On-Site Sewage and Septic Tanks

What is an On-Site Sewage System (OSS)? 

An on-site sewage system is defined by the Washington Administrative Code (WAC) as an integrated arrangement of components for residence, building, industrial establishments or other places not connected to public sewer system which:

1) Convey, store, treat and/or provide subsurface treatment and disposal on the property where it originates, upon adjacent or nearby property; and

2) Includes piping, treatment devices, other accessories, and soil underlying the disposal component of the initial and reserve areas.

---

Looking to install a new on-site sewage disposal system, or replace a failing one?  Contact the Environmental Health Department for an On-Site Sewage Disposal Permit Application.  A site evaluation may be necessary as well.  The purpose of the site evaluation is to determine the "soil criteria" of the location.  The majority of soil found in Whitman County is silt loams, and are excellent soils for a drainfield.  Sandy clay or strongly cemented or firm soils are unsuitable for treatment or disposal.  The proposed location must provide enough area for the new system plus area for a replacement system.  (This is typically 100 linear feet per bedroom). 

Depth and texture of soil are important variables in deciding what type of septic system is suitable for a location.  The depth of unsaturated, original, undisturbed soil between the bottom of a disposal component and the highest seasonal water table is called the "Vertical Separation". It is this distance that will determine the type of on-site sewage disposal system can be used.

Greater than 16'', but less than 3'-Pressure Mound System

Greater than 3'- Pressure-Distribution System

4' or less- Mound System

5' or more- Traditional On-Site Sewage System

Sample Backhoe Trenches

 

Click here for the list of approved septic system installers and pumpers for 2010.

Adobe Acrobat Reader must be installed on your computer to open PDF's. Click the icon at the left to download and install the Reader for free.

---

Septic Tanks & On-Site Sewage Information

A quick reference guide that covers the essentials of home septic tank maintenance. Provides sludge measurement techniques, cleanout frequency, and explanations of household "do's" and "don'ts."

This bulletin presents an overview of on-site home sewage treatment systems, both conventional and alternative. Discussion includes aerated tanks, septic tanks, drainfields, site evaluation, fill systems, evapotranspiration systems, incinerating toilets, composting toilets, graywater systems, and sand filters.

This bulletin provides basic scientific background on the role of soils in wastewater treatment. This information relates to the principles behind Washington's rules and guidelines on issuing permits for and designing on-site wastewater treatment (septic) systems. Subtopics include: chemical properties of soil surfaces, soil microorganisms and soil environment, chemical components of wastewater, microorganisms in wastewater, and practical  considerations.

Explains how a septic system using a sand filter works. Describes maintenance and troubleshooting for the tank, pump chamber, drainfield, and replacement area.

Printed copies of the on-site sewage information are available from Washington State University's Extension Office.  For additional information visit them online at http://ext.wsu.edu/, or http://www.whitman.wsu.edu/.  Visit the Whitman County Extension offices at:

WSU Cooperative Extension - Whitman County
310 North Main, Room 209
Whitman County Public Service Building

Second Floor
Colfax, WA  99111

Phone: 509-397-6290
Fax: 509-397-6256

---

 Washington State Department of Health's website has additional information on managing on-site wastewater systems.  The Wastewater Management Program is designed to:

• Protect public health by promoting the safe treatment and disposal of domestic and other non-industrial wastewater in areas of Washington not served by municipal sewage treatment works.

• Provide assistance to local health jurisdictions regarding on-site wastewater issues.

• Review and approve plans for large on-site sewage systems.

For questions, please contact the Wastewater Management Program at wastewatermgmt@doh.wa.gov, or call 360-236-3062.

---

Home*A*Syst begins with checklist questions to identify problem areas:

 

*How safe is your drinking water?

*Do you use and store household hazardous products safely?

*Is there lead-based paint in your home?

 

When you find potential concerns, Home*A*Syst can help you develop an action plan to reduce the risks.

 

By examining daily routines in and around the home, we can all learn to better protect our health and the quality of the environment. Home*A*Syst is a good place to start!

 

---

The Environmental Protection Agency (EPA) announces a new and improved website on septic systems for  homeowners, state and local governments, and industry professionals.                              

Septic systems treat and disperse relatively small volumes of wastewater from individual or small numbers of homes and commercial buildings. Septic system regulation is usually a state, tribal, and local responsibility. EPA provides information to homeowners and assistance to state and local governments to improve the management of septic systems to prevent failures that could harm human health and water quality.

---

Need Additional Information?