What is the first action in preparing the pre-treatment cells for bioretention?

• A. Excavate pre-treatment cells first and seal to trap sediments
• B. Rip bottom soils 6-12 inches
• C. Excavate bioretention from sides
• D. Install geotextile fabric

Answer: (A)

The first action is to excavate the pretreatment cell and seal it to trap sediments. Pretreatment acts as a sediment-trapping forebay that protects the main bioretention media from clogging by coarse particles. By creating this space up front and sealing it, sediments settle out before runoff moves into the main planting area, making maintenance easier and extending the life of the bioretention bed. The other steps described—ripping bottom soils, excavating the bioretention area from the sides, or installing geotextile fabric—are completed after the pretreatment cell is established or are not the initial action needed to create the sediment-trapping forebay.