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that any precipitation would be transmitted efficiently by this soil type to the critical root layer of <br />the trees. The depth to the water table is approximately 12 to 42 inches below the ground surface, <br />and flooding is frequent. These soils typically consist of a stratified sandy loam to very gravelly <br />sand. The interbedded layers of sandy loam (fine - textured sand -based soil) and gravel will both <br />readily transmit water to the root zone, and store water for plant use. The soils present in the <br />project area will help transport available water to the cottonwood trees from precipitation runoff <br />and from the river during normal flow. <br />To supplement literature -based information, Olsson consulted Colorado certified arborist Michael <br />Arat with Eco Irrigation and Landscaping, Inc., about cottonwood trees and potential risks <br />associated with both dewatering and construction projects in general. Mr. Arat was of the opinion <br />that if efforts to protect the trees — including protection from grading, compaction, and other <br />disturbances —are implemented, no adverse effects to the trees should result from this project. <br />He noted that the temporary reduction in the water table should not endanger the lives of these <br />trees due to the short duration of the dewatering activities. Little effect on tree health should occur <br />because the dewatering will occur during the winter when the trees are dormant and transpire <br />very little water. <br />Following this guidance, Olsson recommends a few best management practices (BMPs) be <br />observed during construction to ensure protection and survival of cottonwood trees during the <br />project. <br />1. Minimize construction traffic within the dripline of the trees to protect the top 6 – 8 inches <br />of soil where critical roots grow (critical root zone). A physical barrier could be placed near <br />areas with a high rate of construction traffic that will serve as a protection buffer around <br />individual or multiple trees. <br />2. Refrain from altering the grade around the trees, specifically within the dripline where the <br />critical roots grow. Addition or reduction of soil within this area will damage the critical root <br />zone of the trees and could result in long -term impacts to tree health. <br />We feel that these BMPs will provide the necessary protection to afford these trees the best <br />possible scenario throughout this project. The literature review presented above indicates that <br />dewatering activities during the winter will not negatively affect the cottonwood trees growing near <br />the Dillon Ranch Pit. The location being near the Animas River as well as the poorly drained soils <br />and time of year for dewatering combine to create a more than adequate situation to sustain the <br />cottonwood trees throughout the dewatering process. We do not anticipate any adverse health <br />problems with the cottonwood trees as a result of this project. <br />Should you require any additional information regarding this project, please feel free to contact <br />me at 913.381.1170 or by email at jstevenot @olssonassociates.com. <br />3 <br />