Figure 1. Soil Suitability of Ohio Soils
On-site wastewater treatment systems collect, treat, and release about 225 million gallons of effluent per day from an estimated 1 million homes in Ohio (Source: U.S. Census Bureau, 1990). The most common on-site wastewater treatment systems are septic systems, consisting of a septic tank and a subsurface wastewater infiltration system (i.e., leachfield).
These systems use soil as the medium for treatment and, according to the Household Sewage Rule (OAC 3701-29) (1977), require a minimum of 4 feet of soil depth to a limiting condition beneath the distribution point to ensure proper treatment. Figure 1 indicates the percentage of Ohio soils suited for wastewater treatment and disposal. Only 6.4% of the land area is suited for a septic tank/leachfield system. An alternative on-site treatment system is a septic tank/mound system where up to 2 feet of sand is used to aid in wastewater treatment. These systems require 2 feet of soil depth to a limiting condition beneath the sand layer to ensure proper treatment. In Ohio, only 25.4% of the land area is suited for a septic tank/mound system. Approximately 32% of Ohio’s land area is suited for on-site wastewater treatment using these two options. Installing these systems in unsuited soils leads to incomplete wastewater treatment and the contamination of surface and ground water with nutrients and pathogens. This poses a significant risk to public health and safety.
Most of Ohio’s soil natural resource is too shallow to use for wastewater treatment. For specific soil types refer to Ohio State University Extension Bulletin 896, Suitability of Ohio Soils for Treating Wastewater. Where sufficient soil depth for treatment is not present, irrigation of treated wastewater may provide an acceptable alternative provided the following conditions are met.
Condition 1: Irrigation systems require the wastewater be treated and disinfected before the effluent can be distributed to the soil. In order to eliminate odors, treatment should achieve a reduction of Carbonaceous Biochemical Oxygen Demand (CBOD) to 25 mg/L. To minimize health risks, a reduction of fecal coliform bacteria to 20 organisms/100 ml is recommended. This is a one-log reduction from the Bathing Beach Standard of 200 organisms/100 ml. These standards can be achieved by various treatment methods including stabilization ponds or sand bioreactors followed by disinfection. Commercially available bioreactors are also used. Consult OSU Extension Bulletin 876, Sand Bioreactors for Wastewater Treatment in Ohio, for more information on constructing sand bioreactors.
Condition 2: The site must have at least 1 foot of soil depth to a limiting condition (Box 1). Natural undisturbed soil is preferred but well-established fill of 20 to 30 years is acceptable if soil structure has been established. In Ohio, nearly 49% of the land area is suited for on-site treatment and dispersal systems. Site and soil investigations are required before a system is installed, to confirm adequate soil depth. Consult OSU Extension Bulletin 905, Soil and Site Evaluation for On-site Wastewater Treatment, for details on conducting a septic system site and soil evaluation.
Permits for wastewater treatment systems are required by the Ohio Legislature under the Ohio Revised Code. The local health department issues permits for systems serving single-family homes, duplexes, or triplexes. Wastewater spray irrigation systems will require a variance from the local Board of Health with concurrence from the Ohio Department of Health.
Systems for all other building types require permits from the Ohio Environmental Protection Agency. They are issued through their district office. The Ohio Legislature now requires that an Ohio registered engineer design all systems permitted by state agencies.
Permits for wastewater treatment systems are required by the Ohio Legislature under the Ohio Revised Code. The local health department issues permits for systems serving single-family homes, duplexes, or triplexes. Wastewater spray irrigation systems will require a variance from the local Board of Health with concurrence from the Ohio Department of Health.
Systems for all other building types require permits from the Ohio Environmental Protection Agency. They are issued through their district office. The Ohio Legislature now requires that an Ohio registered engineer design all systems permitted by state agencies.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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