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FINDINGS OF THE SAMPLE ANALYSIS Four soil samples were found to contain gasoline contamination in various amounts. The last of these samples (MW1 @ 35') was taken at a depth of thirty-five feet and had only one part per million of TPH-Gasoline. That sample (MW1 @ 35')was+/- 11' above the water table, at 46.5' below the surface. Soil samples taken below the water table did not indicate any gasoline contamination. Soil analysis for lead were ND at MW I @ 30'. A groundwater sample taken from the monitoring well on 8126197 indicated small amounts of gasoline contamination. Soil samples from the soil boring do not support the direct migration method of contamination of the groundwater. The samples taken at a depth of 40', 45', 50', and 55'were not contaminated. The main question is how did the groundwater get contaminated from this tank if the soil directly above is not contaminated? CONCLUSIONS The area of the soil contamination is more than ten feet above the existing water table. It highly unusual that gasoline from the removed underground storage tank could migrate though the soil above the water table without contaminating that soil. The contamination of the water in the monitoring well could have accidently occurred during construction. The monitoring well construction was supervised by the author and a representative of the San Joaquin County Public Health Services Environmental Health Division. The well construction was done with normal standard of care and no contamination was noted. Ground water movement is the most likely mode of water contamination on the site. Contaminated water may be moving onto the site from another source. Payless Building Supply is directly south of an abandoned service station site on Cherokee Lane that is a known gasoline contaminated site. The typical groundwater gradient in this area of Lodi is to the southeast, which may put Payless Building Supply in the direct path of any contaminated water flow movement. The fact that the water was contaminated, and the soil below water table was not, would give strong indication that the contamination was spreading by water movement. Dissolved BTEX in groundwater may not contaminate to soil as it passes though. RECOMMENDATIONS It is recommended that MWI be purged and re-sampled in the last quarter of this year to determine if any changes have occurred in the groundwater analysis. If the groundwater samples continue to show contamination, it can be assumed that the monitoring well construction was not at fault. Please address any questions, corrections, or additions to Ery Rifenburg, Foothill Engineering, phone 2091368-9381. Respectfully submitted, Q�OFESS/1 �c0 � (�2 Fo 'll Engi en IFENBG�Q� c� m LU N 762 z, Ervin Rif nburg E SOF CA41P�Q�P cc: John Graffigna