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− | This method of determining [[design infiltration rate]] is only approved for sandy native soils with d<sub>10</sub> between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)<ref>San Francisco Public Utilities Commission. (2017). Determination of Design Infiltration Rates for the Sizing of Infiltration‐based Green Infrastructure Facilities. Retrieved from http://sfwater.org/modules/showdocument.aspx?documentid=9681</ref>. This method is not allowed within areas of fill. | + | This method of determining [[design infiltration rate]] is only approved for sandy native soils with d<sub>10</sub> between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)<ref>San Francisco Public Utilities Commission. (2017). Determination of Design Infiltration Rates for the Sizing of Infiltration‐based Green Infrastructure Facilities. Retrieved from http://sfwater.org/modules/showdocument.aspx?documentid=9681</ref>. This method must not be applied within areas of fill. |
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| ==Procedure== | | ==Procedure== |
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| ===Data Analysis=== | | ===Data Analysis=== |
− | # 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. | + | # 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: |
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| # Soil permeability shall be considered to be the measured infiltration rate: | | # Soil permeability shall be considered to be the measured infiltration rate: |
| + | <math>K=C\cdot {\left (d_{10}\right )^{2}}</math> |
| + | {{plainlist|Where: |
| + | ''d<sub>10</sub>'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), |
| + | ''C'' = is a shape fitting parameters (see below), and |
| + | ''K'' = permeability (mm/hr) |
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| + | ==Safety Correction Factor== |
| + | Adjust it! |
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− | K = C (D10)
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− | 2
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− | Where K is in cm/s, C = 1, and D10 is the soil particle diameter in mm for which 10% of all soil
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− | particles are finer (smaller) by weight.
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− | 2. Adjust the measured infiltration rate using the correction factor described in Section 4 to
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− | establish the Design Infiltration Rate in inches per hour (in/hr).
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