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in the site vicinity, it will be necessary to consider other slope protection materials or hauling in <br />suitable rock from off-site (likely from a long distance given the local geology and <br />considerations of land ownership and environmental permitting of a new hard rock quarry). One <br />potentially feasible option to consider is soil cement given the relative abundance of sand <br />aggregate at the site or nearby off-site. Downstream slope protection is necessary to prevent <br />potentially deep rilling and cumulative erosion of the anticipated fine-grained fill material. This <br />may require salvaging growth media ("topsoil") from the foundation preparation to the extent <br />that it is present, amending that material with organic matter if needed, or importing more <br />suitable soil from off-site. The growth media would be reclaimed with grasses/forbs suited to <br />the local climatic conditions. <br />Earthquake Effects. Based on the preliminary assessment of potential earthquake shaking at <br />this site and the nature of the foundation and available borrow materials, it appears feasible to <br />construct an earthquake resistant dam without extraordinary measures required. Measures that <br />will mitigate earthquake effects include: removing any relatively low density soils from the <br />foundation; placing all fill to required density and moisture content; providing a properly <br />designed and constructed chimney and blanket drain system within the dam; and providing <br />adequate freeboard and camber on the dam crest to accommodate any anticipated deformation <br />during a design earthquake event. <br />Based on available information reviewed for this study, site reconnaissance, and experience with other <br />dam sites in similar geologic settings, it does not appear that there are any fatal flaws to construction of <br />an earth dam at the proposed Grand Valley Dam and Reservoir site. However, as noted in the above <br />discussions, there are a number of conditions and issues that will require very thorough investigation, <br />careful design, and close attention to QA/QC during construction. All of these conditions will result in <br />higher costs of both design and construction to mitigate them than would be the case if they were not <br />present. <br />33 <br />AECOM <br />2/22/10 <br />