A septic system has two working parts. The tank holds wastewater long enough for solids to settle to the bottom as sludge and for grease to float to the top as scum. The liquid in the middle flows out to the drain field, a set of trenches or beds where the soil filters and treats it.
Tanks can be pumped. Drain fields can’t. Once the soil under a field is clogged, the field has to be repaired or replaced, which is why it pays to catch problems early.
Signs something is wrong
- Slow drains or gurgling in several fixtures at once, not just one sink.
- Sewage backing up into the lowest drains in the house, like a basement floor drain or shower.
- Soggy ground or standing water over the drain field when it hasn’t rained.
- Bright green, fast-growing grass over the field, especially in a dry stretch when the rest of the yard is brown.
- A sewage smell outside, near the tank or the field.
- The tank needs pumping much more often than it used to.
If you’re on a private well and a water test comes back with bacteria or high nitrate, a nearby septic system is one possible cause worth checking.
Is it the drain field, or something simpler?
Not every backup means a failed field. Before you assume the worst:
- One slow fixture usually means a clog in that drain, not a septic problem.
- The whole house backing up can be a blocked line between the house and the tank, or a tank that’s overdue for pumping.
- A broken or missing baffle in the tank lets solids flow out toward the field. It’s a cheap fix if it’s caught before the field clogs.
The first step is almost always the same: have the tank pumped and inspected. The person pumping it can see the liquid level, the condition of the baffles, and whether liquid runs back into the tank from the field once it’s pumped down. That last sign points to a field that isn’t taking water.
Why drain fields fail
- Solids carried over from the tank. A tank that’s never pumped, or one with a broken outlet baffle, sends sludge and scum into the field, where it clogs the soil.
- Too much water at once. Every load of laundry on one day, a running toilet, or a roof drain or sump pump that empties onto the field can flood it.
- Compaction. Driving or parking on the field crushes pipes and squeezes the air out of the soil it depends on.
- Roots from trees and shrubs planted too close.
- Age. Every field eventually reaches the end of its life.
Repair or replace?
That depends on what failed. A broken line, a crushed section or a bad baffle can often be repaired. A field whose soil is clogged throughout usually has to be replaced, sometimes in a new spot in the yard. Since the tank is often still sound, it can usually stay in place if it’s in good condition and sized for the house.
In South Dakota, on-site wastewater systems have to meet the state’s design rules in ARSD chapter 74:53:01, and they have to be installed by an installer certified through the state Plumbing Commission. Many counties also require a permit and a soil or percolation test before a new field goes in, so call your county planning or zoning office early.
Keeping a system working
The EPA’s septic guidance covers the basics:
- Have a typical household system inspected at least every three years. Tanks are usually pumped every three to five years, depending on household size and tank size.
- Don’t park or drive on the drain field, and keep trees far enough away that roots can’t reach it.
- Keep roof drains and sump pumps away from the field.
- Spread laundry out across the week instead of doing it all in one day.
- Only flush human waste and toilet paper. Wipes (even “flushable” ones), grease, diapers, cat litter, medications and chemicals don’t belong in a septic system.
Knowing where your tank and field are helps, too. Draw a sketch or take measurements the next time the tank is pumped, so nobody builds a shed or parks a camper on top of the field.
Need a new system or drain field?
Black River Contracting is a South Dakota certified on-site wastewater installer. We install new septic systems and replace drain fields around Rapid City and the Black Hills. See septic system installation or request a quote.