Protecting your well from your septic system

Many homes that have a septic system also have a private well, often on the same lot. That's why we cover both on one site. Your wastewater goes into the ground, and your drinking water comes out of the ground. EPA's guidance on septic systems and drinking water explains how to keep the two apart.

How contamination happens

Wastewater contains bacteria, viruses, and nutrients such as nitrate. In a working system, the tank holds back solids and the soil under the drainfield removes most pathogens and some nutrients before the water reaches groundwater. EPA stresses that soil can't remove everything. Medicines, some cleaning products, and other chemicals can pass through.

Problems arise when:

• the system is failing and untreated wastewater surfaces in the yard, where it can enter a well through an unsecured cap or cracks in the casing;
• the well is too close to the drainfield;
• the well is downgradient, meaning groundwater flows from the septic system toward the well;
• the soil is very sandy or porous, so effluent moves quickly with little treatment.

Lower risk, higher risk

EPA sums it up this way. Your well's risk is lower when the well and septic system are far apart, the well is deep (especially in bedrock or below a layer of silt or clay), and the septic system is pumped and serviced regularly. The risk is higher when the well is shallow and in permeable soil, sits downgradient of the septic system, or the system isn't maintained.

Setback distances

EPA notes that most states or local governments require a minimum horizontal distance, or setback, between a septic system and a drinking water well. The numbers vary by state and by the type of well and system, so check with your local health department. EPA adds that where the soil is sandy or porous, you may want more distance than the minimum. Remember that your neighbors' systems count too.

What you can do

• Maintain the septic system. Inspect it at least every three years and pump on schedule. Our pumping calculator gives a starting point.
• Keep chemicals and medicines out of drains. They can pass through the soil into groundwater.
• Protect the wellhead. Keep the cap tight and vented, make sure the casing sticks up above the ground, and slope the ground so water drains away.
• Test the well every year. Coliform and nitrate are the two most likely to show septic influence. Use our test reader to interpret the results.
• Know where everything is. A sketch showing the well, tank, and drainfield with distances helps contractors avoid mistakes. A new drainfield or well should never be placed without checking the setbacks.

Warning signs

EPA lists high nitrate or coliform in drinking water wells among the signs of a failing septic system. If your well test changes suddenly, check the septic system. If your septic system shows signs of failure, such as soggy ground, odors, or backups, test the well. See signs your septic system is failing.