Septic reserve area
A septic reserve area is ground held back for a replacement drainfield, should the first one fail or prove inadequate. Where Virginia's onsite sewage regulation or Carroll County's subdivision ordinance requires one, it equals 50 percent of the required drainfield area.
The same 50 percent, triggered two different ways
Two rules can call for a reserve area on a Carroll County lot. They share a percentage and not much else.
| Point | Virginia onsite sewage regulation | Carroll County subdivision ordinance |
|---|---|---|
| Trigger | An estimated or measured percolation rate that exceeds 45 minutes per inch | Drainfields for onsite septic or sewage systems in a subdivision |
| Size | A separate area equal to 50 percent of the required absorption area | 50 percent of the required and permitted drainage field |
| The ground itself | Sufficient suitable soils must be available for both the system and the reserve | No structure may be built on it |
| Rule | 12VAC5-610-710 and 12VAC5-610-500 | Subdivision ordinance, April 14, 2014 text as posted |
Read across the table and the difference is the trigger. The state rule turns on the soil: the reserve is required where the estimated or measured percolation rate exceeds 45 minutes per inch. Carroll County's rule turns on subdividing: the ordinance asks for a 50 percent reserve on subdivision drainfields and bars structures on it. The county's rule is local and broader within its scope, and neither one stands in for the other.
each such area shall reserve a fifty percent (50%) reserve area for the construction of a replacement facility, should the first facility fail or prove inadequate
Carroll County Subdivision Ordinance, April 14, 2014 text
The reserve exists for a drainfield that has not been needed yet, and that is the reason to keep it open. Under the state rule, sufficient suitable soils have to be available for both the absorption system and the reserve, so the reserve has to be suitable soil too, not whatever ground is left over.
Where the reserve gets fixed: on the subdivision plat
A reserve area matters most before anyone builds, because that is when it gets drawn.
Where a local ordinance requires health department review of subdivision plats, 12VAC5-610-360 has the reserve area, when one is required, identified for each lot before the department signs the plat, and each lot still needs its own construction permit before building begins.
What a reserve takes off a lot, and whether a given lot needs one, belongs to the septic reserve area answer. What a sewage site and reserve on every lot does to the number of lots a tract can hold is part of land development and feasibility.
Trying to read the reserve area on a plat?
Send the plat or the tax map number, and Lowell will point to where on the drawing and its notes a reserve area would show up. No cost, no obligation.
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We'll be in touch shortly with an honest read.
Questions about this term
Can a house addition go on the reserve area of a Carroll County subdivision lot?
No, according to the county's subdivision ordinance as posted. It requires a reserve area equal to 50 percent of the drainfield and states that no structure may be constructed on it, which keeps the ground open for a replacement facility. Confirm the current ordinance text, and where the reserve falls on a specific lot, with the county and the local health department.
Where this page's facts come from
Every rule, office and figure above traces to one of these. Rules change; check the office before you act on one.
- 12VAC5-610-710: reserve absorption area Virginia Administrative Code
- 12VAC5-610-500: suitable soils for the absorption system and reserve area Virginia Administrative Code
- 12VAC5-610-360: review of subdivision plats for individual sewage disposal systems when required by local ordinance Virginia Administrative Code
- 12VAC5-610-700: easements for absorption systems on another owner's property Virginia Administrative Code
- Subdivision Ordinance, April 14, 2014 Carroll County, Virginia