A private well and a septic system on one Central Ohio lot

Across rural London, West Jefferson, Richwood, and Ashville, most homes have two systems in the ground: a well that brings water up and a septic system that sends it back down. They coexist safely when they are spaced, built, and maintained properly. Here is what that means in Ohio, and what an owner can check without calling anyone.

The distance Ohio requires

Ohio's private water system rule, OAC 3701-28-07 (effective January 1, 2020), sets isolation distances between a private well and possible sources of contamination. Any component of a sewage treatment system has to be at least 50 feet from the well. Leaching pits, drywells that were never properly abandoned, and leaching privies must be at least 100 feet away. The state septic rules apply the same 50-foot separation from the sewage side.

Those distances govern wells and systems built or replaced under the current rules. Older farmsteads can have wells and tanks placed long before, occasionally much closer together, and an old dug well or cistern is sometimes closer still.

If you do not know where both are, find out before you plant, build, or dig anything new.

Why the soil changes the risk

A septic system protects groundwater by giving effluent enough unsaturated soil to filter through before it reaches the water table. Ohio's septic rules require a minimum vertical separation between the bottom of the soil absorption component and the first limiting condition: 18 inches by default, and 36 inches where a site sits over high-risk conditions such as fractured bedrock or an aquifer.

Central Ohio has both extremes. The dense till across Madison and Union counties drains slowly, which limits how much effluent the soil will accept but also slows its movement toward groundwater. The sandy, gravelly outwash along the Scioto in Pickaway County is the opposite: the county soil survey warns of possible pollution of underground water supplies when those soils are used for sewage disposal, and the Ohio Division of Geological Survey counts outwash among the state's most productive sources of groundwater. A well drilled into outwash near an older septic field deserves closer attention.

Test the water every year

EPA's guidance for private well owners is to test annually for total coliform bacteria, nitrates, total dissolved solids, and pH, and to test more often when infants, pregnant or nursing household members, or older adults live in the home, or after repairs, flooding, or a noticeable change in taste, odor, or clarity.

For a well near a septic system, three results matter most:

• Total coliform positive: the well may be drawing in surface water or shallow groundwater. Check the cap, the casing, and the grading around the wellhead before blaming the septic system.
• E. coli positive: fecal contamination is present. Stop drinking the water and get guidance from the county health district.
• Nitrate creeping up over several years: a sign of nutrient loading, which can come from fertilizer, livestock, or septic effluent.

One result is a snapshot; five annual results are a trend you can act on.

Warning signs above ground

• A well casing that ends at or below grade, or a missing or cracked well cap
• Surface water ponding around the wellhead after rain
• A soggy or striped septic field uphill of the well
• A basement floor drain that backs up during wet weeks, pointing to a stressed field
• Old wells or cisterns on the property that were never properly sealed

Sorting out the likely source

A positive bacteria result near a septic system does not automatically make the septic system the cause. Start with the well itself, because a loose cap, a cracked casing, or a wellhead sitting in a low spot lets surface water straight in, and that route is common on older farmsteads. Then look at timing: a result that turns positive only after heavy rain points toward surface water or a shallow, poorly sealed well, while nitrate that climbs steadily over several years points toward a persistent source such as fertilizer, livestock, or effluent. Finally, look at the septic system's condition: a tank long overdue for pumping, a field surfacing uphill of the well, or an old drywell or leaching pit still in use somewhere on the property. The county health district can advise on retesting and on disinfecting the well, and a septic evaluation answers the other half of the question.

Maintenance that protects both systems

Keep the septic tank pumped on the interval your tank size and household call for, and keep the outlet filter clean, so solids stay out of the soil. Keep chemicals, solvents, and pesticides out of drains; EPA specifically warns against disposing of them in a septic system or dry well. Keep downspouts and sump lines from flooding the field. And protect the well: a sealed cap, a casing that rises above grade, and fuel, fertilizer, and livestock kept well away from it.

Buying a rural home with both

Book the septic evaluation and the water test in the same inspection window. Ask for the septic permit file from the county health district and the well log, which records how and how deep the well was drilled; Ohio's well logs are held by the Ohio Department of Natural Resources. Measure the distance between the well and the septic components yourself if no drawing shows it. A system inside the 50-foot distance is not automatically a crisis, but it is a reason to test more often and to plan any future septic replacement with the well in mind.

If a water test just came back positive for bacteria and you are wondering whether the septic system is involved, start with a septic evaluation and bring the lab report with you.