Can a septic tank fill up from too much rain?

Can Septic Tank Fill With Rainwater, Causing Flooding?

Q. Is rain water supposed to go into my septic tank?

A. No.

Q. Should my downspouts or gutters be routed into my septic tank?

A. No. No.

Q. Should the sump pump in my basement be routed into my septic tank?

A. No. No. No.

Q. Can a septic tank fill up from too much rain?

A. Unfortunately, yes, this happens sometimes for a few different reasons, and often with disastrous results.

The Septic System on your property has been designed through much scientific study using lots of data, including a specific soil analysis of your property by a soil scientist, a site study by a contractor, all reviewed by the local Health Department to determine exact parameters for your septic system.

It has been designed to treat the contaminated water from your home, and eventually release clean, safe water back into the groundwater of the earth.

Think of your backyard like a huge sponge.

If you pour dirty water on the top of a dry sponge, the sponge will retain most of the dirt particles and allow the cleaner water to pass through and be released below.

This is a simplified picture of your home’s Septic System.

All the wastewater that goes down your drains must flow through the Septic Tank, where nearly all of the solids, (poop, toilet paper, kitchen waste), are retained. Then the water is sent out into your backyard sponge through a network of piping to be absorbed and filtered through the soil before being released back into the groundwater of Indiana.

If storm water from any source is allowed to enter the Septic System, it could overwhelm the capacity of the system to treat the water, and will likely result in an overflow of the system to the surface, and/or a severe backup in the house.

A few ways that could happen with your system:

Improper connection of any of the drainage plumbing to the Septic System.

  • Sump pump connected to the Septic System
  • Downspouts connected to the Septic System
  • Floor drains, footer drains, or yard drainage connected to the Septic System

Improper Surface Water Routing

  • Water from your downspouts dumps out right on top of your Septic Tank, or your Backyard sponge, (Leach Field).
  • Water from all of your yard puddles right on top of your Backyard Sponge, (Leach Field), each time it rains.

Improper Subsurface Drainage

  • An underground drainage pipe is dumping water into some portion of your Septic System.
  • Subsurface water in your yard is flowing downhill through the soil and flooding out your leach field below the surface of your yard.

Fortunately, all of these terrifying scenarios are possible to correct. Some of them are easier and less costly than others.

Remember that your Septic System was carefully designed according to soil analysis and calculation of residual water levels on your property. It was calibrated to receive and treat an amount of water consistent with the size of your home. If an overzealous previous owner was in a do-it-yourself mode and decided to hook up some piping to drain some of the water in the yard, that could be why your toilet is refusing to flush when it rains…!

The goal with a Septic System, (Or Leach Field), is to preserve a relatively dry sponge in your backyard, so the soil can adequately treat the wastewater it is designed to absorb. To attain this, we need to make sure that the storm water is not being fed into your system either by piping or simply by ponding on top of your Septic System.

Look for more detail on this subject in my next blog titled “Two types of Water”!