Environmental Guidance Note for Sewage Pumping Stations which is not a Designated Project

6. Environmental Considerations and Mitigation Measures for Sewage Pumping Station

6.2 c.  Water
 
i. avoid the occurrence of sewage bypass/overflow which would have detrimental impacts on the quality of the receiving water bodies;
(Note : sewage bypass/overflow should be prohibited except during an emergency in order to avoid danger to life or property. All practicable measures for avoidance of sewage bypass have to be carefully considered and adopted before considering the need of sewage bypass. The sewage pumping station operator is required to prepare a contingency plan detailing the procedures to handle sewage bypass and the mitigation measures to be taken to reduce the likely environmental impact. Should sewage bypass be unavoidable, the bypass duration should be restricted to the practicable minimum through good planning of the sequence of works in advance and through adoption of the appropriate method of works. EPD should be consulted beforehand and provided with a detailed account of the proposed temporary mitigation measures for treating the bypassed sewage.)
ii. provide standby pumps and screens to facilitate maintenance and repairing of equipment;
iii. provide back-up power supply for larger pumping station (handling dry weather flow (DWF) larger than 1500 m3/day). Back-up power supply could be in the form of dual power supply (ring main), or an automatic-operated emergency generator with sufficient capacity to cope with the demand loading of essential plant equipment. When none of these measures can be implemented, consultation with EPD is required;
iv. whereas the provision of a ring main may not be feasible for a smaller pumping station (handling DWF up to 1500 m3/day), provide an automatic-operated emergency generator with sufficient capacity. If neither form of back-up power supply can be provided, the discharge points of the overflows should be located no less than 150m from sensitive receivers such as bathing beaches, mariculture zones, seawater intakes, marinas, boat parks, nature reserves, sites of special scientific interest and marine parks/marine reserves. Otherwise, a two-hour storage capacity, measured from pump cut-in level, and under average DWF should be provided. For those sewerage systems with spare capacity even under daily peak flow condition, the spare capacity can be used to make up the two hour storage requirement, but the availability of such spare capacity would have to be demonstrated;
v. for unmanned pumping stations, provide telemetry system to the nearest manned station/plant so that swift action can be taken in the case of malfunction of the unmanned facilities;
vi. for both manned and unmanned facilities, provide a hand-cleaned bar screen to cover the lower half of the opening of any overflow bypass. This will prevent the discharge of floating solids into receiving water bodies as far as practicable while ensuring flooding at the facilities will not occur even if the screen is blocked. The clear spacing of the bar screen should normally be about 25mm;
vii. keep discharge points of the bypass below the low water mark;
viii. keep discharge points of the bypass away from sensitive receivers such as gazetted beaches, mariculture zones, seawater intakes, water gathering grounds, streams with water for human consumption and so forth, and waters with low assimilative capacity such as typhoon shelter or embayed waters;
ix. follow the appropriate guidelines for the handling and disposal of site discharges as stipulated in the ProPECC PN 1/94 "Construction Site Drainage" during construction.
  d.  Waste
 
i. Screenings should be properly handled to avoid causing odour and hygienic nuisance;
ii. de-water screenings and sludge before disposal at strategic landfills;
iii. for chemical waste,
 
  • use good quality containers compatible with the chemical wastes to be stored;
  • store incompatible chemical wastes separately;
  • securely label each container according to the chemical waste characteristics, i.e. explosives, flammable, oxidizing, irritant, toxic, harmful, corrosive, etc.;
  • provide a dedicated storage area for large quantity of chemical waste. For those less than 300 litres of storage capacity, chemical waste storage cupboard could be used;
  • inspect chemical waste storage areas regularly and provide warning signs; and
  • provide good training for staff in charge of handling chemical waste on site and provide them with proper equipment and safety/protective device suited for the job.

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