by Nick Gromicko, CMI® and Kenton Shepard
A septic system receives, treats and disposes of unwanted wastewater and solids from a building’s plumbing system. Solids are partially broken down into sludge within a septic tank and are separated from effluent (water) and scum (fat, oil and grease). Effluent regularly exits the tank into a drainfield where it is naturally filtered by bacteria and reentered into the groundwater. Scum and sludge must be pumped periodically and should never enter the drainfield. 
When should a septic system be inspected?
The septic system should be inspected once a year, including as soon as the house is put on the market for sale. This will enhance the home’s value and avoid any liability issues that might result from a malfunctioning system. It is in the interest of a prospective buyer to insist that the septic system be inspected before they purchase the home if it has not been done recently.
How to locate the septic system:
Since they perform their essential functions underground and out of sight, it is not uncommon for a homeowner to not have any idea where the septic system is located. This is usually not an issue except for when it comes time to inspect or pump the tank!
The following suggestions can be used by inspectors to locate a septic tank if the homeowner does not already know where it is:
- An “as-built” drawing of the house should include the tank’s location. These drawings are often held in local health and zoning agencies. Old systems might not have any such record.
- The previous homeowner can be contacted.
- Newer tanks contain risers that rise visibly above the ground surface.
- A thin metal rod can be inserted into the earth and used to probe a suspected area. It is important to do this gently and only in soft, wet soil to avoid damaging the tank and associated pipes. A shovel can also be used but it requires a bit more work.
- A metal detector can be used if enough tank components are metal.
- A small radio transmitter can be flushed down the toilet and followed with a receiver.
- The greenest grass in a yard is often directly above the septic tank. Snow also melts faster above the tank than the rest of the yard. While these are not foolproof location methods, they have been known to be helpful.
What might InterNACHI inspectors look for?
- Find the date that the tank was last pumped. Ultimately, sludge level should determine whether a tank should be pumped, but knowledge of previous pumping dates can be a helpful reference.
- Check the sludge level with a “sludge judge” or a similar device. Sludge accumulates on the tank bottom and should not occupy more than 1/3 of the tank’s total volume or rise to the level of the baffles.
- The septic tank and drainfield should be far from wells and streams.
- Ensure that the system is large enough for the home that it serves. A four-bedroom home, for instance, typically requires a 1,200-gallon tank. The more occupants living in the home, the larger the tank that is required. Capacity in gallons can be calculated by tank dimensions. For rectangular tanks, length x width x depth in feet x 7.5 = capacity in gallons. For round tanks, 3.14 x radius squared x depth in feet x 7.5 = capacity in gallons.
- Check for liquid waste that has made its way to the ground surface. This condition is unsanitary and indicates that the system is overloaded. Make sure that the tank is watertight so that wastewater does not contaminate groundwater, and groundwater does not flow into the tank and cause it to overfill.
- If riser lids are present, they should be inspected for cracks and made sure they are secure.
- Make sure that the baffles are firmly connected to the tank’s inlet and outlet pipes.
- Drain lines should each receive the same amount of wastewater. They can be examined by opening the distribution box. If the box becomes tipped or clogged, it will disproportionately allocate effluent, and potentially flood sections of the drainfield.
What are baffles?
Baffles are septic tank components that slow wastewater entry sufficiently to ensure the distillation of solids, and prevent their release (as well as the release of scum) into the drainfield. In doing so, they protect the absorptive quality of the soil and prolong the life of the septic system as a whole. They are normally made from the same material as the septic tank — either fiberglass, steel or concrete.
Inspectors should check baffles for the following:
- solids covering the baffle. This should be reported immediately, as it indicates overflow.
- erosion from chemicals and water flow.
- evidence of previous overflow.
- sewage level should be several inches below the baffle top. A lower level indicates leakage and a higher level indicates blockage.
Maintenance Tips
Inspectors should know the following information so they can inform their clients about ways they can inadvertently damage their septic system:
- Only bath tissue can be flushed down the toilet. Tampons, paper towels, cigarette butts and diapers should be put in the trash. Household chemicals such as gasoline, paint, medication, antifreeze and pesticides can damage bacteria in the septic system and should never be flushed or dumped down the sink. Detergents and bleach can enter the plumbing system in moderate amounts.
- Cars should not be driven on or near the drainfield. Their weight can unknowingly damage subterranean piping.
- Only grass should be planted above the septic tank and drainfield. Roots from trees and large shrubs can cause unseen damage.
- No one should ever dig or build on top of the drainfield.
- All water drainage from rainwater, sump pumps, or any surface water should be diverted away from the drainfield. An over-saturated drainfield can retard the water treatment process and cause plumbing fixtures to back up.
- An easy way to prolong a septic system’s life and prevent a very costly replacement is to fix leaky faucets and toilets immediately. Any household water waste should be avoided. Taking shorter showers and not using a garbage disposal are ways to limit water use.
Some Precautions:
- Inspectors should not enter the septic tank to look for cracks. Tank interiors are very dirty and entrance should be avoided. If a crack is present, it will likely be at the level of the effluent, which will have drained from the tank through the crack. A strong sign that a crack is present is an effluent level significantly below the level of the tank outlet. A tank with cracks that allow effluent to leak into the surrounding earth is essentially a cesspool and needs to be replaced.
- Above-ground water indicates an overloaded septic system, if this water originates from the tank. Inspectors sometimes use a dye flushed down the toilet to confirm that the water originates from the house and not elsewhere. While this measure can be helpful, it is not an acceptable method to test septic system functionality. Flushed dye that appears in the puddle will confirm a faulty septic system, but dye that does not appear does not ensure a working system. Dye can take days to appear and may be too diluted to see clearly.
- Septic system inspection is outside the scope of general home inspection and requires special training. Laws vary by jurisdiction, and inspectors should know them well before performing this service. They should disclaim any part of the inspection of the septic system that they did not inspect.
Septic System Dangers
Septic systems are designed to handle dangerous waste and can pose serious health hazards to homeowners and inspectors. The following are a list of precautions:
- A professional septic tank pumping service, not an inspector, should remove solid waste.
- No one besides a licensed, equipped professional should enter a tank. Noxious fumes such as methane can cause rapid asphyxiation and death.
- If a septic tank shows signs of weakness, tread with caution! Collapse can be fatal. Beware of tanks with rusting metal, homemade lids, or anything else that appears unstable.
In summary, septic system inspections should be performed on an annual basis to ensure proper function. The septic tank is the most expensive household fixture and its lifespan will be shortened significantly if it is not maintained.