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2026 Statistics
Key Facts: NM CID GF-4 Exam
70 Q
Official Combined Questions
PSI NM Contractor Bulletin 4/3/2026
75%
Passing Score Each Portion
PSI NM Contractor Bulletin 4/3/2026
USD 68.88
Specialty Exam Fee
PSI NM Contractor Bulletin 4/3/2026
NM CID GF-4 is GF Core (40 Q, free) plus a 30-question drainage/flood-control specialty, 75% each, USD 68.88 (bulletin 4/3/2026).
Sample NM CID GF-4 Practice Questions
Try these sample questions to test your NM CID GF-4 exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.
1In U.S. customary units, the Rational Method peak-runoff equation used in ASCE urban stormwater design is Q = CiA. What do C, i, and A represent?
A.C = runoff coefficient, i = rainfall intensity in inches per hour, A = drainage area in acres
B.C = conveyance factor, i = infiltration rate in inches per hour, A = wetted area in square feet
C.C = channel coefficient, i = rainfall depth in inches, A = drainage area in square miles
D.C = storage coefficient, i = time of concentration in minutes, A = impervious area in acres
Explanation: ASCE Design and Construction of Urban Stormwater Management Systems presents the Rational Method as Q = CiA, where Q is peak discharge in cubic feet per second, C is the dimensionless runoff coefficient, i is average rainfall intensity in inches per hour for a duration equal to the time of concentration, and A is the contributing drainage area in acres. The equation is the standard starting method for small urban catchments used to size inlets, storm sewers, and small channels.
2A 4.0-acre paved industrial pad has a runoff coefficient of 0.90. For a design intensity of 3.5 inches per hour, what is the Rational Method peak discharge?
A.5.6 cfs
B.8.8 cfs
C.12.6 cfs
D.14.0 cfs
Explanation: Q = CiA = 0.90 × 3.5 in/hr × 4.0 acres = 12.6 cfs. In U.S. customary units the product CiA already yields cubic feet per second, so no extra conversion factor is applied. GF Core stormwater items routinely require this multiplication on small drainage areas.
3On a flood-control project, what is the primary functional difference between a detention basin and a retention basin?
A.A detention basin temporarily stores runoff and releases it at a controlled rate; a retention basin holds a permanent pool or has no designed surface outlet
B.A detention basin is always lined with concrete; a retention basin is always earthen
C.A detention basin treats only water quality; a retention basin is used only for 100-year peak shaving
D.A detention basin must be underground; a retention basin must be an open pond
Explanation: ASCE urban stormwater practice distinguishes quantity-control storage by outlet behavior. Detention (including extended dry detention) stores the increased runoff from development and releases it slowly so downstream peaks stay near predevelopment rates. Retention holds water in a permanent pool or relies on infiltration and evaporation rather than a designed surface discharge. Both may be above or below grade; lining and water-quality function are separate design choices.
4Time of concentration for a Rational Method design is best defined as the time required for:
A.The design storm to deliver its total rainfall depth at the rain gauge
B.A detention pond to drain from the 100-year water surface to the permanent pool
C.Runoff to travel from the hydraulically most distant point of the catchment to the design point
D.A storm sewer to flow full from the first inlet to the outfall after the rain stops
Explanation: Time of concentration (Tc) is the travel time from the hydraulically most remote point in the drainage area to the design point. Rational Method intensity is taken from the intensity-duration-frequency curve for a duration equal to Tc, because the peak discharge occurs when the entire basin is contributing. Sheet, shallow-concentrated, and channel flow segments are added to obtain Tc.
5All else equal, which land-cover change most increases the Rational Method runoff coefficient C?
A.Replacing native desert range with a concrete-lined drainage channel and rooftops
B.Replacing a paved parking lot with irrigated turf
C.Replacing a warehouse roof with an open-graded gravel lot
D.Replacing a storm sewer with an equivalent grass-lined swale
Explanation: C is the ratio of runoff to rainfall and rises as a surface becomes more impervious and smoother. Converting native range to rooftops and concrete lining greatly reduces infiltration and depression storage, so C increases and peak Q increases. ASCE tables list downtown/impervious C values commonly in the 0.70 to 0.95 range versus much lower values for undeveloped ground.
6In urban stormwater quality practice, the "first flush" refers to:
A.The last portion of a storm after the detention pond starts to overflow the emergency spillway
B.The clear water that remains after a sediment basin has been dewatered
C.The initial runoff from impervious surfaces that typically carries a disproportionate share of accumulated pollutants
D.The base flow that a perennial arroyo carries between storms
Explanation: ASCE/WEF stormwater guidance treats the first flush as the initial washoff of dust, metals, oil, and sediment that built up on streets and roofs between storms. Water-quality BMPs such as extended detention, inlet devices, and sand filters are sized to capture and treat that early volume. Peak-only flood-control storage that dumps quickly does not provide the same treatment.
7Under the EPA Construction General Permit framework used in New Mexico, a Stormwater Pollution Prevention Plan (SWPPP) is required when construction disturbs:
A.Any area larger than 1,000 square feet, regardless of drainage
B.Only projects that include a permanent detention pond
C.Only sites that discharge directly to a FEMA-mapped floodway
D.One or more acres, or a smaller site that is part of a larger common plan of development that will disturb one or more acres
Explanation: The Construction General Permit covers stormwater discharges from construction that disturbs one acre or more, including smaller parcels that are part of a larger common plan of development or sale totaling one acre or more. The SWPPP identifies erosion and sediment controls, housekeeping BMPs, inspections, and the sequence of stabilization. Flood-control contractors on GF-4 work commonly trip this threshold when grading basins, channels, and storm-sewer corridors.
8A combination curb-and-grate inlet is selected at a sag on an urban street. What is the principal hydraulic reason for using both openings together?
A.The grate intercepts gutter flow while the curb opening continues to take water if debris blinds the grate
B.The curb opening is only decorative and the grate carries the entire design storm
C.Combination inlets are used only on steep grades and never in sags
D.The grate is intended only for bicycle safety and does not convey stormwater
Explanation: Urban inlet design (ASCE/HEC-22 practice) uses curb openings, grates, or combinations. In a sag, all approaching gutter flow must be captured or it ponds. A combination inlet gives two paths: the grate takes most clear flow, and the curb opening still functions if leaves or trash cover the grate. That redundancy is why combination inlets are preferred at sags and at locations with heavy debris.
9For the same diameter and slope, why does a corrugated metal pipe (CMP) carry less discharge than a smooth concrete pipe when both flow full?
A.CMP has a higher Manning n, so friction head loss is greater and full-flow capacity is lower
B.CMP always has a smaller inside diameter than the nominal size, while concrete does not
C.Concrete pipe cannot be laid on a slope, so the comparison is invalid
D.CMP is pressure pipe and concrete is gravity pipe, so Manning's equation does not apply to CMP
Explanation: Manning capacity decreases as n increases. ASCE closed-conduit n values for concrete pipe are typically about 0.011 to 0.015, while unlined annular CMP is substantially rougher (often near 0.024). Higher n means more friction, a lower full-flow velocity, and less Q for the same area and slope. Contractors who substitute CMP for RCP without checking hydraulics can undersize the line.
10A long concrete box culvert under a fill is flowing full with a high tailwater. Which statement correctly describes the hydraulic control?
A.The culvert is under inlet control, so barrel roughness and length do not affect headwater
B.Culverts never operate under outlet control if the inlet is submerged
C.The culvert is under outlet control, so barrel friction, length, slope, and tailwater all affect headwater
D.Outlet control occurs only in corrugated pipe, never in concrete boxes
Explanation: FHWA/ASCE culvert hydraulics classify flow as inlet control or outlet control. Inlet control means the inlet geometry limits capacity and the barrel can take more flow than the inlet will admit. Outlet control means the barrel and downstream tailwater limit capacity, so length, roughness, slope, and tailwater set the headwater. A long barrel flowing full with high tailwater is the classic outlet-control case.
About the NM CID GF-4 Exam
The New Mexico CID GF-4 classification covers drainage or flood control systems and requires the shared GF Core plus the GF-4 specialty. GF Core is 40 questions in 100 minutes with no charge. GF-4 is 30 questions in 75 minutes for USD 68.88. Each portion requires 75% (bulletin updated 4/3/2026). Specialty references include ASCE urban stormwater design, NMDOT 2019 specifications, Construction Planning, Equipment, and Methods, and DIPRA ductile-iron pipe installation. This English-language MCQ bank is a study aid, not an official PSI form.
Assessment
GF Core plus GF-4 specialty, retained as one classification identity.
Time Limit
175 minutes (100 + 75)
Passing Score
75% on GF Core (30 of 40) and 75% on GF-4 (23 of 30)
Exam Fee
USD 68.88 (GF Core has no charge) (PSI Services LLC (for New Mexico Construction Industries Division))
NM CID GF-4 Exam Content Outline
57%
GF Core
Stormwater, OSHA, project management, surveying, NM One Call, building code/inspections (40 official items)
43%
GF-4 Specialty
Earthwork, culverts and pipe, concrete, project management (30 official items)
How to Pass the NM CID GF-4 Exam
What You Need to Know
- Passing score: 75% on GF Core (30 of 40) and 75% on GF-4 (23 of 30)
- Assessment: GF Core plus GF-4 specialty, retained as one classification identity.
- Time limit: 175 minutes (100 + 75)
- Exam fee: USD 68.88 (GF Core has no charge)
Keys to Passing
- Work through all 100 available questions
- Review every answer and explanation
- Track weak areas and revisit them
- Use our AI tutor for tough concepts
NM CID GF-4 Study Tips from Top Performers
1Earthwork, culverts/pipe, and concrete are 9 items each. Study DIPRA pipe installation with GF Core stormwater.
2This bank is an English-language MCQ study aid, not an official PSI form
Frequently Asked Questions
Do I take a separate GF Core exam?
Yes. PSI requires all GF candidates to take the shared GF Core plus the classification specialty. This bank treats them as one GF-4 identity.