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October 9, 2009 <br />2.2 Placement of Underdrainage Systems <br />4 <br />Construction of the underdrain system was the principle construction activity performed on the HGF <br />during the third quarter of 2009. Work included cutting of channels for a lateral drain and for the upper <br />portion of the main drain. Rock fill was added to portions of these channels, in accordance with the <br />design submitted as part of PR-06, and Section 4.09.2(2). In addition, filtration fabric (Mirafi 140N) was <br />used to cover completed sections of rock drains to prevent infiltration of fines into the drainage <br />structure. Additional sediment control was accomplished through construction of roads and ditches <br />along either side of the channel. This provided access for placement of rock, and prevented sediment <br />from entering the channel. The head of each rock drain was covered with Mirafi 140N after rock <br />placement to prevent sediment from entering the rock core. <br />Lateral Drain <br />The following series of photographs depict the stages of construction for the lateral drain. This drain is <br />referred to as a Finger Drain in AAI's Horse Gulch Fill Stability Analysis. <br />Photograph 4 shows the cut channel for the lateral drain. The channel was primarily cut with CAT 637 <br />scrapers, assisted with a GPS equipped dozer. <br />Photograph 3: looking South from Z-Pit (9130109)