穨 EIA DFR SEPT2001 Final 7__

Agreement No. CE 98/98 Environmental Impact Assessment Preliminary Design and Ground Investigation for Widening of Final Report Yuen Long Highway Between Lam Tei and Shap Pat Heung Interchange December 2001

5. WATER QUALITY

5.1 Introduction

This Chapter presents an assessment of the potential for the YLH widening scheme to impact upon the aquatic environment and includes the following:

· definition of applicable water-related legislation; · a description of the existing water environment along the YLH corridor; · the identification and preliminary assessment of the potential impacts during the project’s construction and operation; · recommendation of potential mitigation measures for the amelioration of adverse impacts such that the proposed scheme can proceed without significant impact upon the aquatic environment; and · a preliminary identification of monitoring requirements.

5.2 Government Standards and Legislation

Under the Water Pollution Control Ordinance (WPCO), Hong Kong waters are divided into Water Control Zones (WCZs). Each WCZ has a designated set of statutory Water Quality Objectives (WQOs).

The majority of the YLH lies within the Deep Bay Water Control Zone (WCZ) which was declared on 1 December 1990. WQOs for the Deep Bay WCZ are detailed in Table 5.1.

Any discharge to the Deep Bay WCZ is required to comply with the standards specified in the Technical Memorandum on Standards for Effluents into Drainage and Sewerage Systems, Inland and Coastal Waters (WPCO, Cap 358,S.21) (referred to hereafter as the Technical Memorandum on Effluent Standards). Inland waters are divided into four different zones based on their beneficial use. It is likely that the inland waters of the Study Area will be defined as Group B which have beneficial uses for irrigation and are those waters draining agricultural areas in the New Territories. In the event that the ponds in the area are used for culture, the standards are those for Group C. As such, depending on classification and the selected effluent disposal method, any discharges from the site to receiving waters will be required to meet the standards given in Table 5.2a/b.

In addition to the above, there is a “zero discharge” requirement within the Deep Bay catchment area with regard to organic wastes.

The Tuen Mun River and its associated catchment at the western end of the YLH lies within the North Western WCZ. Therefore, discharges generated in this part of the highway must comply with the standards specified for the North Western WCZ as detailed in the Technical Memorandum on Effluent Standards.

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Table 5.1 Summary of Water Quality Objectives (WQOs) for the Deep Bay Water Control Zone

Water Quality Objective Part of Parts of Zone A. AESTHETIC APPEARANCE (a) Waste discharges shall cause no objectionable odours or discoloration of the water. Whole zone (b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other Whole zone substances should be absent. (c) Mineral oil should not be visible on the surface. Surfactants should not give rise to Whole zone a lasting foam. (d) There should be no recognisable sewage-derived debris. Whole zone (e) Floating, submerged and semi-submerged objects of a size likely to interfere with Whole zone the free movement of vessels, or cause damage to vessels, should be absent. (f) Waste discharges shall not cause the water to contain substances which settle to Whole zone form objectionable deposits.. B. BACTERIA (a) The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the Secondary Contact Recreation Subzones and geometric mean of all samples collected in a calendar year. Mariculture Subzone (b) The level of Escherichia coli should be less than zero per 100 mL, calculated as the Yuen Long & Kam Tin (Upper) Subzone, Beas running median of the most recent 5 consecutive samples taken at intervals of Subzone, Indus Subzone, Ganges Subzone and between 7 and 21 days. Water Gathering Ground Subzones (c) The level of Escherichia coli should not exceed 1 000 per 100 mL, calculated as Yuen Long & Kam Tin (Lower) Subzone and the running median of the most recent 5 consecutive samples taken at intervals of other inland waters between 7 and 21 days. (d) The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the Yung Long Bathing Beach Subzone geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days. C. COLOUR (a) Waste discharges shall not cause the colour of water to exceed 30 Hazen units. Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (b) Waste discharges shall not cause the colour of water to exceed 50 Hazen units. Yuen Long & Kam Tin (Lower) Subzone and other inland waters D. DISSOLVED OXYGEN (a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg Inner Marine Subzone excepting Mariculture per litre for 90% of the sampling occasions during the whole year; values should be Subzone taken at 1 metre below surface. (b) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg Outer Marine Subzone excepting Mariculture per litre for 90% of the sampling occasions during the whole year; values should be Subzone calculated as water column average (arithmetic mean of at least 2 measurements at 1 m below surface, and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 m of the seabed for 90% of the sampling occasions during the year (c) The dissolved oxygen level should not be less than 5 mg per litre for 90% of the Mariculture Subzone sampling occasions during the year; values should be taken at 1 metre below surface. (b) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg Yuen Long & Kam Tin (Upper and Lower) per litre. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters of the Zone E. pH (a) The pH of the water should be within the range of 6.5-8.5 units. In addition, waste Marine waters excepting Yung Long Bathing discharges shall not cause the natural pH range to be extended by more than 0.2 Beach Subzone units. (b) Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 Yuen Long & Kam Tin (Upper and Lower) units. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (c) The pH of the water should be within the range of 6.0-9.0 units. Other inland waters

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Water Quality Objective Part of Parts of Zone (d) The pH of the water should be within the range of 6.0-9.0 units for 95% of Yung Long Bathing Beach Subzone samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units. F. TEMPERATURE Waste discharges shall not cause the natural daily temperature range to change by Whole zone more than 2.0 oC. G. SALINITY Waste discharges shall not cause the natural ambient salinity level to change by Whole zone more than 10%. H. SUSPENDED SOLIDS (a) Waste discharges shall neither cause the natural ambient level to be raised by 30% Marine waters nor give rise to accumulation of suspended solids which may adversely affect aquatic communities. (b) Waste discharges shall not cause the annual median of suspended solid to exceed Yuen Long & Kam Tin (Upper and Lower) 20 mg per litre. Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters I. AMMONIA The un-ionised ammoniacal nitrogen level should not be more than 0.021 mg per Whole zone litre, calculated as the annual average (arithmetic mean). J. NUTRIENTS (a) Nutrients should not be present in quantities sufficient to cause excessive or Inner and Outer Subzones nuisance growth of algae or other aquatic plants. (b) Without limiting the generality of objective (a) above, the level of inorganic Inner Marine Subzone nitrogen should not exceed 0.7 mg per litre, expressed as annual mean. (c) Without limiting the generality of objective (a) above, the level of inorganic Outer Marine Subzone nitrogen should not exceed 0.5 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid- depth and 1m above seabed. K. 5-DAY BIOCHEMICAL OXYGEN DEMAND (a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed Yuen Long & Kam Tin (Upper) Subzone, Beas 3 mg per litre. Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (b) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed Yuen Long & Kam Tin (Lower) Subzone and 5 mg per litre other inland waters L. CHEMICAL OXYGEN DEMAND (a) Waste discharges shall not cause the chemical oxygen demand to exceed 15 mg per Yuen Long & Kam Tin (Upper) Subzone, Beas litre. Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones (b) Waste discharges shall not cause the chemical oxygen demand to exceed 30 mg per Yuen Long & Kam Tin (Lower) Subzone and litre. other inland waters M. TOXIC SUBSTANCES (a) Waste discharges shall not cause the toxins in water to attain such levels as the Whole zone produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interaction with each other. (b) Waste discharges shall not cause a risk to any beneficial use of the aquatic Whole zone environment. N. PHENOL Phenols shall not be present in such quantities as to produce a specific odour, or in Yung Long Bathing Beach Subzone concentration greater than 0.5 mg per litre as C6H5OH O. TURBIDITY Waste discharges shall not reduce light transmission substantially from the normal Yung Long Bathing Beach Subzone level

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Table 5.2a Standards for Effluents Discharged into Group B Inland Water (all units in mg/L unless otherwise stated; all figures are upper limits unless otherwise indicated)

Flow rate (m3/day) £ 200 >200 >400 >600 >800 >1000 >1500 >2000 and and and and and and and Determinant £ 400 £ 600 £ 800 £ 1000 £ 1500 £ 2000 £ 3000 pH (pH units) 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 Temperature (°C) 35 30 30 30 30 30 30 30 Colour (lovibond 1 1 1 1 1 1 1 1 units) (25 cell length) Suspended solids 30 30 30 30 30 30 30 30 BOD 20 20 20 20 20 20 20 20 COD 80 80 80 80 80 80 80 80 Oil & grease 10 10 10 10 10 10 10 10 Iron 10 8 7 5 4 3 1 1 Boron 5 4 3 2.5 2 1.5 1 0.5 Barium 5 4 3 2.5 2 1.5 1 0.5 Mercury 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Cadmium 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Selenium 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 Other toxic metals 0.5 0.5 0.2 0.2 0.2 0.1 0.1 0.1 individually Total toxic metals 2 1.5 1 0.5 0.5 0.2 0.2 0.2 Cyanide 0.1 0.1 0.1 0.08 0.08 0.05 0.05 0.03 Phenols 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Sulphide 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fluoride 10 10 8 8 8 5 5 3 Sulphate 800 800 600 600 600 400 400 400 Chloride 1000 1000 800 800 800 600 600 600 Total phosphorus 10 10 10 8 8 8 5 5 Ammonia nitrogen 5 5 5 5 5 5 5 5 Nitrate + nitrite 30 30 30 20 20 20 10 10 nitrogen Surfactants (total) 5 5 5 5 5 5 5 5 E.coli 100 100 100 100 100 100 100 100 (count/100ml)

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Table 5.2 b Standards for Effluents Discharged into Group C Inland Waters (all units in mg/L) unless otherwise stated; all figures are upper limits unless otherwise indicated)

Flow rate(m3/day) £ 100 >100 and £ 500 >500 and >1000 and £ 1000 £ 2000 Determinant pH (pH units) 6-9 6-9 6-9 6-9 Temperature (°C) 30 30 30 30 Colour (lovibond units) 1 1 1 1 (25mm cell length) Suspended solids 20 10 10 5 BOD 20 15 10 5 COD 80 60 40 20 Oil & grease 1 1 1 1 Boron 10 5 4 2 Barium 1 1 1 0.5 Iron 0.5 0.4 0.3 0.2 Mercury 0.001 0.001 0.001 0.001 Cadmium 0.001 0.001 0.001 0.001 Silver 0.1 0.1 0.1 0.1 Copper 0.1 0.1 0.05 0.05 Selenium 0.1 0.1 0.05 0.05 Lead 0.2 0.2 0.2 0.1 Nickel 0.2 0.2 0.2 0.1 Other toxic metals 0.5 0.4 0.3 0.2 individually Total toxic metals 0.5 0.4 0.3 0.2 Cyanide 0.05 0.05 0.05 0.01 Sulphide 0.2 0.2 0.2 0.1 Fluoride 10 7 5 4 Sulphate 800 600 400 200 Chloride 1000 1000 1000 1000 Total phosphorus 10 10 8 8 Ammonia nitrogen 2 2 2 1 Nitrate + nitrite nitrogen 30 30 20 20 Surfactants (total) 2 2 2 1 E. coli (count/100ml) 1000 1000 1000 1000

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5.3 Sensitive Receivers

The Study Area includes the following aquatic environments that could potentially be affected by the proposed project:

· isolated ponds; · streams and rivers; and · drainage nullahs, culverts and channels.

These water features are shown in Figure 5.1 and are discussed below. It is noted that the proposed Yuen Long Bypass Floodway (due for completion by December 2003 – Binnie Consultants Ltd 1998) will pass to the south of YLH from Sham Chung Tsuen and connect to the Kam Tin River. Following completion, the Yuen Long Highway Floodway will be defined as a water sensitive receiver.

Ponds

Whilst the predominant land uses along the YLH corridor are village and agricultural developments, there are a number of discrete pond areas towards the eastern portion of the existing road alignment. Existing ponds are located at the following locations:

· south of the Shap Pat Heung Interchange (No 4 in Figure 5.1); · east of Lam Hau Tsuen (No 5 in Figure 5.1); · north and south of Tong Yan San Tsuen Interchange (No 6 in Figure 5.1); · west of Fui Sha Wai (No 7 in Figure 5.1); and · west of Tong Yan San Tsuen (No 8 in Figure 5.1).

A number of these isolated ponds may be lost as a result of the Yuen Long Bypass Floodway Project.

Rivers, Streams and Nullahs

There are three main drainage conduits within the Study Area, these being the Tuen Mun River, the Tin Shui Wai Nullah and the Shan Pui River (which includes Yuen Long Creek), the latter two draining into Deep Bay and the former to the coastal waters off Tuen Mun. The other secondary streams, nullahs and drainage features within the Study Area are all associated with these primary drainage channels.

The surface water courses associated with the three primary drainage channels are as follows:

· Tuen Mun River System - including the river tributary from Lam Tei Reservoir, the stream near Tsoi Yuen Tsuen and the main Tuen Mun River;

· Tin Shui Wai Nullah System - streams near Tan Kwai Tsuen and the stream from Tai Tao Tsuen which flows towards Fui Sha Wai/Ping Shan; and

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· Shan Pui River System - including the nullah which passes beneath YLH at Tong Yan San Tsuen Interchange, the stream at Lam Hau, nullahs at Sham Chung Tsuen and associated drainage channels, the stream which passes through Sham Chung Tsuen and flows beneath the YLH to Fraser Village and the stream at Kong Tau San Tsuen.

In addition to the above, after December 2003 the proposed Yuen Long Bypass Floodway which aims to divert part of the flows entering the Yuen Long drainage system from the south of Yuen Long into the Kam Tin River (currently under construction) will be defined as a water sensitive receiver. Under the Yuen Long Bypass Floodway, some of the streams currently discharging into the Shan Pui River system will be intercepted and diverted towards the Kam Tin River.

Groundwater and Deep Bay

On a regional scale, the whole Study Area is a water gathering ground for Deep Bay. Due to the ecological importance of the Deep Bay area, the groundwater in the Study Area should be considered as a sensitive receiver, although it is likely that it is affected by local activities. Whilst groundwater in the Study Area is not considered to be used for potable water supply, there may be isolated groundwater use for irrigation purposes (Binnie 1998).

Deep Bay itself should also be viewed as a regional water sensitive receiver, since the majority of the water discharges from the area, whether via surface water channels or groundwater routes, eventually discharge there. Any adverse impacts on the water quality in the Study Area will ultimately affect Deep Bay.

5.4 Existing Conditions

The following sections consider the existing water quality conditions in the main water sensitive receivers as identified above.

Shan Pui River System

The Shan Pui River System includes Yuen Long Creek which has a catchment area of 26.7km2. Water quality in Yuen Long Creek is routinely monitored by EPD at four main locations - refer to Figure 5.1. Data for the monitoring stations closest to the YLH (i.e. YL1 and YL2) are presented in Table 5.3.

Table 5.3 Water Quality at EPD Monitoring Stations in Yuen Long Creek (mg/L unless indicated) (EPD 1997)

Parameter YL1 YL2 Dissolved oxygen 2.63 5.38 PH (pH units) 7.41 7.16 Suspended solids 242 51.46

BOD5 286 31.86 COD 333.75 36.3 Oil and grease 26.11 2.26 E.coli (cfu/100mL) 16,571,667 nm Ammoniacal-N 36.7 13.08 Nitrate-N 0.018 0.49

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Parameter YL1 YL2 Total Kjeldahl N 59.91 17.93 Ortho-phosphate 11.37 2.6 Total phosphate 15.85 3.13 Sulphide 0.51 0.18 Aluminum (mg/L) 495 335.8 Cadmium (mg/L) 0.94 0.188 Chromium (mg/L) 5.1 2.1 Copper (mg/L) 513 14.16 Lead (mg/L) 13.92 8.6 Zinc (mg/L) 363 72.5 Flow (m3/sec) 0.161 0.198 Notes: Data are presented are the annual medians of monthly samples nm - not monitored

The data presented in Table 5.3 illustrates that water quality in Yuen Long Creek is classified as being “bad” to “very bad” and is characterised by non-compliances with the relevant WQOs for BOD, COD, DO and suspended solids (refer to Table 5.1). Water quality is poorest at YL1 where water quality in the river has been consistently bad over the past 4 years with DO levels around 2 - 3mg/L, BOD concentrations exceeding 200mg/L and elevated E.coli levels.

The poor water quality in Yuen Long Creek is considered to be caused by numerous discharges from livestock farms and industrial premises. In addition, due to the population growth in the Yuen Long area, the quantity of sewage being treated at the Yuen Long Sewage Treatment Works (STW) and correspondingly the amount of treated effluent discharged into Yuen Long Creek has increased. Nevertheless, implementation of the Livestock Waste Control Scheme (LWCS) has resulted in a significant reduction in livestock waste being discharged into the river system.

Tin Shui Wai Nullah System

The Tin Shui Wau Nullah comprises a concrete lined channel, which drains the areas of Tin Shui Wai and discharges into Deep Bay. EPD routinely monitors two locations in the Tin Shui Wai Nullah, namely TSR1 and TSR2 (refer to Figure 5.1) which are in the vicinity of the Study Area. Water quality monitoring data for TSR1 and TSR2 are presented in Table 5.4.

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Table 5.4 Water Quality Monitoring Results for the Tin Shui Wai River (mg/L unless indicated otherwise)

Parameter Year 1995 1996 1997 1998 TSR1 Dissolved oxygen 5.2 4.9 8.8 6.6 (1.5-8.9) (0.3-15.6) (5.9-17.3) (0.36-11.0) Dissolved oxygen (% - - 104.5 74.2 Sat.) (60.8-215.9) (4.7-132.9) pH (pH units) 7.5 7.9 7.95 7.6 (7.3-8.0) (7.4-9.1) (7.59-9.56) (7.3-8.0) Suspended solids 28 48 11.1 88 (3-170) (10-260) (6.6-140) (10-170) E.coli (cfu/100mL) 1,075,682 1,497,468 282,133 1,187,881 (0.14M-4.4M) (0.22M-4.8M) (0.05M-2.4M) (0.23M-14M) Ammoniacal-N 4.0 7.95 2.7 7.55 (1.0-19.0) (2.7-21.0) (0.36-11.0) (1.9-8.8)

BOD5 18 31 10.5 13.5 (5-57) (8-78) (2.8-76.0) (7.2-47.0) COD 33 35 14.0 48.5 (11-140) (18-340) (11.0-130) (21.0-160) WQ Index Bad Bad Fair Bad TSR2 Dissolved oxygen 7.1 10.6 10.52 8.73 (4.9-9.0) (4.0-18.1) (7.8-15.45) (7.48-10.5) Dissolved oxygen (% - - 116.5 99.8 Sat.) (97.6-225.9) (93.5-134.2) pH (pH units) 7.7 8.4 8.2 7.68 (7.5-9.0) (7.8-9.6) (7.63-9.45) (7.36-8.48) Suspended solids 51 31 14.5 51 (9-290) (10-140) (4.7-93) (22-1400) E.coli (cfu/100mL) 1,269,750 159,687 40,658 85,316 (0.06M-12M) (0.017M-23M) (0.006M-0.12M) (0.009M-0.28M) Ammoniacal-N 4.25 0.78 0.46 1.0 (0.26-24.0) (0.17-29.0) (0.12-10.0) (0.39-2.5)

BOD5 31 7 3.15 2.6 (2-110) (2-62) (0.53-6.9) (0.33-18.0) COD 29 15 14.0 33.0 (6-110) (7-49) (4.0-41.0) (13.0-52.0) WQ Index Fair Fair Good Excellent

Data presented in Table 5.4 illustrates that water quality has improved at TSR2 over recent years. This is probably due to the implementation of the WPCO and the LWCS, both of which have reduced the number of discharges from pollution sources such as livestock waste and industrial discharges.

Downstream of TSR2, water quality remains poor with elevated levels of COD, ammonia etc. The extremely high E.coli levels highlight the polluted nature of the nullah water. The condition

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of the nullah in this area is still largely influenced by livestock discharges, as such the implementation of the revised LWCS in this area is expected to result in improvements in nullah water quality.

Tuen Mun River System

The Tuen Mun River system has a catchment of some 16.5km2. There are some 6 routine EPD water quality monitoring stations along the Tuen Mun River - the closet to the Study Area being TN1 and TN2 - refer to Figure 5.1. TN2 is located in the tributary, which passes to the south of the YLH at Fu Tei. Water quality data for TN1 and TN2 are presented in Table 5.5.

Table 5.5 Water Quality at EPD Monitoring Stations along Tuen Mun River (mg/L unless indicated) (EPD 1997)

Parameter TN1 TN2 Dissolved oxygen 2.1 8.3 (0.3-4.7) (7.4-11.4) pH (pH units) 8.3 7.4 (7.1-9.3) (7.0-8.7) Suspended solids 88 19 (30-290) (2-130)

BOD5 120 7 (31-410) (2-26) COD 87 13 (32-360) (6-39) Oil and grease 16.0 1.6 (1.0-57) (0.5-7.6) E.coli (cfu/100Ml) 1,184,435 117,163 (0.6M-3.5M) (0.07M-0.53M) Ammoniacal-N 7.75 0.76 (4.3-19) (0.29-22.6) Nitrate-N 0.01 1.8 (0.01-0.17) (0.11-4.40) Total Kjeldahl N 12.5 1.35 (9.5-34) (0.51-7.0) Ortho-phosphate 2.65 0.28 (1.3-5.8) (0.09-0.59) Total phosphate 3.55 0.40 (1.7-8.8) (0.15-0.95) Sulphide 0.09 0.02 (0.02-0.94) (0.02-0.07) Aluminum (mg/L) 280 230 (90-1,100) (170-640) Cadmium (mg/L) 0.2 0.10 (0.10-0.30) (0.10-0.60) Chromium (mg/L) 3.0 1.0 (2.0-17) (1.0-4.0) Copper (mg/L) 7.5 2.0 (3.0-15) (1.0-5.0)

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Parameter TN1 TN2 Lead (mg/L) 5.0 3.0 (2.0-72) (2.0-9.0) Zinc (mg/L) 60 20 (20-150) (10-30) Flow (m3/sec) 73 29 (31-194) (7-261)

Notes: Data are presented are the annual medians of monthly samples, except E.coli which are annual geometric means Figures in brackets show range of recorded values

EPD’s routine water quality monitoring data illustrates that water quality in the Tuen Mun River has improved over recent years due to rectification of expedient connections and reductions in industrial pollution. Water quality in the tributary Fu Tei (TN2) was upgraded from fair to good in 1996, principally due to the clearance of village houses in the Fu Tei area. Upstream at Lam Tei (TN1) water quality is very poor, although some improvements have occurred in recent years. Major sources of pollution to the river near TN1 include domestic sewage and rural industrial discharges from unsewered areas.

Ponds and Groundwater

There are no water quality data for either the ponds identified in the Study Area (refer to Section 5.3) or the areas groundwater resources. However, during site visits water in the identified ponds appeared to be clear, potentially indicating low levels of inorganic pollution.

5.5 Construction Phase Impact Assessment

5.5.1 Impact Sources

During the implementation of the YLH road widening works, there are a number of activities which have the potential to impact upon the water environment - these activities are highlighted below:

· spillages of oil/fuel, construction chemicals etc.;

· generation of silt-laden surface run-off from vegetation stripping and reworking of embankments, dust suppression activities, wheel washing facilities, spoil importation, soil/material storage/stockpiling areas; and

· discharge of construction worker generated sewage and wastewaters.

It is considered that the principal concern will relate to the discharge of surface run-off heavily laden with suspended solids, from the works sites and stockpiling areas into the nullahs and pond areas during periods of rain. Potential impacts will include increased sediment accumulation, turbidity, discoloration, BOD and nutrient enrichment. This is of concern given that spoil material will need to be brought onto site. However, as discussed in Chapter 6, there will be an incentive to the contractor to reduce the stockpiling area as far as is practicable to minimise ‘double handling’ of material. The potential water quality impacts arising due to construction activities are assessed further below.

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Chemical Spillage

During the road widening construction phase, construction plant fuel may need to be stored on site. Spillages of fuels and oil have the potential to migrate towards the aquatic environment and impact upon the aquatic life therein. In order to prevent impacts associated with such accidental spillages, the mitigation measures detailed in Section 5.7 will be required.

Construction Run-off

During the construction phase, there is the potential that the water quality in the vicinity of the Study Area to be impacted through the generation of wastewater and construction site run-off. The principal concern relates to the generation of silt-laden run-off during rain events from areas used to store imported fill and during vegetation stripping and reworking of road embankments. Such run-off, if discharged directly into the aquatic environment, has the potential to elevate the suspended solids load in the watercourse and impact upon any life forms therein. It is noted that no works will be carried out in the identified nullah systems.

In order to mitigate impacts related to silt-laden run-off, mitigation measures will be required to prevent the generation of run-off, as well as measures to minimise the potential of such effluents to reach the aquatic environment. Applicable mitigation techniques are presented in Section 5.7 and are in accordance with the Practice Note for Professional Persons on Construction Site Drainage, Professional Persons Environmental Consultative Committee, 1994 (ProPECC PN 1/94) which provides good practice guidelines for dealing with various discharges from construction sites and should be followed as far as possible during any construction activities in order to minimise water quality impacts.

Construction Worker Generated Wastes

Site workers will generate solid and liquid wastes during the road widening construction phase. The total quantity of waste generated will be dependent of the number on site workers the contractor proposes to use. Chapter 6, identified that an anticipated 200 workers will be on site during the peak period. Measures will need to be defined that specify how waste generated by such workers needs to the collected, handled, transported and disposed of. Measures for solid waste management are presented in Chapter 6.

5.6 Operational Phase Impact Assessment

The potential for water quality impacts during the operation of the widened YLH may result from the following:

· discharges of road surface run-off containing sediment and chemical contaminants, into the nullahs via the road drainage system; and

· spillages of chemicals onto the road and discharge into the nullah.

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Road Run-Off

Road run off currently occurs during periods of rain resulting in discharges to the existing waterway and nullah system - as such, during operation of the widened YLH there will be no new contamination sources. However, the road widening scheme will increase the surface area of the road surface and thus increase the volume of road runoff and the total pollutant load.

Material will accumulate on the widened road during dry periods, both from surface run-off from adjacent areas and from dust generated by vehicles using the road. Most accumulation is expected in slightly depressed and at grade sections where sediment and silt will be carried and deposited. Material deposited on the road will contain a whole array of organic and inorganic chemicals.

Material deposited on the road surface will be removed from the carriageway during rain events. A large proportion of the rainfall landing on road hard surfaces may reach the surface water drainage system. Climatic conditions and intensity of precipitation have a particular significant influence on the characteristics of run-off. Rain events in excess of 0.5 - 0.7 millimetres per hour are expected to remove up to 80% of the contaminant mass accumulated on the road and pavement. Any further rainfall run-off is likely to be relatively less polluted. The initial run-off which contains most of the particulate matter and the associated contaminants is referred to as the "first flush" and can impact upon sensitive receiving watercourses. This is especially the case following high intensity storms which tend to scour the road surface and can result in a relatively greater run-off pollutant load. Pollutant levels tend to be dependent on the local conditions, topography, climate and the degree of urbanisation.

A wide range of concentrations have been reported for contaminants in road run-off. Contaminants of greatest concern with respect to water quality are particulates and heavy metals (such as iron, lead and zinc). Particulates may settle out rapidly in any receiving water system and can cause smothering of the bed, while some heavy metals are toxic to some sensitive life forms.

Whilst road run-off has the potential to cause adverse environmental impacts if discharged into particularly sensitive aquatic environments, it is currently considered that surface run-off from the road area will be directed towards the main Tin Shui Wai nullah, the Shan Pui River System (i.e. Yuen Long Creek) and the Yuen Long Bypass Floodway.

5.7 Mitigation Measures

5.7.1 Construction Phase

Control and Mitigation of Silt-laden Run-off

Silt-laden surface run-off should be prevented from directly entering the sensitive receivers as defined in Figure 5.1 during the works. The mitigation measures described below for the construction phase are in accordance with ProPECC PN 1/94:

· works sites and areas used for imported fill stockpiling should, as far as possible, avoid the water sensitive receivers as defined in Figure 5.1;. · stripping of existing vegetation should be sequential to avoid exposure of large areas of embankment slopes;

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· special precautions should be taken when working in the near vicinity of nullahs and streams, especially when bridges along the YLH are being widened. This may involve the installation of temporary drainage works to ensure that runoff does not enter the nullahs directly; typical example of this type of measure is the provision of suitable temporary drainage system, such as peripheral channels around the site, to intercept all on-site runoff to water quality treatment devices such as sedimentation pond / sand trap. Only treated runoff from these devices will be discharged offsite. Sizes and arrangement details of these drainage works depend on local conditions and will be addressed during the detailed design stage; · perimeter cut-off drains to direct off-site water around the works sites should be constructed and internal drainage works and erosion and sedimentation control facilities implemented. Channels, earth bunds or sandbag barriers should be provided on site to direct stormwater to silt removal facilities. The design of efficient silt removal facilities should be based on the guidelines provided in ProPECC PN 1/94; · sediment tanks of sufficient capacity, constructed from pre-formed individual cells of approximately 6-8 m3 capacity are adopted as a general mitigation measure which can be used for settling wastewaters prior to disposal. The tanks are readily available and used primarily for recycling water for bored piling operations. The system capacity is flexible and able to handle multiple inputs from a variety of sources and particularly suited to applications where the influent is pumped. Various physical and chemical filters such infiltration tank can be added should refinement of the sedimentation process be required; · Construction works should be programmed to minimise surface excavations/ cutting during the rainy season (April to September). If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by a tarpaulin or other means. Other measures that need to be implemented before, during and after rainstorms are summarised in ProPECC PN 1/94. Particular attention should be paid to the control of silty surface run-off during storms events, especially for sites located near steep slopes; · all exposed earth areas should be completed and re-vegetated promptly after earthworks have been completed, or alternately, within 14 days of the cessation of earthworks. · earthworks final surfaces should be well compacted and subsequent permanent work or surface protection should be carried out immediately after final surfaces are formed in order to prevent rainstorm erosion; · the overall slope of the site should be kept to a minimum to reduce the erosive potential of surface water flows and all trafficked areas and access roads protected by coarse stone ballast. An additional advantage accruing from the use of crushed stone is the positive traction gained during prolonged periods of inclement weather and the reduction of surface sheet flows; · silt contained in ground water and drilling water collected from any boring operations, dewatering etc. should be removed with properly designed silt removal facilities, such as the specified portable sedimentation tanks referred to above, such that Technical Memorandum on Effluent Standards are achieved prior to the discharge of waters; · all drainage facilities and erosion and sediment control structures should be inspected monthly and maintained to ensure proper and efficient operation at all times and particularly following rainstorms. Deposited silt and grit should be removed monthly and disposed of by spreading evenly over stable, non-sensitive vegetated areas;

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· measures should be taken to minimise the ingress of site drainage into excavations. If the excavation of trenches in wet periods (June – October) is necessary, they should be dug and backfilled in short sections. Water pumped out from trenches or foundation excavations should be discharged into the silt removal facilities; · open stockpiles of construction materials (e.g. aggregates, sand and fill material) of more than 50m3 should be covered with a tarpaulin or similar fabric during rainstorms. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system; · manholes (including newly constructed ones) should always be covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system; · all vehicles and plant should be cleaned before leaving the construction site to ensure no earth, mud and debris is deposited on roads. An adequately designed and sited wheel washing bay should be provided at every site exit and wash-water should have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process. · The section of access road leading to, and exiting from the wheel-wash bay to the public road should be paved with sufficient backfill toward the wheel-wash bay to prevent vehicle tracking of soil and silty water to public roads and drains; · water used for construction purposes on site should, as far as practical, be recycled for use; · information detailing storm run-off and wastewater discharge points, and the corresponding maximum (or range of) volumes of discharges expected from the construction sites on a dry day should be provided in the WPCO license application. In general, assuming adequate information has been provided together with the license application, EPD would need at least 20 days for the processing of a license for a discharge. It is therefore recommended that the Contractor submit the licence application to EPD as early as possible before the commencement of any discharge.

If the good management practices as defined above are implemented, adverse impacts on the aquatic environment due to surface run-off should be avoided.

Construction Materials

In order to prevent unacceptable water quality impacts associated with construction material, the following mitigation techniques are recommended:

· stockpiles of cement and other construction material should be kept covered when not being used; · stockpiles of cement and other construction material should not be located adjacent to nullahs and streams; · entry points into the surface drainage system should be fitted with oil interceptors; · waste oils and other chemical wastes as defined in the Waste Disposal (Chemical Waste) (General) Regulation will require disposal by an appropriate means and could require pre- notification to EPD prior to disposal. An appropriate disposal facility could be the Chemical Waste Treatment Centre (CWTC) at Tsing Yi. If chemical wastes are to be generated, the contractor will need to register with EPD as a chemical waste producer and observe the

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requirements for chemical waste storage, labelling, transportation and disposal. The requirements for waste storage, transportation and disposal are considered in the Waste Management Chapter 6; · impacts associated with spillages should be managed through careful handling procedures. Oils and fuels should only be used and stored in designated areas which have pollution prevention facilities. Fuel tanks and drums of fuel oils and other polluting fluids/chemicals should be provided with locks and bunded to a capacity of 110% of the storage capacity of the largest tank. The bund should be drained of rain water after raining event.

Construction Worker Sewage

Sewage effluents arising from the on-site construction workforce have the potential to cause water pollution. Therefore, plans for the collection, treatment and disposal of sewage wastewater during the construction phase must be specified. Sewage generated on site should be disposed of through connection of the sanitation facilities with the existing foul sewerage system. Where this is not possible, temporary portable chemical toilets, septic tanks or package sewage treatment plants may need to be used. Overall it is considered that no water quality impacts are expected to arise from on site generated sewage if such sewage facilities are provided.

5.7.2 Operational Phase

The amount of sediment accumulating on the road surface during operation is not expected to be large, particularly due to the proposals for landscaping of adjacent embankments, which will minimise soil exposure immediately next to the carriageways. The road drainage system will be incorporated as part of the general road improvement scheme and will facilitate drainage of run- off of flood-waters directly into the nullahs thus preventing run-off into any adjacent ponds. The increase in road surface will marginally increase the amount of pollutants discharge to nullahs and eventually to Deep Bay. To achieve zero discharge policy to Deep Bay, Trapped Gully with Gully Former such as the Standard HyD Gully H3110 will need to be installed along the drainage systems to trapped the sediments in the first flush of the runoff. Since majority of the heavy metals in the runoff attach to the sediments, these Trapped Gully will also be able to remove majority of the heavy metals.

If the measures highlighted above are adopted, and if the drainage network is maintained appropriately, the impacts on the water environment should be minimal.

5.8 Monitoring and Environmental Management

For protection of the water quality during construction of the road widening works, the following environmental monitoring and management measures should be incorporated into the Environmental Protection and Pollution Control Requirements in the Contractor’s specification, as a minimum :

· discharges should be monitored to ensure that they comply with the Technical Memorandum on Effluent Standards and any applicable discharge licenses; and

· effluents containing cement-generated material should be checked periodically with respect to pH.

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5.9 Conclusions

Road widening works have the ability to impact upon identified water sensitive receivers, principally through the generation and discharge of silt-laden surface runoff from spoil stockpiling areas and during landscape stripping and embankment reworking. Specific mitigation measures have been specified to control such impacts.

Road run-off from the operational widened YLH will contain sediment and organic/inorganic pollutants. If the measures highlighted above are adopted, and if the drainage network is maintained appropriately, the impacts on the water environment should be minimal.

This water quality impact assessment has not highlighted any particular insurmountable problems associated with either the road widening construction works or the completed road operation. A number of mitigation measures have been recommended, which generally relate to good site management. Given the implementation of these measures, potential impacts associated with the construction and operation of the Highway are not considered significant.

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