The water moves from the flash mixer to the flocculation basins which are baffled chambers containing horizontal paddle systems. The design of the flocculation basins results in a gentle, constant mixing of the microfloc formed during coagulation. This stirring provides maximum contact of the floc particles and promotes formation of larger and heavier floc. Once the flow is of sufficient size and density to be settled, the water moves into the sedimentation basins. After the water leaves the flocculation basins, it enters the sedimentation or settling basins.
Sedimentation is the removal of solids from water by gravity settling.
Basins are designed to hold large volumes of water for several hours and to give a smooth, even flow. This design allows the velocity and turbulence of the water to be decreased to the point that the water will no longer transport the flocculated solids and they will settle to the bottom of the basin. There are three basins of equal size that each hold about 1.4 million gallons of water. The inlet side of each basin is 16 feet deep and tapers up to a depth of 10.8 feet at the outlet. The solids that collect as sludge are periodically removed, de-watered and disposed of by landfill.