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<br />standards by the Company's contractor during the reconstruction of the dam. <br /> <br />The locations of the toe drains and their discharge points are not known. The downstream <br />face of the dam does not show indications of seepage. The SEO has required that the toe drain <br />system be rehabilitated or reconstructed so that possible embankment seepage can be monitored. <br /> <br />Alternative 1 - Replacement <br />The outlet works alternative includes replacing the failed 24-inch CMP outlet pipe with a 24- <br />inch concrete encased steel pipe as shown in Figure IV -2. The inlet structure will not be modified or <br />replaced for the project. The CMP will be removed from the inlet tower and the steel pipe will be <br />connected to the tower at the same location with a concrete collar. The outlet capacity will increase <br />slightly due to the use of the smooth steel pipe compared with the existing ribbed CMP. Figure IV-I <br />shows that the outlet pipe discharges into USBR impact basin to reduce the flow velocity before the <br />flow is returned to the downstream channel. <br /> <br />The alternative also includes locating the existing toe drain system and plugging the system <br />so that it cannot act as a flow path through the embankment in the future. A new toe drain system <br />will be constructed along the toe of the embankment. As Figure VI-l shows, the toe drain system <br />will include a perforated 6-inch diameter PVC pipe, enclosed in filter material, that discharges into <br />two manholes located on each side of the outlet pipe. The manholes shown in Figure VI-l can be <br />used for cleaning and maintenance of the toe drains. The seepage water is then directed downstream <br />using solid PVC pipe which then discharges along side the impact basin. The elevations of the <br />discharge pipes will be set so that the amount of seepage can be measured using a bucket and stop <br />watch. <br /> <br />Alternative 2 - No-Action Alternative <br /> <br />A non-structural alternative to rehabilitating the dam is to do nothing. If improvements to the <br />dam are not completed, the SEO could restrict the reservoir; and could require breaching of the dam <br />and loss of the storage reservoir. <br /> <br />Lake Arrowhead Dam Rehabilitation Feasibility Study <br /> <br />7 <br /> <br />13DVLE <br />