Recommendations for Infiltration Practices

J.L. Nieber, A.J. Erickson, P.T. Weiss, J.S. Gulliver, R.M. Hozalski


During proper operation of an infiltration basin or trench, solid particles will be filtered at the soil surface as well as within the soil matrix. Over time, accumulation of solids will result in lower infiltration rates, thus the practice must be regularly inspected to insure it is functioning properly. The required frequency of inspection is dependent on the watershed land use (e.g. urban, rural, farm, etc.) and rainfall amounts and intensity, however, it is recommended that visual inspection be performed a minimum of once per year.

Synthetic runoff testing is recommended for assessment of hydraulic conductivity for small infiltration practices, if an adequate water supply is available. For assessment of hydraulic conductivity on practices too large for synthetic runoff testing, capacity testing is recommended.

Due to the inability to collect downstream water samples, pollutant removal performance of infiltration practices can be difficult, if not impossible. If collection of downstream water samples is possible and there is an adequate water supply, performance can be assessed by synthetic runoff testing. If there is not an adequate water supply, pollutant removal performance can be assessed by monitoring.


All infiltration practices are designed to reduce require regular maintenance if they are to remain effective. The required frequency of inspection and maintenance is dependent on the watershed land use (e.g. urban, rural, farm, etc.), construction practices in the watershed and rainfall amounts and intensity.

In order to increase the longevity of infiltration practices, the installation of pretreatment stormwater practices which remove large sediment and other solids upstream of infiltration practice is recommended.

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