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048 <br /> Septic tank absorption fields are subsurface systems of tile or perforated pipe that distribute <br /> effluent from a septic tank into the soil. Soil properties and site features that affect the absorption <br /> of the effluent and/or the construction of the system include slow permeability, shallow depth to <br /> bedrock, wetness, and steep slopes. For example, areas with impermeable soils or high water <br /> tables can limit the ability of the soil to assimilate septic effluent. Where the depth to bedrock or <br /> some other impermeable layer is shallow, drainage from septic systems can flow too close to the <br /> surface, often emerging and standing or flowing on the surface. Similarly, the drainage from septic <br /> fields located on steep slopes can flow to the downslope surface before sufficient filtration has <br /> taken place. Hence, soil characteristics are an important factor in limiting development that <br /> utilizes septic tanks. <br /> Soil limitations for septic tank absorption fields are summarized in the following table. If the <br /> degree of soil limitation is expressed as slight, sods are generally favorable for the specified use <br /> and limitations are minor. If moderate, soil properties or site features are unfavorable for the <br /> specified use, but limitations can be overcome through proper system design and at additional <br /> cost. For example, if permeability is a factor, that limitation may be overcome by modifying the <br /> field or increasing the size of the absorption area. If severe, sod properties or site features may be <br /> so unfavorable or difficult to overcome that major sod reclamation, special design or intensive <br /> maintenance is required. <br /> SOIL LEVUTATIQNS FOR SEPTIC TANK ABSORPTION FIELDS <br /> Degree of Soil Limitation <br /> Characteristic Slight Moderate Severe <br /> Permeability Rapid to Moderate Slow to <br /> moderately rapid very slow <br /> Wetness No limitations No limitations Seasonal high water <br /> table and flooding <br /> Depth to bedrock More than 72 inches 48 - 72 inches Less than 40 inches <br /> Slope 0 - 8 percent 8 - 15 percent More than 15 percent <br /> Source: Soil Sun=of Orangg CgmWE,N.C., U.S.DA Soil Conservation Service, 1977. <br /> Sods with severe limitations fcir—*&'tank-Absorption fields are illustrated on the following map. <br /> Of the 38 soil types identified in the Soil SUM of Orange Cog=N.C., 63 percent (24) present <br /> severe limitations for septic tank absorption fields, while 37 percent (14) have moderate <br /> limitations. There are no soils in Orange County rated as having slight limitations. <br /> While a majority of soil types pose severe problems for septic tank absorption field installation, <br /> only 41 percent of the county's land area(103,420 acres) is comprised of such soils. As shown on <br /> the accompanying map, most are located in the northwestern and southeastern portions of the <br /> county, and are characterized by slow permeability. <br /> Limitations for Dwellings. Most of the soils characterized as having severe limitations for septic <br /> tank absorption fields present similar limitations for dwelling construction, especially those <br /> without basements. Of the 38 soil types identified in the Soil Smaa of Orange CowAL N.C., 53 <br />