Septic System Contamination Risks

Can a septic system contaminate a well?

Have you ever thought about where the water goes when you flush a toilet? If you have a septic system, this question may be more important than you think. Whether it is the largest advanced wastewater treatment plant in the world or the septic system in your back yard, all wastewater systems need regular maintenance. This will not only extend the life of your system, but it will also help prevent it from potentially contaminating the surface water and groundwater.

How does a septic system contaminate the surface water and groundwater?

Water from your toilets, showers, and other appliances contains harmful bacteria, viruses, and nutrients that could make you sick if it were to enter your well without being properly treated first. Maintenance issues like a full or cracked septic tank or a plugged drainfield can cause untreated wastewater to enter the surface water or groundwater.  
According to the United States Environmental Protection Agency (EPA), the most serious documented problems involve contamination of surface waters and ground water with disease-causing pathogens and nitrates.

Let’s take a peek at a conventional septic system and see how contamination can occur:

Your House:

• Most of the wastewater will generate from the kitchen and bathroom. Watch what you put down your drains. 
• Remember the three P’s: poop, pee, and (toilet) paper. Those are the only things that should be flushed down a toilet. 
• Avoid flushing other chemicals or medications down the drain or toilet as they could contaminate your well. 

Septic Tank: 

• Wastewater exits the home through a pipe and enters the septic tank which is buried and watertight.
• The solids settle at the bottom forming sludge, while fats, oils, and grease float to the top and form scum. Sludge is broken down by microorganisms that also destroy some of the contaminants in the wastewater. 
• If a tank is leaking, contaminated wastewater will exit the tank before it is treated. A septic tank needs serviced and pumped on a regular basis to ensure it is working properly.

Drainfield: 

• In your yard, a series of shallow trenches were placed to create the drainfield. The partially treated wastewater flows from the septic tank into the drainfield and slowly filters down through the soil until it reaches the groundwater.  
• Overloading your drainfield with too much water or having it clogged with solids will cause sewage to surface in your yard or even back into your house.

Treatment in the Soil: 

• Most bacteria, viruses, and some nutrients are removed when the wastewater filters through the soil.
• Soil cannot remove all medicines, cleaning products, and other harmful chemicals, so they pose the risk of entering the groundwater. 
• Wastewater that surfaces in the yard may contaminate your drinking water through an unsecured cap or cracks in the well casing.

Groundwater: 

• Groundwater is water that is beneath the Earth’s surface and is held in the soil or in the pores and crevices of rocks. 
• Any contaminants that remain after leaving the septic system may seep into the groundwater. 
• The biggest risk for a well to become contaminated is if it is in the path of groundwater flow beneath a septic system.

Further Resources:

• Septic Systems and Drinking Water | Diagram & Table from EPA
• Understand Your Pump Septic System | 3D model from TPC HD
• How does a Septic System Work? | Video from SEFC