Construction Phase

5.77

4.35

No-dig method using Horizontal Directional Drilling (HDD) would be used for the installation of outfall pipe of about 480 m from shore to minimize the potential water quality impacts arising from the dredging works required for the submarine outfall construction.

Silt curtains will be installed around the exit area of the pilot drill.

Marine works site /

During construction of submarine outfall

Contractor

Ö

5.73 – 5.78

4.36

Dredging Works

Implementation of following measures during the dredging works:

·          dredging should be undertaken using closed grab dredgers with a maximum total production rate of 55m³/hr;

·          deployment of 2-layer silt curtains with the first layer enclosing the grab and the second layer at around 50m from the dredging area while dredging works are in progress;

·          dredging operation should be undertaken during ebb tide only;

·          all vessels should be sized such that adequate clearance (i.e. minimum clearance of 0.6m) is maintained between vessels and the sea bed at all states of the tide to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;

·          all pipe leakages should be repaired promptly and plant should not be operated with leaking pipes;

·          excess material should be cleaned from the decks and exposed fittings of barges before the vessel is moved;

·          adequate freeboard (i.e. minimum of 200mm) should be maintained on barges to ensure that decks are not washed by wave action;

·          all barges should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;

Marine works site and at the identified water sensitive receivers/

During construction

Contractor

Ö

·          loading of barges should be controlled to prevent splashing of dredged material to the surrounding water, and barges should not be filled to a level which will cause the overflow of materials or polluted water during loading or transportation; and

·          the decks of all vessels should be kept tidy and free of oil or other substances that might be accidentally or otherwise washed overboard.

5.79

4.37

Construction Run-off and Drainage

Implementation of the following site practices outlined in ProPECC PN 1/94 for “Construction Site Drainage”

·          Provision of perimeter channels to intercept storm-runoff from outside the site.  These should be constructed in advance of site formation works and earthworks.

·          Works programmes should be designed to minimize works areas at any one time, thus minimizing exposed soil areas and reducing the potential for increased siltation and runoff.

·          Sand / silt removal facilities such as sand traps, silt traps and sediment basins should be provided to remove the sand / silt particles from run-off. These facilities should be properly and regularly maintained. These facilities should be carefully planned to ensure that they would be installed at appropriate locations to capture all surface water generated on site.

·          Careful programming of the works to minimise soil excavation works during rainy seasons.

·          Exposed soil surface should be protected by paving or hydroseeding as soon as possible to reduce the potential of soil erosion.

Construction works sites

Contractor

Ö

ProPECC PN 1/94

·          Trench excavation should be avoided in the wet season, and if necessary, these should be excavated and backfilled in short sections.

·          Open stockpiles of construction materials on site should be covered with tarpaulin or similar fabric.

5.80

4.38

General Construction Activities

Debris and rubbish generated on-site should be collected, handled and disposed of properly to avoid entering the nearby coastal waters and stormwater drains. All fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank. Open drainage channels and culverts near the works areas should be covered to block the entrance of large debris and refuse.

Construction works sites

Contractor

Ö

5.81

4.39

Wastewater Arising from Workforce

Portable toilets should be provided by the Contractors, where necessary, to handle sewage from the workforce. The Contractor should also be responsible for waste disposal and maintenance practices.

Construction works sites

Contractor

Ö

5.96

Section 4

Water quality monitoring 

Designated water monitoring locations/ throughout construction period

Contractor

Ö

EM&A Manual

Operation Phase

5.84 – 5.90

4.40

The following mitigation measures and contingency measures implemented in order to minimize the potential impact from emergency discharge on the nearby FCZ:

·          Provision of standby pump at all pumping stations and the STW in case of pump failure;

·          Provision of standby generator at all pumping stations in case of interruption of electrical power supply;

·          Provision of 24-hour temporary storage for all pumping stations in emergency;

·          Use of SBR units as storage tanks in case STW failure;

·          No emergency discharge is allowed at Pumping Station P2 and the STW;

·          Automatically shutdown the pumping station at Lo So Shing in case of Pumping Station P1a failure;

·          Automatically shutdown the upstream pumping stations (Pumping Station P1a and Lo So Shing pumping station) in case of Pumping Station P1b failure;

·          Automatically shutdown the upstream pumping stations (including Pumping Stations P1a and P1b, and Lo So Shing pumping station) in case of Pumping Station P2 failure;

·          Automatically shutdown all pumping stations (including Pumping Stations P1a, P1b and P2, Lo So Shing and Mo Tat Wan Pumping Stations) in case of STW failure;

·          Implement a telemetry system to ensure prompt action to be undertaken in an emergency occasion.

Proposed pumping station & STW

DSD/Contractor

Ö

Ö

5.83

4.42

The proposed STW would provide a full secondary level sewage treatment with nitrogen removal and UV disinfection.

STW / During operation of the STW

DSD

Ö

5.92

4.41

A detailed emergency response plan for emergency discharges based on the major components in Appendix 5.4 should be prepared during the subsequent detailed design stage.

Pumping stations and STW / During operation phase

DSD

Ö

Ö

5.96

Section 4

Water quality monitoring 

Designated water monitoring locations/ 1 year following operation of the STW

DSD

Ö

EM&A Manual