9 WATER QUALITY IMPACT ASSESSMENT
9.1 Introduction
9.1.1 This section provides an assessment of potential water quality impacts associated with the demolition of Existing Crematorium as well as construction and operation of the New Crematorium, in accordance with the Study Brief as well as Annexes 6 and 14 of the EIAO-TM.
9.2 Assessment Methodology
9.2.1 The assessment of potential impacts of land based construction, demolition and operation activities on water quality at identified Water Sensitive Receivers (WSRs) have been carried out in a qualitative manner. Consideration had been given to control potentially harmful impacts from the Project and mitigation measures are recommended to minimize the potential for discharges of pollutants to nearby receiving watercourses in vicinity of the Project site.
9.3 Baseline Condition
9.3.1 The location of the Project site is shown in Figure 2.1. Along the eastern side of the Project site, there is a stream approximately 20 m away. The Project site is located inland and falls within the Victoria Harbour (Phase Two) Water Control Zone (WCZ).
9.3.2 Based on the visual inspection during site visits, water in the streams appears to be clear during dry weather. A small amount of rubbish and debris was observed on the sides of stream. No river quality monitoring data is available from this stream.
9.3.3 According to EPD’s River Water Quality in Hong Kong in 2001, this stream should connect to Kai Tak Nullah as it is the major storm water channel in the South-East Kowloon, and its catchment includes San Po Kong, Diamond Hill, Tsz Wan Shan, Wan Shan, Wong Tai Sin, Wang Tau Hom, Lok Fu and Kowloon City. The Nullah also receives about 29,000 m3/day of treated secondary effluent from Sha Tin and Tai Po Sewage Treatment Works (STWs) under the Tolo Harbour Effluent Export Scheme.
9.3.4
The river water quality monitoring
station closest to the Project site is KN7 of Kai Tak Nullah. The location of KN7 is illustrated in Figure 9.1. Summary of the selected KN7 monitoring data for 2001 is given
in Table 9.1.
Table 9.1 Summary of Water Quality Monitoring Data for Kai Tak Nullah Monitoring Station KN7 in 2001
|
Parameter |
Unit |
Sampling Station |
|
|
Kai Tak Nullah –KN7 |
|||
|
WQOs |
Monitoring data |
||
|
Dissolved oxygen |
mg / L |
³ 4 |
7.4 (6.7-8.1) |
|
PH |
|
6.0-9.0 |
7.3 (6.8-7.9) |
|
Suspended solids (SS) |
mg / L |
£ 25 |
16 (6-75) |
|
5-day Biochemical Oxygen Demand (BOD5) |
mg / L |
£ 5 |
14 (8-30) |
|
Chemical Oxygen Demand (COD) |
mg / L |
£ 30 |
32 (11-42) |
|
Oil & Grease |
mg / L |
|
0.5 (0.5-2.0) |
|
Faecal Coliforms |
cfu / 100mL |
|
130,000 (58,000-530,000) |
|
E. coli |
cfu / 100mL |
£ 1,000 |
48,000 (20,000-420,000) |
|
Ammonia-nitrogen |
mg / L |
|
5.70 (0.34-14.00) |
|
Nitrate-nitrogen |
mg / L |
|
2.45 (1.40-4.40) |
|
Total Kjeldahl nitrogen, SP |
mg / L |
|
7.15 (1.40-16.00) |
|
Flow |
L / s |
|
No Measurement Taken |
Notes: (1) Data presented are in annual medians of monthly samples; exempt those from faecal
coliforms and E. coli which are in annual geometric means
(2) Figures in brackets are annual ranges
(3) cfu – colony forming unit
(4) SP – soluble and particulate fractions i.e. total value
(5) Shaded cells indicate non-compliance with Water Quality Objectives (WQOs)
9.3.5 According to the Water Quality Index published by EPD, the water quality at KN7 is generally ranked as fair. Based on the monitoring results, water in KN7 is characterized with high organic aggregates (as reflected by BOD5 and COD values) and E. coli counts, indicating its close linkage with sewerage.
9.3.6 As shown in Figure 9.2, the key water sensitive receivers (WSRs) during the construction and demolition phase are: (i) the stream on the eastern side of the Project site and (ii) storm drains near the Project site. During the operation phase, all the sewage should be connected to sewer and therefore the WSR will be the receiving water body of the relevant Preliminary Treatment Works (i.e. Victoria Harbour).
9.4 Potential Sources of Impacts
Construction and Demolition Phase
9.4.1 The major potential sources of impacts upon water quality from the construction and demolition works would include the following activities:
· Construction and demolition run-off and drainage
· General construction and demolition activities
· Sewage generated from on-site workforce
· Soil remediation procedures
9.4.2 The potential water quality impact during operation of the New Crematorium include:
· Wastewater generate from air pollution control system
· Sewage generated from staff and visitors as well as wastewater from general cleaning activities
9.4.3 Since the tendering process for the air pollution control system in the New Crematorium is yet to be commenced, the type and design of air pollution control system could not be confirmed at this stage. However, the air pollution control system in the New Crematorium would only adopt “dry” process (see Sections 4 and 7) and would not generate any effluent. Therefore the potential impact during operation phase will mainly be sewage generated from staff and visitors as well as wastewater from general cleaning activities.
9.5 Prediction and Evaluation of Environmental Impacts
Construction and Demolition Phase
Construction and Demolition Run-off and Drainage
9.5.1 Run-off and drainage from the construction and demolition activities may mainly contain increased loads of SS. The key potential sources of such water pollution will include:
· Run-off and erosion from site surfaces, drainage channels, earth working areas, construction and demolition stockpiles
· Release of any bentonite slurries and other grouting materials with construction and demolition run-off
· Wastewater from dust suppression sprays and wheel washing facilities
· Fuel, oil and lubricants from maintenance of on-site vehicles and equipment.
9.5.2 The construction and demolition run-off and drainage may cause physical, chemical and biological effects on the downstream water quality in the Kai Tak Nullah. Although the construction and demolition run-off is considered to be small (except during heavy rain storm), water quality impacts could be significant due to the sloping nature of the site and if the run-off and drainage are allowed to discharge directly into the receiving water body without any treatment.
9.5.3 It is important that the mitigation measures, as described in Section 9.6, should be strictly followed to prevent run-off and drainage water with high levels of SS from entering the nearby WSRs.
General Construction and Demolition Activities
9.5.4 General construction and demolition activities have the potential to cause water pollution as a result of stockpile, debris and rubbish, concrete dust and demolish materials entering the water body. This could result in increased SS in the water body or floating refuse at the stream nearby that reduce the aesthetic quality of the receiving water body. Spillage of chemicals, such as oil and diesel for construction and demolition equipment, could also result in water quality impacts if they enter the soil or nearby WSRs.
9.5.5 However, the effects on water quality from general construction and demolition activities are likely to be minimal, provided that the site boundaries are well maintained and good construction practices are observed to ensure that litter, fuels and solvents are managed, stored and handled properly (see Section 9.6).
Sewage Generated From On-site Workforce
9.5.6 Sewage will be generated through on-site workforce and thus have the potential to cause water pollution. Sewage is characterized by high levels of BOD5, ammonia and E. coli counts. Provided that adequate and proper sewage collection and disposal facilities are installed (see Section 9.6), no adverse water quality impact to nearby WSRs is anticipated.
Soil Remediation Activities
9.5.7 According to the CAR and RAP stipulated in Appendix C2, no ground water was detected during site investigation and no pretreatment is required for soil remediation (disposal of at landfill) at locations S3 and S5. Therefore the presence of ground water would be limited and no water quality impacts associated with dewatering in the soil remediation activities is expected. Provided the contractor implementing the mitigation measures described in Section 9.6, minimal water quality impact associating with soil excavation works of the currently identified soil remediaiton activities would be expected.
9.5.8 Nevertheless, with reference to the CAP and RAP, as further land contamination investigation (around CLP secondary substation during Phase I and locations S1 to S6 during Phase II) will be required before demolition of the Existing Crematorium, relevant water quality impact may need to be identified by the contractor prior to demolition, if further soil remediation is found to be necessary.
Transitional Stage
9.5.9 As “dry” process will be adopted in the air pollution control system of the New Crematorium, wastewater generated from the operation of new cremators is expected to be minimal. With administrative measures controlling no more than 6 cremators operating at any one time, no substantial increment in visitors is also expected. Therefore, no additional water quality impact is anticipated during the transitional stage between the operation of Existing Crematorium and commissioning of New Crematorium.
Cumulative Impacts
9.5.10 According to the information provided by Planning Department, Water Supplies Department and KCRC Shatin to Central Link Project Profile submitted under EIA Study Brief ESB-106/2002, two other projects will be implemented during the construction and demolition phase of this Project. They are (i) The Diamond Hill No. 2 Freshwater Service Reservoir, which is scheduled from 4 July 2002 to end of 2005, and (ii) the KCRC Shatin to Central Link, which is undergoing preliminary feasibility study and the construction is scheduled from 2004 to 2008.
9.5.11 With the proper implementation of the mitigation measures as specified in Section 9.6, it is expected that the extra water pollution impacts that this Project would add to those of the other two projects will not be significant.
Wastewater Generate from Air Pollution Control System
9.5.12 No effluent will be generated from the air pollution control system in the New Crematorium as ‘dry’ process would be adopted for the control system.
Sewage Generated from Staff and Visitors as well as Wastewater from General Cleaning Activities
9.5.13 All the sewage generated by visitors and workers as well as from cleaning activities in the New Crematorium will be connected to sewer and directed to Preliminary Treatment Works. Due to the unavailability of existing sewage generation rate of the Existing Crematorium, estimation is made based on the volume of water consumed. According to FEHD, average monthly water consumption of the Existing Crematorium from March 2002 to March 2003 was about 420 m3. Assuming the water consumption would be doubled in the New Crematorium due to the increase in the number of service halls from 2 to 4, the generation of sewage by the New Crematorium would be 840 m3 per month or 28 m3 per day. It is expected that the corresponding Preliminary Treatment Works should be able to deal with the increased sewage loading, and no adverse water quality impacts to receiving water body will be anticipated.
9.6 Mitigation of Adverse Environmental Impacts
Construction and Demolition Phase
9.6.1 To safeguard the water quality of the WSRs potentially affected by the Project works, the contractor should implement appropriate mitigation measures with reference to the Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94) published by EPD. Such measures are highlighted as follows.
Construction and Demolition Run-off and Drainage
9.6.2 Exposed soil areas should be minimized to reduce the potential for increased siltation, contamination of run-off and erosion. Any effluent discharge from the Project site is subject to the control of Water Pollution Control Ordinance (WPCO) discharge license and should be treated to meet the discharge standard set out in the relevant license. In addition, no site run-off should enter the stream on the eastern side of the Project site. Run-off impacts associated with the construction and demolition activities can be readily controlled through the use of appropriate mitigation measures, which include:
· Temporary ditches should be provided to facilitate run-off discharge into appropriate watercourses, via a silt retention pond
· Boundaries of earthworks should be marked and surrounded by dykes
· Open material storage stockpiles should be covered with tarpaulin or similar fabric to prevent material washing away
· Exposed soil areas should be minimized to reduce the potential for increased siltation and contamination of run-off
· Earthwork final surfaces should be well compacted and subsequent permanent work should be immediately performed
· Use of sediment traps wherever necessary
· Maintenance of drainage systems to prevent flooding and overflow
9.6.3 All temporary drainage pipes and culverts provided to facilitate run-off discharge should be adequately designed to facilitate rapid discharge of storm flows. All sediment traps should be regularly cleaned and maintained. The temporarily diverted drainage should be reinstated to its original condition, when the construction/demolition work is completed.
9.6.4 Sand and silt in wash water from wheel washing facilities should be settled out and removed from discharge into temporary drainage pipes or culverts. A section of the haul road between the wheel washing bay and the public road should be paved with backfall to prevent wash water or other site run-off from entering public road drains.
9.6.5 Oil interceptors should be provided in the drainage system downstream of any significant oil and grease sources. They should be regularly maintained to prevent the release of oil and grease into the storm water drainage system after accidental spillage. The inceptor should have a bypass to prevent flooding during periods of heavy rain, as specified in ProPECC PN 1/94.
General Construction and Demolition Activities
9.6.6 All the solid waste and chemical waste generated on site should be collected, handled and disposed of properly to avoid affecting the water quality of the nearby WSRs. The proper waste management measures are detailed in S.7.7.6 – S.7.7.8.
Sewage Generated from On-site Workforce
9.6.7 The sewage from construction work force is expected to be handled by portable chemical toilets if the existing toilets in the Project site are not adequate. Appropriate and adequate portable toilets should be provided by licensed contractors who will be responsible for appropriate disposal and maintenance of these facilities.
Soil Remediation Activities
9.6.8 Mitigation measures will need to be implemented during the currently identified soil remediation activities. If further land contamination investigation results (at CLP secondary substation during Phase I and at locations S1 to S6 during Phase II) confirm the needs for further soil remediation prior to demolition of the Existing Crematorium, relevant water quality mitigation measures (in addition to the current RAP) will need to be identified and implemented by the contractor. In addition, the mitigation measures recommended for minimizing water quality impacts for construction and demolition run-off and drainage as well as for general construction and demolition activities should also be adopted where applicable.
9.6.9 In order to avoid impacts on water quality during further remedial works, care will be taken to minimise the mobilisation of sediment during excavation and transport. Measures to be adopted will be based on the recommendations set out in Practice Note for Professional Persons ProPECC PN1/94 “Construction Site Drainage”. The results of the site investigation suggest that there is unlikely to be any requirement for dewatering of excavations, since groundwater was not encountered in any of the exploratory holes.
9.6.10 The contractor carrying out the remedial works will be required to submit a method statement detailing the measures to be taken to avoid water quality impacts. Typical measures would include:
Ÿ Carry out the works during the dry season (i.e. October to March) if possible
Ÿ Use bunds or perimeter drains to prevent run-off water entering excavations
Ÿ Sheet or otherwise cover excavations whenever rainstorms are expected to occur
Ÿ Minimise the requirements for stockpiling of material and ensure any stockpiles are covered
Ÿ Temporary on-site stockpiling of contaminated materials should be avoided, all excavated contaminated soils/materials should be disposed of on a daily basis
Ÿ Ensure that any discharges to storm drains pass through an appropriate silt trap
9.6.11 While the sewage generation in the New Crematorium (28 m3 per day) is estimated to be doubled that of the Existing Crematorium (14 m3 per day), the quantitative increase in sewage generation is not substantial. At this stage the actual location of public sewerage connection in the New Crematorium has not been fixed yet. However, Arch SD will, during detail design stage, ensure the public sewer where the connection will be made is capable of handling the extra sewage (i.e., 14 m3 per day) generated by the New Crematorium. Given that this extra quantity is not substantial, it is expected that the sewerage system of the corresponding Government Sewage Treatment Work will be able to accommodate the loading, and hence no adverse impacts to the receiving water body would result.
9.7 Conclusions