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• 6. Pond Lining <br />Ponds MB-1 and FW-1, and the wastewater treatment plant polishing pond are lined with a <br />flexible 60 mil HDPE liner to prevent infiltration of water into the landslide mass. The <br />flexible liner allows for significant landslide movement without tearing. <br />7. Relocating Water Malns <br />Water mains were originally buried and occasionally broke as a result of the movement of the <br />landslide. The buried water mains were replaced with aboveground pipelines so that breaks <br />could be identified quickly and repaired and to minimize infiltration of water into the landslide <br />mass. <br />3.2 Potential Corrective Measures <br />As discussed previously, the Observation Approach is being used to stabilize the landslide. <br />Potential corrective measures are ready to be implemented if conditions warrant. These potential <br />• corrective measures are as follows: <br />1. Dewatering Trenches <br />The major groundwater source is from near surface sources near the head of the landslide, and <br />dewatering trenches are proposed to intercept the near surface groundwater. The trenches are <br />designed to be 30 feet deep and constructed in a phased manner as the need arises. The <br />drainage material is a gravel that will filter sand size material from the pressurized sand <br />layers. The drains are aligned perpendicular to the slope so they do not shear as the landslide <br />continues to move. Figures 1 and 4 show the location of these trenches and a detail of the <br />trench design is in Appendix B. <br />2. Capping French Drains <br />French drains, located on the upper slope above the landslide, intercept both groundwater and <br />surface water. The drains are aligned parallel to the slope so that these French drains tend to <br />act as infiltration galleries to saturate the head of the landslide. The drains are planned to be <br />• capped to prevent surface water infiltration. <br />oszsoza~sassi-vnsM 5 <br />