Visual Inspection for Filtration Practices

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

Visual inspection (level 1) is useful for identifying obvious problems with a filtration practice. Visual indicators that the filter media may be clogged include: standing water more than 48 hours after a storm event, the presence of a visible layer of fine material (i.e., mud) on the surface of the filter, or a lack of vegetation. If standing water is present in a filtration practice 48 or more hours after a storm event, the practice is not functioning as designed. A layer of fine material on the surface of the sand filter is an indication that stormwater was present for an extended period of time such that fine material was allowed to settle out of the stormwater. A lack of vegetation may indicate that stormwater inundates the filtration practice longer than normal dry surface vegetation can withstand. Underground filtration practices will not have vegetation, so this criterion is not indicative of a failing underground filtration practice.

A simple approach for visual inspection of a filtration practice involves inspecting the practice approximately 48 hours following a large storm event to look for standing water. A properly functioning filtration practice should filter and treat the maximum volume for which the filtration practice was designed (i.e., design storm) in 48 hours or less (Claytor and Schueler 1996). Thus, the presence of standing water after 48 hours suggests that the filtration system may be clogged. Storms larger than the design storm will likely overflow the filtration practice (e.g., through the emergency spillway), and the amount of stormwater runoff captured by the filtration practice should still drain within 48 hours. Smaller storms are expected to drain in less than 48 hours. Visual inspection of filtration practices should be conducted at least annually.

Checklists have been developed to simplify visual inspection for filtration practices, which are available for download here:

Visual Inspection Checklist

Once visual inspection is complete, the appropriate maintenance can be selected and scheduled. 

Continue to Scheduling Maintenance or to Capacity Testing.

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