InterNACHI Certified Septic System Inspector

What is the primary function of the inlet baffle in a septic tank?

• ATo filter solids before they enter the drainfield
• BTo direct incoming wastewater downward and prevent disturbance of the scum and sludge lay…
• CTo vent sewer gases to the atmosphere
• DTo increase the effective volume of the tank

What is the primary function of the outlet baffle or tee?

• ATo prevent floating scum and disturbed solids from exiting the tank with the effluent
• BTo aerate the effluent before it enters the drainfield
• CTo equalize pressure between compartments
• DTo act as a clean-out for the building sewer

What is the typical minimum septic tank capacity, in gallons, for a three-bedroom single-family home under most state codes?

• A500 gallons
• B750 gallons
• C1,000 gallons
• D1,500 gallons

Which statement BEST describes the advantage of a two-compartment septic tank over a single-compartment tank?

• AIt eliminates the need for periodic pumping
• BIt provides additional settling in a second chamber, reducing solids carryover to the dra…
• CIt doubles the effective hydraulic retention time per unit volume
• DIt eliminates the need for an effluent filter

An effluent filter installed at the outlet tee primarily protects which downstream component?

• AThe septic tank itself
• BThe building sewer line
• CThe drainfield (soil absorption system)
• DThe inlet baffle

Which tank material is MOST susceptible to deterioration from hydrogen sulfide gas corrosion?

• APolyethylene
• BFiberglass
• CConcrete
• DHDPE plastic

An inspector observes that the inlet sanitary tee in a concrete tank has separated and dropped into the liquid. What is the MOST significant consequence?

• ALoss of tank ventilation through the building stack
• BIncoming wastewater can short-circuit and disturb scum, allowing solids to exit
• CThe tank will overflow within 24 hours
• DEffluent filter will clog more slowly

Where in a properly functioning septic tank is the clarified zone located?

• AAbove the scum layer
• BBetween the floating scum and the settled sludge
• CBelow the settled sludge
• DInside the outlet baffle only

What is the MINIMUM working clearance typically required between the bottom of the outlet tee and the floor of the tank for proper sludge storage?

• AApproximately 6 inches
• BApproximately 12 inches
• CApproximately 24 inches
• DApproximately 36 inches

Why is an access riser brought to grade preferred over a buried tank lid for ongoing maintenance?

• AIt allows the tank to be pumped and inspected without excavation
• BIt ventilates the tank
• CIt reduces hydraulic retention time
• DIt serves as an emergency overflow

An inspector observes a heavy chain or rope attached to the inlet sanitary tee. What is its purpose?

• ATo retrieve the tee if it falls into the tank
• BTo weigh down the floating scum mat
• CTo anchor the tank against buoyancy
• DTo act as a grounding conductor for static electricity

Which of the following is the MOST appropriate location to install an effluent filter?

• AInside the inlet sanitary tee
• BInside the outlet sanitary tee
• COutside the tank at the building cleanout
• DInline at the drainfield distribution box

An inspector finds that the dividing wall between two compartments of a concrete tank has a deteriorated, oversized opening. What is the LIKELY effect on performance?

• AImproved second-compartment retention
• BSolids will pass freely into the second compartment and shorten effective treatment
• CThe tank will fail watertightness immediately
• DNo measurable effect on effluent quality

What is the typical reason for using a baffle wall (or partition wall) inside a single-compartment tank?

• ATo act as a second septic tank
• BTo direct flow and increase the effective settling path
• CTo support the tank lid
• DTo filter effluent before it leaves the tank

Which of the following is NOT typically required of a septic tank under most state codes?

• AWatertight construction
• BAn inlet and outlet baffle or tee
• CA built-in aerator or compressor
• DAccess for inspection and pumping

What is the PRIMARY purpose of a gas deflector or scum baffle on the outlet tee?

• ATo divert gas bubbles away from the outlet and prevent solids from being lifted into the…
• BTo increase the volume of the scum layer
• CTo dose effluent to the drainfield in pulses
• DTo convert hydrogen sulfide to elemental sulfur

Which drainfield design uses pipes installed in trenches surrounded by gravel and dispersed by gravity?

• AMound system
• BPressure-dosed system
• CConventional gravity trench
• DDrip distribution system

A mound system is MOST commonly used in which site condition?

• ADeep, well-drained sandy soil
• BShallow soil over a limiting layer such as bedrock or seasonal high water table
• CSites with very high percolation rates (less than 1 MPI)
• DLots smaller than 0.25 acre

What is the PRIMARY purpose of pressure dosing a drainfield?

• ATo eliminate the need for a septic tank
• BTo distribute effluent evenly across the entire absorption area
• CTo increase soil percolation rate over time
• DTo reduce odors from the tank

A drip distribution drainfield uses which of the following components?

• AOpen-bottom infiltrator chambers buried in gravel-free trenches
• BSmall-diameter tubing with pressure-compensating emitters spaced along the lines
• CA mound of sand fill above the natural grade
• DAn aerator and a clarifier

What is the function of a sand filter in an onsite wastewater system?

• ATo replace the septic tank entirely
• BTo provide additional treatment between the tank and the drainfield using a sand bed
• CTo act as a pumping station
• DTo act as the only treatment when soil is rocky

Which statement BEST describes gravelless chamber drainfields?

• AThey are aerobic treatment units that do not require dispersal
• BThey use open-bottom plastic chambers in lieu of gravel-filled trenches for soil dispersal
• CThey use compressed air to disperse effluent into the soil
• DThey require no soil percolation test

Why are pressure-dosed systems often required for sites with steep slopes?

• AGravity systems cannot follow contour lines
• BEven distribution prevents downhill end-loading and surfacing on the slope
• CPressure dosing eliminates the need for a septic tank on slopes
• DIt allows the drainfield to be installed directly on bedrock

Which drainfield type is commonly installed in shallow trenches close to the surface to take advantage of more biologically active topsoil?

• AMound system
• BDrip distribution
• CCesspool
• DSeepage pit

Which advanced treatment system is commonly used where standard tank effluent quality is not sufficient to meet local discharge or soil-loading requirements?

• ACesspool
• BAerobic Treatment Unit (ATU)
• CSingle-compartment septic tank
• DDistribution box

What is the function of a distribution box (D-box) in a gravity drainfield?

• AIt treats the effluent biologically
• BIt splits flow evenly among multiple drainfield trenches
• CIt serves as a pumping chamber
• DIt filters solids before they reach the drainfield

An inspector observes that a mound drainfield's sand fill is much smaller in footprint than expected for the home size. What is the LIKELY consequence?

• AImproved treatment efficiency due to higher hydraulic loading rate
• BHydraulic overloading that may cause surfacing on the side of the mound
• CReduced odors due to faster movement of effluent
• DReduced freezing risk in winter

What is a seepage pit (or cesspool), and what is its status under most modern codes?

• AA pressurized treatment device required for all new installations
• BA buried pit that receives raw wastewater directly; generally prohibited or restricted fo…
• CAnother name for an effluent filter
• DA required component of any modern septic system

What is the role of a pump tank or dosing chamber in a pressure distribution system?

• AIt replaces the septic tank's settling function
• BIt stores effluent and houses a pump that doses the drainfield in measured cycles
• CIt treats nitrogen biologically
• DIt allows for direct stream discharge

Within an acceptable range, what range of percolation rate (in minutes per inch) is generally suitable for a conventional septic drainfield?

• ALess than 1 MPI
• BApproximately 5 to 60 MPI
• C120 to 240 MPI
• DOver 300 MPI

Many state codes base residential design flow on bedroom count. What is the most common design flow per bedroom per day?

• A50 gallons
• B100 gallons
• C150 gallons
• D300 gallons

Which soil texture generally exhibits the FASTEST percolation rate (lowest MPI)?

• AHeavy clay
• BSilty clay loam
• CSandy loam
• DCoarse sand

A perc test result of 4 MPI raises which concern?

• AThe soil drains too slowly for any drainfield
• BThe soil may drain too fast to provide adequate biological treatment before effluent reac…
• CThe soil is excellent for clay-lined drainfields
• DThere is no concern at all

What does a 'limiting layer' refer to in soil evaluation for an onsite system?

• AThe deepest soil horizon
• BAny layer that restricts the vertical movement or treatment of effluent, such as bedrock,…
• CThe topsoil layer of the site
• DThe depth of installed pipe

What is typically the MINIMUM vertical separation required between the bottom of a conventional drainfield trench and the seasonal high water table?

• A6 inches
• B12 to 36 inches depending on state
• CDrainfields may sit directly in groundwater
• D10 feet in all states

A four-bedroom home is being designed using 150 gpd per bedroom. What is the design flow?

• A300 gpd
• B450 gpd
• C600 gpd
• D900 gpd

Which of the following soil characteristics is MOST important for evaluating drainfield suitability beyond just perc rate?

• ASoil color only
• BSoil structure, texture, depth to limiting layer, and presence of redoximorphic features
• CThe presence of earthworms
• DWhether grass grows on the surface

What are redoximorphic features in soil and why are they significant in site evaluation?

• AColor patterns indicating periodic saturation and the seasonal high water table
• BEarthworm tunnels
• CMineral deposits indicating bedrock
• DFrost-heave layers

Why is a properly designed septic system typically sized based on bedroom count rather than current occupancy?

• ALocal codes are arbitrary
• BBedroom count is a long-term proxy for potential occupancy that survives changes in house…
• CBedroom count determines tank shape
• DSoils respond to bedrooms, not water flow

An inspector reviews a soil log showing 18 inches of sandy loam over fractured bedrock. The state requires 36 inches of unsaturated soil above bedrock. What is the implication?

• AThe site is acceptable for a conventional drainfield
• BA conventional in-ground drainfield is likely not allowed; an alternative such as a mound…
• CThe state code does not apply to this site
• DAdding gravel will solve the problem

Which of the following best describes a 'soil application rate' (loading rate) in onsite design?

• AThe rate at which effluent is dosed by the pump
• BThe gallons per square foot per day a soil can accept based on texture and structure
• CThe rate at which septic tanks are pumped
• DThe amount of dye used in a dye test

A soil with a perc rate slower than 120 minutes per inch is generally considered:

• AExcellent for any system
• BUnsuitable for conventional drainfields and likely unsuitable for any subsurface system w…
• CSuitable for cesspools
• DThe same as a 30 MPI soil

What is the FIRST step of a maintenance inspection of a septic system as taught by InterNACHI?

• APump the tank immediately
• BLocate the system components using records, observation, and probing as needed
• CConduct a hydraulic load test
• DTrace plumbing with dye

What is the BEST safety practice when opening a septic tank for inspection?

• ALean over the open access to inspect the interior closely
• BNever lean over or enter the open tank; use mirrors, cameras, or measurement tools from a…
• CSmoke a cigarette near the opening to mask odors
• DOpen the tank on a windy day to clear out gases quickly

When measuring the sludge layer with a sludge judge or coring device, when is the tank generally considered to need pumping?

• AWhen sludge plus scum exceeds approximately 25-33% of tank volume, or when sludge is with…
• BWhen sludge exceeds 5% of tank volume
• COnly when sludge reaches the tank lid
• DSludge depth has no relevance

When measuring the scum layer, which condition typically calls for pumping?

• AAny visible scum at all
• BScum thicker than approximately 6 inches or within about 6 inches of the bottom of the ou…
• COnly when scum is solidified
• DOnly when scum has changed color

How is a typical dye test performed during a septic inspection?

• APouring dye into the drainfield directly
• BIntroducing non-toxic dye through the plumbing system and then watching the ground over t…
• CAdding dye to the well water
• DPutting dye into the building's hot water heater only