Mississippi Administrative Code › Title 15 - Mississippi Department of Health › Part 18 - Division of On-site Wastewater › Subpart 77 - On-site Wastewater Regulations › Chapter 5 - INDIVIDUAL ONSITE WASTEWATER DISPOSAL DESIGN STANDARD › Subchapter 4 - AGGREGATE › Rule 15-18-77-5.4.5 - Underground Absorption

Current through June 25, 2024
1. The size of the
					 subsurface sewage disposal system shall be determined by soil texture [See
					 Table II].
2. 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.
3. Soils with
					 excessively slow permeability rates, silty clay and clay, shall be considered
					 unsuitable for conventional subsurface disposal.
4. Subsurface disposal systems shall be
					 placed no deeper than 36 inches below the surface.
5. Conventional subsurface disposal systems
					 shall have a minimum 12 inches of soil backfill [Figure 1][Figure 2].
6. The minimum distance between
					 absorption trench sidewalls shall be six feet.
7. Aggregate -type absorption trenches shall
					 be a minimum of 24 inches and a maximum of 36 inches in width.
8. Trenches shall not be excavated when the
					 soil is wet enough to smear or compact easily.
9. The bottom of the trenches or bed and the
					 distribution lines shall have a grade from level to no greater than two inches
					 fall per 100 feet.
10. 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.
11. Media for the
					 disposal fields shall extend from at least two inches above the top of the
					 perforated field line pipe to at least six inches below the bottom of the
					 perforated field line pipe a minimum of 12 inches total [Figure 1].
12. Stone media for the disposal fields shall
					 consist of crushed rock, gravel or other suitable material, as approved by the
					 Mississippi Department of Health, Division of Onsite Wastewater, varying in
					 size from- to 2- inches. The material shall be free from dust, sand, clay, or
					 excessive fines.
13. Tire chips
					 shall be allowed for use as coarse aggregate in onsite wastewater treatment and
					 disposal system drainfields and may substitute for stone aggregate on a
					 one-for-one basis, volumetrically when the following physical properties are
					 met:
a. Tire chips are to be a normal two (2)
					 inches in size and may range from one-half (1/2) inch to a maximum of four (4)
					 inches in any direction.
b. Exposed
					 wire may protrude no more than one-half (1/2) inch from the sides of the chip.
					 No more than (10%) by weight shall exceed this standard.
c. No more than (10%) by weight shall pass
					 through a one-half (1/2) inch screen.
d. At least 80% of the bead wire must be
					 removed from the tires to be chipped.
e. Fines of less than 2 mm in size are
					 prohibited. Fines in this context is defined as particles or substances which
					 can settle to the bottom of the absorption trench and contribute to the
					 clogging or blocking of infiltrative surfaces (dirt, dust, grit, crumb rubber
					 and similar substances).