August 22, 2006:
Making the right decision on a sewage treatment system depends largely on soil profile. Currently, the Private Sewage Standard of Practice accepts a "soils percolation test" or a "soils particle or grain size analysis test" done by a lab to arrive at the acceptable effluent loading rate of a field or mound. Of the two tests, the latter is usually more accurate, says Joe Petryk, a senior field inspector with Alberta Municipal Affairs.
"The 'perc test' determines the rate at which water is absorbed by the soil after the test hole is saturated. If not done properly, the results can jeopardize the design of the sewage treatment system," he says.
"Meanwhile, the particle or grain size analysis test accurately establishes the amounts of clay; sand and silt in the soil and provides a soil classification to properly design the sewage treatment system. As designs of systems become more critical to prevent system failures, percolation tests are less reliable and the particle or grain size analysis is highly recommended."
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