Rule 15-18-77-5.5.5 - Underground Absorption1. Aggregate replacement systems shall comply with all criteria for subsurface gravel disposal systems except in sections pertaining to the gravel media or as specified in this regulation.2. The size of the subsurface sewage disposal system shall be determined by soil texture and estimated wastewater flow.3. Soils with excessively rapid permeability rates, gravel and coarse sand, shall be considered unsuitable for subsurface disposal unless the native soil is replaced with a suitably thick (greater than two feet) layer of loamy sand or sand textured soil.4. Soils with excessively slow permeability rates, silty clay and clay, shall be considered unsuitable for conventional subsurface disposal.5. Subsurface disposal systems shall be placed no deeper than 36 inches below the surface. 6. Aggregate replacement subsurface disposal systems shall have a minimum 12 inches of soil backfill. 7. The minimum distance between absorption trench sidewalls shall be six feet.8. Trenches shall not be excavated when the soil is wet enough to smear or compact easily.9. There shall be a minimum of three feet of undisturbed soil between the excavation for the septic tank or treatment plant and the beginning of the absorption trench, bed or effluent line.10. The bottom of the outlet of the septic tank, aerobic treatment plant or vessel supplying effluent to the pipe must be a minimum of one inch above the top of the aggregate replacement system. 11. Care must be taken when backfilling to prevent the pipe from shifting during the backfilling process. 12. Soil material excavated from trenches shall be used in backfilling and should be left mounded over the trenches until initial settling has taken place.13. Standard manufactured fittings compatible with the pipe shall be used to connect all pipes within the effluent disposal field.15 Miss. Code. R. 18-77-5.5.5