Protect Your Septic Drainfield and Spot Trouble Early

The septic tank gets most of the attention, but the drainfield does the final treatment. The U.S. Environmental Protection Agency describes it as a shallow, covered excavation in unsaturated soil. Liquid from the tank trickles into it, and the soil accepts, treats, and disperses that wastewater, removing harmful bacteria, viruses, and nutrients along the way.

That only works while the soil can do its job. A drainfield can be damaged from above, by weight, roots, or extra water, and from inside, by solids, grease, and chemicals that should never have left the house. Most of the protection is simply knowing what to keep away from it. If you haven't located your drainfield yet, start with finding your septic system.

Keep weight off the drainfield

The EPA's first drainfield rule is to never park or drive on it. The Washington State Department of Health extends that to heavy equipment and livestock, and to the tank and any drainfield replacement area set aside on the lot as well as the drainfield itself.

Weight matters most when the ground is wet. After flooding, the EPA warns that saturated soil is especially easy to compact, and that compacting the soil over the drainfield can reduce its ability to treat wastewater and lead to system failure.

Covering the system causes its own problems. Washington's health department advises against putting concrete or plastic over a septic system and says grass is the best cover. Before planning a patio, shed, deck, pool, driveway, or addition anywhere near the system, ask your local health department what setbacks apply and whether the project needs a septic review.

Plant with roots in mind

The EPA does not recommend planting trees, shrubs, or vegetable gardens on the drainfield. Tree and shrub roots can ensnarl and damage drainfield pipes, and the EPA notes that vegetables grown there could be exposed to sewage effluent and be unsafe to eat. It advises planting trees an appropriate distance from the drainfield, and its SepticSmart homeowner guide says a septic service professional can advise on that distance for your tank and landscape. There is no single number for every yard, so ask at your next service visit before planting anything larger than grass near the system.

Send rainwater somewhere else

A drainfield has to handle the water from the house. The EPA advises keeping roof drains, sump pumps, and other rainwater drainage systems away from the drainfield area, because excess water slows down or stops the wastewater treatment process.

Walk the yard with your septic sketch and follow each downspout and any sump pump discharge to where it ends. If one empties toward the drainfield, turning a movable extension so it points elsewhere may be enough. Anything that involves digging or rerouting pipes near the system should wait for a septic professional's advice. Where the Water Goes covers the rest of a yard's drainage.

Use water steadily and efficiently

The SepticSmart guide points out that all the water a household sends down its drains ends up in the septic system, so the more water you conserve, the less the system has to handle. The EPA suggests:

• high-efficiency toilets, faucet aerators, and high-efficiency showerheads
• choosing the right load size on the washing machine
• spreading laundry across the week instead of running many loads in one day
• fixing leaks promptly, since the SepticSmart guide notes a single leaky toilet can waste as much as 200 gallons a day

A few household habits send large volumes at once. The SepticSmart guide advises against draining a hot tub into the septic system, because the rush of water stirs up solids and pushes them into the drainfield. Drain cooled hot tub water onto turf or landscaped areas well away from the tank and drainfield, following local rules. The same guide notes that some water softeners and purification systems send hundreds of gallons into a septic tank, and recommends asking a licensed plumbing professional about routing them elsewhere.

For a quick check of the fixtures most likely to leak, see Spot Early Leaks Under Sinks and Appliances.

Keep the wrong things out of the drains

The EPA's rule for the toilet is short: only flush human waste and toilet paper. It also lists items that should never be flushed or poured down a drain in a home with a septic system, including:

• cooking grease and oil
• non-flushable wipes, diapers, and feminine hygiene products
• dental floss, cigarette butts, and paper towels
• coffee grounds and cat litter
• medications
• household chemicals such as gasoline, oil, pesticides, antifreeze, and paint

An in-sink garbage disposal adds food solids to the tank, and the EPA notes that using one can mean pumping more often. The SepticSmart guide recommends limiting or eliminating its use. Good drain habits work alongside regular inspection and pumping, not in place of it.

Know the warning signs

The EPA and its SepticSmart guide list these signs of a septic problem:

• water and sewage from toilets, drains, and sinks backing up into the house
• bathtubs, showers, and sinks draining very slowly
• gurgling sounds in the plumbing
• standing water, damp spots, or muddy soil near or over the tank or drainfield
• sewage odors around the tank or drainfield
• bright green, spongy grass over the drainfield, even in dry weather
• pooling water in the basement

If your home has a private well, the EPA also lists elevated nitrate or coliform bacteria levels in well water among the signs of a septic problem.

The SepticSmart guide advises calling a septic professional when you notice signs like these. Describe what you saw, where, and when it started, and have your septic records ready.

After a flood or very heavy rain

The EPA explains that wastewater from a system in saturated, flooded soil will not be treated and will become a source of pollution. It advises not using the system, if possible, while the soil is saturated, and not using it until the water in the drainfield is lower than the water level around the house. Keep vehicles and equipment off the wet ground, and don't have the tank pumped yet: the EPA warns that pumping while the ground is saturated could cause the tank to try to float out of the ground and damage its inlet and outlet pipes. If you suspect damage once the water recedes, have the system professionally inspected and serviced.

Protecting a drainfield is mostly about restraint: less weight, less water, and fewer things in the drains that don't belong there. Those habits cost almost nothing and give the system the conditions it was designed for.