1975-1976

APPENDIX CC Contd.

(11) Chemical Treatment

Principal Chemicals used in treatment:

1974-75 1975-76 Long tons Average dose (parts per million) Long tons Average dose (parts per million) Fresh Water Alum 4 051 11.8 3 802 10.3 Hydrated lime 4 050 11.8 3 926 10.7 Liquid Chlorine 469 1.4 548 1.5 Sodium silicofluoride (as fluoride) 368 0.7 475 0.8 Salt Water Liquid Chlorine 107 1.7 101 1.6

(12) Quality of Supply

(a) Chemical quality (values expressed in parts per million)

1974-75 1975-76 Range Average Range Average Total hardness (as CaCO3) 10-55 31 10-36 24 Salinity (as NaCl) 8-97 39 10-74 26 Total dissolved solids 23-148 73 27-107 53 Fluoride (as F) (Target level 1.0 p.p.m.) 0.8 0.8

(b) Bacteriological quality

1974-75 1975-76 Free from Coliform No. taken orgs/100 ml Free from Coliform No. taken orgs/100 ml Samples from treatment works and service reservoirs 99.88% 3 324 100% 3 654 Samples from consumers' taps 99.24% 4 088 99.67% 5 113

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