Replacing a drain field or tank, installing a new system, or altering one requires a permit from your county health district and a registered installer under OAC 3701-29-09. A true repair that restores a damaged part, such as a baffle or lid, needs no permit, and pumping never does.
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Ohio's household sewage rules (Ohio Revised Code Chapter 3718 and Ohio Administrative Code Chapter 3701-29, in effect since January 1, 2015) sort septic work into three buckets. Under OAC 3701-29-01, a repair means fixing or replacing substandard or damaged devices to restore a system to working order, and it does not require a permit. A replacement means installing a new system in place of an existing one, and the rule adds that replacing or relocating the soil absorption component, or the component doing most of the treatment, counts as a replacement. So yes, replacing your drain field needs a permit. An alteration covers changes such as new components, an expanded treatment or dispersal area, or a change in design flow. OAC 3701-29-09 says no one may install, replace, or alter a system without a permit from the board of health, and only a registered installer may do that work. The permit comes from the district where the house sits: Hamilton County Public Health for Hamilton County outside Cincinnati, Norwood, and Springdale; the Cincinnati Health Department inside Cincinnati city limits, where systems are licensed and inspected yearly under OAC 3701-29 and the city's Board of Health regulation 00077; Butler County General Health; Warren County Health District; or Clermont County Public Health. Fees vary, so compare before you budget. Hamilton County charges $700 for a permit to install (including the $74 state fee) and $225 to $450 for an alteration depending on job cost; Butler County charges $569 to install and $510 to alter; Warren County charges $524 to install, $460 to alter, and $135 for a minor alteration; Clermont County charges $674 to install and $335 to alter. Most also require a paid site review first, and all four add a 25 percent penalty when work starts before the permit is issued. Every system also carries an operation permit, which Ohio caps at ten years between renewals. South of the river the logic is similar: under 902 KAR 10:085 a Kentucky permit to construct, install, or alter follows a site evaluation, is issued only to a certified installer or a qualifying homeowner, and expires after one year, with the Northern Kentucky Health Department handling Boone, Campbell, Grant, and Kenton counties. See our county permit guide for contacts, and our drain field services page for what a replacement involves.