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 A - Gravel System

Universal Citation: 77 IL Admin Code ยง A
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

18 - 60

200

1.0

90

210

.95

3 feet

120

235

.85

150

265

.75

180

290

.69

240

320

.62

300

350

.57

2 feet

360

385

.52

NOTE:

1.

Absorption area is figured as trench bottom area in absorption trenches and bottom area in seepage beds.

2.

Seepage beds require 11/2 times the seepage field absorption area specified.

3.

Over 360 is unsuitable for subsurface seepage systems.

4.

Under 18 is unsuitable for subsurface seepage systems.

5.

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

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