South Carolina Septic Tank Installer License Exam 2026 | Practice Questions & Correct Answers with Detailed Rationales | SCDES Onsite Wastewater Licensing Exam Prep | Instant Download PDF

South Carolina Septic Tank Installer License
Exam 2026 | Practice Questions & Correct
Answers with Detailed Rationales | SCDES
Onsite Wastewater Licensing Exam Prep |
Instant Download PDF

SOUTH CAROLINA SEPTIC TANK INSTALLER LICENSE EXAM 2026
Practice Questions & Correct Answers with Detailed Rationales

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DOCUMENT OVERVIEW:

• This practice exam contains 200 comprehensive multiple-choice questions
designed to prepare you for the official SCDES Onsite Wastewater Licensing Exam,
covering all major competency areas tested by South Carolina Department of
Environmental Services.

• Study this material by working through questions systematically, identifying weak
areas, reviewing rationales thoroughly, and retesting on challenging topics until you
achieve 80% or higher—the typical passing threshold for professional licensing
exams.

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1. What is the primary function of a septic tank in an onsite wastewater
system?

A) To permanently remove all wastewater from a property

B) To filter wastewater through sand and gravel layers

C) To provide initial settling and anaerobic decomposition of solids

D) To supply disinfection chemicals to treated effluent

E) To pump wastewater directly to surface streams

CORRECT ANSWER: C) To provide initial settling and anaerobic decomposition
of solids

,RATIONALE: The septic tank's primary function is to receive raw wastewater and
allow heavier solids to settle to the bottom where anaerobic bacteria begin
breaking down organic matter. The lighter effluent moves to the drainage field
while settled solids (sludge) remain in the tank. This is fundamental to all onsite
wastewater treatment systems and is the essential first stage of treatment.

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2. According to South Carolina regulations, what is the minimum liquid depth
required in a septic tank?

A) 12 inches

B) 18 inches

C) 24 inches

D) 36 inches

E) 48 inches

CORRECT ANSWER: D) 36 inches

RATIONALE: SCDES regulations specify that septic tanks must maintain a minimum
liquid depth of 36 inches (3 feet) to allow adequate settling time for solids and
proper bacterial action. This depth ensures sufficient retention time for particles to
settle while maintaining proper anaerobic conditions for decomposition.

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3. What soil percolation rate (in minutes per inch) indicates the soil is suitable
for conventional septic system installation in South Carolina?

A) Less than 2 minutes per inch

B) 2 to 30 minutes per inch

C) 30 to 60 minutes per inch

D) 60 to 120 minutes per inch

E) Greater than 120 minutes per inch

,CORRECT ANSWER: B) 2 to 30 minutes per inch

RATIONALE: SCDES regulations specify that soil with a percolation rate of 2 to 30
minutes per inch is suitable for conventional septic system drainage fields. Rates
faster than 2 minutes per inch indicate excessively sandy soil, while rates slower
than 30 minutes per inch indicate poor drainage and may require alternative
systems such as mounds or sand filters.

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4. Which of the following is NOT a required component of a South Carolina
onsite wastewater system?

A) Septic tank

B) Drainage field

C) Biosolids treatment facility

D) Distribution box

E) Soil

CORRECT ANSWER: C) Biosolids treatment facility

RATIONALE: A biosolids treatment facility is not a component of standard
residential onsite wastewater systems. Required components include a septic tank
(primary treatment), distribution system (drainage field, distribution box), and
appropriate soil for treatment and dispersal. Biosolids treatment occurs at
centralized municipal facilities, not at individual sites.

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5. What is the minimum setback distance required from a septic tank to a
water supply well in South Carolina?

A) 25 feet

B) 50 feet

C) 100 feet

, D) 150 feet

E) 200 feet

CORRECT ANSWER: C) 100 feet

RATIONALE: SCDES regulations require a minimum 100-foot horizontal setback
distance from a septic tank to any potable water well to protect groundwater
quality and prevent contamination. This distance provides reasonable protection
while accounting for typical groundwater flow patterns and contaminant transport
in South Carolina soils.

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6. A dwelling with 3 bedrooms would require a septic tank with a minimum
capacity of what volume?

A) 750 gallons

B) 1,000 gallons

C) 1,250 gallons

D) 1,500 gallons

E) 2,000 gallons

CORRECT ANSWER: D) 1,500 gallons

RATIONALE: SCDES sizing requirements specify 500 gallons for the first bedroom
plus 250 gallons for each additional bedroom, or 250 gallons per bedroom plus 500
gallons base capacity. For 3 bedrooms: 500 + 250 + 250 = 1,000 gallons minimum,
but standard practice and code require 1,500 gallons (500 + 500 + 500) for
adequate retention time of 24-48 hours.

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7. What is the maximum slope permitted for a septic tank drainage field in
South Carolina?

A) 2 percent