Changes

This method of determining [[design infiltration rate]] is only approved for native Clean Sand and Dune Sand (SP) with d₁₀ between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable). This method is not allowed within areas of fill.

This method of determining [[design infiltration rate]] is only suitable for coarse-textured native soils with d₁₀ 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>.  

# Collect [[soil]] samples for each defined soil layer below the bottom of the proposed infiltration facility. Layers must be evaluated to the following depths, depending upon facility type:

## 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].

'''This method shall not be applied within areas of fill or in regions where hydraulic conductivity is controlled by vertical fractures in the soil matrix.'''

# As the Soil Grain Size Analysis method is only approved for soils with D10 between 0.1 and 2.5 millimeters, the Hazen formula (below) may be used to calculate the soil permeability (K). Soil

K = C (D10)

==Procedure==

2

Where K is in cm/s, C = 1, and D10 is the soil particle diameter in mm for which 10% of all soil

particles are finer (smaller) by weight.

2. Adjust the measured infiltration rate using the correction factor described in Section 4 to

#* 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 water storage reservoir depth, but not less than 3 m.  

 

NB:  The Hazen formula method of estimating soil permeability based on grain size distribution analysis is only suitable for coarse-textured soils with d₁₀ 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>f=C\cdot {\left (d_{10}\right )^{2}}</math>

 

*''d₁₀'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), median value of all samples tested.

 

! colspan =2| Shape factors (C) to yield f in mm/h

 

==Don't forget to apply [[Design infiltration rate#Safety correction| a safety correction factor]] before beginning your sizing calculations==