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I <br />I <br />I <br />I <br />D <br />JP <br />17 <br />4-5 <br />4.3 EFFECTIVENESS OF GROUTING <br />The effectiveness of the experimental grouting program in terms of reducing <br />the seepage rate can be assessed from the observation of changes in ground <br />water levels and pump -back rates with time. Figure 4 presents a plot of <br />ground water levels versus time for selected piezometers in and near the <br />dam. Sample points 3, 4, 5 and 6 are piezometers located on the crest of dam, <br />3 and 5 being screened in the alluvium and 4 and 6 being screened in the rock <br />(see Figure 2). <br />Points 5 and -6,. which. are located amongst ;.the_grout%.boring s,. responded. to the <br />grouting by initially increased water levels which.are now. decreasing.. Since'= <br />these points are within or immediately adjacent to -,the grout zone beneath the <br />dam, their rise may indicate that some seepage is being sealed by the grouting <br />with the result that the seepage rate may be reduced. There was no evidence <br />of grout in the piezometers. Stabilized levels in these piezometers, which <br />will require more time, will be useful in the evaluation of grout effective- <br />ness. Points 3 and 4, which are located west of the grouted area, show a <br />slight decrease in water level with time since grouting began. However, the <br />response currently does not appear significantly different than previous <br />response to similar pond level decreases. The exception may be that the water <br />level at Sample Point 4 is the lowest of available historic readings. The <br />pond reached levels similar to the September 1982 levels in September 1981 yet <br />the level at Sample Point 4 was higher. <br />Points 8, 9, 12, 27 and 28, which are located along the toe of the dam, also <br />show slight decreases in water level with time. All these readings show <br />values equal to or lower than the lowest historic readings. This; could"be`.a ' <br />r sponse to 'the low; pond,;.level _.or to :"effective a s'-bf theme<Rrouting: 0'A '. <br />continued drop in levels at current pond.elev or?aa constant level with-' <br />'increasing''pond "elevation will `:indicate 'positive =effectiveness of ahs• grout <br />