Verified as of 2026-09-09. We re-check these pages quarterly.
The soil evaluation: what the county is really deciding
Every new system and most replacements in Georgia start with a site evaluation by the county sanitarian. It's the single most important step, and it's the one homeowners understand least.
What happens. The sanitarian visits the lot, digs test pits (typically with a backhoe), and reads the soil profile: texture, structure, depth to rock or a restrictive layer, mottling that shows where the seasonal water table sits. From that they classify the soil and determine the absorption rate, the required drain field size, and which system types are permitted.
What the finding controls
- Whether a conventional gravity system is allowed at all
- The size of the field per bedroom
- Whether you need a pump chamber, a mound, drip dispersal, or an aerobic unit
- Setbacks from wells, property lines, streams and the lake
This is not the contractor's call. A contractor can recommend, design and install. They cannot override the sanitarian. If a contractor quotes an engineered system before the county has evaluated the site, ask what the evaluation said.
What North Georgia soils typically produce
- Piedmont red clay (most of Cherokee, Forsyth, north Fulton): slow absorption → larger fields, often engineered on replacement
- Blue Ridge transition (north Cherokee, Dawson): shallow rock → engineered systems are the norm
- Lanier shoreline sandy loam: better absorption but high seasonal water table → elevated design
For land buyers. A site evaluation before closing tells you what a system will cost — or whether the lot supports one at all. Lots that fail evaluation are not rare in the Blue Ridge transition.
Cost impact. Conventional system $8,000–$20,000 installed; engineered $12,000–$25,000+ when clay fails the perc test (mound, ATU, drip). The evaluation is what moves you between those two lines.