Changes

The measured infiltration rate (q, mm/hr) at the proposed bottom elevation of the BMP must be divided by a safety correction factor (SCF) to calculate the infiltration coefficient: :<math>q'=\frac{q}{SCF}</math>

The measured infiltration rate (q, mm/hr) at the proposed bottom elevation of the BMP must be divided by a safety correction factor (SCF) to calculate the infiltration coefficient: :<math>q'=\frac{q}{SCF}</math>

To select a safety correction factor, calculate the ratio of the mean (geometric) measured infiltration rate at the proposed bottom elevation of the BMP to the rate in the least permeable soil horizon within 1.5 metres below the bottom of the BMP. Based on this ratio, a safety correction factor is selected from the Table below.  

To select a safety correction factor, calculate the ratio of the mean (geometric) measured infiltration rate at the proposed bottom elevation of the BMP to the rate in the least permeable soil horizon within 1.5 metres below the bottom of the BMP. Based on this ratio, a safety correction factor is selected from the Table below. Where the soil horizon is continuous within 1.5 metres below the proposed bottom of the BMP, the mean infiltration rate measured at the bottom elevation of the BMP should be divided by a safety correction factor of 2.5 to calculate the design infiltration rate.

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From the table the SCF is 3.5, and the design infiltration rate can be calculated:  

From the table the SCF is 3.5, and the design infiltration rate can be calculated:  

 

:<math>q'=\frac{q}{SCF}\ =\ \frac{30}{3.5}=\ 8.6 mm/hr</math>

 

 

would be 8.6 mm/h. Where the soil horizon is continuous within 1.5 metres below the proposed bottom of the BMP, the mean infiltration rate measured at the bottom elevation of the BMP should be divided by a safety correction factor of 2.5 to calculate the design infiltration rate.