University of Illinois Extension

Quiz

Practice Problems: Sizing Septic Tanks 2

Residential sizing is based on the number of bedrooms and if there is a garbage grinder present. Sizing residential tanks can be found in section 905, Appendix A, Illustration F Commercial sizing is based on gallons of flow expected per day, either by actual use figures; code derived estimates, or approved IDPH estimates. Commercial sizing can be found in section 905, Appendix A, Illustration A. Tank size for commercial sites require a minimum of 750 gallon size for flows less than 500 gallons per day, or 1.5 times the average daily flow for amounts over 500 gallons per day.

Size the septic tank for the following commercial situations. 

  1. Practice Problems: Sizing Septic Tanks 2

    A boarding home with 10 people:

    Average daily flow: 500 gallons
    Minimum tank size: 750 gallons
    • 50 gallons/person
  2. Practice Problems: Sizing Septic Tanks 2

    A church with 300 members and a kitchen:

    Average daily flow: 1800 gallons
    Minimum tank size: 2700 gallons
    • 6 gallons/day/seat
  3. Practice Problems: Sizing Septic Tanks 2

    A church with 100 members and no kitchen:

    Average daily flow: 300 gallons
    Minimum tank size: 750 gallons
    • 3 gallons/day/seat
  4. Practice Problems: Sizing Septic Tanks 2

    A campground with mobile homes and 25 sites:

    Average daily flow: 3750 gallons
    Minimum tank size: 5625 gallons
    • 150 gallons/day/site