144 NEW WATER SUPPLY SYSTEM AT TAMPA, FLORIDA.

 A novel sludge drainage system has been installed as indicates on
 Figs. 16 and 17. Through the first half of each settling basin, a serial of
 lateral drains, consisting of 6-in. vitrified bell and spigot pipe tees, have en
 laid in the floor of the basin, with the branch of the tee pointed up an et
 flush with the finished floor. A 6-in. vitrified plug, with a 1-in. orifice, Was
 placed in each bell. Sloping concrete ridges separate the rows of 1ipe.
 The underdrains are connected up to the headers at the side of the brain
 which collect and discharge from sections consisting of five lines of unjir-
 drains. Each header is controlled by a gate valve and discharges in a
 12-in. cast-iron pipe leading to the sewer. By opening the gate valve,,lthe
 water in the basins is utilized to flush out the sludge which has ien
 Deposited over the bottom of the basin.
















 FIG. 15. SETTING BASIN.
 An interesting feature of the sludge drainage system is that it m'
 be backwashed with water under moderate pressure so that if the slude
 surrounding the drains becomes hard or caked it may be loosened. As:i
 great portion of the sludge is deposited in the first half of the basins, it wp
 not considered necessary to continue this construction through the second
 half. A 4-in. flushing line with hose nozzles has been provided for cleanij
 this portion of the basins. I
 Conduits. Because of the wide variations in the character of the water
 to be treated, a great deal of attention was given to the attainment of
 flexibility in operation so that any order or combination of treatment would
 be possible. This flexibility is secured by means of an additional conduit
 serving the various mixing tanks and settling basins, together with addi-
 tional inlet and outlet openings controlled by stop planks.
 Figure 17 shows the construction used. One wall along the mixixi
tanks and settling basins has been made double and contains a bank of foit
conduits. The upper or raw-water conduit conveys the raw water to any
 !' f