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'0#1 <br /> d. 011'k .a-ls- t3�k -ate MIR, .. <br /> s <br /> Fa <br /> S, 2 <br /> E <br /> To remove a potential long term source of groundwater <br /> contamination, we would recommend the excavation and surface <br /> p treatment/disposal of soils within the former waste oil tank <br /> pit. Because sampling of the angle soil boring detected <br /> only 40 ppm O&G in the 17.5 foot sample, it is our opinion <br /> based on the absence of an action li3vel for 0&G in soil aid <br /> s; the nindetectable levels of O&G in the groundwater sample <br /> from MW1, that this level does not pose a signizicant threat <br /> " to health and safety. As such, it is our opinion that <br /> demolition of the on site building should not be considered. <br /> � The excavation should extend 3.aterally two feet from the <br /> current pit walls and vertically to a depth of approximately <br /> 20 feet. Confirmation samples should be collected from the <br /> excavation floor and the ds yet unsampled north and west <br /> walls. Subsequent to completing the excavation the pit <br /> should be filled with clean material and covered with a low <br /> permeability surface. <br /> Although the majority of the diesel contaminated soils have <br /> been removed frorc the west end of the former middle diesel <br /> tank and soil sampling indicates the residual contamination <br /> y of 30.6 ppm TPHD at 6.0 feet is limited to the upper 16.0 <br /> feet Of soil the relatively shallow depth to groundwater <br /> . warrants the installation and sampling of a groundwater <br /> monitoring well This well should be drilled adjacent to the <br /> ' area of highest documented contamination. Sampling for BTEX <br /> and TPHD in accordance with state and EPA methodologies <br /> should provide the necessary data to assess groundwater <br /> ' qup. ll'y. <br /> 8.0 REFERENCES <br /> Tri Regional Guidelines Regional Board Staff Recommendations <br /> for Initial Evaluation and investigation of Underground <br /> Tanks (Tri-Regional Recommendatio,as) Revised May 18, 1969, <br /> Regional Water Quality Control Boards. <br /> San Joaquin Flood Control and Conservation District Semi- <br /> Annual Groundwater Report, Spring 1989, San Joaquin County <br /> Flood Control and Water Conservation District. <br /> 9 <br />