Table: Statement of Water Quality Objectives (North Western Water Control Zone)
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Item |
Water Quality Objective |
Part or Parts of Zone |
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A.
Aesthetic Appearance |
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(a) |
Waste discharges shall cause no objectionable odours or discolouration of the water. |
Whole Zone |
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(b) |
Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent. |
Whole Zone |
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(c) |
Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam. |
Whole Zone |
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(d) |
There should be no recognizable sewage-derived debris. |
Whole Zone |
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(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 |
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(f) |
Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits. |
Whole Zone |
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B. Bacteria |
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(a) |
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 |
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(b) |
The level of Escherichia coli should be less than 1 per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days. |
Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones |
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(c) |
The level of Escherichia coli should not exceed 1000 per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days. |
Tuen Mun (C) Subzone and other inland waters |
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(d) |
The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive. Samples should be taken at least 3 times in one calendar month at intervals of between 3 and 14 days. |
Bathing Beach Subzones |
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C. Colour |
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(a) |
Waste discharges shall not cause the colour of water to exceed 30 Hazen units. |
Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones |
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(b) |
Waste dischareges shall not cause the colour of water to exceed 50 Hazen units. |
Other Inland Waters |
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D. Dissolved Oxygen |
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(a) |
Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the whole year; vales should be calculated as 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. |
Marine waters |
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(b) |
Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg per litre. |
Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones, Water Gathering Ground Subzones and other inland waters |
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E. pH |
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(a) |
The pH of the water should be within the range of 6.5-8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 units. |
Marine waters excepting Bathing Beach Subzones |
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(b) |
Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 units. |
Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones |
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(c) |
The pH of the water should be within the range of 6.0-9.0 units. |
Other inland waters |
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(d) |
The pH of the water should be within the range of 6.0-9.0 units for 95% of samples collected during the whole year. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 unit. |
Bathing Beach Subzones |
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F. Temperature |
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(a) |
Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 degrees Celsius. |
Whole zone |
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G. Salinity |
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(a) |
Waste discharges shall not cause the natural ambient salinity level to change by more than 10%. |
Whole zone |
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H. Suspended Solids |
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(a) |
Waste discharges shall neither cause the natural ambient level to be raised by more than 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities. |
Marine waters |
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(b) |
Waste discharges shall not cause the annual median of suspended solids to exceed 20 mg per litre. |
Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones |
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(c) |
Waste discharges shall not cause the annual median of suspended solids to exceed 25 mg per litre. |
Other inland waters |
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I. Ammonia |
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(a) |
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 |
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J. Nutrients |
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(a) |
Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants. |
Marine waters |
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(b) |
Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 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). |
Castle Peak Bay Subzone |
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(c) |
Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 05 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). |
Marine waters excepting Castle Peak Bay Subzone |
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K. 5-day Biochemical Oxygen Demand |
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(a) |
Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 mg per litre. |
Tune Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones |
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(b) |
Waste discharges shall not cause the 5-day biochemical oxygen to exceed 5 mg per litre. |
Other Inland Waters |
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L. Chemical Oxygen Demand |
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(a) |
Waste discharges shall not cause the chemical oxygen demand to exceed 15 mg per litre. |
Tune Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones |
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(b) |
Waste discharges shall not cause the chemical oxygen demand to exceed 30 mg per litre. |
Other Inland Waters |
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M. Toxins |
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(a) |
Waste discharges shall not cause the toxins in water to 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 toxicant interactions with each other. |
Whole Zone |
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(b) |
Waste discharges shall not cause a risk to any beneficial use of the aquatic environment. |
Whole Zone |
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N. Phenol |
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(a) |
Phenols shall not be present in such quantities as to produce a specific odour, or in concentration greater that 0.05 mg per litre as C6H5OH. |
Bathing Beach Subzones |
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O. Turbidity |
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(a) |
Waste discharges shall not reduce light transmission substantially from the normal level. |
Bathing Beach Subzones |