On Site Wastewater Treatment Systems

6. On-Site Wastewater Treatment Systems

On-site wastewater treatment systems serve an estimated over 93 percent of the land and approximately 40 percent of the watershed people and homes (See Figure 27).

Figure 27: On-Site Wastewater Treatment
	Total Acres	Total People	Total Homes
On-Site Areas	331,500	28,141	10,339
Entire Watershed	355,600	71,456	25,813
Percentage On-Site	93.2%	39.4%	40.1%

A variety of systems exist in the watershed but the most common system is a septic system which treats domestic wastewater through soil-based leaching. In order for a septic system to function properly two feet of “useable” soil is needed to properly treat and remove all bacteria and viruses for wastewater. Very few “useable” soils exist in the watershed because the soils are limited by poor or excessive drainage, seasonably high water table, low soil permeability rates, and a variety of other limitations. Figure 28 below provides an overview by county of soil suitability for the placement of septic systems.

Figure 28: Percent of Soils Suitable for Placement of listed Onsite Wastewater Treatment Systems
County	Acres	Traditional or Mound	Mound only	Onsite w/ Irrigation	Non Suited (hydric)
Champaign	277,120	1.9%	45.2%	29.1%	23.8%
Franklin	344,064	3.8%	18.1%	62.1%	16.0%
Logan	294,464	1.7%	35.0%	39.6%	23.7%
Madison	296,320	0.4%	16.1%	45.3%	38.2%
Pickaway	322,560	7.0%	45.5%	26.2%	21.3%
Union	277,760	1.4%	14.2%	54.2%	30.2%
Statewide		6.4%	25.4%	49.1%	19.1%
Watershed Avg.		2.7%	29.0%	42.8%	25.5%

Source: Mancl and Slater, 2002. Suitability of Ohio Soils for Treating Wastewater. The Ohio State University Extension. Appendix 1

County Health Departments attempted to overcome severe soil limitations through the installation of alternative systems such as aeration systems and sand filters. Aeration systems were designed to create an aerobic treatment system in which air would be incorporated into the holding tank to promote the growth of oxygen-using bacteria. Newer aeration systems then discharge into a small absorption field for additional treatment whereas older systems may discharge to tiles, ditches, or streams. In order to create the aerobic treatment process a mechanical device is necessary to pump or agitate the wastewater. Such systems require additional maintenance to ensure that proper treatment. There are approximately 1,076 known aeration systems in the watershed (See Figure 29).

Figure 29: Aerators by County
County	Known Aerators
Champaign	10
Franklin	674
Logan	20
Madison	96
Pickaway	34
Union	242
Total	1076

Health Department officials from each county estimated there were an additional 10 to 25 percent more aeration systems existing in the watershed that were not yet documented.

As mentioned above sand filters have been installed in areas across the watershed that suffer from soil limitations due to high seasonal water table or low permeability rates. The installation of sand filters was a common practice in Union County in the past. Currently, the installation of sand filters is discouraged but still occurs under certain circumstances. As previously stated, two feet of “useable” soil is necessary to treat wastewater effectively. In situations where less than two feet of useable soil is available, sand is used in place of the soil to assist in the treatment process. However, sand does not effectively treat bacteria and viruses. Elevated bacteria levels were found throughout the watershed (See IV. Water Quality for additional information on Ohio EPA sampling results for bacteria). The exact number of sand filters in the watershed is not known at this time.

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Last updated: June 09, 2008.