Arkansas AR-STW Stormwater
Systems Contractor Practice
Exam | Questions, Verified
Answers & Detailed Rationales |
Complete Contractor License
Exam Prep Study Guide |
Updated 2026
1. What is the primary purpose of a stormwater
drainage system?
A. To increase surface-water evaporation
B. To provide drinking water
C. To collect, convey, control, and discharge stormwater
runoff
D. To eliminate all groundwater
Answer: To collect, convey, control, and discharge
stormwater runoff
Rationale: Stormwater systems are designed to safely
manage runoff, reduce flooding and erosion, and
protect property and water quality.
2. Which factor generally causes runoff to increase the
most on a developed site?
A. Increased vegetation
B. Increased soil permeability
C. Increased impervious surface area
D. Increased soil depth
Answer: Increased impervious surface area
,Rationale: Pavement, roofs, and other impervious
surfaces prevent infiltration and cause more rainfall to
become surface runoff.
3. What is an example of an impervious surface?
A. Grass
B. Mulch
C. Topsoil
D. Concrete pavement
Answer: Concrete pavement
Rationale: Concrete substantially restricts infiltration
and is therefore considered impervious.
4. What is the purpose of a catch basin?
A. To produce potable water
B. To increase pipe pressure
C. To collect stormwater and capture sediment and
debris
D. To measure rainfall
Answer: To collect stormwater and capture sediment
and debris
Rationale: Catch basins receive surface runoff and
commonly include a sump that allows sediment and
debris to settle before water enters the drainage
system.
5. What is the primary function of a storm drain inlet?
A. Store wastewater permanently
B. Allow surface runoff to enter the drainage system
C. Increase groundwater pressure
D. Treat drinking water
,Answer: Allow surface runoff to enter the drainage
system
Rationale: Inlets provide controlled openings through
which surface runoff enters underground or surface
drainage conveyance systems.
6. Why is proper pipe slope important in a stormwater
system?
A. It eliminates the need for structures
B. It helps maintain the intended hydraulic capacity and
flow
C. It prevents all sediment from entering the pipe
D. It makes pipe bedding unnecessary
Answer: It helps maintain the intended hydraulic
capacity and flow
Rationale: Proper slope provides the hydraulic gradient
needed for gravity flow and helps prevent excessive
ponding or inadequate drainage.
7. What does the term "invert" refer to in a drainage
structure?
A. The top elevation of the structure
B. The outside wall of the structure
C. The bottom elevation of the pipe or channel
D. The elevation of the surrounding pavement
Answer: The bottom elevation of the pipe or channel
Rationale: The invert is the lowest inside elevation of a
pipe, channel, or drainage structure and is critical for
establishing drainage grades.
, 8. A pipe has an upstream invert of 100.0 ft and a
downstream invert of 98.0 ft over a horizontal run of
200 ft. What is the approximate slope?
A. 0.1%
B. 1.0%
C. 2.0%
D. 10.0%
Answer: 1.0%
Rationale: Slope = elevation difference ÷ horizontal
distance = 2 ÷ 200 = 0.01, or 1.0%.
9. What is a common purpose of a manhole in a
stormwater system?
A. Increase rainfall
B. Provide access for inspection, maintenance, and
changes in alignment or grade
C. Eliminate the need for pipe bedding
D. Store potable water
Answer: Provide access for inspection, maintenance,
and changes in alignment or grade
Rationale: Manholes provide personnel and equipment
access and are commonly located where pipes intersect,
change direction, size, or elevation.
10. What should be done if installed pipe does not
match the approved plan elevation?
A. Cover the pipe immediately
B. Ignore the difference
C. Stop and have the discrepancy evaluated and
corrected or approved
D. Add gravel above the pipe
Systems Contractor Practice
Exam | Questions, Verified
Answers & Detailed Rationales |
Complete Contractor License
Exam Prep Study Guide |
Updated 2026
1. What is the primary purpose of a stormwater
drainage system?
A. To increase surface-water evaporation
B. To provide drinking water
C. To collect, convey, control, and discharge stormwater
runoff
D. To eliminate all groundwater
Answer: To collect, convey, control, and discharge
stormwater runoff
Rationale: Stormwater systems are designed to safely
manage runoff, reduce flooding and erosion, and
protect property and water quality.
2. Which factor generally causes runoff to increase the
most on a developed site?
A. Increased vegetation
B. Increased soil permeability
C. Increased impervious surface area
D. Increased soil depth
Answer: Increased impervious surface area
,Rationale: Pavement, roofs, and other impervious
surfaces prevent infiltration and cause more rainfall to
become surface runoff.
3. What is an example of an impervious surface?
A. Grass
B. Mulch
C. Topsoil
D. Concrete pavement
Answer: Concrete pavement
Rationale: Concrete substantially restricts infiltration
and is therefore considered impervious.
4. What is the purpose of a catch basin?
A. To produce potable water
B. To increase pipe pressure
C. To collect stormwater and capture sediment and
debris
D. To measure rainfall
Answer: To collect stormwater and capture sediment
and debris
Rationale: Catch basins receive surface runoff and
commonly include a sump that allows sediment and
debris to settle before water enters the drainage
system.
5. What is the primary function of a storm drain inlet?
A. Store wastewater permanently
B. Allow surface runoff to enter the drainage system
C. Increase groundwater pressure
D. Treat drinking water
,Answer: Allow surface runoff to enter the drainage
system
Rationale: Inlets provide controlled openings through
which surface runoff enters underground or surface
drainage conveyance systems.
6. Why is proper pipe slope important in a stormwater
system?
A. It eliminates the need for structures
B. It helps maintain the intended hydraulic capacity and
flow
C. It prevents all sediment from entering the pipe
D. It makes pipe bedding unnecessary
Answer: It helps maintain the intended hydraulic
capacity and flow
Rationale: Proper slope provides the hydraulic gradient
needed for gravity flow and helps prevent excessive
ponding or inadequate drainage.
7. What does the term "invert" refer to in a drainage
structure?
A. The top elevation of the structure
B. The outside wall of the structure
C. The bottom elevation of the pipe or channel
D. The elevation of the surrounding pavement
Answer: The bottom elevation of the pipe or channel
Rationale: The invert is the lowest inside elevation of a
pipe, channel, or drainage structure and is critical for
establishing drainage grades.
, 8. A pipe has an upstream invert of 100.0 ft and a
downstream invert of 98.0 ft over a horizontal run of
200 ft. What is the approximate slope?
A. 0.1%
B. 1.0%
C. 2.0%
D. 10.0%
Answer: 1.0%
Rationale: Slope = elevation difference ÷ horizontal
distance = 2 ÷ 200 = 0.01, or 1.0%.
9. What is a common purpose of a manhole in a
stormwater system?
A. Increase rainfall
B. Provide access for inspection, maintenance, and
changes in alignment or grade
C. Eliminate the need for pipe bedding
D. Store potable water
Answer: Provide access for inspection, maintenance,
and changes in alignment or grade
Rationale: Manholes provide personnel and equipment
access and are commonly located where pipes intersect,
change direction, size, or elevation.
10. What should be done if installed pipe does not
match the approved plan elevation?
A. Cover the pipe immediately
B. Ignore the difference
C. Stop and have the discrepancy evaluated and
corrected or approved
D. Add gravel above the pipe
