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YAM �.� I��I �•, �•Ys- d � 1 j- <br /> In E <br /> 4 . 0 FIELD INVESTIGATION <br /> The first phase cf the field investigation program was based <br /> primarily on that proposed (and approved by both Anheuser- <br /> Busch, and the San Joaquin Local Health District ) in the <br /> Contamination Assessment Plan, dated June, 1987 ( ESE, 1987 ) . <br /> During ,i:he field investigation program, which took place <br /> during the week of July 6, 1987, the first monitor well, MW-1 , <br /> located northeast of the excavation area was installed. It 's <br /> approximate location I's shown in Figure 4-1 , with a scaled <br /> sketch presented in the Appendix. <br /> The second phase of the investigation took place from <br /> Septembe,: 3 through September 8, and included the installation <br /> of MW-2 and MW-3, whose locations are similarly shown in <br /> Figure 4-1 . <br /> During Vell construction, soil and ground water samples were <br /> collected for lithologic description and chemical analyses. <br /> Sampling methodology and field investigation results are <br /> summarized in the following sections. <br /> 4 . 1 MEIrEiODOLOGY <br /> 4. 1 . 1 ?hase I <br /> During 'Phase I, one monitor well was constructed using mud <br /> rotary ,te,chniques. Mud rotary drilling was selected over <br /> hollow sham techniques because flowing sands were suspected in <br /> the az,ea (based on ESE's drilling experience within a 10 mile <br /> radius of the Site ) . Because rotary drilling stabilizes the <br /> wales sof 'the wells, preventing sands from flowing upwards, it <br /> was presumed that this technique would have the advantage of <br /> assuring a true, depth discrete sample from the depth of <br /> interest. Mud--rotary similarly accommodates the installation <br /> of a larger, 4 inch diameter well, which may prove <br /> advantageous if site remediation is required. The mud rotary <br /> 4-1 <br />