Understanding Your Septic System

Approximately 30% of U.S. households have on-site “septic systems.” Septic systems consist of a tank that receives household effluent from toilets, sinks, showers, and washing machines; a leachfield/drainfield, and plumbing pipes to connect the system. Septic “leachate” is the liquid that remains after wastewater drains though septic solids. The liquid contains elevated concentrations of bacteria and organic compounds from waste and other household materials.

When properly placed, functioning, and maintained, septic systems are designed to collect wastewater and neutralize contaminants before they enter ground or surface water systems. This is particularly important where ground and surface water drain to water bodies such as lakes. Decomposition of waste begins in the septic tank and ends in a leachfield after undergoing a series of treatments whereby wastewater is chemically, physically, and biologically processed to remove contaminants.

Healthy shoreline development. Photo courtesy Whitefish Lake Institute

Modern septic systems are considered cost-effective wastewater treatment, however improper initial system design, impermeability of soil, improper soil drainage, incorrect vertical distance between the absorption field and water table, unsuitable slope, or improper maintenance may lead to system failures.

Even when properly installed and maintained, septic systems have a finite life expectancy.

Many of the septic systems around Montana lakes have remained in function long past their life expectancy, posing a great threat to lakes and other waterbodies. There are a number of steps you can take to ensure that your septic system does not contaminate your lake.


  • Be sure your professional installer follows the rules and codes in your area for proper septic system design and installation.
  • Install a properly designed and approved septic system located as far as possible from water, at least 100 feet.

Operating and Knowing What to Flush

Typical Septic System. Graphic courtesy U.S. Environmental Protection Agency
  • Have the sludge level in your septic tank checked every one to three years. When checking the sludge level, also have them look at the tank to be sure the concrete is in good condition. A tank may last many years, but if you see signs of cracking or chipping, check with your county sanitarian.
  • Conserve water. The less water you use, the better your septic system will work. Also give the system a rest after heavy use.
  • DON’T use commercial products that claim to clean your septic tank without pumping. These products can clog your leach field and many contain chemicals that can contaminate groundwater.


  • Have your septic system professionally inspected and pumped every 3-5 years depending on household size and use. If solids are not removed, they can wash into and clog the leach field.
  • Avoid using chemicals that kill microorganisms.
  • Organize neighborhood septic tank pumping. Pumpers usually reduce the price for large volume jobs.

Septic System Facts

Nationally, over 28 thousand miles of streams are designated as “threatened or impaired” because of septic system failure and sewage pit waste, and lakes across the country are suffering eutrophication from septic leachate. Numerous studies show that septic leachate from household systems is transported by groundwater through lake bottom sediments into lake water, elevating nutrient concentrations and decreasing water quality and safety.

Septic leachate is a Nonpoint Source Pollution which comes from dispersed human activities such as septic systems, excess fertilization, high densities of livestock, domesticated pets, airborne deposition, and industrial runoff. Great strides have been made to deploy Best Management Practices in decreasing fertilization, protecting waterways from livestock and pets, installing wells at great distances from septic systems, and managing stormwater. However, decreasing septic leachate pollution is difficult because individuals are responsible for their own systems.

Although parasitic diseases, hormones, pharmaceutical compounds, and increased levels of nitrogen and phosphorus from these systems are compounding in our lakes and streams, there are no federal regulations for septic systems.

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