Illinois Administrative Code
Title 77 - PUBLIC HEALTH
Part 905 - PRIVATE SEWAGE DISPOSAL CODE
Appendix A - Illustrations and Exhibits
ILLUSTRATION H - Subsurface Seepage System Size Determination
Exhibit B - Gravelless System

Universal Citation: 77 IL Admin Code ยง B
Current through Register Vol. 48, No. 12, March 22, 2024

Time (minutes) required for last 6 inches of water to fall

FOR RESIDENTIAL USE Required Absorption Area (sq ft)/bedroom)

FOR INSTITUTIONAL OR COMMERCIAL USE Allowable application rate (GPD/sq ft) (5)

Recommended depth from bottom of the trench to the limiting layer

8 inch

10 inch

8 inch

10 inch

18 - 60

100

70

2.00

3.00

90

105

70

1.90

2.86

3 feet

120

120

80

1.66

2.50

150

135

90

1.48

2.22

180

145

100

1.38

2.00

240

160

110

1.25

1.82

300

175

120

1.14

1.66

2 feet

360

195

130

1.0

1.54

NOTE:

1.

Over 360 is unsuitable for subsurface seepage systems.

2.

Under 18 is unsuitable for subsurface seepage systems.

3.

Divide the required total gallons per day by this number to get the number of lineal feet required.

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