1|Page
ILLINOIS PRIVATE SEWAGE CONTRACTOR EXAM 2025–2026 WITH
UPDATED PRACTICE QUESTIONS, VERIFIED SOLUTIONS, AND A+
SCORED STUDY GUIDE FOR GUARANTEED SUCCESS.
1 — Definition / scope
Question: Which statement best matches the Illinois legal definition / scope
of a Private Sewage Disposal System under state law?
A. Any sewage system treating municipal sewage discharged to public
sewers.
B. Any sewage handling facility receiving domestic sewage from more than
15 people or discharging more than 1,500 gpd.
C. A sewage handling or treatment facility receiving domestic sewage
from less than 15 people (population equivalent) and having a ground-
surface discharge, or any such facility with no surface discharge
(regulated under the Private Sewage Disposal Act/Part 905).
D. Any industrial waste treatment system regulated by EPA only.
Answer: C.
Explanation: The Illinois Private Sewage Disposal Licensing Act and Part
905 define a "private sewage disposal system" as domestic sewage systems
,2|Page
that generally serve fewer than 15 people (population equivalent) and that
either have no surface discharge or (in certain permitted cases) discharge
treated effluent to the ground surface (IDPH regulates systems up to certain
limits). This is the legal scope used to determine when Part 905 applies.
Illinois General Assembly+1
2 — Design flow (bedroom method)
Question: Using the common Illinois design convention referenced in
general permits, what is the design daily flow (gpd) for a 3-bedroom single
family home when the “bedroom method” from IL guidance/permits is
used?
A. 200 gpd
B. 300 gpd
C. 400 gpd
D. 600 gpd
Answer: C.
Explanation & calculation: Many Illinois designs (and the EPA/ILG62
guidance used for surface discharge permitting) use 100 gpd + 100 gpd per
bedroom as a conservative design flow method for homes. For a 3-bedroom
house: 100 + (3 × 100) = 400 gpd design flow. (If a local health department
,3|Page
uses a different formula in a particular circumstance they will state it, but
this is the common approach used for permit-level sizing in Illinois
guidance.) US EPA+1
3 — Minimum septic tank liquid volume (low flows)
Question: According to Part 905 Illustration F, what is the minimum liquid
capacity required for septic tanks serving systems with flows up to 500
gpd?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons
D. 1,500 gallons
Answer: B.
Explanation: Part 905’s Appendix (Illustration F) specifies minimum tank
liquid volumes. For flows up to 500 gpd, the code requires a minimum
liquid capacity of at least 750 gallons. This is the baseline minimum before
larger flow rules apply. Always check Appendix F for specific bedroom-
based or flow-based values. ilrules.elaws.us
4 — Septic tank sizing for higher flows
, 4|Page
Question: For a system with estimated daily flow greater than 500 gpd,
Part 905 requires septic tank liquid volume to be:
A. The same 750 gallons minimum regardless of flow.
B. At least 1.5 × the estimated daily sewage flow.
C. Exactly equal to the estimated daily flow.
D. Sized by local ordinance only.
Answer: B.
Explanation & calculation method: Part 905 directs that when flows
exceed 500 gpd, the liquid capacity of the septic tank shall be at least 1.5
times the estimated daily sewage flow.
Example: if estimated flow = 800 gpd → required tank volume ≥ 1.5 × 800
= 1,200 gallons (liquid capacity). Always round up to available standard
tank sizes and observe any additional local minimums. Illinois General
Assembly
5 — Tank liquid depth limits
Question: What are the minimum and maximum liquid depths for septic
tanks required by Part 905?
A. Min 24" — Max 60"
B. Min 42" — Max 72"
ILLINOIS PRIVATE SEWAGE CONTRACTOR EXAM 2025–2026 WITH
UPDATED PRACTICE QUESTIONS, VERIFIED SOLUTIONS, AND A+
SCORED STUDY GUIDE FOR GUARANTEED SUCCESS.
1 — Definition / scope
Question: Which statement best matches the Illinois legal definition / scope
of a Private Sewage Disposal System under state law?
A. Any sewage system treating municipal sewage discharged to public
sewers.
B. Any sewage handling facility receiving domestic sewage from more than
15 people or discharging more than 1,500 gpd.
C. A sewage handling or treatment facility receiving domestic sewage
from less than 15 people (population equivalent) and having a ground-
surface discharge, or any such facility with no surface discharge
(regulated under the Private Sewage Disposal Act/Part 905).
D. Any industrial waste treatment system regulated by EPA only.
Answer: C.
Explanation: The Illinois Private Sewage Disposal Licensing Act and Part
905 define a "private sewage disposal system" as domestic sewage systems
,2|Page
that generally serve fewer than 15 people (population equivalent) and that
either have no surface discharge or (in certain permitted cases) discharge
treated effluent to the ground surface (IDPH regulates systems up to certain
limits). This is the legal scope used to determine when Part 905 applies.
Illinois General Assembly+1
2 — Design flow (bedroom method)
Question: Using the common Illinois design convention referenced in
general permits, what is the design daily flow (gpd) for a 3-bedroom single
family home when the “bedroom method” from IL guidance/permits is
used?
A. 200 gpd
B. 300 gpd
C. 400 gpd
D. 600 gpd
Answer: C.
Explanation & calculation: Many Illinois designs (and the EPA/ILG62
guidance used for surface discharge permitting) use 100 gpd + 100 gpd per
bedroom as a conservative design flow method for homes. For a 3-bedroom
house: 100 + (3 × 100) = 400 gpd design flow. (If a local health department
,3|Page
uses a different formula in a particular circumstance they will state it, but
this is the common approach used for permit-level sizing in Illinois
guidance.) US EPA+1
3 — Minimum septic tank liquid volume (low flows)
Question: According to Part 905 Illustration F, what is the minimum liquid
capacity required for septic tanks serving systems with flows up to 500
gpd?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons
D. 1,500 gallons
Answer: B.
Explanation: Part 905’s Appendix (Illustration F) specifies minimum tank
liquid volumes. For flows up to 500 gpd, the code requires a minimum
liquid capacity of at least 750 gallons. This is the baseline minimum before
larger flow rules apply. Always check Appendix F for specific bedroom-
based or flow-based values. ilrules.elaws.us
4 — Septic tank sizing for higher flows
, 4|Page
Question: For a system with estimated daily flow greater than 500 gpd,
Part 905 requires septic tank liquid volume to be:
A. The same 750 gallons minimum regardless of flow.
B. At least 1.5 × the estimated daily sewage flow.
C. Exactly equal to the estimated daily flow.
D. Sized by local ordinance only.
Answer: B.
Explanation & calculation method: Part 905 directs that when flows
exceed 500 gpd, the liquid capacity of the septic tank shall be at least 1.5
times the estimated daily sewage flow.
Example: if estimated flow = 800 gpd → required tank volume ≥ 1.5 × 800
= 1,200 gallons (liquid capacity). Always round up to available standard
tank sizes and observe any additional local minimums. Illinois General
Assembly
5 — Tank liquid depth limits
Question: What are the minimum and maximum liquid depths for septic
tanks required by Part 905?
A. Min 24" — Max 60"
B. Min 42" — Max 72"
