Pocket Sand Filter System Components
Simplified low cost alternative
Primarily for very small sites
Level spreader, grass filter, plunge pool pretreatment
Exfiltration or underdrain system
Cover crop with pea gravel window
Notes:
The pocket sand filter is a simplified and low cost design that may be used on smaller sites. Runoff is usually diverted within a manhole. A bypass pipe sends excess runoff along the storm drain system, and a flow diversion pipe routes the water quality volume into the system. Pretreatment is provided by a concrete flow spreader, a grass filter strip and a plunge pool. The filter bed is also a relatively simple affair. A shallow basin is excavated, and contains the sand filter layer. Most of the water quality volume is temporarily stored above the filter bed. The surface of the filter bed contains a soil layer and grass cover crop. In the event of clogging, the pocket sand filter has a pea gravel �window� to direct runoff into the sand, as well as a cleanout and observation well. In most cases, the filtered runoff is allowed to exfiltrate into the underlying soils, although underdrains may be needed if the soils are not suitably permeable.