Septic on the Scioto terraces around Circleville and Ashville

Most septic advice around Columbus is about soil that drains too slowly. Along the Scioto River in Pickaway County, the trouble can run the other way. Here is why lots around Circleville and Ashville need their own thinking.

Two landscapes in one county

The Soil Survey of Pickaway County groups the county's soils into broad associations, and two of them tell the story. On the uplands, the Kokomo-Crosby-Miamian association covers about 37 percent of the county: glacial till soils, with Crosby carrying a seasonal water table 12 to 36 inches below the surface. That is the same slow, wet ground found across Madison and Union counties.

Down along the river, the Eldean-Genesee-Warsaw association covers about 18 percent of the county on terraces and flood plains. Eldean soils formed over outwash, the sand and gravel laid down by glacial meltwater, and the official series description rates the permeability of that underlying material as rapid or very rapid. Genesee soils sit on flood plains subject to periodic flooding.

Same county, same health district, opposite soil problems.

Why fast-draining soil is not automatically good news

Effluent needs time in unsaturated soil to be treated. Soil that passes water very quickly can carry effluent to groundwater before bacteria and viruses are filtered out, and the Pickaway survey says as much, warning of a possible hazard of pollution to underground water supplies when those soils are used for sanitary facilities. The Ohio Division of Geological Survey notes that outwash deposits are among the state's most productive sources of groundwater, which is exactly why so many wells are drilled into them.

Ohio's septic rules respond to that risk. The default vertical separation between the bottom of a soil absorption component and a limiting condition is 18 inches, but it rises to 36 inches over high-risk conditions such as an aquifer or fractured bedrock. A design on the terraces may add pretreatment, use pressure distribution to spread small doses across the whole area instead of dumping into one end of a trench, or add sand fill to slow and filter effluent.

Flood plains add a different limit

On Genesee and similar flood plain soils, flooding is its own problem. A system that goes underwater can take in floodwater through lids and cleanouts, and a field under water cannot accept effluent at all. Flood-prone ground is a poor place for a new system, and the design options there are narrow. Existing systems benefit from watertight lids and risers and a plan for high water.

After a flood covers a system, the usual guidance is to use water sparingly until the ground drains, to hold off pumping the tank while the surrounding soil is still saturated (an empty tank in waterlogged ground can shift or float), and to have the system checked once the water recedes.

What owners on the terraces should do

• Learn which landscape you are on. The county soil survey maps and the permit file at Pickaway County Public Health will tell you.
• Keep the tank pumped on schedule and the outlet filter clean, because solids that reach a fast-draining field move straight into it.
• Test a private well every year for bacteria and nitrate, as EPA advises for all private wells.
• Keep the operation permit current if the system has a pump or aerator. Pickaway uses a one-year permit with a manufacturer-approved service contract for mechanical systems and a three-year permit for the rest, $70 either way, and the district has routinely monitored aerator systems since 1988.
• Keep lids and risers watertight, especially on lots that see standing water.

Buying on the terraces: questions to settle first

A house on the river terraces can be a fine purchase, as long as the septic questions get asked in the right order:

• Is the lot on the terrace or the upland? The answer changes what a future replacement would look like.
• Does the permit file show pretreatment, pressure distribution, or sand fill? If it does, what service does the design need, and is there a record of it being done?
• Where is the well, and how deep is it cased? Ask for the well log and the most recent water test.
• Has the property flooded? Ask the seller directly, and check that lids and cleanouts are watertight.
• Is the property inside a planned sewer project area? Check with the city or the county before assuming the septic system is permanent.
• When was the tank last pumped, and does the operation permit show current service?

Sewer is coming to some of it

Ohio EPA's 2026 Water Pollution Control Loan Fund plan lists a Circleville HSTS Elimination project at $3,044,000, a sewer extension meant to take household systems out of service. For owners inside a project area like that, the calculation changes: under Ohio Revised Code 6117.51, connection can become mandatory when the board of health ties the project to an existing health problem and the house sits within 200 feet of the sewer right-of-way. Watch the city and county notices, and go to the public meetings where assessments and deadlines get set.

The uplands are a different conversation

On the till uplands east and west of the river, the concerns match the rest of the region: perched water, slow acceptance, and a design that often ends up as a mound or drip field. The high water table FAQ covers that side.

If you own a home on the terraces and are not sure what kind of system you have or how it was designed, start with the county file and a system evaluation. A phone call is the quickest way to get the scope right.