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Your Septic System After a Flood or Heavy Rain

When the yard is under water, the instinct is to call a pump truck. That is usually the wrong first move. Here is what to do instead, in order, and why.

Why the system struggles when the ground is soaked

A septic system only works if the drainfield can take water. The tank separates solids, but treatment happens in the soil under the field, and saturated soil has nowhere to put more water. On a lot of DeSoto County ground the problem is worse than it looks from the surface: the loess silt sits over a dense fragipan that water will not move through easily, so water stacks up above it after long rain. Our soil page explains that layer.

While the field is flooded, wastewater leaving the house is not being treated. EPA's advice is blunt: if the soil is saturated and flooded, do not use the system if you can avoid it, because the wastewater will not be treated and becomes a source of pollution.

Should I pump my septic tank while the yard is flooded?

No. EPA answers this one with a plain "No!" Pumping a tank in saturated ground is at best a temporary fix, and at worst the emptied tank can try to float out of the ground and damage its inlet and outlet pipes. A system that was installed recently is more likely to do this, because the soil around it has not had time to settle and compact.

Opening the tank while the soil is still wet also lets mud and silt in, and that silt can end up in the drainfield. The fix while the water is up is to use less water, not to empty the tank.

What to do while the water is still up

• Cut water use hard. Fewer flushes, short showers, no laundry or dishwasher if you can wait. The only way to relieve pressure on a flooded system is to use it less.
• Keep off the drainfield. Saturated soil compacts easily. Driving or running equipment over the field can reduce its ability to treat wastewater and lead to failure. Do not dig in the tank or field area while it is wet.
• Do not drain floodwater from the house into sinks or toilets. Pushing it through the tank raises the flow and can carry solids out to the field, where they clog it.
• Stay away from flooded electrical parts. If you have an advanced treatment system with an aerator, pump or control panel, leave flooded equipment alone until it is dry and clean.

After the water goes down

Wait until the water in the drainfield area is lower than the water level around the house before using the system normally. Then work through this list:

1. Pump the tank, once the field has drained

   EPA recommends pumping as soon as possible after the flood, meaning after the ground is no longer saturated. Pump the tank and any lift station or pump chamber, to remove silt and debris that washed in.

2. Check electrical connections before restoring power

   Examine every connection on pumps, aerators and alarms for damage first.

3. Check the lids and ports

   Make sure the tank's manhole cover is secure and that inspection ports have not been blocked or damaged.

4. Clean the filters

   Aerobic plants, upflow filters, trickling filters and other media filters tend to clog with mud and sediment and need washing and raking. That is a job for the maintenance provider on an advanced system.

5. Repair the ground cover

   Fix erosion over the tank and field, and reseed or re-sod so there is grass cover again.

Signs the flood did real damage

Most tanks come through a flood fine, because they are buried and covered. The things that go wrong are silt and the field. Have the system professionally inspected if you see settling over the tank or the system will not accept water. Tanks and pump chambers that filled with silt have to be professionally cleaned, and if the drainfield itself is clogged with silt, a new system may have to be installed. Only trained specialists should open or repair a tank, because tanks can contain dangerous gases.

EPA's advice is to contact the health department for help, including a list of contractors who work in your area. See repair and the permit page before anyone starts digging.

Well water and sewage cleanup

If you are on a private well, do not drink the water until it has been tested. Contact the health department about testing.

If sewage backed up into the house, clean the area and disinfect the floor. EPA gives the mix as half a cup of chlorine bleach to each gallon of water. If a backup happens after the water drops, check the tank outlet first: flooding lifts the floating layer of fats and grease in the tank, and some of it can partly plug the outlet tee.

Questions people ask

Can I use my septic system while the yard is flooded?

Avoid it as far as you can. While the soil is saturated the wastewater is not treated, so use as little water as possible until the field drains.

Should I pump my septic tank after heavy rain?

Not while the ground is saturated. An emptied tank in waterlogged soil can float and damage its pipes. Pump once the drainfield area has drained.

Does a flood ruin a septic tank?

Usually not. Most tanks are not damaged because they are buried. Silt in the tank or pump chamber needs professional cleaning, and a drainfield clogged with silt may need replacing.

My system backed up after the water went down. What is the likely cause?

Check the tank outlet first. Flooding lifts the scum layer of fats and grease, and it can partly plug the outlet tee.