Today, instead of a perc test, a soils evaluation and Site Registration are done. A Site Registration filed with the Environmental Health Division registers the findings of the soils evaluation in a particular spot. It states soil conditions when the evaluation was done, and what type(s) of septic system could be used on the site according to current regulations.
Soils Evaluation Process
Holes are dug five to seven feet deep. The texture, compaction and color of the soil are analyzed. Using State standards, this information is then used to determine not only the percolation rate but also the soils limitations.
A soils evaluation can be done at any time of year. Soil color will give indications of soils that may be seasonally wet. If there is a disagreement or uncertainty about a seasonal water table, a decision should be delayed until the site is observed through the winter months.
Digging the Test Holes
Usually two holes are required, however, each site is different. Sites where soils are marginal or where soil types vary over a short distance may require more than two holes. Test holes are usually dug 50 to 100 feet apart, usually using a backhoe. They must meet Department of Labor & Industries standards. They must be large enough for a person to get in and out of. If you wish to dig your own test holes, contact Environmental Health for more information.
The holes should be dug in the location of the proposed drainfield. Your designer should determine this, but here are a few hints:
- Downhill from the house site if possible.
- Stay away from swales and drainage ways, and areas that are seasonally wet.
- Keep 100 feet away from all wells and surface water, including irrigation ditches.
- Septic systems cannot be located on slopes in excess of 45% (24 degrees).
- It is helpful if property boundaries and the proposed house site are marked ahead of time.
Refilling Test Holes
It is the property owner's responsibility to refill test pits. This should be done as soon as possible after the soils have been evaluated. Unfilled test pits may be a danger to wildlife and man. The owner may be liable for injuries or loss if the test holes are not refilled.
Is it true that some areas can ‘perc' too well or not at all?
Yes. Sites with soils that drain too fast require a special (alternative) system to treat the sewage more effectively before it goes into the drainfield. Although alternative systems allow more sites to be developed, they cannot solve all problems. For example, some sites do not have deep enough soils, or have shallow water tables. Some sites do not have room for required setbacks to be met. These constraints may prevent approval of a septic permit.
How long is a Site Registration good for?
A Site Registration does not have an expiration date. It simply states soil conditions at the time the evaluation was done. It is sometimes necessary to re-evaluate the soil if conditions change. For example, a building location may require the drainfield to be in a different area. Vegetation removal or logging may significantly deplete the soil, or stormwater may damage the site.
Please Note: A Site Registration does not allow your site to be `grandfathered´ for the specified type of system at some future date. At the time of installation, any septic design must meet current codes.