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2.0 MONITORING WELLS <br />Prior to slurry wall construction and dam grouting, five monitoring wells, <br />numbered P-16 through P-20 (sample points 27 through 31 on Figure 2), were <br />installed downstream of the lower tailings dam. The installation of these <br />wells began on June 29, 1982. Drilling began with hole number 16 and pro— <br />gressed sequentially through hole number 20. The monitoring well installation <br />program was completed on July 9, 1982. <br />Three monitoring wells, P-16, P-17, and P-18 were installed approximately 100 <br />feet downstream of the slurry wall centerline near existing sampling point <br />number 25. The screened sections were sealed into rock at varying depths <br />ranging from 42 to 80 feet. Two other wells, P-19 and P-20, were installed <br />through the toe of the embankment near its intersection with the ground <br />surface. These wells were also sealed into rock, at depths of 28 to 33 <br />feet. Appendix A contains the boring logs for each well borehole. Appendix B <br />contains the as—built drawings for the wells. <br />The purpose of the wells was to: <br />0 Evaluate piezometric surface changes with construction <br />of the slurry wall and completion of the grouting <br />program. <br />o Measure piezometric pressures at each screened horizon <br />in order to define zones and directions of seepage <br />flow. <br />o Provide water quality data to evaluate changes in <br />ground water quality after slurry wall construction. <br />The borings were advanced with a Mobile B-80 drill rig using a roller bit and <br />NW casing to top of competent rock and with a NX diamond bit to core into <br />rack. Standard penetration test samples were taken at regular intervals in <br />the soil above the rock. <br />