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Vermillion Ranch Limited Partnership/Surface Water Impoundment 13659-RX <br /> ' Summary <br /> Based on information obtained from our subsurface exploration and laboratory testing of <br /> recovered samples, it is our opinion that the site is marginally suitable for construction of the <br /> proposed earthen dam and is subject to considerations for site preparation and materials which <br /> are described in this report. Our field exploration included advancing nine test borings to <br /> depths of 26.5 to 80.0 feet below the existing ground surface elevation. Six of the test borings <br /> were drilled along the approximate dam centerline and three were drilled at the approximate <br /> dam spillway area located south of the dam. <br /> The test borings include varying conditions in terms of suitable soils to support the weight of <br /> 1 the earth dam and impound water. While the abutment on the north end appears satisfactory, <br /> the south abutment soils are poor. Compressible loose or soft sediment was encountered in <br /> ' thicknesses ranging from 14 feet to in excess of 60 feet along the dam centerline. Soils south <br /> of the existing creek channel are comprised largely of very loose sand with moderate <br /> permeability to depths of at least 80 feet. In our opinion, the above conditions would result in <br /> significant settlement of the embankment. Such settlement could distress outlet works or level <br /> control structures. The foundation soil conditions are also highly susceptible to liquefaction <br /> and severe deformation under seismic load. Moderately permeable fine-grained soils are <br /> subject to subsurface erosion and relatively high seepage either below or around the south end <br /> of the proposed dam. <br /> The subsoil conditions described above will require further evaluation outside of the scope of <br /> this subsurface exploration and geotechnical engineering report. Specifically, the evaluation <br /> will involve: <br /> 1. Detailed deformation analysis of the embankment due to compression or <br /> consolidation of the foundation soils, and evaluation of the outlet or level control <br /> structures in response to the deformation. Development of options to improve <br /> foundation soils and reduce settlement, deformation and distress will likely be <br /> required, in addition to additional field and laboratory analysis to more thoroughly <br /> assess engineering properties of site soils. <br /> i <br /> 2. Detailed seepage analysis of the overall impoundment and below and around the <br /> dam. Moderate permeability soils exist along the south side of the creek channel, at <br /> least at the dam area and potentially up the entire south side of the impoundment. <br /> Water loss through the soil may be a factor in viability of the dam as an irrigation <br /> I impoundment. Subsurface erosion and potential impact to dam stability due to <br /> increased hydraulic head on the moderate permeability silty sediment is also a <br /> critical area of needed evaluation. <br /> INBERG-MILLER ENGINEERS 1 February 26, 2009 <br />