Licensing Exam Practice Questions And

Onsite Wastewater System Installer Licensing Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• A primary function of a septic tank in an onsite wastewater system is

to:

• Evaporate all wastewater
• Filter wastewater using sand
• Allow solids to settle and begin biological breakdown
• Pump effluent to drinking water supplies

Rationale: Septic tanks are designed for primary treatment,

separating solids (sludge/scum) from liquid effluent for further treatment.

2. The soil treatment area primarily:

• Increases wastewater flow 1 / 3

• Removes pathogens and nutrients
• Absorbs and treats effluent
• Stores wastewater long-term

Rationale: Soil provides natural filtration and biological treatment of

effluent as it percolates.

• Which component conveys effluent from the septic tank to the soil

absorption field?

• Inspection ports
• Distribution box
• Effluent filter
• Sewage ejector pump

Rationale: A distribution box evenly distributes effluent to multiple

trenches or laterals.

4. The scum layer in a septic tank consists mostly of:

• Inorganic solids
• Sand and grit
• Fats, oils, and grease
• Fully treated water

Rationale: FOG floats to the top creating a scum layer requiring

maintenance.

• What is the minimum separation typically required between a septic

drainfield and a private well (varies by jurisdiction)?

• 10 feet 2 / 3

• 25 feet
• 50–100 feet
• 300 feet

Rationale: Well setbacks prevent groundwater contamination from

effluent; most codes require 50–100 ft.

6. Hydraulic loading rate of soil refers to:

• Soil nutrient content
• The amount of effluent soil can receive per area per day
• Soil air-exchange rate
• Soil acidity level

Rationale: Determines system sizing based on infiltration capacity.

7. Percolation testing measures:

• Soil alkalinity
• Organic content
• Water infiltration rate
• Groundwater hardness

Rationale: Percolation tests show how quickly soil absorbs water,

essential for design.

8. Pump chambers are used when:

• Effluent can flow downhill by gravity
• Elevation prevents gravity flow to the field
• The tank is too large
• Drinking water must be pumped
• / 3