Environmental Impact Assessment Ordinance

Technical Memorandum

Annex 6


1. General Criteria

1.1 The Aquatic Environment

1.1.1 Criteria for protection of the aquatic environment against water pollution include consideration of all the aquatic components: water quality, hydrology, bottom sediments, and ecology.

1.2 The Water Quality Objectives (WQOs)

1.2.1 Under the Water Pollution Control Ordinance (WPCO), the Water Quality Objectives (WQOs) are established in terms of measures of physical, chemical and biological water quality in each WCZ to achieve the required level of protection of the beneficial uses. Based on the beneficial uses, the WQOs can be broadly categorised as follows:

  1. Aesthetic Enjoyment: criteria concerning these aesthetic characteristics are general and descriptive. They depend on subjective senses of sight, smell, taste and touch. Criteria include, without limitation,:

    • not to cause discolouration of water;
    • not to cause visible matters on the water surface;
    • not to cause tainting of seafood.

  2. Human Health: criteria concerning the quality of water for abstraction of water for potable water supply and irrigation, waters for bathing and other recreational purposes; and contamination of seafood. Key criteria include:

    • to limit the maximum levels of E.coli and other pathogenic indicators in waters where shellfish are harvested, in mariculture zones, or in waters used for bathing and other recreational proposes;
    • to prevent concentration of substances that will accumulate in water, sediment or biota, from reaching the levels that are harmful to human health.

  3. Aquatic Life: criteria concerning protection of the water quality to maintain the integrity and balance of the aquatic ecosystem. Criteria include:

    • not to alter the natural properties e.g. turbidity, temperature, salinity, pH and dissolved oxygen of the water to such an extent that will upset the maintenance and the balance of primary and secondary production;
    • not to cause alteration of the hydrology or increases in nutrient inputs that lead to eutrophication or objectionable algal growth;
    • to prevent concentration of persistent, bio-accumulative and toxic substances from reaching harmful levels;
    • not to alter the physical environment e.g. hydrology and sedimentation, that lead to aggravation of water pollution.

  4. Industrial Use: criteria concerning prevention of deleterious chemicals, floatables, settleable matters, and biological growths affecting important industrial uses of the water such as that for cooling systems or for shipping.

1.3 The Mixing Zone Criteria

1.3.1 It is not always necessary to meet all water quality criteria in all areas to protect the integrity of the aquatic environment. The Authority under the WPCO may allow for the receiving water quality not to meet water quality criteria. These areas e.g. water near the sewage outfall discharge, are subjected to greater impacts and are called mixing zones. A mixing zone is therefore a region of a waterbody where initial dilution of a pollution input takes place and where water quality criteria can be exceeded. The WQOs must be met at the boundary of a mixing zone. The characteristics of a mixing zone such as the size, siting, shape, quality, depend on the assimilative capacity of the receiving system and are determined on a case-by-case basis. In general, the criteria for acceptance of a mixing zone are that:

  1. it must not impair the integrity of the water body as a whole;
  2. it must not interfere with the migratory pathways of important species to a degree which is damaging to the ecosystem;
  3. it must not endanger sensitive uses e.g. beaches, breeding grounds, or diminish beneficial uses;
  4. it must not result in the accumulation of substances to such levels as to produce significant toxic effects in human or aquatic organisms;
  5. within a mixing zone the following basic water quality criteria shall be met

    • materials not in such concentrations that settle to form objectionable deposits;
    • floating debris, oil, scum, and other matter not in such concentrations that form nuisances; and
    • substances not in such concentrations that produce objectionable colour, odour, taste, or turbidity.

1.4 Waters under Stressed Conditions

1.4.1 A water body is defined as stressed if the existing water quality is in breach of or likely to breach the water quality objectives or that necessary to protect the beneficial uses designated for that particular water body. A water body under stress must be protected against further degradation, using the following criteria:

  • activity must not contribute to, increase or perpetuate stressed conditions;

  • activity must not retard recovery of the water body if level of pollution from other sources decrease.

1.5 Cumulative Impacts

1.5.1 Cumulative impacts occur when multiple inputs of pollutants enter the same aquatic environment, leading to overlapping zones of exposure, or where there is cumulative reduction in assimilative capacity such as due to reclamations. Cumulative impact over a period of time shall also be considered. Criteria for evaluation are based on identification of all the pollution inputs and their impact zones, and the determination of the assimilative capacity of the water body that encompasses all or most of the overlapping zones of influence.

2. Activity / Project Specific Criteria

These criteria are to supplement and to be considered in conjunction with the General Criteria.

2.1 Waste Discharges

2.1.1 Criteria for control of waste discharges are outlined in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM) issued under section 21 of the Water Pollution Control Ordinance. The TM sets the limits that make effluents acceptable for discharge. These limits on the physical, chemical and microbial quality of the effluents are imposed in licences issued under the Water Pollution Control Ordinance by the relevant authority. For large discharges or discharges into sensitive areas e.g. stressed water, criteria for discharges shall be determined on the basis of the assimilative capacity of the receiving water body and more stringent standards than those stipulated in the TM may apply.

2.2 Dumping of Wastes

2.1.2 Criteria for acceptability and control of dumping of wastes in the aquatic environment are governed by the Dumping at Sea Ordinance. The criteria laid down in the annexes to the London Dumping Convention also apply.

2.3 Stormwater Runoff

2.3.1 Criteria for control of diffuse pollution shall be based on measures to control pollution at source and to abate pollutants in the stormwater runoff. These criteria are to be met through the implementation of Best Management Practices (BMPs) which include, but not be limited to:

  1. erosion and sedimentation control;
  2. runoff quantity and quality control;
  3. identification and elimination of point source discharges;
  4. prevention of "first flush" pollution;
  5. elimination of discharges into poor flushing areas except artificial wetlands designed for pollution abatement.

2.4 Toxic and Prohibited Substances

2.4.1 The criteria are that there shall be no threat to ecological and human health and that pollution must be controlled at source by pollution prevention, pretreatment, and recycle and reuse. Substances that are toxic, persistent and accumulative in water, sediment or biota, and that cannot be rendered harmless by dilution, dispersion and other natural processes of the aquatic system and for which no numerical water quality criteria are available must be controlled vigorously at source with the ultimate aim to achieve complete elimination. Discharges of substances of high-level radioactivity are prohibited.