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North Carolina Onsite Wastewater Contractors & Inspectors
Certification Board (NCOWCICB) Questions And Correct Answers Plus
Rationales 2025.
- What is the minimum setback distance required between an onsite wastewater system and a private well in North Carolina? 100 feet This distance helps prevent contamination of potable water sources.
- What soil horizon is generally evaluated to determine suitability for an onsite wastewater system? B horizon The B horizon typically provides information on restrictive layers and drainage.
- What is the purpose of a septic tank in an onsite wastewater system? To separate solids from liquids and allow anaerobic digestion The septic tank retains solids and grease while effluent moves to the drainfield.
- Who enforces the onsite wastewater rules in North Carolina? Local health departments Local health departments issue permits and inspect systems under state guidelines.
- Which soil texture generally provides the best conditions for effluent absorption?
Loamy sand Loamy sand allows adequate percolation without excessive permeability.
- A Type V system in NCOWCICB classifications indicates what level of complexity? Most complex systems requiring the highest certification Type V systems often include advanced treatment technologies or unique site constraints.
- When should a licensed inspector submit a system inspection report to the client? Within 10 business days Timely reporting ensures compliance with NCOWCICB guidelines.
- Which factor most affects the size of a drainfield? Soil percolation rate Faster percolation allows smaller fields; slower rates require larger fields.
- Which is a sign of a failing septic system? Surfacing effluent Surfacing indicates hydraulic overload or system failure. 10.What is the required separation between trenches in a conventional drainfield? At least 6 feet This spacing prevents hydraulic interference between trenches. 11.Which document must be issued before installing an onsite system? Authorization to Construct This ensures the design is approved and complies with rules.
19.What must be verified before backfilling an onsite system? Inspection by the local health department This ensures the installation meets the approved design. 20.Which system is suitable for sites with limited space or poor soils? Mound system Mounds provide additional separation above natural grade. 21.Which material is commonly used for septic tank baffles? Concrete or PVC These resist corrosion and provide durability. 22.What does the term “hydraulic loading rate” refer to? Amount of effluent applied per unit area per day This determines the size of the absorption field. 23.What is the purpose of a pump tank? To dose effluent to a higher elevation or pressure system Pump tanks move effluent when gravity flow isn’t feasible. 24.What is the typical slope requirement for a gravity sewer line? Minimum 1/8 inch per foot Adequate slope ensures flow without solids deposition. 25.Which site condition would require an alternative system design? Shallow bedrock Limited depth restricts trench placement and necessitates alternatives.
26.When is an inspector required to hold a Level IV certification? When inspecting systems with advanced treatment units Higher levels are needed for complex or innovative systems. 27.What is the primary function of a drainfield? To disperse and treat effluent through soil filtration Soil microbes and filtration remove pathogens and nutrients. 28.Which measurement indicates soil percolation rate? Minutes per inch This reflects how quickly water moves through soil. 29.What is the acceptable range for effluent pH in advanced systems? 6.0 to 9. This range supports biological treatment processes. 30.Which type of onsite system requires the most frequent maintenance? Aerobic treatment unit (ATU) ATUs need regular inspections and component servicing. 31.Which condition indicates soil compaction? Platy structure Compaction impedes water flow and root growth. 32.Which drainfield design promotes uniform loading? Pressure distribution system Pressure dosing ensures equal effluent distribution.
40.What is the purpose of a flow equalization tank? To balance influent flow and prevent surges Equalization tanks protect downstream components. 41.What is the typical life expectancy of a conventional drainfield? 20 to 30 years Proper maintenance can extend lifespan. 42.What is required if a system must be installed during wet weather? Soil must be dry enough to prevent smearing and compaction Wet soil conditions damage soil structure and reduce absorption. 43.What does an inspector check for in a septic tank? Structural integrity, baffles, and scum/sludge levels These checks ensure proper operation. 44.Which standard applies for setback from a property line? At least 10 feet This prevents encroachment and ensures maintenance access. 45.How often must an operator report maintenance of a Type V system? As specified in the permit, typically quarterly or semi-annually Frequent reporting ensures performance and compliance. 46.What is the best indicator of drainfield trench failure? Standing water or surfacing effluent Indicates saturation or clogging.
47.Which factor most affects effluent treatment in soil? Soil texture and structure These control filtration and biological treatment. 48.What is an inspector required to do before certifying a system? Verify it meets design and code requirements Certification ensures regulatory compliance. 49.Who is responsible for system maintenance after installation? Property owner Owners must maintain their systems per NC rules. 50.Which state rule governs onsite wastewater systems in North Carolina? 15A NCAC 18A. This administrative code contains detailed onsite wastewater regulations. 51.What is the main reason for using serial distribution in drainfields? To maximize the use of available trench length Serial distribution allows each trench to fill before the next receives flow, improving soil utilization. 52.What is the maximum slope allowed for a trench bottom? 0 to 6 inches per 100 feet Minimal slope prevents effluent from flowing too quickly through trenches. 53.What is the minimum separation between the trench bottom and a restrictive layer?
61.When is a low-pressure pipe (LPP) system used? When soil conditions require shallow, uniform dosing LPP systems help in sites with shallow restrictive features. 62.What is a soil restrictive horizon? A layer that impedes water movement Restrictive horizons limit infiltration and treatment. 63.What does a pump alarm indicate? Pump or system malfunction Alarms alert owners to potential system failure. 64.Who is responsible for submitting an Operations and Maintenance (O&M) agreement for a system requiring one? Property owner Owners must ensure their systems are properly maintained. 65.What is the purpose of an equalization basin in advanced systems? To balance flow variations This prevents overload of treatment components. 66.What is the recommended depth for soil observation pits? At least 48 inches Deeper pits reveal full soil profiles for accurate evaluation. 67.Which of the following is a sign of anaerobic soil conditions? Gray soil colors with mottles Gray colors indicate poor aeration and seasonal saturation.
68.What is the setback from a septic tank to a swimming pool? 15 feet This distance prevents contamination and structural issues. 69.What is required if a system modification changes the original design? Amended Authorization to Construct Any change must be reviewed and approved. 70.Which inspection finding requires immediate correction? Cracked septic tank lid This poses a safety hazard and potential system failure. 71.What is the purpose of an access riser on a tank? To provide easy maintenance access Risers make inspection and pumping easier and safer. 72.What does a site plan include? System location, setbacks, and topography Site plans ensure systems are properly placed. 73.What is the setback from a septic tank to a stream or body of water? 50 feet Protects water quality and prevents contamination. 74.When must an inspector hold Level III certification? For inspecting large or complex systems Level III is needed for intermediate complexity.
82.What must an inspector do if a system does not meet code? Deny certification and issue corrections Systems must comply before approval. 83.What is the setback from a drainfield to a drainage ditch? 25 feet Protects nearby drainage features. 84.What is a suitable backfill material for trenches? Native soil free of large rocks Proper backfill ensures soil contact and treatment. 85.Which practice is prohibited when installing trenches? Using heavy machinery on wet soils This causes soil compaction and failure. 86.What is the purpose of gravel in a trench? To provide storage and support for distribution pipes Gravel maintains void space for effluent dispersal. 87.How often must advanced treatment systems be inspected? As specified by the permit (often quarterly) Frequent inspections ensure they function properly. 88.What does a flow meter measure? Volume of wastewater processed Used for monitoring flow rates and system performance.
89.What is the purpose of a control panel? To manage pumps and alarms Control panels automate dosing and alert owners to issues. 90.What is the setback between two separate drainfields? 6 feet minimum Maintains proper separation to avoid hydraulic interference. 91.Which trench shape provides maximum treatment area? Rectangular and level Maximizes infiltration surface and efficiency. 92.What is the first step before beginning excavation for a system? Verify site layout and permit approval Prevents placement errors and regulatory issues. 93.When is a flow equalization tank most needed? When flow rates vary significantly during the day Equalization reduces peak loading. 94.What is a “soil texture triangle” used for? Classifying soil by sand, silt, and clay percentages Determines permeability and suitability. 95.What is the purpose of a siphon dose system? To discharge large volumes at once Helps prevent clogging and improves distribution.
- What is the setback for a pump tank to a well? 100 feet Same setback applies as for drainfields and tanks.
- What is the effect of smearing trench walls? Reduces infiltration capacity Smearing closes soil pores, impeding flow.
- How should effluent filters be maintained? Cleaned regularly per manufacturer specs Keeps solids from clogging the drainfield.
- What is the setback from a drainfield to an interceptor drain? 15 feet Ensures adequate separation for drainage management.
- When is drip irrigation used for wastewater dispersal? In shallow or restrictive soils Allows slow, controlled effluent release.
- What is the setback for a tank to a property line? 5 feet Ensures access and prevents encroachment.
- Which soil texture requires larger drainfield sizing? Clay Slow permeability requires more area.
- How often must records be submitted for a Type V system? As specified, typically quarterly Monitors compliance and performance.
- What does the term “unsaturated zone” mean? Soil above the seasonal water table This is where treatment occurs.
- What must be done if a drainfield is installed too deep? Modify system to meet code Depth impacts oxygen exchange and treatment.
- What does “freeboard” refer to in a tank? Vertical space above the normal liquid level Prevents overflow and allows scum storage.
- What is the purpose of observation wells? Monitor groundwater levels Helps verify seasonal high water table.
- What should never be discharged into a septic system? Paints, solvents, or chemicals These kill beneficial bacteria and harm treatment.
- What does “hydraulic overload” mean? More flow than design capacity Leads to surfacing and system failure.
- What is the setback from a system to a stormwater pond? 50 feet Protects water bodies from contamination.
- What is the setback from a drainfield to a driveway? No minimum, but protect from traffic loads Avoids soil compaction and system damage.
- What happens if trench sidewalls are compacted? Reduced infiltration Compaction closes soil pores.
- What is required if a system is abandoned? Tank must be pumped and properly filled or removed Prevents safety hazards and groundwater contamination.
- Who is responsible for accurate recordkeeping? Contractor and inspector Ensures compliance and future reference.
- What is the role of the NCOWCICB? Certify and regulate contractors and inspectors Maintains standards for onsite wastewater professionals.
- What is the minimum slope for gravity flow in a building sewer? 1/8 inch per foot Ensures adequate flow to the tank.
- What does a hydraulic gradient in soil indicate? Direction and rate of groundwater movement Knowing this helps prevent system contamination of groundwater.
- Which soil texture typically has the slowest percolation rate? Clay Clay has small pores, restricting water movement.
- What is the main function of a distribution box? To evenly distribute effluent to multiple trenches Prevents overloading one part of the drainfield.
- What does “BSL” stand for in soil evaluation? Boundary of Seasonal Limiting Layer Indicates the depth to restrictive conditions.
- What is the setback from a drainfield to a livestock barn? 100 feet Protects animals and prevents cross-contamination.
- What is the function of an inspection port in a drainfield? To monitor liquid levels in trenches Helps detect ponding or clogging early.
- What does a “resting trench” mean? Trench not receiving effluent to allow recovery Alternating trenches extends drainfield life.
