Slide 6 of 39
Notes:
The equation above is used to size pretreatment settling basin surface area. It was derived by the Washington State Department of Ecology from the Camp-Hazen.
As = Sedimentation basin surface area (ft2)
E = Trap efficiency; which is the target removal efficiency of suspended solids (set equal to 90%)
w = Particle settling velocity; for target particle size (silt) use settling velocity = 0.0004 ft/sec (0.0033 ft/sec for I > 75%, where I is percentage impervious area)
Qo = rate of outflow from the basin; which is equal to the water quality volume (WQv) divided by the detention time (td); use 24 hours.
The equations simplify to:
As = 0.066 ( (WQV) ft2 for I < 75%
As = 0.0081 (WQV) ft2 for I >= 75%