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Land Buyers’ Septic System Guide for Oklahoma

If you are buying land in a residential or commercial area that cannot be connected to a municipal or city sewer system, you will need an on-site septic system to treat wastewater. Decisions that pertain to on-site septic systems in Oklahoma are based on soil properties in the area of interest.

 

A septic system labeling the pipe, soil, septic tank and absorption field.

 

You have to investigate before you invest!

 

Important Note: This material is meant to be a septic systems guide for initial screening of potential properties to buy. Before you decide to purchase a property, contact your local Oklahoma DEQ office at:

 

http://www.deq.state.ok.us/eclsnew/localOffices.htm

 

How to go about your investigation?

 

1. Open up an internet browser

and access the Web Soil Survey (WSS) by going to: http://websoilsurvey.nrcs.usda.gov.

 

Click “Start WSS” to begin

 

Start WSS

 

 

2. Locate your Area of Interest (AOI)

at the left side of the webpage, click “Address” under Quick Navigation.

 

The Area of Interest form on the Web Soil Survey with sections labeled "search," "area of interest," "import AOI," "Quick Navigation," "Address," "State and County."

 

 

  • Type-in the address of your interest and click "view" button  to open a pageshowing a map that include your AOI.
  • Click the "zoom" button and zoom-in to the location of your AOI.
  • Click either of the "AOI" buttons to establish the boundaries of your AOI on the map.
  • After setting boundaries, click “Soil Map” to view boundaries of soil mapping units.
  • A page, like the one below, will show the names and percent area covered as well as the location of each soil mapping unit in the AOI.

 

3. Extract the information about the soil mapping units in the AOI

 

The soil mapping form with a search bar and map unit legend.

 

 

  • Click the Map Unit Name to view the Map Unit Description of each soil mapping unit.

 

A report-map unit description showing "Payne County, Oklahoma 45-Refrow silt loam, 1 to 3 percent slopes Map Unit Setting Landscape: Uplands Elevation: 800 to 1,300 feet Mean annual precipation: 34 to 39 inches Mean annual air temperature: 57 to 60 degrees F Frost-free period: 200 to 215 days."

 

  • Scroll down to particularly focus on the following site and soil properties:
  • Slope: if less than 10 percent, the system may require more advanced wastewater distribution system.
  • Depth from surface to restrictive feature and to water table: preferably less than 48 inches.
  • Frequency of flooding and ponding: this should be “none.” If there is potential for flooding and ponding, the area should NOT be used for onsite septic systems.
  • Drainage class: Preferably “Well-drained.”
  • Devote particular attention to description of Typical Profile.

 

A Typical profile labeled "0 to 9 inches: Silt loam, 9 to 16 inches: Silty clay loam, 16 to 31 inches: Clay, 31 to 80 inches: Clay."

 

  • Determine the soil texture classifications in the upper 48 inches.
  • Important Note: Soils can be highly variable. Texture classes listed in the WSS should be viewed as best estimate.

 

4. Identify the finest soil texture class (or the soil with greatest fraction of fine separates) in the upper 48 inches.

 

How do I know which textural class is the finest? Use the Textural Triangle.

 

Trends in the Textural Triangle
  • Soil textural classes at the top of the triangle are finer than those at the bottom.
  • Soils at the right are finer than those at the left.

 

A textural triangle with each side labeled "Clay Separate, %,"Silt Separate, %," "Sand Separate, %," and 10 through 100; the inside is divided into groups labeled clay, sandy clay, silty clay, clay loam, silty clay loam, sandy clay loam, sand, loamy sand, sandy loam, loam, sily loam and silt.

 

5. Determine under what Oklahoma DEQ Soil Group does the finest soil identified in step 4 belong

Soil Group  

Corresponding Soil Textural Class

1

  • Coarse Sand
  • Loamy Coarse Sand

2

  • Sand
  • Loamy sand (not including coarse sand or loamy coarse sand)

2a

  • Sandy loam

3

  • Sandy clay loam
  • Loam
  • Silt loam with < 20% clay
  • Silt

3a

  • Sandy clay without slickensides with moderate and strong soil structure
  • Silt loam with > 20% clay

4

  • Clay loam
  • Silty clay loam

5

  • Sandy clay with slickensides or weak soil structure
  • Clay
  • Silty clay

 

6. Determine what Septic System Option that may be permitted in the area of interest.

           
      Septic System Options    
    Conventional System Low Pressure Dosing Field With Aerobic Treatment Units 
  Soil Group     Drip Irrigation Field Spray Irrigation Field
  1 not allowed allowed

-depending upon the depth to the restricting layer or the water table
allowed

-depending upon the depth to the restricting layer or the water table
allowed
  2 allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed
  2a

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed
  3

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed
  3a

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed
  4

allowed

-depending upon the depth to the restricting layer or the water table

allowed

-depending upon the depth to the restricting layer or the water table

allowed


-depending upon the depth to the restricting layer or the water table

allowed
  5 not allowed not allowed

allowed

-depending upon the depth to the restricting layer or the water table

allowed

 

Other Septic System Options

  • Evapotranspiration/Absorption (ET/A)System - allowed in all soils but requires an area of at least 1 acre.
  • Lagoons - allowed in all soils but requires an area of at least 2 ½ acres.

 

Estimated Cost of Septic Systems

For a three-bedroom family home, the following are the estimated cost (as of 2013):

     
 

Conventional System

$3,000 - $4,000

 

Low Pressure Systems

$4,500 - $5,000

 

Aerobic Treatment Units

Spray Irrigation

Drip Irrigation

 

$5,500 - $6,000

$7,500 - $8,000

 

ET/A Systems

$4,000 - $12,000

 

Online Resources

Oklahoma rules on septic systems: http://www.deq.state.ok.us/eclsnew/index.htm Oklahoma Certified Installers Association: http://www.ocia.s5.com

 

For more information about onsite septic systems, contact:

Dr. Sergio Abit

Dept. of Plant and Soil Sciences, OSU

Stillwater, OK

Phone: (405)744-9586

E-mail: sergio.abit@okstate.edu

http://nonagriculturalsoils.okstate.edu/


Prepared with some information gathered by Paige Klein.

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