NPDES Level 1A Practice Test WITH
QUESTIONS AND VERIFIED ANSWERS
GRADED A+
SECTION I: SOIL EROSION FUNDAMENTALS
Q1. A slope gradient of 25% (4:1) would indicate that in a horizontal length of
100 feet, the vertical rise would be ______ feet.
A) 2.5
B) 12.5
C) 25
D) 4
Correct Answer: C) 25
Rationale: Slope percentage = (vertical rise / horizontal run) × 100. For a 100-ft
horizontal run: 25% = (rise / 100) × 100 = 25 ft. A 4:1 slope (horizontal:vertical)
equals 25% .
Q2. As rain falls to the earth, what is the very first function of vegetation?
A) It reduces detachment
B) It increases infiltration
C) It slows runoff
D) It traps sediment
Correct Answer: A) It reduces detachment
Rationale: The first function of vegetation is to intercept rainfall. Leaves and stems
absorb the kinetic energy of raindrops, preventing them from directly impacting
the soil surface and detaching soil particles. Infiltration and slowing runoff are
secondary functions .
,Q3. The primary agent of erosion on construction sites is:
A) Wind
B) Channelized flow
C) Sheet flow
D) Raindrop splash
Correct Answer: D) Raindrop splash
Rationale: Raindrop splash is the initial mechanism that dislodges soil particles,
making them available for transport by overland flow. A single raindrop can splash
soil particles several feet .
Q4. What is the Revised Universal Soil Loss Equation 2 (RUSLE2) used for?
A) Calculate the volume of a sediment basin
B) Predict the long-term average annual rate of soil erosion on a slope
C) Determine the required slope of a swale
D) Calculate the required height of a silt fence
Correct Answer: B) Predict the long-term average annual rate of soil erosion on a
slope
Rationale: RUSLE2 is a computer program that predicts long-term average annual
erosion rates by considering factors such as rainfall pattern, soil type, topography,
cropping system, and management practices .
Q5. What are the four primary types of erosion caused by water?
A) Splash, sheet, rill, gully
B) Splash, channel, stream, bank
C) Sheet, wind, tidal, glacial
D) Rill, gully, streambank, shoreline
Correct Answer: A) Splash, sheet, rill, gully
, Rationale: Water erosion on construction sites progresses through these stages:
splash erosion (raindrop impact dislodges particles), sheet erosion (thin uniform
layer removed), rill erosion (small channels form), and gully erosion (large
channels) .
Q6. Which of the following is NOT a stage in erosion and sedimentation?
A) Detachment
B) Solubility
C) Transport
D) Deposition
Correct Answer: B) Solubility
Rationale: The three stages are detachment (soil particles dislodged), transport
(particles moved by water/wind), and deposition (particles settle). Solubility is not
considered a stage in the erosion and sedimentation process .
SECTION II: BEST MANAGEMENT PRACTICES (BMPs)
Q7. When installing a silt fence, the bottom of the fabric should be:
A) Left loose to allow water to flow underneath
B) Placed on top of the ground surface
C) Trenches 6 to 8 inches into the ground and backfilled
D) Elevated 12 inches above ground
Correct Answer: C) Trenches 6 to 8 inches into the ground and backfilled
Rationale: The bottom of a silt fence must be trenched into the ground 6-8 inches
deep and backfilled to prevent water from flowing under the fence .
Q8. At what depth must sediment be removed from a silt fence barrier?
QUESTIONS AND VERIFIED ANSWERS
GRADED A+
SECTION I: SOIL EROSION FUNDAMENTALS
Q1. A slope gradient of 25% (4:1) would indicate that in a horizontal length of
100 feet, the vertical rise would be ______ feet.
A) 2.5
B) 12.5
C) 25
D) 4
Correct Answer: C) 25
Rationale: Slope percentage = (vertical rise / horizontal run) × 100. For a 100-ft
horizontal run: 25% = (rise / 100) × 100 = 25 ft. A 4:1 slope (horizontal:vertical)
equals 25% .
Q2. As rain falls to the earth, what is the very first function of vegetation?
A) It reduces detachment
B) It increases infiltration
C) It slows runoff
D) It traps sediment
Correct Answer: A) It reduces detachment
Rationale: The first function of vegetation is to intercept rainfall. Leaves and stems
absorb the kinetic energy of raindrops, preventing them from directly impacting
the soil surface and detaching soil particles. Infiltration and slowing runoff are
secondary functions .
,Q3. The primary agent of erosion on construction sites is:
A) Wind
B) Channelized flow
C) Sheet flow
D) Raindrop splash
Correct Answer: D) Raindrop splash
Rationale: Raindrop splash is the initial mechanism that dislodges soil particles,
making them available for transport by overland flow. A single raindrop can splash
soil particles several feet .
Q4. What is the Revised Universal Soil Loss Equation 2 (RUSLE2) used for?
A) Calculate the volume of a sediment basin
B) Predict the long-term average annual rate of soil erosion on a slope
C) Determine the required slope of a swale
D) Calculate the required height of a silt fence
Correct Answer: B) Predict the long-term average annual rate of soil erosion on a
slope
Rationale: RUSLE2 is a computer program that predicts long-term average annual
erosion rates by considering factors such as rainfall pattern, soil type, topography,
cropping system, and management practices .
Q5. What are the four primary types of erosion caused by water?
A) Splash, sheet, rill, gully
B) Splash, channel, stream, bank
C) Sheet, wind, tidal, glacial
D) Rill, gully, streambank, shoreline
Correct Answer: A) Splash, sheet, rill, gully
, Rationale: Water erosion on construction sites progresses through these stages:
splash erosion (raindrop impact dislodges particles), sheet erosion (thin uniform
layer removed), rill erosion (small channels form), and gully erosion (large
channels) .
Q6. Which of the following is NOT a stage in erosion and sedimentation?
A) Detachment
B) Solubility
C) Transport
D) Deposition
Correct Answer: B) Solubility
Rationale: The three stages are detachment (soil particles dislodged), transport
(particles moved by water/wind), and deposition (particles settle). Solubility is not
considered a stage in the erosion and sedimentation process .
SECTION II: BEST MANAGEMENT PRACTICES (BMPs)
Q7. When installing a silt fence, the bottom of the fabric should be:
A) Left loose to allow water to flow underneath
B) Placed on top of the ground surface
C) Trenches 6 to 8 inches into the ground and backfilled
D) Elevated 12 inches above ground
Correct Answer: C) Trenches 6 to 8 inches into the ground and backfilled
Rationale: The bottom of a silt fence must be trenched into the ground 6-8 inches
deep and backfilled to prevent water from flowing under the fence .
Q8. At what depth must sediment be removed from a silt fence barrier?
