6                                            WATER QUALITY

6.1                                      Introduction

This section presents the water quality impact assessment for the construction and operational phases of the Project.  As the construction works of the Project will be land-based, the main concern is the impacts, if any, to the Water Gathering Ground (WGG) and watercourses in the vicinity of the Development Site and along Sha Lo Tung Road Improvement, as well as the temporary footbridge within the Ecological Reserve. 

The assessment of potential impacts of land based construction and operation activities on water quality upon identified Water Sensitive Receivers (WSRs) has been carried out.  Consideration has been given to control potentially adverse impacts from the development, and mitigation measures are recommended to avoid and minimise the potential for discharges of pollutants to the nearby receiving watercourses in the vicinity of the Project area.

6.2                                      Relevant Legislation and Guidelines

The Environmental Impact Assessment Ordinance (EIAO, Cap 499. S.16), Annexes 6 and 14 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) provide general guidelines and criteria to be used in assessing water quality issues.

The Water Pollution Control Ordinance (WPCO, Cap 358) is applicable to the evaluation of water quality impacts associated with the Project.  Table 3 of Technical Memorandum of Standards for Effluent Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters provides the standards for effluent discharged into Group A inland waters, which include the water gathering grounds (WGGs) and within the boundaries of country parks.

The Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94) and Drainage Plan subject to comment by the Environmental Protection Department (ProPECC PN 5/93), issued by EPD, also provide useful non-statutory guidelines on the management of construction site drainage and prevention of water pollution associated with the construction activities.

The Waterworks Ordinance (Cap 102) is relevant to this Project and prohibits polluting discharges in the water gathering grounds (WGGs).

The Building (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A  - Drains and sewers in gathering grounds to be watertight provides the code of practice for the sanitary fitments, plumbing, drainage works and latrines to be placed within the WGGs which are controlled by the Water Supplies Department (WSD). 

The construction activities of the Project are also required to fully comply with the standard “Conditions for Working within Gathering Grounds” to be issued by WSD for this Project.

6.3                                      Baseline Conditions

The Project area is located inland at Sha Lo Tung in Tai Po, the New Territories, which is a rural area.  The Project includes three components, Ecological Reserve, Development Site and Sha Lo Tung Road Improvement (Figure 3.1).

The streams identified within the Study Area are not included in the EPD river monitoring programme and hence no routine monitoring data are available for this assessment.  Based on the visual inspection during site visits conducted during 2006 to 2010 and water quality measured in November 2009 and May 2010 at sampling locations as shown in Figure 6.1, water in the streams appeared to be good with water flow present .  The results of the water quality measurement are presented in Table 6.1.

Table 6.1        Results of Water Quality Measured at Sha Lo Tung and Fung Yuen

 

Sampling Stations

 

Fung Yuen Stream

Sha Lo Tung Stream

Parameters

1

2

3

4

5

6

Nov 09 data (Mean Value of 3 Replicates)

 

 

 

 

 

 

pH (at 25oC)

7.3

7.1

7.1

7.8

7.7

7.7

Dissolved Oxygen (mg/L)

6.6

3.7

7.7

8.5

8.2

8.0

Suspended Solid (mg/L)

<5

5.7

<5

<5

<5

<5

Biochemical Oxygen Demand (BOD) (mg/L)

<3

<3

<3

<3

<3

<3

Chemical Oxygen Demand (COD) (mgO2/L)

<10

<10

14.7

<10

<10

11

Ammonia Nitrogen (mg/L)

<0.025

0.05

<0.025

<0.025

<0.025

<0.025

Unionized Ammonia (mg/L)

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

E. coli (cfu/100ml)

39

147

9

1

14

0

May 2010 data (Mean Value of 2 Replicates)

 

 

 

 

 

 

Flow Rate (m3/day)

-

-

>500 & ≤1000

>100 & ≤500

≤10

>100 & ≤500

pH Value (at 25oC)

-

-

Note (1)

Water Temperature (oC)

-

-

21.6

21.6

22.0

21.7

Colour (Lovibond colour unit)

-

-

25

20

20

10

Conductivity (µS/cm)

-

-

41.5

41.5

40

36.5

Salinity (ppt)

-

-

<0.1

<0.1

<0.1

<0.1

Suspended Solids (mg/L)

-

-

<10

<10

<10

<10

Turbidity (NTU)

-

-

2.195

1.775

2.24

2.335

Dissolved Oxygen (mg/L)

-

-

8.00

7.57

5.97

7.45

Dissolved Oxygen Saturation (%)

-

-

90.75

85.95

69.1

85.05

Biochemical Oxygen Demand (5-day) (mg/L)

-

-

<2

4.0

<2

<2

Chemical Oxygen Demand (mgO2/L)

-

-

26

28

43

25

Oil & Grease (mg/L)

-

-

<5

<5

<5

<5

Boron (µg/L)

-

-

<10

15

<10

<10

Barium (µg/L)

-

-

13.5

15

16

14

Iron (mg/L)

-

-

0.31

0.28

0.44

0.10

Arsenic (µg/L)

-

-

<10

<10

<10

<10

Chromium (µg/L)

-

-

<1

<1

<1

<1

Mercury (µg/L)

-

-

<0.05

<0.05

<0.05

<0.05

Cadmium (µg/L)

-

-

<0.2

<0.2

<0.2

<0.2

Selenium (µg/L)

-

-

<10

<10

<10

<10

Copper (µg/L)

-

-

<1

<1

<1

<1

Lead (µg/L)

-

-

<1

<1

1.25

<1

Manganese (µg/L)

-

-

23

18.5

60

14

Zinc (µg/L)

-

-

<10

<10

15

<10

Nickel (µg/L)

-

-

<1

<1

<1

<1

Silver (µg/L)

-

-

<1

<1

<1

<1

Total Toxic Metals (mg/L)

-

-

0.35

0.31

0.53

0.13

Total Cyanide (mg/L)

-

-

<0.01

<0.01

<0.01

<0.01

Total Phenols (mg/L)

-

-

<0.1

<0.1

<0.1

<0.1

Sulphide (µg/L)

-

-

83.5

85

84.5

85.5

Fluoride (mg/L)

-

-

<0.1

<0.1

<0.1

<0.1

Sulphate (mg/L)

-

-

<12

<12

<12

<12

Chloride (mg/L)

-

-

<5

<5

<5

<5

Total Reactive Phosphorus (mg/L)

-

-

0.04

0.05

0.02

<0.01

Ammonia nitrogen (mg/L)

-

-

<0.025

<0.025

<0.025

<0.025

Nitrate + Nitrite (mg/L)

-

-

0.021

0.0435

0.0245

0.0145

E. coli (cfu.100ml)

-

-

Note (1)

Note: (1) Samples did not meet QA/QC requirements

The Ecological Reserve comprises Sha Lo Tung Site of Special Scientific Interest (SSSI) and natural streams, and is surrounded by Pat Sin Leng Country Park.  A temporary wooden footbridge to Lei Uk will be built across a stream within the Sha Lo Tung Stream SSSI which is located inside the Ecological Reserve, to the northeast of the Development site (Figure 6.1).  The temporary footbridge will be removed manually after the erection of fencing around Lei Uk.

Besides the stream, the Development Site is surrounded by a number of environmental sensitive areas, which include Fung Yuen Valley SSSI, Sha Lo Tung SSSI and Pat Sin Leng Country Park.  Among these three areas, Sha Lo Tung SSSI is considered to be sensitive to anthropogenic induced variations in water quality.

The Development Site is a rural knoll area, originally with a farming area located at the northern part of the area and some graveyards located within the site.  There are no watercourses passing through this area along the northern side of the site, Sha Lo Tung SSSI stream runs parallel to the northern construction works boundary (Figure 6.2).  Sha Lo Tung stream extends approximately 1.8 km upstream of the proposed Development Site towards Cloudy Hill and contributes runoff from an upstream catchment area of about 61 ha.  Downstream of the proposed Development Site Sha Lo Tung stream flows through abandoned agricultural lands in an upland valley towards Hok Tau Reservoir.  The compensation flows and peak overflow from the reservoir are discharged to Plover Cove Reservoir, the water of which is abstracted for potable use.  

The total area of water catchment land draining into the Sha Lo Tung valley stream system upstream of, and including the development site area, is illustrated in Figure 3.1 of Annex C and is shown to be approximately 39.9 ha.  When one examines the land classification for this area only 1.625 ha of this represents flow through areas of proposed development comprising paved surfaces and buildings with rooftop gardens.  This represents only 4.07% of the area contributing flow into the Sha Lo Tung stream at the location of the development and only 0.29% of the total land area draining into the Sha Lo Tung stream system upstream of the Hok Tau Reservoir which is in the region of 555 ha.

The associated access road, Sha Lo Tung Road, located to the south of the site linking to Ting Kok Road, will be improved and widened before the commencement of the Development Site formation works.  Beside the road, there are some dry valleys which likely carry seasonal flows only (mainly after rainfall).  In addition, Fung Yuen Valley SSSI and the downstream reaches of a stream (unnamed but notated Fung Yuen Stream in this Report) are located to the west of the access road (Figure 6.2).  The stream runs southwards and eventually discharges to Tolo Harbour via the existing drainage system underneath Ting Kok Road and Dai Wah Street.

Coverage of the Development Site is within Drainage Basin 11 (Indus) and Drainage Basin 15 (Tai Po).  Approximately 88% of the Development Site falls inside Drainage Basin 11 (see Figure 6.2).  The remaining part at the southern part of the Development Site is within Drainage Basin 15.  The surface runoff from the part of the Development Site within Drainage Basin 11 is collected by Sha Lo Tung Stream to the north of the Site.  Sha Lo Tung Stream runs northwards and discharges its flow to Hok Tau Reservoir.  The overflow from Hok Tau Reservoir (except for the managed abstraction to Plover Cove Reservoir) is discharged into River Indus via River Jhelum.  The flow in River Indus is discharged into Shenzhen River.  The surface runoff generated from the part of Development Site within Drainage Basin 15 is discharged to an adjacent stream running to the south.  The runoff will be finally discharged to Tolo Harbour via the existing drainage system underneath Ting Kok Road and Dai Wah Street. 

The Development Site and the northern part of the Sha Lo Tung Road fall within the Water Gathering Ground (WGG) (see Figure 6.2) which is currently controlled by the Water Supplies Department (WSD). 

6.4                                      Water Quality Sensitive Receivers

A 500 m boundary has been drawn from the project boundary (Figure 6.2).  Water Quality Sensitive Receivers (WSRs) situated within this area were identified.  The proposed temporary footbridge will be located across Sha Lo Tung stream which considered as one of the WSRs.  The identified WSRs close to the Development Site and Sha Lo Tung Road are illustrated in Figure 6.2 and described in Tables 6.2 and 6.3 respectively:

Table 6.2        Water Quality Sensitive Receivers in the Vicinity of the Development Site

WSRs

Minimum Distance

away from the Site Boundary (m)

Minimum Distance away from the Actual Works Area (m)

Sha Lo Tung SSSI and Streams

Located next to Site

At least 20m (non-building buffer)

Pat Sin Leng Country Park

Located next to Site

Located next to Site

Wet Abandoned Agricultural Land to the East of the Development Site

Located next to Site

At least 10m

Water Gathering Ground

Site located within WGG

Site located within WGG

Table 6.3 Water Quality Sensitive Receivers in the Vicinity of Sha Lo Tung Road

WSRs

Minimum Distance

away from the Site Boundary (m)

Fung Yuen Stream

70

Fung Yuen Valley SSSI

11

Water Gathering Ground

Northern part located within WGG

Some dry valleys adjacent to the site were also identified.  During the visual site inspections in 2006 to 2010, most of them were unable to be identified by the team and they seem to carry only limited flows after rainfall.  Hence, they were not considered as WSRs.

Since the Study Area is located within the Tolo Harbour and Channel Water Control Zone and the nearest river monitoring stations are TR4 (Shan Liu Stream) and TR6 (Tung Tze Stream) (location refer to Figure 6.2), the Key Water Quality Objectives (WQOs) for this Project is suggested to follow the criteria as stipulated in Shan Liu Stream and Tung Tze Stream (Table 6.4).

Table 6.4        Key Water Quality Objectives to be used

Watercourse

pH range

Maximum 5-Day Biochemical Oxygen Demand (mg/L)

Maximum Chemical Oxygen Demand (mg/L)

Maximum Annual Median Suspended Solids (mg/L)

Minimum Dissolved Oxygen (mg/L)

Shan Liu Stream

6.0 - 9.0

5

30

25

4

Tung Tze Stream

6.0 - 9.0

5

30

25

4

6.5                                      Water Quality Impact Assessment

6.5.1                                Potential Sources of Impacts

Construction Phase

The major construction activities include site formation, excavation, foundation, superstructure and building construction, landscaping, slope stabilisation and E&M work.  Only small construction plants will be required and no demolition work is required.  Therefore, potential sources of water quality impacts associated with the construction of the Development Site comprise:

·            Construction runoff and drainage;

·            Runoff from general construction activities; and

·            Domestic sewage effluent produced by the on-site construction workers.

The improvement for Sha Lo Tung Road (mainly widening of existing alignment) will cause the same potential water quality impacts as at the Development Site.  Since the exposed area per section of road will be small and with larger distance from the water quality sensitive receivers, it is expected that the potential impacts would be insignificant.

The establishment of the Ecological Reserve to the north of the Development Site will only require small scale and minor work activities.  The enhancement works will include installation of a drop bar at the road entrance to Sha Lo Tung Valley, footpath maintenance, weed removal, enrichment planting, marsh restoration, plantation, trail enhancement, and provision of alternative country park access.  Other works within the Ecological Reserve will also include construction and removal of the temporary footbridge, fencing at Lei Uk and minor improvement of the existing new footpath to Lei Uk.  The temporary footbridge will be made mainly of wooden materials and spanned over the streambed to minimise the impacts to the stream.  Prefabricated timber sections will be transported near the site and hand carried to the proposed site for assembling on site.  The temporary footbridge will be removed manually following completion of the safety measures work.  In addition, the existing damaged footpaths alongside the natural streams will be maintained and enhanced manually (natural stones but not concrete will be used).  These works will be carried out with hand tools only.  No major excavation works will be required within the Ecological Reserve and hence it is anticipated that the potential water quality impacts due to the enhancement work would be minimal, and therefore they not are discussed further.

Operational Phase

Potential sources of water quality impacts during operation of the Project include:

·           Surface runoff and drainage including the Development Site and the road; and

·           Domestic sewage effluent produced by the operators and visitors.

In view of small scale and minor work activities, it is also anticipated that the potential water quality impacts due to the operation of the Ecological Reserve (including implementation of the Conservation Management Plan) and associated maintenance work would be minimal.

6.5.2                                Assessment of Water Quality Impacts

Development Site

Construction Phase

Construction Runoff and Drainage

Runoff and drainage from construction sites may contain considerable loads of suspended solids and possible contaminants.  Potential sources of water pollution from site runoff include:

·            Runoff and erosion of exposed bare soil and earth, drainage channels and temporary stockpiles;

·            Release of cement materials with rain wash;

·            Wash water from dust suppression sprays and vehicle wheel washing facilities; and

·            Fuel, oil, and lubricant from maintenance of construction vehicles and mechanical equipment.

Local water pollution could be an issue if the construction site runoff is allowed to spill outside the construction site area and drain into the nearby streams, the storm drain or natural drainage without treatment.  However, with the proper implementation of a specific suite of mitigation measures, good site practices and housekeeping, as discussed in Section 6.6, unacceptable water quality impacts due to construction runoff and drainage are not expected.  Any stormwater discharged to the Group A inland waters, including all waters in WGGs and within boundaries of country parks will comply with the TM Standards.

General Construction Activities

On-site construction activities may cause water pollution due to:

·            Uncontrolled discharge of wastewater generated from concrete washing and vehicle washing;

·            Uncontrolled discharge of debris and rubbish such as packaging, construction waste and refuse etc; and

·            Spillages of liquid and chemicals stored on-site, such as oil, diesel and solvents etc.

The wastewater from the above activities may contain high levels of suspended solids and high pH value.  Direct discharge of such wastewater would have potential impacts to the WGG and nearby WSRs located below the Development Site, in particular Sha Lo Tung stream and the wet abandoned agricultural land.  The debris and rubbish could enter the drainage systems on site and cause blockages.  The spillage of liquids may also result in water quality impacts if they enter storm water drains or open drainage channels.

However, the effects on water quality from the construction activities are likely to be minimal, provided that site boundaries are well maintained and sealed, and that good construction practices and well designed temporary drainage system and mitigation measures, as described in Section 6.6, are implemented to ensure that litter, fuel and solvents are managed, stored and handled properly.

The chemicals stored for use during building construction will include paints, varnishes and the like for application to steel, timber and plywood formwork, concrete additives, solvents and thinners, adhesive, bituminous compounds and tars.  Since they will be stored in small quantities and will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.  All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas and located next to the temporary stockpiling area at the south of the Development Site (Figure 3.11).  The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.  As such, the risk of the chemical spillage to the water sensitive receivers, especially the WGG, is expected to be low.  The storage area will be located at the southern side and the lower part of the Development Site to provide at least 320m buffer distance from the Sha Lo Tung SSSI and Stream.

Sewage Effluent

No canteen facilities will be provided on-site.  The on-site work force will generate a small quantity of sewage; however, no public sewerage connection within the Site is available for the workforce.  There is one public toilet located at the end of Sha Lo Tung Road.  In addition, no trade effluent discharge will be generated during the construction phase.

In accordance with Section 9.1 of the Technical Memorandum of Standards for Effluent Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters, no treated effluent is allowed to be discharged within 100 m of the landward boundaries of an SSSI.  Only portable chemical toilets will be used and they will be located at the southern side and the lower part of the Development Site.  In order to further reduce the risks of contaminations to the nearby sensitive areas, the toilets will be located at a substantial distance of approximately 320 m away from the SSSI and Sha Lo Tung Stream (see Figure 6.3) and will also be surrounded by temporary interceptor drains and bunds.  In addition, the portable toilets will be mounted appropriately on site (ie by steel wires) to ensure that they would not be overturned (ie due to strong wind).  A licensed contractor will be appointed to carry out appropriate disposal (by replacing the used portable chemical toilets and no on site cleansing to be allowed) and maintenance of these facilities.  Thus, as there will be no discharge of treated or untreated sewage on site, the impacts on water quality from sewage effluent are likely to be minimal.

Operational Phase

Change in Hydrology and Flow Regime

The overall design philosophy for the stormwater drainage is to retain the rainfall-runoff response as close to the existing regime as possible to minimise impacts.  Calculations are presented in Annex C that consider the overall site as a series of discrete elements.  Proposed changes to the topography and land use are analysed and the resultant change to the hydrology identified in terms of quantity and quality for each discrete area.

The total area of water catchment land draining into the Sha Lo Tung Valley stream system upstream of, and including the Development Site area, is shown in Figure 3.1 of Annex C to be approximately 39.9 ha.  When one examines the land classification for this area which provides the run-off for the drainage that impacts on the development only 1.625 ha of this represents flow through areas of proposed development that comprises paved surfaces and buildings with rooftop gardens.  This represents only approximately 4.07% of the area contributing flow into the Sha Lo Tung stream at the location of the development and only 0.29% of the total land area draining into the Sha Lo Tung stream system upstream of the Hok Tau Reservoir which is in the region of 555 ha.

It should be noted that much of the drainage regimes within sub-catchment areas of the proposed development site are unaffected by the operational phase activities (Annex C).  Where the proposed development introduces changes to the existing run-off characteristics of sub-catchment areas within the Development Site, measures will be introduced to ensure that the run-off characteristics at exits from the site and into the existing Sha Lo Tung drainage system have nominal deviation from those currently in place in terms of volume and flow rate. 

The approach to the drainage impact mitigation measures has as an overriding objective to retain and maintain the existing quality and quantity of water flow into the Sha Lo Tung natural stream systems as well as the wet abandoned agricultural land downstream of the Development Site.  In doing so it is intended to draw clear distinctions between the following run-off and drainage circumstances:

·            Development Site subject to vehicular traffic (“development vehicular zones”);

·            Developments Site with no vehicular traffic (“development non-vehicular zones”); and

·            Areas within the Developments Site that are either naturally vegetated, landscaped and/or undisturbed areas (“non-development zones”).

The approach and measures proposed to mitigate the impact on the existing hydrology regime are described in more detail in Annex C.

Therefore the potential for adverse hydrological changes to Sha Lo Tung Stream as well as the wet abandoned agricultural land and impacts on flow regime have been “designed out” of the proposed stormwater management system and adverse impacts either in terms of quantity or quality are not anticipated during operation of the Project.

Surface Runoff and Drainage

Given the nature of the Project (provision of Nature Interpretation Centre, Multi-Cultural Education Retreat and Columbarium) and the activities undertaken within the Development Site (visitors mainly come for day visit to the Ecological Reserve and columbarium, and for training/ retreat, and the prohibition of burning of effigies and paper offerings, application of pesticides, insecticides and chemical fertilizers), there will be no pollution generated during the operation of Nature Interpretation Centre, and Multi-Cultural Education Retreat cum Columbarium. 

The improved Sha Lo Tung Road and the new car park within the Development Site will be kerbed and will have back of kerb filter drains, trapped road gullys and a piped stormwater system.  This will discharge run-off to a pumping station located beneath the car park area with all flows being discharged back over the crest of the access road (Figure 6.3) and into the structured road drainage to be provided as part of the road improvements.  The pumping station pumps and wet well will be sized to control the rate of discharge from the development vehicular zone such that the road drainage system will not be overloaded and to have a sufficient capacity in which be able to hold all carpark and access road runoff from the "first flush" flow.  Removing the improved Sha Lo Tung Road and car park runoff from the Development Site will not only eliminate the risk of oil leakage spillage contaminating the natural stream courses it will also offset the potential for increased runoff from the proposed Development Site and therefore maintain the hydrological balance of the Sha Lo Tung stream system.

For non-vehicular development areas porous or semi permeable paved surfaces will be used in association with grassed swales and soakaways to attenuate run-off.  Terraced construction will control the rate of surface runoff with catchpits providing oxygenation and solids removal at the steps formed.  The run-off from the development non-vehicular zone will be routed to pass through vortex grit separator beneath the proposed car park (location refer to Figure 3.8) to remove sediments associated with “first flush” flow.

Burning of effigies and paper offerings, application of pesticides, insecticides and chemical fertilizers for the landscaping purpose and vegetation maintenance will be prohibited during operation.  Should organic fertilizers be used for encouraging the growth of planted vegetation, prior approval from the AFCD, EPD and the Director of Water Supplies will be required.  Water quality impacts to the downstream wetland habitats and the watercourses within the WGG are hence not anticipated.

Sewage Effluent

There is one public toilet with septic tank soak-away systems located at the end of Sha Lo Tung Road, next to the Sha Lo Tung stream and within the Sha Lo Tung SSSI zone.  New toilets connecting to new sewerage system and finally discharged to the Tai Po STW will be provided within the Development Site (Nature Interpretation Centre and Multi-Cultural Education Retreat) allowing for public uses during operation.  Such arrangement can help to minimise the potential water quality impacts due to the public toilet.  The feasibility of (1) disuse of the existing public toilet (direct visitors using the new toilets in the Development Site and (2) discharging the sewage generated from the existing public toilet to the new sewerage system for the Development Site will be investigated during the Detailed Design stage and approval by Food and Environmental Hygiene Department will be required.

No restaurant will be provided within the Development Site.  In addition, no trade effluent discharge will be generated during the operational phase.

According to the sewerage impact assessment (Section 7) for this Project, the quantity of wastewater is estimated to be approximately 11.1 m3 day-1, which is assumed to be generated by 30 occupants who will use the dining room/hall.  On normal days, the maximum number of visitors may be up to 200 and the quantity of wastewater is estimated to be approximately 16.0 m3 day-1. 

In order to enhance the protection to the Sha Lo Tung SSSI and Sha Lo Tung Stream, the sewage effluent generated from the Development Site (including wastewater from dining room/ hall) will be discharged of at the Tai Po STW and there will be no facility for bypassing and overflowing the sewage effluent to those WSRs.  This will also satisfy TM requirement that no treated sewage effluent is allowed to be discharged within 100 m of the landward boundaries of the Sha Lo Tung SSSI: 

·            The sewage generated from the site will be collected and may be temporarily stored (if the pumping system malfunctioned) in a storage (equalisation) tank (with capacity of 180 m3 and design similar to that used for fuel tank, ie with double layer).  The sewage will be discharged regularly to the Tai Po STW.

·            The sewage storage tank should be fitted with a level indicator and a high level alarm system.  The detailed design of the sewage tank and the associated facilities will submit to WSD for approval prior the construction. 

·            The sewage storage tank will be located at least 40 m away from Sha Lo Tung Stream. 

·            An approximately 2 km long 225 mm diameter twin sewerage rising mains will be installed from the Development Site running along Sha Lo Tung Road to the existing sewerage network at Ting Kok Road. 

·            As a statutory requirement, the storage tank and all sewers within the WGGs will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A to ensure that they are watertight.  Through the circulation of drainage plans to the Building Authority, other requirements of WSD on the design and details of construction will be complied.  As such, the risk of leakage of sewage from the sewerage system is considered to be very low, through the use of the best quality piping materials (typical example: vitrified clay or PVC or concrete pipe, which are common materials for sewer and are anti-corrosive; materials selected will subject to result of detailed design of proposed sewerage) and provision of hatch box access covers within chambers. 

·            An adequately maintained duty pump with a 100% standby pumping capacity and alternative power supply is considered to be adequate to address pumping requirements in emergency situations.

Based on the above, there will be no direct discharge of sewage into the nearby WSRs, small quantity of sewage, provision of a storage (equalisation) tank for off-peak discharge and use of best designed sewers and chambers, water quality impacts arising from domestic sewage effluent are not anticipated.

Sewage Effluent during Special Festivals

Maximum 7,400 visitors per day are allowed to enter the Multi-Cultural Education Retreat and Columbarium during Ching Ming or Chung Yeung Festival (refer to Section 3.8.1).  It is foreseen that sewage generated would be abruptly increased these festival days.  At least 10 female W.C., 4 male W.C. and 7 male urinals are assumed to be provided in the Multi-Cultural Education Retreat and Columbarium for public use during the operation phase.  According to Section 7, the estimated maximum sewage generated during festival days is 60.8 m3/day.  This flow rate is based on a very conservative estimation which assumes that the visitors will non-stop use the sanitary facilities during the open hours (from 9:00am to 5:00pm).  Nevertheless, the proposed storage tank of minimum size of 180 m3 is considerably sufficient (with a buffer of 3 days withholding time to cater for the situation if the pumping facilities malfunctioned, usually the public holidays during Ching Ming and Chung Yeung Festival not more than 3 consecutive days) to cater for the abrupt increase in generated sewage during festival days.  As the sewage flow rate of 0.0005 m3/s is controlled by the pump, the increase in flow to the Tai Po STW will be 43.2 m3/day, ie 0.036% of the capacity of the STW.  It is concluded that the impact on the STW due to abrupt increase in sewage flow during festival days is insignificant.  In addition, the sewage storage tank should also be emptied regularly in particular before, during and immediately after, the festivals.

Any leakage from the storage tank due to overflow will be collected by channels around the tank.  In case of leakage is occurred, the operator is recommended to close the permanent toilets until the leakage is cleared and the tank is repaired.  100% stand-by pumping units will be put in place in each of the storage tanks for contingency purpose.  If the permanent sanitary (eg the closets and urinals) and/or the sewerage facilities (eg spare pump and the storage tank) are malfunctioned during the festival days, the operator is recommended to close the permanent toilets and divert the visitors to use the portable chemical toilets to be located at the entrance of Sha Lo Tung Road.  Emergent maintenance for the malfunctioned facilities should be carried out as soon as practicable.

Approximately 3 portable toilets will be erected at the pick up/drop off point at the entrance of Sha Lo Tung Road (next to Ting Kok Road) as contingency measures.  In order to provide a contingency against leakage from the toilets, they will be surrounded by temporary intercept drains and appropriately mounted on site.  Replacement of these used toilets will be conducted during the mid-day period such that the number of persons using a portable toilet could be maximized and the leakage from the toilets could be minimized.  Generally, the maximum number of persons using a portable toilet is 380 after every cleaning exercise.  Should the permanent sanitary facilities in the Development Site be closed due to malfunction or emergency maintenance, additional portable toilets can be arranged within a short period of time to cater the visitors, ie a total of 10 portable toilets can cater for a maximum of 380 x 10 x 2 = 7,600 visitors if cleaning exercise is performed. 

Sha Lo Tung Road Improvement

Construction Phase

Construction Runoff and Drainage

Runoff and drainage from linear construction sites may contain considerable loads of suspended solids and possible contaminants.  Potential sources of water pollution from site runoff include:

·            Runoff and erosion of exposed bare soil and earth, drainage channels and temporary stockpiles;

·            Release of cement materials with rain wash;

·            Wash water from dust suppression sprays and vehicle wheel washing facilities; and

·            Fuel, oil, and lubricant from maintenance of construction vehicles and mechanical equipment.

With the proper implementation of good site practices and housekeeping, as discussed in Section 6.6, unacceptable water quality impacts due to construction runoff and drainage are not expected.

General Construction Activities

On-site construction activities may cause water pollution due to:

·            Uncontrolled discharge of wastewater generated from concrete washing and vehicle washing;

·            Uncontrolled discharge of debris and rubbish such as packaging, construction waste and refuse etc; and

·            Spillages of liquid stored on-site, such as oil, diesel and solvents etc.

Wastewater from the above activities may contain high levels of suspended solids and high pH value.  Direct discharge of such wastewater would have potential impacts to the nearby WSRs located below the existing Sha Lo Tung Road, in particular Sha Lo Tung Stream at the northern end and Fung Yuen Valley SSSI at the south.  The debris and rubbish could enter the drainage systems on site and cause blockage.  The spillage of liquids may also result in water quality impacts if they enter storm water drains or open drainage channels.

However, the effects on water quality from the construction activities are likely to be minimal, provided that major earthworks are undertaken during the dry season (fast-track programme totally avoids the wet season while only part of the section (Phase 1) located close to Ting Kok Road will be conducted during part of the wet season under the normal programme), and that the adoption of good construction practices, and well designed temporary drainage system and mitigation measures, as described in Section 6.6, are implemented to ensure that litter, fuel and solvents are managed, stored and handled properly. 

Operational Phase

Vehicles will enter the Nature Interpretation Centre, and a Multi-Cultural Education Retreat cum Columbarium along the improved Sha Lo Tung Road to the car park which will be situated at the western side of the Development Site.  The road runoff may contain minimal amounts of oil, grease and grit that may cause water quality impacts to the watercourses, if uncontrolled as in the existing condition. 

However, it is expected that with effective layers of drainage mitigation measures employing stormwater best management practices including provision of trapped gullies and catchpits, as discussed in Section 6.6, the risk of adverse impacts to the water quality is as low as reasonably practicable and an improvement on the existing situation.  Furthermore, it is noted that traffic is expected to remain relatively light except during festival periods.

6.6                                      Mitigation Measures

In order to minimise the impacts of wastewater/ runoff generated on site to the nearby WSRs, mitigation measures and good site practices will be adopted during the construction and operation phases of the Project based on the ProPECC PN 1/94 and ProPECC PN 5/93.  The following sub-sections described the practices and measures to be adopted.

6.6.1                                Ecological Reserve

In view of minor works during construction and operation, no mitigation measures will be required for the enhancement and operation/ maintenance of the Ecological Reserve. 

With the implementation of good construction practice (see below), no adverse water quality impact is anticipated for the small scale of the works associated with the fencing at Lei Uk, construction and removal of the temporary footbridge and minor improvement of the existing new footpath to Lei Uk. 

Good Construction Practice

·            Conduct all the works during dry season and using hand tools; 

·            Locate the footing of the temporary footbridge at bare land and avoid vegetated areas as much as practical;

·            Avoid or minimize vegetation removal as much as possible;

·            Restricting the number of workers within the Ecological Reserve during construction;

·            Regularly check the work site boundaries to ensure that they are not breached and that damage does not occur to surrounding habitats in particular the secondary woodland and Sha Lo Tung streams; and,

·            No pesticide or herbicide be used for pest and weed control.

6.6.2                                Development Site

Construction Phase

Sha Lo Tung Valley comprises water quality sensitive receivers including Sha Lo Tung SSSI and stream, which is also considered of high ecological and conservation significance.  To avoid ecological risk to the downstream Sha Lo Tung Valley, any discharge of construction runoff from the Development Site is prohibited.  The following practices and measures are proposed to ensure that no discharge of construction runoff occurs to the downstream ecologically sensitive areas.

Prevention of Construction Runoff from Polluting the Nearby Watercourse and Ecological Sensitive Areas

The following mitigation measures are considered to be adequate to practically minimise and control the construction runoff so that they would effectively prevent any contamination of the nearby water and ecological sensitive receivers.

·            Minimisation of the Development Footprint.  The preliminary Master Layout Plan minimised the development footprint within the Development Site (of approximately 1.625 ha and comprised only about 39.6% of the total site area) so as to reduce the extent of site formation and earth work activities, and the subsequent potential risk of construction runoff. 

·            Completion of Sha Lo Tung Road Improvement in advance.  Before any construction works are undertaken within the Development Site, the Sha Lo Tung Road should be improved with well designed drainage systems.  All of the surface run-off will be collected by the temporary drainage system with sufficient number of sandtraps (with sufficient capacity) and then discharged to the newly constructed stormwater drainage system along the improved Sha Lo Tung Road. 

·            Restrict Earthworks to the Dry Season.  Earthworks within the Development Site will only be undertaken during the dry season (November through March) in order to avoid the risk of construction runoff reaching ecological sensitive areas.  With the implementation of this measure, the risk from excessive construction runoff in the event of a heavy rainstorm can be reduced.  Major earthworks will be strictly prohibited during the wet season to minimise ecological risk to the Sha Lo Tung Valley. 

·            Adoption of Construction Sequences.  Given that the Development Site is elongated in shape and hilly in nature, the construction sequence should be well managed in order to limit the volume of surface runoff and treated effluent generated on-site, in particular during the wet season (works other than earthworks).  In order to limit the size of exposed areas and volume of the surface runoff, the construction activities will be carried out sequentially (phase by phase and sub-area to sub-area) rather than in parallel (refer to Site Formation Construction Sequence as shown in Figure 3.13).  The site formation works in the northern part of the Development Area will be carried out at a later phase in order to avoid early exposure of the soil and hence to prevent muddy water from spilling over into the Sha Lo Tung SSSI and Sha Lo Tung Stream as well as the wet abandoned agricultural land.  Such arrangement will assist in ensuring that construction runoff is not discharged into Sha Lo Tung Stream.

·            Provision of Temporary Drainage Channels.  Peripheral temporary drainage channels (special designed U-channel, like a “J” shape will be used) (see Figure 6.3) should be constructed along the lower side of all of the works areas within the Development Site prior to the commencement of the construction works.  All of the natural surface run-off will be collected by the temporary drainage system with a sufficient number of sandtraps and oil interceptors and then discharged to the newly constructed stormwater drainage system along Sha Lo Tung Road.  The drainage system capacity shall be designed for a 1:20 year storm event.  A sandtrap of large capacity is proposed to connect between the temporary drainage system within the Development Site and the newly constructed stormwater drains beneath Sha Lo Tung Road.  All surface runoff within the site will be continuously pumped to this sandtrap through a bendable water pipe (e.g. rubber pipe) before it is discharged from the site.  Due to the lower level at the surface water collection point within the Development Site, the surface water within the Site will be transferred to temporary storage tanks (after passing through sandtraps) in which a submersible pump will operate to continuously pump the surface runoff to the proposed sandtrap.  A spare submersible pump will be put in place in the storage tank for contingency purpose.

·            Provision of Silt Removal Facility.  Sandtraps will be provided on site for wastewater treatment before discharge.  The Contractor will ensure that the sandtraps will be large enough to handle the site runoff / discharges and will be properly maintained.  The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94.  The effectiveness of the sand trap will be checked and maintained regularly.  The sand traps should be cleaned out when the volume of settled sediments amounts to 10% of the total volume of the trap.

·            Separate Temporary Drainage System for Natural Runoff.  The temporary drainage system may not be able to handle high volume of natural surface runoff from the surrounding hills during heavy rainfalls.  The surface runoff from the Site will be separated from the natural hinterland surface runoff by deployment of two drainage systems.  To cater for the surface water running from the hinterland in particular at the southern end to the low profile of the Site, a separate temporary drainage system including catchpits and drainage pipes/ channels will be used to direct the natural surface runoff without any contamination due to site activities to north side of the site (Figure 6.3).

·            Erection of Site Hoardings and Chain-link Fence with Seal.  Continuous site hoarding and chain-link fence will be erected along the temporary drainage system enclosing the entire Development Site (Figure 6.4).  The hoardings and chain-link fence should be firmly attached to the channel (any gaps are to be filled and cemented) in order to avoid any accidental spilling over the peripheral channel to the nearby streams.  All of the excessive runoff due to heavy rainfall or overflow of storage tanks/ sandtraps could be retained within the Site and avoid any accidental discharges into the Sha Lo Tung SSSI Stream as well as the wet abandoned agricultural land.  The erection of the hoardings and chain-link fence will avoid any additional impacts to the existing trees.

·            Daily Inspection.  Green Power will provide a Conservation Specialist to stay on-site during the construction phase.  The Green Power representative will inspect the site daily to inspect of the sandtraps and channels and check the implementation and effectiveness of the runoff control measures.  The person will have the authority to stop the construction works should the implementation and effectiveness of the runoff control measures not be satisfactory.

Operational Phase

Surface Runoff and Drainage

After identifying the sub-divisions in the natural topography based on their drainage characteristics it is possible to develop mitigation measures to minimize the impact of the development on the existing drainage system and in particular the discharge into Sha Lo Tung Stream as well as the wet abandoned agricultural land.  The approach to the drainage impact mitigation measures has as an overriding objective to retain and maintain the existing quality and quantity of water flow into the Sha Lo Tung natural stream systems downstream of the Development Site.  In doing so it is intended to draw clear distinctions between the following run-off and drainage circumstances (also summarised in Table 6.5):

·            Development Site subject to vehicular traffic (“development vehicular zones”) – where the run-off will be collected using back of kerb filter drains, trapped road gullies and a piped stormwater system.  This will discharge run-off to a pumping station located beneath the car park area with all flows being discharged back over the crest of the access road and into the structured road drainage to be provided as part of the road improvements ;

·            Developments Site with no vehicular traffic (“development non-vehicular zones”) – where porous or semi permeable paved surfaces will be used in association with grassed swales and soakaways to attenuate run-off.  Terraced construction will control the rate of surface runoff with catchpits providing oxygenation and solids removal at the steps formed.  The run-off from the development non-vehicular zone will be routed to pass through vortex grit separator beneath the proposed car park (location refer to Figure 3.8) to remove sediments associated with “first flush” flow (details refer to Annex C).  After removal of sediments clear water can be discharged via a storage tank and non-developed buffer zones (undeveloped naturally vegetated land between the development boundary and the existing stream system) into the existing stream system, which act to reduce the energy and volume of run-off flows before they enter the existing Sha Lo Tung stream system.  The vortex grit separator will be regularly cleaned and maintained in good working condition.  The initial frequency for clearing the vortex grit separator would be based on systematic monitoring at the start of the wet season, after each significant rainfall event (amber/T3 or above) and at intervals not exceeding one month between April and October.  Removal with clearing/disposal as required.  This will provide the required information on the volume of washed down material and this can be used to determine an effective and efficient clearing frequency programme. 

·            Areas within the development site that are either naturally vegetated, landscaped and/or undisturbed area (“non-development zones”) where run-off will not have any interaction with the development and can pass into the existing stream system via buffer zones.

·            The hazards and risk associated with accidental oil spillage and leakage are negligible because all storm water run-off from the access road and car park within the Development Site will be isolated, collected in pumping station located beneath the proposed car park and then pumped back into the stormwater drainage system for the upgraded access road where it will re-enter the existing main storm water drainage system for the Ting Kong Road.

·            Adoption of the proposed measures in Annex C (Drainage Assessment and Mitigation Measures).

Domestic Sewage Effluent

It should be noted that no restaurant will be provided within the Development Site, and no trade effluent discharge will be generated during the operational phase.  The sewerage system is also summarised in Table 6.5.

·            To cater for this increase in generated sewage during the festival days, the sewage storage tank will be emptied before the festivals and immediately after the festivals.  Several portable toilets will also be erected at the pick up/ drop off point at the entrance of Sha Lo Tung Road (next to Ting Kok Road) during those days.  All of them will be surrounded by temporary intercept drains and appropriately mounted for contingency purpose.  The sewage storage (equalisation) tank should also be emptied before and immediately after the festivals and should be maintained regularly.

·            The sewage will be discharged into the foul sewer.  The storage tank and all sewers within the water gathering ground will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A to ensure that they are watertight.  Other requirements of WSD on the design and details of construction will be complied with through the circulation of drainage plans to the Building Authority.  The sewage tank should be fitted with a level indicator and a high level alarm system.  The detailed design of the sewage tank and the associated facilities will submit to WSD for approval prior the construction.  The sewage storage tank will be located at least 40 m away from Sha Lo Tung Stream.  An adequately maintained duty pump with a 100% standby pumping capacity and alternative power supply is considered to be adequate to address pumping requirements in emergency situations.  An approximately 2 km long 225 mm diameter twin sewerage rising mains will be installed from the Development Site running along Sha Lo Tung Road to the existing sewerage network at Ting Kok Road.  The sewage will be discharged regularly to the Tai Po STW.

·            Regular inspection and maintenance for the storage tanks, piping materials and joints of sewers will be conducted to ensure that leakage of sewage effluent from the tank and pipeline does not occur. 

·            If leakage or spillage of sewerage does occur, it should be contained and cleaned up promptly.

 

Table 6.5        Summary of the Drainage and Sewerage Systems in the Development Site During Operation

 

 

 


6.6.3                                Sha Lo Tung Road Improvement

Construction Phase

Prevention of Construction Runoff from Polluting the Nearby Watercourses and Ecological Sensitive Areas

·            Arrange the Earthworks to maximise avoidance of the Wet Season.  All the earthworks under Phases 1, 2 and 3, particularly close to the WSRs including Sha Lo Tung SSSI, stream and Fung Yuen Valley SSSI, will be undertaken during the dry season (November to March) in order to avoid the risk of construction runoff overflow to the downstream ecological sensitive areas. 

·            Adoption of Construction Sequences.  Given that the total length of Sha Lo Tung Road is approximately 2.3 km, the construction sequence will be well managed in order to limit the volume of surface runoff and treated effluent generated on-site, in particular during the wet season (works other than earthworks).  In order to limit the size of the exposed area and volume of the surface runoff, the construction activities will be carried out sequentially (phase by phase) rather than in parallel (refer to Road Improvement Work Plan as shown in Figure 3.22). 

·            Provision of Temporary Drainage Channels.  To prevent the discharge of silty surface run-off to the existing watercourse, an effective temporary drainage system will be introduced for the road improvement work.  Prior to the construction, temporary hoarding will be erected and sandbags be placed at toe of the hoarding within the works site (refer to Figure 6.4) as to prevent any silty water flowing out of the works site.  As shown in Figure 3.22, at least two temporary sandtraps connecting with temporary surface drainage will be proposed at each phase of road improvement works (except Phase 3) prior to discharging into the nearest watercourse to avoid any excessive sediment or blockage of existing natural drainage system.  Similar to the construction activities within the Development Site, all of the surface run-off generated along the section close to Sha Lo Tung Valley (approximately half of the Phase 3) will be collected by the temporary drainage system with a sufficient number of sandtraps (with sufficient capacity) and oil interceptors and then discharged to the newly constructed stormwater drainage system along the improved Sha Lo Tung Road.  The drainage system capacity shall be 1 in 10 years return period, after taking into account of the importance of site, a conservative approach of 1 in 20 years return period was adopted.  A sandtrap of large capacity is proposed to connect between the temporary drainage system within the Development Site and the newly constructed stormwater drains beneath Sha Lo Tung Road.  All surface runoff within the site will be diverted to this sandtrap before it is discharged out from the site.  Due to the lower level at the surface water collection point within the Development Site, the surface water within the Site will be stored in temporary storage tanks (after passing through sandtrap) in which a submersible pump will operate to continuously pump the surface runoff to the proposed upstream sandtrap.  A spare submersible pump will be put in place in the storage tank for contingency purpose.

Operational Phase

Surface Runoff and Drainage

·            It has been demonstrated that the majority of contaminants in stormwater runoff are transported on sediments.  The runoff from the concrete paved areas including the improved Sha Lo Tung Road and car park will be collected using back of kerb filter drains and trapped roads gullies to Highways Department’s standard drawings H3110.  The gullies on the access road and car park within the Development Site will discharge to a piped drainage system linked by backdrop catchpits and collected in a pumping station located beneath the car park.  The collected run-off will then be pumped back over the crest of the access road and back into the structured highway drainage system that ultimately connects to the existing stormwater system in Ting Kok Road.

·            Any oil leakage or spillage will be contained and cleaned up immediately. 

·            Surface runoff will be diverted and discharged into the newly constructed stormwater drainage system along the improved Sha Lo Tung Road to Tai Po. 

Domestic Sewage Effluent

·            All sewers within the water gathering ground will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A - Drains and sewers in gathering grounds to be watertight.  Other requirements of WSD on the design and details of construction will be complied with through the circulation of drainage plans to the Building Authority.

·            Regular inspection and maintenance for the piping materials and joints of sewers will be conducted to ensure that leakage of sewage effluent from the pipeline does not occur. 

6.6.4                                Mitigation Measures for Both Development Site and Sha Lo Tung Road Improvement

Construction Phase

Good Site Practices

·            Discharges to the natural water courses shall only take place when the effluent complies with the requirements under the Water Pollution Control Ordinance.  Discharges in the water gathering ground should meet Group A standards for inland waters specified in the Technical Memorandum, Standards for Effluent Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters.

·            During the construction works, the adoption of the following good site practices will further reduce the potential water quality impacts to the WSRs. 

-            All exposed earth areas will be paved or hydroseeded as soon as possible after earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks, where practicable.  In the event of rain or at any time when rainstorms are likely to happen, exposed surfaces should be covered by tarpaulin or by other means.

-            All drainage facilities and erosion and sediment control structures will be regularly inspected and maintained to ensure proper and efficient operation at all times and particularly following rainstorms.  Deposited silt and grit will be removed regularly and disposed of by spreading evenly over stable, vegetated areas.

-            Measures will be taken to reduce the ingress of site drainage into excavations.  If the excavation of trenches in wet periods is necessary, they will be dug and backfilled in short sections wherever practicable.  Water pumped out from trenches or foundation excavations will be discharged into storm drains via silt removal facilities.

-            Open stockpiles of construction materials (for example, aggregates, sand and fill material) should be covered with tarpaulin or similar fabric during rainstorms.  Measures will be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

-            The wheels of all vehicles leaving and entering the construction site will be washed to minimise the carry over of mud onto Sha Lo Tung Road and into the water gathering grounds.  Wheel wash water will be recycled and only discharged into the temporary drainage system.

-            Manholes (including newly constructed ones) will always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system.

-            Precautions to be taken at any time of year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted, and actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94.  Particular attention will be paid to the control of silty surface runoff during storm events, especially for areas located near steep slopes.

-            Oil interceptors will be provided in the drainage system and regularly emptied to prevent the release of oil and grease into the storm water drainage system after accidental spillages.  The oil interceptors should be cleaned when the volume of oil amounts to 30% of the total volume of the oil interceptor.  The interceptor will have a bypass to prevent flushing during periods of heavy rain.

-            The sandtraps should be cleaned out when the volume of settled sediments amounts to 10% of the total volume of the traps.

General Construction Activities

·            Debris and rubbish generated on-site will be collected, handled and disposed of properly to avoid entering the nearby stormwater drains and open drainage channels.   The refuse collection point will be properly constructed with covers and will be bunded and drained to the sewerage system.

·            Open storm water drains and culverts near the works area will be covered to block the entrance of large debris and refuse. 

·            Earthworks will be scheduled in the dry season (November to March) only and construction sequenced accordingly.

Storage and Handling of Oil, Other Petroleum Products and Chemicals

·            Waste streams classifiable as chemical wastes will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.

·            All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas at the south of the Development Site.

·            The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.

·            Oil leakage or spillage will be contained and cleaned up immediately.  Waste oil should be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.  The Contractors will prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

Sewage Effluent

·            Appropriate sanitary facilities, such as portable chemical toilets, will be employed at the areas where the temporary connection is not feasible.  Only portable chemical toilets should be used and they will be deployed at a location as far away from the SSSI as possible and at least 320m away from Sha Lo Tung Stream.  The toilets should also be surrounded by temporary interceptor drains and appropriately mounted.  A licensed contractor would be responsible for appropriate disposal (by replacing the used portable chemical toilets and no on site cleansing to be allowed) and maintenance of portable toilets.

6.6.5                                Water Gathering Ground

The following are the proposed mitigation measures for the water quality that may later on form the “Conditions for Working within the WGG” to be specified by the WSD.  The Conditions will apply, through the permit process; in totality to the Project. 

For all works within the WGG, the Contractor will be required to comply with the following practical measures to ensure that no pollution or siltation occurs to the catchment:

·            No earth, building materials, fuel, soil or toxic materials or any other materials which may cause contamination to the WGG are allowed to be stockpiled close to any watercourses within the WGG.

·            No discharge of flammable or toxic solvents, petroleum oil or tar and other toxic substances will be allowed within the WGG.  Any chemicals to be stored or used within the WGG will be subject to the approval of the Director of Water Supplies.  The chemicals stored for use during building construction will include paints, varnishes and the like for application to steel, timber and plywood formwork, concrete additives, solvents and thinners, adhesive, bituminous compounds and tars.  Since they will be stored in small quantities and will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.  All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas and located next to the temporary stockpiling area at the south of the Development Site (Figure 3.11).  The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.  As such, the risk of the chemical spillage to the water sensitive receivers, especially the WGG, is expected to be low.  The storage area will be located at the southern side and the lower part of the Development Site to provide at least 320m buffer distance from the SSSI and Sha Lo Tung Stream.

·            In order to prevent the washing away of construction materials, soil, silt or debris into any drainage system and the watercourses within the WGG, the stockpile of such materials will be placed within a designated area measuring about 3m x 20m in the southern part of the Development Site (Figure 6.3).  The designated stockpile area will occupy a proposed cut platform formed within the first phase works area and is located at a substantial distance of approximately 320m from Sha Lo Tung SSSI and streams.  The area will be provided with concrete paving, concrete bunds and interceptor drains along its perimeter to prevent the loss of materials such as soil, silt or debris to the surrounding area.  The stockpile will also be covered with tarpaulin or similar impermeable covering materials during rainstorms to ensure that no impact on the water gathering ground, Sha Lo Tung SSSI and streams will arise.  All unavoidable surplus excavated materials will be removed from the works area and delivered by truck on a daily basis to one of the Government’s public fill reception facilities, eg Tuen Mun Area 38 Fill Bank.

·            Regular cleaning of the silt/grease traps will be carried out to ensure that they function properly at all times.

·            All excavated or filled surfaces which have the risk of erosion will always be protected from erosion.

·            Facilities for washing the wheels of vehicles before leaving the site will be provided.

·            No maintenance activities which may generate chemical wastes shall be undertaken in the water gathering grounds.

·            Any construction plant which causes pollution to catchwaters or catchment due to leakage of oil or fuel will be removed off site immediately.

·            Any soil contaminated with fuel leaked from plant will be removed off site and the voids arising from removal of contaminated soil will be replaced by suitable material to the approval of the Director of Water Supplies.

·            Temporary toilet facilities will be provided at a designated area located at the southern part of the Development Site (next to the temporary stockpiling area).  Only portable toilets will be used and the toilets will be located at a substantial distance of approximately 320m away from the SSSI and the watercourse within the WGG (see Figure 6.3) and will also be surrounded by temporary interceptor drains and appropriately mounted.  The details of the chemical toilets shall be submitted to WSD prior to the construction commencement.  A licensed contractor will be appointed to carry out appropriate disposal (by replacing the used portable chemical toilets and no on site cleansing to be allowed) and maintenance of these facilities.  All waste shall be cleared away daily and disposed of outside the WGG. 

·            All mud and debris will be removed from any waterworks access roads and associated drainage systems.

·            For drainage and sewerage diversions within or affecting the WGG, the agreement of the Director of Water Supplies will be required prior to the commencement of the diversion works.

·            The use of pesticide, herbicides or fertilisers will not be allowed within the WGG without the prior approval from the Director of Water Supplies.

·            Disposal of the containers for fuel, oil and other chemicals or their residues within the WGG is strictly prohibited.  They must be disposed of properly outside the WGG.

·            Watertight and leak-proof sewers will be used in the WGG in order to prevent any leakage of sewage.

·            In the unlikely event of spillage of oil and fuel, oil spill control measures (eg application of oil booms in the streams) and decontamination kit will be deployed to confine the spreading.  Please note that oil will not be stored on site.

·            Construction site runoff will not be allowed to be discharged to the existing water courses within the WGG. 

6.7                                      Residual Impacts

It has been predicted in the previous sections that there would not be any insignificant environmental impacts, provided that the mitigation and pollution control measures, as mentioned in Section 6.6, are properly and fully implemented.  Hence no adverse residual water quality impacts were predicted to occur due to construction and operation of the Project with full implementation of the above described mitigation measures.  

It is unlikely that the polluted water will flow from the construction site into Sha Lo Tung Stream during the construction phase in view of the following measures.  These measures will minimise the site run-off and avoid any contaminated run-off discharging into Sha Lo Tung Stream as well as the wet abandoned agricultural land and hence no residual impacts are expected. 

·            Complete the Sha Lo Tung Road Improvement (with well designed drainage systems) before any construction works are undertaken within the Development Site;

·            Restrict earthworks to the dry season in order to minimise the site run-off;

·            Manage the construction sequences to limit the volume of surface runoff generated on-site, in particular during the wet season;

·            Provide temporary drainage channels with sandtraps to divert site runoff to the sandtrap of large capacity before discharging it from the site;

·            Provide silt removal facilities such as sand traps;

·            Provide a separate temporary drainage system to divert the natural upslope runoff away from the site and minimise the site runoff;

·            Erect continuous site hoardings with seal along the northern boundary of the Development Site in order to contain the run-offs within the site and avoid overflow into Sha Lo Tung Stream; and

·            Carry out daily inspection to monitor the effectiveness of the measures by an on-site conservation specialist.

Similarly, no residual water quality impacts were predicted to occur during the operation of the Project with the suggested mitigation measures in place.  The key water quality impact assessment and the associated mitigation measures as well as the residual water quality impacts are summarised in Table 6.6.

6.8                                      Cumulative Impacts

At present there are no planned projects to be constructed in sufficient proximity to the Project Sites (including Ecological Reserve, Development Site and Sha Lo Tung Road Improvement) to cause cumulative environmental impacts.  No construction works will be undertaken within the villages (e.g. Cheung Uk and Lei Uk) within the Sha Lo Tung Valley.  It should also be noted that the construction of the Development Site and Sha Lo Tung Road Improvement would not be undertaken concurrently, as the existing Sha Lo Tung Road has to be improved before the construction activities of the Development Site can occur. 

6.9                                      Environmental Monitoring and Audit Requirements

6.9.1                                Construction Phase

Although no unacceptable impacts have been predicted to occur during the construction phase of the Project, water quality monitoring at the discharge points and WSRs during the construction works at the Development Site is recommended in order to ensure that the water quality at the WSRs is not impacted by the construction works.  Details of the EM&A programme are presented in Section 12.

6.9.2                                Operational Phase

Although there are no unacceptable impacts predicted to occur during the operation of the Project, water quality monitoring will be carried out on a monthly basis during the first twelve months of the operational phase.  Two of the monitoring events should be scheduled on the day just after the Ching Ming Festival Day and Chung Yeung Festival Day.  Although the purpose of the monitoring is to verify that contamination to the watercourses by sewage, oil or chemicals arising from the operational activities is not occurring, it should be noted that adverse impacts of this nature are not predicted to occur.  The monitoring results will be submitted to EPD and WSD after each monitoring event.  After the first twelve-months of monitoring, the monitoring results will be reviewed by the Sha Lo Tung Development Co., Ltd to determine whether it is necessary to extend the monitoring.  The review results will be provided to EPD and WSD for agreement.  Details of the EM&A programme are presented in Section 12.

6.10                                  Conclusion

6.10.1                            Environment and Water Quality Sensitive Receivers

Sha Lo Tung Valley comprises water quality sensitive receivers including Sha Lo Tung SSSI and stream, which are also considered of high ecological and conservation significance, as well as the wet abandoned agricultural land to the east of the Development Site.  It has been identified that the water quality sensitive receivers (WSRs) of the Development Site and Sha Lo Tung Road Improvement include Sha Lo Tung SSSI, Fung Yuen Valley SSSI and streams.

6.10.2                            Ecological Reserve

The enhancement works will include installation of a drop bar at the road entrance to Sha Lo Tung Valley, weed removal, enrichment planting, marsh restoration, plantation, trail enhancement, provision of alternative country park access and enhancing the existing damaged footpath alongside the natural streams.  No pesticides or herbicide will be used for weed removal.  Other works within the Ecological Reserve will also include construction and removal of the temporary footbridge, and fencing at Lei Uk and minor improvement of the existing new footpath to Lei Uk.  These works will be carried out with hand tools only.  No major excavation works will be required and no water quality impact is anticipated.

Only minor works will be required during emergencies or routine maintenance.  No wastewater generating activity will occur and no water quality impact is expected during the operational phase.

6.10.3                            Development Site

During the construction phase of the Project water quality impacts have the potential to arise from construction runoff, general construction activities and domestic sewage discharge.  To avoid ecological risk to the downstream Sha Lo Tung Valley, any discharge of construction runoff from the Development Site is prohibited.  The following practices and measures to be proposed are targeted to ensure no discharge of construction runoff to the downstream ecological sensitive areas:

·            Complete the Sha Lo Tung Road improvement (with well designed drainage and sewerage systems) before any construction works are undertaken within the Development Site;

·            Restrict earthworks to the dry season;

·            Manage the construction sequences, in particular during the wet season;

·            Provide temporary drainage channels to divert site runoff to the sandtrap before discharging it from the site;

·            Provide silt removal facilities such as sandtraps;

·            Provide a separate temporary drainage system to divert the natural runoff away from the site and minimise the site runoff;

·            Erect a continuous site hoarding with seal along the northern boundary of the Development Site;

·            Carry out daily inspection; and

·            Carry out water quality monitoring programme during and after construction.

Effective controls, including but not limited to the construction of peripheral channels and erection of the site hoarding (with any gaps to be filled and cemented) in advance of site formation works and a restriction that earthworks are undertaken only during the dry season, will be implemented.  Consequently, the potential water quality impacts will be controlled and are expected to be minimal.  

The principal impacts on the existing drainage that require mitigation are as follows:

·            Increase in the total volume of run-off;

·            Increase in peak intensity of run-off flow; and

·            Increase in risk of pollution.

The increase in water quantity has been addressed by minimising the creation of impermeable surfaces, encouraging natural ground water recharge through soakaways/filter drains and transferring all highway runoff into the adjacent urban catchment.  The increase in peak intensity has been addressed by controlled run-off attenuation using swales, naturally lined channels, catchpits, and vortex grit separator with outlet control and undeveloped buffer zones.  The risk of pollution has been addressed by transferring runoff from high risk area to the adjacent urban catchment, and the use of catchpits, filter drains and vortex grit separator in the traffic free, low risk Development Site. 

The hazards and risk associated with accidental oil spillage and leakage are negligible because all storm water run-off from the access road and car park within the Development Site will be isolated, collected in the pumping station located beneath the proposed car park and then pumped back into the stormwater drainage system for the upgraded access road where it will re-enter the existing main storm water drainage system for the Ting Kong Road.

6.10.4                            Sha Lo Tung Road Improvement

During the construction phase of the Sha Lo Tung Road Improvement, the water quality impacts have the potential to arise mainly from construction runoff and general construction activities.  It is anticipated that the effects on water quality from the construction activities are likely to be minimal, provided that major earthworks are undertaken during dry season, and that good construction practices and a well designed temporary drainage system are implemented.

Vehicles will enter the Ecological Reserve, Nature Interpretation Centre, and a Multi-Cultural Education Retreat cum Columbarium along the improved Sha Lo Tung Road to the car park which will be situated at the western side of the Development Site.  The road runoff may contain minimal amounts of oil, grease and grit that may cause water quality impacts to the watercourses, if uncontrolled.  With the collection of the run-off and then pumping back into the structured highway drainage system along the improved Sha Lo Tung Road that ultimately connects to the existing stormwater system in Ting Kok Road, no adverse impacts to the WSRs are anticipated.  Furthermore, it is anticipated that the number of vehicles entering the area will be relatively low when compared to the main roads and this will further minimise water quality impacts.

Table 6.6             Key Water Quality Impact Assessment and the Associated Mitigation Measures

(I)            Improvement to Sha Lo Tung Road (excluded sections within the Development Site boundary)

Phase

Activities & Pollutants

Affected receivers & shortest distance from project boundary

Design changes to avoid & minimize impact

Impact against acceptable criteria

Mitigation measures

Residual impact & acceptability

Construction

Construction Runoff and Drainage

·      Runoff and erosion of exposed bare soil and earth, drainage channels and temporary stockpiles

·      Release of cement materials with rain wash

·      Wash water from dust suppression sprays and vehicle wheel washing facilities; and

·      Fuel, oil, and lubricant from maintenance of construction vehicles and mechanical equipment

 

·      Fung Yuen stream (minimum Distance away from the Site Boundary = 70m)

·      Fung Yuen Valley SSSI (minimum Distance away from the Site Boundary = 11m)

·      Water Gathering Ground (majority of the SLT Road located within WGG)

·      Widening the existing access road to a minimum width of 4.5 m, which under the TPDM is suitable for use of emergency vehicles;

·      The access road shall follow the existing road alignment and profile to minimise earthworks and impacts to the existing environment.  Nevertheless, the road shall be re-profiled to ensure a maximum gradient less than 16% because a gradient more than 16% is not suitable for use of emergency vehicles; and

·      Provision of a drainage system with additional verges and a sewer.

WQO

·      Arrange the Earthworks to maximise avoidance of the Wet Season.  All the earthworks under Phases 1, 2 and 3, particularly close to the WSRs including Sha Lo Tung SSSI, stream and Fung Yuen Valley SSSI, will be undertaken during the dry season (November to March) in order to avoid the risk of construction runoff overflow to the downstream ecological sensitive areas. 

·      Adoption of Construction Sequences.  Given that the total length of Sha Lo Tung Road is approximately 2.3 km, the construction sequence will be well managed in order to limit the volume of surface runoff and treated effluent generated on-site, in particular during the wet season (works other than earthworks).  In order to limit the size of the exposed area and volume of the surface runoff, the construction activities will be carried out sequentially (phase by phase) rather than in parallel. 

·      Provision of Temporary Drainage Channels (details refer to Section 6.6.3). 

·      Good site practices (refer to Section 6.6.4/ Construction Phase/ Good Site Practices)

For all works within the WGG, the Contractor will be required to comply with the following practical measures to ensure that no pollution or siltation occurs to the catchment:

·      No earth, building materials, fuel, soil or toxic materials or any other materials which may cause contamination to the WGG are allowed to be stockpiled close to any watercourses within the WGG.

·      No discharge of flammable or toxic solvents, petroleum oil or tar and other toxic substances will be allowed within the WGG.  Any chemicals to be stored or used within the WGG will be subject to the approval of the Director of Water Supplies.  The chemicals stored for use during building construction will include paints, varnishes and the like for application to steel, timber and plywood formwork, concrete additives, solvents and thinners, adhesive, bituminous compounds and tars.  Since they will be stored in small quantities and will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.  All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas and located next to the temporary stockpiling area at the south of the Development Site (Figure 3.11).  The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.  As such, the risk of the chemical spillage to the water sensitive receivers, especially the WGG, is expected to be low.  The storage area will be located at the southern side and the lower part of the Development Site to provide at least 320m buffer distance from the SSSI and Sha Lo Tung Stream.

·      Locate the designated stockpile area (with concrete paving, concrete bunds and interceptor drains along its perimeter) at a substantial distance of approximately 320m from Sha Lo Tung SSSI and streams.  All unavoidable surplus excavated materials will be removed from the works area and delivered by truck on a daily basis.

·      Regular cleaning of the silt/grease traps will be carried out to ensure that they function properly at all times.

·      All excavated or filled surfaces which have the risk of erosion will always be protected from erosion.

·      Facilities for washing the wheels of vehicles before leaving the site will be provided.

·      No maintenance activities which may generate chemical wastes shall be undertaken in the water gathering grounds.

·      Any construction plant which causes pollution to catchwaters or catchment due to leakage of oil or fuel will be removed off site immediately.

·      Any soil contaminated with fuel leaked from plant will be removed off site and the voids arising from removal of contaminated soil will be replaced by suitable material to the approval of the Director of Water Supplies.

·      Temporary toilet facilities will be provided at a designated area located at the southern part of the Development Site.  Only portable toilets will be used and the toilets will be located at a substantial distance of approximately 320m away from the SSSI and the watercourse within the WGG (see Figure 6.3) and will also be surrounded by temporary interceptor drains and appropriately mounted.  A licensed contractor will be appointed to carry out appropriate disposal (by replacing the used portable chemical toilets and no on site cleansing to be allowed) and maintenance of these facilities. 

·      All mud and debris will be removed from any waterworks access roads and associated drainage systems.

·      For drainage and sewerage diversions within or affecting the WGG, the agreement of the Director of Water Supplies will be required prior to the commencement of the diversion works.

·      The use of pesticide, herbicides or fertilisers will not be allowed within the WGG without the prior approval from the Director of Water Supplies.

·      Disposal of the containers for fuel, oil and other chemicals or their residues within the WGG is strictly prohibited.  They must be disposed of properly outside the WGG.

·      Watertight and leak-proof sewers will be used in the WGG in order to prevent any leakage of sewage.

·      In the unlikely event of spillage of oil and fuel, oil spill control measures (eg application of oil booms in the streams) and decontamination kit will be deployed to confine the spreading.  Please note that oil will not be stored on site.

·      Construction site runoff will not be allowed to be discharged to the existing water courses within the WGG. 

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

General Construction Activities

·      Uncontrolled discharge of wastewater generated from concrete washing and vehicle washing;

·      Uncontrolled discharge of debris and rubbish such as packaging, construction waste and refuse etc; and

·      Spillages of liquid stored on-site, such as oil, diesel and solvents etc.

·      Fung Yuen stream (minimum Distance away from the Site Boundary = 70m)

·      Fung Yuen Valley SSSI (minimum Distance away from the Site Boundary = 11m)

·      Water Gathering Ground (majority of the SLT Road located within WGG)

 

WQO

General Construction Activities

·      Debris and rubbish generated on-site will be collected, handled and disposed of properly to avoid entering the nearby stormwater drains and open drainage channels.   The refuse collection point will be properly constructed with covers and will be bunded and drained to the sewerage system.

·      Open storm water drains and culverts near the works area will be covered to block the entrance of large debris and refuse. 

·      Earthworks will be scheduled in the dry season (November to March) only and construction sequenced accordingly.

Storage and Handling of Oil, Other Petroleum Products and Chemicals

·      Waste streams classifiable as chemical wastes will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.

·      All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas at the south of the Development Site.

·      The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.

·      Oil leakage or spillage will be contained and cleaned up immediately.  Waste oil should be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.  The Contractors will prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

No adverse residual impact anticipated after implementation of mitigation measures

Operation

·      Vehicles will enter the Nature Interpretation Centre, and a Multi-Cultural Education Retreat cum Columbarium along the improved Sha Lo Tung Road to the car park which will be situated at the western side of the Development Site.  The road runoff may contain minimal amounts of oil, grease and grit that may cause water quality impacts to the watercourses, if uncontrolled as in the existing condition. 

·      Fung Yuen stream (minimum Distance away from the Site Boundary = 70m)

·      Fung Yuen Valley SSSI (minimum Distance away from the Site Boundary = 11m)

·      Water Gathering Ground (majority of the SLT Road located within WGG)

·      using back of kerb filter drains and trapped roads gullies to Highways Department’s standard drawings H3110

WQO

Surface Runoff and Drainage

·      It has been demonstrated that the majority of contaminants in stormwater runoff are transported on sediments.  The runoff from the concrete paved areas including the improved Sha Lo Tung Road and car park will be collected using back of kerb filter drains and trapped roads gullies to Highways Department’s standard drawings H3110.  The gullies on the access road and car park within the Development Site will discharge to a piped drainage system linked by backdrop catchpits and collected in a pumping station located beneath the car park.  The collected run-off will then be pumped back over the crest of the access road and back into the structured highway drainage system that ultimately connects to the existing stormwater system in Ting Kok Road.

·      Any oil leakage or spillage will be contained and cleaned up immediately. 

·      Surface runoff will be diverted and discharged into the newly constructed stormwater drainage system along the improved Sha Lo Tung Road to Tai Po. 

Domestic Sewage Effluent

·      All sewers within the water gathering ground will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A - Drains and sewers in gathering grounds to be watertight.  Other requirements of WSD on the design and details of construction will be complied with through the circulation of drainage plans to the Building Authority.

·      Regular inspection and maintenance for the piping materials and joints of sewers will be conducted to ensure that leakage of sewage effluent from the pipeline does not occur. 

No adverse residual impact anticipated after implementation of mitigation measures

 

 

(II)        Development Site

Phase

Activities & Pollutants

Affected receivers & shortest distance from project boundary

Design changes to avoid & minimize impact

Impact against acceptable criteria

Mitigation measures

Residual impact & acceptability

Construction

Construction Runoff and Drainage

·      Runoff and erosion of exposed bare soil and earth, drainage channels and temporary stockpiles

·      Release of cement materials with rain wash

·      Wash water from dust suppression sprays and vehicle wheel washing facilities; and

·      Fuel, oil, and lubricant from maintenance of construction vehicles and mechanical equipment

 

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

·      Provision of a minimum additional 20 m wide Non-Building Buffer from the Sha Lo Tung SSSI – To avoid impacts to the Sha Lo Tung SSSI and natural stream, the proposed Master Plan will have a minimum 20 m wide additional buffer area from the existing SSSI zone to further safe guard the Sha Lo Tung Stream which is already protected by the existing general 30 m wide buffer areas (designated under the SSSI zone). 

·      Retrofitting Development to the Natural Topography Profile - Rather than one continuous form of development, the master plan proposes a number of separate structures to maximise retention of the existing natural topography and trees.  This results in a building footprint, access and earthworks which are contoured largely around the existing terrain profile.  By so doing, the extent of site formation and excavated materials is reduced and potential ecological impacts due to construction runoff on the SSSI zone are minimised. 

·      Locating Development back from the Sha Lo Tung SSSI and Stream - In addition to the proposed 20m buffer setback for development from the “SSSI” zone, building works along the southern edge of this setback are limited to that for the proposed parking area and the northern lower building of the Multi-Cultural Education Retreat.  Reducing the extent of development along the southern edge of the 20m wide buffer minimises the potential for accidental spillage of construction runoff and enables any such spillage to be directed to the southeast side, where the temporary storage tanks and drainage system are provided, not toward the SSSI stream.

WQO

·      Completion of Sha Lo Tung Road Improvement in advance.  Before any construction works are undertaken within the Development Site, the Sha Lo Tung Road should be improved with well designed drainage systems.  All of the surface run-off will be collected by the temporary drainage system with sufficient number of sandtraps (with sufficient capacity) and then discharged to the newly constructed stormwater drainage system along the improved Sha Lo Tung Road. 

·      Restrict Earthworks to the Dry Season.  Earthworks within the Development Site will only be undertaken during the dry season (November through March) in order to avoid the risk of construction runoff reaching ecological sensitive areas.  With the implementation of this measure, the risk from excessive construction runoff in the event of a heavy rainstorm can be reduced.  Major earthworks will be strictly prohibited during the wet season to minimise ecological risk to the Sha Lo Tung Valley. 

·      Adoption of Construction Sequences.  Given that the Development Site is elongated in shape and hilly in nature, the construction sequence should be well managed in order to limit the volume of surface runoff and treated effluent generated on-site, in particular during the wet season (works other than earthworks).  In order to limit the size of exposed areas and volume of the surface runoff, the construction activities will be carried out sequentially (phase by phase and sub-area to sub-area) rather than in parallel.  The site formation works in the northern part of the Development Area will be carried out at a later phase in order to avoid early exposure of the soil and hence to prevent muddy water from spilling over into the Sha Lo Tung SSSI and Sha Lo Tung Stream.  Such arrangement will assist in ensuring that construction runoff is not discharged into Sha Lo Tung Stream.

·      Provision of Temporary Drainage Channels.  Peripheral temporary drainage channels (special designed U-channel, like a “J” shape will be used) (see Figure 6.3) should be constructed along the lower side of all of the works areas within the Development Site prior to the commencement of the construction works.  All of the natural surface run-off will be collected by the temporary drainage system with a sufficient number of sandtraps and oil interceptors and then discharged to the newly constructed stormwater drainage system along Sha Lo Tung Road.  The drainage system capacity shall be designed for a 1:20 year storm event.  A sandtrap of large capacity is proposed to connect between the temporary drainage system within the Development Site and the newly constructed stormwater drains beneath Sha Lo Tung Road.  All surface runoff within the site will be continuously pumped to this sandtrap through a bendable water pipe (e.g. rubber pipe) before it is discharged from the site.  Due to the lower level at the surface water collection point within the Development Site, the surface water within the Site will be transferred to temporary storage tanks (after passing through sandtraps) in which a submersible pump will operate to continuously pump the surface runoff to the proposed sandtrap.  A spare submersible pump will be put in place in the storage tank for contingency purpose.

·      Provision of Silt Removal Facility. 

·      Separate Temporary Drainage System for Natural Runoff. 

·      Erection of Site Hoardings and Chain-link Fence with Seal.  Continuous site hoarding and chain-link fence will be erected along the temporary drainage system enclosing the entire Development Site (Figure 6.4).  The hoardings and chain-link fence should be firmly attached to the channel (any gaps are to be filled and cemented) in order to avoid any accidental spilling over the peripheral channel to the nearby streams.  All of the excessive runoff due to heavy rainfall or overflow of storage tanks/ sandtraps could be retained within the Site and avoid any accidental discharges into the Sha Lo Tung SSSI Stream.  The erection of the hoardings and chain-link fence will avoid any additional impacts to the existing trees.

·      Daily Inspection.  Green Power will provide a Conservation Specialist to stay on-site during the construction phase.  The Green Power representative will inspect the site daily to inspect of the sandtraps and channels and check the implementation and effectiveness of the runoff control measures.  The person will have the authority to stop the construction works should the implementation and effectiveness of the runoff control measures not be satisfactory.

·      Good site practices (refer to Section 6.6.4/ Construction Phase/ Good Site Practices)

 

For all works within the WGG, the Contractor will be required to comply with the practical measures as presented above (Improvement to Sha Lo Tung Road) to ensure that no pollution or siltation occurs to the catchment.

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

General Construction Activities

·      Uncontrolled discharge of wastewater generated from concrete washing and vehicle washing;

·      Uncontrolled discharge of debris and rubbish such as packaging, construction waste and refuse etc; and

·      Spillages of liquid stored on-site, such as oil, diesel and solvents etc.

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

 

 

General Construction Activities

·      Debris and rubbish generated on-site will be collected, handled and disposed of properly to avoid entering the nearby stormwater drains and open drainage channels.   The refuse collection point will be properly constructed with covers and will be bunded and drained to the sewerage system.

·      Open storm water drains and culverts near the works area will be covered to block the entrance of large debris and refuse. 

·      Earthworks will be scheduled in the dry season (November to March) only and construction sequenced accordingly.

Storage and Handling of Oil, Other Petroleum Products and Chemicals

·      Waste streams classifiable as chemical wastes will be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.

·      All fuel tanks and chemical storage areas will be provided with locks and be sited on paved areas at the south of the Development Site.

·      The storage areas will be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.

·      Oil leakage or spillage will be contained and cleaned up immediately.  Waste oil should be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.  The Contractors will prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

No adverse residual impact anticipated after implementation of mitigation measures

 

Sewage Effluent

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

No canteen facilities will be provided on-site. 

WQO

·      Appropriate sanitary facilities, such as portable chemical toilets, will be employed at the areas where the temporary connection is not feasible.  Portable chemical toilets should be deployed at a location as far away from the SSSI as possible and at least 320m away from Sha Lo Tung Stream.  The toilets should also be surrounded by temporary interceptor drains and appropriately mounted.  A licensed contractor will be appointed to carry out appropriate disposal (by replacing the used portable chemical toilets and no on site cleansing to be allowed) and maintenance of these facilities. 

 

Operation

·      Change in Hydrology and Flow Regime

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

l     The overall design philosophy for the stormwater drainage is to retain the rainfall-runoff response as close to the existing regime as possible to minimise impacts.

l     It should be noted that much of the drainage regimes within sub-catchment areas of the proposed development site are unaffected by the operational phase activities (Annex C).  Where the proposed development introduces changes to the existing run-off characteristics of sub-catchment areas within the Development Site, measures will be introduced to ensure that the run-off characteristics at exits from the site and into the existing Sha Lo Tung drainage system have nominal deviation from those currently in place in terms of volume and flow rate.

l     The approach to drainage impact mitigation measures has as an overriding objective to retain and maintain the existing quality and quantity of water flow into the Sha Lo Tung natural stream systems downstream of the Development Site. 

-

·      Refer to the design consideration.

·      Minimise the creation of impermeable surfaces, encouraging natural ground water recharge through soakaways/filter drains. 

·      Control run-off attenuation using swales, naturally lined channels, catchpits, and vortex grit separator with outlet control and undeveloped buffer zones. 

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

·      Surface Runoff and Drainage

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

l     Given the nature of the Project (provision of Nature Interpretation Centre, Multi-Cultural Education Retreat and Columbarium) and the activities undertaken within the Development Site (visitors mainly come for day visit to the Ecological Reserve and columbarium, and for training/ retreat, and the prohibition of burning of effigies and paper offerings, application of pesticides, insecticides and chemical fertilizers), there will be no pollution generated during the operation of Nature Interpretation Centre, and Multi-Cultural Education Retreat cum Columbarium.

l     The improved Sha Lo Tung Road and the new car park within the Development Site will be kerbed and will have back of kerb filter drains, trapped road gullys and a piped stormwater system. 

l     For non-vehicular development areas porous or semi permeable paved surfaces will be used in association with grassed swales and soakaways to attenuate run-off.  Terraced construction will control the rate of surface runoff with catchpits providing oxygenation and solids removal at the steps formed.  The run-off from the development non-vehicular zone will be routed to pass through vortex grit separator beneath the proposed car park to remove sediments associated with “first flush” flow. 

l     Should organic fertilizers be used for encouraging the growth of planted vegetation, prior approval from the AFCD, EPD and the Director of Water Supplies will be required. 

WQO

·      Refer to the design consideration.

·      Should organic fertilizers be used for encouraging the growth of planted vegetation, prior approval from the AFCD, EPD and the Director of Water Supplies will be required. 

For all works within the WGG, the Contractor will be required to comply with the following practical measures to ensure that no pollution or siltation occurs to the catchment:

·      No storage and discharge of flammable or toxic solvents, petroleum oil or tar and other toxic substances will be allowed within the WGG.

·      Regular cleaning of the silt/grease traps will be carried out to ensure that they function properly at all times.

·      No maintenance activities which may generate chemical wastes shall be undertaken in the water gathering grounds.

·      For drainage and sewerage diversions within or affecting the WGG, the agreement of the Director of Water Supplies will be required prior to the commencement of the diversion works.

·      Any chemicals to be used within the WGG will be subject to the approval of the Director of Water Supplies.

·      The use of pesticide, herbicides or fertilisers will not be allowed within the WGG without the prior approval from the Director of Water Supplies.

·      Disposal of the containers for fuel, oil and other chemicals or their residues within the WGG is strictly prohibited.  They must be disposed of properly outside the WGG.

·      Watertight and leak-proof sewers will be used in the WGG in order to prevent any leakage of sewage.

·      In the unlikely event of spillage of oil and fuel, oil spill control measures (eg application of oil booms in the streams) and decontamination kit will be deployed to confine the spreading.  Please note that oil will not be stored on site.

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

·      Sewage Effluent

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

·      No restaurant will be provided within the Development Site and no trade effluent discharge will be generated during the operational phase.

·      In order to enhance the protection to the Sha Lo Tung SSSI and Sha Lo Tung Stream, the sewage effluent generated from the Development Site will be discharged of at the Tai Po STW and there will be no facility for bypassing and overflowing the sewage effluent to those WSRs. 

·      The sewage generated from the site will be collected and temporarily stored in a storage (equalisation) tank (with capacity of 180 m3 and design similar to that used for fuel tank, ie with double layer).  The sewage tank should be fitted with a level indicator and a high level alarm system.  The detailed design of the sewage tank and the associated facilities will submit to WSD for approval prior the construction.  The sewage storage tank will be located at least 40 m away from Sha Lo Tung Stream. 

·      An approximately 2 km long 225 mm diameter twin sewerage rising mains will be installed from the Development Site running along Sha Lo Tung Road to the existing sewerage network at Ting Kok Road.  The sewage will be discharged regularly from the sewage storage tank to the Tai Po STW.

·      As a statutory requirement, the storage tank and all sewers within the WGGs will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A to ensure that they are watertight.  An adequately maintained duty pump with a 100% standby pumping capacity and alternative power supply is considered to be adequate to address pumping requirements in emergency situations.

 

WQO

·      To cater for this increase in generated sewage during the festival days, the sewage storage tank will be emptied before the festivals and immediately after the festivals.  Several portable toilets will also be erected at the pick up/ drop off point at the entrance of Sha Lo Tung Road (next to Ting Kok Road) during those days.  All of them will be surrounded by temporary intercept drains for contingency purpose.  The sewerage storage (equalisation) tank should also be emptied before and immediately after the festivals and should be maintained regularly.

·      The sewage will be discharged into the foul sewer.  The storage tank and all sewers within the water gathering ground will be designed and constructed to comply with the Buildings (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations (Cap 123I) reg. 47A - Drains and sewers in gathering grounds to be watertight.  Other requirements of WSD on the design and details of construction will be complied with through the circulation of drainage plans to the Building Authority.

·      Regular inspection and maintenance for the storage tanks, piping materials and joints of sewers will be conducted to ensure that leakage of sewage effluent from the tank and pipeline does not occur. 

·      If leakage or spillage of sewerage does occur, it should be contained and cleaned up promptly.

For all works within the WGG, the Contractor will be required to comply with the following practical measures to ensure that no pollution or siltation occurs to the catchment:

·      For drainage and sewerage diversions within or affecting the WGG, the agreement of the Director of Water Supplies will be required prior to the commencement of the diversion works.

·      Watertight and leak-proof sewers will be used in the WGG in order to prevent any leakage of sewage.

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

·      Sewage Effluent during Special Festivals

·      Sha Lo Tung SSSI and Stream (minimum Distance away from the actual works area = 20m)

·      Pat Sin Leng Country Park (Located next to Site)

·      Wet Abandoned Agricultural Land (next to the Site)

·      Water Gathering Ground (located within WGG)

·      The proposed storage tank of minimum size of 180 m3 is considerably sufficient (with a buffer of 3 days withholding time to cater for the situation if the pumping facilities malfunctioned, usually the public holidays during Ching Ming and Chung Yeung Festival not more than 3 consecutive days) to cater for the abrupt increase in generated sewage during festival days.

·      Any leakage from the storage tank due to overflow will be collected by channels around the tank. 

·      In case of leakage is occurred, the operator is recommended to close the permanent toilets until the leakage is cleared and the tank is repaired. 

·      100% stand-by pumping units will be put in place in each of the sewage storage tank for contingency purpose. 

WQO

Additional measures (apart from those listed above) include:

·      Approximately 3 portable toilets will be erected at the pick up/drop off point at the entrance of Sha Lo Tung Road (next to Ting Kok Road) as contingency measures. 

·      In order to provide a contingency against leakage from the toilets, they will be surrounded by temporary intercept drains. 

·      Replacement of these used toilets will be conducted in mid-day such that the number of persons using a portable toilet could be maximized and the leakage from the toilets could be minimized. 

·      Should the permanent sanitary facilities in the Development Site be closed due to malfunction or emergency maintenance, additional portable toilets can be arranged within a short period of time to cater the visitors, ie a total of 10 portable toilets can cater for a maximum of 380 x 10 x 2 = 7,600 visitors if cleaning exercise is performed. 

No adverse residual impact anticipated after implementation of proper design and mitigation measures

 

 

(III)       Ecological reserve (CMP, fencing at Lei Uk, temporary bridge, future village houses, etc)

Phase

Activities & Pollutants

 

Affected receivers & shortest distance from project boundary

Design changes to avoid & minimize impact

Impact against acceptable criteria

Mitigation measures

Residual impact & acceptability

Construction

·      Enhancement works will include installation of a drop bar at the road entrance to Sha Lo Tung Valley, footpath maintenance, weed removal, enrichment planting, marsh restoration, plantation, trail enhancement, and provision of alternative country park access

·      Within Sha Lo Tung Valley and Water Gathering Ground

·      Only require small scale and minor work activities

·      These works will be carried out with hand tools only. 

·      No major excavation works will be required within the Ecological Reserve

-

·      Refer to the design consideration

No adverse residual impact anticipated

 

·      Construction and removal of the temporary footbridge, fencing at Lei Uk and minor improvement of the existing new footpath to Lei Uk

·      Within Sha Lo Tung Valley and Water Gathering Ground

·      The temporary footbridge across Sha Lo Tung stream (within SLT SSSI)

·      Only require small scale and minor work activities

·      These works will be carried out with hand tools only. 

·      No major excavation works will be required within the Ecological Reserve

·      The temporary footbridge will be made mainly of wooden materials and spanned over the streambed to minimise the impacts to the stream. 

·      Prefabricated timber sections will be transported near the site and hand carried to the proposed site for assembling on site. 

·      The temporary footbridge will be removed manually following completion of the safety measures work. 

·      In addition, the existing damaged footpaths alongside the natural streams will be maintained and enhanced manually (natural stones but not concrete will be used).

WQO

·      Refer to the design consideration

No adverse residual impact anticipated

Operation

·      small scale and minor maintenance work

·      Within Sha Lo Tung Valley and Water Gathering Ground

-

-

-

No adverse residual impact anticipated