6.1.1 Key environmental issues in respect of the water quality impact associated with the Project are identified below.
· Water quality impacts during construction phase of the Project due to construction site runoff and wastewater arising from workforce and general site activities.
· Water quality impacts during operation phase of the Project due to polluted storm runoff.
· Water quality impacts from sewerage and sewage treatment facilities.
· The water quality impacts from the reclamation have been assessed and described in the Yau Tong Bay Reclamation EIA Report.
Environmental Impact Assessment Ordinance (EIAO), Cap. 499, S16
6.2.1 This Project is a Designation Project under the Schedule 3 of the EIAO. The “Technical Memorandum (TM) on Environmental Impact Assessment Process” was issued by the Environmental Protection Department (EPD) under Section 16 of the EIAO. This TM specifies the assessment method and criteria that will be followed in this Study. Reference sections in the TM providing the details of assessment criteria and guidelines that are relevant to the water quality assessment include:
Annex 6 - Criteria for Evaluating Water Pollution
Annex 14 - Guidelines for Assessment of Water Pollution
Water Quality Objectives (WQO)
6.2.1
The Water Pollution Control
Ordinance (Cap.358) provides the major statutory framework for the protection
and control of water pollution in
Technical Memorandum (TM)
6.2.2 Besides setting the WQO, the WPCO controls effluent discharging into the WCZ through a licensing system. A Technical Memorandum (TM) on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters was issued under the WPCO which gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluents. Sewage from the proposed construction activities should comply with the TM standards for effluents discharged into the marine waters of Junk Bay WCZ. Relevant TM standards are listed in Table 6.2.
Practice Note (PN)
6.2.3 A practice note (PN) for professional persons was issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with ten types of discharge from a construction site. These include surface runoff, groundwater, boring and drilling water, bentonite slurry, water for testing and sterilization of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities. Practices given in the PN should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.
6.2.4 The Hong Kong Planning Standards and Guidelines (HKPSG), Chapter 9 (Environment), provides additional information on regulatory guidelines against water pollution for sensitive uses such as aquaculture and fisheries zones, bathing waters and other contact recreational waters.
Water Supplies Department Water Quality Objectives
6.2.5 Besides the WQO set under the WPCO, the Water Supplies Department has also specified a set of seawater quality objectives for water quality at the seawater intake. The list is shown in Table 6.3. The relevant criteria for suspended solids (SS) are the target limit of 10mgL-1 and the tolerable limit of 20mgL-1. WSD have indicated in the EIA study for the SEKD[1] that the tolerable limit should be met at all times.
Table 6.1 Summary
of Water Quality Objectives for the
|
Objectives |
Sub-Zone |
|
|
Offensive
Odour, Tints |
Not to be present |
Whole zone |
|
Colour |
Not to exceed 50 Hazen
units, due to human activity |
Inland waters |
|
Visible foam,
oil scum, litter |
Not to be present |
Whole zone |
|
E. coli. |
Not to exceed 1000 counts
per 100 mL, calculated as the geometric mean of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days |
Inland waters |
|
Dissolved Oxygen
(DO) within 2 m of the seabed |
Not less than 2.0 mgL-1
for 90% of samples |
Marine waters |
|
Depth averaged
DO |
Not less than 4.0 mgL-1
for 90% of samples |
Marine waters |
|
Dissolved
Oxygen |
Not less than 4.0 mgL-1 |
Inland waters |
|
pH |
To be in the range of 6.5
- 8.5, change due to human activity not to exceed 0.2 |
Marine waters |
|
|
Not to exceed the range of
6.0 - 9.0 due to human activity |
Inland waters |
|
Salinity |
Change due to human
activity not to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to
human activity not to exceed 2 oC |
Whole zone |
|
Suspended
solids |
Not to raise the ambient
level by 30% caused by human activity |
Marine waters |
|
|
Annual median not to
exceed 25 mgL-1 due to human activity |
Inland waters |
|
Ammonia |
Annual mean not to exceed
0.021 mg L-1 as unionised form |
Whole zone |
|
Nutrients |
Shall not cause
excessive algal growth |
Marine waters |
|
|
Annual mean depth averaged
inorganic nitrogen not to exceed 0.4 mgL-1 |
Marine waters |
|
BOD5 |
Not to exceed 5 mgL-1 |
Inland waters |
|
Chemical Oxygen Demand |
Not to exceed 30 mgL-1 |
Inland waters |
|
Toxic
substances |
Should not attain such
levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic
effects in humans, fish or any other aquatic organisms. |
Whole zone |
|
|
Human activity should not
cause a risk to any beneficial use of the aquatic environment. |
Whole zone |
Source: Statement
of Water Quality Objectives (
Table
6.2 Standards for Effluent
Discharged into the inshore waters of the
|
Flow
rate (m3 day-1) Determinand |
<=10 |
>10
and <200 |
>200
and <400 |
>400
and <600 |
>600
and <800 |
>800
and <1000 |
>1000
and <1500 |
>1500
and <2000 |
>2000
and <3000 |
>3000
and <4000 |
>4000
and <5000 |
>5000
and <6000 |
|
pH (pH units) |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
6 - 9 |
|
Temperature (oC) |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
|
Colour (lovibond units) (25 mm cell
length) |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
Suspended solids |
50 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
|
BOD |
50 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
|
COD |
100 |
80 |
80 |
80 |
80 |
80 |
80 |
80 |
80 |
80 |
80 |
80 |
|
Oil & Grease |
30 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
|
Iron |
15 |
10 |
10 |
7 |
5 |
4 |
2.7 |
2 |
1.3 |
1 |
0.8 |
0.6 |
|
Boron |
5 |
4 |
3 |
2.7 |
2 |
1.6 |
1.1 |
0.8 |
0.5 |
0.4 |
0.3 |
0.2 |
|
Barium |
5 |
4 |
3 |
2.7 |
2 |
1.6 |
1.1 |
0.8 |
0.5 |
0.4 |
0.3 |
0.2 |
|
Mercury |
0.1 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
|
Cadmium |
0.1 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
|
Other toxic metals individually |
1 |
1 |
0.8 |
0.7 |
0.5 |
0.4 |
0.25 |
0.2 |
0.15 |
0.1 |
0.1 |
0.1 |
|
Total toxic metals |
2 |
2 |
1.6 |
1.4 |
1 |
0.8 |
0.5 |
0.4 |
0.3 |
0.2 |
0.14 |
0.1 |
|
Cyanide |
0.2 |
0.1 |
0.1 |
0.1 |
0.1 |
0.1 |
0.05 |
0.05 |
0.03 |
0.02 |
0.02 |
0.01 |
|
Phenols |
0.5 |
0.5 |
0.5 |
0.3 |
0.25 |
0.2 |
0.13 |
0.1 |
0.1 |
0.1 |
0.1 |
0.1 |
|
Sulphide |
5 |
5 |
5 |
5 |
5 |
5 |
2.5 |
2.5 |
1.5 |
1 |
1 |
0.5 |
|
Total residual chlorine |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
Total nitrogen |
100 |
100 |
100 |
100 |
100 |
100 |
80 |
80 |
50 |
50 |
50 |
50 |
|
Total phosphorus |
10 |
10 |
10 |
10 |
10 |
10 |
8 |
8 |
5 |
5 |
5 |
5 |
|
Surfactants (total) |
20 |
15 |
15 |
15 |
15 |
15 |
10 |
10 |
10 |
10 |
10 |
10 |
|
E. coli. (count per 100mL) |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
5000 |
Notes:
1. All units are in mgL-1 unless otherwise stated.
2. All figures are upper limits unless otherwise indicated.
Source: EPD Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters, Table 9a.
Table 6.3 WSD Standards at Sea Water Intakes
|
WSD Target Limit |
|
|
Colour (HU) |
< 20 |
|
Turbidity (NTU) |
< 10 |
|
Threshold Odour Number (odour unit) |
< 100 |
|
Ammoniacal Nitrogen |
< 1 |
|
Suspended Solids |
< 10 |
|
Dissolved Oxygen |
> 2 |
|
Biochemical Oxygen Demand |
< 10 |
|
Synthetic Detergents |
< 5 |
|
E. coli. (count per 100 mL) |
< 20,000 |
Existing water sensitive receivers (WSRs)
6.3.1 Existing water sensitive receivers in the vicinity of the site are identified below. Figure 6.2 shows the locations of the water sensitive receivers.
· Seawater intakes of two major WSD saltwater pumping stations, namely the Cha Kwo Ling Saltwater Pumping Station (CKLSPS) and Yau Tong Saltwater Pumping Station (YTSPS), which supply flushing water to the neighbouring areas;
· The Dairy Farm Factory Saltwater Cooling Intake (DFSI).
Planned sensitive receivers
6.3.2 Planned sensitive receivers include:
· Seawater intakes at the potential sites for future reprovisioning of the Cha Kwo Ling (NCKLSPS) and Yau Tong saltwater pumping stations (NYTSPS) after completion of the reclamation of Yau Tong Bay (Full Reclamation option) and the Western Coast Road (WCR-Coastal option). The proposed locations of the NCKLSPS and NYTSPS are also shown in Figure 6.2.
6.3.3
The nearest WSD saltwater
intake on
6.4
Baseline Conditions In
Existing Water Quality in
6.4.1
EPD has been conducting routine
monitoring of the quality of
· VM1 – to the south of YTB, near Lei Yue Mun.
·
VM2 – to the west of YTB, near
6.4.2
The suspended solid (SS)
concentration is the most crucial parameter pertinent to the water quality
assessment during the construction phase of the project where silty site runoff
may be directly discharged into the marine waters. The depth average SS reading between the
period 1/1996 to 8/1998 at VM1 and VM2 are shown in Table 6.5. The variance at station VM1
is higher than that in VM2 which may be attributed to reclamation activities,
such as
Future Water Quality in
6.4.3 Under the YTB reclamation, the existing ship building and repairing facilities at all marine lots in the site will be decommissioned, thus removing direct sources of pollution into the bay. The demolition of industries and workshops along the waterfront will also remove potential sources of effluent discharge into the bay and the neighbouring water body.
6.4.4
With the increased enforcement
exerted over industrial effluents to comply with the TM on Effluent Standards
for the VHWCZ under the WPCO, the water quality in
Table 6.4 Summary statistics
of EPD Marine Water Quality Data for 1999
|
Determinand |
|
|
|
|
|
|
VM1 |
VM2 |
|
Number of
samples |
|
12 |
12 |
|
Temperature (°C) |
|
23.1 (17.7-27.3) |
23.3 (17.7-27.3) |
|
Salinity (ppt) |
|
32.1 (31.1-33.9) |
31.8 (30.8-33.7) |
|
Dissolved Oxygen (mg L-1) |
Surface |
4.7 (3.6-6.2) |
4.4 (2.9-5.9) |
|
|
Bottom |
4.8 (3.7-6.4) |
4.5 (3.2-5.9) |
|
Dissolved Oxygen (% Saturation) |
Surface |
65 (52-81) |
62 (43-77) |
|
|
Bottom |
67 (53-82) |
62 (48-77) |
|
pH |
|
8.0 (7.7-8.5) |
8.0 (7.7-8.4) |
|
Secchi Disc Depth (m) |
|
2.6 (2.0-3.0) |
2.3 (1.9-3.5) |
|
Turbidity (NTU) |
|
8.8 (3.7-21.7) |
7.8 (3.8-19.2) |
|
Suspended Solids (mg L-1) |
|
5.8 (1.8-14.5) |
4.7 (1.6-8.3) |
|
5-day Biochemical Oxygen
Demand (mg L-1) |
|
0.7 (0.4-1.1) |
0.9 (0.5-1.6) |
|
Ammoniacal Nitrogen (mg L-1) |
|
0.19 (0.01-0.34) |
0.23 (0.03-0.37) |
|
Unionized Ammonia (mg L-1) |
|
0.007 (0.001-0.013) |
0.008 (0.003-0.015) |
|
Nitrite Nitrogen (mg L-1) |
|
0.02 (0.01-0.04) |
0.02 (0.01-0.04) |
|
Nitrate Nitrogen (mg L-1) |
|
0.08 (0.03-0.14) |
0.10 (0.03-0.18) |
|
Total Inorganic Nitrogen
(mg L-1) |
|
0.30 (0.15-0.45) |
0.35 (0.20-0.46) |
|
Total Kjeldahl Nitrogen
(mg L-1) |
|
0.48 (0.22-0.71) |
0.53 (0.33-0.74) |
|
Total Nitrogen (mg L-1) |
|
0.59 (0.35-0.83) |
0.65 (0.51-0.83) |
|
Ortho-phosphate Phosphorus
(mg L-1) |
|
0.04 (0.02-0.06) |
0.04 (0.03-0.07) |
|
Total Phosphorus (mg L-1) |
|
0.06 (0.03-0.09) |
0.07 (0.04-0.09) |
|
Silica (as SiO2) (mg L-1) |
|
0.9 (0.3-1.3) |
1.0 (0.5-1.5) |
|
Chlorophyll-a (mg L-1) |
|
2.6 (1.2-5.2) |
2.3 (1.1-5.2) |
|
Phaeo-pigment (mg L-1) |
|
1.0 (0.2-3.8) |
0.8 (0.2-3.2) |
|
E.coli.
(cfu/100mL) |
|
8900 (2400-26000) |
11000 (1900-93000) |
|
Faecal Coliforms
(cfu/100mL) |
|
16000 (3700-45000) |
22000 (4500-150000) |
Notes:
1. Data presented are depth-averaged data, unless specified otherwise.
2. Data presented are annual arithmetic means except for E.coli. and faecal coliform data which are geometric means.
3. Data enclosed in brackets indicate the ranges.
Table 6.5 Depth average suspended solid concentration for stations VM1 and VM2.
|
Depth averaged SS [mgL-1] |
1996 |
1997 |
1998(1) |
Overall average |
|
Monitoring station VM1 |
||||
|
Mean(2) |
8.63 (5.7) |
5.64 (3.26) |
4.64 (3.89) |
6.51 (4.33) |
|
Range |
3.9-17.1 |
2.63-10.8 |
1.77-7. |
1.77-17.1 |
|
90 percentile |
15.87 |
7.95 |
6.7 |
10.68 |
|
Monitoring station VM2 |
||||
|
Mean |
7.19 (6.68) |
5.48 (4.26) |
5.03 (4.83) |
6.01 (5.31) |
|
Range |
3.4-11.5 |
2.23-10.43 |
2.6-13. |
2.23-13. |
|
90 percentile |
9.91 |
9.48 |
7.54 |
9.98 |
Notes:
1. Average is obtained for the first 8 months, i.e. between 1/98 – 8/98.
2. Surface layer values are shown in brackets.
Data source: EPD routine marine water quality monitoring program.
6.5 Environment Conditions in Other Water Systems
6.5.1
Besides the marine water
system, other major water systems covered by the study would be the Kwun Tong Nullah
in the vicinity of the site as well as the future stormwater system of
6.5.3 The background information on the Kwun Tong Nullah has been reviewed and is discussed in Sections 6.5.4 to 6.5.8. No data can be obtained for the existing storm water drains at Yau Tong area. Future pollution load in the stormwater system of Yau Tong area was estimated under the current study and is presented in Table 6.10 and Sections 6.7.7 to 6.7.11.
Water Quality in Kwun Tong Nullah
Existing Condition
6.5.4 Kwun Tong Nullah is a large water channel adjacent to the study area. No regular monitoring data are available for this nullah. However, monitoring work has been conducted regarding the water and sediment quality at the existing Kwun Tong Nullah by various recent studies. Data have been reviewed from the Feasibility Study for Nullah Decking and Associated Improvement.
6.5.5 Table 6.6 shows the water quality monitoring results for selected parameters. The water quality in the upper section is classified according to the WQI as fair. However, in the downstream section, the water quality is very bad. The heavy organic load is indicated in the high BOD5 value (48 mgL-1) and the low DO (0.8 mgL-1). In the lower section, water quality is affected by contaminated sediment which has a high organic matter content reflected by high total organic carbon level (7.58%).
Table 6.6 Summary of Water Quality Monitoring Results for Kwun Tong Nullah in March 1997
|
|
Section Name |
|
|
Parameter |
|
|
|
PH Value |
7.4 |
7.1 |
|
Temperature (°C) |
21.8 |
22.9 |
|
Salinity (ppt) |
1.9 |
11.5 |
|
Dissolved Oxygen (mgL-1) |
4.9 |
0.8 |
|
Dissolved Oxygen Saturation (%) |
56 |
9 |
|
Suspended Solids (mgL-1) |
53 |
293 |
|
E.coli (cfu 100 mL-1) |
4,500,000 |
380,000 |
|
Ammoniacal Nitrogen (mgL-1) |
0.32 |
5.9 |
|
Biochemical Oxygen Demand (mgL-1) |
35 |
48 |
|
Water Quality Index |
9 (Fair) |
15 (Very Bad) |
6.5.6
With the implementation of
water pollution control measures under the East Kowloon SMP, it is assumed that
only 5% of the total sewage flow generated in the
6.5.7
Note that the effluent
dissolved oxygen (DO) content of 3.78 mgL-1 at the outfall is
above the WSD target limit at saltwater intake of 2 mgL-1 but
slightly lower than the WQO of 4 mgL-1. With further mixing in
6.5.8 Based on the predicted effluent quality at the new KTN outfall, the effective loading at the outfall of the new KTN (Table 6.9) is then estimated by multiplying the effluent pollutant concentration and the discharge flow rate, including the tidal flow within the nullah.
Table 6.7 Flow and loads into the Kwun Tong Nullah in year 2011
|
Parameter |
5% residual flows from expedient connections |
1% residual flows from expedient connections |
|
Flow (m3 d-1) |
10,121 |
2,024 |
|
DO (mgL-1) |
2 |
2 |
|
BOD5 (kg d-1) |
2,305 |
461 |
|
SS (kg d-1) |
2,029 |
406 |
|
Ammoniacal Nitrogen (kg d-1) |
178.4 |
35.7 |
|
E. coli (count per day) |
1.48 x 1015 |
2.97 x 1014 |
Table 6.8 Predicted Effluent Quality at the Outfall of the New Kwun Tong Nullah
|
Assumption |
Flow Rate (3) [m3
d-1] |
DO [mgL-1] |
BOD5
[mgL-1] |
SS [mgL-1] |
Ammoniacal
Nitrogen [mgL-1] |
E. coli
[count per 100 mL] |
|
with 5% residual flows from expedient connections |
77000 |
3.78 |
0.83 |
31.2 |
0.15 |
24040 |
|
with 1% residual flows from expedient connections |
68900 |
4.73 |
0.04 |
11.3 |
0.01 |
1060 |
Notes:
1. Calculations were based on EPD routine monitoring data at station VM1 in year 1997.
2. Depth averaged values were assumed.
3. Flow rate include the tidal flow within the new Kwun Tong nullah.
Table 6.9 Effective load at the outfall of the Kwun Tong Nullah in year 2011
|
Parameter |
5% residual flows from expedient connections |
1% residual flows from expedient connections |
|
BOD5 (kg d-1) |
64 |
3 |
|
SS (kg d-1) |
2404 |
780 |
|
Ammoniacal Nitrogen (kg d-1) |
11.6 |
0.6 |
|
E. coli (count per day) |
1.48 x 1015 |
2.97 x 1014 |
6.6 Construction Phase Assessment
6.6.1 During construction phase of the project, the nearby marine water quality is potentially affected by:
· construction site runoff;
· wastewater arising from workforce; and
· accidental spillage of chemical waste from general site activities.
6.6.2 During site formation and construction, topsoil would be exposed and an elevated level of suspended particles would be present in the surface run-off. Water used for wheel washing would also have an increased level of suspended solids. Sediment laden runoff may carry pollutants (adsorbed onto the particle surfaces) which would contaminate the receiving marine waters. If uncontrolled, an excessive amount of sediments may be washed into the downstream receiver waters.
6.6.3 Wastewater generated from the canteen and mechanical workshops, if any, and domestic sewage from the workforce would also be generated during the construction phase. It has been estimated that there would be about 300 people working on site during the construction phase of the project, and about 23 m3 of wastewater would be generated from the workforce each day [2]. There would be an impact on the nearby environment if this wastewater is not properly treated before it is disposed to public sewers or marine waters.
6.6.4 The excavation, site formation/preparation and construction of new developments will require numerous and various earth moving equipment, on-site concrete batching plant and crushing plant. Provision of refuelling and mechanical servicing facilities for this construction plant and equipment will involve the storage of potentially hazardous materials. The intensity of activity at the project sites could give rise to spillage of these materials including oil, lubricants, cleaning fluid, solvents and rags. Accidental spillage of fuel oil could also arise from the fleet of construction vehicles on site. Without effective management, the use and disposal of these substances could contaminate the air, ground and marine environment.
6.6.5 During excavation works, no groundwater will be discharged into the stormwater drains or marine waters and therefore the impacts arising from the discharge of groundwater is anticipated to be minimal.
6.7 Operational Phase Assessment
Sewerage Impact
6.7.3 While the KTPTW will have sufficient capacity to handle the additional flow from the development until 2011, the HATS tunnel will become under-capacity by 2011. A mitigation/contingency measure in the form of an on-site retention tank will be provided for the phases of development which come on-line after 2011 in the event that the KTPTW is overloaded after 2011, ensuring that the peak flow to the KTPTW is not increased. The necessity or the exact size of the retention tank will need to be reviewed during the detailed design stage. If the retention tank is provided, stand-by pumps and dual power supply should be installed to ensure reliable operation of the tank and to minimise overflow. If the retention tank is not manned 24 hours, telemetry system should be provided to other 24-hour facilities to ensure the operation of the retention tank will be monitored continuously and any malfunctioning of the retention tank will be readily detected and rectified.
6.7.5 There would be no major water quality issues associated with the proposed development based on the sewage treatment and disposal method recommended above.
Polluted Storm Water Impact
6.7.6 Another potential water quality impact during the operational phase of the project would be due to the stormwater generated from the site. As part of the YTB development, a concrete decking will be built over the existing submarine pipelines near the northern part of YTB. Since the water flow under the decking may be relatively low, polluted stormwater discharges from the Yau Tong area including the proposed development as well as the new Kwun Tong Nullah may be accumulated under the decking and deteriorate the local water quality. The potentially reprovisioned Cha Kwo Ling (NCKLSPS) and Yau Tong (NYTSPS) Saltwater Pumping Stations, are the future WSRs which may be affected by the stormwater pollution. Information on the NCKLSPS and NYTSPS can be referred to Section 6.3 and Figure 6.2.
6.7.7 It is considered that pollutants in the storm water discharged from Yau Tong catchment would be contributed by two major sources (a) surface runoff during the wet seasons and (b) expedient connections of sewage discharges to the storm water drains. Estimated pollution loads from the Yau Tong stormwater system for year 2011 are summarised in Table 6.10.
Table 6.10 Year 2011 Stormwater Pollution loads at Yau Tong Area
|
Parameter |
Yau Tong Stormwater Catchment (including the Proposed Development) |
||
|
Expedient Connections |
Surface Runoff |
Total |
|
|
BOD5 (kg d-1) |
588 |
150 |
738 |
|
SS (kg d-1) |
503 |
289 |
792 |
|
NH3-N (kg d-1) |
48 |
1.3 |
49 |
|
E. coli (count per day) |
4.09 x 1014 |
-- |
4.09 x 1014 |
6.7.8 The pollution loads due to expedient connections in Table 6.10 are based on the assumption that 5% of the total pollution load generated in the area from residential, commercial and industrial sources would remain in the storm system by year 2011. Methodology of quantifying the total pollution load generated in the Yau Tong stormwater catchment including the proposed development is detailed in Appendix 6A.1.
6.7.9 Pollution loads due to surface runoff generated in the Yau Tong catchment are based on the pollutant concentrations of urban runoff samples collected under the EPD Pilot Study of Stormwater Pollution. Detailed calculations are also given in Appendix 6A.2.
6.7.10 Figure 6.4 shows the future stormwater catchment for Yau Tong area including the proposed development (Full Reclamation option). As shown in Figure 6.4, the Yau Tong stormwater catchment would be divided into 4 small stormwater basins. Stormwater generated in the catchment would be diverted to the coastal waters via 3 individual storm outfalls.
Particle Modelling
6.7.11 Particle model will be employed to simulate the water quality effects due to the polluted stormwater discharges from the Yau Tong area including the proposed development (Full Reclamation option) as well as the Kwun Tong Nullah. The water quality impact on the planned water sensitive receivers, namely the potentially reprovisioned Cha Kwo Ling Saltwater Pumping Station and Yau Tong Saltwater Pumping Station, will be assessed. The 2-dimension MIKE 21 model developed by Danish Hydraulic Institute (DHI) will be used for the calculations. The model set-up and the grid size adopted are given in Appendix 6B.
6.7.12
The Scenario 1B coastline
configuration, as adopted in the Reclamation of YTB, EIA Study, will be used as
a base for the model (Figure 6.5). Scenario 1B represents the operation
phase with YTB reclaimed under the Full Reclamation option. It also reflects
the development of SEKD study1 as at March 1999 that the Kwun Tong
Nullah is extended and the proposed breakwater for the cargo working area is
shifted towards Kwun Tong. (In contrast
to various scenarios of the SEKD development proposed in 2001, the 1999
scenario contains larger extent of reclamation and, thus, represents the worst
case hydrodynamic impact upon the
6.7.13
Pollution load discharges from
the Yau Tong stormwater catchment would be simulated as a single point source
at the month of the central stormwater culvert of the new development (Figure 6.5). A conservative source for the particle model
would be discharged at the mouth of the new Kwun Tong Nullah and the central
box culvert of the proposed development respectively, with an arbitrary
discharge rate of 1 kg/s. The pollutant
elevation in
Impact due to the Polluted Stormwater from the New Kwun Tong Nullah (KTN)
Water Quality in Victoria Harbour Water Control Zone (VHWCZ)
6.7.14 Dilution and dispersion in the vicinity of the outfall for the Full Reclamation option is simulated using the 2D particle model and the details are given in Appendix 6C. In general, the particle model result suggests that the pollutant concentration will be diluted by more than 10 times within 500 m from the outfall of the new KTN.
6.7.15 Based on the effective loading at the new KTN outfall (Table 6.9) and the particle model results (Appendix 6C), the predicted increase in biochemical oxygen demand (BOD5), SS, Ammoniacal Nitrogen and E. Coli. in Victoria Habour and at the WSRs are shown in Table 6.11. No decay factor was incorporated in the particle model giving a conservative prediction. Comparing the predicted and ambient values, obtained from EPD routine monitoring data at station VM1 in year 1997 (Table 6.4), only slight increase in the above parameters is observed in the Victoria Harbour WCZ, satisfying the WQOs. Typically, SS in the VHWCZ increases by 0.14 mgL-1 (3%) above the ambient of 5.6 mgL-1, which is lower than the WQO requirement. Since no secondary contact recreation zone nor bathing beach zone has been identified in the study area, the predicted increase in E. Coli. of 11 counts per 100mL, over the ambient of 5780 counts per 100mL (Table 6.11), is considered acceptable. From the particle model results (Appendix 6C), the pollutant concentration will be diluted by more than 10 times within 500 m from the outfall of the new Kwun Tong nullah. Assuming the ambient DO level of 4.85 mgL-1 from EPD’s routine monitoring data at station VM1 (Table 6.4), the 10 times dilution corresponds to an increase in the DO level from 3.78 mgL-1 to 4.74 mgL-1. Taking into account the BOD5 of less than 0.7 mgL-1, the DO level in the VHWCZ is expected to meet the WQO.
Water Quality under the Proposed Concrete Decking
6.7.16 For the Full Reclamation option, the water quality under the proposed concrete decking also satisfies the WQOs with small increase in BOD5, SS, Ammoniacal Nitrogen and E. Coli. (Table 6.11). Based on the predicted pollutant dilution of 2.85 times from the outfall to under the decking, the DO level is estimated to be approximately 4.5 mgL-1. Considering the low level of predicted BOD5 and ammoniacal nitrogen from the furture Kwun Tong nullah, no odour problem is expected.
6.7.17
The particle model result also
revealed that the pollutants discharged from the new Kwun Tong nullah will take
an average time of less than 4 hours to be flushed out of the decking section
and into
6.7.18
With a smaller reclamation area
and concrete decking at the mouth of YTB, and a more streamline water front in
the Minimized Reclamation option, the tidal flushing under the proposed
concrete decking is expected to improve as the inner part of the embayment is
more exposed to the flow current in
Table 6.11 Impact of the Kwun Tong Nullah - Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes
|
Description |
BOD5 [mgL-1] |
SS [mgL-1] |
Ammoniacal
Nitrogen [mgL-1] |
E. Coli. [count per 100mL] |
|
Victoria
Harbour Water Control Zone (VHWCZ) |
||||
|
Ambient level (1) |
0.7 |
5.6 |
0.22 |
5780 |
|
Predicted
increase in VHWCZ |
<0.01 |
< 0.14 |
< 6.71 x 10-4 |
< 11 |
|
Predicted increase
under the proposed concrete decking |
< 0.01 |
< 0.56 |
< 2.68 x 10-3 |
< 43 |
|
WQO |
N/A (6) |
< 30% over ambient and
median < 25mgL-1 |
< 0.44 (5) |
N/A (4) |
|
Existing Water Sensitive Receivers (WSRs) |
||||
|
Maximum
increase at CKLSPS (2) |
0.01 |
0.54 |
2.6 x 10-3 |
41 |
|
Maximum
increase at YTSPS (2) |
0.01 (7) |
0.31 (7) |
1.48 x 10-3 (7) |
24 (7) |
|
Planned Water Sensitive Receivers (WSRs) |
||||
|
Maximum
increase at NCKLSPS (2) |
0.02 |
0.68 |
3.3 x 10-3 |
53 |
|
Maximum
increase at NYTSPS (2) |
0.01 |
0.31 |
1.48 x 10-3 |
24 |
|
WSD target
limit at saltwater intake |
< 10 |
< 10 |
<1 |
< 20000 |
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year 1997.
2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively, while NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation respectively.
3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.
5. With reference to the WQO of 0.021 mgL-1 for unionized ammonia, the total ammonia present at 23oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.
6. No WQO standards for BOD5 in marine waters.
7. The existing YTSPS intake location will be reclaimed by the WCR development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the Kwun Tong Nullah as the YTSPS, similar impact is expected.
8. The results presented are based on the Full Reclamation option for YTB.
Water Quality at the WSD Saltwater Pumping Stations
6.7.19 In the Full Reclamation option, the BOD5, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS), taking into account the predicted maximum increases associated with the NKTN and the ambient levels, are well within the WSD target limit (Table 6.11), and thus, unacceptable impact is not expected. For the two planned water sensitive receivers, namely the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS) under the WCR-Coastal option reclamation and the potential site reserved for the reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) under the YTB reclamation (Full Reclamation option), the relevant water quality parameters is also expected to satisfy the WSD target limit (Table 6.11).
6.7.20 Despite of the compliance of the WSD target limit at the existing and the potential site for future reprovisioning of the CKLSPS, the predicted results suggested that the water quality at the existing CKLSPS intake will be slightly better than that at the potential site for its reprovisioning. Hence, reprovisioning of the existing CKLSPS intake will not be required in the YTB reclamation (Full Reclamation option).
6.7.21 The existing Yau Tong saltwater intake location will be reclaimed by the WCR-Coastal option development and the Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of the uncertainties in the programme of various projects, there may be possibility that YTSPS is not completely relocated during the construction phase of the project. However, considering that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS) are located at approximately the same distance from the new Kwun Tong Nullah outfalls, it is expected that the water quality at the existing YTSPS will be similar to those predicted at the reprovisioned YTSPS. In light of the large margin between the predicted water quality and the WSD target limit at saltwater intake, unacceptable impact is not expected at the existing YTSPS.
6.7.22 For the Minimized Reclamation option, the more streamline flow in the vicinity of YTB favours the dispersion and dilution of pollutants from the NKTN and thus the water quality at the existing YTSPS intake is expected to be similar to, if not better than, that at the reprovisioned location in the Full Reclamation option, satisfying the WSD’s target limit at saltwater intakes. As discussed in the previous paragraphs, the water quality at the existing CKLSPS under the proposed concrete decking is expected to improve in the Minimized Reclamation option for YTB, as compared to that in the Full reclamation option, satifying the WSD’s target limit at saltwater intakes. Hence, no reprovisioning of the existing CKLSPS and the YTSPS intakes will be required in the Minimized Reclamation for YTB.
Impact due to the Polluted Stormwater from the Future Yau Tong Stormwater Catchment
Water Quality in Victoria Harbour Water Control Zone (VHWCZ)
6.7.23 Using the 2D particle model, similar to that used in the study of the new KTN (Appendix 6C), the pollutant dilution and dispersion near the box culvert of the new development in the Full Reclamation option is simulated (Appendix 6D). In general, the particle model result indicated that the pollutant concentration will be diluted by more than 6 times within 100m from the new water front near the month of the stormwater culvert (Appendix 6D).
6.7.24
Based on the pollution loads,
as adopted in the Reclamation of YTB, EIA Study, in Table 6.10 and the
particle model results, the predicted increase in biochemical oxygen demand
(BOD5), SS, Ammoniacal Nitrogen and E. Coli. in Victoria Habour and at the WSRs are shown in Table 6.12.
The predicted increases generally satisfy the WQOs in the VHWCZ. Based on the ambient DO level of
4.85 mgL-1, from EPD’s rountine monitoring data at station VM1
in year 1997 (Table 6.4), and the predicted
pollutant dilution of more than 6 times within 100 m from the outfall of
the storm culvert, it is predicted that the DO level would increase from
2 mgL-1 at the storm culvert outfall to 4.38 mgL-1
in the VHWCZ. Taking into account the
BOD5 of less than 0.74 mgL-1, the DO level is
expected to meet the WQO in the VHWCZ.
Since mixing and decay within the Yau Tong stormwater system have not been
taken into account, it is anticipated that the actual pollutant concentration
will be lower than those predicted in Table 6.12. The cumulative water quality impact of the
New Kwun Tong Nullah and New YTB Stormwater Culvert is shown in Table 6.12a.
Non-compliance of WSD water quality criteria or WQOs within the
Water Quality under the Proposed Concrete Decking
6.7.25 In the Full Reclamation option for YTB, the water quality under the proposed concrete decking due to the polluted stormwater discharge from Yau Tong area also satisfies the WQOs with small increase in BOD5, SS, Ammoniacal Nitrogen and E. Coli. (Table 6.12). It is predicted that the pollutant concentration will be diluted by more than 3 times from the outfall of the subject storm culvert to the area under the proposed concrete decking. Correspondingly, the DO level is estimated to be approximately 3.9 mgL-1. Taking into account tidal mixing within the stormwater system, the WQO for DO is expected to be satisfied. At low level of BOD5 and ammoniacal nitrogen, no odour problem is expected under the decking.
6.7.26
For the Minimized Reclamation
option, with a reduction in the size of the proposed concrete decking, the
tidal flushing under the proposed concrete decking is expected to improve as
the inner part of the embayment is more exposed to the flow current in
Water Quality at the WSD Saltwater Pumping Stations
6.7.27 In the Full Reclamation option, the BOD5, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS), taking into account the predicted maximum increases associated with the New Yau Tong Bay Stormwater Culvert and the ambient levels, are well within the WSD target limit (Table 6.12), and thus, unacceptable impact is not expected. For the two planned WSRs, namely the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS) under the WCR-Coastal option reclamation and the potential site reserved for the reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) under the YTB reclamation (Full Reclamation option), the relevant water quality parameters is also expected to satisfy the WSD target limit (Table 6.12). As noted under the discussion of the NKTN impact, the water quality at the existing CKLSPS intake will be slightly better than that at the potential site for its reprovisioning. Hence, reprovisioning of the existing CKLSPS intake will not be required in the YTB reclamation (Full Reclamation option).
6.7.28 The existing Yau Tong saltwater intake location will be reclaimed by the WCR-Coastal option development and the Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of the uncertainties in the programme of various projects, the YTSPS may continue to operate at the existing locations during the construction phase of the project. However, considering that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS) are located at approximately the same distance from the new YTB stormwater culvert, the water quality at the existing YTSPS will be similar to those predicted at the reprovisioned YTSPS. In light of the large margin between the predicted water quality and the WSD target limit at saltwater intake, unacceptable impact is not expected at the existing YTSPS.
Potential Impact due to
Effluent Discharge from Dairy Farm Ice Factory
6.7.29 Although the restricted water circulation under the decked structure may result in rise of water temperature below the decked structure due to cooling water discharge from Dairy Farm Ice Factory, its enhancement upon the algal growth is offset by the decked structure that will substantially reduce the exposure of marine water below from daylight (which is also an important factor that governs algal growth). Thus, it is considered that the formation of small embayment below the concrete decking should have no major impact upon the algal growth.
6.7.30 Table 6.12 Impact of the Stormwater Discharges from the Yau Tong Area – Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes
|
Description |
BOD5 [mgL-1] |
SS [mgL-1] |
Ammoniacal
Nitrogen [mgL-1] |
E. Coli. [count per 100mL] |
|||
|
Victoria
Harbour Water Control Zone (VHWCZ) |
|||||||
|
Ambient level (1) |
0.7 |
5.6 |
0.22 |
5780 |
|||
|
Predicted increase in VHWCZ |
< 0.04 |
< 0.05 |
< 2.86 x 10-3 |
< 2370 |
|||
|
Predicted increase under the proposed concrete decking |
< 0.09 |
< 0.09 |
< 5.72 x 10-3 |
< 4740 |
|||
|
WQO |
N/A (6) |
< 30% over ambient and median < 25mgL-1 |
< 0.44 (5) |
N/A (4) |
|||
|
Existing
Water Sensitive Receivers (WSRs) |
|||||||
|
Maximum increase at CKLSPS
(2) |
0.08 |
0.09 |
5.4 x 10-3 |
4455 |
|||
|
Maximum increase at YTSPS (2) |
0.12 (7) |
0.13 (7) |
8.12 x 10-3 (7) |
6730 (7) |
|||
|
Planned
Water Sensitive Receivers (WSRs) |
|||||||
|
Maximum increase at NCKLSPS (2) |
0.22 |
0.24 |
1.48
x 10-2 |
12228 |
|||
|
Maximum increase at NYTSPS (2) |
0.12 |
0.13 |
8.12 x 10-3 |
6730 |
|||
|
WSD target limit at saltwater intake |
< 10 |
< 10 |
<1 |
< 20000 |
|||
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year 1997.
2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively, while NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation respectively.
3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.
5. With reference to the WQO of 0.021 mgL-1 for unionized ammonia, the total ammonia present at 23oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.
6. No WQO standards for BOD5 in marine waters.
7. The existing YTSPS intake location will be reclaimed by the WCR development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the new YTB stormwater outfall as the YTSPS, similar impact is expected.
8. The results presented are based on the Full Reclamation option for YTB.
Table 6.12a Cumulative Impact of the New Kwun Tong Nullah and New YTB Stormwater Culvert – Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes
|
Description |
BOD [mg L-1] |
SS [mg L-1] |
Ammoniacal Nitrogen [mg L-1] |
E. coli [count per 100 mL] |
|
Victoria Harbour Water control Zone (VHWCZ) |
||||
|
Ambient level (1) |
0.7 |
5.6 |
0.22 |
5780 |
|
Predicted increase in VHWCZ |
< 0.05 |
< 0.19 |
< 3.531 x 10-3 |
< 2381 |
|
Predicted increase under the proposed concrete decking |
< 0.1 |
< 0.65 |
8.40 x 10-3 |
< 4783 |
|
WQO |
N/A (6) |
< 30% over ambient and median <
25 mg L-1 |
< 0.44 (5) |
N/A (4) |
|
Existing Water Sensitive Receivers (WSRs) |
||||
|
Maximum increase at CKLSPS (2) |
0.09 |
0.63 |
8.0 x 10-3 |
4496 |
|
Maximum increase at YTSPS (2) |
0.13 (7) |
0.44 (7) |
9.60 x 10-3 (7) |
6754 (7) |
|
Planned Water Sensitive Receivers (WSRs) |
||||
|
Maximum increase at NCKLSPS (2) |
0.24 |
0.92 |
1.81 x 10-2 |
12281 |
|
Maximum increase at NYTSPS (2) |
0.13 |
0.44 |
9.60 x 10-3 |
6754 |
|
WSD target limit at saltwater intake |
< 10 |
< 10 |
< 1 |
< 20000 |
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year 1997.
2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively, while NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation respectively.
3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.
5. With reference to the WQO of 0.021 mgL-1 for unionized ammonia, the total ammonia present at 23oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.
6. No WQO standards for BOD5 in marine waters.
7. The existing YTSPS intake location will be reclaimed by the WCR-Coastal option development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the new YTB stormwater outfall as the YTSPS, similar impact is expected.
8. The results presented are based on the Full Reclamation option.
6.8 Impact from the emergency discharge of the DSD Yau Tong Sewage Pumping Station
6.8.1
There is an existing emergency
outfall for the Yau Tong Sewage Pumping Station (YTSPS) located along
6.8.2 As assessed in the previous sub-sections on the impact from the NKTN and the new YTB stormwater culvert at the existing WSD CKLSPS intake, reprovisioning of the CKLSPS will not be required under the YTB reclamation (Full Reclamation option). However, a potential site for future reprovisioning of the CKLSPS saltwater intake have been proposed on the new waterfront of the YTB reclamation (Full Reclamation option),which is closer to the YTSPS emergency outfall than the existing case. The potential water quality impact from the emergency discharge at the potential site for reprovisioning of the CKLSPS saltwater intake in the Full Reclamation option has been assessed using the Cornell Mixing Zone Expert System (CORMIX). The CORMIX3 model has been run for the existing (year 2002) and future (year 2016) scenarios of the YTSPS emergency outfall with the model parameters given in Table 6.13 below.
Table 6.13 CORMIX Modelling Parameters
|
Parameter |
Existing (1) |
Future (1) |
|
Outfall Parameters |
||
|
Outfall Invert Level |
+0.02 mPD |
|
|
Outfall Cross Sectional Area |
1.594 m2 |
|
|
Effluent Density |
1000 kg m-3 |
|
|
Effluent Flow |
6,683 m3 day-1 |
50,717 m3 day-1 |
|
Environmental parameters |
||
|
High Water Level |
+2.35mPD |
|
|
Low Water Level |
+0.35mPD |
|
|
Ambient Water Depth |
10m |
|
|
Ambient Current Speed |
0.1m s-1 |
|
|
Ambient Water Density |
1,018 kg m-3 (wet season) and 1,023 kg m-3 (dry season) |
|
|
Darcy-Weisbach Friction Factor |
0.023 |
|
Note: 1. The
existing and future scenarios are based on the sewage flow served by the YTPS
in year 2002 and year 2011 respectively.
6.8.3 As the density difference between the effluent and the ambient receiving waters will affect the buoyancy of the sewage plume, the model was run for a range of ambient water densities representing the wet and dry season conditions. The model results are presented graphically in Figures 6.6 and 6.7 for the existing and future scenarios respectively.
6.8.4 For both the existing and future scenarios, the sewage plume will attach to the shoreline due to the relatively low effluent velocity. It will also be buoyant due to the density difference between the sewage effluent and the ambient marine water in both the wet and dry seasons. The initial dilution values shown in Figures 6.6 and 6.7 represent the average dilution within the plume at various distances. The potential site for future reprovisioning of the Cha Kwo Ling saltwater pumping station intake (NCKLSPS) will be approximately 360m from the YTSPS emergency outfall. At this distance from the outfall, the sewage plume thickness range between 0.19–0.37m from the surface in the existing and future scenarios, wet and dry seasons. The existing Cha Kwo Ling saltwater intake (CKLSPS) will be approximately 250 m further away from the emergency outfall than that of the NCKLSPS and less impact is expected. Hence, the present assessment at the NCKLSPS intake represents the worst case scenario.
6.8.5 Assuming the following typical raw sewage strength of:
·
BOD 250
mg L-1
·
Suspended Solids (SS) 250 mg L-1
·
E. coli 2.00E+07
counts per 100mL
·
Ammoniacal Nitrogen (NH3-N) 25 mg L-1
6.8.6 With the background mean ambient water quality concentration as given in Table 6.4, the predicted water quality levels within the sewage plume and the depth averaged values at a distance of approximately 360m from the outfall are given in Table 6.14.
Table 6.14 Predicted water quality within sewage plume
|
|
Pollutant Concentration
at 360m from Outfall |
WSD Standards at
Saltwater Intake |
|||
|
Within the Plume |
Depth Averaged (1,2) |
||||
|
Existing |
Future |
Existing |
Future |
||
|
Wet Season Scenario |
|||||
|
Dilution Factor |
57.0 |
8.4 |
1532.3 |
386.3 |
N/A |
|
BOD (mg L-1) |
5.1 |
30.3 |
0.9 |
1.3 |
<10 |
|
SS (mg L-1) |
10.0 |
35.2 |
5.8 |
6.2 |
<10 (target), <20 (tolerable) |
|
NH3-N (mg L-1) |
0.66 |
3.18 |
0.24 |
0.28 |
<1 |
|
E. coli (count per 100 mL) |
3.57 x 105 |
2.37 x 106 |
1.88 x 104 |
5.76 x 104 |
<20,000 |
|
Dry Season Scenario |
|||||
|
Dilution Factor |
51.8 |
8.2 |
1626.0 |
431.4 |
N/A |
|
BOD (mg L-1) |
5.5 |
31.1 |
0.9 |
1.3 |
<10 |
|
SS (mg L-1) |
10.4 |
36 |
5.8 |
6.2 |
<10 (target), <20 (tolerable) |
|
NH3-N (mg L-1) |
0.7 |
3.3 |
0.24 |
0.28 |
<1 |
|
E. coli (count per 100 mL) |
3.92 x 105 |
2.44 x 106 |
1.81 x 104 |
5.21 x 104 |
<20,000 |
Notes:
1. The wet season plume thickness for the exisiting and future scenarios are 0.37 m and 0.22 m respectively, while those of the dry season are 0.32 m and 0.19 m respectively.
2. The depth averaged values are calculated based on a water depth of 10 m and the corresponding plume thickness.
3. The results presented are based on the Full Reclamation option.
Table 6.14a Cumulative Impact of the New Kwun Tong Nullah, New YTB Stormwater Culvert and Emergency Discharge from the Yau Tong Sewage Pumping Station – Comparison of Predicted Water Quality with WQO within sewage plume at the NCKLSPS Saltwater Intake
|
|
Pollutant Concentration at 360 m from Outfall |
WSD Standards at Saltwater Intake |
|
|
Depth Averaged |
|||
|
|
Within the Plume (1) |
Depth Averaged (2) |
|
|
Wet Season Scenario |
|
|
|
|
BOD (mg L-1) |
30.54 |
1.54 |
< 10 |
|
SS (mg L-1) |
36.12 |
7.12 |
< 10 (target), < 20 (tolerable) |
|
NH3-N (mg L-1) |
3.20 |
0.30 |
< 1 |
|
E. coli (count per 100 mL) |
2.38
x 106 |
69,881 |
< 20,000 |
|
Dry Season Scenario |
|
|
|
|
BOD (mg L-1) |
31.34 |
1.54 |
< 10 |
|
SS (mg L-1) |
36.92 |
7.12 |
< 10 (target), < 20 (tolerable) |
|
NH3-N (mg L-1) |
3.32 |
0.30 |
< 1 |
|
E. coli (count per 100 mL) |
2.45 x 106 |
64381 |
< 20,000 |
Notes:
1. The wet season plume thickness for the existing and future scenarios are 0.37 m and 0.22 m respectively, while those of the dry season are 0.32 m and 0.19 m respectively.
2. The depth averaged values are calculated based on a water depth of 5 m and the corresponding plume thickness.
3. The results presented are based on the Full Reclamation option.
6.8.7 The depth averaged results indicated that the WSD water quality standards, in terms of BOD5, SS and ammoniacal nitrogen, at the saltwater intake will be satisfied, while the E. coli standards will be exceeded in the future scenario (Tables 6.14 and 6.14a). However, the sewage plume is buoyant at the surface, where pollutants are concentrated with a thickness of less than 0.37m. To avoid abstracting the sewage plume water, it is therefore recommended that the saltwater intake should be located below a depth of approximately ‑2.0 mPD. The intake water will then be expected to meet all the WSD standards.
6.8.8 Discharge through the emergency outfall is a rare event. Should a discharge be made through the emergency outfall, it is recommended that DSD should inform WSD of the details of such discharge, e.g. volume, timing and duration, in advance if possible. It is also recommended that DSD should minimize the discharge and liaise with WSD to avoid discharge during the peak operation hours of the WSD’s saltwater pumping station. Details of the liaison mechanisms between DSD and WSD should be established for the operation stage, notably with regard to discharges through the emergency outfall and potential impacts on WSD saltwater pumping station performance, during the detail design stage of the project.
6.8.9 In the Minimized Reclamation option, the CKLSPS saltwater intake and the Yau Tong Sewage Pumping Station emergency outfall will remain at their existing location, which are separated further apart than that in the proposed reprovisioned locations. Hence, unacceptable water quality impact at the existing CKLSPS intake is not anticipated.
Conclusion
6.8.10 Considering the minor impact of the polluted stormwater discharges from the new Kwun Tong nullah and the future Yau Tong stormwater system (Tables 6.11 and 6.12), their cumulative effects are still within the WQO and WSD target limit at the saltwater intakes (Table 6.12a). Hence, no major impact is expected in the VHWCZ, at the WSRs and under the proposed concrete decking. Also, as a result of the minor impact, the effect of stratification is considered insignificant and only the 2D particle model is used in this scenario.
Construction Phase
Good Site Practices to Minimise Impacts from Site Runoff
6.9.1 The good site practices outlined in ProPECC PN 1/94 “Construction Site Drainage" should be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids prior to discharge. These practices include, inter alia, the following items:
· Provision of perimeter channels to intercept storm-runoff from outside the site. These should be constructed in advance of site formation works and earthworks.
· Sediment removal facilities such as sand traps, silt traps and sedimentation tanks should be provided to remove particles from run-off. These facilities should be properly and regularly maintained. The solids removed from these facilities during maintenance desilting should be disposed of to landfill.
· Programming of the works to minimise soil excavation works during rainy seasons.
· Exposed soil surface should be protected by shotcrete or hydroseeding as soon as possible to reduce the potential for soil erosion.
· Temporary access roads should be protected by crushed gravel and exposed slope surfaces should be protected when rainstorms are likely.
· Trench excavation should be avoided in the wet season, and if necessary, these should be excavated and backfilled in short sections.
· Open stockpiles of construction materials on site should be covered with tarpaulin or similar fabric during rainstorms.
Wastewater Arising from Workforce
6.9.2 Septic tanks or chemical toilets should be employed as far as practicable. Grease traps should also be provided for wastewater generated from canteens. Any such treatment facilities should be frequently maintained to ensure proper function. Production water should be re-cycled to minimise the wastewater discharge, where possible.
Accidental Spillage of Hazardous Materials
6.9.3 Potential impacts from chemical spillages can be considerably reduced by implementation of proper storage and handling procedures. Chemicals stored in tanks should be surrounded by bunding that can contain at least the volume of the tank and a free-board, sumps and oil interceptors should be provided. Bunded areas should be isolated from the stormwater drains and have an impermeable base or membrane liner if the ground is porous. Where possible, chemicals should be handled and used in areas appropriately equipped to control these discharges.
6.9.4 The service shop and maintenance facility should also be located on hard standings within a bunded area with sumps and oil interceptors.
6.9.5 Waste fuel and oil collected from the interception system should be disposed off-site at approved locations. This will either be for oil recovery or disposal at the Government Chemical Waste Treatment Facility.
6.9.6
A strategy should be developed
for dealing with chemical spills, based on manufacturers’ recommendations. As for fuel spills, clean-up procedures
should involve the use of absorbents and under no circumstances should spilled
materials be washed down into storm drains or into the
Discharge of Groundwater
6.9.7 During excavation works, no groundwater will be discharged into the stormwater drains or marine waters. It is proposed that groundwater be re-discharged back into the ground by use of the recharge well method.
Design Consideration for the future reprovisioning or upgrading of Cha Kwo Ling Saltwater Intake
6.9.8
The modelling results suggested
that the potential sewage plume arising from the Yau Tong Sewage Pumping
Station emergency outfall at
Operational Phase
6.9.9 All surface runoff generated from the proposed development during the operational phase should be controlled and routed via sedimentation tanks or silt traps to minimise pollution load to the Victoria Harbour.
6.9.10 As described in para 6.7.3, an on-site retention tank is proposed as a mitigation/contingency measure to attenuate the sewage flow generated by the population in-take in YTBD after 2011 in the event that there is no spare capacity of the KTPTW. The on-site retention tank, which is in fact a holding facility, will store the additional sewage generated by the subsequent phases of development in YTBD after 2011 during the peak hours and discharge it during the off-peak hours of the day. This ensures that the peak flow to the KTPTW is not increased. However, the necessity and exact size of the retention tank should be reviewed during the detailed design stage when the need and programme of KTPTW upgrading from the findings of future studies, including the ‘Environmental and Engineering Feasibility Assessment Studies’, and the development schedule of the YTBD and other developments within the catchment are confirmed.
6.9.11 Should a sewage discharge be made through the emergency outfall of Yau Tong Sewage Pumping Station, it is recommended that DSD should inform WSD of the details of such discharge, e.g. volume, timing and duration, in advance if possible. It is also recommended that DSD should minimize the discharge and liaise with WSD to avoid discharge during the peak operation hours of the WSD’s saltwater pumping station. Details of the liaison mechanisms between DSD and WSD should be established for the operation stage, notably with regard to discharges through the emergency outfall and potential impacts on WSD saltwater pumping station performance, during the detailed design stage of the project.
6.10 Environmental Monitoring And Auditing Requirements
6.10.1 It is recommended that environmental monitoring and auditing (EM&A) program will be required to ensure the implementation of the measures during the construction works. Details of the EM&A requirements and procedures will be presented in a separate EM&A Manual.
Introduction
6.11.1 The water quality impacts associated with the project are summarised in the following sections. An implementation schedule of the proposed mitigation measures is attached in Appendix 6E.
Construction Phase
6.11.2 During construction phase of the new development, the nearby water environment is potentially affected by:
· construction site runoff;
· wastewater arising from workforce; and
· accidental spillage of chemical waste from general site activities.
6.11.3 However, the construction phase impacts would be unlikely to pose a great threat to the water quality provided that proper mitigation measures are provided and good site practices are implemented. It is recommended that the good site practices outlined in ProPECC PN 1/94 “Construction Site Drainage" should be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids prior to discharge.
Operational Phase
Sewerage Impact
6.11.4 It is proposed that future sewage generated from the YTBD will be discharged to the HATS system for treatment at Stonecutter Island Sewage Treatment Plant via the HATS tunnel and the KTPTW. The KTPTW will have sufficient capacity to handle the additional flow from the development until 2011, whereas the HATS tunnel will become under-capacity by 2011. A mitigation/contingency measure in the form of an on-site retention tank will be provided for the phases of development which come on-line after 2011 in the event that the KTPTW is overloaded after 2011, ensuring that the peak flow to the KTPTW is not increased. The necessity or the exact size of the retention tank will need to be reviewed during the detailed design stage. If the retention tank is provided, stand-by pumps and dual power supply should be installed to ensure reliable operation of the tank and to minimise overflow. If the retention tank is not manned 24 hours, telemetry system should be provided to other 24-hour facilities to ensure the operation of the retention tank will be monitored continuously and any malfunctioning of the retention tank will be readily detected and rectified.
6.11.5 The solution to the potential shortfall to the HATS tunnel, and the need and the programme of upgrading the KTPTW will be investigated in detail under the further studies, including the upcoming ‘Environmental and Engineering Feasibility Assessment Studies’, recommended by the International Review Panel (IRP).
Polluted Stormwater Impact
6.11.6 Another potential water quality impact during the operational phase of the project would be due to the stormwater generated from the site. As part of the YTB development, a concrete decking will be built over the existing submarine pipelines near the northern part of YTB. Since the water flow under the decking may be relatively low, polluted stormwater discharges from the proposed development may be accumulated under the decking and deteriorate the local water quality. The cumulative effect of future polluted stormwater discharges from the proposed development and the nearby Yau Tong area as well as the Kwun Tong Nullah may also affect the nearby seawater intakes of the potentially reprovisioned Cha Kwo Ling (NCKLSPS) and Yau Tong (NYTSPS) saltwater pumping stations.
6.11.7
No adverse water quality impact
in Victoria Harbour and, in particular, at the existing and potentially
reprovisioned CKLSPS, under the YTB reclamation (Full Reclamation option), and the reprovisioned YTSPS, under the
WCR-Coastal option reclamation, is expected from polluted stormwater discharges
from the proposed development and the nearby stormwater systems including the
Kwun Tong Nullah. The model results suggested that tidal flushing will prevent
the accumulation of pollutants under the proposed concrete decking at the mouth
of YTB and the water quality is expected to comply with the WSD’s target limits
at the saltwater intakes. Since the
proposed concrete decking under the Minimized Reclamation will be reduced in
size and is more exposed to the tidal flow in
6.11.8
It is recommended that silt
traps or sedimentation tanks should be provided for urban run-off generated at
the proposed development to minimise the potential pollution load to
Estimation
of Total Pollution Load Generated in the Yau Tong Area
(from Residential, Commercial and Industrial Source)
Methodology
of Estimating Pollution Load in
Stormwater
Drains of Yau Tong Area
Particle Model Setup and Modelling Scenarios
Particle
Modelling of Pollutant Dispersion from the
New Kwun Tong Nullah – Scenario 1B
Particle
Modelling of Pollutant Dispersion form the
YTB Stormwater Culvert – Scenario 1B
Implementation Schedule of Mitigation Measures (Water Quality)
[1] Feasibility Study for South
[2] The design flow from the workforce was calculated according to the wastewater generation rate for employed population provided in the DSD Sewerage Manual (0.06 m3/employee/day) and the water demand figure for restaurant provided in the Civil Engineering Manual (0.015 m3/customer).
