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.
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