Page 475 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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12.5 Urban Runoff Control Practices 433

Plan view
Flow A

Grated cover
Sediment
trap

Sand
Drain

Outfall pipe

A

Section A-A
Grated cover Solid cover
6 in. 6 in.
Flow Paving
10 in.
12 in.
1 2 -in. reinforcement bars Sand
6-in. on center each way Outfall pipe
3,000 psi concrete
6 in.
Provide nipple, fittings,
etc. as required
Grate (fabric wrapped
over entire grate opening)

Figure 12.19 Schematic Design of a Sand Filter. Conversion factors: 1 in. 25.4 mm;
1 psi 6.94 kPa.
(Source: Delaware Department of Natural Resources)

12.5.6.2 Sand Fitters Sand filters are similar to the filtration basins outlined above but can
be built underground to reduce the amount of land required. These systems consist of a catch
basin for settling of heavy solids and a filtration chamber (see Fig. 12.19). Runoff enters the
catch basin and collects to the basin capacity, overflows into a sand-filled chamber that pro-
vides filtration, and is discharged through an outlet pipe in the bottom of the filtration cham-
ber. Other types of systems can be designed in conjunction with wet ponds or other practices,
using natural or imported soil banks or bottoms, to increase their pollutant removal capability.

Pollutant Removal. Sand filters use the same pollution removal mechanisms as filtration
basins and provide similar pollutant removal. Initial removal of heavy solids occurs
through settling in the catch basin and further treatment is provided by filtration through
the sand-filled chamber.
Design Considerations. The catch basin section must be designed to provide some sediment
removal and to ensure that flow enters the filtration chamber as sheet flow to prevent scouring