University of Illinois Extension

Quiz

Practice Problems: Sizing Commercial Subsurface Seepage Systems 2

Sizing of subsurface seepage systems is done by applying the soil loading rate to the average daily flow, or the number of bedrooms for residential settings.

The soil loading rate can be calculated by using either a percolation (perc) test or a soil evaluation.  The procedure for conducting percolation tests is found in section 905, Appendix A, Illustration G of the administrative code.

Information on using soil evaluations and loading rates is found in Section 905, Appendix A, Illustration M

Information on calculations for gravel trenches is found in Appendix A, Illustration H, Exhibit A.  Exhibit B is used for gravelless pipe.

Commercial practice problems.

A church wants to construct a youth camp with a kitchen, and a maximum capacity of 30 people.
  1. Practice Problems: Sizing Commercial Subsurface Seepage Systems 2

    What is the estimated average daily flow?

    1800 gallons
  2. Practice Problems: Sizing Commercial Subsurface Seepage Systems 2

    What minimum size septic tank is required?

    2700 gallons
    • 1800 x 1.5 = 2700 gallons
  3. Practice Problems: Sizing Commercial Subsurface Seepage Systems 2

    If a perc test rate is 300 minutes, how many linear feet of 24 inch wide gravel trench would be required?

    1570 linear feet
    • 1800/.57 = 3158 ft²/2 = 1570 linear feet
  4. Practice Problems: Sizing Commercial Subsurface Seepage Systems 2

    If the perc test rate is 300 minutes, how many feet of 10 inch gravelless pipe would be required?

    1084 linear feet
    • 1800/1.66 = 1084 linear feet