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Down the Drain: Household Wastewater Treatment Systems

Regular care of septic tanks can keep unwanted nutrients out of our rivers and lakes.

This story was written by the Our Gem Collaborative team for the CDA Press on Sunday, Sept. 20, 2020. Read the original article.

Fall is a good time to button up your place; whether it is a summer home or year-round residence. One often overlooked annual maintenance item is your wastewater treatment system. For many homes in the Coeur d’Alene Basin, where municipal sewer service is unavailable, homeowners rely on self-maintained, on-site subsurface wastewater treatment systems. Commonly known as septic systems, these treat sewage and household wastewater from showers, baths, sinks and washing machines.

Inadequate performance by these systems allows excess nutrients to reach nearby lakes or streams through groundwater, promoting algae or weed growth. Algal blooms and abundant aquatic plants make water unpleasant for swimming and boating and deteriorate water quality for fish and wildlife habitat. As plants die, settle to the bottom and decompose, they use up oxygen fish need to survive. In Coeur d’Alene Lake, this can also release toxic metals sequestered at the bottom.

Subsurface septic systems are a common form of on-site wastewater treatment and are the most desirable option where soil conditions are suitable. Since the septic tank and treatment process are covered with soil, the system is generally not visible and odor is nonexistent, when functioning properly. For this reason, it may be easy to forget about maintaining them.

A conventional septic system has two parts: the sewage tank and the drainfield. Three layers form in the septic tank: solids settle to the bottom and a layer of scum or grease floats above a liquid layer. As sewage is added to the tank, some liquid from the tank flows to the drainfield. The primary treatment of wastewater occurs in the drainfield which is usually a series of trenches, each containing a distribution pipe embedded in gravel or rock. The effluent flows from holes in the pipe, through the gravel and into the soil. The soil filters and treats the remaining solids and pathogens as the wastewater percolates through. These processes only work in soil that is not saturated with water.

Maintaining Septic Systems

For a septic system to function, it needs to be designed, installed and maintained with site-specific criteria in mind. When properly designed and installed, the system will minimally impact our environment.

Follow these guidelines to help your system function at its best, and protect our lakes and groundwater:

  • Chemical or biological additives can have negative affects to your system. Ask a licensed professional before using.
  • Have your septic system inspected annually.
  • Pump septic tanks every three to five years or before it reaches 40% full of scum and sludge. A licensed professional can make recommendations during annual inspections.
  • Keep a grass cover over the drainfield to help consume some of the nutrients available and aid in evapotranspiration.
  • Do not allow trees to grow over the system. Roots from the trees can cause damage to lines and plug them.
  • Do not drive over an absorption drainfield. Compaction from vehicles will cause settling, shifting or breakage of lateral lines.

Pumping frequency is driven by the number of people using household water and the percentage of the year the house is occupied. A licensed professional can determine if the tank needs to be pumped and can perform any required maintenance including checking for potential tank leaks and evaluating performance. Keeping a record book of all system maintenance procedures will provide a reminder for annual system maintenance and assist homeowners in fulfilling their responsibility for safe and effective sewage and wastewater treatment.

University of Idaho

Physical Address:
1031 N. Academic Way,
Suite 242
Coeur d'Alene, ID 83814

Phone: 208-667-2588

Fax: 208-664-1272



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