Perc test
A perc test, short for percolation test, measures how fast water soaks into soil in test holes on a proposed septic absorption area. Under Virginia's onsite sewage regulation a percolation test may be required, and it counts as only one of many criteria within the soil evaluation.
One of many criteria, beneath the soil evaluation
Virginia's onsite sewage regulation settles the test's weight in a single sentence.
Percolation tests shall be analyzed as only one of many criteria in determining soil suitability for absorption of treated sewage.
12VAC5-610-450, Soil evaluations
The work above it is the soil evaluation, which 12VAC5-610-450 frames as a systematic look at the site and its soil profile, meant to settle whether the site can take an onsite sewage system.
The test itself is conditional. Under 12VAC5-610-450 a percolation test "may be required" as a prerequisite to a permit, and the district or local health department may require one when it questions the estimated percolation rate. The full sequence, from the evaluation through the letter and the permit, is walked through in how perc tests work.
Texture gives an estimated rate; test holes answer a doubt about it
Most of what a perc test would measure, the regulation first estimates from the soil itself.
12VAC5-610-490 sorts soils into four groups by texture and assigns each group an estimated percolation rate, in minutes per inch, for the purpose of design. When those estimated rates are in question, percolation tests may be performed, and the health department may require them to determine measured rates. That is what makes a test result a measured rate: a number taken in the ground in place of an estimate.
When tests are done, they are performed under the supervision of the district or local health department, which also has a say in where the holes go.
A hole of water cannot show everything the profile does. The regulation reads soil color for signs of a seasonal water table, a point taken up in the questions below, and estimates texture by field testing. The soil pass in the five-factor read of land looks at the same ground as a read, not an approval.
When a land ad says the lot perced
In land listings, perced is a one-word claim that can stand for several different documents.
It may mean someone ran percolation tests. It may mean a licensed onsite soil evaluator completed a soil evaluation. It may mean the health department issued a certification letter, which may be recorded in the land records and transfers with the title when the land is sold, or it may mean a construction permit. Those are not the same paper. The soil evaluation, and what the health department did with it, is what speaks to whether the site can take a system.
The practical questions each have their own answer: who orders the perc test, buyer or seller, how long a perc test takes, where to get a perc test in Carroll County, and what a failed perc test does to a signed contract.
A slow rate starts the conversation about a site; it does not end it
Because the test is one criterion, a poor result is information about one criterion.
A slow measured rate feeds the design and the soil evaluation it sits under. It is not, by itself, a ruling that nothing can be built on the land. What remains possible where the numbers came back poorly is taken up in can you build on land that failed a perc test.
Selling land that was marketed as perced?
Send the county and whatever soil papers came with the land, and Lowell will tell you which of the documents behind that word you actually hold. No cost, no obligation.
Got it. Thank you.
We'll be in touch shortly with an honest read.
Questions about this term
What is the difference between an estimated and a measured percolation rate?
An estimated rate comes from the soil itself: 12VAC5-610-490 sorts soils into four texture groups and assigns each an estimated rate, in minutes per inch, for design. A measured rate comes from percolation tests, which may be performed when the estimated rates are in question, or which the health department may require to determine measured rates. Either way, the rate is analyzed as only one of many criteria in deciding soil suitability.
Can a perc test show a seasonal water table?
Virginia's regulation looks to soil color for that, not to a percolation rate. Red and yellow mottling may indicate a seasonal water table, and gray mottling indicates seasonal water tables lasting at least three weeks. Those observations belong to the soil evaluation, which is why a perc rate alone leaves the water table question open.
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.
- 12VAC5-610-450: soil evaluations, and percolation tests as one of many criteria Virginia Administrative Code
- 12VAC5-610-490: estimated percolation rates, test holes and soil color Virginia Administrative Code
- Va. Code 32.1-164: certification letters recorded and transferred with title Code of Virginia