Soil can filter, treat wastewater

Farming became a major industry in northwestern Ohio because the area was blessed with naturally fertile soils ideal for crop production.
However, farmers were unable to take advantage of this resource until drainage systems were built in the latter part of the 1800s to remove excessive soil water so crops could be planted and grown in a timely manner.
Just as soils can be used to raise food, they can also be used as a filter to treat wastewater in ways to protect existing ground and surface water. The ability of the soil to treat wastewater is very important for anyone who isn’t tied in to a municipal sewer system.
Layers of the proper type of soil can remove suspended solids, organic material, ammonia, bacteria and viruses in wastewater. However, the pores of these soils must be fine enough to trap the suspended solids and disease-causing organisms in the wastewater.
The soil must also have sufficient pore space to allow adequate populations of aerobic microorganisms that will feed on and degrade organic material and ammonia. Besides the right pore space, these soils must be deep enough to have the capacity to absorb viruses and potential water pollutants such as phosphorus.
Four feet or more of unsaturated soil above a limiting physical feature is necessary to protect the environment and public health. Types of limiting features found in Ohio include seasonable high water tables, hard bedrock, dense clays and glacial till zones, and zones of gravel and sand.
In our area, only about 1 percent of soils have depths greater than 3 feet before hitting a limiting condition for wastewater treatment. The majority of our soils have a depth of 12 to 18 inches before a limiting condition.
Seasonable high water tables account for most of the limiting features, and for some soils, a dense till sublayer. This should not be a surprise, since many of the fields in our area have surface and subsurface drainage systems and most basements and crawl spaces have sump pumps.
Historically, wastewater systems for rural homes relied on a buried leach field. These systems are fine when the soil depth is 3 to 4 feet before a limiting barrier. Otherwise, the leech field may prevent sewage from reaching the surface of the yard or backing up into the house, but it will fail to remove pollutants from the wastewater.
In our area, most soils are not deep enough for a leach field to adequately protect the environment and groundwater. In fact, depending on the county in our area, 39 to 80 percent of the soils are less than 1 foot in depth before hitting a limiting feature.
Engineers have developed alternative systems to leach fields for wastewater treatment in shallow soils. These systems are more complicated, require more maintenance, and are more expensive than the traditional leach field.
Northwestern Ohio has been blessed with abundant natural resources that include our productive soils and our abundant sources of water. However, all of us must work together to protect these resources for future generations.
Our state Legislature is currently discussing ways to reduce phosphorus losses from farm fields to protect the Lake Erie watershed. Proper treatment of wastewater will also be discussion point for communities as we work together to protect our environment and ensure safe water for the public.
More information on treating wastewater may be found in Extension Bulletin 896, Suitability of Ohio Soils for Treating Wastewater ( and Bulletin 813, Mound Systems for Onsite Wastewater Treatment: Siting, Design, and Construction in Ohio (
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.


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