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050 <br /> percent (20) have severe limitations, 29 percent (11) have moderate limitations, and 18 percent <br /> (7) have slight limitations. <br /> Soil properties and site features that contribute to failures in building foundations and footings <br /> include depth to the water table, depth to bedrock, stability, and problems associated with these <br /> characteristics that are compounded by conditions such as steep slopes and flooding tendencies. <br /> The presence of bedrock close to the surface not only increases excavation costs but can also <br /> result in drainage problems after construction. Unstable soils can slip and slide easily, and organic <br /> materials in soils may decompose or dry out and shrink, resulting in a loss of foundation support. <br /> Some soils that shrink and swell can change in volume by as much as 20 percent, putting great <br /> strain on building foundations. These limitations can and should be considered on a detailed basis <br /> prior to development. <br /> Soil limitations for dwellings without basements are summarized in the following table and shown <br /> on the accompanying map. As was the case with septic system suitability, the amount of land area <br /> comprised of soil types with severe limitations for dwellings is considerably less. Of the county's <br /> total land area, 39 percent (98,310 acres) has severe limitations, 28 percent (70,850 acres) has <br /> moderate limitations, and 33 percent (85,560 acres) has slight limitations. <br /> SOIL LIMITATIONS FOR DWELLINGS WITHOUT BASEMENTS <br /> Degree of Soil Limitation <br /> Characteristic Slight Moderate Severe <br /> Drainage Rapid Moderately Poorly drained <br /> Shrink-swell potential Very low to low Moderate High to very high <br /> Slope 0 - 8 percent 8 - 15 percent More than 15 percent <br /> Source: Soil Survey of Orange County.N.C. U.S.D.A. Soil Conservation Service, 1977. <br />