South Carolina DHEC Onsite Wastewater
Contractor Permit Questions And Correct Answers
Plus Rationales 2025.
The questions cover general installation, operation, maintenance, state
regulations, site evaluation, and safety topics relevant to SC DHEC standards.
1. What is the minimum setback distance for an onsite wastewater system
from a private drinking water well in South Carolina?
75 feet
A 75-foot setback is required to prevent contamination of the water
supply.
2. Which soil horizon is most suitable for effluent absorption?
B horizon
The B horizon often has good structure and permeability for wastewater
absorption.
3. When is a soil permeability test required during site evaluation?
When soil texture alone cannot determine suitability
If texture is uncertain, percolation tests help verify infiltration rates.
4. What is the primary purpose of the septic tank in an onsite wastewater
system?
To separate solids from liquids
, The tank settles solids and retains them, while effluent moves to the drain
field.
5. What is the minimum size for a septic tank serving a 3-bedroom house in
SC?
1000 gallons
South Carolina requires a minimum 1000-gallon tank for up to 3
bedrooms.
6. Which document must be submitted before installing a new system?
Site plan and application for permit
A permit application and detailed site plan are required by DHEC
regulations.
7. Which factor most affects trench length in a conventional drain field?
Soil permeability
More permeable soils require shorter trench lengths, and vice versa.
8. What is the maximum slope allowed for a standard trench system in SC?
15%
South Carolina restricts standard trench installation to slopes of 15% or
less.
9. Which tool is commonly used to determine seasonal high water table?
Soil auger
A soil auger helps observe soil color and mottling to estimate water table
levels.
10.What is the minimum depth of soil required above bedrock for a
conventional system?
, 48 inches
At least 4 feet of suitable soil is needed to treat effluent adequately.
11.What is the required cover depth over drain field lines?
6 to 18 inches
This range protects lines while allowing oxygen exchange for aerobic
bacteria.
12.When should the DHEC be notified for an inspection?
Before covering the system
Inspections must be done before backfilling to ensure code compliance.
13.What is the maximum distance effluent should travel in a distribution pipe
without drop boxes?
100 feet
Longer distances may require drop boxes to maintain equal distribution.
14.What is the function of an effluent filter?
To prevent solids from leaving the tank
It helps protect the drain field by trapping suspended solids.
15.Which of the following is prohibited near an onsite system?
Parking heavy vehicles
Driving or parking can compact soil and damage drain field pipes.
16.What is the purpose of a distribution box?
To distribute effluent evenly
A D-box splits flow equally to each trench for balanced loading.
Contractor Permit Questions And Correct Answers
Plus Rationales 2025.
The questions cover general installation, operation, maintenance, state
regulations, site evaluation, and safety topics relevant to SC DHEC standards.
1. What is the minimum setback distance for an onsite wastewater system
from a private drinking water well in South Carolina?
75 feet
A 75-foot setback is required to prevent contamination of the water
supply.
2. Which soil horizon is most suitable for effluent absorption?
B horizon
The B horizon often has good structure and permeability for wastewater
absorption.
3. When is a soil permeability test required during site evaluation?
When soil texture alone cannot determine suitability
If texture is uncertain, percolation tests help verify infiltration rates.
4. What is the primary purpose of the septic tank in an onsite wastewater
system?
To separate solids from liquids
, The tank settles solids and retains them, while effluent moves to the drain
field.
5. What is the minimum size for a septic tank serving a 3-bedroom house in
SC?
1000 gallons
South Carolina requires a minimum 1000-gallon tank for up to 3
bedrooms.
6. Which document must be submitted before installing a new system?
Site plan and application for permit
A permit application and detailed site plan are required by DHEC
regulations.
7. Which factor most affects trench length in a conventional drain field?
Soil permeability
More permeable soils require shorter trench lengths, and vice versa.
8. What is the maximum slope allowed for a standard trench system in SC?
15%
South Carolina restricts standard trench installation to slopes of 15% or
less.
9. Which tool is commonly used to determine seasonal high water table?
Soil auger
A soil auger helps observe soil color and mottling to estimate water table
levels.
10.What is the minimum depth of soil required above bedrock for a
conventional system?
, 48 inches
At least 4 feet of suitable soil is needed to treat effluent adequately.
11.What is the required cover depth over drain field lines?
6 to 18 inches
This range protects lines while allowing oxygen exchange for aerobic
bacteria.
12.When should the DHEC be notified for an inspection?
Before covering the system
Inspections must be done before backfilling to ensure code compliance.
13.What is the maximum distance effluent should travel in a distribution pipe
without drop boxes?
100 feet
Longer distances may require drop boxes to maintain equal distribution.
14.What is the function of an effluent filter?
To prevent solids from leaving the tank
It helps protect the drain field by trapping suspended solids.
15.Which of the following is prohibited near an onsite system?
Parking heavy vehicles
Driving or parking can compact soil and damage drain field pipes.
16.What is the purpose of a distribution box?
To distribute effluent evenly
A D-box splits flow equally to each trench for balanced loading.
