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As the soil grain size analysis method is only approved for soils with d<sub>10</sub> between 0.1 and 2.5 millimeters, the Hazen formula <ref>Hazen, A. (1893). Some physical properties of sand and gravel with special reference to the use in filtration. 4th Annual Report, State Board of Health, Boston.</ref> may be used to calculate the soil permeability. The calculated soil permeability shall be considered to be the measured infiltration rate:
*''K'' = permeability (mm/hr)}}
→Procedure
#* For [[permeable paving]], analyze each defined layer below the proposed facility bottom to a depth of at least 3 times the maximum depth of water within the base course, but not less than 1 m.
#* For [[permeable paving]], analyze each defined layer below the proposed facility bottom to a depth of at least 3 times the maximum depth of water within the base course, but not less than 1 m.
#* For other types of infiltration facilities serving drainage areas up to 4 Ha, analyze each defined layer below the proposed facility bottom to a depth of at least 2.5 times the maximum depth of water in the facility, but not less than 3 m.
#* For other types of infiltration facilities serving drainage areas up to 4 Ha, analyze each defined layer below the proposed facility bottom to a depth of at least 2.5 times the maximum depth of water in the facility, but not less than 3 m.
# Submit the soil samples for laboratory testing of particle size analysis according to [https://www.astm.org/Standards/D422.htm ASTM D422].
# Submit the soil samples to a certified soil testing laboratory for grain-size, or particle-size distribution analysis according to [https://www.astm.org/Standards/D422.htm ASTM D422].
===Data Analysis===
===Data Analysis===
NB: The Hazen formula method of estimating soil permeability based on grain size distribution analysis is only suitable for soils with d<sub>10</sub> between 0.1 and 2.5 millimeters <ref>Hazen, A. (1893). Some physical properties of sand and gravel with special reference to the use in filtration. 4th Annual Report, State Board of Health, Boston.</ref>. The soil permeability value estimated using the Hazen method can be considered to be the measured infiltration rate of the soil, f, in mm/h:
<math>K=C\cdot {\left (d_{10}\right )^{2}}</math>
<math>f=C\cdot {\left (d_{10}\right )^{2}}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''d<sub>10</sub>'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm),
*''d<sub>10</sub>'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), median value of all samples tested.
*''C'' = is a shape factor (see below), and
*''C'' = is a shape factor (see below)
{| class="wikitable"
{| class="wikitable"