Guide · Soils and septic
Florida soil map for septic: hydric soils, hydrologic groups and the permit
Find the lot in the USDA soil survey and read two ratings: whether its main soil is hydric, and its hydrologic group, where D or a split group such as A/D means water sits near the surface for part of the year. Those ratings warn you; they do not decide. The septic permit rests on a site evaluation by the county health department under Chapter 62-6 of the Florida rules, which looks at the soil and the wet-season water table on the lot itself.
Step 1: find the lot's map unit
The soil survey divides each county into map units: polygons drawn by soil scientists, each named for the soils in it, such as a fine sand on 0 to 5 percent slopes. On the Web Soil Survey, draw an area of interest around the lot and open the map unit's description. Most units hold one main soil and smaller patches of others, so a lot can sit on an inclusion the map does not draw.
If the unit is called Urban land, the survey mapped the ground as already built over and gives no rating at all. That is common: 912,941 Florida parcels sit on the single unit "Urban land, 0 to 2 percent slopes".
Step 2: read the hydric rating
A hydric soil formed under saturation, flooding or ponding long enough to go without oxygen near the surface. A Yes on the main soil does not make the lot a wetland, but it does say water stood there long enough to mark the soil. For a drainfield, that is the first warning.
Step 3: read the hydrologic group
The group rates how fast water soaks in when the soil is wet. Group A is sandy and takes water fast; D takes it slowly, or has a water table close to the surface. Florida has many split groups. The National Engineering Handbook gives A/D, B/D or C/D only to wet soils whose water table rises within 24 inches of the surface: the first letter is how the soil behaves once drained, the second how it behaves as it is. A/D is the most common rating under Florida parcels after plain A, which is why sandy ground can still fail a septic evaluation.
Step 4: know what the permit looks at
Since 1 July 2021 the Department of Environmental Protection has run Florida's septic program, which used to sit with the Department of Health. The county health department offices still take the application and do the evaluation and inspections. The standards are Chapter 62-6 of the Florida Administrative Code.
- The site evaluation (rule 62-6.006) bores the lot, reads the soil's texture down the profile and rates it slightly, moderately or severely limited.
- The wet-season high water table must sit at least 24 inches below the bottom of the drainfield. Where it does not, the system is often raised on fill, which costs more and changes the lot's grade.
- The soil survey is one of the references the rule names, beside what the evaluator finds in the borings. The borings win.
The soils under vacant lots, by county
| County (vacant residential lots) | Lots with a map unit | Hydric main soil | Group D or split D | Group A |
|---|---|---|---|---|
| Brevard | 45,324 | 55.3% | 88.6% | 11.0% |
| Collier | 15,268 | 48.6% | 80.4% | 12.5% |
| Lee | 116,967 | 34.9% | 78.8% | 1.8% |
| Volusia | 34,136 | 30.1% | 60.9% | 38.0% |
| St. Lucie | 15,929 | 27.3% | 83.4% | 14.8% |
| Charlotte | 86,567 | 21.5% | 84.1% | 1.5% |
| Polk | 40,515 | 11.9% | 45.7% | 52.2% |
| Levy | 18,809 | 4.7% | 12.7% | 83.7% |
| Alachua | 8,286 | 3.3% | 22.2% | 69.1% |
| Marion | 75,940 | 2.7% | 7.5% | 91.4% |
The split is coastal against ridge. On the flatwoods of Brevard, Charlotte, Lee and St. Lucie, four in five vacant lots sit on a soil rated D when wet. On the sand ridges of Marion and Levy, most are plain A. Statewide, the water management inventory records 1,982,878 parcels as on septic, known or likely; 41.0% of them sit on a group D or split-D soil and 13.3% on a hydric one. Those systems work because they were designed for the site, often mounded, which is what a buyer on the same soil should budget for.
Where the map stops
- One point per parcel. We read the soil at the parcel's centre. A large tract can span several map units; turn the soils layer on to see them all.
- Fill and ditches. The survey describes the natural soil. A lot that was filled or drained can behave differently, either way.
- Vacant lots have no septic record. The inventory describes what serves a building. In St. Lucie, Lee and Marion, 92.6% of vacant residential lots carry its NA code, so look at what the neighbours use.
- No perc test. Nothing on a map replaces the evaluator's borings.
On Map Views
Open a parcel and the report's Soil line gives the map unit's name, its hydrologic group and whether its main soil is hydric; the Sewer, water line gives the Department of Health inventory's own terms, such as LikelySeptic or KnownWell. In the Layers tab, the Soils folder draws the map units with their symbols from close zoom, and Septic and well, in the Parcels folder, labels every parcel's record, so you can read a whole street. The wetlands, flood zone and 5-foot contours sit in the same report and tabs; more in the vacant land checklist, building on wetlands and elevation and contours for a lot.
The soil survey and the water management inventory are shown as the USDA and the Department of Health published them. The county health department's site evaluation and permit under Chapter 62-6 are the authority on whether a lot can take a septic system.