Agreement No. CE 66/2001(EP)
EIA and TIA Studies
for the Stage 2 of PWP Item No. 215DS -
Yuen Long and Kam Tin Sewerage and Sewage Disposal (YLKTSSD)
Environmental Impact Assessment (Final)
Sections 10 to 11
Ove Arup & Partners Hong Kong Ltd
In association with Archeological Assessment, Ecosystems and Urbis
Level 5, Festival Walk, 80 Tat Chee Avenue, Kowloon Tong, Kowloon, Hong Kong
Tel +852 2528 3031 Fax +852 2268 3950
10.1 Legislation and Standards
10.3 Water Sensitive Receivers
10.4 Assessment Methodology for Construction Phase
10.5 Assessment Methodology for Operational Phase
10.6 Assessment Results and Recommendation
11.1 Legislation and Standards
11.2 Assessment Methodology For Construction Phase
11.3 Assessment Findings and Recommendations
11.4 Potential Impact During Operational Phase
11.7 Residual Environmental Impacts
11.8 Environmental Monitoring and Audit
The following legislation, standards and guidelines are considered in the water quality assessment:
* Water Pollution Control Ordinance (WPCO) CAP 358[11]: The WQOs for the Deep Bay Water Control Zone (DBWCZ) are shown in Appendix 10.1;
* Water Pollution Control Ordinance (WPCO) CAP 358[11]: The WQOs for the North Western Water Control Zone (NWWCZ) are shown in Appendix 10.2;
* Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems Inland and Coastal Waters[12]: The effluents discharge limits for the DBWCZ are shown in Appendix 10.3;
* Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems Inland and Coastal Waters[12]: The effluents discharge limits for the NWWCZ are shown in Appendix 10.4;
* Water Quality Index proposed by the Netherlands Ministry of Transport;
* Practice Note for Professional Persons ProPECC PN 1/94 “Construction Site Drainage” [13].
* Recommended Pollution Control Clauses for Construction Contracts
* Environmental Guidance Note for Sewage Pumping Stations which is not a designated Project[14]
* Marine Water Quality in Hong Kong in 2000, EPD, 2001[84]
* River Water Quality in Hong Kong in 2000, EPD, 2001[16].
In the vicinity of the study area, lots of natural streams and channels are identified. These streams or channels will join into several main watercourses (Tin Shui Wai Nullah, Yuen Long Creek and Fairview Park Nullah) before discharging into the Deep Bay. Table 10.1 shows the baseline data of the EPD routine river quality monitoring stations in some main streams. The station locations are given in Figure 10.1.
Table 10.1: Key EPD routine river quality monitoring data at Year2000
|
Water Quality Parameter |
Tin Shui Wai Nullah |
Yuen Long Creek |
Fairview Nullah |
|
|
TSR1 |
YL1 |
YL2 |
FVR1 |
|
|
Dissolved Oxygen (mg L-1) |
6.7 |
6.1 |
7.6 |
4.4 |
|
PH |
7.5 |
7.5 |
7.6 |
7.2 |
|
Suspended Solids (mg L-1) |
18 |
19 |
14 |
28 |
|
BOD5 (mg L-1) |
8 |
15 |
9 |
7 |
|
COD (mg L-1) |
20 |
39 |
33 |
28 |
|
E. coli (cfu 100mL-1) |
1,050,000 |
263,000 |
90,200 |
47,600 |
|
Ammonia-nitrogen (mg L-1) |
2.1 |
11.30 |
9.75 |
3.65 |
|
Oil & grease (mg L-1) |
0.5 |
0.9 |
0.6 |
0.5 |
|
Nitrate-Nitrogen (mg L-1) |
1.0 |
1.45 |
1.25 |
1.45 |
|
Total Kjeldahl nitrogen (mg L-1) |
2.95 |
14 |
12 |
4.60 |
|
Ortho-phosphate (mg L-1) |
0.2 |
2.2 |
2.2 |
0.51 |
|
Total phosphorous (mg L-1) |
0.44 |
3.2 |
2.85 |
1.05 |
Notes:
Data from River Water Quality in Hong Kong in Year 2000, EPD(2001)
Data presented are in annual medians of monthly samples; except for E. coli which are in annual geometric means
cfu – colony forming unit
Tin Shui Wai Nullah is a concrete channel draining into Deep Bay. Due to the vigorous enforcement actions taken against pollution farms and construction sites, the water quality of the Nullah has improved substantially. Suspended Solid, COD and BOD5 are reduced. The Water Quality of the nullah is considered as fair and the compliance rate was 88% in Year 2000.
Yuen Long Creek is 60km long and covers an area of 26.7km2. It passes through Yuen Long Town before flowing into inner Deep Bay. The water quality of Yuen Long Creek was unsatisfactory and the E. Coli counts remained very high due to pollution from nearby unsewered villages and livestock farms. The compliance rate was 48% in Year 2000.
Fairview Park Nullah is a man-made nullah passing through the Fairview Park, and Mai Po Nature Reserve before discharging into the Deep Bay. The water quality of Fairview Park Nullah is considered as fair with the compliance rate of 53% in Year 2000. The major source of pollutants is from the upstream livestock waste.
Most of the streams within the study area will discharge into inner Deep Bay ultimately. Tidal current inside Deep Bay are extremely slow, resulting in long residence times in the marine waters. There is one routine EPD water quality monitoring station, DM1, located in the vicinity of the discharge locations for the streams, which may be affected by the construction works. The marine water quality data and locations of the EPD Routine Marine Water Quality Monitoring locations are shown in Table 10.2 and Figure 10.2 respectively.
After the commencement of the YLKTSSD Stage II Scheme, the effluent from Yuen Long STW, sewage collected from Lau Fau Shan and Southern Yuen Long will be delivered to the San Wai Sewerage Treatment Works (San Wai STW) for treatment before discharging into the North Western Water Control Zone (NWWCZ). The representative monitoring station near the outfall is NM5. The monitored data is shown in Table 10.2 for comparison.
Table 10.2 : EPD marine water quality monitoring data in Year 2000
|
Water Quality Parameter |
Inner Deep Bay |
North Western |
|
DM1 |
NM5 |
|
|
Temperature (oC) |
22.8 (14.0-30.7) |
23.6 (17.6 – 28.2) |
|
Salinity (ppt) |
18.2 (4.8-25.8) |
27.7 (20.4 –32.2) |
|
Dissolved Oxygen (mg L-1) |
4.8 (3.6-6.2) |
6.0 (3.7 – 8.6) |
|
BOD5 (mg L-1) |
2.7 (1.2-5.5) |
0.8 (0.2 –2.0) |
|
Suspended Solids (mg L-1) |
30.8 (15.0-69.0) |
11.1 (2.0 – 26.1) |
|
Total Inorganic Nitrogen (mg L-1) |
4.08 (2.42-9.52) |
0.51 (0.27 – 0.99) |
|
Unionised Ammonia (mg L-1) |
0.053 (0.024-0.127) |
0.005 (0.002 - 0.014) |
|
Chlorophyll-a (mg L-1) |
4.3 (0.9 – 9.7) |
3.8 (0.2 – 25.0) |
|
E. coli (cfu 100mL-1) |
3600 (150-130000) |
480 (170 – 2300) |
Notes:
Data from Marine Water Quality in Hong Kong in 2000, EPD (2001)
Data presented are depth averaged, except as specified.
Bolded values indicate the exceedance of WQOs
Data presented are annual arithmetic means except for E. coli which are geometric means
Data enclosed in brackets indicate the ranges.
For station DM1 in inner Deep Bay, exceedance of the WQOs for Total Inorganic Nitrogen (TIN), Unionised Ammonia and E. Coli was reported in Year 2000. The marine waters of Deep Bay were heavily affected by discharges from rivers in both Hong Kong and Shenzhen. The high level of TIN and Unionised Ammonia reflect the high nutrient inside Deep Bay, while that the high E. Coli. level indicates the high sewage contamination of the water. In summary, Deep Bay faces long-term pollution problems including: nutrient enrichment, ammonia toxicity and bacterial contamination, which threaten the sensitive ecosystem and oyster culture in Deep Bay.
The water quality in the North Western Water Control Zone (NWWCZ) is influenced by the discharge from major sewage outfalls and the Pearl River flow. In the vicinity of the study area, there are three major sewage outfalls, namely Northwest New Territories (NWNT), Pillar Point and Siu Ho Wan sewage outfalls. The monitoring results in Year 2000 indicated that higher E. Coli and faecal coliform counts were observed at NM5 near the outfalls. This is due to the increasing sewage discharge from the NWNT outfall into Urmston Road. In addition, the NWWCZ also exhibited decreasing nitrogen and phosphorus gradients from North to South in line with the direction of Pearl River flow.
Representative inland WSRs, such as ponds, streams and nullahs in the vicinity of the study area, are identified and shown in Table 10.3 – Table 10.6 and Figure 10.3 – Figure 10.5.
Major Streams
Table 10.3: Major streams
|
WSR No. |
WSR Description |
|
IW 1 |
Yuen Long Creeks |
|
IW 2 |
Tin Shui Wai Nullah |
|
IW 3 |
Fairview Nullah |
Other Local Ponds, Streams and Nullahs
Table 10.4: Local ponds, streams and nullahs in Lau Fau Shan
|
WSR No. |
WSR Description |
|
IL1 |
Local stream in Hang Hau Tsuen |
|
IL2 |
Ponds along the western bank of the Tin Shui Wai Nullah |
|
IL3 |
San Pui River |
|
IL4 |
Ponds in Fung Kong Tsuen |
|
IL5 |
Ponds in San Wai |
|
IL6 |
Ponds in Mong Tseng Tsuen |
|
IL7 |
Ponds in Tai Tseng Wai |
Table 10.5: Local ponds, streams and nullahs in San Tin
|
WSR No. |
WSR Description |
|
IS1 |
Kam Tin River |
|
IS2 |
Local streams in San Wai Tsuen and Man Yuen Chuen |
|
IS3 |
Local streams in Yau Mei Shan Tsuen |
|
IS4 |
Ngau Tam Mei Main Drainage Channel |
|
IS5 |
Local stream in San Lung Tsuen |
|
IS6 |
Ponds along the northern bound of Castle Peak Road – San Tin Section |
|
IS7 |
Ponds in San Tin Tsuen |
Table 10.6: Local ponds, streams and nullahs in Shap Pat Heung
|
WSR No. |
WSR Description |
|
IP1 |
Local stream in San Ha Tsuen |
|
IP2 |
Kung Um Road Nullah |
|
IP3 |
Drainage Channel from Sham Chung Tsuen to Shui Tsiu San Tsuen |
|
IP4 |
Tai Shu Ha Road Nullah |
The Water Control Zones in concern in this study are DBWCZ and NWWCZ. The WSRs in these regions are shown in Table 10.7 and Figure 10.6.
Table 10.7: Marine water sensitive receivers
|
No. |
WSR Description |
Potential Impact |
|
MW 1 |
Inner Deep Bay and Mai Po Marshes Site of Special Scientific Interest (SSSI) |
Pumping stations emergency discharge to Deep Bay through channels or other local stream |
|
MW 2 |
Shellfish culture ground |
|
|
MW 3 |
Tsim Bei Tsui Site of Special Scientific Interest (SSSI) |
|
|
MW 4 |
Pak Nai Site of Special Scientific Interest (SSSI) |
Discharge from SWSTW through Urmston Road outfall in normal operation. |
|
MW 5 |
Cooling water intake for CLP Black Point Power Station |
|
|
MW 6 |
Chinese White Dolphin feeding ground in the Urmston Road |
|
|
MW 7 |
Marine Park at Sha Chau / Lung Kwu Chau |
|
|
MW 8 |
Non-gazetted beaches |
|
|
MW 9 |
Gazetted beaches |
|
|
MW 10 |
Cooling water intake for CLP Pillar Point Power Station |
|
|
MW 11 |
Seawater abstraction point (cooling) |
|
|
MW 12 |
Seawater abstraction point (flushing) |
|
|
MW 13 |
Tuen Mun Typhoon Shelter |
|
|
MW 14 |
Ma Wan Fish Culture Zone |
|
|
MW 15 |
Secondary contact recreational areas |
The types of discharge within the construction site of the proposed project and other interfacing projects are identified in this study. Their potential water quality impacts are assessed accordingly. Mitigation measures as recommended on ProPECC PN 1/94 and RPCC are proposed.
Emergency Discharge
During operational phase, potential water quality impact issue as a result of pumping station failure, repairing and maintenance of pressurized sewers may be experienced. Under these circumstances, raw sewer will be overflown from the emergency discharge and enters the nearby water body. Section 10.6.4 gives recommendations for minimizing the duration of untreated sewage discharges.
Normal Operation
In normal operation, the sewage will be collected and treated in the upgraded San Wai STW before final discharge to the Urmston Road. The capacity of the upgraded San Wai STW has already catered for the future population change. The potential cumulative impact is addressed in the approved EIA report of “Upgrading and Expansion of San Wai Sewage Treatment Works and Expansion of Ha Tsuen Pumping Station[82]’. The findings have been incorporated in this assessment.
Potential impacts during the construction phase will be arisen from pollutants in surface run-off, which may enter surface water or the stormwater drain directly before discharging into Deep Bay.
Temporary site facilities may also generate wastewater from different activities. Such activities may include sewage effluent from toilets and water from plant maintenance facilities, which may be contaminated with lubricant and other petroleum products.
For sewers crossing the local streams, the sewers will be laid using the trenchless pipe jacking method. This method avoids direct disturbance of any sediments on the bed of the channels. The trenchless pipe jacking methodology is shown in Appendix 10.5. However, in the event of malfunction of the tunnelling machine, a rescue pit would be sunk into the streams. Dredging works will be required. This could potentially cause localised impacts on water quality, particularly if the sediments are contaminated.
Mitigation measures will be necessary to prevent the transport of sediment in suspension away from the works area. In addition, embankments along the sides of the channels will need to be removed and reinstated once the sewers have been laid, which could result in spillage of material to the channels. Besides, if pumped groundwater is not controlled properly, it will have potential adverse impacts on the nearby surface water quality.
In accordance with Practice Note for Professional Persons on “Construction Site Drainage”, Environmental Protection Department, 1994 (ProPECC PN 1/94), construction phase mitigation measures will include the following:
· In advance of site formation works of the sewage pumping station or excavation, perimeter cut-off drains to direct off-site water around the site should be constructed, with internal drainage works, erosion and sedimentation control facilities implemented. Channels, earth bunds or sand bag barriers should be provided on site to direct stormwater to silt removal facilities. The design of the temporary on-site drainage system will be undertaken by the contractor prior to the commencement of construction.
· Efficient silt removal facilities should be designed based on the guidelines in Appendix A1 of ProPECC PN 1/94, which states that the retention time for silt/sand traps should be 5 minutes under maximum flow conditions. As sizes may vary depending upon the flow rate, for flow rate of 0.1 m3s-1 a sedimentation basin of 30m3 would be required and for a flow rate of 0.5 m3 s-1 the basin would be 150 m3. The detailed design of the sand/silt traps will be undertaken by the contractor prior to the commencement of construction.
· Construction works should be programmed to minimise surface excavation works during the rainy seasons (April to September). All exposed earth areas should be completed and vegetated as soon as possible after earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks where practicable. If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or other means.
· The overall slope of the site should be kept to a minimum to reduce the erosive potential of surface water flows, and all trafficked areas and access roads protected by coarse stone ballast. An additional advantage accruing from the use of crushed stone is the positive traction gained during prolonged periods of inclement weather and the reduction of surface sheet flows.
· All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure proper and efficient operation at all times and particularly following rainstorms. Deposited silt and grit should be removed regularly and disposed of by spreading evenly over stable, vegetated areas.
· Measures should be taken to minimise the ingress of site drainage into excavations. If excavation of trenches in wet seasons is necessary, they should be dug and backfilled in short sections wherever practicable. Water pumped out from trenches or foundation excavations should be discharged into stormwater drains via silt removal facilities.
· Open stockpiles of construction materials (for example, aggregates, sand and fill material) of more than 50 m3 should be covered with tarpaulin or similar fabric during rainstorms. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.
· Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system and storm runoff being directed into foul sewers.
· Precautions to be taken at any time of year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted, and actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94. Particular attention should be paid to the control of silty surface runoff during storms events, especially for areas located near steep slopes.
· All vehicles and plant should be cleaned before leaving a construction site as far as possible to ensure no earth, mud, debris and the like is deposited by them on roads. An adequately designed and sited wheel washing bay should be provided at the exit of Sewage Pumping Station construction site and wash-water should have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process. The section of access road leading to, and exiting from, the wheel-wash bay to the public road should be paved with sufficient backfall toward the wheel-wash bay to prevent vehicle tracking of soil and silty water to public roads and drains.
· On-site drainage system should be equipped with oil interceptors to separate oil / fuel from contaminated storm water.
· Construction solid waste, debris and rubbish on site should be collected, handled and disposed of properly to avoid water quality impacts. Requirements for solid waste management are detailed in Section 11 of this Report.
· All fuel tanks and storage areas should be provided with locks and sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled fuel oils from reaching water sensitive receivers nearby.
Construction work force sewage should be handled by portable chemical toilets or sewage holding tanks with the sewage regularly collected by a reputable sewage collector for disposal at for example, Yuen Long STW.
The adoption of Pipe Jacking method in crossing stream will prevent adverse impacts on water quality, as discussed in Section 10.6.1.
If there is a malfunction of pipe jacking machine at one end of the tunnel, jacking can be operated at another end of the tunnel for rescue operation. The chance of failure at both ends is very low unless the rock type is extreme hard. If there is equipment malfunction when crossing the stream, a rescue pit may need to be excavated. However, in accordance with DSD previous experience, there was no such excavation exercise in the past since the sediment underneath the stream is generally soft in nature. If a rescue pit is required in an extreme worse case situation then the following precautionary/ mitigation measures should be implemented during excavation:
· Containment of suspended solid by silt curtain. However, this method is only effective at current velocity less than 0.01 m/s. A second silt curtain shall be applied at a further downstream location (10-20m away) from the first silt curtain. These configurations will mininise the dispersion of containment.
· Shielding the cutterhead or using specially design cutterheadand enclosures to minimize the leaking of suspended solid during excavation.
· Mechanical grab shall be seal tightly to avoid spillage while being lift.
· Marine works shall not cause visible foam, oil, grease, scrum, litter or other objectionable matter to be present on the waters within the site.
If vessels are going to be used in wide nullah (e.g Tin Shui Wai Nullah), the following additional mitigation measures shall be adopted:
· Vessels should be sized such that adequate clearance is maintained between vessels and the seabed at all states of the tide to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash.
· Barges and grab dredgers shall be fitted with tight-fitting seals to their bottom opening to prevent leakage of material.
· Excess materials shall be cleaned from the decks and exposed fittings of barges and grab dredgers before the vessel departs.
· Adaquate freeboard shall be maintained on barges to ensure that decks are not washed.
Material excavated from any rescue pits is likely to be stockpiled for disposal. This material should be covered with impermeable sheets and placed on an impermeable liner in order to prevent rainfall eroding the material leading to stormwater runoff or other surface runoff with high suspended solid concentrations. The disposal of excavated material will be discussed in Section 11.
In the vicinity of the proposed project site, numerous interfacing projects are identified. Table 10.8a – 10.8d summarizes the projects in different work areas and their proposed mitigation measures.
Table 10.8a: Interfacing projects for package 2A-1T (Tin Shui Wai Area)
|
Item |
Concurrent Project |
Scheduled Construction Period |
Over-lapping Months |
Distance > 500m from represent-ative WSR |
Potential to Cause Cumulative Water Quality Impact |
Mitigation Measures |
|
|
Start |
Compl-ete |
||||||
|
1 |
DD901 – West Rail Environmental Support Services Essential Public Infrastructure Works: Yuen Long, Tin Shui Wai and Tuen Mun Centre |
May 99 |
Nov 03 |
0 |
Yes |
û |
--- |
|
2 |
Tin Shui Wai Phase 4 Extension |
2001 |
2004 |
0 |
No |
û |
--- |
|
3 |
Light Rail Transit (LRT) Extension in Tin Shui Wai Reserve Zone and Grade Separation of the LRT with Pui To Road and Tsing Lung Road in Tuen Mun |
2001 |
2004 |
0 |
No |
û |
--- |
|
4 |
Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange |
Aug 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
5 |
Yuen Long Bypass Floodway - Feasibility Study |
Mar 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
6 |
Deep Bay Link (San Wai Section) |
Jul 2003 |
Jun 2006 |
12 |
No |
ü |
Implement mitigation measures stated in approved EIA report AEIAR 064/2002 |
|
7 |
San Wai Sewerage Treatment Works |
2004 |
2007 |
30 |
No |
ü |
Implement mitigation measures stated in approved EIA report AEIAR 072/2002 |
|
8 |
Shenzhen Western Corridor |
Mar 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
9 |
Ping Ha Road Improvement Remaining Works |
--- |
2006 |
6 |
No |
ü |
ProPECC Note PN 1/94 |
|
10 |
Alternative 4 Bypass Culvert |
2003 |
2007 |
18 |
No |
ü |
ProPECC Note PN 1/94 |
|
11 |
Main Drainage Channels and Poldered Village Protection Schemes for San Tin[1] |
Jun 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
12 |
Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 1 (1B-2T) |
Aug 2004 |
Feb 2008 |
30 |
No |
ü |
Implement mitigation measures stated in approved EIA report AEIAR 063/2002 |
|
13 |
Tin Shui Wai Further Development
|
July 1998 |
2003 |
0 |
Yes |
û |
--- |
|
14 |
157DS Phase 3B/3C San Wai and Tung Tau Tsuen |
June 2005 |
June 2007 |
24 |
No |
ü |
ProPECC Note PN 1/94 |
|
15 |
Lau Fau Shan Remaining Development |
No construction schedule |
--- |
Yes |
û |
--- |
|
Note [1] : MDC-Eastern Section is more than 300 m from the present project
Table 10.8b: Interfacing Projects for Package 2A-3T (Lau Fau Shan Area)
|
Item |
Concurrent Project |
Scheduled Construction Period |
Overlapping Months |
Distance > 500m from represent-ative WSR |
Potential to Cause Cumulative Water Quality Impact |
Mitigation Measures |
|
|
Start |
Complete |
||||||
|
1 |
DD901 – West Rail Environmental Support Services Essential Public Infrastructure Works: Yuen Long, Tin Shui Wai and Tuen Mun Centre |
May 99 |
Nov 03 |
0 |
Yes |
û |
--- |
|
2 |
Tin Shui Wai Phase 4 Extension |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
3 |
Light Rail Transit (LRT) Extension in Tin Shui Wai Reserve Zone and Grade Separation of the LRT with Pui To Road and Tsing Lung Road in Tuen Mun |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
4 |
Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange |
Aug 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
5 |
Yuen Long Bypass Floodway - Feasibility Study |
Mar 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
6 |
Deep Bay Link |
Jul 2003 |
Jun 2006 |
12 |
Yes |
û |
--- |
|
7 |
San Wai Sewerage Treatment Works |
2004 |
2007 |
30 |
Yes |
û |
--- |
|
8 |
Shenzhen Western Corridor |
Mar 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
9 |
Ping Ha Road Improvement Remaining Works |
--- |
2006 |
6 |
No |
ü |
ProPECC Note PN 1/94 |
|
10 |
Alternative 4 Bypass Culvert |
2003 |
2007 |
18 |
Yes |
û |
--- |
|
11 |
Main Drainage Channels and Poldered Village Protection Schemes for San Tin[1] |
Jun 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
12 |
Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 1 (1B-2T) |
Aug 2004 |
Feb 2008 |
30 |
Yes |
û |
--- |
|
13 |
Tin Shui Wai Further Development |
July 1998 |
2003 |
0 |
No |
û |
--- |
|
14 |
157DS Phase 3B/3C San Wai and Tung Tau Tsuen |
June 2005 |
June 2007 |
24 |
No |
ü |
ProPECC Note PN 1/94 |
|
15 |
Lau Fau Shan Remaining Development |
No construction schedule |
--- |
No |
û |
--- |
|
Note [1] : MDC-Eastern Section is more than 300 m from the present project
Table 10.8c: Interfacing Projects for Package 2B-2T (Shap Pat Heung Area)
|
Item |
Concurrent Project |
Scheduled Construction Period |
Overlapping Months |
Distance > 500m from represent-ative WSR |
Potential to Cause Cumulative Water Quality Impact |
Mitigation Measures |
|
|
Start |
Compl-ete |
||||||
|
1 |
DD901 – West Rail Environmental Support Services Essential Public Infrastructure Works: Yuen Long, Tin Shui Wai and Tuen Mun Centre |
May 99 |
Nov 03 |
0 |
Yes |
û |
--- |
|
2 |
Tin Shui Wai Phase 4 Extension |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
3 |
Light Rail Transit (LRT) Extension in Tin Shui Wai Reserve Zone and Grade Separation of the LRT with Pui To Road and Tsing Lung Road in Tuen Mun |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
4 |
Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange |
Aug 2003 |
Dec 2005 |
6 |
No |
ü |
Implement mitigation measures stated in approved EIA report AEIAR 059/2002 |
|
5 |
Yuen Long Bypass Floodway - Feasibility Study |
Mar 2001 |
Dec 2003 |
0 |
No |
û |
--- |
|
6 |
Deep Bay Link |
Jul 2003 |
Jun 2006 |
12 |
Yes |
û |
--- |
|
7 |
San Wai Sewerage Treatment Works |
2004 |
2007 |
30 |
Yes |
û |
--- |
|
8 |
Shenzhen Western Corridor |
Mar 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
9 |
Ping Ha Road Improvement Remaining Works |
--- |
2006 |
6 |
Yes |
û |
--- |
|
10 |
Main Drainage Channels and Poldered Village Protection Schemes for San Tin[1] |
Jun 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
11 |
Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 1 (1A-1T) |
Aug 2003 |
Feb 2006 |
8 |
Yes |
û |
--- |
|
12 |
Tin Shui Wai Further Development
|
July 1998 |
2003 |
0 |
Yes |
û |
--- |
|
13 |
157DS Phase 2 Yuen Long South Pumping Station, Rising Main to Castle Peak Road and Sewers |
Jan 2003 |
May 2006 |
12 |
No |
ü |
ProPECC Note PN 1/94 |
|
14 |
274DS Phase 1 Shap Pat Heung Rising Main and Gravity Sewer; Au Tau Sewage Pumping Station and Ancillary Works |
Jan 2003 |
May 2006 |
12 |
No |
ü |
ProPECC Note PN 1/94 |
|
15 |
274DS Phase 7A/ 7B San Sang Tsuen and Tin Sum, Shan Ha and Tai Tong Tsuen |
June 2007 |
July 2009 |
6 |
No |
ü |
ProPECC Note PN 1/94 |
|
16 |
Lau Fau Shan Remaining Development |
No construction schedule |
--- |
Yes |
û |
--- |
|
Note [1]: MDC-Eastern Section is more than 300 m from the present project
Table 10.8d: Interfacing Projects for Package 2A-2T and 2B-1T (Ngau Tam Mei Area)
|
Item |
Concurrent Project |
Scheduled Construction Period |
Overlapping Months |
Distance > 500m from represent-ative WSR |
Potential to Cause Cumulative Water Quality Impact |
Mitigation Measures |
||
|
Start |
Compl-ete |
|||||||
|
1 |
DD901 – West Rail Environmental Support Services Essential Public Infrastructure Works: Yuen Long, Tin Shui Wai and Tuen Mun Centre |
May 99 |
Nov 03 |
0 |
Yes |
û |
--- |
|
|
2 |
Tin Shui Wai Phase 4 Extension |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
|
3 |
Light Rail Transit (LRT) Extension in Tin Shui Wai Reserve Zone and Grade Separation of the LRT with Pui To Road and Tsing Lung Road in Tuen Mun |
2001 |
2004 |
0 |
Yes |
û |
--- |
|
|
4 |
Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange |
Aug 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
|
5 |
Yuen Long Bypass Floodway - Feasibility Study |
Mar 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
|
6 |
Deep Bay Link |
Jul 2003 |
Jun 2006 |
12 |
Yes |
û |
--- |
|
|
7 |
San Wai Sewerage Treatment Works |
2004 |
2007 |
30 |
Yes |
û |
--- |
|
|
8 |
Shenzhen Western Corridor |
Mar 2003 |
Dec 2005 |
6 |
Yes |
û |
--- |
|
|
9 |
Ping Ha Road Improvement Remaining Works |
--- |
2006 |
6 |
Yes |
û |
--- |
|
|
10 |
Main Drainage Channels and Poldered Village Protection Schemes for San Tin [1] |
Jun 2001 |
Dec 2003 |
0 |
Yes |
û |
--- |
|
|
11 |
Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 1 (1A-1T) |
Aug 2003 |
Feb 2006 |
8 |
No |
ü |
Implement mitigation measures stated in approved EIA report AEIAR 063/2002 |
|
|
12 |
Tin Shui Wai Further Development |
July 1998 |
2003 |
0 |
Yes |
û |
--- |
|
|
13 |
92CD Package NTM1 |
Nov 2003 |
Jun 2006 |
12 |
Yes |
û |
--- |
|
|
14 |
Lau Fau Shan Remaining Development |
No construction schedule |
--- |
Yes |
û |
--- |
||
Note [1] : MDC-Eastern Section is more than 300 m from the present project
Most of the interfacing works listed in Table 10.8 are land-based operation and similar in nature. The release of construction runoff into Deep Bay may result in cumulative impacts. For the designated projects identified, the mitigation measures listed in the corresponding EIA reports are supposed to be implemented in their construction sites. For the non-designated projects, the mitigation measures listed in ProPECC Note PN 1/94 would also be adopted. Basically, construction site run-off will be effectively controlled by appropriate mitigation measures including site drainage system, effluent monitoring and audit. Generation of wastewater, sewage from workforce, accidental spillage will be minimized through the provision of chemical toilets, wastewater treatment facilities, off site disposal and spill contingency plan.
In order to assess the effectiveness of these mitigation measures, a similar existing construction project "Village Flood Protection Works for Mai Po Lo Wai & Mai Po San Tsuen” has been reviewed for this study. The major items of the project are to construct the Village Flood Protection Works for Wang Chau, Mai Po Lo Wai and Mai Po San Tsuen and drainage improvement works at Tan Kwai Tsuen.Water quality mitigation measures proposed in its EIA report were adopted. According to their monthly EM&A monitoring data, the monthly average suspended solid concentration varied from 25 to 186 mg/L, which are well below the triggering level of 203mg/L. Hence, it is considered that the mitigation measures are very effective.
Based on the review, with the proposed mitigation measures, the interfacing construction projects will not have imparted detrimental impact on the nearby water environment. Cumulative impacts from other interfacing construction projects are, thus, not anticipated. Hence, no water quality monitoring will be required.
The operation of Yuen Long / Kam Tin Sewerage and the associated Sewage Pumping Stations will result in an improvement to the quality of inland waters through enhancement of the efficiency of the sewer system. However, during the maintenance periods of the pumping stations and pressurized sewers, or the failure of the pumping station, potential environmental impact will be the discharge at emergency bypass on adjacent streams as well as accidental damage and subsequent repair of the pressurized sewers causing overspillage.
In case emergency discharge occurs (due to emergency repair and maintenance works of pressurized sewers) the raw sewage from the emergency discharge (except that of the Yuen Long Effluent Pumping Station) will be directly discharged to the nearest nullahs, streams or stormwater drainage leading to Deep Bay. As a worst scenario, the emergency discharge is assumed to continue for approximately 15 days (such as urgent repair / replacement of the main control panel). During this period, the water quality in the nearby nullahs, streams and stormwater drainage will be affected. One potential impact will include the reduction of light into the water due to the suspended solid in the sewage, which will affect the aquatic organism. However, the ecological value of the nullahs and streams in the vicinity of the project site is low and long-term impact on the nullahs, and streams is therefore not expected. Normally the decay of pollutants inside the nullahs, streams and stormwater drainage are very low. Once the pollutants reach the Deep Bay, it will cause an increase in E. Coli, Unionised Ammonia (UIA) and TIN concentrations.
Given that the capacities of the proposed pumping stations are smaller than that of the Ha Tsuen Pumping station (246,000m3/day) and most of the emergency outflow of the proposed pumping stations will be discharged into the inner deep bay (except the Lau Fau Shan SPS), the findings of the approved EIA report for “Updating and Expansion of San Wai STW and the Expansion of Ha Tsuen PS” (EIA-SWSTW) can be applied here.
According to the approved EIA-SWSTW report, the emergency discharge of raw sewage into the Inner Deep Bay will cause an increased in E. Coli, UIA and TIN in the Tsim Bei Tsui SSSI in both wet and dry seasons. The influence on water quality at EPD Marine Monitoring stations at DM1, DM2, DM3 and Pak Nai SSSI (which is located further away) will be reduced with increasing distance. Normally, the pollutant levels will be reduced rapidly after termination of emergency discharge. The approved EIA report predicts that the TIN and UIA levels will drop to levels almost the same as the baseline conditions in 5 - 8 days. For E.Coli, its concentration will decrease rapidly and return to the baseline level in a shorter period after the emergency discharge ceases. Since the capacities of the proposed pumping stations are much smaller than that of the Ha Tsuen Pumping Station, it is anticipated that the time required for E. Coli, UIA and TIA to return to the baseline value would be much shorter.
For the Lau Fau Shan SPS, the emergency discharge will be near Hang Hau Tsuen in Deep Bay, which is far away from the Tsim Bei Tsui SSSI. Hence its impact on the Tsim Bei Tsui SSSI will be minor. For the Yuen Long Effluent Pumping Station, it conveys the treated effluent from the Yuen Long STW to San Wai STW through the Effluent Pipeline. As the effluent is already treated, the emergency discharge from the Yuen Long Effluent Pumping Station will not cause adverse water quality impact on Deep Bay.
Due to the presence of backup facilities (standby pumps, backup power and twin rising mains), the occurrence of emergency discharge is exceptionally rare. According to DSD’s record, emergency discharge in the vicinity of the study area has been occurred. Should a breakdown of the pumping station occur due to power supply failure, based on the past experience in Hong Kong, the pumping station operation will be recovered in hours. In the proposed sewerage system, twin rising mains are adopted. During sewer repair, either one of the twin sewers will be left operational. The chance of failure of both sewers in twin rising mains is very low.
Table 10.9 summarizes the emergency bypass locations at each pumping station site. Detailed mitigation measures, which would serve to minimise the risk of failure and facilitate a rapid response in the event of failure, are described in Section 10.6.4.
Table 10.9 Pumping stations and emergency bypass locations
|
Item |
Sewage Pumping Station |
Emergency Bypass Locations |
|
Lau Fau Shan Area |
||
|
A1 |
Lau Fau Shan SPS |
Streams near Hang Hau Tsuen |
|
A2 |
Mong Tseng Tsuen SPS |
Nearby stormwater drains or surface channel |
|
Yuen Long Area |
||
|
AP1 |
Yuen Long Effluent SPS |
San Pui River |
|
San Tin Area |
||
|
P1 |
Ngau Tam Mei SPS |
Planned Main Drainage Channel, Local steams near Yau Mei San Tsuen |
|
P2 |
Tam Mei Barrack SPS |
Yau Tam Mei Main Drainage Channel |
|
P3 |
San Tin SPS |
Local streamwater drains near San Tin Tsuen Road |
|
P4 |
San Lung Tsuen SPS |
Nearby stormwater drains or surface channel |
|
P5 |
San Tin Barrack SPS |
Nearby stormwater drains or surface channel |
|
Shap Pat Heung |
||
|
B1 |
Shan Ha Tsuen SPS |
Nearby stormwater drains or surface channel |
|
B2 |
Muk Kiu Tau SPS |
Kung Um Road Nullah |
|
B3 |
Sham Chung Tsuen SPS |
Kung Um Road Nullah |
|
B4 |
Shui Tsiu San Tsuen SPS |
Planned drainage channel near Shui Tsiu San Tsuen |
|
B5 |
Shung Ching San Tsuen SPS |
Planned drainage channel near Shung Ching San Tsuen |
|
B6 |
Nga Yiu Tau SPS |
Tai Shiu Ha Road Nullah |
|
B7 |
Pak Sha Tsuen SPS |
Kung Um Road Nullah |
The sewage collected from the proposed sewer mains will be connected and delivered to San Wai STW, where the sewage will be treated and discharged into the NWWCZ. This will result in an increase in treated sewage effluent discharges from the San Wai STW. However, due to the upgrading of the San Wai STW, it will not increase the total pollutant load to NWWCZ. Potential interfacing project during the operation will include the Yuen Long Kam Tin Sewerage and Sewage Disposal Stage 1. The potential cumulative water quality impact on NWWCZ would be the same as that derived from the water quality modelling in the EIA-SWSTW.
The detailed derivation of the input parameters for the water quality modelling was presented in EIA-SWSTW. Four treatment level options were investigated in the EIA-SWSTW, and the options of chemical enhanced primary treatment (CEPT) with disinfection are proposed in the study. The modeling results of the preferred option are presented in this study.
The modelling results allow a comparison to be made with the relevant Water Quality Objectives for both the Baseline Condition and Commissioning Scenarios (the cumulative water quality impact). The statistical analysis of water quality changes are presented in the following parameters:
· depth averaged 90%ile dissolved oxygen;
· bottom values 90%ile dissolved oxygen;
· depth averaged mean total inorganic nitrogen;
· depth averaged mean suspended sediment;
· depth averaged mean unionised ammonia;
· depth averaged geometric mean of E. coli; and
· depth averaged mean of 5-day biochemical oxygen demand.
The results of the water quality modelling at the WSRs identified in this study are incorporated from the EIA-SWSTW and are summarized in Tables 10.11 and 10.12 for both wet and dry seasons respectively.
Table 10.11: Wet season water quality modelling results
|
WSR |
Pos. No in EIA -SWSTP |
DO (mg/L) |
DO (Bottom) (mg/L) |
TIN (mg/L) |
NH3-N (mg/L) |
SS (mg/L) |
E. Coli (cfu 100mL-1) |
BOD5 (mg/L) |
|||||||
|
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
||
|
MW1 |
A1 |
0.4 |
0.6 |
0.4 |
0.5 |
3.52 |
3.21 |
0.247 |
0.221 |
63.0 |
60.7 |
2560 |
2309 |
12.12 |
11.27 |
|
MW2 |
DM 3 |
3.3 |
3.4 |
3.3 |
3.4 |
1.15 |
1.11 |
0.024 |
0.021 |
21.2 |
20.8 |
94 |
89 |
1.03 |
0.99 |
|
MW3 |
F1 |
2.1 |
2.4 |
2.1 |
2.3 |
2.48 |
2.14 |
0.159 |
0.127 |
43.1 |
40.7 |
4031 |
2696 |
6.27 |
5.25 |
|
MW4 |
F2 |
4.4 |
4.4 |
4.4 |
4.4 |
0.90 |
0.87 |
0.010 |
0.008 |
18.0 |
17.7 |
4630 |
2823 |
0.78 |
0.69 |
|
MW5 |
D1 |
3.9 |
3.9 |
3.8 |
3.9 |
0.80 |
0.79 |
0.004 |
0.004 |
15.2 |
15.2 |
293 |
47 |
0.47 |
0.46 |
|
MW6 |
G1 |
4.0 |
4.1 |
4.1 |
4.1 |
0.75 |
0.75 |
0.004 |
0.004 |
13.4 |
13.3 |
518 |
22 |
0.42 |
0.41 |
|
MW7 |
H1 |
4.0 |
4.0 |
4.0 |
4.0 |
0.76 |
0.75 |
0.003 |
0.003 |
13.3 |
13.2 |
111 |
6 |
0.40 |
0.39 |
|
MW8 |
B1 |
4.4 |
4.4 |
4.0 |
4.1 |
0.76 |
0.76 |
0.004 |
0.004 |
12.9 |
12.8 |
41 |
25 |
0.40 |
0.39 |
|
B2 |
4.2 |
4.2 |
4.1 |
4.1 |
0.77 |
0.77 |
0.004 |
0.004 |
11.9 |
11.8 |
183 |
101 |
0.50 |
0.49 |
|
|
MW9 |
E1 |
5.1 |
5.1 |
5.0 |
5.0 |
0.48 |
0.48 |
0.002 |
0.002 |
7.0 |
7.0 |
32 |
32 |
0.26 |
0.26 |
|
E2 |
5.0 |
5.0 |
5.0 |
5.0 |
0.50 |
0.50 |
0.002 |
0.002 |
6.9 |
6.8 |
24 |
23 |
0.24 |
0.24 |
|
|
E3 |
5.0 |
5.0 |
4.9 |
4.9 |
0.51 |
0.50 |
0.002 |
0.002 |
6.9 |
6.9 |
93 |
92 |
0.24 |
0.24 |
|
|
E4 |
5.0 |
5.0 |
4.9 |
4.9 |
0.51 |
0.51 |
0.002 |
0.002 |
6.9 |
6.9 |
33 |
31 |
0.24 |
0.24 |
|
|
E6 |
5.0 |
5.0 |
5.0 |
5.0 |
0.50 |
0.49 |
0.002 |
0.002 |
6.9 |
6.8 |
17 |
15 |
0.24 |
0.24 |
|
|
E7 |
5.0 |
5.0 |
5.0 |
5.0 |
0.50 |
0.50 |
0.002 |
0.002 |
7.0 |
7.0 |
22 |
20 |
0.24 |
0.24 |
|
|
E8 |
4.8 |
4.8 |
4.6 |
4.6 |
0.63 |
0.62 |
0.002 |
0.002 |
8.6 |
8.5 |
146 |
138 |
0.31 |
0.31 |
|
|
E11 |
4.9 |
5.0 |
4.7 |
4.7 |
0.62 |
0.62 |
0.002 |
0.002 |
8.4 |
8.3 |
154 |
149 |
0.33 |
0.33 |
|
|
E13 |
4.6 |
4.6 |
4.5 |
4.5 |
0.63 |
0.63 |
0.002 |
0.002 |
8.9 |
8.9 |
88 |
71 |
0.31 |
0.30 |
|
|
MW10 |
D2 |
4.3 |
4.4 |
4.4 |
4.4 |
0.67 |
0.66 |
0.003 |
0.003 |
10.6 |
10.6 |
64 |
8 |
0.31 |
0.31 |
|
MW11 |
D3 |
5.4 |
5.4 |
4.7 |
4.7 |
0.57 |
0.57 |
0.002 |
0.002 |
9.2 |
9.2 |
147 |
147 |
0.54 |
0.54 |
|
MW12 |
J1 |
5.0 |
5.0 |
4.6 |
4.6 |
0.60 |
0.60 |
0.002 |
0.002 |
8.8 |
8.8 |
197 |
196 |
0.43 |
0.43 |
|
MW14 |
C1 |
4.9 |
5.0 |
5.0 |
5.0 |
0.52 |
0.51 |
0.002 |
0.002 |
7.2 |
7.1 |
3 |
2 |
0.24 |
0.24 |
Note: 1. Base refers to the Baseline Scenario, and Com refers to the Commissioning Scenario under the preferred option
2. MW13 & MW15 are not included in the EIA-SWSTW waster quality assessment
Table 10.12: Dry season water quality modelling results
|
WSR |
Pos. No in EIA-SWSTP |
DO (mg/L) |
DO (Bottom) (mg/L) |
TIN (mg/L) |
NH3-N (mg/L) |
SS (mg/L) |
E. Coli (cfu 100mL-1) |
BOD5 (mg/L) |
|||||||
|
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
Base |
Com |
||
|
MW1 |
A1 |
3.0 |
3.1 |
3.0 |
3.1 |
3.69 |
3.29 |
0.117 |
0.104 |
50.3 |
45.7 |
6715 |
4462 |
10.17 |
8.56 |
|
MW2 |
DM 3 |
5.5 |
5.6 |
5.5 |
5.5 |
1.00 |
0.97 |
0.015 |
0.015 |
17.5 |
17.1 |
460 |
431 |
2.17 |
2.09 |
|
MW3 |
F1 |
4.6 |
4.6 |
4.6 |
4.6 |
2.64 |
2.35 |
0.072 |
0.063 |
38.8 |
35.2 |
15210 |
10090 |
7.58 |
6.23 |
|
MW4 |
F2 |
6.2 |
6.2 |
6.1 |
6.2 |
0.93 |
0.89 |
0.013 |
0.012 |
17.1 |
16.6 |
7527 |
4522 |
2.20 |
2.04 |
|
MW5 |
D1 |
6.0 |
6.1 |
6.0 |
6.0 |
0.47 |
0.47 |
0.004 |
0.004 |
9.2 |
9.1 |
454 |
78 |
0.83 |
0.81 |
|
MW6 |
G1 |
6.1 |
6.1 |
6.1 |
6.1 |
0.40 |
0.40 |
0.004 |
0.004 |
8.0 |
7.9 |
387 |
38 |
0.69 |
0.67 |
|
MW7 |
H1 |
6.1 |
6.1 |
6.1 |
6.1 |
0.40 |
0.40 |
0.003 |
0.004 |
8.1 |
8.1 |
177 |
12 |
0.70 |
0.69 |
|
MW8 |
B1 |
6.2 |
6.2 |
6.0 |
6.0 |
0.40 |
0.40 |
0.003 |
0.003 |
8.9 |
8.8 |
115 |
53 |
0.79 |
0.78 |
|
B2 |
6.2 |
6.2 |
6.0 |
6.1 |
0.40 |
0.40 |
0.004 |
0.004 |
8.3 |
8.2 |
602 |
422 |
0.75 |
0.74 |
|
|
MW9 |
E1 |
7.4 |
7.4 |
7.3 |
7.3 |
0.14 |
0.14 |
0.002 |
0.002 |
5.1 |
5.0 |
1 |
1 |
0.56 |
0.56 |
|
E2 |
6.4 |
6.4 |
6.3 |
6.3 |
0.19 |
0.19 |
0.002 |
0.002 |
4.8 |
4.8 |
51 |
49 |
0.32 |
0.32 |
|
|
E3 |
6.3 |
6.3 |
6.3 |
6.3 |
0.19 |
0.19 |
0.002 |
0.002 |
4.8 |
4.8 |
146 |
143 |
0.33 |
0.33 |
|
|
E4 |
6.3 |
6.4 |
6.3 |
6.3 |
0.19 |
0.19 |
0.002 |
0.002 |
4.8 |
4.8 |
83 |
78 |
0.34 |
0.34 |
|
|
E6 |
6.4 |
6.4 |
6.3 |
6.3 |
0.19 |
0.19 |
0.002 |
0.002 |
4.8 |
4.8 |
31 |
29 |
0.32 |
0.32 |
|
|
E7 |
6.3 |
6.4 |
6.3 |
6.3 |
0.19 |
0.19 |
0.002 |
0.002 |
4.8 |
4.8 |
31 |
28 |
0.33 |
0.33 |
|
|
E8 |
6.5 |
6.5 |
6.3 |
6.4 |
0.22 |
0.22 |
0.002 |
0.002 |
6.1 |
6.0 |
174 |
167 |
0.52 |
0.52 |
|
|
E11 |
6.6 |
6.7 |
6.3 |
6.3 |
0.21 |
0.21 |
0.002 |
0.002 |
7.0 |
7.0 |
168 |
166 |
0.71 |
0.70 |
|
|
E13 |
6.3 |
6.4 |
6.3 |
6.3 |
0.24 |
0.24 |
0.002 |
0.002 |
5.8 |
5.7 |
232 |
177 |
0.46 |
0.46 |
|
|
MW10 |
D2 |
6.2 |
6.2 |
6.2 |
6.2 |
0.31 |
0.31 |
0.003 |
0.003 |
6.6 |
6.5 |
141 |
31 |
0.53 |
0.52 |
|
MW11 |
D3 |
7.2 |
7.3 |
6.8 |
6.8 |
0.18 |
0.18 |
0.002 |
0.002 |
7.6 |
7.5 |
453 |
452 |
0.99 |
0.99 |
|
MW12 |
J1 |
7.0 |
7.0 |
6.6 |
6.6 |
0.20 |
0.20 |
0.002 |
0.002 |
6.2 |
6.2 |
602 |
597 |
0.71 |
0.71 |
|
MW14 |
C1 |
6.4 |
6.4 |
6.3 |
6.3 |
0.20 |
0.20 |
0.002 |
0.002 |
4.9 |
4.9 |
9 |
6 |
0.34 |
0.34 |
Note: 1. Base refers to the Baseline Scenario, and Com refers to the Commissioning Scenario under the preferred option
2. MW13 & MW15 are not included in the EIA-SWSTP water quality assessment
The data in Tables 10.11 and 10.12 illustrate that the SWSTW would significantly improve the water quality in inner Deep Bay as a result of collecting and diverting a great portion of pollution loads into the SWSTW and then discharge through the Urmston Road outfall. The overall reduction of NH3-N, TIN, E. Coli and BOD5 levels at MW1 in the Inner Deep Bay are 18%, 12%, 33%, and 17% respectively.
The water quality near the Urmston Road Outfall has also shown improvement due to the upgrading of the plant. Based on the modeling result, the E. Coli level will be significantly reduced and the predicted E.Coli levels at the sensitive receivers near the Urmston Road Outfall (e.g MW 5 and MW6) are well below the relevant WQOs under the preferred treatment option of SWSTW.
In order to prevent the uncontrolled discharge of untreated sewage effluent to surface waters there will be a need to minimise the risk of failure of the pumping stations.
The following measures should be implemented to reduce the risk of failure of the pumping stations, which could result in an emergency discharge of untreated sewage effluent.
· Twin rising mains are provided for backup and repairing purpose;
· The discharge point of the overflow bypass should be below the low water mark (i.e. location of minimum water level in stream in dry season);
· The discharge point of the overflow bypass should be away from sensitive receivers such as fish ponds, water gathering grounds, country parks, nature reserves, sites of special scientific interest, marine parks/marine reserves, streams with water for human consumption, etc.; and
· A contingency plan for emergency discharge shall be developed.
· The overflow bypass should be operated only in an emergency, such as prolonged power failure. Overflow mechanism must not occur to facilitate routine maintenance on a regular basis;
· If the pumping station is unmanned, a telemetry system should be provided to the nearest manned station/plant so that swift actions could be taken in the case of malfunction of the unmanned facilities;
· Hand-cleaned screens should be provided at the overflow bypass to prevent the discharge of floating solids into receiving water bodies. The clear spacing of the bar screen should normally be about 25mm;
· Standby pump should be provided to facilitate maintenance and repairing of equipment; and
· Dual (back-up) power supply should be provided. Dual power supply could be in the format of ring main, or an automatic-operated emergency generator with sufficient capacity to cope with the demand loading of the essential plant equipment.
With the above mitigation measures incorporated, it is anticipated that the chance of emergency discharge and consequently its impact on the adjacent environment will be minimal.
The normal operation of the Yuen Long / Kam Tin Sewerage and Sewage Disposal Stage 2 works will result in improvement of water quality in both the inland and marine waters in the NWWCZ and Deep Bay WCZ after the treatment of the San Wai Sewage Treatment Plant. Therefore no other mitigation measures will be required.
In order to prevent the uncontrolled discharge of untreated sewage effluent to surface waters there will be a need to minimise the risk of failure of the rising mains:
· Twin rising mains are provided for backup and repairing purpose
· Spare/Standby parts for rising mains should be provided to facilitate maintenance and repairing of equipment; and
· Should the twin rising mains be failure, tankers will be used to store the emergency discharge and transport to the YLSTW or SWSTW for disposal.
The following legislations relate to the handling, treatment and disposal of waste in HKSAR, and are considered in assessing potential impacts and their avoidance or mitigation:
* Waste Disposal Ordinance (Cap 354) [17];
* WBTC No. 6/2002A Enhanced Specification for Site Cleanliness and Tidiness;
* Waste Disposal (Chemical Waste) (General) Regulation (Cap 354) [18];
* Land (Miscellaneous Provisions) Ordinance (Cap 28) [19]; and
* Public Health and Municipal Service Ordinance (Cap 132) – Public Cleansing and Prevention of Nuisances (Regional Council) By-laws [20].
The Waste Disposal Ordinance (WDO) prohibits the unauthorised disposal of wastes. Construction and Demolition (C&D) waste is not directly defined in the WDO but is considered to fall within the category of “trade waste”. Trade waste is defined as waste from any trade, manufacturer or business, or any wasted building, or civil engineering materials, but does not include animal waste. Under the WDO, wastes can only be disposed of at sites licensed by EPD. A breach of these regulations can lead to the imposition of a fine and/or prison sentence. The WDO also provides for the issuing of licenses for the collection and transport of wastes. Licenses are not, however, currently issued for the collection and transport of C&D waste or trade waste.
Chemical waste as defined under the Waste Disposal (Chemical Waste) (General) Regulation includes any substance being scrap material, or unwanted substances specified under Schedule 1 of the Regulation, if such a substance or chemical occurs in such a form, quantity or concentration so as to cause pollution or constitute a danger to health or risk of pollution to the environment.
A person should not produce, or cause to be produced, chemical wastes unless he is registered with the EPD. Any person who contravenes this requirement commits an offence and is liable to a fine and/or imprisonment. Procedures of chemical wastes must treat their waste, utilising on-site plant licensed by the EPD or have a licensed collector take the wastes to a licensed facility. For each consignment of wastes, the waste producer, collector and disposer of the wastes must sign all relevant parts of a computerised trip ticket. The system is designed to allow the transfer of wastes to be traced from cradle-to-grave.
The regulation prescribes the storage facilities to be provided on site including labeling and warning sign. To minimise the risks of pollution and danger to human health or life, the waste producer is required to prepare and make available written procedures to be observed in the case of emergencies due to spillage, leakage or accidents arising from storage of chemical wastes. The waste producer must also provide employees with training in such procedures.
The inert portion of Construction and Demolition Materials (C&DM) (also called Public Fill) may be taken to public filling facilities. Public filling areas usually form part of land reclamation schemes and are operated by the Civil Engineering Department (CED) and others. The Land (Miscellaneous Provisions) Ordinance requires that Dumpling Licenses are obtained by individuals or companies, who deliver public fill to the public filling areas. The licenses are issued by the CED under delegated authority from the Director of Lands.
Individual Licenses and windscreen stickers are issued for each vehicle involved. Under the license conditions public filling area will accept only inert building debris, soil, rock and broken concrete. There is no size limitation on the rock and broken concrete, and a small amount of timber mixed with inert material is permissible. The material should, however, be free from marine mud, household refuse, plastic, metal, individual and chemical wastes, animal and vegetable matters and any other materials considered unsuitable by the Filling Supervisor.
These by-laws provide a further control on the illegal tipping of wastes on unauthorised (unlicensed) sites. The illegal dumping of wastes can lead to a fine and imprisonment.
Table 11.1 summarises documents that are related to waste management and disposal in Hong Kong.
Table 11.1 : Other relevant documents and information
|
Bureau / Department |
Documents / Guidelines / Technical Circulars |
|
Planning, Environmental and Lands Branch, Hong Kong Government Secretariat; |
Waste Disposal Plan for Hong Kong (December 1989) Waste Reduction Framework Plan, 1998 to 2007 |
|
Environment, Transport and Works Bureau |
Works Bureau TC No. 32/92, The Use of Tropical Hard Wood on Construction Site Works Bureau TC Nos. 2/93, Public Dumps Works Bureau TC No 2/93B, Public Filling Facilities Works Branch TC No. 16/96, Wet Soil in Public Dumps Works Bureau TC Nos. 4/98 and 4/98A, Use of Public Fill in Reclamation and Earth Filling Project Works Bureau TC Nos. 25/99, 25/99A and 25/99C, Incorporation of Information on Construction and Demolition Material Management in Public Works Sub-committee Papers Works Bureau TC No. 12/2000, Fill Management Works Bureau TC No. 19/2001, Metallic Site Hoardings and Signboards Works Bureau TC No. 06/2002, Enhanced Specification for Site Cleanliness and Tidiness Works Bureau TC No. 12/2002, Specification Facilitating the Use of Recycled Aggregates Works Bureau TC No. 21/2002, Trip-ticket System for Disposal of Construction and Demolition Material Environment, Transport and Works Bureau Technical Circular (Works) No, 33/2002, Management of Construction and Demolition Material Including Rock. Environment, Transport and Works Bureau Technical Circular (Works) No, 15/2003, Waste Management on Construction Sites |
|
EPD / CED |
New Disposal Arrangements for Construction Waste (1992) |
|
EPD |
Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes (1992) |
|
- |
Environmental Guidelines for Planning In Hong Kong (1990), Hong Kong Planning Standards and Guidelines [21] |
According to Environment, Transport and Works Bureau Technical Circular (Works) No, 33/2002, Management of Construction and Demolition Material Including Rock dated August 2002, A C&D Material Management Plan has to be submitted to the Public Fill Committee in case the C&DM to be generated would exceed 50,000m3.
Excavated contaminated soil has to meet certain criteria before disposal to landfill is allowed. The criteria as set out in the Guidance Notes for Investigation and Remediation of Contaminated Sites of: Petrol Filling Stations; Boatyards and Car Repair/Dismantling Workshops[22] issued by the EPD and relate primarily to Toxic Characteristic Leaching Procedure (TCLP) limits, as shown in Table 11.2.
Table 11.2 : Landfill disposal criteria for contaminated soil
|
Parameter |
TCLP Limits (ppm) |
|
Cadmium (Cd) |
10 |
|
Chromium (Cr) |
50 |
|
Copper (Cu) |
250 |
|
Nickel (Ni) |
250 |
|
Lead (Pb) |
50 |
|
Zinc (Zn) |
250 |
|
Mercury (Hg) |
1 |
|
Tin (Sn) |
250 |
|
Silver (Ag) |
50 |
|
Antimony (Sb) |
150 |
|
Arsenic (As) |
50 |
|
Beryllium (Be) |
10 |
|
Thallium (Tl) |
50 |
|
Vanadium (V) |
250 |
|
Selenium (Se) |
1 |
|
Barium (Ba) |
1000 |
During the construction phase, the main activities, which will potentially result in waste generation involve site clearance, trench excavation and construction of pumping station.
The typical waste types associated with these activities include:
· Site clearance waste;
· Construction and Demolition Materials (C&DM);
· Chemical waste;
· Sewage; and
· General refuse.
Most of the sewers/rising mains will be laid under existing roads/pavement and the pumping stations will only occupy a small area, and hence minimal site clearance waste is expected. If not properly managed, the handling and disposal of the clearance waste may cause adverse environmental impacts.
As most of the sewers/rising mains will be laid under existing roads/pavement, excavated materials will be generated from excavation of the pipe trenches. These materials are expected to be mostly soil, plus concrete/tarmac, which are inert. The anticipated quantities of excavated and backfilling material are presented in Table 11.4 (in the subsequent section).
Two sections of the proposed twin rising mains of Yuen Long Effluent Pipeline in Tin Shui Wan will be laid by the trenchless pipe jacking method. Those two trenchless sections are:
· Twin rising mains (approx. 200m) across the drainage channel beside Tin Wah Estate; and
· Twin rising mains (approx. 380m) across the Lai Yeun Fishing Pond beside Kenswood Court, Kingswood Villas.
Jacking pits and receiving pits will need to be constructed in the vicinity of the channel embankments and the existing channel embankment will need to be demolished, removed and subsequently reinstated. It should be noted that one of the risks inherent to the trenchless pipe jacking method is that the lead shield may breakdown before it reaches the receiving pit. In such an event, a rescue pit will be sunk to remove the studded shield and therefore some dredging works over the drainage channel and fishing pond may be required. In order to avoid dredging and excavation of sediment from the drainage channel and fishing pond, it is proposed to use the trenchless pipe jacking method to lay the twin rising mains. The mains will be laid at 1 to 2 m below the bottom of the drainage channel and fishing pond. It is estimated that approximately 1,790m3 of inert materials will need to be excavated, of which about 1,250m3 (about 70%) could be used for backfilling the launch and reception shafts. Approximately 540m3 of surplus excavated materials will need to be disposed of off-site.
In the event that the lead shield of the tunnelling machine is broken before it completes the whole length, a rescue pit will be sunk to remove it and therefore some dredging works over the channel and/or fishing pond will be required. It is estimated that about 50m3 of sediment will be required to be excavated for the construction of the rescue pit. Some of these sediments will be used for backfilling of the rescue pit.
The construction of the proposed pumping stations will generate C&DM which includes packaging wastes, excess or damaged materials, hoarding etc. The proposed pumping stations will typically consist of a superstructure and a substructure. Most of the E&M equipment will be housed within the superstructure. The best means to estimate the generate rate of C&DM will be to base the estimate on the gross floor area. The typical floor areas of the proposed pumping stations are shown in Table 11.3.
Table 11.3 : Typical floor areas of proposed pumping stations
|
Pumping Station |
Dimensions (m) |
Gross Floor Area (m2) |
|
Cassino Line PS |
25 x 20 |
500 |
|
Fan Tin San Tsuen/San Lung Tsuen PS |
40 x 30 |
1,200 |
|
San Tin PS |
40 x 30 |
1,200 |
|
Ngau Tam Mei PS |
40 x 40 |
1,600 |
|
Tam Mei Camp PS |
40 x 30 |
1,200 |
|
Mong Tseng PS |
40 x 30 |
1,200 |
|
Lau Fau Shan PS |
25 x 20 |
500 |
|
Proposed PS beside Yuen Long Sewage Treatment Works |
100 x 70 |
7,000 |
|
Shan Ha Tsuen PS |
40 x 30 |
1,200 |
|
Muk Kiu Tau Tsuen PS |
40 x 30 |
1,200 |
|
Pak Sha Tsuen PS |
25 x 20 |
500 |
|
Sham Chung Tsuen PS |
25 x 20 |
500 |
|
Shiu Tsiu San Tsuen PS |
25 x 20 |
500 |
|
Shung Ching San Tsuen PS |
25 x 20 |
500 |
|
Nga Yiu Tau PS |
25 x 20 |
500 |
|
Total |
19,300 |
|
Chemical waste, as defined under the Waste Disposal (Chemical Waste) (General) Regulation, includes any substance being scrap material, or unwanted substances specified under Schedule 1 of the Regulation. A complete list of such substances is provided under the Regulation; however, substances likely to be generated from the construction activities for the proposed gravity sewers/rising mains and pumping stations will, for the most part, arise from the maintenance of equipment. These may include, but need not be limited to the following:
· Scrap batteries or spent acid/alkali from their maintenance;
· Used paint, engine oils, hydraulic fluids and waste fuel;
· Spent mineral oils/cleaning fluids from mechanical machinery; and
· Spent solvents/solutions, some of which may be halogenated, from equipment cleaning activities.
Chemical waste may pose serious environmental, health and safety hazards if not stored and disposed of in an appropriate manner as outlined in the Waste Disposal (Chemical Waste) (General) Regulation and the Code of Practice on the Packing, Labelling and Storage of Chemical Waste [23]. These hazards may include:
· Toxic effects to workers;
· Adverse effects on air, water and land from spills; and
· Fire hazards.
Sewage will arise from amenity facilities used by the construction workforce and site office’s sanitary facilities. Night soil from chemical toilets will also be generated. If not properly managed, the sludge could cause odour and potential health risks to the workforce by attracting pests and other disease vectors.
The presence of a construction site with workers and site office will result in the generation of a variety of general refuse requiring disposal. General refuse will mainly consist of food waste, aluminium cans and waste paper.
The storage of general refuse has the potential to give rise to adverse environmental impacts. These include odour if the waste is not collected frequently (for example, daily), windblown litter, water quality impacts if waste enters water bodies, and visual impact. The sites may also attract pests, vermin, and other disease vectors if the waste storage areas are not well maintained and cleared regularly. In addition, disposal of wastes at sites other than approved landfills, can also lead to similar adverse impacts at those sites.
The potential environmental impacts associated with the handling and disposal of waste arising from the construction and operation of the Project were assessed in accordance with the criteria presented in EIA study brief No. ESB-082/2001 and Annexes 7 and 15 of the EIAO-TM, which are summarised as follows:
· Estimation of the types, timing and quantities of the wastes to be generated;
· Assessment of the secondary environmental impacts due to the management of waste with respect to potential hazards, air and odour emissions, noise wastewater discharges and traffic; and
· Assessment of the potential impact on the capacity of waste collection, transfer and disposal facilities.
As the proposed sewers/rising mains are located under existing roads/pavement and the pumping stations only occupy a small area, the quantity of vegetation that needs to be cleared will be minimal. No adverse waste impact from the disposal of site clearness waste is expected.
As indicated in Table 11.4, most of the excavated materials could be used for backfilling the trenches. The quantities of excavated materials and the volume to be disposed of are also summarised in Table 11.4. It is expected that the majority of excavated material will be inert soil.
Table 11.4:Disposal of excavated materials (with detailed breakdown)
|
Works Package |
Works Item |
Excavation Volume (m3) |
Backfilling Volume (m3) |
Volume to be Disposed (m3) |
Construction Period |
Disposal Rate (Average/Peak(a)) (m3/day) |
|
Works Packages and Works Items for Stage 2 Works |
||||||
|
Tin Shui Wai and San Wai Areas |
||||||
|
2A-1T |
OP1 (DE) |
105,000 |
68,113 |
36,887 |
11/05 – 10/06 (@365 days) (b) |
101.06 / 151.59 |
|
Conforming |
OS1 (DE) |
37,240 |
31,205.6 |
6,034.4 |
11/05 – 11/07(@763 days) |
7.91 / 11.87 |
|
|
OS2, OS3, OS4 & OS5 (NDE) |
12,4378 |
10,3973.4 |
20,404.6 |
11/05 – 11/07(@763 days) |
26.74 / 40.11 |
|
|
|
|
|
|
Combined: |
135.71 / 203.57 |
|
Tin Shui Wai and San Wai Areas |
||||||
|
Alternative scheme of |
AP1 (DE) |
105,000 |
68,113 |
36,887 |
11/05 – 10/06 (@365 days) (b) |
101.06 / 151.59 |
|
2A-1T |
AS1 (DE) |
10,450 |
8,756.7 |
1,693.3 |
11/05 – 11/07(@763 days) |
2.22 / 3.33 |
|
|
AS2, AS3, AS4, AS5 & AS6 |
143,348 |
119,857.2 |
23,490.8 |
11/05 – 11/07(@763 days) |
30.79 / 46.19 |
|
|
|
|
|
|
Combined: |
134.07 / 201.11 |
|
Ngau Tam Mei and San Tin Areas |
||||||
|
2A-2T |
P1 (DE) |
21,600 |
14,011.8 |
7,588.2 |
11/05 – 10/06 |
20.79 / 31.19 |
|
and |
P2 |
13,200 |
8,562.8 |
4,637.2 |
(@365 days) (b) |
12.70 / 19.05 |
|
2B-1T |
P3 |
12,000 |
7,784.3 |
4,215.7 |
|
11.55 / 17.33 |
|
|
P4 |
15,600 |
10,119.6 |
5,480.4 |
|
15.01 / 22.52 |
|
|
P5 |
4,500 |
2,919.1 |
1,580.9 |
|
4.33 / 6.50 |
|
|
S1, S2, S3, S4, S5, S6 & S7 |
72,639 |
69,257.6 |
3,381.8 |
11/05 – 11/07 (@763 days) |
4.43 / 6.65 |
|
|
|
|
|
|
Combined: |
68.81 / 103.24 |
|
Lau Fau Shan and Mong Tseng Areas |
||||||
|
2A-3T |
A1 |
5,000 |
3,243.5 |
1,756.5 |
11/05 – 10/06 |
4.81 / 7.22 |
|
|
A2 |
12,000 |
7,784.3 |
4,215.7 |
(@365 days) (b) |
11.55 / 17.33 |
|
|
G1 & G2 |
23,286 |
22,634.6 |
651.4 |
11/05 – 11/07 (@763 days) |
0.85 / 1.28 |
|
|
|
|
|
|
Combined: |
17.21 / 25.83 |
|
Shap Pat Heung Area |
||||||
|
2B-2T |
B1 |
12,000 |
7,784.3 |
4,215.7 |
11/05 – 10/06 |
11.55 / 17.33 |
|
|
B2 |
10,200 |
6,616.7 |
3,583.3 |
(@365 days) (b) |
9.82 / 14.73 |
|
|
B3 |
3,500 |
2,270.4 |
1,229.6 |
|
3.37 / 5.06 |
|
|
B4 |
3,750 |
2,432.6 |
1,317.4 |
|
3.61 / 5.42 |
|
|
B5 |
4,500 |
2,919.1 |
1,580.9 |
|
4.33 / 6.50 |
|
|
B6 |
4,500 |
2,919.1 |
1,580.9 |
|
4.33 / 6.50 |
|
2B-2T |
B7 |
4,500 |
2,919.1 |
1,580.9 |
|
4.33 / 6.50 |
|
|
H1. H2, H3, H4, H5, H6, H7, H8, H9, H10 & H11 |
37,297 |
36,503.9 |
793 |
11/05 – 11/07 (@763 days) |
1.04 / 1.56 |
|
|
|
|
|
|
Combined: |
42.38 / 63.60 |
|
2A-1T (conforming) +2A-2T/2B-1T+2A-3T+2B-2T: |
DE: 163,840 NDE: 362,850 Comb: 526,690 |
DE: 113,330 NDE: 300,645 Comb: 413,975 |
DE: 50,510 NDE: 62,206 Comb: 112,716 |
DE: 129.76/194.65 NDE: 134.35/201.59 Comb: 264.11 / 396.24 |
||
|
2A-1T (alternative) +2A-2T/2B-1T+2A-3T+2B-2T: |
DE: 137,050 NDE: 381,820 Comb 518,870 |
DE: 90,882 NDE: 316,528 Comb: 407,410 |
DE: 46,168 NDE: 65,292 Comb: 111,460 |
DE: 124.07/186.11 NDE:138.4/207.67 Comb: 262.47 / 393.78 |
||
Note: (a) Assume a peak generation rate of 1.5
(b) Assume the materials will be excavated in the first 12 months of construction
(c) DE – Designated Element; NDE – Non Designated Element
From the detailed breakdown, it is estimated that approximately 137,050m3 and 381,820m3of material will be extracted from 3 DE items and 38 NDE items respectively under four separated packages. Due consideration should be taken for reuse of as much excavated material as possible (approximately 90,882m3 of material from DE and 316,528m3 from NDE, i.e. about 79% of the excavated materials should be reused for the Project). Under four separated work packages, there will be 46,168m3C&D generated from the Designated Elements (3 work items – AP1, AS1 & P1), and 65,292m3 from the non-Designated Elements (38 work items).
In accordance with the ETWB’s Technical Circular No. 33/2002, which was enacted (13 Aug 02)well after the issue of the EIA study brief (ESB-082-2001 version 21 Sept 01), submission of C&D Material Management Plan (C&DMMP) is not required under the EIAO legislative framework for less than 50,000m3 C&D material from Designated Element and less than 300,000m3 from the non-Designated Elements.
As confirmed by DSD, there is neither a programme nor funding earmarked for the construction of the pumping stations and sewerage for Stage 2 works. A separate C&DMMP will be prepared by the DSD project office for departmental vetting before upgrading of this project to Category “A” in Public Works Programme. An overall Waste Management Plan (WMP) should incorporate DEP’s comments and be approved by DEP. Since the project site is located closed to the WBA or WCA, it is important to put control clauses in the contract to disposal waste away from the ecological sensitive areas. The WMP should also include the following:
· The type of C&D generated;
· The amount for each type of C&D material;
· The location of waste sorting; and
· The location of disposal.
The average and peak disposal rates for excavated materials are approximately 262m3/day and 394m3/day, respectively (DE: average 124.07 m3/day and peak 186.11 m3/day; NDE: average 138.4 m3/day and peak 207.67 m3/day). Due to the relatively small volume of excavated materials requiring disposal, it is not envisaged to have adverse impacts on the capacity of the available public filling facilities.
There are currently only a few development projects being planned that may require fill material for reclamation works which match the anticipated disposal schedule of C&D surplus material. These development projects, together with their tentative dates for reclamation and earth filling activities are shown below:
Table 11.5: Major development projects accept C&D materials
|
Development project |
Tentative date for reclamation activities |
|
Central Reclamation Phase III |
April 2003 to mid 2007 |
|
Wan Chai Development Phase II |
January 2004 to December 2007 |
|
Penny’s Bay Reclamation Phase II |
mid 2003 to mid 2007 |
|
South East Kowloon Development |
July 2004 to December 2010 |
In order to minimise the reuse option, DSD is requested to review whether there will be any confirmed concurrent projects that would take up some of the C&D material (mid 2005 until late 2007). If such projects exist, DSD should advise the possibility, timing and amount of material that could be reused within the department.
The final destinations of the excavated materials will be determined, subject to the availability of public filling facilities, by the Waste Management Plan to be submitted by the Contractors and agreed with CED. DSD has also formulated a master plan for handling C&D material from all DSD projects. The plan will be updated annually and submitted to CED. Regarding this project, DSD should consult the Public Fill Committee of the CED about the possible outlets for such excavated materials when the actual construction programme is finalized or this project is upgraded to Category A. This can ensure that the C&D material from all projects can be best utilised.
A Traffic Impact Assessment (TIA) has been prepared for this Project and the report indicated that the construction traffic generated by this Project (including the traffic associated with the of-site disposal of the surplus excavated material) volume is insignificant and will not cause adverse traffic impacts, provided that the recommended temporary traffic measures are implemented.
As certain sections of the proposed sewers/rising mains alignments pass close to potentially contaminated sites in some areas (e.g. car repair / dismantling works and mechanics cleaning activities), there is the possibility that the excavated materials will be contaminated. Section 12 addresses the land contamination issues. The disposal of contaminated materials, if any, needs to comply with the Landfill Disposal Criteria for Contaminate Soil as stipulated in Table 11.2.
The actual quantities of contaminated soil can only be estimated after conducting intrusive site investigation works after land resumption and hence cannot be estimated at this stage. If contaminated soils are found, the remediation methods proposed in Section 12 shall be followed.
Standard formwork should be used as far as practicable in order to minimise the arising of C&D materials. The use of more durable formwork or plastic facing for the construction works should be considered. The purchasing of construction materials should be carefully planned in order to avoid over ordering and wastage.
The Contractor should recycle as much of the C&D materials as possible on-site. Public fill and C&D waste should be segregated and stored in different containers or skips to enhance reuse or recycling of materials and their proper disposal. Where practicable, concrete and masonry can be crushed and used as fill. Steel reinforcing bar can be used by scrap steel mills. Different areas of the sites should be considered for such segregation and storage. The use of wooden hoardings should be avoided, and metal hoarding should be used to enhance the possibility of being recycled.
A charging policy for the disposal of waste to landfill will be enforced in the HKSAR. When it is implemented, this will provide additional incentive to reduce the volume of waste generated and to encourage proper segregation of inert material for disposal to public filling areas.
Excavated sediment (less than 50 m3) will be generated in the event that a rescue pit is required during pipe jacking across the drainage channel or fishing pond. They should be reused as far as possible and disposal of surplus excavated sediment to landfill should be considered as the last resort. The sediment should be dewatered and the disposal of the sediment should also comply with the Landfill Disposal Criteria for Contaminated Soil as stipulated in Table 11.2. The final disposal management should be agreed in advance with EPD (for landfill disposal) via the Waste Management Plan to be submitted by the Contractor.
If the excavated soil contains other contaminants in addition to the parameters in Table 11.2, approval for disposal will be assessed on a case-by-case basis by the EPD. It should be noted that in situ remediation methods for the contaminated soil should be adopted wherever possible and disposal of at landfill should always be considered as the last resort. Apart from landfill, another disposal outlet is the Chemical Waste Treatment Center (CWTC) if volume is small and the concentration of contaminants is too high that the soil can be classified as chemical waste.
As indicated in Section 11.2.1, the best means to estimate the generation of C&DM is based on the floor area. Table 11.3 indicates that the total floor area to be constructed is approximately 19,300m2. In accordance with the Reduction of Construction Waste Final Report[85], the C&DM generation rate of 0.1 m3 per 1m3 of gross floor area (GFA) is adopted for assessing the C&DM from construction of pumping stations. It is estimated that approximately 1,930m3 of C&DM will be generated from the construction of the pumping stations over a period of 25 months between November 2005 to November 2007. This represents the average and peak C&DM generation of 2.5m3/day and 3.8m3/day, respectively. With proper segregation, the volume of C&DM that could be reused as public fill is approximately 1,540m3 and the volume to be disposed of to landfills (C&D waste) is approximately 390m3. The average and peak generation of C&D waste which requires disposal at landfill is approximately 0.50m3/day and 0.76m3/day, respectively. The public fills will be transported to public filling areas at average and peak rate of 2.0m3/day and 3.0m3/day, respectively.
The generation of C&DM from construction of pumping stations is considered to be small and is not envisaged to have any adverse impact on the capacity of landfills and public filling area.
It is difficult to quantify the amount of chemical waste, which will arise from the construction activities as it will be highly dependent on the Contractor’s on-site maintenance intention and the quantities of plant and vehicles utilized. However, it is anticipated that the quantity of chemical waste, such as lubricating oil and solvent produced from plant maintenance will be small and in the order of less than hundred liters per month. The chemical waste to be generated from the construction activities will be readily accepted by the Chemical Waste Treatment Center (CWTC) at Tsing Yi.
Storage, handling, transport and disposal of chemical waste should be arranged in accordance with the Code of Practice on the Packaging, Labelling and Storage of Chemical Waste published by the EPD. Provided that this is followed, the potential environmental impacts arising from the handling, storage and disposal of a small amount of chemical waste generated from the construction activities will be negligible.
The number of construction workers to be employed on site is not available at this stage, however, it is expected to be small. As the workers will be scattered along the proposed gravity sewer alignment, a cost-effective solution will be to provide adequate number of portable toilets along the alignment to ensure that domestic sewage from site staff is properly collected. Depending on site conditions, land availability and site activities, the locations and number of portable toilets should be determined in the Waste Management Plan to be submitted by the Contractors and agreed by Engineer or Project Proponent. No adverse waste impact is envisaged provided that maintenance by licensed contractors is conducted regularly.
The number of workers to be employed for the project is not available at this stage, however it is expected to be small. Provided that the mitigation measures recommended in Section 11.6 are adopted, the potential environmental impacts caused by the storage, handling, transport and disposal of general refuse should be minimal. It is recommended that the general refuse should be collected on a daily basis and be delivered to the WENT or NENT Landfill for disposal. With respect to the anticipated small quantity of general refuse to be disposed of, adverse impacts to the operation of the landfills are not expected.
During the operational phase, the main waste types will include screenings and chemical waste generated from the operation of the pumping stations and the silt and debris from the maintenance of the sewers. If not properly managed, these could have potential to cause adverse environmental impacts. These include odour if the waste is not collected frequently and water quality impacts if waste enters water bodies.
The screenings, silt and debris, from the operation and maintenance of the proposed pumping stations and the maintenance of the gravity sewer will be disposed of at the WENT or NENT Landfill. Based on record from existing Ha Tsuen Pumping Station and associated sewer/rising mains (average daily flow of 60,000m3/day generated approximately 17m3 of screening, solid waste, silt and debris per month), it is estimated that the total volume of screenings, solid waste, silt and debris, arising from the fifteen proposed pumping stations, will amount to approximately 14.5m3 per month (Table 11.6).
Table 11.6: Screening generation rates
|
Package |
Pumping Stations |
Averaged hourly flow (m3/hr) |
Average daily flow (m3/day) |
Estimated Production Rate Per Month for Screening, Solid Waste, Silt and Debris (m3) |
|
2A-1T (Conforming and Alternative) |
Yuen Long Effluent (OP1/AP1) |
6,240 |
149,760 |
- (1) |
|
2A-2T and 2B-1T |
Cassino Line (P5) |
43 |
1,032 |
0.2924 |
|
2A-2T and 2B-1T |
Fan Tin San Tsuen/ San Lung Tsuen (P4) |
147 |
3,528 |
0.9996 |
|
2A-2T and 2B-1T |
San Tin (P3) |
230 |
5,520 |
1.564 |
|
2A-2T and 2B-1T |
Tam Mei Camp (P2) |
153 |
3,672 |
1.0404 |
|
2A-2T and 2B-1T |
Ngau Tam Mei (P1) |
882 |
21,168 |
5.9976 |
|
2A-3T |
Mong Tseung (A2) |
108 |
2,592 |
0.7344 |
|
2A-3T |
Lau Fau Shan (A1) |
63 |
1,512 |
0.4284 |
|
2B-2T |
Shan Ha Tsuen (B1) |
150 |
3,600 |
1.02 |
|
2B-2T |
Nga Yiu Tau (B6) |
46 |
1,104 |
0.3128 |
|
2B-2T |
Pak Sha Tsuen (B7) |
71 |
1,704 |
0.4828 |
|
2B-2T |
Sham Chung Tsuen (B3) |
42 |
1,008 |
0.2856 |
|
2B-2T |
Muk Kiu Tau Tsuen (B2) |
99 |
2,376 |
0.6732 |
|
2B-2T |
Shiu Tsiu San Tsuen (B4) |
32 |
768 |
0.2176 |
|
2B-2T |
Shung Ching San Tsuen (B5) |
64 |
1,536 |
0.4352 |
|
Total: |
200,880 |
14.484 |
||
Note: (1) YLEPS will only convey treated effluent; therefore, there is no screening generation.
Small quantities of chemical waste (mainly lubricant oil and paints) to be generated from the maintenance of the pumping station could be readily accepted at the CWTC. Provided that this occurs, the potential environmental impacts arising from the handling, storage and disposal of a small amount of chemical waste generated from the operation activities will be negligible.
Table 11.7 summarises the impacts during the construction and operation of the Project.
Table 11.7 : Summary of waste management impacts
|
Waste Type |
General Evaluation |
|
Construction Phase |
|
|
Site Clearance |
Vegetation cleared from proposed pumping stations site can be disposed of as general refuse. As most of the proposed pumping stations are located on developed land, the amount of site clearance waste will be minimal. |
|
C&DM |
Excavated Materials With detailed breakdown, it is estimated that approximately 137,050m3 and 381,820m3 of material will be extracted from 3 DE items and 38 NDE items respectively under four separated packages. Due consideration should be taken for reuse of as much excavated material as possible (approximately 90,882m3 of material from DE and 316,528m3 from NDE, i.e. about 79% of the excavated materials should be reused for the Project). Under four separated work packages, there will be 46,168m3 C&D generated from the Designated Elements (3 work items), and 65,292m3 from the non-Designated Elements (38 work items). The average and peak disposal rates for excavated materials from various packages are approximately 262m3/day and 394m3/day, respectively. Due to the relatively small volume of excavated materials, which requires disposal, it is not envisaged that this will have adverse impacts on the capacity of the public filling facilities. The final destinations of the excavated materials will be determined, subject to availability of public filling facilities, by the Waste Management Plan to be submitted by the Contractors and agreed by CED. A Traffic Impact Assessment has been conducted for this Project it concluded that the construction traffic generating from this Project (including the traffic associated with the off-site disposal of the surplus excavated material) will not cause adverse traffic impacts, provided that the temporary traffic measures as recommended are properly implemented. The actual quantities of contaminated soil can only be estimated after conducting intrusive site investigation works after land resumption. If contaminated soils are found, they shall be managed in accordance with the procedures as stipulated in the Working Paper for Land Contamination Assessment. C&DM from Construction of Pumping Stations Based on the C&DM generation rate of 0.1 m3 per 1m3 of gross floor area (GFA) constructed, it is estimated that approximately 1,930m3 of C&DM will be generated from the construction of the pumping stations over a period of 25 months between November 2005 to November 2007. This represents the average and peak C&DM generation of 2.5m3/day and 3.8m3/day, respectively. With proper segregation, the volume of C&DM that could be reused as public fill is approximately 1,540m3 and the volume to be disposed of to landfills (C&D waste) is approximately 390m3. The average and peak generation of C&D waste which requires disposal at landfill is approximately 0.50m3/day and 0.76m3/day, respectively. The public fills will be transported to public filling areas at average and peak rate of 2.0m3/day and 3.0m3/day, respectively. With respect to the small quantity of C&DM to be generated from the Project, it is not envisaged that the disposal of which to landfills and public filling areas will have affect the operations of these facilities. |
|
Chemical Waste |
It is difficult to quantify the amount of chemical waste, which will arise from the construction activities as it will be highly dependent on the Contractor’s on-site maintenance intention and the quantities of plant and vehicles utilized. However, it is anticipated that the quantity of chemical waste produced will be small and in the order to a few hundred litres per month. The chemical waste to be generated from the construction activities will be readily accepted at the Chemical Waste Treatment Center (CWTC) at Tsing Yi. Storage, handling, transport and disposal of chemical waste should be arranged in accordance with the Code of Practice on the Packaging, Labelling and Storage of Chemical Waste published by the EPD. Provided that this occurs, the potential environmental impacts arising from the handling, storage and disposal of a small amount of chemical waste generated from the construction activities will be negligible. |
|
Sewage |
The number of construction workers to be employed on site is not available at this stage, however, it is expected to be small. As the workers will be scattered along the proposed gravity sewer alignment, the more cost-effective solution will be to provide adequate number of portable toilets along the alignment. No adverse waste impact is envisaged provided that maintenance by licensed contractors is conducted regularly. |
|
General Refuse |
The number of workers to be employed for the project is not available at this stage, however it is expected to be small. Provided that the mitigation measures recommended in Section 11.6 are adopted, the potential environmental impacts caused by the storage, handling, transport and disposal of general refuse are expected to be minimal. With respect to the anticipated small quantity of general refuse to be disposed of, there will be no adverse impacts to the operation of the strategic landfills. |
|
Operational Phase |
|
|
Screenings, Silt and Debris from Operation and Maintenance |
The screenings, silt and debris, from the operation and maintenance of the proposed facilities will be disposed of at the WENT or NENT Landfill. With respect to their relatively small quantity (i.e. at a total of 14.5m3 per month of screenings, solid waste, silt and debris from the proposed pumping stations), it is not anticipated that the disposal of these wastes will cause any adverse impacts to the operation of the strategic landfills. |
|
Chemical Waste |
It is anticipated that the quantity of chemical waste arising during operation, such as lubricant oil and paints will be small and no adverse environmental impacts are envisaged. |
This section recommended the mitigation measures to avoid or minimize potential adverse environmental impacts associated with handling, collection and disposal of waste arising from the Project. The Contractors should incorporate these recommendations into a Waste Management Plan for the construction works. The Contractors should submit the plan to the Engineer for approval prior to the commencement of the construction works. Such a management plan should incorporate site specific factors, such as the designation of areas for the segregation and temporary storage of reusable and recyclable materials.
It is the Contractor’s (for the construction phase) and the Project Proponent’s (for the operational phase) responsibility to ensure that only reputable licensed waste collectors are used and that appropriate measures to minimize adverse impacts, including windblown litter and dust from the transportation of these wastes are in place. In addition, the Contractor must ensure that all the necessary waste disposal permits are obtained throughout the construction and operational phases.
Wherever practicable, excavated materials should be segregated from other wastes to avoid contamination thereby ensuring acceptability at public filling areas or land formation or reclamation sites and avoiding the need for disposal at landfill. The Contractor should obtain approval from EPD, and written agreement from relevant third party of those land formation or reclamation sites such as the Project Proponent, Engineer and Contractor for disposal. The priority for off-site disposal of surplus excavated material should be as follows:
· Transport to other land formation or reclamation sites for re-use as fill materials; and
· Transport to public filling areas.
The various waste management options can be categorised in terms of preference from an environmental viewpoint. The options considered to be more preferable have the least impacts and are more sustainable in the long term. Hence, the waste management hierarchy is adopted as follows:
· Avoidance and minimisation, that is, not generating waste through changing or improving practices and design;
· Reuse of materials, thus avoiding disposal (generally with only limited reprocessing);
· Recovery and recycling, thus avoiding disposal (although reprocessing may be required); and
· Treatment and disposal, according to relevant law, guidelines and good practice.
This hierarchy should be used to evaluate the waste management options, thus allowing maximum waste reduction and often reducing costs. For example, by reducing or eliminating over-ordering of construction materials, waste is avoided and costs are reduced both in terms of the purchasing of raw materials and in disposing of wastes. Records of quantities of wastes generated, recycled and disposal (locations) should be properly kept.
Standard formwork should be used as far as practicable in order to minimise the arising of C&DM. The use of more durable formwork or plastic facing for the construction works should be considered.
Any uncontaminated soil should be reused on site as far as possible, e.g. for landscape works, in order to minimise the amount of public fill to be disposed off-site. The Project Proponent should liaise with the Public Fill Committee to identify as far as possible suitable reclamation or site formation projects near the project site to reuse the material.
The design of the foundation works will minimise the amount of excavated material to be generated. Should piling be required, H-piling should be used as far as practical.
The purchasing of construction materials should be carefully planned in order to avoid over ordering and wastage.
The Contractor should recycle as much of the C&DM as possible on-site. Public fill and C&D waste should be segregated and stored in different containers or skips to enhance reuse or recycling of materials and their proper disposal. Concrete and masonry, for example, can be crushed and used as fill. Steel reinforcing bar can be used by scrap steel mills. Different areas of the sites should be designated for such segregation and storage.
The use of wooden hoardings shall not be allowed. An alternative material, which can be reused or recycled, for example, metal (aluminium, alloy, etc) shall be used.
Government has developed a charging policy for the disposal of waste to landfill. When it is implemented, this will provide additional incentive to reduce the volume of waste generated and to ensure proper segregation to allow disposal of inert material to public filling areas.
Chemical waste producers should be registered with the EPD. For those processes which generate chemical waste, it may be possible to find alternatives which generate reduced quantities or even no chemical waste, or less dangerous types of chemical waste.
Chemical waste that is produced, as defined by Schedule 1 of the Waste Disposal (Chemical Waste) (General) Regulation, should be handled in accordance with the Code of Practice on the Packaging, Handling and Storage of Chemical Wastes as follows. Containers used for storage of chemical wastes should:
· Be suitable for the substance they are holding, resistant to corrosion, maintained in a good condition, and securely closed;
· Have a capacity of less than 450 L unless the specification has been approved by the EPD; and
· Display a label in English and Chinese in accordance with instructions prescribed in Schedule 2 of the Regulations.
The storage area for chemical wastes should:
· Be clearly labelled and used solely for the storage of chemical wastes;
· Be enclosed on at least 3 sides;
· Have an impermeable floor and bunding, of capacity to accommodate 110% of the volume of the largest container or 20% by volume of the chemical waste stored in the area, whichever is greater;
· Have adequate ventilation;
· Be covered to prevent rainfall entering (water collected within the bund must be tested and disposed as chemical waste, if necessary); and
· Be arranged so that incompatible materials are adequately separated.
Disposal of chemical waste should:
· Be via a licensed waste collector; and
· Be to a facility licensed to receive chemical waste, such as the CWTC which also offers a chemical waste collection service and can supply the necessary storage containers; or
· Be to a re-user of the waste, under approval from the EPD.
Adequate numbers of portable toilets should be provided for the number of workers along the proposed gravity sewer alignment. The portable toilets should be maintained in a state, which will not deter the workers from utilizing these portable toilets. Night-soil should be collected by the licensed collectors regularly.
General refuse generated on-site should be stored in enclosed bins or compaction units separately from construction and chemical wastes. A reputable waste collector should be employed by the Contractor to remove general refuse from the site, separately from construction and chemical wastes, on a daily basis to minimize odour, pest and litter impacts. The burning of refuse on construction sites is prohibited by law.
Aluminium cans are often recovered from the waste stream by individual collectors if they are segregated and made easily accessible, so separate labelled bins for their deposit should be provided if feasible.
Office wastes can be reduced through the recycling of paper if volumes are large enough to warrant collection. Participation in a local collection scheme should be considered if one is available. In addition, waste separation facilities for paper, aluminium cans, plastic bottles etc., should be provided.
A trip-ticket system should be established in accordance with Works Bureau Technical Circular No. 21/2002 to monitor the disposal of public fill and solid wastes at public filling facilities and landfills, and to control fly-tipping. A trip-ticket system will be included as one of the contractual requirements and implemented by the Engineer. The Engineer should audit the result of the system.
A recording system for the amount of waste generated, recycled and disposed of (including the disposal sites) should be established during the construction stage.
Owing to the close proximity to the Wetland Conservation Area at Mai Po and North of Yuen Long EPS, training should be provided to workers on the concepts of site cleanliness and on appropriate waste management procedures, including waste reduction, reuse and recycling at the beginning of the Contract.
The main type of wastes generated during operational phase will be screenings from the pumping stations and silt and similar materials removed during the maintenance of the sewers/raising mains, which will be similar in nature to general refuse. The waste generated at the proposed pumping stations and sewer/raising mains should be stored in enclosed bins or compaction units separately. A reputable waste collector should be employed by the operators to remove the screenings from the pumping stations, on a daily basis to minimize odour, pest and litter impacts.
For chemical wastes generated during the operational phase, the mitigation measures are the same as those in Section 11.6.1 for Construction Phase.
With the implementation of recommended mitigation measures, in particular the establishment and implementation of a Waste Management Plan, minimal residual impacts are anticipated from either the construction or operation of the proposed Project.
It is recommended that audit of each waste stream should be periodically carried out during the construction phase to determine if wastes are being managed in accordance with the Waste Management Plan. The audits should look at all aspects of waste management including waste generation, storage, recycling, transport and disposal. Attention should also be paid to the site areas close to the Wetland Conservation Area (Mai Po and South of Yuen Long STW) to ensure there is no waste impact. Staff and workforce training should also emphasis on the prohibition of waste dumping. An appropriate audit programme would be to undertake a first audit at the commencement of the construction works and then quarterly audits, thereafter.
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