6. WATER QUALITY IMPACT ASSESSMENT

Introduction

6.1 The Sheung Shui to Lok Ma Chau Spur Line Project crosses a number of watercourses within Long Valley, Kwu Tong, Chau Tau and Lok Ma Chau areas. This section of the report assesses the potential of the Spur Line to impact water bodies, all of which ultimately discharge to the Deep Bay Water Control Zone (DBWCZ). The section is divided as follows:

· assessment methodology and relevant legislation;

· description of water bodies in the Study Area and their existing conditions;

· identification of construction and operational activities with potential impact;

· concurrent projects;

· assessment of impacts from these activities;

· recommendations for mitigation measures; and

· assessment of residual impacts after implementation of mitigation measures.

6.2 Impact from the construction phase will include temporary filling of ponds for the construction of piles, site run-off, concrete washings, and generation of sewage and other wastes from the workforce. Impacts from the operational phase include rail track run-off and sewage from the station. In addition, other projects being carried out in the areas may contribute to the cumulative impact within the Study Area.

6.3 The potentially impacted water bodies all ultimately discharge to Deep Bay, a highly sensitive water body and an ecologically important area with international significance.

Assessment Methodology

6.4 This assessment is conducted in accordance to the EIA Ordinance, the Technical Memorandum on EIA Process (Annexes 6 and 14), and the EIA Study Brief. The Study Area, as specified in the Brief, is a corridor 300m to each side of the Alignment. Environmental effects of the Project have been quantified where feasible.

Relevant Environmental Legislation

6.5 The principal legislation for protecting water quality in Hong Kong is the Water Pollution Control Ordinance, which defines Water Control Zones, Water Quality Objectives for each Zone, and standards for effluent discharges. The Zero Discharge Policy for Deep Bay has also been implemented by EPD, requiring that effluents discharged directly or ultimately into Deep Bay be subject to appropriate prior treatment and disposal such that no net increase in pollution load to Deep Bay occurs.

6.6 The Livestock Waste Control Scheme (LWCS) under the Waste Pollution Control Ordinance was in 1994 to prevent further deterioration in water quality as a result of livestock waste discharged into rivers.

6.7 The LWCS aims to impose a guideline and control on the livestock farming activities to minimise their impacts on the water quality of local watercourses. In addition to complying with the Waste Disposal (Livestock Waste) Regulation, all livestock farmers in these areas are required to achieve discharge standards for BOD₅and SS (BOD₅:SS) in planned stages. Hong Kong is divided into prohibited, restricted control areas. In the Sheung Shui area, the Spur Line alignment passes through a prohibited area. The rest of the alignment is within restricted areas.

6.8 The details of legal requirements are presented in Appendix A.

Water Quality Sensitive Receivers

6.9 All water bodies that are potentially sensitive receivers in the Study Area are shown on Figure 6.1, together with the Spur Line Alignment and concurrent projects. The alignment falls into four topographically different sections which relate to the water body catchments.

6.10 In Long Valley, west of the existing Sheung Shui station, the viaduct section of the alignment crosses River Sutlej (Shek Sheung Ho), River Beas (Sheung Yue Ho), a fish pond, and an area of agricultural fields. Shek Sheung Ho and Sheung Yue Ho are tributaries of the River Indus, the flood waters from which are pumped to Plover Cover Reservoir during storm events. The River Indus and the Pumping Station in the Indus are therefore also considered to be sensitive receivers.

6.11 Passing through Kwu Tung and Pak Shek Au, the embankment and cutting sections of the alignment cross a number of small streams, some of which have been concreted within this developed area.

6.12 In Chau Tau, the alignment rises onto viaduct again and crosses several inactive or filled fishponds before passing into the Lok Ma Chau area which comprises a contiguous area of ponds.

6.13 Within the Lok Ma Chau area, the viaduct crosses a stream (which drains into Shenzhen River) before crossing the Lok Ma Chau Boundary Crossing. At the future Lok Ma Chau station, a number of fish ponds will be filled during construction of the station building.

6.14 In addition to the water bodies directly in the path of the alignment, other water bodies are also present within the 600m Study Area corridor (300m either side of the alignment). These include the River Indus, Shenzhen River, and a large number of small streams. River Beas, River Indus, Shek Sheung Ho, and all of the streams drain into Shenzhen River and ultimately into Deep Bay.

Existing Conditions at Water Quality Sensitive Receivers

6.15 A considerable amount of water quality data for the water sensitive receivers of the area has been collected from a number of studies. In addition, field surveys have been conducted in several locations of the alignment for the purposes of this assessment.

Long Valley

EPD data

River Beas (Sheung Yue Ho)

6.16 Similar to most water courses in the New Territories, the River Beas suffers from pollution by sewage, livestock waste, contaminated runoff, and industrial effluent.

6.17 With the efforts of the Government in the past years, especially with the enactment of the Livestock Waste Control Scheme, the conditions of this water course has improved from a Water Quality Index (WQI) of “Very Bad” in the years preceding 1996 to “Bad” (locations RB2 and RB3) or “Fair” (location RB1) in 1997. The location of the EPD monitoring points is shown in Figure 6.1. The most recent water quality data available from the EPD, presented in Table 6.1, indicate that the existing water quality within River Beas is still unsatisfactory. Throughout 1997, suspended solids did not reach the WQO level, and BOD₅ was compliant only 6% of the time.

Table 6.1

Summary water quality data for River Beas during recent years

(EPD River 1995, 1996, 1997)

(a) RB1 Monitoring Location

	1995	1996	1997	1998
DO (mg/l)	3.7 (0.9-8.0)	3.8 (0.2-6.9)	6.8 (1.9-10.5)	7.2 (4.7 - 10.2)
PH	7.1 (6.8-7.4)	7.1 (6.7-7.5)	7.4 (7.2-7.8)	7.4 (7.2 - 7.8)
SS (mg/l)	24 (11-39)	28 (11-80)	26 (6-69)	8.3 (6.5 - 28.0)
BOD5 (mg/l)	71 (14-150)	70 (12-160)	19 (2-170)	5.3 (2.2 - 24.0)
COD (mg/l)	68 (24-140)	53 (17-100)	34 (8-110)	15.2 (7.0 - 25.0)
E.coli (cfu/100ml)	681,245 (130000-8000000)	157,013 (15000-900000)	57373 (15000-510000)	19095 (3600 - 66000)
NH3-N (mg/l)	4.40 (1.40-11.00)	2.50 (0.99-13.00)	2.85 (0.06-10.00)	2.1 (0.9 - 7.5)

(b) RB2 Monitoring Location

	1995	1996	1997	1998
DO (mg/l)	4.4 (0.8-7.7)	3.5 (0.3-6.4)	5.4 (1.7-9.5)	5.5 (1.8 - 8.2)
PH	7.1 (6.8-7.3)	7.1 (6.6-7.3)	7.2 (6.9-7.6)	7.2 (6.6 - 7.5)
SS (mg/l)	21 (7-63)	26 (12-260)	28 (11-170)	74.5 (5.3 - 310.0)
BOD5 (mg/l)	43 (4-110)	20 (11-86)	10 (3-21)	5.7 (1.7 - 35.0)
COD (mg/l)	38 (9-120)	30 (19-280)	29 (4-44)	24.0 (6.0 - 68.0)
E.coli (cfu/100ml)	472,514 (20000-4700000)	245,686 (40000-1200000)	62067 (14000-430000)	9703 (1300 - 470000)
NH3-N (mg/l)	9.50 (0.91-23.00)	6.90 (1.30-20.00)	6.95 (0.95-11.00)	3.7 (1.4 - 21.0)

(c) RB2 Monitoring Location

	1995	1996	1997	1998
DO (mg/l)	1.2 (0.4-5.4)	1.0 (0.2-4.4)	3.1 (0.1-6.8)	2.9 (0.4 - 5.5)
PH	7.1 (6.8-7.4)	6.9 (6.5-7.2)	6.8 (6.7-7.5)	7.1 (6.7 - 7.4)
SS (mg/l)	24 (13-76)	24 (13-630)	22 (6-44)	6.9 (9.7 - 53.0)
BOD5 (mg/l)	44 (5-140)	32 (6-68)	22 (3-77)	11.7 (3.8 - 48)
COD (mg/l)	54 (17-180)	47 (18-120)	39 (12-81)	26.8 (17.0 - 43.0)
E.coli (cfu/100ml)	696,631 (50000-4400000)	440505 (70000-1900000)	185059 (57000-1500000)	57681 (5800 - 380000)
NH3-N (mg/l)	14.00 (1.90-29.00)	10.95 (1.30-22.00)	9.75 (2.00-20.00)	6.8 (1.7 - 25.0)

River Indus (Ng Tung Ho)

6.18 River Indus has attained a higher degree of improvement in water quality than River Beas over recent years. The Water Quality Index at IN2 and IN3 has improved from “Bad” to “Fair” in 1997 while at IN3, the water quality remains “Bad” (locations shown in Figure 6.1). Compliance with WQOs was less than 50% for suspended solids, BOD₅ and COD. The most recent water quality data available from the EPD are presented in Table 6.2. These data indicate that the existing condition of River Indus is still unsatisfactory.

Table 6.2

Summary water quality data for River Indus during recent years

(EPD River 1995, 1996, 1997)

(a) IN1 Monitoring Location

Parameter	1995	1996	1997	1998
DO (mg/l)	4.0 (2.3-8.5)	3.2 (0.3-7.4)	4.0 (0.6-7.1)	4.2 (1.2-7.1)
PH	7.1 (6.8-7.3)	6.9 (6.7-7.4)	7.0 (6.7-7.6)	7.2 (7.1-7.5)
SS (mg/l)	40 (24-93)	24 (4-430)	32 (10-79)	37.9 (14.0-94.0)
BOD5 (mg/l)	18 (3-34)	8 (6-28)	9 (3-21)	8.1 (1.9-17.0)
COD (mg/l)	27 (12-120)	20 (13-49)	24 (14-40)	22.6 (14.0-37.0)
E. Coli (cfu/100ml)	346130 (25000-2400000)	290602 (80000-2500000)	318506 (58000-3000000)	92881 (11000-1400000)
NH3-N (mg/l)	4.75 (0.98-15.00)	3.60 (1.00-17.00)	6.65 (0.96-13.00)	5.5 (0.7-11.0)

(b) IN2 Monitoring Location

Parameter	1995	1996	1997	1998
DO (mg/l)	2.7 (0.7-5.9)	3.1 (0.6-8.2)	3.2 (0.8-7.9)	3.2 (0.6-6.8)
PH	6.9 (6.5-7.2)	7.0 (6.7-7.6)	7.2 (7.0-7.5)	7.0 (6.7-7.3)
SS (mg/l)	26 (11-58)	14 (7-280)	20 (8-40)	36.5 (8.3-180.0)
BOD5 (mg/l)	8 (2-17)	6 (3-10)	3 (2-6)	4.2 (2.6-7.7)
COD (mg/l)	21 (12-49)	15 (6-28)	20 (6-42)	14.8 (9.0-23.0)
E. Coli (cfu/100ml)	70816 (16000-310000)	42205 (10000-180000)	34717 (11000-180000)	32623 (800-1400000)
NH3-N (mg/l)	2.60 (0.52-7.30)	2.35 (0.49-4.00)	1.75 (0.56-2.90)	1.7 (0.4-3.0)

(c) IN3 Monitoring Location

Parameter	1995	1996	1997	1998
DO (mg/l)	4.6 (1.5-7.4)	5.2 (2.1-7.4)	5.9 (2.1-9.1)	3.2 (0.6-6.8)
PH	7.1 (6.8-7.2)	7.0 (6.8-7.5)	7.2 (6.8-7.5)	7.2 (6.8-7.5)
SS (mg/l)	20 (6-160)	17 (4-330)	23 (7-160)	37.3 (7.7-120.0)
BOD5 (mg/l)	18 (4-70)	7 (3-35)	9 (3-39)	7.7 (2.5-24.0)
COD (mg/l)	24 (9-79)	14 (8-42)	22 (8-78)	16.5 (7.0-33.0)
E. Coli (cfu/100ml)	652257 (150000-3900000)	67,352 (14000-1000000)	95031 (13000-1800000)	28639 (3500-140000)
NH3-N (mg/l)	5.90 (0.52-18.00)	2.55 (0.28-12.00)	4.30 (0.32-16.00)	2.6 (0.2-9.0)

Water Quality Data from other EIA studies

6.19 In the Fanling, Sheung Shui and Hinterland Main Drainage Channels EIA undertaken by the TDD between 1996 and 1997 (Maunsell 1997), water quality monitoring was conducted at a number of points along both River Beas and River Indus (Locations S1, S3 and S4 are shown in Figure 6.1). The EIA (Maunsell 1997) presented the data as Water Quality Indices (WQI) for each station and for the EPD station RB3 (Table 6.3a). Water quality at stations close to each other (S1 and 1N1, and S3, S4 and RB3) indicates that the water quality along this watercourse is still poor.

6.20 Sediment testing indicated high concentrations of zinc at location S3 (Table 6.3b), probably due to livestock waste discharges. Upstream, at location S4, metal concentrations are lower, possibly due to the coarser sediment which cannot adsorb as many pollutants. Elutriate testing indicated this metal may be released upon washing of the sediment, particularly in the wet season (Table 6.4).

Table 6.3

Sediment quality in River Beas (Maunsell 1997)

a) Water Quality Indices for Monitoring Stations in River Beas

Date	Location
	S1	S3	S4	EPD Station RB3	EPD Station INI
1990	-	-	-	Bad	Bad
1991	-	-	-	Very Bad	Very Bad
1992	-	-	-	Very Bad	Bad
1993	-	-	-	Very Bad	Bad
1994	-	-	-	Very Bad	Bad
1996	Bad to Very Bad	Bad to Fair	Fair to Good	Very Bad	Bad

b) Sediment Quality in the River Beas

Date	Location	Cd Mg/kg	Cr mg/kg	Cu Mg/kg	Ni mg/kg	Pb mg/kg	Zn mg/kg	Hg mg/kg
20/02/97	Site 1	0.78	53.3	216	36.8	78.6	1270	0.2
	Site 3	0.29	1.8	23.9	1.8	8.8	502	<0.1
	Site 4	0.13	2.5	21.9	2.1	19.4	88	<0.1
23/7/97	Site 1	1	64.7	208	40.5	94	2070	0.2
	Site 3	<1	1.8	34.2	0.9	13.7	218	<0.1
	Site 4	1	0.2	0.2	0.2	0.2	2	0.1

REMARKS:

All values in mg/kg dry weight.

Results are based on mass of sample dried at 103-105°C.

Values in shaded boxes are Class B. Bold values in shaded boxes are Class C.

Location of sample sites are shown in Figure 6.1.

Table 6.4

Elutriate test results for sediment from River Beas (Maunsell 1997)

Date	Location	Total Organic Carbon Mg/l	NH4-N mg/l	Cd µg/l	Cr µg/l	Cu µg/l	Ni µg/l	Pb µg/l	Zn µg/l	Hg µg/l
20/2/97	Site 1	33	24.3	<0.2	7	42	19	8	100	<0.5
	Site 3	13	17.3	<0.2	<1.0	18	5	6	350	<0.5
	Site 1 Blank	8	1.7	<0.2	2	5	20	<1	50	<0.5
	Site 3 Blank	10	13.9	<0.2	<1	2	3	<1	20	<0.5
23/7/97	Site 1	28	29.2	0.6	21	182	21	36	480	<0.5
	Site 3	17	4.4	1.0	30	66	19	140	1080	<0.5
	Site 1 Blank	3	3.6	<0.2	<1	4	8	<1	50	<0.5
	Site 3 Blank	<1	1.3	<0.2	<1	3	3	<1	410	<0.5

Kwu Tung, Pak Shek Au and Chau Tau

6.21 The only data available to assess water quality in this area is from field observations as described in Table 6.5. The water quality in several streams is poor, with livestock waste being the main source of pollution at Kwu Tong, while the water quality at Chau Tau is contaminated by run-off from construction sites, container storage sites and vehicle maintenance and repair workshops.

Table 6.5

Field Observations at Water Courses in Kwu Tong and Chau Tau areas

Location	Stream Description	Observation of Water Quality
Along Lok Ma Chau Road south-east of the Boundary Crossing Plaza	Part of the stream is channelized with concrete sloping sides. Thin vegetation on the upper sides.	Water was darkish grey in colour, slightly odorous and slow flowing. Oil and grease, and large quantity of garbage observed flowing on water surface. Pollution sources are mainly nearby small construction sites, container yards, and garages.
Kwu Tung, near the junction between the viaduct and Embankment Sections	Part of the stream is channelized with concrete sloping sides. Vegetation on the sides beyond concreted banks.	Water was darkish grey in colour and odorous. Debris/sediments on the bottom observed. Pollution sources are mainly livestock farms in nearby villages.

Lok Ma Chau

Lok Ma Chau water courses and fishponds

6.22 No EPD water quality data is available for this section of the Spur Line alignment. However, some data available from the EIA study on expansion of Lok Ma Chau Boundary Crossing (Tables 6.6 and 6.7) indicates that the San Tin River water quality is poor, with low DO and high ammoniacal-N concentrations. Water quality was also measured in two inactive fishponds on the east side of the Crossing (Figure 6.1). Water quality was generally good, with low nutrient levels. Sediment in these unmanaged fishponds is in the uncontaminated category (Table 6.7). Active fishponds are expected to be higher in nutrient levels due to waste discharges from fish.

Table 6.6

Water quality in water courses and unmanaged ponds alongside Lok Ma Chau Boundary Crossing (Binnie 1999)

Date of sampling : January 1999

Parameter	Location
	Fishpond 1	Fishpond 2	Stream W1	Stream W2 (Upstream)	Stream W2 (Downstream)
PH	9.2	9.0	7.4	7.6	7.6
Turbidity (NTU)	76.0	28.0	43.0	3.6	1.2
DO	13.0	13.0	0.5	9.5	8.5
BOD5	28	14	24	<2	2
SS	-	-	59	7	18
Ammonia as N	<0.01	<0.01	44.0	0.35	5.50
NO2 + NO3 as N	0.02	0.02	0.78	2.00	1.40
Total Inogranic N	0.02	0.02	45.0	2.40	6.9
Total Phosphorous	0.2	0.1	12.0	<0.1	0.4
E. Coli (cfu/100 ml)	60	150	-	-	-

Notes: All values are in mg/l unless otherwise indicated.

Table 6.7

Sediment Quality in unmanaged ponds alongside

Lok Ma Chau Boundary Crossing

(Binnie 1999)

Date of sampling : January 1999

Metal	Location and Category
	Fishpond 1	Fishpond 2
Cadmium	0.06	0.05
Chromium	21.6	10.0
Copper	17.8	14.1
Nickel	4.5	3.8
Lead	39.1	26.8
Zinc	91.0	38.0
Mercury	0.04	<0.04
Ammonia as N	8	3
Total Phosphorous	244	172
Overall Classification	A	A

Shenzhen River Water Quality

6.23 All of the watercourses described ultimately flow into the Shenzhen River. This receiving water body may therefore be impacted by construction and operational related activities. The water quality in Shenzhen River has been monitored intensively in the on-going Regulation Project, however, these data are not available until the Regulation Project is complete. Data reported in the San Tin EIA (ERM 1999) indicate poor water quality with low DO and high BOD₅ and SS, due to discharge of untreated effluent from industry, agriculture, poultry and livestock farming, and human sewage (Table 6.8).

6.24 Sediment testing indicated that high levels of copper, zinc and lead were present (Table 6.9). However, in contrast to the Fanling Drainage Channel results, elutriate testing showed that minimal pollutants are released from the sediment (Table 6.10).

Table 6.8

Water quality data for Shenzhen River (high and low water levels)

in dry season of 1994 (ERM 1999)

Station No.	W2		W3		W4
Water Levels	High	Low	High	Low	High	Low
Dissolved Oxygen (DO)	1.0	0.8	0.7	0.6	0.8	0.7
SS	250	241	120	87	135	125
BOD5	74	75	63	62	25	46

All values in mg/l.

Table 6.9

Sediment quality data for Shenzhen River

(Shenzhen River Regulation Project, reported in ERM, 1999)

Location		Cr	Cu	Hg	Ni	Pb	Zn	Cd
River	Zhanmatou	106.0	207.0	0.30	-	102.0	523.0	0.43
	Hekou	65.0	99.0	0.13	-	82.0	308.0	0.24

All values are in mg/kg.

Bold values are Class C.

Shaded values are Class B.

Table 6.10

Elutriate test results for sediment from Shenzhen River (ERM 1999)

		TN	TP	COD	Cu	Pb
River Water	No sediment	26.97	2.82	19.39	0.018	0.048
	1:100	24.50*	0.55*	20.13 (+3.8%)	0.014+	0.048
	1:1000	28.48 (+5.6%)	1.87*	21.06 (+8.6%)	0.014+	0.048

Note: * Decrease due probably to adsorption or degradation.

All values in mg/l.

Deep Bay

6.25 Deep Bay is a large shallow bay fed by outflow from the Shenzhen River and runoff from the surrounding land. It has a surface area of approximately 112 km² and a length of about 15 km with an average depth of 3m. Water from Deep Bay flows into the main Pearl River estuary. The complex hydrography of the Bay results in water flow from the NWNT area being trapped in Inner Deep Bay, an estuarine area with exposed mudflats during low tides. The current hydrological conditions are the result of natural accretion in Deep Bay, reclamation, and intensive anthropogenic disturbances in recent years. These anthropogenic disturbances include discharges of domestic sewage, industrial effluent, agricultural runoff and livestock waste.

6.26 The rivers, streams and nullahs flowing into the Deep Bay from Hong Kong and Shenzhen contribute domestic sewage and livestock waste generated in the catchment to the Bay. This pollution is a source of concern for the Inner Deep Bay area which provides a feeding area for thousands of migratory birds and is an internationally recognised Ramsar site for waterfowl and other birds. The total catchment area of Deep Bay is about 535 km².

Current Water Quality of Deep Bay

6.27 EPD has established five monitoring stations in the Deep Bay Water Control Zone. Stations DM1, DM2 and DM3 are located within the inner subzone whereas DM4 and DM5 are located in the outer subzone (Figure 6.2). Tables 6.11 and 6.12 present selected water quality data within Inner Deep Bay and the Outer Deep Bay subzone within the last 4 years.

6.28 During 1996, levels of TIN, TN and ammoniacal-N were higher than previous years, particularly in Inner Deep Bay. Levels decreased in 1997, however, non-compliance with Water Quality Objectives (Appendix A) were experienced for TIN, DO and, in Inner Deep Bay, unionised ammonia. Long term trends have been examined and are presented in EPD’s Marine Water Quality 1997 publication. The main concerns for Deep Bay water quality are:

· The decrease in DO at some locations (particularly DM2 and DM5), leading to anoxic conditions.

· Increasing unionised ammonia at DM2.

· Increase in TIN within Deep Bay.

6.29 Data in Tables 6.11 and 6.12 show that the water quality improves as one moves from Inner Deep Bay into the Outer Deep Bay zones. At location DM1, DO levels fluctuate around the WQO level of 4.0 mg/l although BOD₅ levels remain low. The low BOD₅ levels are largely a result of the enforcement of the Livestock Waste Control Scheme and improvement of sewerage provision in NWNT. E.coli levels decrease as one moves out of Inner Deep Bay, but increase again at location DM5, possibly due to additional discharges from Hong Kong and China sides, and influence from the Pearl River.

Table 6.11

Monitoring Results from Inner Deep Bay in Recent Years

(EPD Marine 1995, 1996, 1997)

	1995	1996	1997	1998*
Station DM1
Surface DO	3.4 0.5 - 6.1	3.5 (0.1 - 8.3)	4.8 1.4 - 14.3	4.0 2.5 - 6.9
Bottom DO	-	-	-	-
PH	7.5 7.3 - 7.9	7.4 (7.0 - 7.9)	7.0 6.2 - 8.3	6.9 6.3 - 7.7
SS	47.7 20.0 - 87.0	89.8 (11.0-320)	72.4 22.0 - 240.0	66.3 23.0 - 130.0
E. Coli	6199 900 – 170000	69.4 (10.0-350)	5754 670 - 55000	2621 410 - 18000
BOD5	1.8 1.0 - 2.9	9.0 (1.4-19.8)	2.6 0.7 - 8.7	2.6 1.6 - 5.2
Ammoniacal Nitrogen	3.58 1.8 - 5.0	7.53 2.40 – 13.0	3.4 1.6 - 4.2	3.5 2.0 - 6.9
TIN	4.09 (2.72 – 5.41)	7.79 (2.82 – 13.04)	4.21 (2.52 – 7.25)	4.21 (2.72 – 7.42)
TN	5.39 (3.49 – 6.61)	10.34 (2.82 – 18.01)	5.06 (2.82 – 9.55)	5.3 (3.22 – 10.52)
Station DM2
Surface DO	4.6 2.3 - 7.0	7.4 (0.6 - 8.6)	5.3 1.8 - 13.0	4.7 2.6 - 7.3
Bottom DO	-	-	-	-
PH	7.6 7.4 - 8.2	7.6 (7.1 - 7.9)	7.1 6.3 - 8.2	7.4 6.6 - 8.3
SS	34.0 8.6 - 130.0	52.0 (5.0-150)	32.9 12.0 - 140.09	27.7 20.0 - 46.0
E. Coli	1105 210 – 4000	32.7 (4.8-151)	1065 22 - 31000	1600 310 – 7600
BOD5	1.3 0.5 - 3.5	4.1 (0.1-12.6)	1.5 0.6 - 6.3	1.6 1.0 - 2.4
Ammoniacal Nitrogen	2.29 1.20 - 3.30	4.29 1.7 - 8.4	2.39 1.4 - 4.0	2.72 1.6 – 4.30
TIN	2.94 (1.40 – 3.70)	4.75 (2.34 – 8.45)	3.26 (2.22 – 5.12)	3.42 (2.46 – 4.93)
TN	3.58 (1.96 – 4.60)	6.55 (2.70 – 11.27)	3.82 (2.60 – 6.02)	4.1 (2.96 – 5.53)
Station DM3
Surface DO	6.4 4.8 - 8.4	7.0 (3.6-10.3)	6.2 3.7 - 11.6	5.5 3.5 - 8.0
Bottom DO	-	-	-	-
PH	7.9 7.7 - 8.2	7.9 (7.2 - 8.8)	7.0 6.2 - 7.9	7.4 6.5 - 8.1
SS	25.9 9.0 – 100.0	28.1 (7.6 - 91)	21.7 3.0 - 37.0	14.2 7.1 – 28.0
E. Coli	339 15 – 3400	23.9 (5.6 - 96.2)	241 10 - 19000	144 21 – 760
BOD5	0.9 0.4 - 1.3	2.3 (0.3 - 7.2)	0.8 0.3 - 2.1	1.0 0.3 - 1.5
Ammoniacal Nitrogen	0.5 0.05 - 1.30	1.33 0.12 - 3.70	1.21 0.20 - 3.60	0.86 0.39 - 2.00
TIN	1.07 (0.42 - 2.39)	1.91 (0.52 - 4.69)	1.99 (1.05 – 4.30)	1.6 (0.88 – 2.64)
TN	1.41 (0.67 – 2.99)	2.57 (0.86 – 7.19)	2.51 (1.29 – 4.60)	2.1 (1.59 – 3.14)

Source: Marine Water Quality in HK 1995 & 1996, EPD

Data presented are depth-average, unless specified

Data presented are annual arithmetic means except for E. Coli which are geometric means

*Data measured from January to June 1998

Table 6.12

Monitoring Results from Outer Zone of Deep Bay in Recent Years

(EPD Marine 1995, 1996, 1997)

	1995	1996	1997	1998*
Station DM4
Surface DO	6.6 4.9 - 8.5	6.1 0.6 - 7.5	6.8 5.1 - 8.5	7.0 4.7 - 9.6
Bottom DO	6.2 4.8 - 8.4	6.5 5.1 - 7.4	6.7 5.3 - 8.6	6.9 4.3 - 9.7
PH	8.0 7.7 - 8.3	8.0 7.8 - 8.3	7.8 6.5 - 8.3	8.1 7.7 - 8.5
SS	19.2 7.3 - 42.5	16.6 3.3 – 51.5	9.4 4.1 - 27.0	8.6 3.6 - 18.0
E. Coli	183 110 – 475	176 30 – 720	99 10 - 700	88 8 – 660
BOD5	0.7 0.4 - 1.1	0.7 0.3 - 1.3	0.9 0.3 - 2.0	1.6 0.4 - 3.40
Ammoniacal Nitrogen	0.17 0.08 - 0.25	0.3 <0.01 – 0.88	0.42 0.13 - 1.10	0.38 0.05 - 1.30
TIN	0.62 (0.18 – 1.16)	0.93 (0.14 – 1.76)	1.06 (0.45 – 1.65)	1.0 (0.39 – 1.36)
TN	0.88 (0.30 – 1.29)	1.20 (0.32 – 2.10)	1.58 (1.35 – 1.85)	1.8 (1.35 – 2.74)
Station DM5
Surface DO	7.3 4.8 - 10.4	6.2 4.7 - 7.4	7.0 4.9 - 9.9	6.5 4.9 - 9.1
Bottom DO	6.5 4.1 - 8.5	5.7 3.4 - 6.9	6.1 3.9 - 7.8	6.0 4.1 - 8.4
PH	8.1 7.9 - 8.3	8.0 7.8 - 8.3	7.8 6.9 - 8.4	8.0 7.3 - 8.5
SS	16.5 6.7 - 41.0	9.7 3.0 – 16.0	11.5 4.1 - 52.0	11.9 3.2 - 34.0
E. Coli	459 105 – 2567	480 52 – 17000	232 5 - 2600	266 23 – 840
BOD5	0.7 0.2 - 2.1	0.5 0.2 - 1.3	0.7 0.2 - 4.9	0.7 0.2 - 2.5
Ammoniacal Nitrogen	0.14 0.02 - 0.25	0.11 <0.01 – 0.20	0.15 0.03 - 0.40	0.18 0.06 - 0.32
TIN	0.49 (0.09 – 0.78)	0.55 (0.14 – 1.07)	0.64 (0.28 – 092)	0.8 (0.38 – 1.66)
TN	0.74 (0.16 – 1.02)	0.80 (0.34 – 1.38)	1.22 (0.74 – 1.50)	1.6 (1.28 – 2.05)

Source: Marine Water Quality in HK 1995 & 1996, EPD

Data presented are depth-average, except as specified

Data presented are annual arithmetic means except for E.coli which are geometric means

*Data measured from January to June 1998

6.30 Sediment data collected by EPD at monitoring locations DS1 and DS2 since 1995 show that there has been an increase in some heavy metals during this period. In particular, higher levels of lead, zinc, copper and mercury have been measured at DS1 in 1997 and the first part of 1998 compared with previous years (Table 6.13). These data may suggest a deterioration in sediment quality which may be due to the increased industrial and commercial discharges from both sides of the border.

Table 6.13

Metal Concentrations in Sediment in EPD Monitoring Locations

in Deep Bay (EPD Marine 1995, 1996, 1997)

Metal (ug/l)	Location	1995	1996	1997	1998
Lead	DS1	45-59	5-64	73.5	68
	DS2	30-44	5-64	64	64
Zn	DS1	³150	1-149	305	270
	DS2	100-149	150-199	205	170
Cu	DS1	15-59	0.1-54	88	84
	DS2	15-59	0.1-54	53	54
Hg	DS1	<0.05	0.05-0.7	0.15	0.15
	DS2	<0.05	0.05-0.7	0.12	0.16
Ni	DS1	10-24	5-34	31	28
	DS2	10-24	5-34	25	28
Cd	DS1	-	0.1-0.9	0.5	0.5
	DS2	-	0.1-0.9	0.35	0.2
Cr	DS1	25-49	5-49	53	47
	DS2	25-49	5-49	42	47

Summary of Water Quality in Study Areas

6.31 Water quality in the rivers within the Study Area is generally poor, with low DO and high BOD₅ and SS concentrations. The major pollution source is livestock waste from farms in the area, although run-off from container sites around Chau Tau also contributes to the pollutant load. With the implementation of the LWCS, the water quality in the major rivers is improving. Sediment data shows contamination by zinc and copper, metals used in food additives for livestock. The difference in elutriate results from different studies may be due to different sediment composition.

6.32 The receiving water body for all waterbodies within the Study Area is Shenzhen River, a highly polluted water course receiving pollutants from many sources. Ultimately, water drains into Inner Deep Bay, where pollutants are easily trapped due to poor flushing. The deteriorating water quality in this water body is of concern because of its ecological importance.

Concurrent Projects with Potential for Cumulative Impacts

6.33 Table 6.14 lists major projects that will be conducted concurrently with the construction of the Spur Line. Each of these projects has the potential to impact water quality in the Study Area and in Deep Bay. The locations of these projects in relation to the Spur Line Alignment are shown on Figure 6.1. Projects of particular significance, due to their proximity to the proposed Lok Ma Chau station, are the construction of the San Tin Eastern Main Drainage Channel, and the expansion of the Lok Ma Chau Boundary Crossing. The drainage from many of the projects listed in Table 6.14 flows into Deep Bay, and therefore the combined impact on Deep Bay water quality from the construction and operational phases of these projects could be significant in the absence of adequate mitigation measures. The recently publicised Kwu Tung SGA as part of the NENT Planning and Development Study will have the potential to impact water quality in the area to a greater extent than the present project. Subsequent projects should take into account the findings and recommendations of the Spur Line in developing mitigation measures to minimize residual impacts.

Table 6.14

Summary of Major Projects Adjacent to the Spur Line

Project description and potential impacts	Commencement Date	Completion Date
Shenzhen River Training Phase III involves the realignment of the Shenzhen River to improve drainage efficiency and prevent flooding. Impacts include sediment suspension, increased river flow.	mid 2001	late 2004
San Tin Eastern Main Drainage Channels – drainage improvement works to alleviate flooding in the San Tin area and provide flood storage ponds for Chau Tau and Pun Uk Tsuen. Impacts of site run-off during construction, increased flow during operation.	Undecided	Undecided
Fanling, Sheung Shui & Hinterland Main Drainage Channels - drainage improvement works to alleviate flooding in the Fanling, Sheung Shui & Hinterland areas. Impacts of sediment suspension, increased flowrate.	1999	2001
Northwest New Territories Planning & Development Study involves examination of the scope and feasibility of accommodating strategic growth development needs in the NWNT. Impacts include site run-off on a large scale, sewage generation and increase in pollutant load and flow of stormwater.	After 2000	-
Northeast New Territories Planning & Development Study involves examination of the scope and feasibility of accommodating strategic growth development needs in the NENT. Impacts include site run-off, sewage generation and increase in pollutant load and flow of stormwater.	After 2000	-
Lok Ma Chau Control Point Expansion Project – kiosk expansion and works to improve vehicle and passenger throughput and circulation. Impacts of increased run-off, higher pollutant load, sewage generation from staff and passengers.	mid 1999	2003

Potential Impacts during Construction

6.34 The construction of the Spur Line will potentially give rise to environmental impacts on the WSRs as a result of various work activities. Construction of the Spur Line includes activities and as site formation, dredging or filling of fishponds, concreting works and bored piling. The following sections will address the possible impacts on the local water quality from each activity.

Site Formation

6.35 Preparation of land for railway construction involves initially leveling the ground surface. This will involve removal of surface vegetation and movement of materials to and from the site area. Construction of some minor, and possibly temporary, infrastructure such as drainage culverts will also be required.

6.36 The site formation process may alter the existing permeability characteristics of the soil, possibly reducing the infiltration of the top soil by introducing finer material, compacting the soil structure and removing the surface vegetation. During wet weather conditions, large quantities of surface run-off with high suspended solids loading may flow off-site in the absence of appropriate mitigation measures. Erosion of soil enriched in organic matter may release nutrients into the adjacent water courses. Erosion of stockpiles may also release suspended solids into nearby water courses.

Dredging of Fishponds or Rivers

6.37 Dredging of pond sediment or bottom mud may be required during the construction of the borepiles along the alignment, particularly in the Lok Ma Chau region. Disturbance and exposure of the pond mud which contains high levels of organic matter, and possibly other contaminants, may lead to release of these pollutants into adjacent water courses through run-off. If the mud is stockpiled, run-off containing potentially contaminated material will have on adverse impact on water quality and on associated aquatic ecology.

6.38 Where the viaduct crosses the River Beas, some dredging of the riverbed may be required. The sediment from the riverbed may be contaminated and its disturbance may result in turbidity and pollutants being released downstream. The location of the piers has not yet been fixed, however, it is possible that at least one pier may be within the channel area. Potential impacts include discharge of concrete washings into the river water, and stirring up of sediment which may carry pollutants downstream.

Temporary Filling of Fishponds

6.39 Where bored piling is carried out in fishpond areas (particularly Lok Ma Chau) it will be necessary to drain the pond to allow works to proceed. Piling may require the pond to be filled, and after work is complete, the pond will be reinstated. There will therefore be a temporary loss of the fishpond, which acts as a storage device for rainwater during storms. Displacement of water during draining and filling may create runoff high in nutrients which may enter adjacent water courses. Mitigation measures in the form of appropriate handling of the water in fishponds is essential to minimize impacts on water quality.

Culverting of Streams

6.40 Within the embankment and at grade sections, some small streams may need to be culverted beneath or alongside the railway. This will involve concreting work close to water courses. Concrete slurry and other grouting materials generated by concreting work may have an adverse impact on the aquatic life in local water bodies by increasing alkalinity which increases the dissociation of, and hence the toxicity of, ammonia. The hydraulics of water flow may also change, although the impact is likely to be small.

6.41 A drain will be constructed to the west of the station through which runoff from the station will be discharged. This will alter the hydraulics of stormwater flow in the area, however, as the proportion of the station area relative to the surrounding fishpond area is small, the impact is likely to be low.

Concrete Washings

6.42 Viaduct structures are likely to be manufactured off site and brought to site by barge. This will minimize impacts from concreting on site. However, construction of the viaduct supporting columns and the Lok Ma Chau Station will involve concreting works on site. A concrete batching plant, and possibly a casting yard, will be established at the temporary works area for the duration of the construction works.

6.43 Concrete will be transported from here to locations along the alignment for viaduct support construction and to Lok Ma Chau area for station construction. There is potential for run-off from the batching and casting yard area to enter drains and watercourses in the area, with consequential impacts on water quality and ecology downstream. Transport of concrete along roads gives rise to potential impacts from run-off entering watercourses and fishpond in the Lok Ma Chau area. During concreting activities, large quantities of concrete will be handled, a proportion of which may be deposited on the ground. Site effluent or run-off may therefore contain waste concrete washings from this source or from washing of concrete mixers.

6.44 During construction of the alignment along the eastern section of the viaduct, there is a potential for sediment to be stirred up within the riverbed. Where cofferdams are used to construct columns in the river, the water pumped out from behind the dam may be contaminated and will require careful handling to avoid water quality impacts. Methods must also be implemented to avoid concrete washings generated during the construction of the pile caps and piers, entering the Rivers Beas and Sutlej that ultimately feed to the River Indus. Water quality in these watercourses is not good, and therefore the introduction of concrete washings, or other pollutants such as oil and grease from works vehicles, will result in a further, unacceptable deterioration in water quality. In particular, the increase in pH caused by concrete washings has the potential to increase the ecotoxic level of ammonia that will have unacceptable impacts on ecological resources downstream.

6.45 Concrete washings raise the pH of the run-off which, if it enters the surrounding fishponds and local streams, will change the dissociation constant of ammonia and hence its ecotoxicity. The magnitude of the impact depends on the existing ammonia concentration in the watercourse.

6.46 A footbridge will be constructed across the Shenzhen River to link Lok Ma Chau station with Huanggang Station. The design and construction of this footbridge will be undertaken by Mainland Chinese engineers. The bridge will therefore not be subject to the requirements of this EIA. However, potential impacts have been assessed and mitigation measures proposed to minimize adverse environmental effects. The current design of the bridge is a cable stay design, with one main pier close to the Shenzhen side, and a smaller pier near the Hong Kong river bank. The construction of these supports will likely be carried out by constructing a cofferdam, forming a sheet pile box and excluding water from the piling and concreting area. Construction in the water environment has the potential to create impacts on water quality through release of river water which needs to be excluded from the sheet piling box, and the discharge of concrete washings during construction of the piers. Dewatering will potentially release turbid water into the environment, which will affect the turbidity of the watercourse downstream. Concrete washings are of more concern, in particular due to the poor water quality and high ammonia content in the Shenzhen River, and potential impacts on the ecologically sensitive Deep Bay downstream. The high pH in concrete washings raises the unionized ammonia level, a contaminant that is highly toxic to many aquatic organisms. Measures to avoid spillage of turbid water and concrete washings into the watercourse should be implemented to minimize impacts on water quality and associated ecology. This is particularly important in view of the ecologically sensitive mud flats downstream within and around Mai Po Marshes Nature Reserve.

6.47 The deck units will either be cast in-situ from the Shenzhen side, or pre-cast units will be brought from a concrete batching area which is located several kms from the bridge site. The works area alongside the bridge will be minimal, due to space constraints, most of the materials being brought by vehicles along paved roads within the urban area. Water quality impacts will be minimized if pre-cast segments are used. If concrete work is carried out in-situ over the river, there is a potential for concrete washings to drip into the watercourse. Suitable mitigation measures must be implemented to prevent this occurrence, which may have adverse effects on water quality and ecologically sensitive areas downstream.

Bored Piling

6.48 Bored piling throughout the alignment may require the use of a chemical lubricant which generates a wastewater stream. If this wastewater is allowed to drain into surrounding water courses, the lubricant may have a toxic effect on aquatic ecology.

Site Workshop or Depot

6.49 A workshop or depot is often set up to provide maintenance and repair services for the equipment on site in the vicinity of the Works Area. The use of engine oil and lubricants, and their storage as waste materials has the potential to create impacts on the water quality of adjacent water courses if spillage occurs and enters watercourses. Waste oil may infiltrate into the surface soil layer, or runoff into local water courses, increasing hydrocarbon levels.

Platform for materials transfer

6.50 A temporary working platform will be required where materials are to be brought on shore, or excavated material removed using barges. This platform is likely to be a steel structure, comprising temporary pilling works to create a working platform for berthing of small barges. The construction of this platform is unlikely to create significant water quality impacts providing steel sheet piles are used and the platform is constructed in situ. Dismantling of the structure will be carried out in reverse and impacts are likely to be minimal providing the work is carried out carefully and no waste materials enter the river.

6.51 Sand fill will be brought in by Pelican Barges. Pelican or perhaps other types of barges will deliver construction materials (cement, bentonite, steel reinforcement, aggregate), prefabricated concrete units or steel structural sections, and possibly plant. Removal of materials by barge from the site is likely to include construction waste and unsuitable excavated material to a landfill or public dumpsite. Providing the transfer of materials is carried out carefully, impacts on water quality should be minimal. Measures should be taken to cover stockpiles that may be formed alongside the platform during operation.

6.52 Pelican barges are 18 to 20m wide and vary between 35 to 40m in length with an average volume capacity of 800m3. In order to deliver the required volume of sand for filling purposes (630,000m³) approximately 790 barges of sand fill will be required to complete the filling of the fishponds. Assuming a 3-hour turnaround time for each barge, and two mooring points at the jetty, 8 barges per day could be handled during each 12-hour shift. This would continue for a period of 100 days. Following filling, other barges would be utilized for delivery of other construction materials and structural sections/units.

6.53 The sand fill is carried in covered tanks below the deck level of the Pelican barges. The sand fill is pumped into these tanks and then the water removed. This means that the fill is washed and the fines content will be minimal. There is potential for the discharged water to be slightly turbid if not settled before discharge to the nearest watercourse. The impact depends largely on the location at which the sand is collected. On delivery a sliding conveyor belt on the barge, with a controlled feed so that no overloading and spillage of materials occurs, will be used to off load the sand directly onto the conveyors feeding the site works. There is a possibility that small spillages of fill could occur during this period. During all deliveries (sand fill and other construction materials, there is a potential impact from barge fuel/lubricants to enter the river. Mitigation measures must be implemented to minimize this impact.

6.54 The sand fill will either be carried by a conveyor belt over the fence or under the fence. It is likely that all other construction materials, concrete units and steel structural sections will be lifted over the fence by vehicle or permanent crane (which would be situated on the HKSAR side of the fence line). The sand from the Pelican Barges will be washed and will therefore have a low fines content, minimizing dust impacts. However, for security purposes, the conveyor is likely to be covered. Potential impacts from handling of the sand fill are primarily related to turbidity in watercourses downstream. As Deep Bay and Mai Po marshes are downstream of this works area, and are ecologically sensitive to increases in pollution, mitigation measures must be implemented to prevent adverse impacts to these ecologically important areas.

Presence of Additional Population (Workers)

6.55 During construction, the increased workforce will contribute to the local population of the area, although the number of workers will vary over the construction period. Impacts include the generation of rubbish and wastewater from eating areas, temporary sanitary facilities and waste disposal areas. Although the impact will be temporary, this additional population may impose significant stress on the quality of water in local water courses.

6.56 The construction activities and their associated impacts on water quality are summarized in Table 6.15.

Table 6.15 Summary of Construction Activities and Potential Impacts

Construction Activity	Potential impact
Site formation	1. Increase of site run-off from exposed surfaces, 2. Increase in suspended solids and nutrient loading into local water courses.
Dredging of fishponds or rivers	1. Increase of suspended solids, nutrient levels and turbidity in water courses.
Filling of fishponds	1. Increase of suspended solids and turbidity in water courses. 2. Temporary loss of storage capacity of ponds.
Culverting of stream	1. Increase of suspended solids and turbidity in water courses through disturbance of stream course, 2. Elevation of pH value by concrete washings, 3. Change of physical hydrology of stream.
Concreting works	1. Generation of concrete washings may increase pH value, suspended solids and turbidity levels, leading to ecotoxic levels of ammonia in receiving water bodies of low water quality. 2. Impacorts from footbridge construction include turbidity and concrete workings affecting downstream water bodies including Deep Bay.
Bored piling	1. Contamination of local water courses with chemical lubricants.
Site workshop and maintenance facilities	1. Land contamination with spillage of waste oils, 2. Contamination of groundwater or runoff into local water courses.
Platform for materials transfer	1. Turbidity due to loess of sand and silt during transfer process. Potential impacts downstream in Deep Bay
Additional workforce	1. Generation of rubbish, additional sewage, and waste / wastewater which may impact water quality locally.

Mitigation Measures for Construction Impacts

6.57 The main potential impacts arising from construction site activities include an increase in the level of suspended solids (SS), pH value and oil & grease content. Mitigation measures are described which are appropriate for inclusion into general site management practices and will minimize impacts during the construction stage of the Project.

Site Surface Runoff

6.58 Under the Water Pollution Control Ordinance (WPCO), turbid water from construction sites must be treated to minimize the solids content before being discharged into storm drains. The suspended solids load can be reduced by directing the runoff into temporary sand traps or other silt-removal facilities. Advice on the handling and disposal of construction site discharge is provided in the ProPECC Paper (PN 1/94) on Construction Site Drainage.

6.59 A temporary channel system or earth bunds or sand barriers should be provided on site to direct stormwater to silt-removal facilities. Stockpile materials susceptible to erosion of rain or wind should be covered as far as practical especially during the wet season. The presence of flat, exposed areas of permeable soil surface can be formed into pits and used effectively as infiltration areas, into which runoff flows, minimizing the amount of runoff into local watercourses. The success of this measure will depend to a large extent on the permeability of the ground, and the site topography. In Long Valley, much of the area is marsh, due to a high water table and therefore infiltration is unlikely to be as successful as in higher land areas around Kwu Tung and Chau Tau. Along parts of the alignment, particularly at the Lok Ma Chau end of the alignment, abandoned fishponds within the works area may act as a sedimentation containment area to receive turbid run-off from the construction areas. Minor modification works such as elevating peripheral earth bunds and maintaining silt removal facilities would contribute to reduction of potentially polluting impacts.

Dredging Activity of Fishponds or Rivers

6.60 The type of mitigation to be used depends on the scale of dredging to be carried out. In large scale works, a silt curtain should be installed around the dredging grab to confine turbid water and prevent its release into the surrounding aquatic environment. On a smaller scale, a barrier made of sand bags may be used to enclose the disturbed area and confine turbid water locally. Wherever possible, dredging work should be undertaken during the dry season. Under all circumstances dredged pond mud or river sediment should be removed immediately or stored away from the watercourse, if it must be stockpiled on site, to prevent erosion of stockpiles, particularly in the case of contaminated mud. The quality of the mud in terms of contaminant concentration should be evaluated prior to dredging. Any metal contaminated material, or large quantities of uncontaminated material, requires disposal in designated areas. Wherever possible, in site strengthening of the mud is recommended to minimize fill requirements. Pollutant measurements of sediment in abandoned ponds (Lok Ma Chau Boundary Crossing Expansion EIA, Binnie, 1999) has shown that nutrients are high in pond mud, however, metal levels are low and there is therefore minimal contamination risk. Heavy metals may be released during initial disturbance of mud in both solids-associated and soluble forms, and these mitigation practices should be strictly implemented to avoid water quality impacts.

6.61 High nutrient levels in pond water have the potential to impact water quality if this draggeddischarged into intercourseswatercourses. The water from fishponds should be pumped to other fishponds or holding barriersbasins for oneuse at a later stage. This will minimize impacts oan adjacent watercourses.

6.62 During construction of the footbridge across Shenzhen River, a cofferdam will be constructed. Sediment is likely to be stirred up during this operation and the turbid water should be discharged onto land where it should be settled before the clearer supernatant is discharged back to the river. This method will minimize impacts from turbidity and pollutant release downstream. The supernatant should only be discharged back into the river if the solids have settled and the supernatant is reasonably clear. If it is still turbid, consideration should be given to the addition of a non-toxic HoeculantFflocculent to help settling of pipefine particles.

Concreting Work

6.63 The highly alkaline lime content in cement increases the pH level in water and may endanger aquatic life if it is washed into natural water bodies. Where concrete work is undertaken, concrete washings may enter surface runoff from the site and should be carefully channeled to prevent concrete-contaminated drainage from entering watercourses. pH increases in the presence of concrete washings and the levels of ammonia and pH have important ecological implications for aquatic life. Where ammonia levels are already high under baseline conditions, monitoring of pH and ammonia levels downstream of concreting work should be carried out to ensure ecotoxic conditions are avoided. The pH levels of surface run-off are particularly important in relation to the active fishponds adjacent to the work site.

6.64 Impacts from concrete washings from the concrete casting yards at Kwu Tung would be minimized if the viaduct units were pre-cast elsewhere and transported to the site. Within the batching planting site, the drainage system should be carefully designed to minimize the likelihood of concrete washings flowing off-site. Sedimentation areas should be established to receive concrete contaminated runoff and works areas covered to minimize runoff from concrete production areas.

6.65 The drainage system for the eastern end of the site must be suitably designed to provide areas of sedimentation and infiltration for turbid water and concrete washings arising from the viaduct and alignment works. Wastewaters must be pumped to shore for settling before it can be discharged. The supernatant should be tested to determine its contamination status before discharge to the river, or to a suitable location for treatment. Polluted waste streams must be prevented from entering watercourses or stormdrains until treated to remove solids (through sedimentation) and soluble pollutants (including pH adjustment) to achieve an acceptable standard of discharge. Regular maintenance is required for all drainage systems to enable the pollutant control devices to function properly.

6.66 Where concreting work is required within a watercourse or fishpond, as in the construction of the viaduct supporting column, the new station and culverting of streams, a dam should be constructed and the water pumped out to an area where solids can be settled out, before sediment removal or concreting works is initiated. Where possible, the concrete washings should be diverted to abandoned fishponds nearby to settle out solids. Adjustment of pH can be achieved by adding lime an acidic additive or other suitable neutralising reagents to the waste water prior to discharge. Re-use of the supernatant from sediment pits for washing out concrete lorries, should be practiced wherever possible. Re-instatement work on the sedimentation pond will be required after the construction works are complete.

6.67 Concreting work for the footbridge will involve piling a sheet pile box around the area of the proposed pier for purposes of piling, pile caps and column work. During creation of the piers, care should be taken to ensure no potentially polluting liquid or solid wastes fall into the watercourse. This is essential to avoid impacts downstream in the ecologically sensitive area of Deep Bay and Mai Po marshes. The sheet pile box should be constructed to minimize contact of the works area with the surrounding waterbody. In order to avoid water quality impacts after the sheet pile box is completed, any waste materials arising should be taken onto the attendant barge and removed for disposal. The pier to be constructed within the Hong Kong boundary is to be located within the alignment of the former riverbank extended for widening of Shenzhen River, and it is therefore unlikely that any of this material will be contaminated. The material can therefore be disposed of as uncontaminated sediment.

6.68 Adverse impacts on water quality from deck construction can be minimized by using pre-cast units constructed off site. Where the deck is constructed in situ, it is essential that a suitable mechanism is put in place to avoid concrete washings falling into the river. This may be done by incorporating a drain into the formwork design to catch any washings and divert them back to the shore where they should be settled in a sedimentation pit and the supernatant treated before discharge. Any works area alongside the river should have appropriate drainage to remove sediment from surface run-off and incorporate oil and grease traps to capture vehicle washings. Regular maintenance of these pollution control devices is essential to ensure their efficient functioning.

6.69 The pier on the Shenzhen side of the river may be located in an area of potentially contaminated sediment. The sediment from the riverbed must first be tested to determine the level and type of contamination, and if necessary, disposed of to a suitable site or treated appropriately before disposal as uncontaminated material. Measures must be put in place to prevent waste from entering the waterbody, including pumping out the solid material onto barges for disposal and pumping liquid wastes onto shore where they can be settled in a pond set aside for this purpose. If the supernatant after settlement is contaminated, disposal via a suitable route will be required, either to sewer, local sewage treatment works, or, if highly contaminated, to an appropriate treatment location, as agreed with EPD.

6.70 These measures are designed to reduce the potential for adverse effects on the water quality and wildlife downstream in Deep Bay. Implemented properly, the potential for pollutants to enter the river will be minimized.

6.71 The contractor carrying out the works should submit a detailed Waste Management Plan, which should include a description of works methods and measures incorporated to minimize potential pollution from contaminated material during the construction process.

Bentonite Slurry Generated by Bore Piling

6.72 The use of bentonite during bore piling requires correct handling and disposal to avoid water impacts. The suspension from bore piling works should be settled in a sedimentation or infiltration pit until the supernatant is clear, after which it can be pumped to a drain, or until it has infiltrated into the ground.

6.73 In some locations along the alignment, abandoned fishponds within the works area may be used as a temporary infiltration or sedimentation pit for settlement of solids, concrete washings or bentonite washings. The pits should be regularly cleared of solids and covered in wet weather, to prevent turbid water from being washed over into storm drains during heavy storms.

Disposal of Waste

6.74 Various types of waste materials will be generated during construction of the Spur Line and the selection of methods to handle and dispose the wastes will have a potential impact on water quality in local watercourses.

6.75 Initial indications of material to be excavated and that required as fill for the station construction and platform areas for EVAs, show that there will be a short-fall of material required for filling and therefore no disposal of uncontaminated material will be required. However, contaminated materials require careful handling and disposal in order to minimize potential water quality impacts.

6.76 If partially contaminated material is excavated, it will require treatment before going to a landfill such as WENT. If heavily contaminated, disposal to SENT may be required.

6.77 Chemical wastes including used lubricants, waste oils, scrap batteries, paints and used solvents should be properly collected and stored in accordance with The Code of Practice on the Packing, Labelling and Storage of Chemical Waste in order to minimize potential water quality impacts arising from spillage or leakage of stored chemicals. The Code provides guidance for complying with the requirements of the Waste Disposal Ordinance (Chemical Waste) (General) Regulations on the packing, labelling and storage of chemicals.

Maintenance Workshop or Depot

6.78 Any contractor generating waste oil or other chemicals as a result of his activities should register as a chemical waste producer and provide a safe storage area for chemicals on site. Hard standing compounds should drain via an oil interceptor. Disposal of the waste oil should be done by a licensed collector. Oil interceptors need to be regularly inspected and cleaned to avoid wash-out of oil during storm conditions. A bypass should be provided to avoid overload of the interceptor's capacity. Good housekeeping practices are required to minimize careless spillage and keep the work space in a tidy and clean condition. Appropriate training including safety codes and relevant manuals should be given to the personnel who regularly handle the chemicals on site.

Platform for materials transfer

6.79 Although impacts from the construction of the platform are likely to be minimal, care should be taken to avoid waste materials falling into the water during both the construction and dismantling process. Transfer of material onto the barge at the sandfill location should be conducted carefully to allow the displaced water to be discharged slowly, thereby minimize impacts on water quality in the receiving waterbody. Where possible, displaced water should be discharged onto land, into a sedimentation pit where the solids can be allowed to settle or infiltrate into the ground before the clearer supernatant is discharged.

6.80 At the construction site, the transfer of materials onto the platform should also be carried out with care to avoid sand falling into the river from the conveyor belt. The conveyor belt should not be overloaded and covering will assist in containing the sand immaterial. Where stockpiles are set up on shore, they should be covered to prevent run-off entering the river during storm conditions. If water is required for washing purposes during the operation, then is should be pumped into a sedimentation area before clearer water is discharged into the waterbody. The barge should be regularly maintained to minimize the potential for fuel or other contaminants entering the waterbody. All waste generated by the workers onto the barge should be disposed of at allocated sites for waste disposal at the site of collection or delivery. Wastewater collected on the barge should similarly be carefully disposed of at suitable locations to avoid water quality impacts. These working practices and design of the transfer system will provide conditions which minimize impacts downstream in Deep Bay and associated ecologically sensitive mud flats.

Additional Population (Workers) on Site

6.81 Sewage arising from the additional population of workers on site should be collected in a suitable storage facility, such as an underground septic tank or mobile toilet. Small scale on-site treatment plants should also be considered if the number of workers in one area indicates that this is more cost-effective. The collected wastewater from sewage facilities and also from canteens or washing facilities must be disposed of properly, in accordance with the WPCO requirements. Wastewater collected should be discharged into foul sewers or septic tanks via grease traps and collected by licensed collectors.

Hydraulic Impacts from Construction of Spur Line

6.82 Culverting of small drainage channels within the site may be required to divert water beneath or away from the alignment and avoid flooding problems. These changes in the hydraulic characteristics of the area are minor compared with changes arising from Main Drainage Channel works in Fanling, Sheung Shui and Hinterland, and in San Tin.

6.83 The construction of supports for the footbridge across the Shenzhen River has the potential to impact the hydraulic flow of the river. This impact will be small, given that the velocities in the Lok Ma Chau area are tidally dominated and therefore much lower than river velocities. The cross sectional area of the supports is likely to be a small proportion of the channel surface area, indicating that the change in the hydraulics of the river flows at this location will be minimal.

Potential Operational Impacts from Spur Line

6.84 The main operational impacts from the operation of Spur Line are:

· Impacts from the presence of an additional pier for the footbridge linking Lok Ma Chau and Huanggang stations across Shenzhen River.

· Stormwater impacts.

· Sewage Generation from the station.

Potential Impacts from Footbridge Pier

6.85 The presence of a pier within the river has the potential to create an impact on the hydraulics of the waterway. The significance of the impact can be evaluated by a consideration of the cross-sectional area of the piers compared with the cross-sectional area of the river. The main pier (on the Shenzhen side) is approximately 8m in diameter. On the Hong Kong side, the pier is much smaller, with a cross-sectional diameter of approximately 1.5m. Each pier comprises a set of two columns, however, these will be joined at the base by an elliptical “cutwater” which will be out of the water in all except the severest storms. These piers and cutwaters will reduce the span of the river, which is 190m at this point, by approximately 5%. From a water quality point of view, the pattern of water flow will change most significantly around the pier base.

6.86 The drainage impact assessment for the bridge has not yet been carried out. Information obtained to date indicates that the bridge piers will be designed to allow minimal headloss in a 100 year storm. In a 2 year storm, the velocity of water is likely to be approximately 0.3m/sec. Assuming that under normal circumstances sediment on the river bed will not be lifted into suspension until the velocity reaches 0.6m/sec, then in the absence of the piers, no sediment suspension would be created. However, around the pier base, the velocity may double, creating conditions that allow sediment to be brought into suspension. Assuming the sediment is fine and settles at a rate of 0.005m/sec, after it has passed the pier the particles will settle to the river bed again within about 200 to 300 metres. As the distance from Lok Ma Chau to Mai Po and Inner Deep Bay is approximately 2.5km, there will be minimal impact of on water quality and downstream ecological resources under these circumstances.

6.87 No data is publicly available on sediment quality in Shenzhen River, however, it is expected that the sediment quality is poor due to the volume and type of discharges which enter the watercourse from both sides of the border. Stirring up of the sediment around the pier bases may release pollutants from the sediment. While the sediment will settle relatively quickly in less turbulent flow regimes downstream of the piers, the soluble pollutants will be carried downstream to Mai Po and Inner Deep Bay. The potential impact can be minimized by design of the bridge to minimize additional turbulence. Tighter control of discharges and a clean-up programme of the sediment would also minimize impacts downstream, in both low flow and high flow conditions. However, this form of mitigation is out of the scope of the current project.

6.88 In more severe storms, sediment will be lifted into suspension more quickly due to the greater velocities of water travelling down the river. The impact from the piers will be minor compared with the force of the water body lifting the sediment across the entire cross-section of the river. This sediment load will be transported downstream into Deep Bay as a plume of turbid water, not due to the presence of the piers, but due to the water flow in storm events.

6.89 Of more concern under these circumstances is the headloss caused by the piers. There is a potential for the piers to hold back the water flow in severe storms. However, the effect due to the footbridge piers would not be greater than the effect of the (much larger) piers at the Lok Ma Chau – Huanggang vehicle bridge further upstream. The shape and number of piers clearly influence the degree of impact, and should be designed to minimize downstream impacts on water quality and hydraulic impacts upstream.

Mitigation for Impacts from Footbridge Pier

6.90 Minimizing hydraulic impacts can be achieved through various mechanisms. A reduction in the number of piers to one large and one small pier at the edges of the river banks has been incorporated into the design to reduce the proportion of the cross-section occupied by the obstruction. This design reduces the velocity around the piers. As described above, there will be a local increase in velocity around the piers, resulting in turbulence and lifting of sediment from the riverbed. The more piers, the greater the amount of material lifted and the longer a stretch of river before settlement occurs. However, more importantly is the designed hydraulic capacity of the river, and the resultant headloss at the piers. The shape and size of the piers should be designed so that their headlosses are within the capacity of the trained Shenzhen River.

6.91 The shape and location of the piers will also affect the extent of the hydraulic and water quality impact. In the current design, the upstream and downstream piers are being combined to minimize flow impedance and thus reduce turbulence effects.

6.92 In conclusion, each pier in the river will have local impacts on the water velocity. This will lead to stirring up of the sediment and scour around the pier base. In low flow situations, this will cause local turbidity. However, the solids lifted are likely to be fine, and downstream of the pier they will quickly settle out. In more severe storms, the sediment on the riverbed will be lifted across the whole river section and the presence of the piers will have minimal additional impact on the water quality downstream. must be calculated based on drainage capacity and headloss allowances during the design of the Shenzhen River training project A turbid stream of water will flow into Deep Bay, the impact from the piers being minimal. In these circumstances, Hhowever, headloss from the presence of piers must be considered in the design. Minimizing the number of piers and modifying the design to an elliptical shape, located in line with existing piers upstream, will minimize headloss. The number and size of piers must be calculated based on drainage capacity and headloss allowances during the design of the Shenzhen River training project. With appropriate design, the additional impact from the presence of the footbridge on the ecological resources of Deep Bay and its associated mudflats, will be minimal.

Railway track run-off

6.93 The subject of urban stormwater run-off is a relatively new study, most of the data on stormwater quality having been collected from roads, residential and commercial areas. There is very little information available on the quality of stormwater run-off from railways, other than reports of impacts such as an increase in run-off due to increased permeability, potential changes to drainage patterns, increased concentrations of metals from rails and enhancement of vegetation growth due to increased moisture in areas alongside the rail track. Although relevant to stormwater impacts from railways at grade, impacts may be somewhat different for railway sections on viaduct, as in the case of the majority of the Spur Line alignment. This section will therefore provide a qualitative description of the types of pollutants which may occur in railway related run-off and hydrological impacts on surrounding land.

6.94 The project includes the construction of a railway on viaduct and at grade across an area of varied habitat, including agriculture, grassland, woodland, fishponds and urban areas (villages, container yards and storage areas). Several emergency vehicle areas will be provided, together with access roads for evacuation. The roads, which mainly involve widening of existing roads, are expected to be used on an infrequent basis and stormwater run-off impacts are therefore considered to be of low significance. The volume of run-off from railways will be less than that from roads because of the smaller contact surface of the track, the design of the plenum units, and the lower frequency of trains compared with cars. The small increase in run-off volume due to the track construction will therefore be of less importance than the pollutant content of the run-off.

6.95 Pollutants which may be present in run-off either from the track or from the train and their potential sources and impacts are listed in Table 6.16. The most significant sources of pollution are considered to be the metal grindings washed off after rail grinding and lubricants present on switch points, a proportion of which will be washed off in storm events. The extent of these impacts will depend on the number of trains using the track, the frequency of rail grinding, the train design, the quantity and type of lubricant used and the type of train maintenance carried out.

Table 6.16

Summary of type of pollutants in run-off from railway lines, their potential environmental effects and relative significance in Spur Line operation

Pollutant	Potential source of contamination	Environmental impact	Relative importance on Spur Line operation
Lubricants	Used at the switch points on the track to ensure ease of movement.	Organic pollutant which is not readily biodegradable, may have toxic effects on organisms in receiving water bodies. Environmental accumulation may lead to sub-lethal effects., reduction in species diversity.	High impact
Metals	Metal grindings (probably mainly iron) after the train runs on the track and after track grinding	May have toxic effects on some species in receiving waters, may have colour effect, promoting enrichment. Potential accumulative effect in organisms.	From train - low impact Track grinding - high impact
Suspended solids	Suspended solids and dust from the train.	Increase in turbidity of receiving waters, light reduction for primary production, blanketing of habitats, physical damage to some organisms.	Low impact
Oil and grease	Used on the train where parts of the train are exposed.	Reduces surface tension of water surface, may be toxic and cause physical damage to some organisms, change in light penetration.	Low impact
Significant increase or decrease of pH	Lubricants and cleaning materials used on the trains	Can cause ecotoxic conditions in polluted waters, especially where ammonia levels are high. Changes solubility of metals and toxicity of organic species.	Medium impact

6.96 At a frequency of approximately twelve trains per hour in each direction, the hydraulic impact of stormwater run-off from trains is expected to be small. At grade sections pass through areas which are raised from the general flood plain level and are currently patchy areas of village, developments and container storage. The presence of the railway therefore poses minimal risk of flooding and little increase in the current stormwater flowrate. In the viaduct section, the train is well above the ground, minimizing flooding risk. However, the run-off will be directed to ground level and locally may increase water levels through increased storm flow rates. At Lok Ma Chau station, the presence of an impermeable concrete structure where fishponds were previously located, will increase the stormwater flowrate locally and may cause an increase in the water levels of streams around the area.

6.97 The concentration of pollutants in the run-off will depend on the maintenance practices within the depots and the train design. During maintenance, the use of oil & grease and lubricants for moving parts, and cleaning agents for the outer train body, have the potential to impact the environment after the train leaves the depot, by wash-off during storms. The type of chemicals used for cleaning and their removal after cleaning operations will determine the extent of impacts from this source.

6.98 Rail grinding is expected to be carried out two or three times annually. During the grinding process, a proportion of the metal dust (probably mainly iron as the tracks is steel construction) will be deposited between the tracks within the plenum unit While dry, these metals grindings have minimal impact. However, during a storm event, the remaining metal grindings will be washed into the drainage system and, depending on the proximity of water courses, may immediately enter water bodies. Potential impacts on water quality and aquatic life are described in Table 6.16. The metal loading from this source during each grinding operation may be small relative to impacts from local roads, container storage areas and urban areas. However, the cumulative impact is likely to be significant if mitigation measures are not incorporated into the design and operation of the railway and trains.

6.99 The section of the rail alignment where potential impacts are of most significance, is within the Lok Ma Chau fishpond area. Run-off from the track will flow into the drainage system of the viaduct which will discharge the run-off through downpipes to ground level. The environmental impact will depend on the location of the discharge. Where run-off flows into nearby fishponds impacts may occur on both the ecology and economics of the ponds. Although the area available for a treatment facility is limited, the drainage should be carefully designed to avoid impacts on fishponds and adjacent water courses.

Station run-off

6.100 The station is likely to be completely enclosed and therefore run-off will be limited to wash-off from the outside of the building, polluting activities within the building which release stormwater into the drainage system, and cooling water discharges. The presence of the physical structure of the building will increase the volume of run-off compared with the current environment of fishponds. A drainage channel is included in the design to transport run-off into the adjacent Shenzhen River. In comparison with the extent of the fishpond area around the station and the current flowrate within the Shenzhen River, the proportional increase in run-off flow from the station structure is considered to be small and therefore of low impact.

6.101 Sources of potentially polluted stormwater which may arise from the station run-off include:

· dust from the roof of the station;

· cleaning agents used for washing outside windows and walls;

· washdown water from car parks (washing of cars within car parks);

· water from trains entering the station during storm events;

· cooling water discharges.

6.102 Run-off from the station roof, walls and windows will contain low levels of suspended solids and surfactants from cleaning agents used for washing. With good washing practice, in dry weather and thorough rinsing and collection of rinsate from surfaces, the concentrations of the latter are likely to be low. However, dust build-up will result in turbid run-off, especially during the first rains of the wet season. This will add to the already heavy solids loading in the receiving water bodies.

6.103 Run-off from within the station includes washdown water from car washing in car parks. Car washing solutions contain surfactants, which may have high COD values and be toxic to aquatic organisms. Suspended solids levels will be high and will increase turbidity if allowed to drain directly to receiving waters. Pollutants from trains entering the station in storms are expected to be low, as most of the dust and any oil and grease is likely to have been washed off during track running. Minor maintenance which may be required on trains before they leave the station is a small potential source of chemicals and lubricants.

6.104 Package air-cooled chillers with condensing in fans will be used in Lok Ma Chau Station. Under normal operation of the chillers, no cooling water will be produced. In emergency conditions, cooling water may be discharged and providing this is directed to the sewage treatment system at the station, no environmental impacts will occur. The type of coolant and volume likely to be released has not yet been decided.

Mitigation measures

6.105 Methods of minimizing pollution impacts include:

· Avoidance of impact

· Minimization of extent of impact

· Minimization of intensity of impact

Mitigation by washing and maintenance practices

6.106 Train maintenance and washing within depots should avoid the use of excessive cleaning agents and should ensure that all cleaning agent is washed off the train before it leaves the depot. Cleaning agents should also be selected which have low toxicity and a neutral pH value. Maintenance practices require the use of oil & grease and lubricants to ensure the safe operation of the train. Good practices should be followed to avoid excessive use of these materials and selection of environmentally friendly chemicals wherever possible.

6.107 Car washing practices within the car parks of the station should follow similar practices of avoiding excessive use of cleaning agents and selecting non-toxic materials for washing purposes. The washings should be passed through a sediment trap and oil interceptor before passing to the wastewater treatment plant. Washdown of high levels of suspended solids from the station roof during storm conditions should be avoided by washing the roof prior to the wet season and passing the washings through a sediment trap before discharge.

6.108 Pollution control systems such as oil interceptors and sediment traps require regular maintenance to provide an efficient system for pollutant removal. Oil interceptor contents should be recycled or disposed of to landfill.

Mitigation by design of trains and drainage system

6.109 The train body has already been designed to minimize exposure of those areas of the train which will have the greatest potential to release pollutants (suspended solids, oil & grease and metals) during operation. Once the pollutants are released into the stormwater, a suitable drainage system is required to minimize environmental impacts on water quality.

6.110 Throughout the length of the railway, a drainage system will be incorporated into the plenum design to divert water from within the viaduct sections down to ground level. The potential impacts from run-off containing metal grindings, suspended solids, and oil & grease can be minimized by several additions to the drainage design:

· Incorporation of a sediment trap in the viaduct sections at the discharge point of the drainage pipes. This trap should be sufficiently large to function effectively in low flow conditions and include a bypass for storm conditions.

· Combining drainage pipes along the sections of the viaduct and reducing the number of sediment traps while increasing their size, will reduce maintenance effort.

6.111 Each of these pollutant control systems should be regularly cleaned and maintained in good working order to ensure their efficiency of function. The contents of sediment traps should be transferred to an appropriate disposal facility.

Mitigation of the extent of the impact

6.112 After discharge from the sediment trap, the run-off is likely to enter the wetland areas in Long Valley and Lok Ma Chau. In order to minimize oil & grease and sediment entering wetland areas, it is recommended to locate an area of gravel at the discharge point to receive the discharge as a final filtration device before it enters the wetland area. Oil & grease is likely to be partially removed in the wetland. This will be especially important in wet weather conditions when much of the stormwater will bypass the sediment trap.

6.113 The increased moisture in these areas may encourage the growth of vegetation in the gravel. This has a positive effect for the entrapment of solids and possibly uptake of some metals by plants, however, in severe storms, the vegetation is likely to be flattened and it would be preferable to keep any grasses short in this area. Maintenance of these gravel areas should be carried out regularly by inspection, and subsequent removal and replacement of the top layer of gravel if the filtration rate has diminished. The gravel should be removed off-site, either to an area where regeneration of the gravel can be carried out (for example washing through with water at a depot) or, if too heavily contaminated with oil & grease, metal grindings and lubricants, disposed of to landfill.

6.114 With the recommended facilities included in the drainage system, the level of pollutants in stormwater run-off from the railway is expected to be minimal.

Sewage Generation

6.115 The development of the Lok Ma Chau station will alter the landuse in this area considerably, bringing a large number of people into the area which was previously largely undisturbed fishponds. The population working at the station and passing through the station will generate a volume of sewage which will require treatment before discharge to the aquatic environment.

6.116 The station will be staffed by approximately 1100 staff members on a daily basis. In addition, the number of passengers expected to cross the border at Lok Ma Chau Station will vary according to the time of day and period of the year as shown below (estimates taken from the Implementation Proposal to Government).

Ultimate scenario (2016)

Weekdays Average number of passengers is 131,000/day

Peak flows during rush hour up to 200,000/hour

Weekends Average number of passengers is 196,000/day

Festivals Average number of passengers is 251,000/day

6.117 Based on these staff and passenger numbers, the volume of sewage generated has been calculated as shown in Table 6.17.

Table 6.17

Daily volume and concentration of sewage generated at Lok Ma Chau Station

Criteria	Staff	Passengers	Total
Number of people/day	1100	251000	252000
Sewage flow (l/head/day)	204**	20**
Percentage of passenger/staff using toilet/sink	100**	20**
Total daily sewage flow (m3)	224	1004	1228
BOD5 load (g/head/day)	55*	14**
Total BOD5 load (kg/d)	60	703	760
Sewage BOD5 concentration (mg/l)			619

* EPD Guidelines for design of small sewage treatment plants

** Percentage use follows usage estimated at Lo Wu Station, which was estimated from

British Railway Recommendation WWO Provisional standing order no. 1309

Sewage flow and BOD₅ load for passengers was also taken from British Railway Recommendation.

6.118 The peak flow during rush hour periods is estimated to be about 20,000 passengers, which multiplies up to a daily passenger flow of 480,000. The sewage flow during this period should be accommodated by including a balancing tank into the design of the sewage treatment works to hold the peak flows, while the overall design would be based only on maximum daily flows (1228m³/day on festival days).

6.119 In order to reduce the environmental impact of sewage generation from this source, a Rotating Biological Contactor (RBC) or equivalent appropriate sewage treatment process, which will meet the performance requirements, will be incorporated into the design of the station to treat the effluent to the standards required for discharge into the adjacent water body (Shenzhen River or the proposed San Tin Drainage Channel). For the purposes of this assessment, the RBC will be quoted as the potential sewage treatment process. The wastewater treatment system will include a chlorination unit for disinfection of the wastewater to reduce E.coli to acceptable levels. As residual chlorine can also cause toxic effects, a chlorine residual limit of 0.5mg/l is included in the discharge limit. As the watercourse is within the Deep Bay Water Control Zone, and is within an area with potential for irrigation use, the effluent must meet the discharge standards for Inland Waters (Group B) as listed in the Technical Memorandum for Standards for Effluents discharged into Drainage and Sewerage Systems, Inland and Coastal Waters and summarized in Table 6.18.

Table 6.18

Discharge Standards for Effluents discharged into Group B Inland Waters

Parameter	Discharge standard based on effluent flowrate of 1208m³/day
PH	6.5 - 8.5
BOD5	20
COD	80
SS	30
E.coli (cfu/100ml)	100
Total residual chlorine (additional standard)	0.5

All values in mg/l unless otherwise stated

6.120 In order to achieve these discharge standards, the RBC must have a BOD₅ removal rate of approximately 97%. Assuming this can be achieved, the resulting BOD₅ loading from the effluent discharge would be 24kgBOD₅/day and 24kgSS/day.

6.121 As this pollutant loading is from a new development in the Deep Bay Water Control Zone, mitigation of impacts must be achieved in accordance with EPD’s Zero Discharge Policy (ZDP). The ZDP states that there must be “no net increase in the pollutant load to Deep Bay from new developments”. Mitigation measures are therefore required to off-set the pollutant load which would be discharged into Deep Bay waters from the RBC treatment plant.

Mitigation measures

6.122 Two steps are recommended to achieve compliance with the ZDP policy. The first involves a further treatment step to “polish” the effluent discharged from the RBC. The second step is to extract a quantity of water from the San Tin River, for appropriate treatment to remove a quantity of BOD₅ equivalent to the BOD₅ loading discharged in the polished RBC effluent.

Effluent polishing

6.123 The effluent discharged from the RBC will contain primarily residual BOD₅, COD, suspended solids and nutrients (N and P in various forms). These pollutants are not highly toxic in the concentrations expected in the discharge and can be reduced further through a “natural” treatment mechanism in the form of reedbeds.

6.124 Vegetation has a natural capacity for removing pollutants from water. This function has been studied in wetland vegetation in a number of countries and for a range of effluent types, including domestic wastewater (Reed et al 1985). Mechanisms which remove BOD₅ from wastewater flowing through the reedbed include:

· quiescent conditions which allow sedimentation of remaining solids;

· bacterial activity on submerged roots;

· adsorption/filtration of dissolved materials by roots and stems; and

· adsorption and ion exchange by sediments.

6.125 There are numerous examples of wetlands being used for wastewater treatment in USA and European countries (Hammer, 1989). Wastewaters that have been treated include domestic sewage, urban stormwater and even mine drainage waters, all of which have a significant organic or inorganic pollution load. Percentage removal efficiencies for these pollutants vary from 50 to 90% for BOD₅, 40 to 94% for SS, 30 to 98% for nitrogen and 20 to 90% for phosphorous (Bastian and Hammer, 1993). Constructed wetlands are often designed on organic loading rates, of which BOD₅ is a good indicator. The lower values reported for BOD₅ removal occur in natural wetlands (not specifically designed for that purpose) or where wastewater concentrations are relatively low, as in the case of Lok Ma Chau station RBC effluent. It is therefore proposed to use the more conservative value of 50% BOD₅ removal for the current assessment, in the absence of proven BOD₅ removal rates in Hong Kong.

6.126 In the case of the Lok Ma Chau station reedbed, it will receive effluent from the sewage treatment plant, which has already been treated to the standard required for discharges to Group B inland waters. The pollutant load entering the reedbed is therefore relatively small compared with other wastewater treatment reedbeds. The low organic loading will reduce the amount of vegetation growth to a lower rate relative to other wetlands, which receive high N and P loads, thus minimizing the need for harvesting.

6.127 There are a number of factors which need to be taken into account in the design of wetlands. An important consideration is the size of the area which is determined by the pollutant loading to the reedbed and the flowrate.

6.128 The proposed location for the reedbed occupies an area of approximately 2 ha to the east of the station and north of the railway track, alongside the future San Tin Drainage Channel (Figure 6.3). This area has been included in the area for ecological compensation for habitat lost or disturbed as a result of the Spur Line, however, it will be highly disturbed due to the close proximity of the station and rail track, discouraging more sensitive birds which require an open area for feeding. Establishment of reedbeds will provide a wastewater polishing function and will also provide a habitat suitable for fauna which require shelter, such as passerines.

6.129 The area of land required for treatment is based on the BOD₅ concentration of the incoming wastewater and the expected performance of the reedbed. A typical upper loading rate is 112kgBOD₅/ha/day (Zirsky et al 1986). Applying a safety factor, and assuming an acceptable loading rate of 80kgBOD₅/ha/day, then approximately 0.25ha of reedbed would be required to reduce 24kgBOD₅ in RBC effluent by 50%. The residual pollutant loading discharged into San Tin Channel would be 12kgBOD₅.

6.130 In addition to pollutant loading from BOD₅, E.coli levels are also of concern. At a discharge standard of 100cfu/100ml, the health risk is considered to be low (WHO, 1998), however, an order of magnitude lower is considered to be the “safe” level in other countries. Studies carried out on E.coli removal in constructed wetlands (Hammer 1989) have reported 80 to 100% removal. Reduction in E.coli levels is achieved through a variety of mechanisms including die-off from ultraviolet exposure, sedimentation, filtration, adsorption, aggregate formation and bactericidal toxins released by other micro-organisms.

6.131 Other factors which require consideration in the design of reedbeds for water clean-up are listed below.

· Water depth should be less then 0.45m. As it is unlikely that there will be high concentrations of sediment in the treated effluent flow, no deep water areas are required for settlement. However, it is recommended that a sediment trap is located upstream of the reedbed to settle out any suspended solids before the effluent enters the reedbed. As a secondary safety measure, the gravel bed at the inlet to the reedbed will enable and overflow solids to be trapped.

· The shape of the wetland has been designed with a high length to width ratio, to prevent short-circuiting and increasing the distance wastewater travels.

· The time the treated effluent remains in the wetland is important, to allow opportunity for treatment to occur. Retention times vary greatly, although average values of 5 days are recommended. The retention time within the Lok Ma Chau wetland, for the treated effluent flow alone, is about 8 days, which is acceptable. With the addition of water from San Tin River as part of the offsetting technique to comply with the Zero Discharge Policy (ZDP), as described later, the retention time would be reduced to 4 days. This is still acceptable, considering the low organic loading that will be applied to the reedbed.

· The type of substrate to be used often depends on what is available, and the type of wastewater to be treated. Treated effluent from the RBC will have low levels of nitrogen and phosphorous present, and will therefore provide some nutrients to the plants in the reedbed system.

6.132 A plan and cross-section of the proposed readbed is shown in Figures 6.4 and 6.5.

Zero Discharge Policy Compliance

6.133 Under ZDP, discharge of 12kg BOD₅ into the Deep Bay Water Control Zone must be off-set by treating 12kgBOD₅ from a source within the same catchment. San Tin river water contains 24mgBOD₅/l at normal flow (which includes tidal flushing). After construction of the San Tin Channel, an inflatable dam will exclude tidal flows and in low flow conditions, the BOD₅ level may be higher. A considerable proportion of this pollution load comes from livestock waste and, with the full implementation of the Livestock Waste Control Scheme (LWCS), the BOD₅ levels are expected to decrease considerably. The present BOD₅ value of 24mg/l is therefore used for the purposes of this assessment.

6.134 In order to offset the 12kg BOD₅ effluent load from the polished effluent, a volume of river water needs to be passed through the RBC or the reedbed. If passed through the RBC, almost total pollutant removal (97%) can be expected. In this case, 500m³ river water (which is equivalent to 12kg pollutant load) would be passed through the RBC. From a BOD₅ loading perspective, the increase from 760kgBOD₅/day (from passengers and staff) to 772kgBOD₅/day, can be readily accommodated. However, the hydraulic load would increase from 1228m³/day to 1728m³/day, requiring a significant increase in the capacity of the RBC.

6.135 If the reedbed is used for treatment, a similar problem arises. Assuming 50% BOD₅ reduction, 24kgBOD₅ (equivalent to 1000m³ San Tin River water) would need to be pumped through the reedbed each day. A total loading to the reedbed of 48kgBOD₅ (24kgBOD₅ from the RBC and 24kgBOD₅ from San Tin River) could be treated within an area of 0.5ha reedbed.

6.136 The hydraulic loading to the reedbed is determined by the allowable retention time in the system. As described above, a 5 day retention time, at a flowrate of 2228m³/day (1228m³ from the RBC effluent and 1000m³ from the San Tin River) would require an area of approximately 2 ha, assuming a water depth of approximately 0.5 m. The area allocated for reedbeds is approximately 2ha. As the system is primarily a subsurface flow wetland, effluent will also be present in the soils, the location where plant roots and the soils absorb much of the pollution present. RBC effluent would be discharged into the reedbed at the eastern side of the station and flow through the reedbed before discharge to San Tin Channel. Water from the San Tin Channel should also be pumped to the same influent location, although it should be passed through the sediment trap to remove solids prior to entering the reedbed.

6.137 In achieving BOD₅ removal and off-setting of the pollution load in this way, together with the disinfection facilities of the wastewater treatment plant, the load of E.coli is expected to be within safety standards (WHO, 1998).

6.138 The following sections describe some of the key factors to be considered in the construction and management of the reedbed.

Construction of the reedbed

6.139 The area in which the reedbed will be located is currently abandoned fishponds, with areas of deep water and bunds. The ground will need to be reprofiled to form channels as shown in Figures 6.4 and 6.5. The channels will be approximately 10 to 15m wide and extend the length of the reedbed area. The bunds should be wide enough to walk on, to allow access for vegetation harvesting.

6.140 The base of the channels will be an impermeable material such as clay, which is similar to that material used for fishponds. The outlet from the RBC should be extended to the inlet of the reedbed, where a sediment trap should be constructed followed by a gravel area for removal of solids. The RBC effluent can enter the gravel area directly, as solids concentration is likely to be low. River water from the San Tin Channel will be required to pass through the sediment trap before entering the wetland.

Vegetation

6.141 Vegetation should be selected from species which establish locally and are effective in removing pollutants. Phragmites is recommended for the Lok Ma Chau wetland as it already grows well in the fishpond area and does not required frequent harvesting, as with some other vegetation such as water hyacinth. Phragmites can establish well in shallow water areas and the main mechanism for pollutant removal is through nutrient uptake through the roots. Water flow should therefore be primarily sub-surface.

6.142 There will be a permanent supply of water from the Lok Ma Chau station RBC, eliminating the need for a separate supply of water in the dry season. The flow of water in the San Tin River may decrease in the dry season, although the concretion of pollutants is likely to increase in the low flow channel. Monitoring of the water quality during the first dry season will enable adjustments to be made to the pump flowrate during this period.

Management

6.143 A management plan will be established for the whole of the ecological compensation area of the Lok Ma Chau station. The reedbed, although not specifically designed for ecology, is likely to have some wildlife value because of its proximity to the fishpond and marshland area being designed for ecological compensation of the Lok Ma Chau station impacts, and the low levels of pollutants which will be present in the system, therefore minimizing the build-up of pollutants in the wildlife using this area.

6.144 Wetlands are usually low maintenance systems. Minimal maintenance is required for the soil complex in which the vegetation is established and pollutants are adsorbed. The sediment chamber for sediment settlement and the gravel bed for removal of fine solids, will require more frequent washing and cleaning. The growth of vegetation is expected to be relatively slow, given the low organic load in the wastewater. However, vegetation trimming will probably be required on an annual basis. This will improve water flow through the system and minimize blockage which may result in rising water levels.

6.145 It is important to ensure that the reedbed is established prior to the discharge of treated RBC effluent into it when the station opens. The reedbed should be established in the year prior to the Spur Line opening, and commissioned through pumping of non-tidal water from the San Tin channel, to monitor the effectiveness of the system in pollutant removal.

6.146 n the unlikely event that the reedbed system is not operational at the time of opening, contingency arrangements should be made to tanker the treated RBC effluent away. An alternative is to liaise with the Lok Ma Chau Boundary Crossing reedbed management team to evaluate the possibility of temporarily passing additional San Tin Channel flow through the Boundary Crossing reedbed until the Spur Line reedbed is fully operational.

6.147 Implementation of the reedbed will be the responsibility of KCRC during design, construction and management stage. It is important that the management of the reedbed is co-ordinated with the remaining compensation areas for ecological mitigation. Details regarding the proposed management under the HKSAR Wetland Management Organisation are described in the Ecology Chapter.

6.148 The present assessment is based on a 50% BOD₅ removal rate, which is taken from reported rates in temperate climate reedbeds. From initial results of studies being carried out on reedbed treatment of pig waste septic tank effluent at Kadoorie Farm in Hong Kong, higher rates for removal of BOD₅ and nutrients can be achieved. Data from this study is not available at this stage. Improvement in the rate of BOD₅ removal from the effluent discharged from the RBC would reduce the quantity of BOD₅ required to be off-set which would reduce the volume of river water required to be pumped from San Tin River.

6.149 In addition, a similar reedbed will be established alongside Lok Ma Chau Boundary Crossing, for the purpose of off-setting pollution loading to Deep Bay, arising from the Boundary Crossing Expansion Project (Binnie 1998) The performance of this system should be carefully evaluated and techniques for improvement of pollution removal incorporated into the design and management of the Spur Line reedbed.

Summary of Impacts and Mitigation Measures during Construction and Operation Phases

Construction Phase

6.150 The Spur Line alignment will cross a number of water bodies in the Long Valley, Chau Tau and Lok Ma Chau areas, including wetlands, rivers and fishponds. Activities which will take place in the construction of the Spur Line include piling works, concreting, draining and filling of fishponds, construction of a footbridge across Shenzhen River, and excavation of potentially contaminated materials.

6.151 Impacts on water quality include generation of turbid run-off, which may contain concrete washings, lubricants, chemicals and other contaminants. Of particular concern is the potential impact on water quality during footbridge construction. Impacts can be substantially reduced through the implementation of good site practices, such as careful handling of chemicals and proper disposal of wastewater, and incorporation of suitable drainage systems including sedimentation and infiltration pits, and temporary grease trap and septic tank systems. A drainage system designed into the footbridge construction technique (particularly if the deck is cast in-situ) will minimise the risk of impacts from concrete washings entering the Shenzhen River.

6.152 Table 6.19 summarizes the mitigation measures for construction impacts. With these mitigation measures in place, the impacts on water quality in watercourses throughout the alignment, and downstream in Deep Bay and the ecologically sensitive areas such as Mai Po marshes, will be minimized.

Table 6.19

Summary of Mitigation Measures for Construction Impacts

Impact from Construction	Mitigation Measures
Increase of SS and turbidity from turbid site runoff, and during river related works.	1. Reduction of site runoff by directing it into temporary sand traps or other sand removal facilities. 2. Use of flat and exposed permeable area to encourage infiltration of site runoff. 3. Careful working practices to minimize sediment disturbance during platform and footbridge construction.
Release of pollutants from contaminated land under remediation.	1. Isolation of area being cleaned. 2. Use of appropriate techniques to collect and treat runoff.
Release of nutrients or other contaminants into water courses during dredging activities.	1. Use of silt curtain or sand bag barrier to confine disturbed area. 2. Quick removal of sediment - laden water away from water courses to an area of infiltration / sedimentation.
Elevation of pH in water courses through discharge of concrete washings into surface runoff. Particularly important in construction of the footbridge across Shenzhen River due to potential impacts on ecologically sensitive areas in Deep Bay.	1. Close monitoring of pH in water courses. 2. Construction of coffer dam and pumping out of water where concreting work is carried out within water courses. 3. Removal of wastewaters to sedimentation pit and treatment to appropriate standard before disposal to mimimize turgidityturbidity and potential impacts downstream.
Contamination of groundwater and water courses with hydrocarbon compounds released from site workshop through spillage or leakages.	1. Removal of waste oil by licensed collectors. 2. Installation and maintenance of oil interceptor of hard standing compound. 3. Good housekeeping practices to minimize careless spillage. 4. Appropriate training given to the personnel to handle the chemicals.
Increase of sewage and wastewater from additional workers.	1. Provision of underground septic tank or mobile toilet to store the sewage. 2. Discharges from site canteen via grease traps and collected by licensed collector.

Operation Phase

6.153 The main operational impacts from the Spur Line railway involve the physical presence of the footbridge piers in Shenzhen River, stormwater run-off from the railway tracks and the trains, and sewage generated by staff and passengers at Lok Ma Chau station. Potential stormwater impacts include both hydraulic and pollution effects. Hydraulic impacts from the railway track will be small. Run-off from the Lok Ma Chau station will marginally change the hydrograph of the area, currently open fishponds.

6.154 Hydraulic impacts from culverting of streams are of low significance given their small scale. Potential hydraulic impacts from the supports for the footbridge crossing Shenzhen River can be minimised through good design to optimise shape and size of the piers to lower the velocities, reduce turbidity and minimise effects downstream. The ecologically valuable areas such as Deep Bay and its associated mud flats will therefore be protected from adverse impact due to this project.

6.155 The most significant potential contaminants in the run-off include lubricants and metal grindings from the track which may have a negative long-term impact on the water quality of receiving watercourses. Other contaminants include oil & grease and cleaning agents from trains and within the station, and suspended solids from dust deposition on the station building. Adverse water quality impacts can be effectively reduced through the implementation of good working practices during cleaning and maintenance, and incorporation of appropriate pollution control measures such as oil interceptors/sediment traps into the drainage system design.

6.156 Sewage generated by passengers and staff will be treated in an on site wastewater treatment plant with disinfection to the required standard for discharge to Deep Bay. EPD’s Zero Discharge Policy (ZDP) will be achieved through two mechanisms:

· polishing of effluent in a constructed reedbed (expected to reduce BOD₅ and E.coli); and

· off-setting the pollution load to Deep Bay by treating an equivalent pollution load extracted from the adjacent San Tin Channel. An area of 2 ha of reedbed to the east of the station will be used for reducing BOD₅ and E.coli to an acceptable standard before discharge to San Tin Channel or Shenzhen River.

6.157 The reedbed should be established in the year preceding the Spur Line operation and monitoring conducted to evaluate the performance in terms of BOD₅ removal. In the event of inadequate reedbed performance, contingency plans include tankering the effluent off-site or diverting to alternative reedbed sites to meet the ZDP.

References

Bastian, P.K., and D.A. Hammer. The Use of Constructed Wetlands for Wastewater Treatment and Recycling. Chapter 5 in Constructed Wetlands for Water Quality Improvement. Ed. G.A. Moshiri (1993).

Binnie Black & Veatch. Expansion of Kiosks and Other Facilities at Lok Ma Chau Boundary Crossing, Environmental Study Report. ASD. 1999.

EPD. River Water Quality in Hong Kong 1995, 1996 and 1997.

EPD Marine Water Quality in Hong Kong, 1995, 1996 and 1997.

ERM. Main Drainage Channels and Poldered Village Protection Scheme for San Tin, NWNT: EIA Study. TDD. 1999.

Gearheart, R.A. and B.A. Finney. Utilization of Wetlands for Reliable Low-Cost Wastewater Treatment - A Pilot Project. Paper presented to IV World Congress on Water Resources, at Buenos Aires, Argentina, September 5-9, 1982.

Hammer, D.A. (ed.). Constructed Wetlands for Wastewater Treatment. Lewis Publishers, Chelsea, MI, USA. 1989.

Hantze, N.N. Wetland Systems for Wastewater Treatment: Engineering Applications. In: Ecological Considerations in Wetlands Treatment of Municipal Wastewater. Van Nostrand Reinhold, NY, pp. 7-25, 1985.

KCRC. Implementation Proposal to Government for Sheung Shui to Lok Ma Chau Spur Line 1999.

Maunsell. Main Drainage Channels for Fanling, Sheung Shui and Hinterland, EIA Study. TDD. (1997).

Reed, S.C. and R.K. Bastian. Wetlands for Wastewater Treatment: An Engineering Perspective. In: Ecological Considerations in Wetlands Treatment of Municipal Wastewater. Van Nostrand Reinhold, NY, pp. 444-450. 1985.

Reed, S.C., E.J. Middlebrooks and R.W. Crites. Natural Systems for Waste Management and Treatment. McGraw-Hill Book Co., NY, 1987.

WHO, Guidelines for Safe Recreational-water Environment: Coastal and Fresh-waters, 1998.

Zirsky, J. Basic Design Rationale for Artificial Wetlands. ERM-Southeast, Inc, prepared for USEPA RSKERL, Ada, OK, 1986.