Agreement No. CE 35/2006(CE)
Kai Tak Development Engineering Study
cum Design and Construction of Advance Works –
Investigation, Design and Construction
Decommissioning
of the
Other than the North Apron
Environmental Impact Assessment Report
Contents
5......... water quality Impact
5.2 Environmental Legislation, Policies, Plans, Standards and Criteria
5.3 Description of the Environment
5.6 Identification of Environmental Impacts
5.7 Prediction and Evaluation of Environmental Impacts
5.8 Consideration of Cumulative Environmental Impacts
5.9 Mitigation Measures of Adverse Environmental Impacts
5.10 Evaluation of Residual Impacts
5.11 Environmental Monitoring and Audit
List of Tables
Table 5.1.......... Summary of Water Quality Objectives for the Victoria Harbour WCZ
Table 5.2.......... WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes
Table 5.3.......... Summary Statistics of Marine Water Quality in the Victoria Harbour WCZ in 2005
Table 5.5.......... Summary Statistics of 2005 River Water Quality for Kai Tak Nullah
Table 5.6.......... Pollution Levels Measured at KTAC in October 2005
Table 5.7.......... Pollution Levels Measured at KTAC in January 2006
Table 5.8 ......... Summary Statistics of 2005 Bottom Sediment Quality
List of Drawings
Drawing 5.1 Location of Victoria Harbour Water Control Zone and 300m Study Area
Drawing 5.2 Locations of Selected Water Quality Sensitive Receivers
5.1 Introduction
5.1.1 This section presents the assessment of the potential water quality impacts associated with the proposed decommissioning works of the Project. The key water quality issues and concerns arising from the Project have been identified and assessed. Recommendations for possible mitigation measures have been made, where necessary, to reduce the identified water quality impacts to an acceptable level.
5.2 Environmental Legislation, Policies, Plans, Standards and Criteria
Water Pollution Control Ordinance (WPCO)
5.2.1
The Water Pollution
Control Ordinance (Cap. 358), in existence since 1980, is the major legislation relating to the
protection and control of water quality in
Table
5.1 Summary of Water Quality Objectives for the
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive odour, tints |
Not to be present |
Whole zone |
|
Visible foam, oil scum, litter |
Not to be present |
Whole zone |
|
Dissolved oxygen (DO) within 2 m of the seabed |
Not less than 2.0 mg/L for 90% of samples |
Marine waters |
|
Depth-averaged DO |
Not less than 4.0 mg/L for 90% of samples |
Marine waters |
|
PH |
To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2 |
Marine 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 (SS) |
Not to raise the ambient level by 30% caused by human activity |
Marine waters |
|
Unionised ammonia (UIA) |
Annual mean not to exceed 0.021 mg/L as unionised form |
Whole zone |
|
Nutrients |
Shall not cause excessive algal growth |
Marine waters |
|
Total inorganic nitrogen (TIN) |
Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg/L |
Marine 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 (
Water Supplies Department (WSD) Water Quality Criteria
5.2.2 Besides the WQOs set under the WPCO, the WSD has specified a set of objectives for water quality at flushing water intakes. The list is shown in Table 5.2. The target limit for suspended solids (SS) at these intakes is 10mg/l or less.
Table 5.2 WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes
|
Parameter (in mg/l unless otherwise stated) |
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 (no. per 100ml) |
< 20,000 |
Technical Memorandum
5.2.3 Besides setting the WQOs, the WPCO controls effluent discharging into the WCZs through a licensing system. Guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters) is provided in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS). The limits given in the TM-DSS cover the physical, chemical and microbial quality of effluents. Any effluent discharge during the decommissioning works should comply with the standards for effluents discharged into the inshore waters of the Victoria Harbour WCZ, as shown in Table 9a of the TM-DSS.
Practice Notes
5.2.4 A practice note (PN) for professional persons was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with various types of discharge from a construction site. Practices outlined in the PN should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.
5.3 Description of the Environment
Marine Water Quality
5.3.1 The EPD water quality monitoring stations, VM2 and VM4, in the Victoria Harbour WCZ is located in the vicinity of the Project area. A summary of the most recently published monitoring data (in 2005) for these stations is presented in Table 5.3. A summary of the published EPD monitoring data (in 2005) collected from the monitoring stations in the Kwun Tong Typhoon Shelter (VT4) and To Kwa Wan Typhoon Shelter (VT11) is presented in Table 5.4. Locations of the monitoring stations are shown in Drawing 5.2. Stations VM2, VM4, VT4 and VT11 are considered to be representative of the water quality in the marine waters of the assessment area.
Table 5.3 Summary
Statistics of Marine Water Quality in the
|
Parameter |
|
Harbour Central |
WPCO WQO (in marine waters) |
|
|
VM2 |
VM4 |
|||
|
Temperature (oC) |
22.9 (15.8 – 28.0) |
22.9 (15.8 – 27.8) |
Not more than 2 oC in daily temperature range |
|
|
Salinity |
31.9 (28.5 – 33.3) |
31.8 (28.9 – 33.2) |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
78 (66 – 92) |
75 (63 – 88) |
Not available |
|
Bottom |
77 (54 – 90) |
74 (51 – 88) |
Not available |
|
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
5.6 (4.4 – 6.8) |
5.4 (4.4 – 6.6) |
Not less than 4 mg/L for 90% of the samples |
|
Bottom |
5.6 (3.8 – 6.8) |
5.3 (3.6 – 6.5) |
Not less than 2 mg/L for 90% of the samples |
|
|
pH |
8.1 (7.7 – 8.3) |
8.0 (7.7 – 8.3) |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc Depth (m) |
2.2 (1.2 – 3.5) |
2.1 (1.5 – 3.2) |
Not available |
|
|
Turbidity (NTU) |
9.8 (4.8 – 15.8) |
9.6 (4.5 – 15.3) |
Not available |
|
|
Suspended Solids (SS) (mg/L) |
3.6 (1.3 – 8.5) |
3.6 (1.3 – 9.8) |
Not more than 30% increase |
|
|
5-day Biochemical Oxygen Demand (BOD5) (mg/L) |
0.9 (0.4 – 1.5) |
0.9 (0.5 – 1.1) |
Not available |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.02 (0.01 – 0.05) |
0.03 (0.01 – 0.05) |
Not available |
|
|
Nitrate Nitrogen (NO3-N) (mg/L) |
0.12 (0.03 – 0.23) |
0.13 (0.05 – 0.24) |
Not available |
|
|
Ammonia Nitrogen (NH3-N) (mg/L) |
0.13 (0.04 – 0.21) |
0.15 (0.06 – 0.27) |
Not available |
|
|
Unionised Ammonia (UIA) (mg/L) |
0.006 (0.002 – 0.015) |
0.006 (0.003 – 0.015) |
Not more than 0.021 mg/L for annual mean |
|
|
Total Inorganic Nitrogen (TIN) (mg/L) |
0.28 (0.08 – 0.46) |
0.31 (0.12 – 0.54) |
Not more than 0.4 mg/L for annual mean |
|
|
Total Nitrogen (TN) (mg/L)
|
0.43 (0.22 – 0.63) |
0.47 (0.26 – 0.69) |
Not available |
|
|
Orthophosphate Phosphorus (OrthoP) (mg/L) |
0.03 (<0.01 – 0.04) |
0.03 (0.01 – 0.04) |
Not available |
|
|
Total Phosphorus (TP) (mg/L) |
0.04 (0.02 – 0.06) |
0.05 (0.03 – 0.06) |
Not available |
|
|
Chlorophyll-a (µg/L) |
2.4 (0.8 – 6.0) |
2.4 (0.9 – 7.2) |
Not available |
|
|
E coli (cfu/100 mL) |
1600 (120 – 31000) |
2400 (310 – 11000) |
Not available |
|
|
Faecal Coliforms (cfu/100 mL) |
3600 (340 – 50000) |
5200 (770 – 33000) |
Not available |
|
Notes:
1. Data source: EPD’s publication: “20 Years of Marine Water Quality
Monitoring in
2. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.
3. Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.
4. Data in brackets indicate the ranges.
|
Parameter |
WPCO WQO (in marine waters) |
|||
|
Temperature (oC) |
22.6 (16.2 – 26.2) |
22.4 (16.0 – 26.3) |
Not more than 2 oC in daily temperature range |
|
|
Salinity (ppt) |
30.0 (27.6 – 31.5) |
31.2 (27.6 – 32.7) |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO) (% saturation) |
Depth average |
60 (37 – 97) |
85 (55 – 115) |
Not available |
|
Bottom |
64 (47 – 72) |
84 (56 – 110) |
Not available |
|
|
Dissolved Oxygen (DO) (mg/l) |
Depth average |
4.3 (2.9 – 6.7) |
6.1 (3.7 – 8.0) |
Not less than 4 mg/L for 90% of the samples |
|
Bottom |
4.7 (3.2 – 5.5) |
6.1 (3.8 – 7.7) |
Not less than 2 mg/L for 90% of the samples |
|
|
pH value |
8.0 (7.7 – 8.1) |
8.2 (8.0 – 8.4) |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc (m) |
1.2 (0.7 – 1.7) |
1.7 (1.0 – 2.2) |
Not available |
|
|
Turbidity (NTU) |
8.6 (4.9 – 9.8) |
8.8 (5.6 – 10.7) |
Not available |
|
|
Suspended Solids (SS) (mg/l) |
2.6 (1.3 – 3.9) |
4.4 (1.3 – 7.3) |
Not more than 30% increase |
|
|
Silica (as SiO2) (mg/l) |
1.3 (0.5 – 2.2) |
0.8 (0.3 – 1.1) |
Not available |
|
|
5-day Biochemical Oxygen Demand (BOD5) (mg/l) |
2.1 (1.4 – 4.4) |
1.5 (0.7 – 3.4) |
Not available |
|
|
Nitrite Nitrogen (NO2-N) (mg/l) |
0.11 (0.03 – 0.22) |
0.03 (0.02 – 0.05) |
Not available |
|
|
Nitrate Nitrogen (NO3-N) (mg/l) |
0.38 (0.22 – 0.63) |
0.16 (0.09 – 0.23) |
Not available |
|
|
Ammoniacal Nitrogen (NH3-N) (mg/l) |
0.44 (0.26 – 0.7) |
0.14 (0.06 – 0.19) |
Not available |
|
|
Unionised Ammonia (UIA) (mg/l) |
0.015 (0.007 – 0.029) |
0.008 (0.004 – 0.015) |
Not more than 0.021 mg/L for annual mean |
|
|
Total Inorganic Nitrogen (TIN) (mg/l) |
0.93 (0.63 – 1.16) |
0.33 (0.27 – 0.41) |
Not more than 0.4 mg/L for annual mean |
|
|
Total Nitrogen (TN) (mg/l) |
1.23 (0.84 – 1.73) |
0.53 (0.51 – 0.58) |
Not available |
|
|
Ortho-Phosphate (PO4) (mg/l) |
0.18 (0.10 – 0.33) |
0.03 (0.01 – 0.04) |
Not available |
|
|
Total Phosphorus (TP) (mg/l) |
0.21 (0.13 – 0.37) |
0.05 (0.04 – 0.09) |
Not available |
|
|
Chlorophyll-a (µg L-1) |
10.6 (0.6 – 44.7) |
7.3 (0.5 – 32.3) |
Not available |
|
|
E. coli (cfu per 100 mL) |
8,200 (1,500 – 26,000) |
690 (150 – 2,800) |
Not available |
|
|
Faecal Coliforms (cfu per 100 mL) |
16,000 (3,200 – 50,000) |
1,900 (880 – 7,200) |
Not available |
|
Notes:
1. Data source: EPD’s publication: “20 Years of Marine Water Quality
Monitoring in
2. Except as specified, data presented are depth-averaged data.
3. Data presented are annual arithmetic means except for E.coli and faecal coliforms that are geometric means.
4. Data enclosed in brackets indicate ranges.
5.3.2 In 2005, marked improvements in the eastern and central Victoria Harbour (VM2) since HATS Stage 1 was commissioned were generally sustained. Full compliance with the WQOs for dissolved oxygen, total inorganic nitrogen and unionized ammonia was achieved in 2005.
5.3.3 In 2005, high levels of E.coli were recorded at the Kwun Tong and To Kwa Wan Typhoon Shelters indicating faecal contamination. A high level of total organic nitrogen was also recorded at the Kwun Tong Typhoon Shelter which breached the WQO.
Kai Tak Nullah
5.3.4 The water quality in Kai Tak Nullah (KTN) is monitored by EPD routinely. There are six monitoring stations (KN1 to KN5 and KN7) in KTN (Drawing 5.2). The downstream section of the KTN (i.e. Station KN1) is located within the Project site boundary. A summary of EPD monitoring data collected in 2005 is presented in Table 5.5. No river water quality objective is available for KTN.
Table 5.5 Summary Statistics of 2005 River Water Quality for Kai Tak Nullah
|
Parameter |
EPD Monitoring Station |
|||||
|
KN1 (downstream) |
KN2 |
KN3 |
KN4 |
KN5 |
KN7 (upstream) |
|
|
DO (mg/L) |
6.5 (4.4 – 7.3) |
6.6 (5.4 – 7.3) |
7.5 (6.5 – 8.0) |
7.7 (7.1 – 8.7) |
7.9 (6.5 – 8.9) |
7.5 (6.7 – 8.0) |
|
pH |
7.3 (7.1 – 7.6) |
7.2 (7.0 – 7.6) |
7.4 (7.2 – 7.5) |
7.3 (7.2 – 7.6) |
7.3 (7.2 – 7.6) |
7.2 (7.1 – 7.4) |
|
SS (mg/L) |
5 (3 – 44) |
35 (5 – 60) |
24 (6 – 47) |
8 (4 – 47) |
8 (5 – 14) |
6 (3 –11) |
|
BOD5 (mg/L) |
6 (2 – 23) |
8 (5 – 14) |
6 (3 – 14) |
4 (2 – 8) |
4 (2 – 9) |
4 (2 – 9) |
|
COD (mg/L) |
32 (24 – 54) |
29 (19 – 44) |
25 (16 – 80) |
33 (18 – 54) |
31 (22 – 58) |
32 (26 – 54) |
|
Oil & grease (mg/L) |
0.5 (0.5 – 0.6) |
0.5 (0.5 – 0.6) |
0.5 (0.5 – 0.6) |
0.5 (0.5 – 0.6) |
0.5 (0.5 – 0.5) |
0.5 (0.5 – 0.5) |
|
Faecal coliforms (cfu/100mL) |
490,000 (95,000 – 18,000,000) |
300,000 (610,000 – 1,200,000) |
290,000 (100,000 – 840,000) |
110,000 (21,000 – 450,000) |
99,000 (30,000 – 370,000) |
89,000 (22,000 – 270,000) |
|
E.coli (cfu/100mL) |
210,000 (36,000 – 9,200,000) |
130,000 (34,000 – 530,000) |
95,000 (55,000 – 160,000) |
39,000 (9,400 – 120,000) |
39,000 (17,000 – 160,000) |
36,000 (15,000 – 100,000) |
|
NH3-N (mg/L) |
0.77 (0.2 – 3.9) |
0.23 (0.05 – 1.5) |
0.16 (0.09 – 0.52) |
0.15 (0.06– 1.4) |
0.13 (0.07 – 1.2) |
0.1 (0.07 – 1.2) |
|
NO3-N (mg/L) |
4.65 (0.95 – 5.5) |
4.95 (0.86 – 5.4) |
5.15 (1.4 – 7.2) |
5.55 (1.4 – 7.9) |
5.25 (4 – 7.7) |
5.25 (3.8 – 7.4) |
|
TKN – soluble & particulate fractions (mg/L) |
1.90 (1 – 5.8) |
1.40 (1.2 – 2.8) |
1.15 (1.0 – 3.1) |
1.20 (0.73 – 2.3) |
1.20 (0.88–2.3) |
1.20 (0.86 – 2.2) |
|
Ortho-P (mg/L) |
1.65 (0.28 – 2.3) |
1.55 (0.21 – 1.8) |
1.5 (0.39 – 1.8) |
1.7 (0.46 – 2.2) |
1.75 (1.2 – 2.2) |
1.75 (1.2 – 2.2) |
|
TP – soluble & particulate fractions (mg/L) |
1.8 (0.49 – 2.4) |
1.8 (0.4 – 2) |
1.95 (0.56 – 2) |
1.9 (0.55 – 2.4) |
1.9 (1.4 – 2.4) |
1.9 (1.4 – 2.4) |
|
Sulphide – soluble and particulate fractions (mg/L)
|
0.05 (0.02 – 0.27) |
0.03 (0.02 – 0.07) |
0.02 (0.02 – 0.02) |
0.02 (0.02 – 0.06) |
0.02 (0.02 – 0.02) |
0.02 (0.02 – 0.02) |
|
Aluminium (µg/L) |
50 (50 – 150) |
95 (50 – 200) |
95 (50 – 410) |
50 (50 – 130) |
50 (50 –100) |
50 (50 – 70) |
|
Cadmium (µg/L) |
0.1 (0.1 – 0.1) |
0.1 (0.1 – 0.1) |
0.1 (0.1 – 0.2) |
0.1 (0.1 – 0.1) |
0.1 (0.1 – 0.1) |
0.1 (0.1 – 0.2) |
|
Chromium (µg/L) |
2 (1 – 5) |
1 (1 – 3) |
2 (1 – 7) |
1 (1 – 6) |
1 (1 – 3) |
2 (1 – 3) |
|
Copper (µg/L)
|
8 (5 – 13) |
9 (7 – 10) |
10 (6 – 25) |
11 (4 – 15) |
10 (4 – 16) |
12 (4 – 16) |
|
Lead (µg/L) |
1 (1 – 3) |
1 (1 – 5) |
2 (1 – 9) |
1 (1 – 3) |
1 (1 – 2) |
1 (1 – 1) |
|
Zinc (µg/L)
|
30 (20 – 70) |
50 (30 – 70) |
55 (20–120) |
30 (20 – 70) |
30 (20 – 60) |
30 (20–50) |
Notes:
1. Data source: EPD’s
publication: “20 Years of River Water Quality Monitoring in
2. Data presented are annual arithmetic means of depth-averaged results except for E.coli and faecal coliforms that are annual geometric means.
3. Data in brackets indicate the ranges.
4. Equal values for annual medians (or geometric means) and ranges indicate that all data are the same as or below laboratory reporting limits.
Upper Section (KN7 and KN5)
5.3.5
These are the two
most upper stations at KTN near
Middle Section (KN4)
5.3.6 This is the middle section of the KTN. The WQI grading was classified as ‘good’ and the geometric mean E.coli count is similar to KN7 and KN5 having a value of 39,000 per 100 ml. Comparing with KN7 and KN5, there are only minor changes in the water quality parameters.
Lower Section (KN3 to KN1)
5.3.7 This lower section is located within an old reclamation area with very flat gradient. The WQI grading was also classified as ‘good’ at these downstream stations. However, under the influence of tidal flows, the flow condition is much slower than the upstream section and considerable deterioration of water quality along this stretch of KTN was observed as reflected by the worsening of water quality parameters. An increase in E.coli count is recorded from 39,000 per 100 ml at KN4 to 130,000 per 100 ml at KN2. At KN1 near the outfall of KTN to Kai Tak Approach Channel (KTAC), the geometric mean E.coli count further increases to 210,000 per 100 ml and DO also dropped from 7.7 mg/L (KN2 to KN1) to 6.5 mg/L.
Kai Tak Approach Channel
5.3.8 Kai Tak Approach Channel (KTAC) is also one of the surrounding water bodies of the Project site and its water quality is currently under stressed condition. No long-term water quality data was collected at KTAC by EPD. Two baseline marine water quality surveys were carried out in October 2005 and January 2006 respectively under the Kai Tak Planning Review (KTPR) ([1]). The survey locations include seven stations within the KTAC, namely AC1 - AC7, as shown in Drawing 5.2. In each of the two baseline surveys, two monitoring events were carried out for typical spring and neap tides respectively. For each monitoring event, water quality measurements were taken once every three hours for a complete tidal cycle (roughly a 26-hour period).
5.3.9 The field survey results are tabulated in Table 5.6 and Table 5.7 for the two monitoring events. The survey results are presented as averaged concentrations (for suspended solids, ammonia nitrogen, total inorganic nitrogen and biochemical oxygen demand) and 10th percentile values (for bottom and depth-averaged dissolved oxygen). The field data showed a gradient of water quality from the inner KTAC to the outer KTAC. The levels of nitrogen nutrients, ammonia and E.coli were found to be very high in the KTAC. The DO levels breached the WQO in October 2005 but complied well with the WQO in January 2006. The TIN levels exceeded the WQO in KTAC for both dry and wet seasons.
Table 5.6 Pollution Levels Measured at KTAC in October 2005
|
WQO: |
Depth-averaged Suspended Solids |
Depth-averaged Ammonia Nitrogen |
Depth-averaged E.coli |
Depth-averaged Total Inorganic Nitrogen |
Depth-averaged BOD5 |
10th Percentile Bottom DO |
10th Percentile Depth-averaged DO |
|
mg/L |
mg/L |
cfu/100mL |
mg/L |
mg/L |
mg/L |
mg/L |
|
|
NA |
NA |
NA |
0.4 |
NA |
2 |
4 |
|
|
25 |
0.9 |
115519 |
3.11 |
11 |
0.99 |
1.48 |
|
|
28 |
1.0 |
17960 |
3.21 |
10 |
0.74 |
1.18 |
|
|
19 |
0.9 |
60517 |
3.53 |
9 |
1.14 |
1.47 |
|
|
20 |
1.2 |
37857 |
3.15 |
10 |
0.93 |
1.33 |
|
|
21 |
1.2 |
28832 |
3.28 |
8 |
1.19 |
1.54 |
|
|
26 |
1.4 |
34375 |
2.76 |
9 |
0.86 |
1.41 |
|
|
27 |
0.8 |
15863 |
2.60 |
7 |
2.06 |
2.20 |
Bolded and shaded – Exceedance of WQO
NA – WQO is not available
Table 5.7 Pollution Levels Measured at KTAC in January 2006
|
WQO: |
Depth-averaged Suspended Solids |
Depth-averaged Ammonia Nitrogen |
Depth-averaged E.coli |
Depth-averaged Total Inorganic Nitrogen |
Depth-averaged BOD5 |
10th Percentile Bottom DO |
10th Percentile Depth-averaged DO |
|
mg/L |
mg/L |
cfu/100mL |
mg/L |
mg/L |
mg/L |
mg/L |
|
|
NA |
NA |
NA |
0.4 |
NA |
2 |
4 |
|
Bolded and shaded – Exceedance of WQO
NA – WQO is not available
Sediment Quality
5.3.10 A summary of published EPD sediment data (in 2005) collected from the monitoring station at the To Kwa Wan Typhoon Shelter (VS20) in vicinity of the disused fuel dolphin is presented in Table 5.8.
Table 5.8 Summary Statistics of 2005 Bottom Sediment Quality
|
Contaminants |
Sediment Quality Criteria |
||
|
LCEL |
UCEL |
||
|
Heavy Metal (mg/kg dry weight) |
|||
|
Cadmium (Cd) |
1 (0.4 – 1.6) |
1.5 |
4 |
|
Chromium (Cr) |
100 (64 – 130) |
80 |
160 |
|
Copper (Cu) |
629 (410 – 810) |
65 |
110 |
|
Mercury (Hg) |
1.12 (0.65 – 1.4) |
0.5 |
1 |
|
Nickel (Ni) |
36 (29 – 40) |
40 |
40 |
|
Lead (Pb) |
99 (77 – 130) |
75 |
110 |
|
Silver (Ag) |
5.7 (3.0 – 9.0) |
1 |
2 |
|
Zinc (Zn) |
264 (180 – 320) |
200 |
270 |
|
Metalloid (mg/kg dry weight) |
|||
|
Arsenic |
7.7 (6.3 – 9.0) |
12 |
42 |
|
Organic-PAHs (g/kg dry weight) |
|||
|
PAHs (Low Molecular Weight) |
8544 (2974 – 17405) |
550 |
3160 |
|
PAHs (High Molecular Weight) |
62412 (2137 – 132600) |
1700 |
9600 |
|
Organic-non-PAHs (g/kg dry weight) |
|||
|
Total PCBs |
78 (18 – 120) |
23 |
180 |
Notes:
1. Data source: EPD’s
publication: “20 Years of Marine Water Quality Monitoring in
2. Shaded value – Exceed the LCEL – Lower Chemical Exceedance Level
3. Shaded and bolded value – Exceed the UCEL – Upper Chemical Exceedance Level
5.3.11 The sediments collected at To Kwa Wan Typhoon Shelter are considered highly contaminated in terms of heavy metals and trace organics (PCBs and PAHs) based on the 2005 field data.
5.4 Water Sensitive Receivers
5.4.1
No existing or planned
water sensitive receiver (WSR) was identified within 300 m from the Project
site boundary. The existing WSD flushing water intakes and cooling water
intakes identified closest to the Project site are shown in Drawing 5.2 and all of them are
located outside the assessment area (i.e. within 300 m from the Project
site boundary). No
planned WSR will be affected by the Project. The recent dive surveys revealed that the
seabed of KTD area was composed of muddy and sandy bottom and of low habitat
quality. Limited marine life was seen except only some small and isolated
patches of single species of hard coral (Oulastrea crispata) were found in the KTD area and this species
is common in
5.5.1 The assessment area for the water quality impact assessment as stated in the EIA Study Brief covers the Victoria Harbour WCZ and all areas within 300m from the Project boundary.
5.5.2 The water sensitive receivers that may be affected by the decommissioning activities for the Project have been identified. Potential sources of water quality impact that may arise during the decommissioning works were described. This task included identifying pollutants from point discharges and non-point sources that could affect the quality of surface water run-off. All the identified sources of potential water quality impact were then evaluated and their impact significance determined. The need for mitigation measures to reduce any identified adverse impacts on water quality to acceptable levels was determined.
5.6 Identification of Environmental Impacts
Decontamination Processes
5.6.1 Upon recommendations in the land contamination assessment provided in Section 3, contaminated soil at the Project site would be excavated and treated on-site. Cement solidification / stabilization and biopiling will be carried out for soil remediation.
Soil Excavation
5.6.2 Excavations of contaminated soil will be required for the decontamination works. No groundwater extraction would be required for the soil excavation works. In case there are temporary stockpiles of contaminated soils on-site or exposed soil surfaces, the associated surface runoff may impact the nearby water bodies if not controlled.
Decontaminated Water and Wastewater from Wheel Washing
5.6.3 After excavation and handling of the contaminated soil, excavators/backhoes and dump trucks are to be decontaminated by steam cleaning. Such decontamination water that may carry contaminants poses water quality impact if not well controlled. Wastewater from wheel washing bay at the site entrance is also potentially contaminated and may pose similar water quality impact.
Operation of Solidification/Stabilization Facility
5.6.4 Cement solidification/stabilization is a recommended remediation method for the treatment of metal-contaminated soil. During the cement solidification/stabilization process, cement, water and other additive(s) (such as fly ash, lime, soluble silicates, and clays) are added to the contaminated soils to form solid block. Mixing of contaminated soils and cement/water/other additive(s) would introduce potential leaching of contaminants, if water addition is not well controlled.
Operation of Biopiling
5.6.5 Biopiling is a bioremediation method for the restoration of the contaminated soils with organic compounds. By using microorganisms to degrade the contaminants in soil, biopiles transform hazardous/toxic materials into harmless element such as water, carbon dioxide, and other innocuous products. Leachate resulting from rain percolation in case that the biopiles are not fully covered and from biodegradation product would be a concern to the underlying soil, groundwater system and water bodies if not properly controlled.
Groundwater Cleanup
5.6.6 Floating oil/free product of total petroleum hydrocarbons (TPH) has only been found in limited area at the ex-GFS apron area. As the free product is likely to be localized, it appears that the quantity of the free product would be small. As such, it is proposed that where free product is detected at the groundwater surface at excavated area, only the free product shall be skimmed off. Full justification of the groundwater cleanup requirement is given in Section 3 of this report. The skimmed free product may potentially affect the marine water system if not properly controlled.
Groundwater Quality, Level, Catchment Nature and Areas
5.6.7 The Project involves excavation of contaminated soil for treatment on-site. All exposed pits from soil excavation shall be backfilled with clean soil. No groundwater extraction would be required for the proposed excavation works. Therefore, the Project will not induce any change in the groundwater quality, groundwater level and groundwater catchment area.
5.6.8 With regard to the nature of groundwater catchment, there will be a cleanup of soil contamination within the catchment under this Project. Hence, the Project would have beneficial effect by removing a source of contaminating groundwater.
Groundwater Seepage
5.6.9 Potential water quality impact may arise from groundwater seeping directly (or indirectly via drainage channels at the Project site) to the nearby marine water.
Decommissioning of the Disused Fuel Dolphin
5.6.10
The disused fuel dolphin is located outside the limit of the former
5.6.11 Since the review of historical sediment quality data indicated the presence of highly contaminated sediment in To Kwa Wan Typhoon Shelter and as discussed in Section 2.4 of this report, it is recommended from the environmental perspective not to adopt dredging works for the removal of the disused fuel dolphin structure and to leave the associated abandoned fuel pipeline in-situ.
5.6.12 The existing fuel dolphin is supported by 26 number of 450mm x 450mm precast concrete piles. It is proposed that the disused fuel dolphin structure would be demolished by cutting off the piles to 1m below existing seabed. The sediment around the piles would be pushed aside to facilitate the pile cutting and no dredging would be required for the demolition works. It is estimated that the total volume of sediments that would potentially be disturbed by the pile cutting would be 130m3 only. The disused fuel pipelines will be left in place and, if necessary, grouted with concrete.
5.6.13 The key water quality concern of the proposed removal works would be the potential disturbance to the marine sediment near the fuel dolphin. Disturbance of marine sediment may release previously bound organic and inorganic constituents such as nutrients, heavy metals, polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) into the water column. Increase of suspended solids could also be resulted from the sediment disturbance, with possible consequence of reducing DO levels in the water column.
Demolition Works
5.6.14
The decommissioning works
also include demolition
of some remaining existing structures / building of the former
5.6.15 Surface runoff may cause potential water quality impact during the demolition activities. Precipitation that falls on unpaved lands and areas with the topsoil exposed during the demolition would wash away soil particles. Such surface runoff and stormwater overflows with high levels of suspended solids if directly discharged into the water bodies or via the drainage channel could lead to a water quality impact.
5.6.16 Effluent discharge from temporary site facilities shall be controlled to prevent direct discharge to the neighbouring marine waters and storm drains. Such wastewater may include wastewater resulting from wheel washing of site vehicles at site entrances.
Sewage from Workforce
5.6.17 Sewage will arise from the on-site workforce. It is characterized by high level of BOD, NH3-N and E.coli counts and may adversely affect the water quality, if not proper controlled.
Accumulation of Solid Waste and Accidental Spillage
5.6.18 Accumulation of solid waste (such as debris, rubbish and demolition materials), and spillage of oil, diesel or solvents by vessels and vehicles involved with the decommissioning works, if uncontrolled, could also lead to deterioration in water quality.
Alteration of Water Courses and Change of Flow Regime
5.6.19 The proposed decommissioning activities will not alter the watercourse (i.e. the KTN) within the site. Decommissioning of the fuel dolphin would reduce a source of friction to the water flow and therefore may increase local current speeds. Other decommissioning works at the south apron and runway area would all be land-based which will not affect the flow regime.
5.7 Prediction and Evaluation of Environmental Impacts
Decontamination Processes
Soil Excavation
5.7.1 During excavation, all exposed pits shall be whenever possible backfilled immediately or covered. Where it is unavoidable to have transient soil piles pending collection for treatment, the transient piles shall be bottom-lined, bunded and covered during rain events with impervious membrane. As such, it is unlikely that the surface runoff would be contaminated. With proper implementation of the above mitigation measures, no adverse water quality impact associated with excavation works is expected on the identified water sensitive receivers
Decontaminated Water and Wastewater from Wheel Washing
5.7.2 It would be a required site practice not to directly discharge decontamination water and the potentially contaminated wheel washing water into the surface channel or nearby water bodies. All decontamination water and wheel washing water would be regarded as contaminated and diverted to a centralized wastewater treatment unit. The centralized wastewater treatment unit shall deploy suitable treatment processes to reduce the pollution level to an acceptable standard and remove key contaminant of concern to an undetectable range. Relevant parameters stipulated in the TM-DSS (refer to Section 5.2.3) will be controlled under the WPCO. Any contaminants and pollutants in the effluent shall be treated before discharged into local drainage channel. Therefore, significant water quality is not expected.
Operation of Solidification/Stabilization Facility
5.7.3 The solidification/stabilization facility will be housed in a shed to minimize dust emissions. The shed will also serve to prevent contaminated runoff. This would minimize the leachate generation from the facility. All leachate shall be diverted to the centralized wastewater treatment unit (refer to Section 5.9) before being discharged. Taking the above considerations and with the implementation of all the recommended mitigation measures, no adverse water quality impact is expected during the solidification/stabilization process.
Operation of Biopiling
5.7.4 As recommended under the land contamination assessment in Section 3 of this report, concrete perimeter bund and impermeable floor sheeting shall be constructed respectively around and underneath the biopile. With the floor sheeting and bund in place, any biopile leachate would be contained and migration of leachate out of the biopiling area is not likely. In operation, low permeability sheeting shall be employed to cover the biopile after formation and during rains. This avoids contaminated runoff as a result of the rainwater washing over the biopile and leaching of the biopile by the rainwater. Any leachate generated from the process shall be recycled to the biopile and no effluent discharge would be expected by the biopiling operation. With the implementation of mitigation measures, adverse water quality impacts associated with the operation of biopiling on the nearby water quality sensitive receivers are not expected.
Groundwater Cleanup
5.7.5 Floating oil/free product (of TPH) has only been found in the ex-GFS apron area. It is proposed that where free product is detected at the groundwater surface at excavated area, only the free product shall be skimmed off. Detailed requirements for removal of free product are given in Section 3 of this report. Provided that the skimmed free product is drummed properly and collected by a licensed chemical waste collector for disposal, no adverse impact on the identified water sensitive receivers is anticipated.
Groundwater Quality, Groundwater Level and Groundwater Seepage
5.7.6 As indicated in the land contamination assessment in Section 3 of this report, no groundwater extraction would be carried out for the decontamination works. This Project would not induce any groundwater seepage. The groundwater quality and level would not be affected by the decontamination activities.
5.7.7 Under the present EIA study, appropriate remediation actions are recommended in the land contamination assessment and shall be implemented to clean up the soil contamination to acceptable levels. The Project would in fact have long term beneficial effect by removing a source of contaminated groundwater seepage.
Decommissioning of the Disused Fuel Dolphin
5.7.8
As no dredging would be
required for the proposed decommissioning works, any loss of fine sediment to
suspension from disturbance of the seabed around the dolphin is expected to be
minor. The dolphin removal works would be undertaken at inner
Demolition Works
5.7.9
As a good site
practice, mitigation measures should be implemented to control site runoff and
drainage and site effluent from the works areas, and to prevent runoff and
drainage water with high levels of suspended solids from entering the adjacent
waters of the
5.7.10
All the demolition
works will be conducted at land side sites of the former
Sewage from Workforce
5.7.11 Domestic sewage would be generated from the workforce during the decommissioning works. Portable chemical toilets can be installed within the site. The chemical toilets should be properly maintained, and licensed contractors should be employed to collect and dispose of the waste off-site at approved locations. Therefore, adverse water quality impacts associated with sewage from workforce would not be expected.
Accumulation of Solid Waste and Accidental Spillage
5.7.12 On-site decontamination and demolition activities may cause water pollution from the following:
l Uncontrolled discharge of debris and rubbish such as demolition materials and refuse
l Spillages of liquids stored on-site, such as oil, diesel and solvents etc.
5.7.13 Good construction and site management practices should be observed, as detailed in Section 5.9 below, to ensure that litter, fuels and solvents do not enter into the adjacent water system.
Change of Flow Regime
5.7.14
Decommissioning of the
fuel dolphin by removing 26 number of 450mm x 450mm concrete piles would reduce
a source of friction to the water flow and increase local current speeds.
However, as removal of the concrete piles would increase the water surface by
about 5 m2 only, the associated change in flow speeds should be
insignificant and localized. The decommissioning of fuel dolphin would not
change the overall flow regime in the
5.8 Consideration of Cumulative Environmental Impacts
5.8.1 Referring to construction programme of the Project and other projects within the Study Area, it is noted that construction period of other projects listed below might overlap with the Project.
l Kai Tak Development Advance Works – Construction of local access roads (Roads TD3, TD4 and Road L14), sewage pumping station, public landing steps cum fireboat berth, electricity substation (by CLP) etc
l Cruise Terminal Construction (including dredging, and construction of berth structure, transition structure, and terminal building)
l Operation of works area for
temporary storage of C&D materials and the barging points for removal of
C&D materials from Development at Choi Wan and
l Operation of the barging point at
southwest of the former
Land-based Activities
5.8.2 As shown in Drawings 2.4a and 2.4b, most of the concurrent projects (except some activities under the Advance Works (e.g. local roads construction) are located at the southwest of the former airport runway, outside the limits of the decontamination areas. For the advance works at the ex-GFS apron area, it will not be commenced until the completion of the decontamination works at that part of the site. Since all possible effluents, leachate and contaminated runoff from the Project site shall be treated and their quality be monitored before discharged, no significant cumulative water quality impact imposed by the Project is expected.
Marine-based Activities
5.8.3 There would not be any permanent works required under the KTD at the existing location of the fuel dolphin. The presence of the disused fuel dolphin would not affect the construction of any of the KTD components and other concurrent projects. Since no major water quality impact from decommissioning of the fuel dolphin was identified in this assessment, cumulative water quality impact is not expected.
5.9 Mitigation Measures of Adverse Environmental Impacts
5.9.1 Proposed mitigation measures for containing and minimizing water quality impacts are summarised below.
Decontamination Processes
Soil Excavation
5.9.2 During excavation, all exposed pits shall be whenever possible backfilled immediately or covered. Where it is unavoidable to transiently pile up soils next to the excavation pit, the transient pile shall be bottom-lined, bunded and covered with impervious membrane during rain event in order to avoid generation of contaminated runoff.
5.9.3 Final surfaces after excavation shall be well compacted and the subsequent permanent work or surface protection shall be carried out as soon as practical after the final surfaces are formed to prevent erosion caused by rainstorms. Appropriate intercepting channels and partial shelters shall be provided where necessary to prevent rainwater from collecting within trenches or footing excavations.
Decontaminated Water and Wastewater from Wheel Washing
5.9.4 During excavation, dump trucks or excavators shall be decontaminated before they leave the site to ensure that no contaminated earth, mud or debris is deposited by them on roads. A wheel washing bay shall be provided at every site exit that equipped with an adequately sized centralized wastewater treatment unit. The wastewater treatment unit shall be able to settle out sands / silts with contaminants cohered and remove other contaminants in wheel washes and decontamination water. The polluting parameters in effluent of the wastewater treatment unit shall be in compliance with the discharge standards stipulated in the TM-DSS (see Section 5.2.3) before the effluent being discharged into the storm drains. Appropriate treatment would include chemical precipitation and activated carbon adsorption. The installation and operation of the wastewater treatment unit shall be licensed and subject to the effluent monitoring as required under the WPCO which is under the ambit of regional office (RO) of EPD. In any case, discharge of wheel wash water shall be minimized and recycled where possible. The haul road between the wheel washing bay and the public road should be paved to reduce vehicle tracking of soil and to prevent surface runoff from entering public road drains.
Operation of Solidification / Stabilization Facility
5.9.5 The solidification/stabilization facility shall be sheltered and the area(s) of soil unloading / loading shall be provided with shed to avoid contaminated runoff. Excessive addition of water shall be avoided during the solidification/stabilization process.
5.9.6 Any pit used for solidification / stabilization area shall be shallower than the water table to minimize the leaching of the contaminated soils. An impermeable membrane / sheet shall be placed at the bottom of any solidification pit during the solidification process.
5.9.7 Any leachate generated from the solidification/stabilization process shall be collected and treated in the centralized wastewater treatment unit before being discharged. The polluting parameters in effluent of the wastewater treatment unit shall be in compliance with the discharge standards stipulated in the TM-DSS (see Section 5.2.3) before the effluent being discharged. Appropriate treatment would include chemical precipitation and activated carbon adsorption. The installation and operation of the wastewater treatment unit shall be licensed and subject to the effluent monitoring as required under the WPCO.
Operation of Biopiling
5.9.8 As recommended under the land contamination assessment in Section 3 of this report, impermeable liner shall be placed at the bottom of the biopiles and leachate collection sump shall be constructed along the perimeter of the biopiles to prevent leachate from contaminating the underlying soil / groundwater. Concrete bund shall be constructed along the perimeter of biopiles to prevent the runoff coming out from the contaminated soil. Biopiles after formation and during rain shall be covered by anchored low permeability geotextiles to prevent contaminated runoff. It is proposed that the exposed biopile section at any time shall not be more than 5 m in length.
5.9.9 All leachate generated from the operation of biopiling shall be collected and recycled to the biopile to avoid effluent discharge.
Groundwater Cleanup
5.9.10 Floating oil / free product (of TPH) has only been found in the ex-GFS apron area. It is proposed that where free product is detected at the groundwater surface at excavated area, only the free product shall be skimmed off. Detailed requirements for removal of free product are given in Section 3 of this report. The skimmed free product shall be drummed properly and collected by a licensed chemical waste collector for disposal.
Groundwater Seepage
5.9.11 With implementation of all the mitigation measures recommended for the decontamination processes, the Project would not induce or pollute any groundwater seeping to the nearby groundwater or surface water system. No further mitigation measure is required.
TPH Removal
5.9.12 Oil/water interceptor should be adopted, where appropriate, as the first tier of treatment to remove TPH contaminant from contaminated runoff and effluent discharge from the decontamination works area.
Failure of Centralized Wastewater Treatment Unit
5.9.13 In the event of wastewater treatment unit failure, all wastewater generating activities should be ceased to avoid emergency discharge.
Decommissioning of the Disused Fuel Dolphin
5.9.14 No unacceptable impact from decommissioning of the disused fuel dolphin was identified in this assessment, water quality mitigation measure is not required.
Demolition Works
5.9.15 The 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. The following measures are recommended to minimize water pollution and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts:
l At the start of site establishment, perimeter cut-off drains to direct off-site water around the site should be constructed with internal drainage works and erosion and sedimentation control facilities implemented. Channels (both temporary and permanent drainage pipes and culverts), earth bunds or sand bag barriers should be provided on site to direct storm water to silt removal facilities. The design of the temporary on-site drainage system shall be undertaken by the contractor prior to the commencement of decommissioning works.
l Sand / silt removal facilities such as sand / silt traps and sediment basins should be provided to remove sand / silt particles from runoff to meet the requirements of the TM-DSS (see Section 5.2.3). The design of efficient silt removal facilities should be 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. The detailed design of the sand / silt traps shall be undertaken by the contractor prior to the commencement of decommissioning works.
l 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 during rainstorms. Deposited silt and grit should be regularly removed, at the onset of and after each rainstorm to ensure that these facilities are functioning properly at all times.
l Measures should be taken to minimize the ingress of site run-off and drainage into excavations. Drainage water pumped out from excavations should be discharged into storm drains via silt removal facilities.
l If surface excavation works cannot be avoided during the wet season (April to September), temporarily exposed slope / soil surfaces should be covered by a tarpaulin or other means, as far as practicable. Interception channels should be provided (e.g. along the crest / edge of the excavation) to prevent storm runoff from washing across exposed soil surfaces. Arrangements should always be in place to ensure that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm. Other measures that need to be implemented before, during and after rainstorms are summarized in ProPECC PN 1/94.
l All vehicles and plant should be cleaned before leaving the site to ensure no earth, mud, debris and the like is deposited by them on roads. An adequately designed and sited wheel washing facility should be provided at every site exit where practicable. 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.
l Open stockpiles of construction materials or construction wastes on-site of more than 50m3 should be covered with tarpaulin or similar fabric during rainstorms.
5.9.16 There is a need to apply to EPD for a discharge licence under the WPCO for discharging effluent from the construction site. The discharge quality is required to meet the requirements specified in the discharge licence. All the runoff, wastewater or extracted groundwater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS (see Section 5.2.3). It is anticipated that the wastewater generated from the works areas would be of small quantity. Regular monitoring of the treated effluent quality from the centralized wastewater treatment unit and stormwater discharges from major storm outfalls within the works areas will be conducted. Monitoring parameters should constantly include SS, turbidity, oil and grease, COD and less frequently include TPH, BTEX and selected metals. Parameters included in the WPCO licence, will also be included in the monitoring programme. The chemical testing of water samples collected in the monitoring programme should be undertaken by a Hong Kong Laboratory Accreditation Scheme (HOKLAS) accredited laboratory. Detail monitoring programme / plan will be submitted at later stage for EPD's agreement.
Sewage from Workforce
5.9.17 Temporary sanitary facilities, such as portable chemical toilets, should be employed on-site where necessary to handle sewage from the workforce. A licensed contractor would be responsible for appropriate disposal of waste matter and maintenance of these facilities.
Accumulation of Solid Waste and Accidental Spillage
5.9.18 Debris and refuse generated on-site should be collected, handled and disposed of properly to avoid entering into the adjacent harbour waters. Stockpiles of cement and other construction materials should be kept covered when not being used.
5.9.19 Oils and fuels should only be used and stored in designated areas which have pollution prevention facilities. To prevent spillage of fuels and solvents to the nearby harbour waters, all fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank. The bund should be drained of rainwater after a rain event.
Change of Flow Regime
5.9.20 The Project would not change the flow regime within the Study Area. No mitigation measure is required.
5.10 Evaluation of Residual Impacts
5.10.1 Provided that all the recommended mitigation measures are implemented properly, no unacceptable residual water quality impacts would be expected.
5.11 Environmental Monitoring and Audit
5.11.1 No off-site water quality impact would be expected from the proposed decommissioning and decontamination activities, marine water quality monitoring is not considered necessary. It is recommended that regular site inspections be undertaken to inspect the decommissioning activities and works areas in order to ensure that the recommended mitigation measures are properly implemented. Regular monitoring of the treated effluent quality from the centralized wastewater treatment unit and stormwater discharges from major storm outfalls within the works areas will be conducted. Monitoring parameters should constantly include SS, turbidity, oil and grease, COD and less frequently include TPH, BTEX and selected metals. Parameters included in the WPCO licence, will also be included in the monitoring programme. The chemical testing of water samples collected in the monitoring programme should be undertaken by a Hong Kong Laboratory Accreditation Scheme (HOKLAS) accredited laboratory. Detail monitoring programme / plan will be submitted at later stage for EPD's agreement.
5.12.1 Water quality impacts from the land-based decontamination works, associated with leachate, and contaminated runoff, can be controlled to acceptable levels by implementing the recommended mitigation measures. All the effluents and runoff generated from the works areas shall be treated and their quality be monitored before discharged. No unacceptable water quality impacts would be expected from the land-based decommissioning activities. Since no off-site water quality impact has been identified form the Project, no cumulative water quality impact would be expected.
5.12.2 The proposed method for decommissioning of the disused fuel dolphin would not involve any dredging and in view that the works area would be small, any potential marine water quality impact arising from the decommissioning works would be minor and localized and no unacceptable marine water quality impact would be expected.
5.12.3 Site inspections should be undertaken routinely to inspect the works areas in order to ensure the recommended mitigation measures are properly implemented.