Protecting Your Septic Drain Field

What does a drain field do?

The tank holds solids back. The drain field, also called the absorption field, takes the liquid that leaves the tank and lets it soak into the soil, where microbes break down pollutants. Virginia Cooperative Extension says the tank protects the field from clogging and failing.

Its size depends on the number of bedrooms and how fast the soil absorbs water. Once a field clogs, pumping the tank does not fix it, so the goal is to protect what you have. That is why the sections below focus on weight, roots and water, the three things that most often damage a field.

How do you find your drain field?

Start with paper. Permits, as-built drawings and the operation permit show the layout; the local health department keeps them, and our guide to septic permits and the health department explains how to request them. Penn State Extension also suggests home purchase documents and township records.

Virginia Tech’s septic guide suggests drawing a scaled map showing the house, tank, distribution box, piping and field, with distances from the house and property lines, and keeping it with the house. It also suggests placing a marker above the tank.

What if there are no records?

Health department staff can help locate components. If that does not turn up the lines, a locating visit finds the tank and traces the field. Mark what is found on your map.

What should stay off the drain field?

The EPA says not to park or drive on it, because vehicle weight compacts soil and can crush pipes. Do not lay concrete or asphalt over it, and do not build on it without checking with a designer or the permitting authority.

Virginia Tech adds that the tank and field should not sit under a patio, garage, storage building, driveway or sidewalk, and that heavy equipment driven over the distribution box can shift it. A damaged or shifted box sends water to one part of the field instead of spreading it.

• Cars, trucks, ATVs and heavy equipment
• Patios, sheds, pools, decks and paved areas
• Permanent play equipment
• Piled snow, per Virginia Tech, which suggests neither piling snow on the field nor clearing it off

What should you plant over a drain field?

Grass. The EPA calls native grasses and ground covers the best choice, and Penn State calls turf grass the safest cover because its shallow roots stay out of the pipes. Healthy cover also prevents erosion.

The EPA says not to plant trees, shrubs or vegetable gardens on the field. Roots can damage pipes, and vegetables may be exposed to effluent. A neighbor’s trees can cause the same trouble.

How far away should trees be?

There is no Virginia figure that we could source. The EPA tells owners to ask a septic professional how far trees should be from the field. Distances you see online often come from other states and do not carry over, so ask your health department or a designer for your soil and tree species.

How do you manage water around the field?

Excess water is the main cause of field trouble. The EPA says to keep roof drains, sump pumps and other rainwater away from the drain field, because extra water disrupts treatment. Virginia Tech adds that the area should be graded to shed water rather than collect it in low spots.

Inside the house, fix leaking toilets and faucets, spread laundry across the week and run full loads. Virginia Tech also says water softener backwash should not enter the system. See what not to put in a septic system for what else to keep out.

What is a reserve area, and why leave it alone?

A reserve area is space set aside for a replacement field. Virginia’s regulations require one for soils with slower percolation rates, and it must be at least half the size of the original field, according to Virginia Tech’s septic guide. Some localities require more, so check local rules.

It does not have to be installed at construction, but it needs to stay clear. Building a pool or shed on the reserve can leave you no place for a new field if the first one fails.

What are the warning signs of a failing field?

Wet, spongy ground, a lush green stripe in dry weather, sewage odor in the yard and slow drains in the house are the classic signs. Find the full list in septic warning signs.

If the signs point to a struggling field, jetting the field can sometimes help. A pumped tank on a regular schedule keeps solids from reaching the field in the first place, as covered in how often to pump.