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SHANNON &WILSON, INC. <br />0 Based on this method and the results of our study, we developed the recommended embankment <br />section shown on Figure 11. Recommendations for site preparation, construction and inspection <br />are also included in Figure 11. <br />We estimate the dam embankment and the underlying stiff clay layer will settle about 2 to 3 <br />inches. Based on the closest boring (CO -103), subsurface conditions include a compressible, <br />deeper clay layer at a depth of about 20 to 37 feet. Although this layer does not reduce stability, <br />it will consolidate under loading by the embankment fill. We estimate settlement on the order of <br />4 to 6 inches could occur. This results in estimated potential total settlements on the order of 6 to <br />9 inches. We anticipate most or all of the settlement will occur within about 1 year after <br />construction. The dam should be crowned and equipment designed to accommodate this <br />magnitude of settlement. In addition, we recommend settlement monitoring of one control point <br />on the crest as outlined in Note 5 on Figure 11. <br />9.0 MONITORING <br />Following is a list of monitoring activities we recommend: <br />■ We understand additional drilling of the X -Seam is likely. Prior to construction <br />of the spoil fill, we should review updated elevation contours to confirm the <br />bedrock dip in our analysis remains appropriate. <br />■ Short term stability of the initial spoil lifts located over the valley bottom may be <br />marginal. Additional analysis and is recommended to evaluate alternatives and <br />develop contingency plans. These may include constructing the initial lifts at <br />lower heights and staging the construction to allow strength gain in the weaker <br />clays prior to placing the next lift. <br />■ A water monitoring well is recommended in the downstream face of the spoil fill <br />to confirm excessive water build up within the fill is not occurring. The well <br />should be located at an elevation about 100 feet in elevation above the toe of the <br />fill and also be located above the low point in the valley. The well should extend <br />through the base of the fill and at least 20 feet into natural soils. An access bench <br />should be provided to the well. <br />■ A settlement monitoring point is recommended in the crest of the sediment pond <br />embankment. This should be monitored about every 3 month through the first <br />year after construction. <br />L ' <br />23 -1 -01101 - 400- R1.docx/wp/1kn <br />15 <br />23 -1- 01101 -400 <br />Exh. 23 -1 -22 <br />Revision Date: 08/05/09 <br />Revision No.: PR -03 <br />