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LID SWM Planning and Design Guide β


Percolation test

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[[File:Perc_test.png|thumb|Schematic of percolation test setup]]{{TOClimit|2}}A percolation test is one way of determining a [[design infiltration rate]]. If a site disturbance must be minimized, this test can be performed in a small augered well. Adding a [[permeameter]] may speed up analysis.  ==Calculations==Percolation test results are not readily cannot be translated into field saturated hydraulic conductivity (''K<sub>fs</sub>'')by simple manuipulation of the units. However, an acceptable approximation can be made by accounting for the soil texture and by making measurements under non-saturated conditions<refname = 'Reynolds'>Reynolds, W.D., Galloway, K., and Radcliffe, D.E. (2015). "The relationship between perc time and field-saturated hydraulic conductivity for cylindrical test holes.", National Onsite Wastewater Recycling Association (NOWRA) 2015 Onsite Wastewater Mega-Conference, Virginia Beach, VA, USA, November 3-6, 2015</ref>.
The required calculations have been written into an easy to use spreadsheet, formatted for printing:
{{Clickable button|[[Media:Perc test.xlsx|Download Percolation test spreadsheet(.xlsx)]]}}
For reference, the relationship between measured percolation test (''PT'') and field saturated hydraulic conductivity (''K<sub>fs</sub>'') used in the spreadsheet is:
<math>K_{fs}=\frac{\bar{C_{i}a^{2}}}{PT_{i}\left [ 2\bar{H_{i}^{2}}+\bar{C_{i}}a^{2}+\left ( \frac{2\bar{H_{i}}}{a^*} \right ) \right ]}</math>
{{Plainlist|1=Where: *''{{overline|H}}'' = Mean water depth during a test*''a'' = the radius of the test pit *''α*'' = the representative soil sorptive number, and *''{{overline|C}}'' = is a shape function.}}Additional details may be found in the original paper<ref name = 'Reynolds'/>.
==Measurement procedure==
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Adapted from<ref>Registered Onsite Wastewater Professional Program BC, PERCOLATION TEST PROCEDURE & FORM (2016)</ref>.
# Place 5 cm of clean fine gravel in the bottom of the hole. If the sidewalls are likely to collapse, use a paper basket to support the sidewalls.
#Place a piece of white plastic or similar provided with clear marks at 12.5 and 15 cm (5" and 6") from the bottom of the test hole prior to adding the gravel. For greater accuracy a float and pointer arrangement can be set up.
# If the soil contains considerable amounts of silt or clay, and certainly for any soil with “clay” as part of the [[Soil groups|texture description]], the test holes should be pre-soaked before proceeding with the test. Pre-soaking is accomplished by keeping the hole filled with water for 4 hours or more. The water should be added carefully and slowly to avoid disturbing the soil (including the sidewall soils). The test should be carried out immediately after pre-soaking;
===Making measurements===