Septic System Red Flags: The Green-Grass Test and Other Warning Signs

A lawn with one strip of grass that's greener and thicker than everything around it looks like good news. Over a septic drainfield, it's often the opposite. A recent story about a home inspector who spotted exactly that, then confirmed a failing system with a quick dye test, has been making the rounds.

About one in five U.S. homes uses a septic system. If yours does, or if you're buying one that does, here's what to watch for.

01How a septic system works (in one minute)

Wastewater from the house flows into a buried tank. Solids sink to the bottom as sludge, grease floats to the top as scum, and the liquid in the middle flows out to a drainfield: a set of buried pipes or chambers in gravel where the soil filters and treats it. The system works as long as solids stay in the tank and the soil can keep absorbing water.

02The EPA's warning signs

The U.S. Environmental Protection Agency lists these as common signs of a failing system:

• Water and sewage backing up into toilets, drains and sinks
• Slow drains in bathtubs, showers and sinks
• Gurgling sounds in the plumbing
• Standing water or damp spots near or over the tank or drainfield
• Sewage odors around the tank or drainfield
• Bright green, spongy, lush grass over the tank or drainfield, even in dry weather

That last one is the green-grass test. Wastewater coming to the surface is acting as fertilizer and water. In a dry spell, when the rest of the lawn is browning, a green stripe pattern over the drainfield is a red flag.

03How often to pump

The EPA recommends having the system inspected every 1 to 3 years and the tank pumped every 3 to 5 years, depending on tank size, the number of people in the house and water use.

Pumping isn't optional maintenance. If the tank fills with sludge, solids can wash out into the drainfield and clog it. A clogged drainfield can't be cleaned out; it usually has to be replaced, and that's one of the most expensive repairs a homeowner can face.

04Habits that kill septic systems

• Flushing anything but toilet paper. "Flushable" wipes, paper towels, feminine products and cat litter clog systems.
• Grease down the drain.
• Running water all at once, like several loads of laundry back-to-back. Spread them out.
• Driving or parking on the drainfield, which crushes pipes and compacts soil.
• Planting trees nearby. Roots go after the water in drainfield pipes.
• Letting gutters and sump pumps drain onto the drainfield. Extra water floods it.

05Buying a house on septic

A standard home inspection usually doesn't include a full septic inspection. Ask for one separately from a qualified septic inspector, and ask the seller for:

• The pumping and inspection records
• A map of the tank and drainfield location
• The age of the system and any repairs

A septic inspection often includes pumping the tank so the inspector can see its condition, plus checking the drainfield. In some areas, a dye test is used: dye goes down a drain, and if it shows up in the yard, there's a problem. Make a septic inspection part of your inspection contingency.

06The bottom line

A septic system out of sight shouldn't be out of mind. Pump it on schedule, treat it kindly, and take the green stripe seriously when you see it.

Sources (3)

EPA: Frequent questions on septic systems; EPA: Resolving septic system malfunctions; EPA: New homebuyer's guide to septic systems.

Related: A Comprehensive Guide to DIY Home Inspection: Safeguarding Your Home Inside and Out