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FINDINGS OF THE PHASE 1 INVESTIGATION <br /> The gasoline contaminated plume is approximately ten feet thick at the bore hole location. The plume <br /> is situated on a very dense and low permeable layer of silty clay. This low permeable layer is <br /> approximately seven feet thick and required a high blow count to drive the sampling device. This <br /> cemented layer can be found in many locations in the Lodi area. The contaminates are mostly xylene <br /> with very small amounts of benzene which confirms Mr. Bruce Burlington's statements that the tank <br /> has not been used for many years. The maximum concentration of the contaminate is 226 mg/Kg <br /> at twenty feet of depth, which is just above the low permeable layer. <br /> Groundwater samples from the monitoring well showed a very small amount of benzene and toluene. <br /> The proportions of the contaminate do not match the proportions in the soil samples. Xylene in the <br /> water sample is ND, while it has the highest fraction in the soil sample. The trace amount in the <br /> groundwater may be cross layer contamination from the soil boring auger or from a completely <br /> different source. Typical gasoline is made up of+/- 109/6 of xylene and less than I%benzene. It seems <br /> very unlikely that the contaminate in the groundwater originated from gasoline. <br /> RESULTS AND RECOMMENDATIONS <br /> The concentration of the gasoline contamination is very low (less than 250 mg/Kg). The low <br /> permeability of the hardpan soil layer under the contamination plume will prevent a risk to the <br /> groundwater at a depth of 42' below the surface. The chemical analysis of the contamination would <br /> lead to the conclusion that lighter fractions (benzene) have oxidized with age, leaving the heavier <br /> fractions(xylene)remaining. This confirms Mr. Burlington's statement that the gasoline storage tank <br /> has not been used for many years. <br /> The benzene and toluene in the groundwater are not likely to have originated from the contaminated <br /> soil plume above the groundwater. <br /> It is recommended that no further investigation of the contaminated soil plume or the groundwater <br /> are necessary. It is also recommended that a site closure be issued by the (PHS-EHD). <br /> Please direct any questions or comments to Ervin Rifenburg of this office. <br /> Respectfully submitted, <br /> ZOKS5lpy <br /> Foothill ne rin ���`N R�fEN�v�Fac <br /> . 19752 <br /> Exp � <br /> Ervin Ri nburg, P CM �P <br /> OFCAu�4 <br /> 3 <br />