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South Carolina DHEC Onsite Wastewater
Contractor Permit Questions And Correct Answers
Plus Rationales 2025.
The questions cover general installation, operation, maintenance, state regulations, site evaluation, and safety topics relevant to SC DHEC standards.
- What is the minimum setback distance for an onsite wastewater system from a private drinking water well in South Carolina? 75 feet A 75-foot setback is required to prevent contamination of the water supply.
- Which soil horizon is most suitable for effluent absorption? B horizon The B horizon often has good structure and permeability for wastewater absorption.
- When is a soil permeability test required during site evaluation? When soil texture alone cannot determine suitability If texture is uncertain, percolation tests help verify infiltration rates.
- What is the primary purpose of the septic tank in an onsite wastewater system? To separate solids from liquids
The tank settles solids and retains them, while effluent moves to the drain field.
- What is the minimum size for a septic tank serving a 3-bedroom house in SC? 1000 gallons South Carolina requires a minimum 1000-gallon tank for up to 3 bedrooms.
- Which document must be submitted before installing a new system? Site plan and application for permit A permit application and detailed site plan are required by DHEC regulations.
- Which factor most affects trench length in a conventional drain field? Soil permeability More permeable soils require shorter trench lengths, and vice versa.
- What is the maximum slope allowed for a standard trench system in SC? 15% South Carolina restricts standard trench installation to slopes of 15% or less.
- Which tool is commonly used to determine seasonal high water table? Soil auger A soil auger helps observe soil color and mottling to estimate water table levels. 10.What is the minimum depth of soil required above bedrock for a conventional system?
17.What does the presence of gray water stains near the surface indicate? System failure Surfacing effluent shows that the system is overloaded or failing. 18.How often should septic tanks generally be pumped? Every 3 to 5 years Regular pumping prevents solids from clogging the drain field. 19.What is the best time of year for soil evaluations in SC? Late winter to early spring This is when the seasonal high water table is most evident. 20.Which condition disqualifies a site for a standard drain field? Frequent flooding Flooded areas cannot maintain proper soil treatment. 21.Which component removes pathogens from wastewater? Soil treatment area The soil naturally filters and treats effluent as it percolates. 22.What is a key sign of improper septic tank installation? Tank settling or tilting Uneven tanks can lead to leaks and backflow. 23.Which safety measure should be taken when entering a tank? Use confined space entry procedures Septic tanks can contain toxic gases; safety protocols are vital.
24.Which material is not approved for drain field pipes? Corrugated flexible pipe South Carolina requires rigid, perforated PVC or equivalent. 25.What is the proper slope for drain field lines? 1 to 2 inches per 100 feet A slight slope ensures even distribution without pooling. 26.Who is responsible for ensuring final grade meets code? Installer The licensed contractor must confirm final cover and grading comply. 27.What can cause bio-mat buildup? Overloading the system Too much wastewater or solids promote clogging. 28.What is the minimum setback from a building foundation? 5 feet To prevent structural damage or wastewater intrusion. 29.What is a key feature of a mound system? Elevated soil absorption area Mounds raise the drain field above limiting conditions like shallow water tables. 30.What test measures soil infiltration rate? Percolation test Percolation tests are standard for determining soil absorption rates.
38.What is the function of a pump tank? Stores and doses effluent Pump tanks hold treated effluent before pumping to the drain field. 39.Which practice protects the drain field during construction? Rope off the area Limiting access prevents soil compaction and damage. 40.What is a sign of tank leakage? Soggy soil around the tank Leaks cause wet spots and potential contamination. 41.Which pipe connection must be watertight? Inlet and outlet baffles Leaks at baffles reduce settling efficiency and allow solids through. 42.What is the setback distance from a stream or pond? 50 feet This protects surface waters from effluent contamination. 43.How deep should you dig test pits for site evaluation? To a depth of 4 feet or to limiting layer You must reach any limiting soil features to evaluate suitability. 44.What is the proper response if unsuitable soils are found? Propose an alternative system Alternative systems like mounds may be required on marginal sites.
45.What is the key benefit of a time-dose control panel? Controls effluent dosing frequency It distributes flow evenly, protecting the drain field. 46.When must a system be abandoned? When it is no longer used Abandoned systems must be properly decommissioned to prevent hazards. 47.What is a primary cause of tank corrosion? Hydrogen sulfide gas This gas forms sulfuric acid, which corrodes concrete tanks. 48.What practice should be avoided near the drain field? Planting trees Roots can clog or damage pipes and soil structure. 49.Which of these requires a variance? Installing closer than required setbacks Any deviation from code requires DHEC approval. 50.What training is required for SC onsite contractors? Pass the DHEC certification exam Contractors must pass the exam to be licensed and permitted. 51.What is the minimum setback from a property line for a septic tank in SC? 5 feet This distance prevents encroachment and potential disputes.
59.Which type of soil texture is ideal for percolation? Sandy loam Sandy loam offers good permeability and treatment capacity. 60.What should be done if unexpected groundwater is found? Stop work and notify DHEC Unexpected conditions must be evaluated by the authority. 61.What is a baffle’s primary function? Prevent scum and solids from exiting the tank Baffles direct flow and trap solids. 62.Why are curtain drains installed near septic systems? To divert surface or subsurface water away This protects the drain field from excess water. 63.What is the setback from an irrigation well? 75 feet Same as potable wells, to prevent contamination. 64.When should the installer backfill the system? Only after inspection approval DHEC must inspect before covering to ensure compliance. 65.Which sign indicates tree root intrusion? Slow drains and backups Roots can clog pipes and block flow.
66.What is the main role of aerobic bacteria in the drain field? Break down organic matter They help treat effluent as it percolates through soil. 67.What happens if you install a system in saturated soil? Smearing and reduced infiltration Working wet soils damages structure, limiting absorption. 68.What is the maximum daily flow for a residential system? Calculated by bedroom count DHEC guidelines base flow on bedrooms and occupancy. 69.Why should heavy machinery be kept off drain fields? To prevent soil compaction Compacted soil loses absorption capacity. 70.What is the minimum fall required between the house and tank inlet? 1/8 to 1/4 inch per foot This ensures proper flow without solids settling in pipes. 71.What is a sign of tank overuse? Frequent pumping needed Excessive loading overwhelms tank capacity. 72.Which system is appropriate for high groundwater? Elevated sand mound It lifts the absorption area above the water table.
80.Which practice extends system life? Water conservation Less flow reduces hydraulic loading on soil. 81.What is the setback from a stormwater ditch? 25 feet Runoff ditches must be separated to prevent cross-contamination. 82.Which soil type has the slowest percolation? Clay Clay holds water and drains poorly. 83.What is the sign of sludge accumulation? Thick layer at tank bottom This reduces treatment capacity and must be pumped. 84.What is the minimum access opening size for tank maintenance? 18 inches Access must be large enough for safe entry and equipment. 85.What is the most common tank material in SC? Concrete Concrete is durable and commonly used. 86.What does a mound system require that conventional does not? Sand fill media Sand improves treatment in elevated systems.
87.Why are effluent pumps installed? Move wastewater to higher elevation They allow distribution where gravity flow isn’t possible. 88.Which practice damages soil structure? Smearing during excavation Wet soil sticks and seals pores. 89.What is a pump alarm’s purpose? Alert to pump failure It warns of high water in the chamber. 90.Which situation requires a replacement area? All new systems A designated area is needed for future repairs. 91.What is the setback from a public well? 100 feet Public wells have stricter setbacks. 92.What is the danger of tank covers not secured? Fall hazard Unsecured lids pose serious safety risks. 93.What is a typical life expectancy for a drain field? 20 – 30 years Proper maintenance extends lifespan.
- Why is uniform distribution important? Prevents overloading parts of the drain field Balanced flow protects soil absorption.
- What is the benefit of alternating trenches? Rest and recovery of soil Alternating fields helps maintain absorption capacity.
- What indicates filter clogging? High tank levels Blockage backs up effluent into the tank.
- Which pipe slope causes solids to settle? Too little slope Flat pipes don’t carry solids effectively.
- What happens if drain field is installed too deep? Anaerobic conditions limit treatment Oxygen is needed for aerobic bacteria.
- What is the setback from a swimming pool? 15 feet Pools must be clear of system components.
- What is the primary concern for high clay content? Poor infiltration Clay retains water and clogs easily.
- How does mulch help mounds? Prevents erosion It stabilizes the soil surface.
- Which test is done to confirm tank watertightness? Water test Tanks should hold water without leakage.
- What is the maximum slope for a mound site? 6% Higher slopes can cause runoff and erosion.
- Why must the contractor provide owner education? Explain system use and maintenance Owners must know how to operate systems properly.
- How often should an effluent pump be serviced? Annually Regular checks prevent failure.
- What must be installed to prevent backflow? Backflow preventer It stops reverse flow into the system.
- What is the role of geotextile fabric? Separate soil and aggregate It keeps soil from clogging the stone.
- What is the setback from a basement wall? 10 feet To avoid seepage into foundations.
- Why is a reserve area important? For future system repairs It allows replacement if failure occurs.
- What is the main purpose of inspections? Ensure code compliance They verify installation matches the permit.
- Why should lint filters be used? Reduce solids entering tank Lint clogs filters and bio-mat.
- What is the best way to protect distribution pipes? Install them level Level pipes ensure even flow.
- Which pipe diameter is typical for laterals? 4 inches Standard for gravity systems.
- What condition requires soil amendments? Poor structure Amendments can improve infiltration.
- Why are diversion valves used? Switch flow between fields They let one field rest and recover.
- What is the first step if a system fails? Contact DHEC and a licensed contractor Professional help is needed to fix it legally and safely.
- What is the required minimum distance from a septic tank to a cistern? 50 feet This setback helps prevent contamination of stored water.
- Which component should be installed to maintain flow equalization? Distribution box It divides flow evenly among multiple trenches.
- What happens if the inlet baffle is missing? Solids may flow into the drain field Baffles keep solids in the tank for settling.
- Why is regular system monitoring important? Detects problems early Early detection prevents costly repairs.
- What must be done before replacing a failed drain field? Soil evaluation of the replacement area The new area must meet standards for soil and setback.
