Section 905.APPENDIX
A Illustrations and Exhibits
Section 905.ILLUSTRATION I Seepage Field Construction
Section 905.EXHIBIT A Gravel System
Trench
length, maximum length from point of discharge into seepage trench

100 feet

Trench bottom, minimum width

8
in.

Trench bottom, maximum width

36
in.

Trench bottom, minimum depth

18
in.

Trench bottom, maximum depth

36
in.

Trench bottom, slope

level

Distribution line, minimum diameter

4
in.

Distribution line, minimum earth cover

6
in.

Distribution line, maximum earth cover

24
in.

Distribution line, maximum slope

level

(Source: Amended at 20 Ill. Reg.
2431, effective March 15, 1996)
Section 905.APPENDIX A Illustrations and Exhibits
Section 905.ILLUSTRATION I Seepage Field Construction
Section 905.EXHIBIT B Size and Spacing Gravel System
Width of Trench
at Bottom

Minimum Center to
Center Spacing of Distribution Lines

Effective
Absorption Area Per Lineal Foot of Trench

Inches

Feet

Square Feet

8

6.0

0.67

12

6.0

1.0

18

6.0

1.5

24

6.0

2.0

30

7.5

2.5

36

9.0

3.0

(Source: Amended at 9 Ill. Reg.
20738, effective January 3, 1986)
Section 905.APPENDIX A Illustrations and Exhibits
Section 905.ILLUSTRATION I Seepage Field Construction
Section 905.EXHIBIT C Gravelless System
STANDARDS FOR
SEEPAGE FIELD CONSTRUCTION (GRAVELLESS)

Trench
Length, maximum length from point of discharge into system

100
feet

Trench Bottom, minimum width

18
inches

Trench Bottom, maximum width

24
inches

Trench Bottom, minimum depth

18
inches

Trench Bottom, maximum depth

36
inches

Trench Bottom, slope

level

Distribution Line, minimum inside diameter

8
inches

Distribution Line, maximum inside diameter

10
inches

Distribution Line, minimum earth cover

6
inches

Distribution Line, maximum earth cover

24
inches

Distribution Line, maximum slope

level

(Source: Amended at 20 Ill. Reg.
2431, effective March 15, 1996)
Section 905.APPENDIX A Illustrations and Exhibits
Section 905.ILLUSTRATION I Seepage Field Construction
Section 905.EXHIBIT D Spacing − Gravelless and
Chamber Systems
SPACING FOR SEEPAGE
FIELD CONSTRUCTION
(GRAVELLESS AND CHAMBER
SYSTEMS)
Gravelless and
Chamber Dimensions

Minimum Center to
Center
Spacing of
Distribution Lines

8 Inch Inside Diameter of
Gravelless Pipe System

7.0 feet

10 Inch Inside Diameter of
Gravelless Pipe System

7.0 feet

12 Inch Wide Chamber System

7.0 feet

18 Inch Wide or Wider Chamber
System

9.0 feet

(Source: Amended at 37 Ill.
Reg. 14994, effective August 28, 2013)
Section 905.APPENDIX A Illustrations and Exhibits
Section 905.ILLUSTRATION I Seepage Field Construction
Section 905.EXHIBIT E Chamber Sizing Requirements
Example: Chamber systems shall be sized on the absorption
area of the chamber that is equivalent to the bottom area of a gravel system.
The equivalent chamber absorption area per lineal foot is equal to the average
inside width of the chamber times an equivalency factor of 2.5. For example, a
chamber that has an average inside width of 1.25 feet provides an equivalent
absorption area of 3.125 square feet per lineal foot. (1.25 feet times the 2.5
equivalency factor equals 3.125 square feet per lineal foot.
To determine the length of chambers required, first
calculate the absorption area required for a gravel system based on Appendix A,
Illustration H, Exhibit A or Appendix A, Illustration M, Exhibit A. Then
divide this area by the equivalent chamber absorption area per lineal foot.
For example, if a 3 bedroom house requires 870 square feet of absorption field
and chambers 1.25 feet wide are being used, then the length of chambers needed
is 278 feet. (870 square feet divided by 3.125 square feet per lineal foot
equals 278 feet.)
Chamber systems with an average inside dimension equal to or
greater than 20 inches shall not be designed to receive an equivalent
absorption area of greater than 54 square feet per lineal foot.
(Source: Amended at 37 Ill.
Reg. 14994, effective August 28, 2013)