CO Septic System Installer Exam Questions
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of a septic tank in an onsite
wastewater treatment system?
A. To disinfect all wastewater before discharge
B. To pump wastewater directly into a drainfield
C. To settle solids and provide anaerobic treatment before effluent
leaves the tank
D. To increase the pressure of wastewater entering the soil
Answer: C. To settle solids and provide anaerobic treatment before
effluent leaves the tank
Rationale: A septic tank is designed primarily to separate solids from
liquid wastewater. Heavier solids settle as sludge, lighter materials form
a scum layer, and the liquid effluent exits toward the treatment or
,dispersal system. The tank provides some anaerobic biological
treatment but is not intended to fully disinfect wastewater.
2. Which layer normally forms at the bottom of a properly
functioning septic tank?
A. Scum
B. Sludge
C. Grease
D. Clear water
Answer: B. Sludge
Rationale: Sludge consists primarily of heavier solids that settle to the
bottom of the septic tank. Scum and floating materials accumulate at
the top, while the liquid zone occupies the area between the two layers.
3. What is the primary function of the soil in a conventional septic
system drainfield?
A. To store sewage permanently
B. To provide final treatment and dispersal of effluent
C. To mechanically pump effluent
D. To produce drinking water
Answer: B. To provide final treatment and dispersal of effluent
,Rationale: Drainfield soil provides both dispersal and treatment. As
effluent moves through suitable unsaturated soil, physical, chemical,
and biological processes help remove contaminants before the treated
wastewater reaches groundwater.
4. Why is a septic tank generally divided into multiple
compartments?
A. To increase electrical capacity
B. To improve solids separation and protect downstream components
C. To eliminate the need for a drainfield
D. To increase wastewater temperature
Answer: B. To improve solids separation and protect downstream
components
Rationale: Multiple compartments can improve settling and reduce the
movement of solids into the effluent treatment or dispersal area. Better
solids retention helps prevent premature clogging of downstream
components.
5. Which material is generally unsuitable for use as clean drainfield
fill because it can restrict wastewater movement?
A. Properly graded sand
B. Approved soil material
, C. Heavy clay
D. Suitable granular material
Answer: C. Heavy clay
Rationale: Heavy clay has very low permeability and can severely
restrict the movement of effluent through the soil. Drainfield soil must
have characteristics that allow adequate treatment and dispersal while
maintaining appropriate hydraulic capacity.
6. What is the purpose of an effluent filter installed at the septic
tank outlet?
A. To heat wastewater
B. To remove larger suspended solids before they reach the dispersal
system
C. To add chlorine to wastewater
D. To increase tank pressure
Answer: B. To remove larger suspended solids before they reach the
dispersal system
Rationale: An effluent filter helps retain suspended solids within the
septic tank. This reduces the likelihood that solids will enter and clog
distribution pipes, treatment units, pumps, or soil absorption areas.
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of a septic tank in an onsite
wastewater treatment system?
A. To disinfect all wastewater before discharge
B. To pump wastewater directly into a drainfield
C. To settle solids and provide anaerobic treatment before effluent
leaves the tank
D. To increase the pressure of wastewater entering the soil
Answer: C. To settle solids and provide anaerobic treatment before
effluent leaves the tank
Rationale: A septic tank is designed primarily to separate solids from
liquid wastewater. Heavier solids settle as sludge, lighter materials form
a scum layer, and the liquid effluent exits toward the treatment or
,dispersal system. The tank provides some anaerobic biological
treatment but is not intended to fully disinfect wastewater.
2. Which layer normally forms at the bottom of a properly
functioning septic tank?
A. Scum
B. Sludge
C. Grease
D. Clear water
Answer: B. Sludge
Rationale: Sludge consists primarily of heavier solids that settle to the
bottom of the septic tank. Scum and floating materials accumulate at
the top, while the liquid zone occupies the area between the two layers.
3. What is the primary function of the soil in a conventional septic
system drainfield?
A. To store sewage permanently
B. To provide final treatment and dispersal of effluent
C. To mechanically pump effluent
D. To produce drinking water
Answer: B. To provide final treatment and dispersal of effluent
,Rationale: Drainfield soil provides both dispersal and treatment. As
effluent moves through suitable unsaturated soil, physical, chemical,
and biological processes help remove contaminants before the treated
wastewater reaches groundwater.
4. Why is a septic tank generally divided into multiple
compartments?
A. To increase electrical capacity
B. To improve solids separation and protect downstream components
C. To eliminate the need for a drainfield
D. To increase wastewater temperature
Answer: B. To improve solids separation and protect downstream
components
Rationale: Multiple compartments can improve settling and reduce the
movement of solids into the effluent treatment or dispersal area. Better
solids retention helps prevent premature clogging of downstream
components.
5. Which material is generally unsuitable for use as clean drainfield
fill because it can restrict wastewater movement?
A. Properly graded sand
B. Approved soil material
, C. Heavy clay
D. Suitable granular material
Answer: C. Heavy clay
Rationale: Heavy clay has very low permeability and can severely
restrict the movement of effluent through the soil. Drainfield soil must
have characteristics that allow adequate treatment and dispersal while
maintaining appropriate hydraulic capacity.
6. What is the purpose of an effluent filter installed at the septic
tank outlet?
A. To heat wastewater
B. To remove larger suspended solids before they reach the dispersal
system
C. To add chlorine to wastewater
D. To increase tank pressure
Answer: B. To remove larger suspended solids before they reach the
dispersal system
Rationale: An effluent filter helps retain suspended solids within the
septic tank. This reduces the likelihood that solids will enter and clog
distribution pipes, treatment units, pumps, or soil absorption areas.
