Illinois Administrative Code › Title 77 - PUBLIC HEALTH › Part 906 - PRIVATE SEWAGE MOUND CODE › Section 906.30 - Soil and Site Requirements

Current through Register Vol. 48, No. 28, July 12, 2024
In order to be suitable for mound construction, the site shall
				meet the following requirements and those listed in Appendix A, Exhibit
				A.
a) Percolation Rates. Percolation
			 rates shall be used to determine the suitability of the site for accepting
			 effluent. Percolation tests shall be performed according to the procedure
			 outlined in Appendix A, Illustration G of the Private Sewage Disposal Code (77
			 Ill. Adm. Code 905). Excepting that, percolation tests shall be performed at a
			 depth of 20-24 in. from the natural surface. However, in cases where a more
			 slowly permeable soil horizon is above this depth the percolation tests shall
			 be conducted in the more slowly permeable soil horizon. Those results shall be
			 used in the design of the mound. For shallow permeable soils over pervious
			 bedrock, the percolation test shall be run at a depth of 12-18 in. below the
			 natural surface. For permeable soils with high water tables, the percolation
			 test shall be run at a depth of 20-24 in. below the natural surface.
b) Depth to Pervious Rock or Seasonal High
			 Water Table. There shall be a minimum of 24 in. of unsaturated soil between the
			 soil surface and pervious bedrock or the seasonal high water table, including a
			 perched water table, at the proposed mound site. High water tables can be
			 determined by direct observation or by soil mottling. Occurrence of grey and
			 red soil mottling patterns can be used to indicate periodic saturation with
			 water.
c) Rocky Soils. If the soil
			 contains 50% rock fragments or more by volume in the upper 24 in. of soil, the
			 mound basal area shall be 25% larger than that normally required.
d) Slopes. The mound shall be placed upslope
			 and not at the base of the slope of the existing ground. On a site where there
			 is a complex slope, (two directions), the mound shall be situated such that the
			 liquid is not concentrated in one area downslope. Upslope runoff shall be
			 diverted around the mound. For the more permeable soils where the percolation
			 rate is 18-179 min., slopes shall not exceed 12%. For tighter soils where the
			 percolation rate is 180-360 min., slopes shall not exceed 6%.
e) Flood Plains. Construction of mound
			 systems shall not be allowed in flood plains, drainage ways or
			 depressions.
f) Sites with Trees
			 and Large Boulders. Sites with large trees, numerous smaller trees or large
			 boulders are unsuitable for the mound system. If no other site is available,
			 the trees shall be cut off at ground level, leaving the stumps. An increase in
			 mound basal area shall be required where stumps are involved, so that
			 sufficient soil is available to accept the effluent. The increase in mound area
			 shall equal the surface area of the stumps on the mound site.
g) Site Preparation
1) Vegetation shall be cut and removed from
			 the site prior to construction. The site must then be plowed with a mold board
			 plow 7-8 in. deep with the plowing done perpendicular to the slope. Plowing
			 shall not be done with the furrow running up and down the slope. Chisel plowing
			 may be used in place of mold board. Roto tilling is prohibited. However, roto
			 tilling may be used to incorporate the vegetative cover in unstructured soil
			 such as sand.
2) Site preparation
			 shall not take place when the soil is too wet. The soil shall be considered too
			 wet when a soil sample taken at a depth of 7-8 in. beneath the surface can be
			 rolled between the palms of the hands into a continuous ribbon of soil. If the
			 soil crumbles, site preparation can then proceed.
3) Once the site is plowed, all construction
			 machinery and other vehicles shall be kept off the mound site. The fill
			 material shall be deposited on the site with a backhoe or pushed on from the
			 side, using a track type tractor, keeping 6 in. of fill beneath the tracks. At
			 no time shall ruts be made in the plowed area. The fill shall be placed
			 immediately after site preparation to avoid the possibility of precipitation
			 falling on the plowed area.
4) All
			 work shall be performed from the ends and upslope side, especially on fine
			 textured soils.