Statement of Water Quality Objectives (North Western Supplementary Water Control Zone)
(Enacting provision omitted—E.R. 6 of 2020)
[24 September 1999]
(Format changes—E.R. 6 of 2020)
The water quality objectives set out in column 1 of the Schedule are established for those parts of the North Western Supplementary Water Control Zone set opposite those water quality objectives in column 2 of the Schedule.
In this Statement—
Map (地圖) means the map marked NWSWCZ and described as “NORTH WESTERN SUPPLEMENTARY WATER CONTROL ZONE”, signed by the Secretary for Planning, Environment and Lands on 3 September 1999 and deposited in the Land Registry; (21 of 2024 s. 78) Secondary Contact Recreation Subzone (次級接觸康樂活動分區) means an area delineated as such on the Map.
| Water Quality Objective | Part or Parts of Zone | ||
| A. | AESTHETIC APPEARANCE | ||
| (a)Waste discharges should not cause any objectionable odour or discolouration of the water. | Whole zone | ||
| (b)Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent. | Whole zone | ||
| (c)Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam. | Whole zone | ||
| (d)There should be no recognizable sewage-derived debris. | Whole zone | ||
| (e)Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent. | Whole zone | ||
| (f)Waste discharges should not cause the water to contain substances which settle to form objectionable deposits. | Whole zone | ||
| B. | BACTERIA | ||
| The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in a calendar year. | Secondary Contact Recreation Subzones | ||
| C. | DISSOLVED OXYGEN | ||
| Waste discharges should not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the whole year; values should be calculated as the water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 m of the seabed for 90% of the sampling occasions during the whole year. | Whole zone | ||
| D. | pH | ||
| Waste discharges should not cause the natural pH range of the water to be extended by more than 0.2 unit. In addition, the pH of the water should be in the range of 6.5‒8.5 units. | Whole zone | ||
| E. | TEMPERATURE | ||
| Waste discharges should not cause the natural daily temperature range to change by more than 2.0oC. | Whole zone | ||
| F. | SALINITY | ||
| Waste discharges should not cause the natural ambient salinity level to change by more than 10%. | Whole zone | ||
| G. | SUSPENDED SOLIDS | ||
| Waste discharges should not cause the natural ambient level to be raised by more than 30% or give rise to accumulation of suspended solids which may adversely affect aquatic communities. | Whole zone | ||
| H. | AMMONIA | ||
| The un-ionized ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean). | Whole zone | ||
| I. | NUTRIENTS | ||
| (a)Nutrients should not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants. | Whole zone | ||
| (b)Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). | Whole zone | ||
| J. | TOXIC SUBSTANCES | ||
| (a)Toxic substances in the water should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to interactions of toxic substances with each other. | Whole zone | ||
| (b)Human activity should not cause a risk to any beneficial use of the aquatic environment. | Whole zone |