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<br />VUoodward~Clycle <br />CDonsuRants <br />piezometers are closer to the threshold levels and are closest for Piezometer A-10 at <br />Study Section 10-10'. The February'92 water level for Piezometer A-10 is 8.8 feet below <br />the threshold level. <br />Comparison of piezometer water levels with threshold levels provide.. a means of <br />evaluating stability based on the position of the phreatic surface. Tlvs should be <br />accomplished on a regulaz basis with attention also given to unusual trends in <br />piezometer readings. These evaluations, however, should be complimented with careful <br />visual observation and documentation of conditions on and around the tailing <br />embanlonent, i.e., seepage azeas, decant pond position, underdrain flows, sink holes, etc. <br />Eazly recognition of problems with the tailing dam is more likely if a comprehensive <br />monitoring program, similaz to your current program, is established and :Followed. <br />3.5 WETLANDS EVALUATION <br />We understand that you aze evaluating construction of a wetlands azea d~~wnstream of <br />Dam No. ] in the flat lying azea upstream of the road berm located atrout 600 feet <br />downstream of the toe of Dam No. 1 as shown on Figure 1. Water issuing from the <br />i underdrain system is currently collected within a system of channels immediately <br />upstream of the road berm. As currently envisioned, the wetlands azea could result in <br />1 ponding of water to a maximum elevation corresponding to about the elevation of the <br />road berm, about Elevation 8590. Considering the existing topography, this would result <br />t in water ponding as close as 200 feet to the toe of Dam No. 1. <br />The phreatic surface across the natural ground downstream of the toe of D:un No. 1 was <br />assumed to be at the ground surface for all of the slope stability analyses presented <br />above. Considering this and considering that all critical shear surfaces aze located closer <br />than 200 feet of the toe of the embartkment, construction and operation of the wetlands <br />should not adversely impact the stability of Dam No. 1. If the nature and position of the <br />~~ wetlands differ from the assumptions described above, these conclusions should be <br />reevaluated. <br />d~ <br />~~ <br />~~ u9svxr.a oa-m.m,err 3-6 <br />