized at other sampling locations. Groundwater contamination by gasoline, volatile aromatic hydrocarbons, and ' MTBE were detected in the Geoprobe groundwater sample collected from 15 feet in boring B3 at the location of the former underground storage tank. Lesser concentrations of gasoline and gasoline components were detected in the Geoprobe` groundwater samples collected from boring BIO, 1311, and B12 at depths 16 to 23 feetand boring B9 at 33 feet. MTBE was not detected in any of the Geoprobe groundwater samples other than boring B3. The analytical laboratory ' reported non-detectable concentrations of gasoline, BTEX, and MTBE for groundwater samples collected in all three monitoring wells. The groundwater sample boring B3 at 15 feet was collected from within the thin j shallow, confined to semi-confined, sandy unit (upper sand). The majority of the ' soil and groundwater contamination appears to be restricted to the thin shallow, confined to semi-confined, sandy unit (upper sand). The groundwater samples with low concentrations of contamination, obtained from boring B9, B 10, B 11, and B 12 ' were discretely collected from within the well-sorted sand present at the base of the borings (lower sand). All three monitoring wells also terminate in the lower sand_ ' High concentrations of groundwater contamination are restricted to the thin shallow, confined to semi-confined, sandy unit (upper sand). Migration of the groundwater contamination has been retarded by the presence of a low permeability ' restrictive unit that underlies the upper sand. Low concentrations of contamination have penetrated the restrictive horizon. A direct down gradient monitoring well has not been installed, however the low concentrations of groundwater contamination ' detected in the lower sand unit preclude the need for additional sampling points. The lateral extent of contaminate migration has been defined by the monitoring wells. The distribution of the gasoline compounds in the groundwater suggests a ' variable groundwater flow possible controlled by the unlined Westside Irrigation District, Lower Main Canal on the western and southern boundary of the site. ' MTBE was only detected in a single soil sample and a grab water sample collected beneath the soil sample at the location of former underground storage tank. Very low concentrations of MTBE were also detected in a water sample collected beneath the former above ground tanks. Soil and groundwater contamination values as detected by the analytical laboratory ' are presented on the lithologic cross section by contaminant and the estimate mass of the contaminate presented (Figure 5 to Figure 11). A table of mass contaminate balance is present in Table 2 Contaminant Mass Balance.