How perc tests workand why the soil evaluation comes before them

The supporting work is a soil evaluation. The health department accepts private evaluations for a septic permit application only from a licensed onsite soil evaluator, and for subdivision review, permits and letters for residential development the Code also has it accept evaluations and designs certified by a licensed professional engineer in consultation with a licensed onsite soil evaluator, subject to the exceptions noted in step five.

The regulation tells the evaluator what to weigh: the physiographic province, the topography, the area available, the degree of slope, and the soil profile, meaning how thick each horizon is and its color, permeability and texture. Texture is estimated by field testing. Color can point to water. Under the regulation, red and yellow mottling may indicate a seasonal water table, and gray is the firmer signal: "Gray and/or gray mottlings indicate seasonal water tables for at least three weeks duration."

The purpose is written into the same regulation. The evaluation is meant to "document sufficient information to conclude whether or not the site can accommodate an onsite sewage treatment and dispersal system". It is a conclusion about the whole site, not a single measurement.

Where a conventional drainfield needs clean soil

For an in-ground system, conventional septic tank drainfield systems included, the infiltrative surface sits 18 inches or more below the original ground. With septic tank effluent, the 18 inches of soil immediately below that installation depth cannot show a limiting factor: bedrock, a seasonal or permanent water table, pans, or other impervious strata. How the tank, the lines and the drainfield fit together is set out in a conventional septic system, explained from the tank to the drainfield.

Ground the regulation rules out

• Absorption trench systems on slopes greater than 50 percent, unless terraced.
• A subsurface absorption system at the low point of a sink hole.
• A subsurface absorption system in a flood plain subject to annual or more frequent sustained (24 hours) flooding.

The soil pass, fourth of the five factors in how Bowman reads land before pricing it, is a read and not an approval. The licensed evaluator's work is what the health department acts on.

One rule runs against the instinct to tidy a homesite before anyone has looked at the soil.

The proposed site for the subsurface soil absorption system shall not be graded until the district or local health department has completed the site evaluation

12VAC5-610-700

The evaluation shows why the order matters. An in-ground system relies on a natural, undisturbed soil horizon, and the evaluator is reading the thickness, color and texture of the horizons that are actually there. Cutting or filling the ground changes the very thing being read.

The same logic follows the permit after it issues. Under the regulation a construction permit is null and void when site conditions, topography and drainage ways among them, are changed from those shown on the application or on the permit. A pad or a drive graded through the area the application shows can be exactly that kind of change.

A favorable answer is only as useful as the document it lands in, and the two documents age differently.

Certification letter

No system design required. May be recorded in the land records of the clerk of the circuit court. Transfers with title when the land is sold. A permit is issued on the basis of the letter unless there has been a substantial, intervening change in the soil or site conditions since it was issued.

Construction permit

Valid 18 months from issuance unless there has been a substantial, intervening change in the soil or site conditions. May be extended another 18 months if a building permit has been obtained or construction has commenced. Null and void when site conditions change from those shown on the application or the permit.

An older permit

Under the regulation, a permit issued under the chapter that is more than 18 months old, on which construction has not commenced, is revalidated when the site conditions are the same as those shown on the application and permit, except as a cross-referenced section provides.

That is why the paperwork matters more than the phrase on a listing. The soil evaluation documents whether a site can take a system, and a percolation test, when one is done, is only one of many criteria. What the Code carries across a sale is the certification letter: it transfers with the title, and it may be recorded in the land records of the clerk of the circuit court.

The letter carries the same condition the permit statute does: a substantial, intervening change in the soil or site conditions. Ground that has been graded, filled or built on since the letter was issued is the question to put to the local health department before anyone relies on the letter.