406.6 Filled Area

A soil absorption system shall not be installed in a filled area unless written approval is received.

The approval of a conventional soil absorption system shall be based on evidence indicating its conformance to code requirements for area, percolation and elevation.

Sites with less than 56 inches (1422 mm) but at least 30 inches (762 mm) of soil over bedrock, where the original soil texture is sand or loamy sand, are permitted to be filled with the same soil texture as the natural soil or coarser material up to and including medium sand to overcome the site limitations. The fill material shall not be of a finer texture than the natural soil.

Sites with less than 56 inches (1422 mm) of soil over high ground water or estimated high ground water, where the original soil texture is sand or loamy sand, are permitted to be filled in accordance with Section 406.6.1 or 406.6.2.

Sites with soils finer than sand or loamy sand shall not be approved for systems in fill.

Sites that will have 36 inches (762 mm) or less of soil above high ground water after the topsoil is removed shall be monitored for high ground water levels in the filled area in accordance with Section 405.2.

Placement of the fill material shall be inspected by the code official.

Filled areas shall be large enough to accommodate a shallow trench system and a replacement system. The site of the area to be filled shall be determined by the percolation rate of the natural soil and use of the building. Where any portion of the trench system or its replacement is in the fill, the fill shall extend 20 feet (6096 mm) beyond all sides of both systems before the slope begins. Soil borings and percolation tests shall be conducted before filling to determine soil textures and depth to high ground water or bedrock. Vegetation and topsoil shall be removed prior to filling. Slopes at the edge of the filled areas shall have a maximum ratio of one unit vertical to three units horizontal (33-percent slope), provided the 20-foot (6096 mm) separating distance is maintained (see Appendix A, Figure A-3).