Cindy writes: When is the best time to have a perc test done? I am supposed to have a perc done next week. There has been snow and unusually cold temperatures lately so I’m not sure this is a good time. I want to move forward with the test so I can submit my building plans to the county and get the permits, which can take several weeks. I really don’t want to delay the perc unless it is necessary.
Steve Bliss, of BuildingAdvisor.com, responds: A perc test measures the rate at which water is absorbed (percolates though) the soil. The time of year can definitely affect perc test results as well as the level of the water table, which is also a concern. In general, the driest season will yield the best results since dry soil readily absorbs water and the water table is lowest.
Soil saturated with water from rain or melted snow will not perc well. A site will also fail if the water table is too high, although most towns require that the tester identify the seasonal high water table by observing the soil in an excavated hole — called a deep hole test.
Frozen soil will also not absorb water readily, but typically you will be excavating below the frost line, allowing cold weather testing. If there’s a delay between excavating and testing, it’s best to cover the hole and possibly add some hay or other insulation to keep the ground from freezing before the test is done.
Many towns specify the time of year that a test can be done and who can do it. Some require that testing be done in the wetter months as they want to test the site under worst-case conditions. After all, your septic system has to work all seasons of the year. Regardless, the standard procedure is to soak the soil in the test hole before measuring the perc rate. In effect, they are simulating wet spring conditions to minimize seasonal effects on test result.
Also every municipality has different rules about what test numbers are acceptable and what options are available for “alternative” systems in poor soil. Check with your local building department or health department about this. Also local septic system inspectors and installers can be a great source of information about local soil conditions and regulations – as well as the options (and their costs) for sites that are not suitable for a conventional system.
You should make any offer to purchase a lot contingent on it passing a perc test. If an alternative system is required, you may be able to negotiate a reduced price to help pay the higher price tag — typically $25,000 plus — for a mound system or other alternative system.
Read More about Perc Testing and Alternative Septic Systems.
See Also:
Are Alternative Systems Allowed?
Chamber System Failure
How Much Slope For Septic Line?
Inspecting a Septic System
Lifespan of Septic System’
Minimum Lot Size For Septic System
Perc Test Cost
Perc Test: Best Time of Year?
Replacing Failed Drain Field in Same Location
Retesting a Site That Failed to Perc
Sand Filter for Existing System
Testing an Existing Septic System
Testing for a New Septic System
Wet Sites, Septic Systems For
Who Performs Perc Test?
View all SEPTIC SYSTEM articles
Cathy Kowalski says
Should I Avoid Perc Test After Rain and Snow?
I have learned a lot about perk tests on your site, thanks. Next week, the engineer, who is designing our new Title 5 (Massachusetts) septic system, is planning to do a perk test in my small backyard after a very heavy snowstorm predicted this Monday-Tuesday. We also had rain and snow today, earlier this week, and last week. I am very worried that I am jinxed by all this bad weather. What do you think?
buildingadvisor says
All things being equal it’s better to do a perc test in dry weather. Perc tests measure the absorption rate of the soil and dry soil absorbs water faster than wet soil. However, since the standard procedure is to soak the soil in the hole prior to the test, the actual effect of seasonal conditions is minimized.
Heavy rain and melting snow can also raise the water table, another concern, since towns require that the seasonal high water table be at least a few feet below the drain field. They normally identify the seasonal high water table by observing the soil in a test pit.
If the soil is so saturated that the perc test holes fill with water, they cannot perform the test until conditions are drier. In some cases, the engineers may leave PVC pipes sticking out of the ground as observation wells to monitor the level of the water table.
Since you are testing in January in New England, frozen soil is also a concern. You cannot test in frozen soil as it does not absorb water well. Tests are generally done below the frost line, but it is important to insulate the top of the hole to prevent freezing once the hole is dug. Engineers in your area should be familiar with cold weather procedures.
I would encourage you to contact the engineers to discuss your concerns. It never hurts to ask questions and you may end up delaying your test until more favorable conditions prevail.
James says
Are Old Perc Test Results Valid?
How long is a perc test usually good for. Can I use the results of someone else who was previously going to purchase the land?
buildingadvisor says
In most jurisdictions, perc test results are valid for 2-5 years, but can often be updated for a fee as long as the original test was recorded properly in the town records. In general, the test “runs” with the land, not the owner. So, in theory, the test results should be transferable to you.
But, as with all things septic, state and local rules vary a great deal from one location to another. Check with your local health or building department. Don’t make any assumptions.
Read more at these links: How Long Are Perc Tests Valid? Are Perc Tests Transferable?