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Tennessee Department of Environment & Conservation (TDEC)
Installer Certification Exam: Questions And Correct Answers Plus
Rationales 2025.
Questions cover key areas like site evaluation, system design, installation, operation, and maintenance of onsite wastewater systems — based on TDEC rules and general best practices.
- What is the minimum horizontal separation distance between a septic tank and a private water supply well in Tennessee? A. 25 feet B. 50 feet C. 100 feet D. 200 feet Rationale: TDEC regulations require a minimum 100-foot separation between septic tanks and wells to protect groundwater from contamination.
- Which soil texture is generally the most suitable for subsurface sewage disposal systems? A. Clay B. Silt C. Loam D. Sand Rationale: Loam provides good permeability and adequate treatment of effluent while preventing rapid percolation or ponding.
- What is the purpose of a distribution box in a conventional septic system? A. Collect solids before treatment B. Aerate the effluent C. Evenly distribute effluent to each lateral line D. Remove nitrogen Rationale: A distribution box ensures equal flow of effluent to all parts of the drainfield for uniform loading.
- Which of the following best describes a limiting layer? A. Layer of topsoil B. Layer with excessive permeability C. Layer that restricts percolation D. Layer that increases infiltration Rationale: A limiting layer (e.g., bedrock, hardpan) impedes effluent movement and must be identified during site evaluation.
- What is the minimum setback from a septic system to a property line? A. 10 feet B. 15 feet C. 20 feet D. 25 feet Rationale: TDEC requires a minimum 10-foot separation to avoid encroachment on neighboring property.
- Which is an acceptable method for stabilizing disturbed soils after installing a drainfield? A. Grass seeding
D. Wildflowers Rationale: Tree roots can clog and damage drainfield lines, so planting trees near a drainfield is prohibited. 10.What does the term "percolation rate" mean? A. Rate at which water evaporates B. Rate of tank fill-up C. Rate at which water moves through soil D. Rate of effluent production Rationale: Percolation rate indicates how quickly soil absorbs effluent, which determines system sizing. 11.The invert of the septic tank outlet must be: A. Higher than the inlet B. Lower than the inlet C. The same as the inlet D. Not important Rationale: The outlet must be slightly lower than the inlet so wastewater flows properly through the tank. 12.What is the purpose of an effluent filter? A. To sterilize sewage B. To pump effluent uphill C. To prevent solids from leaving the tank D. To aerate effluent Rationale: Effluent filters help reduce clogging of the drainfield by trapping solids.
13.Which of the following is an acceptable fill material around drainfield trenches? A. Washed gravel or stone B. Clay soil C. Concrete D. Bedrock chips Rationale: Clean gravel allows effluent to disperse evenly and provides storage space. 14.Which factor is most critical when sizing a drainfield? A. Tank color B. Effluent filter type C. Soil percolation rate D. Pipe diameter Rationale: The soil’s ability to absorb effluent determines how much area is needed for proper treatment. 15.Which condition would require an alternative system design? A. Large backyard B. Sandy loam soil C. Shallow depth to bedrock D. Site with gentle slope Rationale: Bedrock close to the surface limits soil treatment depth and may require alternative solutions like mound systems. 16.How often should a homeowner have their septic tank pumped? A. Annually
D. Upside down Rationale: A slight slope allows even effluent flow; too much slope causes uneven distribution. 20.What must be done before excavating for a drainfield? A. Install electrical lines B. Order pump trucks C. Call for utility locates D. Add topsoil Rationale: Tennessee law requires checking for buried utilities to prevent damage or injury. 21.What is an important factor for a pump tank in a pumped system? A. Alarm system B. Heated lines C. UV disinfection D. Underground storage Rationale: An alarm alerts the homeowner of pump failure, preventing backup. 22.Which is true about greywater systems in Tennessee? A. Greywater can be discharged to the ground untreated B. Greywater must be treated similar to blackwater C. Greywater must be piped to the street D. Greywater can be disposed in storm drains Rationale: State rules treat all wastewater similarly to protect public health.
23.How should slopes greater than 15% be handled for system installation? A. Special design approval required B. No restriction C. Install without inspection D. Use only conventional trenches Rationale: Steep slopes may cause surface breakout; special design and approval are needed. 24.If surface ponding occurs on a drainfield, it indicates: A. Proper operation B. Low flows C. System failure D. Good percolation Rationale: Standing water means the soil is saturated and the system is not functioning properly. 25.Which of these is a key reason to keep heavy vehicles off the drainfield? A. Keep grass green B. Reduce odors C. Prevent soil compaction D. Reduce noise Rationale: Compaction reduces soil absorption capacity and can cause system failure. 26.Which of the following must be done when replacing a failed drainfield? A. Reuse old trenches
Rationale: Mottling indicates periodic saturation and poor drainage, which can limit absorption. 30.When is a soil percolation test typically performed? A. After tank installation B. Before system design approval C. After covering trenches D. After backfilling Rationale: A perc test must be done before design approval to size the system correctly. 31.Which factor is NOT considered when determining daily design flow? A. Number of bedrooms B. Number of televisions C. Number of occupants D. Plumbing fixtures Rationale: Appliances like TVs have no impact; bedrooms and fixtures estimate daily wastewater flow. 32.If a site has shallow soils with poor drainage, which type of system is often required? A. Conventional trench B. Mound system C. Seepage pit D. Dry well Rationale: A mound system elevates the absorption area to provide proper treatment where soil depth is inadequate.
33.Which is an advantage of pressure distribution systems? A. Eliminates need for inspections B. Never clogs C. Distributes effluent evenly D. Works well without electricity Rationale: Pressure systems promote uniform effluent application over the entire drainfield. 34.Which must be done when decommissioning an old septic tank? A. Leave it empty B. Burn it C. Remove or properly fill it D. Use it as a swimming pool Rationale: Abandoned tanks pose safety hazards; they must be pumped, removed, or filled with inert material. 35.Which inspection record must be submitted to TDEC after installation? A. Only a receipt B. None if the system looks fine C. Verbal approval D. Record of inspection and approval Rationale: The installer must ensure the system is approved and documented per TDEC rules. 36.A soil test pit should be at least how deep for evaluation? A. 6 inches B. 12 inches
Rationale: Curtain drains intercept and divert groundwater to protect the drainfield from saturation. 40.Which practice is prohibited within the drainfield area? A. Planting grass B. Parking vehicles C. Adding topsoil D. Installing observation ports Rationale: Vehicles compact soil and damage pipes, so driving or parking on the drainfield is not allowed. 41.Which system component must have access for inspection and maintenance? A. Effluent hose only B. Underground utilities C. Septic tank manhole and filter D. Distribution box lid must be sealed permanently Rationale: Access allows for pumping, filter cleaning, and checking system function. 42.Why is it important to protect the drainfield from surface runoff? A. To add extra water B. To attract wildlife C. To prevent hydraulic overload D. To grow larger trees Rationale: Extra surface water can flood the system and cause premature failure.
43.Which condition is a sign of septic system failure? A. Lush green grass in summer B. Sewage odor and soggy soil C. Slow-growing plants D. Dry soil in trenches Rationale: Odors and wet areas indicate that untreated effluent is surfacing. 44.When must an installer renew their certification? A. Annually B. Every 5 years C. Only once D. Never Rationale: TDEC requires annual renewal and continuing education to keep certification current. 45.Which is true about effluent dosing? A. Should occur once per month B. Must be consistent and timed properly C. Should flood the trenches daily D. Must be stopped in winter Rationale: Proper dosing prevents overload and allows soil to rest between cycles. 46.If a site fails a soil test, what is the next step? A. Install anyway B. Dump gravel to fix it
Rationale: A designated reserve area is required for future repairs or system failures. 50.What does a properly installed inspection port allow? A. Adding chlorine B. Checking effluent levels C. Installing new tanks D. Connecting to a well Rationale: Inspection ports make it easy to monitor drainfield conditions without digging up the system. 51.When installing a new tank, the tank must be set: A. On soft fill dirt B. Directly on bedrock C. On stable, level native soil D. Hanging partially above ground Rationale: A stable, level base prevents settling or shifting that could damage tank connections. 52.How should a riser be attached to a septic tank? A. Watertight seal B. With duct tape only C. Left unsecured D. Buried without access Rationale: A watertight riser connection prevents infiltration of groundwater and allows access for maintenance.
53.Which factor would require an engineer-designed system? A. Flat site with deep loamy soil B. Standard 3-bedroom home C. Flood-prone or restrictive soil conditions D. Gentle 5% slope Rationale: Non-standard sites often need an engineered design to meet TDEC requirements. 54.If the installer discovers a buried spring near the proposed drainfield, they should: A. Ignore it B. Redirect effluent toward it C. Stop work and notify TDEC D. Use the spring for dilution Rationale: Springs and seeps can saturate the site and lead to contamination, so it must be addressed. 55.Which is acceptable backfill material for covering a drainfield? A. Native soil free of debris B. Concrete C. Asphalt D. Clay lumps and boulders Rationale: Proper backfill maintains system function and prevents soil compaction. 56.How is trench depth for conventional systems determined? A. Randomly
Rationale: Compacting or contaminating the sand layer reduces treatment performance. 60.What is the main reason to have a reserve area? A. For livestock B. For future system repair or replacement C. For parking D. For storage sheds Rationale: A reserve area ensures a compliant replacement site if the original fails. 61.Which is true for alternative treatment systems? A. No maintenance needed B. Must be maintained per manufacturer specs C. Never inspected D. Cannot be used in Tennessee Rationale: Alternative systems must meet TDEC rules and have documented maintenance. 62.When using a step-down system, what must be installed? A. Sprinklers B. Drop boxes or serial distribution C. Chlorinator D. Deep pits Rationale: Drop boxes control flow to lower trench levels in step-down systems.
63.An installer should avoid trench excavation when soil is: A. Dry B. Moist C. Frozen or saturated D. Slightly damp Rationale: Frozen or wet soil smears, reducing infiltration and harming long-term performance. 64.Which document must be on-site during installation? A. Homeowner’s ID B. Approved permit and layout C. Tank manufacturer’s warranty D. Food menu Rationale: TDEC requires the installer to follow the approved plan and permit. 65.What is the effect of compacting trench bottoms? A. Increases flow B. Decreases infiltration C. No impact D. Improves treatment Rationale: Compaction seals soil pores, preventing proper effluent absorption. 66.When sizing systems for multi-family dwellings, you must: A. Use standard single-family flow B. Ignore bedroom count
