Illinois Administrative Code › Title 77 - PUBLIC HEALTH › Part 905 - PRIVATE SEWAGE DISPOSAL CODE › Section 905.60 - Subsurface Seepage System Construction Requirements

Current through Register Vol. 48, No. 28, July 12, 2024
a) Seepage Field Requirements - Gravel,
			 Gravelless and Chamber Systems. Subsurface seepage fields shall be designed and
			 constructed in accordance with Appendix A, Illustrations H, I and J and the
			 following:
1) All subsurface seepage systems
			 using soils information for sizing shall use the soil suitability table in
			 Appendix A, Illustration M to determine the size requirements of the subsurface
			 seepage system. The least permeable soil layer between the top of the gravel or
			 gravelless pipe or chamber system and 2 feet below the bottom of the trench
			 shall be used to determine the size of the subsurface seepage system. For mound
			 or at-grade systems, the least permeable soil layer in the upper 2 feet of the
			 soil shall be used to determine system size.
2) The bottom of the subsurface seepage
			 field, each trench and its distribution line shall be level. Level for this
			 Part shall mean plus or minus 1/2 inch in any direction over the entire area of
			 the subsurface seepage system.
3)
			 There shall be a minimum of 6 inches and a maximum of 24 inches of earth
			 backfill over the bedding materials, gravelless pipe or chamber
			 system.
4) There shall be a minimum
			 of 5 feet of undisturbed earth between the septic tank and the nearest
			 trench.
5) If precipitation falls
			 onto the excavation and evidence of soil washing into the excavation of the
			 subsurface seepage system exists, the damaged portion of the seepage system
			 shall be reconstructed to comply with this Section.
6) The top of the gravel, gravelless pipe, or
			 chamber system in the subsurface seepage field shall be at least one inch below
			 the invert of the outlet pipe from the septic tank or distribution box in a
			 gravity flow system.
7) Site
			 Evaluation for Subsurface Seepage Systems. Subsurface seepage systems receiving
			 septic tank effluent shall have at least 2 feet of vertical separation distance
			 between the bottom of the subsurface seepage system and the top of the limiting
			 layer. For soils in Design Group I-VI or with a loading rate of greater than
			 0.62 gallons per day per square foot, there shall be at least a vertical
			 separation distance of 3 feet between the bottom of the subsurface seepage
			 system and the top of the limiting layer. When the limiting layer is the
			 estimated seasonal high water table, artificial drains, which are designed to
			 lower the estimated seasonal high water table, may be installed to achieve the
			 specified vertical separation distances.
8) Sizing of a Seepage System in Fill Soil
A) The least permeable soil layer between the
			 top of the gravel, gravelless pipe or chamber system and 2 feet below the
			 bottom of the trench shall be used to determine the size of the subsurface
			 seepage system.
B) The use of fill
			 for installing subsurface seepage systems shall not be approved for lots
			 platted after March 15, 1996.
C)
			 Fill soils may be used to cover a private sewage disposal system, provided that
			 no part of the system is located in the fill and the fill material is at least
			 equal to or better than the original soil or meets the requirements in
			 subsection (a)(9).
9)
			 Soil Criteria for Use of Fill in Subsurface Seepage Systems
A) Soils to be used for fill shall be
			 identified by a soil classifier or licensed Professional Engineer and a report
			 submitted to the Department or local authority. The report shall contain
			 specific information on the fill soil, including location, depth, permeability,
			 and texture. Soils that can be used as fill are those identified in Appendix A,
			 Illustration M as 2A, 2B, 2K, 3A, 3B, 3C, 3K, 3L, 4B, 4D and 4K (Design Group
			 II, III and IV).
B) In addition to
			 the requirements in subsection (a)(9)(A), fill soil shall not contain
			 extraneous material such as tires, concrete, brick, reinforcing bar, demolition
			 material, etc.
C) All of the
			 following conditions shall be met for a subsurface seepage system to be
			 installed in fill.
i) Satisfactory original
			 soil shall be at least 3 feet above bedrock.
ii) A maximum of 2 feet of fill soil shall be
			 used.
iii) Fill shall not be placed
			 on original soil with a slope greater than 10%.
iv) The fill shall be placed at the site so
			 that a minimum of compaction occurs, and the fill shall be allowed to settle
			 undisturbed for a period of at least 12 months. Soils in Design Group II, when
			 used for fill, shall not be required to settle for a period of at least 12
			 months.
v) After the fill has been
			 settled, a percolation test shall be conducted in accordance with the procedure
			 outlined in Appendix A, Illustration G and a percolation rate of not greater
			 than 270 minutes/6 inch fall or less than 60 minutes/6 inch fall shall be
			 achieved.
10)
			 Site Preparation for Use of Fill Soil
A)
			 Excess vegetation shall be cut and removed. The site shall be plowed with a
			 mold board plow 7 to 8 inches deep with the plowing done perpendicular to the
			 slope. It 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.
B) Once the site is
			 plowed, all traffic shall be kept off the site. The fill material can be
			 deposited on the top with a backhoe or pushed on from the side, preferably the
			 upslope side, using a track type tractor, keeping 6 inches 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.
C) Traffic on the downslope side of the fill
			 area shall be minimal to reduce compaction. All work shall be performed from
			 the ends and upslope side. Compaction of the natural soil downslope will reduce
			 the lateral movement of the effluent.
D) The fill shall not be placed on frozen
			 ground or when the soil is wet. Moisture content of the soil is very important
			 when filling. Site preparation shall not take place when the soil is too wet.
			 To check moisture content, a soil sample may be taken from the plow layer (7 to
			 8 inches) and rolled between the palms of the hands. If the soil rolls into a
			 ribbon, it is too wet to prepare. If the soil crumbles, site preparation can
			 then proceed.