Sand filters are sand-filled basins or trenches that capture, temporarily store, and filter stormwater runoff. Sand filters can be designed as surface filters or underground filters. The design guidelines in this section focus on surface sand filters. Sand filters require less space than other filtering practices but must be in locations with adequate elevation to provide the necessary hydraulic head. Sand filters have higher longevity than other filtering practices and generally have a lower land requirement than bioretention basins.

Sand filters are frequently designed to infiltrate but are always equipped with an underdrain to capture filtered water and assist with drainage from the system. Following pretreatment, stormwater is temporarily stored above the surface of the sand filter and flows downward through a layer of sand that filters the runoff before discharging from the system through an underdrain or into the underlying soil via infiltration. Pollutants in runoff are treated in sand filters through the processes of settling, filtration, and adsorption. Surface sand filters may also be used to provide stormwater quantity control when designed as on-line facilities.

Sand filters are better suited for impervious drainage areas. They are not recommended for use in pervious drainage areas where high sediment loads, and organic material can clog the sand bed.