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Agreement No. CE 98/98 Environmental Impact Assessment Preliminary Design and Ground Investigation for Widening of Final Report Yuen Long Highway Between Lam Tei and Shap Pat Heung Interchange December 2001 5. WATER QUALITY 5.1 Introduction This Chapter presents an assessment of the potential for the YLH widening scheme to impact upon the aquatic environment and includes the following: · definition of applicable water-related legislation; · a description of the existing water environment along the YLH corridor; · the identification and preliminary assessment of the potential impacts during the project’s construction and operation; · recommendation of potential mitigation measures for the amelioration of adverse impacts such that the proposed scheme can proceed without significant impact upon the aquatic environment; and · a preliminary identification of monitoring requirements. 5.2 Government Standards and Legislation Under the Water Pollution Control Ordinance (WPCO), Hong Kong waters are divided into Water Control Zones (WCZs). Each WCZ has a designated set of statutory Water Quality Objectives (WQOs). The majority of the YLH lies within the Deep Bay Water Control Zone (WCZ) which was declared on 1 December 1990. WQOs for the Deep Bay WCZ are detailed in Table 5.1. Any discharge to the Deep Bay WCZ is required to comply with the standards specified in the Technical Memorandum on Standards for Effluents into Drainage and Sewerage Systems, Inland and Coastal Waters (WPCO, Cap 358,S.21) (referred to hereafter as the Technical Memorandum on Effluent Standards). Inland waters are divided into four different zones based on their beneficial use. It is likely that the inland waters of the Study Area will be defined as Group B which have beneficial uses for irrigation and are those waters draining agricultural areas in the New Territories. In the event that the ponds in the area are used for culture, the standards are those for Group C. As such, depending on classification and the selected effluent disposal method, any discharges from the site to receiving waters will be required to meet the standards given in Table 5.2a/b. In addition to the above, there is a “zero discharge” requirement within the Deep Bay catchment area with regard to organic wastes. The Tuen Mun River and its associated catchment at the western end of the YLH lies within the North Western WCZ. Therefore, discharges generated in this part of the highway must comply with the standards specified for the North Western WCZ as detailed in the Technical Memorandum on Effluent Standards. Scott Wilson (Hong Kong) Ltd C 64 enviro\r\98232\EIA_DFR_SEPT2001_final(7)_6_dks_5_32__1 Agreement No. CE 98/98 Environmental Impact Assessment Preliminary Design and Ground Investigation for Widening of Final Report Yuen Long Highway Between Lam Tei and Shap Pat Heung Interchange December 2001 Table 5.1 Summary of Water Quality Objectives (WQOs) for the Deep Bay Water Control Zone Water Quality Objective Part of Parts of Zone A. AESTHETIC APPEARANCE (a) Waste discharges shall cause no objectionable odours or discoloration of the water. Whole zone (b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other Whole zone substances should be absent. (c) Mineral oil should not be visible on the surface. Surfactants should not give rise to Whole zone a lasting foam. (d) There should be no recognisable sewage-derived debris. Whole zone (e) Floating, submerged and semi-submerged objects of a size likely to interfere with Whole zone the free movement of vessels, or cause damage to vessels, should be absent. (f) Waste discharges shall not cause the water to contain substances which settle to Whole zone form objectionable deposits.. B. BACTERIA (a) The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the Secondary Contact Recreation Subzones and geometric mean of all samples collected in a calendar year. Mariculture Subzone (b) The level of Escherichia coli should be less than zero per 100 mL, calculated as the Yuen Long & Kam Tin (Upper) Subzone, Beas running median of the most recent 5 consecutive samples taken at intervals of Subzone, Indus Subzone, Ganges Subzone and between 7 and 21 days. Water Gathering Ground Subzones (c) The level of Escherichia coli should not exceed 1 000 per 100 mL, calculated as Yuen Long & Kam Tin (Lower) Subzone and the running median of the most recent 5 consecutive samples taken at intervals of other inland waters between 7 and 21 days. (d) The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the Yung Long Bathing Beach Subzone geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days. C. COLOUR (a) Waste discharges shall not cause the colour of water to exceed 30 Hazen units. Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (b) Waste discharges shall not cause the colour of water to exceed 50 Hazen units. Yuen Long & Kam Tin (Lower) Subzone and other inland waters D. DISSOLVED OXYGEN (a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg Inner Marine Subzone excepting Mariculture per litre for 90% of the sampling occasions during the whole year; values should be Subzone taken at 1 metre below surface. (b) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg Outer Marine Subzone excepting Mariculture per litre for 90% of the sampling occasions during the whole year; values should be Subzone calculated as water column average (arithmetic mean of at least 2 measurements at 1 m below surface, 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 year (c) The dissolved oxygen level should not be less than 5 mg per litre for 90% of the Mariculture Subzone sampling occasions during the year; values should be taken at 1 metre below surface. (b) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg Yuen Long & Kam Tin (Upper and Lower) per litre. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters of the Zone E. pH (a) The pH of the water should be within the range of 6.5-8.5 units. In addition, waste Marine waters excepting Yung Long Bathing discharges shall not cause the natural pH range to be extended by more than 0.2 Beach Subzone units. (b) Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 Yuen Long & Kam Tin (Upper and Lower) units. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (c) The pH of the water should be within the range of 6.0-9.0 units. Other inland waters Scott Wilson (Hong Kong) Ltd C 65 enviro\r\98232\EIA_DFR_SEPT2001_final(7)_6_dks_5_32__1 Agreement No. CE 98/98 Environmental Impact Assessment Preliminary Design and Ground Investigation for Widening of Final Report Yuen Long Highway Between Lam Tei and Shap Pat Heung Interchange December 2001 Water Quality Objective Part of Parts of Zone (d) The pH of the water should be within the range of 6.0-9.0 units for 95% of Yung Long Bathing Beach Subzone samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units. F. TEMPERATURE Waste discharges shall not cause the natural daily temperature range to change by Whole zone more than 2.0 oC. G. SALINITY Waste discharges shall not cause the natural ambient salinity level to change by Whole zone more than 10%. H. SUSPENDED SOLIDS (a) Waste discharges shall neither cause the natural ambient level to be raised by 30% Marine waters nor give rise to accumulation of suspended solids which may adversely affect aquatic communities. (b) Waste discharges shall not cause the annual median of suspended solid to exceed Yuen Long & Kam Tin (Upper and Lower) 20 mg per litre. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters I. AMMONIA The un-ionised ammoniacal nitrogen level should not be more than 0.021 mg per Whole zone litre, calculated as the annual average (arithmetic mean). J. NUTRIENTS (a) Nutrients should not be present in quantities sufficient to cause excessive or Inner and Outer Subzones nuisance growth of algae or other aquatic plants. (b) Without limiting the generality of objective (a) above, the level of inorganic Inner Marine Subzone nitrogen should not exceed 0.7 mg per litre, expressed as annual mean. (c) Without limiting the generality of objective (a) above, the level of inorganic Outer Marine Subzone 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 1m above seabed. K. 5-DAY BIOCHEMICAL OXYGEN DEMAND (a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed Yuen Long & Kam Tin (Upper) Subzone, Beas 3 mg per litre. Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (b) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed Yuen Long & Kam Tin (Lower) Subzone and 5 mg per litre other inland waters L. CHEMICAL OXYGEN DEMAND (a) Waste discharges shall not cause the chemical oxygen demand to exceed 15 mg per Yuen Long & Kam Tin (Upper) Subzone, Beas litre.