a succession of three typhoons caused almost complete turnover and mixing of the reservoir by August, although this had no adverse effect on the overall quality of the stored water, which continued to be very satisfactory throughout the year. Summer inflows reduced the salinity only slightly from 260 parts per million (p.p.m.) expressed as sodium chloride (NaCl) to 230 p.p.m. by November, the total of all dissolved salts being then 310 p.p.m. A further 794,000 fish fry bred by the Agriculture and Fisheries Department were introduced, bringing the total number stocked to 1.769 million and for the first time since initial impoundment in 1967 no algal blooms were experienced.
Water Treatment
10.71 Full-scale trials in dosing polyelectrolyte chemicals to improve sedimentation in clarifiers at Sha Tin treatment works were begun, with a view to increasing the efficiency of treatment and reducing operating costs.
10.72 Experimental dosing of an emulsifier to a salt water flushing system was carried out as a possible means of controlling infestation of pipes by marine molluscs, with encouraging results.
Quality of Supply
10.73 The concentration of dissolved salts in Plover Cove Reservoir was about 7 times greater than in other reservoirs, consequently the chemical quality of supply continued to be variable, depending on the area served and the degree of blending of different qualities of water. Principal characteristics given in p.p.m. were as follows:
Hardness (as CaCO3) Salinity (as NaCl) Total dissolved salts Average 43 ... ... Range 15-80 14-250 45-360 100 158Fluoridation of supplies, started in 1961 to reduce dental decay in children, continued, the average level achieved being 0.8 p.p.m. fluoride compared with a nominal target of 1.0 p.p.m.
10.74 The standard of bacteriological quality of supply aimed at throughout the distribution system is absence of coliform organism in 100 millilitres of sample. Of 2,658 samples taken regularly from service reservoirs 99.89% conformed to this standard. Random samples
148
a succession of three typhoons caused almost complete turnover and mixing of the reservoir by August, although this had no adverse effect on the overall quality of the stored water, which continued to be very satisfactory throughout the year. Summer inflows reduced the salinity only slightly from 260 parts per million (p.p.m.) expressed as sodium chloride (NaCl) to 230 p.p.m. by November, the total of all dissolved salts being then 310 p.p.m. A further 794,000 fish fry bred by the Agriculture and Fisheries Department were introduced, bringing the total number stocked to 1.769 million and for the first time since initial impoundment in 1967 no algal blooms were experienced.
Water Treatment
10.71 Full-scale trials in dosing polyelectrolyte chemicals to im- prove sedimentation in clarifiers at Sha Tin treatment works were begun, with a view to increasing the efficiency of treatment and reducing operating costs.
10.72 Experimental dosing of an emulsifier to a salt water flushing system was carried out as a possible means of controlling infestation of pipes by marine molluscs, with encouraging results.
Quality of Supply
10.73 The concentration of dissolved salts in Plover Cove Reservoir was about 7 times greater than in other reservoirs, consequently the chemical quality of supply continued to be variable, depending on the area served and the degree of blending of different qualities of water. Principal characteristics given in p.p.m. were as follows:
Hardness (as CaCO3) Salinity (as NaCl)
Total dissolved salts
...
...
Average
Range
15-80
43
14-250
...
...
100
45-360
158
Fluoridation of supplies, started in 1961 to reduce dental decay in children, continued, the average level achieved being 0.8 p.p.m. fluoride compared with a nominal target of 1.0 p.p.m.
10.74 The standard of bacteriological quality of supply aimed at throughout the distribution system is absence of coliform organism in 100 millilitres of sample. Of 2,658 samples taken regularly from service reservoirs 99.89% conformed to this standard. Random samples
148
No comments yet.
Private notes are available after approval.