Stormwater Management Inspector Prep
Exam Q&A Guaranteed Pass
What are the types of disconnection allowed for rooftop disconnection? -
✔✔1) simple disconnection - rooftops and/or on-lot residential impervious
surfaces are directed to pervious areas
2) disconnection leading to an alternative runoff reduction practice adjacent
to the roof (ex: soil compost amended filter path)
Why have a rooftop disconnection to an alternative practice? - ✔✔-lot size
too small
-filter width is too narrow
-need more water quality credit
Functions provided by simple rooftop disconnection - ✔✔-annual runoff
volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
Alternative rooftop disconnection types - ✔✔-soil compost-amended filter
path
1
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
,-dry-well or french drain
-rain-garden//front yard bioretention
-rainwater harvesting//cistern
-stormwater planter
How does sheet flow to a vegetated filter strip or conserved open space
work? - ✔✔Filter strips are vegetated areas that treat sheet flow delivered
from adjacent impervious and managed turd areas by slowing runoff
velocities and allowing sediment and attached pollutants to settle and/or be
filtered by the vegetation
Gravel diaphragm - ✔✔-pretreatment device
-maintains sheet flow
-not necessary if contributing drainage area is solely turf
-trench is 2 ft. wide and 1 ft. deep
-runs on same contour at top of filter strip
-drop at least 3 inches
-fabric between gravel and soil
Engineered level spreader - ✔✔-forebay: max. 3ft. deep, transition to 1 ft.
at level spreader lip
-level spreader lip - concrete, wood, or prefabricated metal, with a well
anchored footer, or other accepted rigid, non-erodible material
2
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
,-location: 3-6 inches above downstream natural grade to avoid turf buildup
-3ft. of VDOT #3 stone, underlain by filter fabric just below spreader
-vegetated receiving area must be stabilized
Construction sequence for conserved open space - ✔✔- no clearing,
grading, heavy equipment
-protect area during construction
-prevent sediment discharge
-mark limits of disturbance
-drainage area stabilized
-grade with tracked vehicles
-install gravel diaphragm and/or level spreader
-mark filter boundaries
-keep vehicles out
-stockpile topsoil for later use
-divert construction runoff
-install gravel diaphragm and/or level spreader
-grade with tracked vehicles
-open to runoff once stabilized
3
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
, Maintenance of Vegetated Filter Strips - ✔✔minimal; spring cleanup,
regular mowing, check dam repairs, and other methods of maintaining
hydraulic efficiency
Grass channel design criteria - ✔✔-the bottom width of the channel should
be between 4-8 feet wide
-the channel side-slopes should be 3H:1V or flatter
-the maximum total contributing drainage area to any individual grass
channel is 5 acres
-the longitudinal slope of the channel is <4%
-max flow velocity of channel must be <1ft/sec during a 1 inch storm event
-the dimensions of the channel should ensure that flow velocity is non-
erosive during the 2-yr and 10-yr design storm events and the 10-yr design
flow is contained within the channel
Grass channel pretreatment - ✔✔-check dams
-tree check dams
-grass filter strip
-gravel or stone diaphragm
-gravel or stone flow spreaders
4
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
Exam Q&A Guaranteed Pass
What are the types of disconnection allowed for rooftop disconnection? -
✔✔1) simple disconnection - rooftops and/or on-lot residential impervious
surfaces are directed to pervious areas
2) disconnection leading to an alternative runoff reduction practice adjacent
to the roof (ex: soil compost amended filter path)
Why have a rooftop disconnection to an alternative practice? - ✔✔-lot size
too small
-filter width is too narrow
-need more water quality credit
Functions provided by simple rooftop disconnection - ✔✔-annual runoff
volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
Alternative rooftop disconnection types - ✔✔-soil compost-amended filter
path
1
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
,-dry-well or french drain
-rain-garden//front yard bioretention
-rainwater harvesting//cistern
-stormwater planter
How does sheet flow to a vegetated filter strip or conserved open space
work? - ✔✔Filter strips are vegetated areas that treat sheet flow delivered
from adjacent impervious and managed turd areas by slowing runoff
velocities and allowing sediment and attached pollutants to settle and/or be
filtered by the vegetation
Gravel diaphragm - ✔✔-pretreatment device
-maintains sheet flow
-not necessary if contributing drainage area is solely turf
-trench is 2 ft. wide and 1 ft. deep
-runs on same contour at top of filter strip
-drop at least 3 inches
-fabric between gravel and soil
Engineered level spreader - ✔✔-forebay: max. 3ft. deep, transition to 1 ft.
at level spreader lip
-level spreader lip - concrete, wood, or prefabricated metal, with a well
anchored footer, or other accepted rigid, non-erodible material
2
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
,-location: 3-6 inches above downstream natural grade to avoid turf buildup
-3ft. of VDOT #3 stone, underlain by filter fabric just below spreader
-vegetated receiving area must be stabilized
Construction sequence for conserved open space - ✔✔- no clearing,
grading, heavy equipment
-protect area during construction
-prevent sediment discharge
-mark limits of disturbance
-drainage area stabilized
-grade with tracked vehicles
-install gravel diaphragm and/or level spreader
-mark filter boundaries
-keep vehicles out
-stockpile topsoil for later use
-divert construction runoff
-install gravel diaphragm and/or level spreader
-grade with tracked vehicles
-open to runoff once stabilized
3
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
, Maintenance of Vegetated Filter Strips - ✔✔minimal; spring cleanup,
regular mowing, check dam repairs, and other methods of maintaining
hydraulic efficiency
Grass channel design criteria - ✔✔-the bottom width of the channel should
be between 4-8 feet wide
-the channel side-slopes should be 3H:1V or flatter
-the maximum total contributing drainage area to any individual grass
channel is 5 acres
-the longitudinal slope of the channel is <4%
-max flow velocity of channel must be <1ft/sec during a 1 inch storm event
-the dimensions of the channel should ensure that flow velocity is non-
erosive during the 2-yr and 10-yr design storm events and the 10-yr design
flow is contained within the channel
Grass channel pretreatment - ✔✔-check dams
-tree check dams
-grass filter strip
-gravel or stone diaphragm
-gravel or stone flow spreaders
4
©NINJANERD 2025/2026. YEAR PUBLISHED 2025.
