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195 <br />.1943 SOIL DEPTH <br />Soil depths to rock, parent material, or saprolite greater than 48 inches are considered suitable for <br />domestic sewage treatment and disposal systems. Soil depths to rock, parent material, or <br />saprolite between 36 and 48 inches are considered provisionally suitable for domestic sewage <br />treatment and disposal systems. Soil depths to rock, parent material, or saprolite less than 36 <br />inches are considered unsuitable for domestic sewage treatment and disposal systems. Saprolite <br />has a massive, rock - controlled structure, and retains the mineral arrangement of its parent rock in <br />at least 50 percent of its volume. Saprolite only forms from metamorphic and igneous rock <br />parent materials and is typically referred to as "rotten rock ". <br />.1944 RESTRICTIVE HORIZONS <br />Restrictive horizons are capable of perching ground water or sewage effluent and are strongly <br />compacted or cemented. Restrictive horizons resist soil excavation or augering. Soils with <br />restrictive horizons three inches or more in thickness at depths greater than 48 inches are <br />considered suitable for domestic sewage treatment and disposal systems. Soils with restrictive <br />horizons three inches or more in thickness at depths between 36 and 48 inches are considered <br />provisionally suitable for domestic sewage treatment and disposal systems. Soils with restrictive <br />horizons three inches or more in thickness at depths less than 36 inches are considered unsuitable <br />for domestic sewage treatment and disposal systems. <br />1950 LOCATION OF SANITARY SEWAGE SYSTEMS <br />No area for domestic sewage treatment and disposal system installation (or repair in Wake <br />County) may be disturbed by clearing, excavation, filling, vehicle or equipment traffic, or <br />storage of building materials. <br />1947 DETERMINATION OF OVERALL SITE SUITABILITY <br />.1948 SITE CLASSIFICATION <br />All of the criteria for the five categories above are to be determined and classified as suitable, <br />provisionally suitable, or suitable according to the respective rules described above. If all criteria <br />are classified the same, that overall site classification will prevail. If there is a variation in the <br />classification of several criteria, the most limiting classification will be used to determine the <br />overall site classification. <br />A suitable classification generally indicates soil and landscape conditions favorable for the <br />operation of a domestic sewage treatment and disposal system or slight limitations that can be <br />readily overcome by proper design and installation. A provisionally suitable classification <br />indicates soil and /or landscape conditions have moderate limitations for the operation of a <br />domestic sewage treatment and disposal system, but modifications and careful planning, design, <br />and installation can result in satisfactory system function. An unsuitable classification indicates <br />severe soil and /or landscape limitations for the operation of a domestic sewage treatment and <br />disposal system. <br />SUMMARY <br />Suitable /provisionally suitable landscapes and soils to a depth of 36 inches can, in general, be <br />used for conventional gravity driven septic systems. Suitable /provisionally suitable landscapes <br />and soils to a depth of 24 —36 inches can, in general, be used for alternative septic systems such <br />