Pollution Control Study for Tuas Desalination and Power Plant Project

Transcription

1 ENVIRONMENTAL PROFESSIONALS for Tuas Desalination and Power Plant Project 70 MGD Desalination Design Build Own Operate (DBOO) Project Tuas Singapore, Natural Gas Power Plant and R & D Facility Prepared for TuasSpring Pte Ltd FINAL REPORT: 31 AUGUST 2011

2 Document quality information Document quality information for Tuas Desalination and Power Plant Project FINAL REPORT: 31 AUGUST 2011 ENVIRONMENTAL PROFESSIONALS Trade Hub 2118 Boon Lay Way # Singapore OFFICE TEL: (+65) MOBILE TEL: (+65) OFFICE FAX: (+65) envpro@starhub.net.sg WEB : Client Client s representative TuasSpring Pte Ltd Project Tuas Desalination and Power Plant Project No. EP-SIN-008 Authors Date Carsten Huttche Renan Orquiza Yurdinus Panji Lelean 31 AUGUST 2011 Approved by Carsten Huttche Revision Description Prepared by Checked by Date 2 Final YPL RO CH Final Draft YPL RO CH Keywords Tuas Desalination and Power Plant Final Report Classification Open Internal Proprietary Distribution Medium Copies 1. TuasSpring Digital 1 2. Enviro Pro Digital 1 ENVIRONMENTAL PROFESSIONALS Page i

3 Table of Contents TABLE OF CONTENTS APPENDICES LIST OF TABLES LIST OF FIGURES GLOSSARY TABLE OF CONTENTS Chapter 1 - INTRODUCTION Purpose of Study Description of the proposed industrial activities of the facility and site plan showing the layout of the process units and storage areas Site plan Layout of Process Units and Storage Areas Description of the processes and the main pollution problems expected including process flow diagrams Pre-Treatment Desalination Plant Reverse Osmosis - Desalination Plant Post-Treatment processes Desalination Plant Other processes Desalination Plant Power generating processes 18 Chapter 2 - AIR POLLUTION CONTROL Sources of air pollution and sources of odour Quality, rates and quantities of air emissions Assessment of the impacts of the air emissions, including odorous emissions using dispersion modelling or other acceptable methods Existing Ambient Air Conditions at Project Location Methodology for Air Dispersion Study Findings of Air Dispersion Study Measures to control air pollution and ensure compliance with emission standards and requirements in the Code of Practice on Pollution Control Measures to control and prevent odour nuisance 29 Chapter 3 - WATER POLLUTION Sources of trade effluent and pollutant Quality, rates and quantities of all wastewater streams and final trade effluent discharges Ambient seawater quality Property of discharged water Potential impact during construction stage Potential impact during operational stage Measures to ensure compliance with requirements in the Code of Practice Measure during construction stage Measure to minimize impacts during operations Measure to minimize water quality impacts during operations Monitoring programme Parameters monitored, type of monitoring equipment, frequency of monitoring 61 Chapter 4 - NOISE POLLUTION Sources of noise pollution Existing ambient noise 62 ii iv v vi vii ENVIRONMENTAL PROFESSIONALS Page ii

4 Table of Contents Estimates of noise levels emitted during construction Impacts of the noise emissions i.e. the noise levels at the receptors surrounding the plant especially residential housing Measures to control noise pollution and ensure compliance with noise emission standards and requirements in the Code of Practice on Pollution Control Monitoring programme Type of monitoring equipment/test carried out, frequency of monitoring 70 Chapter 5 - MANAGEMENT OF HAZARDOUS CHEMICALS Inventory and storage of hazardous chemicals Evaluation of the acute and chronic hazardous impacts of each hazardous chemical and/or by-products to the environment and public health Human Health Risk Environment Measures for safe storage and handling of hazardous substances to ensure compliance with requirements in the code of practice on Pollution Control and EPMA and to safeguard the environment and public health 75 Chemicals include: Caustic soda Policy and procedure to ensure all necessary measures to prevent accidents involving hazardous substances would be adopted Monitoring programme Type of monitoring equipment to detect any leakage of hazardous substances, frequency of checks 77 Chapter 6 - TOXIC WASTES MANAGEMENT Inventory and storage of toxic industrial wastes, including waste oil, solvent and other solid wastes Measures for safe storage and handling of toxic industrial wastes to ensure compliance with requirements in the code of Practice on pollution control System of checks on the safe storage and handling of toxic industrial wastes 78 Chapter 7 - RECYCLING AND RESOURCES CONSERVATION Study the feasibility and recommend measures to reduce, reuse and recycle wastes generated from the plants Water Study the feasibility and recommend measures to conserve energy and water use in the plant Energy 79 Chapter 8 - PREVENTION OF LAND CONTAMINATION Sources of potential land contamination Estimates of impacts from such sources on land contamination Measures to prevent land contamination Monitoring programme, if appropriate 82 Chapter 9 - CONCLUSION Whether the proposed measures in part 2 to 8 are adequate to insure compliance with statutory requirements and the Code of Practice on Pollution Control Air Water Noise Management of Hazardous Substances Toxic Waste Management Recycling and Resources Conservation Prevention of Land Contamination 85 ENVIRONMENTAL PROFESSIONALS Page iii

5 Table of Contents 9.2 Whether the proposed plants and their operations would pose any significant pollution impact on the environment and on developments in their vicinity, including odour, noise and dust nuisances Limitations 87 REFERENCES 88 APPENDICES Appendix A - Trade Effluent Regulations of Singapore Appendix B - NEA Emission Standard for Air Pollutant from Power Plant Built After 2008 Appendix C - National Ambient Air Quality Standard (NAAQS) of the United States Environmental Protection Agency (US-EPA) Appendix D - Evaluation of the Brine Discharge from the Proposed Tuas Desalination Plant Appendix E Appendix F - Air Dispersion Study - Evaluation of the Short Term Dredging Work at the Proposed Tuas 2nd Desalination Plant Appendix G - Seawater Sampling Report Appendix H - Construction Equipment Noise Emission Levels ENVIRONMENTAL PROFESSIONALS Page iv

6 List of Tables LIST OF TABLES Table 1.2-1: Desalination Water Flows... 2 Table 1.2-2: Potential operational scenarios of proposed plants... 3 Table 2.1-1: Identified sources of air pollution Table 2.1-2: Possible sources of odours and fugitive air emission from proposed plants Table 2.1-3: Fossil Fuel Emission Levels at Pounds per Billion Btu of Energy Input Table 2.2-1: The emission rate of air pollutants of natural gas power plant Table 2.3-1: Summary of potential health impact of air pollutants Table 2.3-2: The Limit of Emission Standard (NEA) and Ambient Standard (US-EPA) Table 2.3-3: Summary of Pollutant Standard Index of Singapore Table 2.3-4: Average ambient conditions of concerned pollutants in Singapore industrial area in Table 2.3-5: Maximum additional ground level concentrations Table 2.3-6: Maximum predicted increase of ground concentrations at border Table 2.3-7: Estimation of Normalized Total Ground Level Concentration Table 3.1-1: Identified sources of water pollution Table 3.2-1: Flow Rates and Characteristics of All Wastewater Stream Table 3.2-2: Average temperature of seawater in the vicinity of the site Table 3.2-3: Seawater surface temperature of adjacent to the proposed site Table 3.2-4: Average salinity of seawater in the vicinity of the site Table 3.2-5: Average DO in the vicinity of the site Table 3.2-6: Average ph in the vicinity of the site Table 3.2-7: Average turbidity in the vicinity of the site Table 3.2-8: Measured secchi depth around the site Table 3.2-9: Measured water quality at Intake and outfall of proposed plants Table : Seawater content for design condition of desalination plant Table : Considered scenario for the purpose of this study Table : Properties of discharged water for Scenario 1 and Table : Assumed Initial Boundary Condition Table : Test scenarios of outfall discharge (TDS and Temperature) Table 4.2-1: Summary of Ambient Noise at Proposed Site Table 4.2-2: Summary of ambient noise at Singspring perimeter Table 4.2-3: Summary of Ambient Noise at Senoko Perimeter Table 4.4-1: Boundary Noise Requirements Table 5.1-1: Chemicals used in proposed facilities Table 5.2-1: Human Health & Environmental Risks of Stored Chemicals Table 9.1-1: Summary of pollutive emissions from proposed plants ENVIRONMENTAL PROFESSIONALS Page v

7 List of Figures LIST OF FIGURES Figure 1.2-1: General Location Map of Proposed Plants... 5 Figure 1.2-2: Overall Site Layout of Proposed Facility... 9 Figure 1.3-1: Process flow of the proposed facilities Figure 1.3-2: Example of intake chamber configuration where intake head is located inside the chamber. Advised maximum intake velocity using this configuration is 30 cm/s; otherwise is10 cm/s Figure 2.3-1: Cross-border profile line and points of predicted concentrations Figure 2.3-2: Estimated ground level concentrations of PM 10 showing typical dispersion pattern of pollutants at ground during different seasons Figure 2.3-3: Spatial profile of additional PM 10 concentration at ground level towards the border 27 Figure 3.2-1: Location of EIA's water quality survey station Figure 3.2-2: Distribution of TSS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2- hour interval Scenario A (source TSS 200 ppt) Figure 3.2-3: Distribution of TSS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2- hour interval Scenario B (source TSS 400 ppt) Figure 3.2-4: A schematic sketch of the outfall pipe Figure 3.2-5: A schematic sketch of the outfall diffuser with discharge nozzle Figure 3.2-6: Figure 3.2-7: A diagrammatic representation of the core flow and the secondary flow as a result of flow entrainment in the receiving water body The trajectory at an inclined 60 degree angle with a terminal rise height (Zt) and return point (Xr). Zo indicates the height of the height of the discharge point above seafloor level. The shades in the plume are indicative of the brine dilution Figure 3.2-8: The dilution profile (minimum and averagetds concentration) Scenario Figure 3.2-9: The dilution profile (minimum and average TDS concentration) Scenario Figure : The dilution profile (minimum and average temperature) Q = MLD at 36.4 deg C Figure : Distribution of TDS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2- hour interval Scenario Figure : Distribution of TDS plume in West Johor Strait over 1 tidal cycle (12 hours), at 2- hour interval Scenario Figure : Distribution of thermal plume in West Johore Strait over 1 tidal cycle (12 hours), at 2-hour interval. The discharge rate is MLD Figure 4.2-1: Ambient Noise at Proposed Site. Point N1 & N5 are located at seaward corner, N2, N3, N4 are located at pedestrian lane at eastern border of the site. The bar indicates the range of recorded value; the dot indicates mean value Figure 4.2-2: Location of noise measurements at Tuas area Figure 4.2-3: Noise level at the perimeter of SingSpring Desalination Plant Figure 4.2-4: Location of noise measurements at Senoko Power Plant Area Figure 4.2-5: Representative noise level data collected at the perimeter of Senoko Power Plant. 68 ENVIRONMENTAL PROFESSIONALS Page vi

8 Glossary GLOSSARY AWQG : Ambient Water Quality Guideline Brine : Highly concentrated salt solution CIP : Cleaning in Place, cleaning of plant membranes in their installed location CPPC : Code of Practice on Pollution Control dba : decibel, units to express the level of noise to approximate the human ear s response to sound DBOO : Design, Build, Own and Operate EIA : Environmental Impact Assessment EPD : Environmental Protection Division of the NEA EPMA : Environmental Protection and Management Act GLC : Ground Level Concentration MGD : Million Gallon per Day MLD : Million Litre per Day MRL : Mean River Level: A tidal datum NAAQS : National Ambient Air Quality Standard of USEPA NEA : National Environmental Agency Permeate Water : Desalinated water produced by the RO process ph : (Logarithmic) concentration of hydrogen ions PM10 : Respirable particulate matters at size of maximum 10 microns (μm) ppt : parts per thousand PSU : Practical Salinity Unit, approximately equal to part per thousand (ppt) PUB : Public Utilities Board RIAM : Rapid Integrated Assessment Matrix RO : Reverse Osmosis TDS : Total Dissolved Solids TSS : Total Suspended Solids UF : Ultra-filtration, removal of fine particles at size of microns USEPA : United States Environmental Protection Agency ENVIRONMENTAL PROFESSIONALS Page vii

9 Chapter 1 - Introduction Chapter 1 - INTRODUCTION To secure Singapore s future demand of water, the country s Four National Taps Strategy lists desalination of seawater as a key strategy. By 2013, 30% of the total water demand will be met by desalinated water. The proposed 70 MGD TuasSpring desalination plant, developed by Hyflux Ltd as a DBOO project, will contribute to this objective and to the overall sustainable water supply strategy for Singapore. TuasSpring Pte Ltd is a fully owned subsidiary of Hyflux Ltd, a water treatment company with operations in Singapore, China and Malaysia. It s wholly owned subsidiary Tuaspring Pte Ltd is developing the combined 70 MGD RO desalination plant and a 530 MW natural gas power plant at Tuas South Avenue 3. The desalination plant is to produce potable water from seawater using the reverse osmosis (RO) process for supply to the Public Utilities Board (PUB). The power plant will, amongst others, support the operation of the desalination plant by providing electrical power and the cooling water. 1.1 Purpose of Study The above mentioned project requires a (PCS) as provided under Section 36 of the Environmental Protection and Management Act (EPMA) and approval of the PCS by National Environmental Agency (NEA) is part of the permitting process. Specifically the PCS will: Identify sources of emission of air pollutants, discharge of trade effluent, generation of waste and emission of noise. Quantify and evaluate the impacts of such pollutive emissions. Recommend the measures to be incorporated in the design and operation of the plant to reduce the pollutive emissions to acceptable levels that would not pose nuisance or harm to the people and to the environment. Recommend a monitoring program to review the effectiveness of implemented mitigation measures on regular basis. To carry out the, TuasSpring Pte Ltd has appointed Environmental Professionals (ENVIRO PRO) as the project s environmental consultant to conduct the necessary pollution control study. Enviro Pro assisted in determining the proposed plant s anticipated pollution load once operational and describing appropriate pollution abatement technologies such that the facility is in compliance with stipulated standards for air emissions, trade effluent discharge, noise emission, waste disposal, etc. Where required, application for a waiver from these standards is considered. ENVIRONMENTAL PROFESSIONALS Page 1

10 Chapter 1 - Introduction The consultant carried out site investigations in 2010 and 2011 to assess the submitted plans in relation to the site. Computer modelling techniques were used to predict the dilution of discharge components into the sea and to estimate the dispersion of air pollutants released by the proposed power plant. It is important to highlight that PUB has conducted an initial Environmental Impact Assessment (EIA) of the proposed activities in 2010, with the technical EIA report submitted by PUB s consultant DHI International in January The EIA study had addressed potential environmental impacts primarily attributed to the increase salinity and temperature of the discharge trade effluent into seawater. At the outfall diffuser, the salinity is estimated to be at 80% higher than the intake seawater; the temperature is expected to be higher than the receiving water bodies within the mixing zone, beyond which ambient condition prevails. Minor disturbances are predicted to happen during construction phase due to various construction activities in the site, inland and offshore. The study, which uses Rapid Integrated Assessment Matrix (RIAM) approach, also classifies the impact of proposed activities as either Slight or No Impact (PUB, 2011). 1.2 Description of the proposed industrial activities of the facility and site plan showing the layout of the process units and storage areas The proposed plant will consist of two components: (i) the desalination of seawater to obtain potable water and; (ii) generation of power to be used by the desalination plant and supply to the national electricity grid. The desalination plant is designed to operate for 25 years using reverse osmosis technology with a warranted capacity of 318,500 m 3 /d (nominally 70 MGD). The power plant will generate electric power of approximately 530 MW. Due to site constrains, the likely type of power plant is a natural gas or a combination of natural gas and fuel oil firing plant. The power plant is expected to use the seawater as cooling water. Flow characteristics of water in the proposed desalination facilities are shown on Table Table 1.2-1: Desalination Water Flows Service Flow rate (MLD) Remarks Desalination Plant intake 828 Under maximum design flow (warranted capacity) Treated water flow Warranted treated water capacity from the plant Brine discharge From Siemens Plant Performance Estimation Program job ID Source: Hyflux design, 2011 ENVIRONMENTAL PROFESSIONALS Page 2

11 Chapter 1 - Introduction To achieve a greater efficiency, integration of the two plants could be realized by several options: (i) use of discharged elevated temperature cooling water from the power plant as source water for the desalination plant; (ii) use of discharged water from power plant as blending water to reduce salinity of rejected brine from desalination plant and; (iii) share of facilities such as intake and outfall structures. Notwithstanding the possible integration, the design will allow each plant to operate independently. This requirement sets out several potential operational modes of both plants (Table 1.2-2). Table 1.2-2: Potential operational scenarios of proposed plants Scenario Plant operation Comments 1 Power Plant in service at 100% load Desalination Plant not in service Outfall temperature higher than incoming seawater temperature 2 Power Plant in service at 100% load Desalination Plant in service at 100% output 3 Power Plant in service at 100% load Desalination Plant in service at 10% output 4 Power Plant not in service Desalination Plant in service at 100% output 5 Power Plant not in service Desalination Plant in service at 10% output 6 Power Plant not in service Desalination Plant in service at 100% output Product water being discharged to the outfall Outfall temperature higher than incoming seawater temperature Outfall temperature higher than incoming seawater temperature During power plant outage for periodic maintenance Outfall temperature same as incoming seawater temperature During power plant outage for periodic maintenance Outfall temperature same as incoming seawater temperature This could be expected at start up during the performance trials. Power Station not available to operate during this time Outfall temperature same as incoming seawater temperature Source: Hyflux design scenario, Site plan The proposed facility will be located at Tuas South Avenue 3. It will occupy 14 hectares of reclaimed land, which is allocated for utility development under the URA Master Plan. The international marine border between Singapore and Malaysia lies in the Western Strait of Johor approximately 850m at west of the site. Figure shows the general site location of the proposed facilities. ENVIRONMENTAL PROFESSIONALS Page 3

12 Chapter 1 - Introduction The Western Strait of Johor is a relatively narrow body of water, approximately 900m wide in the north at the Singapore-Malaysia Causeway, extending to approximately 8 km wide at the northern tip of Tuas Peninsula. The western entrance of the straits is used for shipping, mainly for serving the Port of Tanjung Pelepas (PTP) in Johor, Malaysia. which is located within 5 km distance west of the site. The Tanjung Piai Ramsar 1 Site of Malaysia is located to the south west of the site at approximately 13 km and is designated as an internationally important wetland site. Other industries operate adjacent to the site. This includes shipping, manufacturing and Singapore s first desalination plant (SingSpring), south of the site. Even further south, the Tuas Seaport and Tuas Incineration Plant are located. 1 The Ramsar Convention is the Convention on Wetlands of International Importance for the conservation and sustainable utilization of wetland. It is named after the town of Ramsar in Iran where the treaty was developed and adopted on February 2, The Ramsar List of Wetlands of International Importance is known as Ramsar sites. ENVIRONMENTAL PROFESSIONALS Page 4

13 Chapter 1 - Introduction Figure 1.2-1: General Location Map of Proposed Plants (Source: EIA Report, 2011) ENVIRONMENTAL PROFESSIONALS Page 5

14 Chapter 1 - Introduction Layout of Process Units and Storage Areas The site, approximately 400mx400m in square, will be separated by internal roadways into several distinct sectors: three sectors for the desalination plant, one for the power plant and one for PUB s R&D facility. The sectors for the desalination plant include the pre-treatment, post-treatment, and UF-RO zone. The pre-treatment zone will be located at the northern end of the site, adjacent to the sea. At the southern end of the site, likewise adjacent to the sea, the UF and RO facilities occupy a large section of the site. The post-treatment facilities are located east of the UF-RO zone and are adjacent to Tuas South Avenue 3. The power plant will be located east of the pre-treatment zone. The R&D facility occupies space at the south-eastern corner of the site, facing Tuas South Avenue 3. Major project components and their locations are listed below. For more details, refer to Figure Pre-treatment Zone The pre-treatment zone is located at northern end of the site and adjacent to the sea. The zone consists of the following equipment and structures: Seawater intake screening and pumping station, which is located at the most northern tip adjacent to the sea and is linked to the seawater intake pipe; UF Feed Auto-strainers; Electro-chlorination facilities that contains NaOCl Tank; Intake water collection tank; Electrical Switchroom area; As part of the pre-treatment zone, the UF facilities consist of the following equipment and structures: RO Feed pumps UF Backwash tank UF Filtered water and Backwash tank UF Buildings UF CIP tanks Transformer room Electrical switchroom Chemical storage area Intermediate sump ENVIRONMENTAL PROFESSIONALS Page 6

15 Chapter 1 - Introduction Reverse Osmosis (RO) Zone The RO facilities consist of the following equipment and structures: RO/LPRO CIP tank and pumps LPRO feed RO Buildings LPRO system LPRO feed/flushing tank RO flush pump LPRO feed pump Electrical switchroom Air compressor Power transformer room Neutralization pit Attenuation tank The administration building is located between the UF building and RO building at the seaward side Post-treatment Zone The post-treatment zone consists of the following equipment and structures: Treated water tank volume size 27,000 m 3 Treated water pumping station Chlorine contact tank Carbon dioxide storage area Lime storage area Electrical switchroom Power substation Canteen, parking lots and guardhouse will be located within this zone ENVIRONMENTAL PROFESSIONALS Page 7

16 Chapter 1 - Introduction Power Plant Zone The Power plant zone consists of the following equipment and structures: Hydrogen storage area NG Booster and conditioning station Turbine house Demin water tank Switchgear facility Fuel oil storage facility Oil waste water facility ENVIRONMENTAL PROFESSIONALS Page 8

17 Chapter 1 - Introduction Figure 1.2-2: Overall Site Layout of Proposed Facility (Source: Hyflux design) ENVIRONMENTAL PROFESSIONALS Page 9

18 Chapter 1 - Introduction 1.3 Description of the processes and the main pollution problems expected including process flow diagrams The desalination process can be separated into 3 main stages, namely pre-treatment, Reverse Osmosis (RO) process and post-treatment. The proposed treatment process is similar to other existing RO plants in California and Florida. 12 Similar plants in other countries include the Dheklia Plant at Larnaca in Cyprus 3 and the Boujdour desalination plant in Morocco 4. Raw seawater is first abstracted from the sea through the shoreline intake pipe located 50m perpendicular to the shoreline at -2mCD depth, situated at the most northern point of the proposed plant. The raw seawater is then pre-treated to prepare the water for the RO process. The main objective of the pre-treatment process is to minimize membrane fouling on the RO plant, which is achieved through the process of screening, chlorination and ultra-filtration (UF). Once the seawater enters the pre-treatment stage, a biocide, chlorine, is added to kill microorganisms such as algae. The chlorinated water is then fed into self-cleaning strainer for removal of solids larger than 200 micron to avoid damage of UF membranes due to unnecessary wear. The screened water then flows to the ultra-filtration process to remove colloidal particles remaining in water. The use of an ultra-filtration system eliminates the requirement for coagulants, which are commonly used in a conventional pre-treatment process. The UF membrane is also able to filter oil contaminated seawater to a certain extent. During the filtration process, solids are retained by the membrane. These solids must be periodically removed via backwashing to maintain system performance. The waste water of this process is discharged through the offshore outfall. Downstream of the UF system, sodium bisulphite and caustic soda are added to remove chlorine and aid in boron reduction downstream, respectively. The last pre-treatment process stage is the injection of a scale inhibitor to reduce scale formation within the RO units. The filtered water produced by the UF trains is stored in the closed filtered water/backwash tank. 1 California Coastal Commission, Seawater desalination in California, (1993) 2 P.J. Malaxos & O.J. Morin, Surface Water Discharge of Reverse Osmosis Concentrates, (1990) Desalination Vol. 78, pp O. V. Sallangos, E. Kantilaftis, Operating experience of the Dhekelia seawater desalination plant, Desalination Vol 139 (2001) pp M. Hafsi, Analysis of Boujdour desalination plant performance, Desalination Vol 134 (2001) pp ENVIRONMENTAL PROFESSIONALS Page 10

19 Chapter 1 - Introduction The RO process consists of two units: the high-pressure Seawater Reverse Osmosis (SWRO) unit and the Lower Pressure Reverse Osmosis (LPRO) unit. The filtered seawater is pumped from the filtered water tank by high pressure pumps to SWRO unit. Water is forced through micro pores of the membranes, leaving behind a highly saline and pressurised brine reject stream. Up to 45% of the input seawater can be recovered as freshwater in this unit. The high-energy brine reject is then allowed to flow through isobaric pressure exchangers to recover hydraulic energy. The recovered energies are then transferred to supplement pump pressure in the LPRO units. The isobaric device is used due to its high recovery efficiency of up to 98%, less maintenance and easy operation. SWRO permeate will flow from SWRO system into LPRO feed tank, which acts as buffer storage; some portion will bypass the LPRO feed tank and flow directly into the chlorine contact tank. The water at LPRO feed tank is then pumped into LPRO unit; 90% of which will be converted to permeate with 10% being the waste stream (brine). The brine reject from the SWRO is returned to the sea through an outfall pipeline. The brine reject from the LPRO is recycled back to be used as backwash water to clean the UF units in the pre-treatment stage and is stored in UF CIP tank. Clean water from the reverse osmosis (RO) process is then pumped to the post-treatment stage for further treatment to produce potable water. Limewater and carbon dioxide are added into the potable water stream to re-mineralise the water to prevent corrosion of pipes downstream. Following this, chlorine and ammonia is dosed as a disinfectant to prevent downstream contamination. Fluoride is also dosed by adding silicofluoride as an additive for hardening tooth enamel. The end product is then pumped to a water storage tank. Schematic flow of the above-mentioned processes is shown on Figure ENVIRONMENTAL PROFESSIONALS Page 11

20 Chapter 1 - Introduction Figure 1.3-1: Process flow of the proposed facilities (Source: Hyflux design) ENVIRONMENTAL PROFESSIONALS Page 12

21 Chapter 1 - Introduction Pre-Treatment Desalination Plant Raw seawater, in most instances, requires pre-treatment to remove particulates in order to prolong the membrane s lifespans. Water is pre-treated so that salt precipitation or microbial growth does not occur on the membranes. The pre-treatment process consists of the followings. Seawater abstraction and Pre-screening Pre-chlorination Screening De-chlorination Ultra-Filtration Anti-scalant injection Seawater abstraction and pre-screening Withdrawal of seawater will be done by submerged intake system. The water will be drawn into the intake chamber located at approximately 50 meter offshore via 2 pipelines. Downstream of the flow, the pipes will be connected to three channels, each of which will be fitted with Coarse Bar Screens (20 mm of aperture openings), Fine Screens (2 mm of aperture openings) and a dedicated pump. All screens will be able to run in automatic mode based on differential levels on the upstream and downstream. The finer screen will also be able to remove debris accumulated overtime by activating its self-cleaning mechanism. Two slots for stop logs will be put at each channel, one at upstream of coarse screen and one at downstream of fine screens. The channels are designed to take full intake load of the plant intake needs. The channels will run at 33% capacity during normal operation. During periodical maintenance, flow to a channel under maintenance will be halted by the stop log, leaving the remaining two being operated at 50% capacity. Several potential problems arise from this process: entrainment of larger fish or other marine life due to high velocity of intake water at intake well screen of intake chamber; entrapment of juvenile fish and smaller organism upstream of coarse bar screen or fine screens, depending on the size of organism. EIA study (PUB, 2011) advises the maximum velocity of 30 cm/s if intake chamber is used; otherwise the velocity shall be less than 10 cm/s. An example of an advised configuration is shown on Figure ENVIRONMENTAL PROFESSIONALS Page 13

22 Chapter 1 - Introduction Figure 1.3-2: Example of intake chamber configuration where intake head is located inside the chamber. Advised maximum intake velocity using this configuration is 30 cm/s; otherwise is10 cm/s. Source: EIA study (PUB, 2001 page 55) Pre-chlorination Periodic or continuous dosing of liquid Sodium Hypochlorite to the influent seawater is carried out at the seawater intake screen to reduce the growth of algae and other microorganisms. This process is required to protect the UF and RO membranes from biological fouling. It is important to note that there will be no chlorine gas stored on site Screening of solids Screening for solids bigger than 200 micron is performed by self-cleaning strainers located upstream of UF system. These strainers protect the UF membrane from unnecessary wear. A pressure switch senses the pressure differential across the strainer and triggers the self-cleaning process when the pre-set differential value is reached. This process will take place downstream of intake tank. As such, the filtered solids and flushing water may contain chlorine that could cause potential pollution problem if directly discharged through offshore outfall. The rejected water from this process needs to undergo de-chlorination before being released through the offshore outfall De-chlorination Sodium bisulphite is added to remove any residual chlorine as the UF, SWRO and LPRO membranes cannot tolerate chlorine. This also prevents the release of chlorinated water from the RO reject brine streams into the environment. ENVIRONMENTAL PROFESSIONALS Page 14

23 Chapter 1 - Introduction Sodium bisulphite is a very reactive chemical that reacts with chlorine and oxygen, with a preference to chlorine. In the event that there is excess sodium bisulphite without the presence of chlorine, dissolved oxygen level in the water may be reduced. However, according to process design, no significant de-oxygenation is expected as a result of the addition of sodium bisulphite. Therefore, no negative net effect in dissolved oxygen levels at the discharge is expected Ultrafiltration Ultrafiltration (UF) is provided to filter the screened seawater to remove colloidal particles remaining in solution and produce filtrate with low SDI and turbidity by using membrane technologies similar to those membranes of RO. As such, the use of this system eliminates the dosing of coagulant, which is commonly used in conventional pre-treatment process. The system is also able to filter seawater contaminated with oil/hydrocarbon to a certain degree. This feature is particularly important during a minor oil spill event at sea. During the filtration process, solids will be retained by the membrane. When accumulation of solids upstream of the membrane exceeds certain pre-set threshold, backwashing will be activated to remove the solids. The automated backwash sequences will be synchronized with the introduction of air scouring to improve the effectiveness of backwashing. This backwashing process will be carried out periodically every minutes, the backwash stream will be discharged directly to the outfall. Complementing the automatic backwash process, continuous UF performance will require regular maintenance cleaning (MC) of the membrane trains. The MC will occur at 5 to 7 days intervals based on the fouling characteristics of the water, using either an alkaline chlorine solution or an acid solution with preferences towards the alkaline chlorine solution. After several weeks in service, the trans-membrane pressure (TMP) may not be able to be controlled by the backwashing and maintenance cleaning alone. At this stage, a Recovery Cleaning-In-Place (CIP) will be effective using an acid CIP, which subsequently followed by a sodium hypochlorite CIP. At the end of the CIP, the train will return to service. Used CIP solutions will be directed to the neutralization tank for pre-discharge treatment. The UF process generates wastewater attributed to backwashing, maintenance MC and CIP. While there is potential hazard presented by the use of chemicals in the process, the risk of it will be minimized at the neutralization tank where used solutions will be treated prior to final discharge through offshore outfall. ENVIRONMENTAL PROFESSIONALS Page 15

24 Chapter 1 - Introduction Anti-scalant injection As water passes through the membrane, the increase concentration of the remaining ions causes the precipitation of inorganic salts including those of calcium carbonate, calcium sulphate, calcium fluoride and barium sulphate. If precipitation is not controlled, membrane performance will quickly decline. Introduction of an anti-scalant will inhibit the precipitation and therefore will extend the membrane lifespan. A tank is provided to store the anti-scalant solution and is continuously dosed into the filtered seawater upstream of the SWRO unit. The organic polyphosphonate anti-scalant is not toxic. Though the chemical composition of the antiscalant is not available in detail, its two main components are water and organic phosphonate. Its estimated discharge concentration is 1.5 mg/l at SWRO feed and 3 mg/l at LPRO Reverse Osmosis - Desalination Plant The proposed RO facilities will perform 2 stages of RO process, first process at SWRO which uses high pressure water and the second at LPRO using lower pressure water SWRO process The pressurized water will be split into 2 streams, a low pressure permeate (product) stream and a high pressure waste or brine stream by forcing the process water through membranes. The major energy requirement is for operating pumps. Process water is pressurized to overcome the natural osmotic pressure of ambient seawater (reverse osmosis). As the pressurized process water flows through the membrane, the salt is removed and permeate is produced as potable water. Of the feed water to the SWRO trains, 45% will be converted to permeate; 55% being waste water (brine). Primary desalination of the seawater will occur in this SWRO system LPRO process Product water quality is improved by adding a second pass of membranes, whereby 72% permeate of SWRO being fed to the LPRO unit consisting of a 2-stage reverse osmosis system. Of the feed water to the LPRO trains, 90% will be converted to permeate; 10% being waste water (brine). To achieve the required standard of potable water, the final product water will consist of 30% SWRO permeate and 70% LPRO permeate. The LPRO brine will be recycled into filtered sea water tank for mixing with the filtered seawater which in turn being fed into SWRO trains. ENVIRONMENTAL PROFESSIONALS Page 16

25 Chapter 1 - Introduction The SWRO reject brine is the main wastewater stream from the proposed plant, totalling up to MLD under full plant capacity. The RO brine may cause an increase in seawater salinity in close vicinity of the discharge point. To mitigate the expected pollution problems, a discharge outfall will transport the brine 120m offshore to a water depth of approximately 8m. A diffuser port with 12 horizontally directed nozzles will be used to induce initial mixing of the discharged brine with the ambient seawater. Modelling studies conducted have shown favourable mixing of brine discharge with ambient seawater given a sufficient operating flowrate. Results from computer simulation suggest that the discharge brine plume is confined to a relatively small area of about 70 m from the outfall location. For more details, refer to Chapter 3 on water pollution. A waiver will be requested by NEA for the discharge concentration of Boron, Iron and TSS Post-Treatment processes Desalination Plant Post treatment is required to make the water potable and non-corrosive. The processes involved in post treatment include limewater dosing, chloramination and fluoride dosing. Limewater dosing consists of the addition of limewater (calcium carbonate), followed by carbon dioxide for remineralization, ph correction and to generate calcium bicarbonate. Calcium bicarbonate acts as an inhibitor to prevent corrosion on the piping and storage systems for the potable water. During chloramination process, chlorine is injected, followed immediately by ammonium sulphate. Adequate mixing and contact time is provided. As a result, chloramines, a mild disinfectant and effective bactericide are formed. Fluoride dosing is carried out in order to harden tooth enamel by the addition of sodium silicofluoride. No wastewater stream is expected from this stage Other processes Desalination Plant Membrane cleaning The membranes of the RO units have to be cleaned approximately 5 times per year, to remove scales and other bio-fouling that may adhere to the membranes. The cleaning chemicals used are dilute alkaline and acid aqueous solutions and phosphate based solutions. Wastewater generated from the cleaning process is then pumped into a neutralization tank for ph adjustment prior to discharge into the sea, together with other wastewater streams. ENVIRONMENTAL PROFESSIONALS Page 17

26 Chapter 1 - Introduction This waste stream cause a temporarily increase in salinity of the final effluent discharge. Short-term elevated levels of polyphosphate may occur in the discharge during the cleaning process. However, these are temporary events linked to the frequencies of membrane cleaning. The hydrolysis product of polyphosphate is orthophosphate, which is a macronutrient used in biological processing. Overall, it is important to realize that, in the absence of corrosion products and with good chemical control and use of non-toxic additives, desalination processes mainly redistribute (concentrate) which is present in the raw water Power generating processes During the course of this study, the design process of the proposed power plant was still on-going. However, it was understood that the plant will run either solely on natural gas or a combination of natural gas and diesel fuel. Although natural gas remains the cleanest amongst all fossil fuels, gaseous emissions containing several pollutants into the atmosphere are expected Potential pollution problems expected Emissions of air pollutants: An air dispersion study was conducted to estimate the concentrations of the following pollutants: Nitrogen Oxide (NO), Carbon Monoxide (CO), Sulfur Dioxide (SO 2), Carbon Dioxide (CO 2) and Respirable Particulate Matters (PM10). Discharge of elevated temperature cooling water at the shoreline outlet and at the offshore outfall: The main concern with regards to the power plant impacts on water is the potential elevated ambient temperature of the receiving water body caused by the cooling water discharges, both at offshore outfall and the shoreline outlet. PUB s EIA study estimated the maximum excess temperature to be 5.8 C at the diffuser port. Detailed hydrodynamic modelling developed during the EIA study suggests that turbulence mixing, dilution and dispersion within the mixing zone will rapidly reduce the temperature back to ambient level, so that at the boundary of the mixing zone the mean temperature should be no more than 1 C above ambient to comply with the recommended Ambient Water Quality Guidelines 1 (PUB, 2011 page 83). 1 The Ambient Water Quality Guidelines (AWQG) sets out the limit of water discharge parameter. It is developed during the EIA study of the proposed plants to preserve high water quality in the ambient marine environment and is specific to regional waters within Singapore. For more details, see section of EIA final report (PUB, 2011) ENVIRONMENTAL PROFESSIONALS Page 18

27 Chapter 2 Air Pollution Control Chapter 2 - AIR POLLUTION CONTROL 2.1 Sources of air pollution and sources of odour The proposed industrial development contains of several potential pollution sources, which emit air pollutants during different operational modes at variable quantities. The main pollutant source will be the power plant. The identified potential pollution sources are presented in Table Table 2.1-1: Identified sources of air pollution Identified source Power Plant Back up generator Description The process to generate the electricity power is expected to emit air pollutants which are to be released through a 60m high stack. The dispersion of pollutants is investigated in this study; findings are presented on Section2.3.3, detail of the dispersion model is given in Appendix E. The activated backup generator is expected to emit air pollutants. Given its role as the back up generator, the operational frequency is difficult to assess and assumed to be low. Therefore, it was not considered for air dispersion modelling. No continuous air emissions are expected from the proposed desalination plant during normal operations. However, there may be fugitive air emissions in event of accidental leakages from chemical storage tanks; some of which will introduce a pungent smell. Identified possible sources of odour are given at Table Table 2.1-2: Possible sources of odours and fugitive air emission from proposed plants Identified source Gas Description Storage tank CO 2 The leakage of Carbon Dioxide storage tank could introduce fugitive emission of such greenhouse gas. Storage tank Cl 2 The leakage of Chlorine gas will introduce pungent smell of bleach. Chlorine also a toxic gas which could cause damage to respiratory system. Combustion process Combustion process SO 2 H 2S Sulphur dioxide is a colourless gas, about 2.5 times as heavy as air, with a suffocating smell, faint sweetish odour. It is a by product of combustion process at power plant and generator burning fuel. Power plant running of natural gas is estimated to have a low SO 2 pollutant. Its odour threshold is 2.7 ppm Hydrogen Sulphide is a highly toxic, flammable and colourless gas associated with pungent smell which resemble those of rotten eggs. Its odour threshold is approximately at 0.2 ppt. ENVIRONMENTAL PROFESSIONALS Page 19

28 Chapter 2 Air Pollution Control It is important to note that the proposed power plant is designed to run on natural gas which is the cleanest of all fossil fuel, as shown in the data comparison chart of the U.S. Environmental Protection Agency as of year 2010 at Table Table 2.1-3: Fossil Fuel Emission Levels at Pounds per Billion Btu of Energy Input Pollutant Natural Gas Oil Coal Carbon Dioxide 117, , ,000 Carbon Monoxide Nitrogen Oxides Sulfur Dioxide 0.6 1,122 2,591 Particulates ,744 Mercury Source: EIA - Natural Gas Issues and Trends Quality, rates and quantities of air emissions No continuous emission of air pollutant is expected to be generated by the desalination plant, except for accidental spills from chemical storage tanks as mentioned before. The power plant is estimated to continuously generating various air pollutants during its operations at the rate shown at Table Table 2.2-1: The emission rate of air pollutants of natural gas power plant No. Pollutant Estimated rate of emission (g/s) 1. NO x CO SO CO 2 52, PM Source: Hyflux, 2011 ENVIRONMENTAL PROFESSIONALS Page 20

29 Chapter 2 Air Pollution Control 2.3 Assessment of the impacts of the air emissions, including odorous emissions using dispersion modelling or other acceptable methods During the course of this study, the design of power plant is still on-going, however, it is understood that the power plant will be running on natural gas or a combination of natural gas and fuel oil. For the purpose of this study, it is assumed that the power plant will run primarily on natural gas; the plant will switch to fuel oil as a backup for a short period when shortages of natural gas may occur. Air pollution from industrial developments such as the proposed power plant could potentially cause environmental and human health impacts. Table below shows some of the potential negative effects on the human body system, when exposed to high concentrations of air pollutants, usually associated with power plants and fuel burning industrial facilities. Table 2.3-1: Summary of potential health impact of air pollutants Air Pollutant Summary of Potential Health Impact NOx (as NO 2) Carbon Monoxide Asphyxiation, reproductive effects, deep breathing, dizziness, nausea and unconsciousness. Reduce oxygen delivery to the body's organs and tissue. Death could occur at when 40-50% of haemoglobin occupied by CO. SO 2 Carbon Dioxide Particulate matter (PM10) Pulmonary edema, permanent lung injury or death. Asphyxiation Cardiovascular and respiratory diseases The National Environmental Agency (NEA) stipulates two compliance standards for any activity potentially polluting the air. The air emission, measured at the discharge point of the source (i.e. tip of stack) shall comply with the NEA emission standard. The ambient air concentrations of pollutants, measured at or near the locations of sensitive receptors, which are located mostly at ground level, shall comply with the National Ambient Air Quality Standard (NAAQS) of the U.S. Environmental Protection Agency (US-EPA). The following Table presents the upper-threshold limit of the mentioned standards for each considered pollutant. ENVIRONMENTAL PROFESSIONALS Page 21

30 Chapter 2 Air Pollution Control Table 2.3-2: The Limit of Emission Standard (NEA) and Ambient Standard (US-EPA) Emission NEA Emission Standards (gas power plant) (mg/nm 3 ) US National Ambient Air Quality Standard (NAAQS) Concentration Averaging Time NOx (as NO2) 700 Carbon Monoxide 625 SO ppb ~ 100,000 μg/m3 Annual (Arithmetic Average) 100 ppb ~ 188,000 μg/m3 1-hour 9 ppm ~ 10,000 μg/m3 8-hour 35 ppm ~ 40,000 μg/m3 1-hour 0.03 ppm ~ 80 μg/m3 Annual (Arithmetic Average) 0.14 ppm ~ 370 μg/m3 24-hour 75 ppb ~ 196 μg/m3 1-hour Particulate matter (PM10) µg/m3 24-hour Carbon Dioxide N.A. N.A. Note: The NEA Emission Standard is applicable for power plant built after 2008, as advised by NEA. The NAAQS at unit of μg/m 3 is provided for a clearer comparison with the result of dispersion model. The NAAQS is available at Existing Ambient Air Conditions at Project Location The air quality of Singapore, according to the 2009 Annual Report of Environmental Protection Division (EPD) of National Environmental Agency (NEA), is classified as Good as shown by the summary of the Pollutant Standards Index (PSI) presented at Table The 2009 data of most pollutants concerned by this study are well below the NAASQ of USEPA which is adopted by the NEA. Exception was found on concentration of fine particulate matter (PM2.5), which is 27% higher than the NAAQS standard. Based on the fact that the proposed site is located in an industrial zone, for the purpose of this study, the industrial concentration level of concerned pollutant at 2009, shown at Table 2.3-4, were retrieved and were used as background ambient air information for the assessment of impacts. ENVIRONMENTAL PROFESSIONALS Page 22

31 Chapter 2 Air Pollution Control Table 2.3-3: Summary of Pollutant Standard Index of Singapore Year Days No. of days in which the PSI was classified as Good (0-50) Moderate (51-100) Unhealthy (0-50) Good (0-50) Percentage Moderate (51-100) Unhealthy (0-50) % 4% 0% % 9% 0% Source: 2009 Annual Report of EPD of NEA, page 30 Table 2.3-4: Average ambient conditions of concerned pollutants in Singapore industrial area in 2009 Pollutant Concentration μg/m 3 USEPA Standard μg/m 3 NO 2 (a) Annual mean Averaging Time Method CO (b) ,000 2 nd max 8 hour mean SO 2 (c) Annual mean PM 10 (d) nd max 24 hour mean NOTE: Values are retrieved from 2009 Annual Report of EPD of NEA for selected air quality parameters Methodology for Air Dispersion Study To estimate the impacts of the air pollutants released by the proposed power plant, an air dispersion study was conducted as part of this PCS. The dispersion study aims to estimate the concentrations of five considered air pollutants (NOx, SO 2, CO, CO 2 and PM 10) expected to be released by the power plant. The dispersion model was carried using the Breeze AERMOD software, a specially designed software application, which provides a convenient graphical user interface to the latest USEPA regulatory air dispersion model known as the version of AERMOD. Input data for the dispersion model are stated as follows: The emission rate for each pollutant, the exit velocity and the stack properties were provided by short-listed vendors for the proposed power plant. The relevant meteorological datasets were retrieved from Changi Meteorological station. The receptors locations are defined purposively to cover the area where the peak concentration can be expected. To investigate the trend of dispersion toward the nearest international border with Malaysia, the profile of concentration for each pollutant were developed. The profile graph is composed from predicted concentration level at 50 m intervals from stack to up to 1,500 m away along the profile line. The profile line crosses the international border at approximately 1150 meter away from the stack, as shown at Figure ENVIRONMENTAL PROFESSIONALS Page 23

32 Chapter 2 Air Pollution Control Figure 2.3-1: Cross-border profile line and points of predicted concentrations. The results from the model are the predicted concentrations for each parameter, which were then being compared to the allowable limit of USEPA ambient air quality standards. The results of the model represent the additional concentrations of air pollutants which are contributed by the proposed power plant. They do not represent the actual ambient air quality in the vicinity of the power plant, which is affected by other industrial facilities and their air pollutant emissions. However, the probability of exceedance at ground level considering background ambient air pollution (based on NEA air pollution monitoring) was assessed here Findings of Air Dispersion Study Dispersion of Pollutant The results of the dispersion model suggest that the additional air pollutants introduced by the proposed power plant are relatively small. When the maximum predicted GLC is normalized by the NAAQS value, it is estimated that a maximum of 1.8 % of the allowable concentration limit is added by the power plant air emissions (see Table 2.3-5). Thus, additional air pollutant emissions remain well below the NAAQS allowable limits according to the air dispersion model results. ENVIRONMENTAL PROFESSIONALS Page 24

33 Chapter 2 Air Pollution Control During the southwest monsoon, the concentrations of air pollutant emissions are higher at the north due to the prevailing wind conditions; peak concentrations are predicted to occur within the distance of 500 m to 1,000 m from the stack. During the northeast monsoon, maximum concentrations are expected to occur south of the stack. During the transitional season, as represented by the month of May, winds will blow air pollutants towards the Johor Strait. There are no exceedances expected at the international marine border with Malaysia. Elevated annual maximum concentrations are expected to occur typically to the south of stack. Typical dispersion of concentrations at ground level is shown in the PM 10 concentration map presented at Figure PM 10 was selected as the indicator pollutant with concentrations closes to the allowable standard limits. Dispersion maps for each of the other pollutants are presented at Appendix E. Table 2.3-5: Maximum additional ground level concentrations Air Pollutant Averaging Time Maximum predicted ground level concentrations μg/m 3 Normalized by NAAQS limit (%) NAAQS Allowable Limit (ug/m 3 ) NO2 1-hour ,000 CO SO2 1-hour , hour ,000 1-hour hour PM10 24-hour CO2 24-hour 36,187 - N/A * Note: Normalization is not applicable to CO2 as its allowable limit is yet to be regulated. ENVIRONMENTAL PROFESSIONALS Page 25

34 Chapter 2 Air Pollution Control Figure 2.3-2: Estimated ground level concentrations of PM 10 showing typical dispersion pattern of pollutants at ground during different seasons. ENVIRONMENTAL PROFESSIONALS Page 26

35 Chapter 2 Air Pollution Control Dispersion of pollutant toward the International Border of Singapore-Malaysia At the nearest border point, the maximum additional concentrations of any investigated air pollutant is estimated to be less than 1% of the allowable limit of NAAQS as shown in Table The highest concentrations are estimated to occur during the transitional season from Northeast monsoon to Southeast monsoon, within which a fraction of wind will blow toward the border located at approximately 1,150 m west of the stack, as shown at Figure Table 2.3-6: Maximum predicted increase of ground concentrations at border Pollutant Averaging Time Maximum predicted increase of ground concentrations at border Concentration, μg/m 3 Normalized concentration by Allowable limit NAAQS US-EPA Allowable Limit (μg/m 3 ) NO x 1-hour % 188,000 CO 1-hour % 40,000 8-hour % 10,000 SO 2 1-hour % hour % 370 PM hour % 150 CO 2 24-hour 8, N/A Regardless of pollutant type, the concentration profiles suggest that the highest concentrations occur at some distance, approximately between 500 m to 800 m away from the stack. Approaching the border and beyond, the concentrations are decreasing. Graph showing the trend for PM10 is presented at Figure Graphs for other pollutants can be found at Appendix E. Figure 2.3-3: Spatial profile of additional PM 10 concentration at ground level towards the border ENVIRONMENTAL PROFESSIONALS Page 27

36 Chapter 2 Air Pollution Control Estimation of Probability of Air Pollution Exceedances at Ground Level Assessment of the probability of exceedances was done using the values normalized by the upper limit of NAAQS, which results in a set of comparable values for each pollutant. The normalized values of background conditions were derived from NEA s monitoring data of 2009 and are considered as baseline of background pollution near the study area. As shown at Table 2.3-7, the highest normalized total concentration is expected to be approximately 55%, slightly higher than a half of permissible limit. Based on this estimation, the likelhood of exceedances of pollutants at ground level is deemed low. Table 2.3-7: Estimation of Normalized Total Ground Level Concentration Pollutant Value μg/m 3 Ambient Concentration (a) NAAQS μg/m 3 Normalized value (b) Normalized Additional Ground Concentration (c) Normalized Total Ground Concentration (d) NO % 0.03% 22.03% CO % 0.80% 17.80% SO % 0.41% 22.91% PM % 1.79% 55.12% Note: (a) the ambient concentration value are based on 2009 Annual Report of EPD-NEA. See Table (b) normalization was done by division of concentration value by NAAQS limit. Normalized value above100% indicates an exceedance of the respected threshold. (c) see Table (d) sum of normalized ground concentration (c) and normalized ambient concentration (b) Limitation of the Air Dispersion Study It is important to note that the dispersion study did not consider the scenario of future development of at the vicinity of the power plant stack. Future buildings near to the site with height of 25 m or higher, - approximately half of stack height -, will potentially introduce diversion of near ground winds and hence affect the distribution of ground level concentration of air pollutants. Further details of the model which include model setup, location of receptors and detailed results are provided at Appendix E. ENVIRONMENTAL PROFESSIONALS Page 28

37 Chapter 2 Air Pollution Control 2.4 Measures to control air pollution and ensure compliance with emission standards and requirements in the Code of Practice on Pollution Control The following measures should be used to prevent and control accidental release of gases from chemical storage tanks and pipes: Leakage indicator devices to be installed with alarms with air operated valves for emergency shut off in event of leakage. Mechanical ventilation shall be provided for all chlorine and carbon dioxide indoor dosing facilities. Limiting the storage quantity of gaseous chemicals to a minimum required for normal operations. The following measures should be used to control the continual release of gases from power plant: Control of NOx emissions can be accomplished by installation of low-nox burners and with the application of post-combustion pollution control equipment such as Selective Catalytic Reduction. Low-NOx burners were installed by Senoko Power Plant and were successful in lowering the NOx emission level in line with the new statutory requirement. Control of CO emissions from incomplete combustion in furnace can be accomplished with the application of post-combustion pollution control equipment. Control of polluted air emissions from air intake system can be accomplished by installation of proper air filter systems and additional precautions may be necessary and require optional filtration or moisture removal equipment (Wilkes, 2007). Control of PM10 emissions by installation of post-combustion pollution control equipment such as gravity settling chamber, mechanical collectors, particulate wet scrubbers, electrostatic precipitators, fabric filters. More specific control measures for power plant emissions will be available upon proposal of a more detailed power plant design by the appointed vendor. 2.5 Measures to control and prevent odour nuisance Both desalination and power plants are designed to ensure minimal fugitive emissions of such gases. Chlorine gas and sulphur dioxide are odorous. Measures to be implemented for chlorine gas are as mentioned in the previous section. Installation of odour monitoring devices. Post combustion treatment technologies such as Wet scrubbing/absorption, mist filtration, thermal oxidation/ Incineration. ENVIRONMENTAL PROFESSIONALS Page 29

38 Chapter 3 - Water Pollution Chapter 3 - WATER POLLUTION 3.1 Sources of trade effluent and pollutant The potential source of trade effluent and pollutants attributed to the proposed facilities during construction phase and operational phase are listed on Table Table 3.1-1: Identified sources of water pollution Identified source Accidental spill from vessel construction Description Construction activities at sea like the installation of intake pipes, outfall structures will be carried out using vessel construction. This will pose the risk of accidental spill of vessel fuel and oil. Increased surface run-off Re-suspension of sediment Inadvertent flow or chlorinated water Release of reject brine from desalination plant Release of reject cooling water from power plant Site clearing activities will convert the land-cover into bare land which will introduce the increase of surface run-off. This process is expected to cause erosion which in turn will increase the turbidity in the receiving water-body. Movement of vessel at shallow water and the installation of offshore pipes and facilities will likely to cause the re-suspension of material which leads to a temporary increased turbidity of seawater in the vicinity of the project. The chlorinated seawater at pre-treatment facilities could flow back to the seawater during times when the seawater intake pumps are not in operational state. The increased salinity of wastewater from desalination plant will be discharged at outfall diffuser. The waste stream will contain increased concentration of existing marine substances by factor of 1.8 as well as additional pollutants introduced along the process of desalination. At times when power plant operates, the cooling water will be used to feed desalination plant; the resulted waste from the integrated operation is anticipated to have elevated temperature at the order of 7 degree Celcius above background. The proposed design allows for both plants to operate independently for greater reliability. At times when desalination plant is off, the power plant shall be able to operate independently delivering power to the national grid. The reject cooling water will not be released through offshore outfall but through the shoreline outlet. It is expected that the waste water will have a temperature of approximately 37.4 C at discharge outlet. ENVIRONMENTAL PROFESSIONALS Page 30

39 Chapter 3 - Water Pollution 3.2 Quality, rates and quantities of all wastewater streams and final trade effluent discharges Table gives a summary of the flow rates and characteristics of all the individual wastewater streams from the desalination plant and power plant, assuming that both plants operate at full capacity. Table 3.2-1: Flow Rates and Characteristics of All Wastewater Stream No. Stream Description Instantaneous flow rate m 3 /hr Maximum Flow rate (MLD) ph Total Suspended Solids (mg/l) Total Dissolved Solids (mg/l) Constituent of final discharge (mg/l) Discharged cooling water from powerplant through shoreline outlet Discharged brine through offshore outfall Reject waste stream from UF- Feed auto strainer Reject waste water from UF- Backwashing process Reject waste water from UF-Cleaning process Wastewater from the CIP activities at SWRO Wastewater from the CIP activities at LPRO Yes 17, ,845 Yes ,200 33,000 Yes ,000 33,000 Yes , Yes 2,000 Yes ,000 Yes Source :Hyflux design, ENVIRONMENTAL PROFESSIONALS Page 31

40 Chapter 3 - Water Pollution Ambient seawater quality During the EIA study of the proposed activities, investigations of ambient seawater quality conditions were conducted extensively. The following description discusses the quality of existing seawater based on baseline data of the EIA report (PUB, 2011), unless stated otherwise. Locations of ambient seawater in-situ measurements and water sampling locations for seawater laboratory analysis are shown on map at Figure Figure 3.2-1: Location of EIA's water quality survey station (Source: EIA report) ENVIRONMENTAL PROFESSIONALS Page 32

41 Chapter 3 - Water Pollution Temperature The measured temperatures revealed a mean seawater temperature of 30.6 C. Changes between depths were small, as typical in shallow tropical waters. The highest average temperature was recorded during the spring ebb at 31.1 C. Average temperature for each station during each tidal season is presented in Table Table 3.2-2: Average temperature of seawater in the vicinity of the site Average Temperature ( C) Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) In December 2010, EnviroPro conducted measurements of seawater surface temperature adjacent to the proposed site. The measured seawater surface temperature has shown variations across sample locations between 29.9 C 33 C, with the mean value of 31.2 C and standard deviation of 0.76 C. Measurement record at each sampling point is presented at Table Measurement report is provided at Appendix G. ENVIRONMENTAL PROFESSIONALS Page 33

42 Chapter 3 - Water Pollution Table 3.2-3: Seawater surface temperature of adjacent to the proposed site Sampling Point Time Latitude Longitude Temp 01 Temp 02 T pm N E T pm N E T pm N E T pm N E T pm N E T pm N E T pm N E T pm N E T pm N E T pm N E MEAN Source: Enviro Pro, Seawater Surface Temperature Measurement Report, Salinity On average, salinity levels recorded as parts of the EIA baseline studies were lower than typical marine water i.e. 30 PSU. This could be due to proximity of survey stations to the shoreline, where rainfall run-off might have diluted the marine water. Similar to the temperature profile, there was a relatively uniform salinity vertically throughout the water column. The highest average salinity level was recorded during the spring flood at 31.5 PPT. Average salinity per station at various tidal seasons is presented in Table Table 3.2-4: Average salinity of seawater in the vicinity of the site Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Average Salinity (PPT) Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) ENVIRONMENTAL PROFESSIONALS Page 34

43 Chapter 3 - Water Pollution Dissolved oxygen and PH The mean dissolved oxygen (DO) concentration in seawater in the vicinity of the site is 6.55 mg/l. The highest average DO was recorded during the Neap Ebb season at 7.39 mg/l. Average DO concentration per station at various tidal seasons is presented in Table Table 3.2-5: Average DO in the vicinity of the site Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Average DO (mg/l) Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) Levels of ph were also relatively consistent through water column. ph levels ranged between 7.92 to The highest average ph was recorded during the Neap Ebb and Spring Flood season at Table 3.2-6: Average ph in the vicinity of the site Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Average ph Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) ENVIRONMENTAL PROFESSIONALS Page 35

44 Chapter 3 - Water Pollution Turbidity &Secchi Depth Generally, turbidity levels were higher during ebb tide, likely as a result of sediment discharge from Malaysian rivers. The lowest recorded value was 0.08 NTU at WQ09 during Neap Flood while the highest value was NTU at WQ1. Average turbidity value is 2.9 NTU. Average turbidity level per station at various tidal seasons is presented in Table Table 3.2-7: Average turbidity in the vicinity of the site Average Turbidity (NTU) Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) All measured Secchi disc depth were above 1.2m depth, the shallowest distance was 1.5 m during spring ebb at WQ01 site while the deepest distance was 4.3 m at WQ11 site. The least clear seawater was recorded during neap ebb season at average vision distance is 2.05 meter. Measured secchi depth per station at various tidal seasons is presented in Table ENVIRONMENTAL PROFESSIONALS Page 36

45 Chapter 3 - Water Pollution Table 3.2-8: Measured secchi depth around the site Secchi Depth (m) Station Neap Flood (22 June 2010) Neap Ebb (8 June 2010) Spring Flood (26 May 2010) Spring Ebb (28 June 2010) WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ WQ MEAN Source: EIA baseline data (PUB, 2011) Heavy Metals Laboratory tests for heavy metal ions included cadmium, chromium, copper, lead, nickel, zinc and mercury were performed on seawater taken from seven stations. With the exception of Boron, all heavy metals were recorded at relatively low levels, mostly below detection limits, and well below the recommended AWQG levels. It is noted that waiver will be requested for the two metals Boron and Iron Total Suspended Solids (TSS) The average laboratory-determined TSS was 5.05 mg/l. Sediment concentrations ranged from 5mg/l to 45mg/l. At certain times, the prevailing suspended solids concentrations within the raw seawater taken in by proposed plan will potentially exceed the NEA Trade Effluent Discharge Standards. It is noted that a waiver will be requested for TSS. ENVIRONMENTAL PROFESSIONALS Page 37

46 Chapter 3 - Water Pollution Seawater Condition at Proposed Outfall and Intake location. As shown at Figure 3.2-1, the nearest survey station to the proposed intake and outfall location is WQ07 and WQ04, respectively. Data from both stations are summarized and compared to NEA limits at Table Table 3.2-9: Measured water quality at Intake and outfall of proposed plants PARAMETERS Unit Intake (WQ07) Outfall WQ04 NEA Effluent Discharge Limits Recommended AWQG Secchi Disc m m (10th percentile) 2.0 m (median) Temperature C C 1 C from background Salinity PPT % from background ph ph 8.5 Turbidity NTU NTU (median) 5.5 NTU (90th percentile) DO mg/l mg/l (any time) 4.0 mg/l (median) BOD mg/l TSS * mg/l % from background Oil and Grease mg/l < 0.1 < mg/l (total) 10 mg/l (hydrocarbons) Iron as Fe * μg/l mg/l or 10,000 μg/l Boron as B- * mg/l Cadmium as Cd μg/l <5 <5 0.1 mg/l 5.5 µg/l Chromium as Cr μg/l <5 <5 1 mg/l 4.4 µg/l Copper as Cu μg/l <5 <5 0.1 mg/l 1.3 µg/l Lead as Pb μg/l <5 <5 0.1 mg/l 4.4 µg/l Mercury as Hg μg/l <0.1 < mg/l 0.4 µg/l Nickel as Ni μg/l <5 <5 1 mg/l - Phospate as PO mg/l (median) 5.0 mg/l (any time) mg/l mg/l 0.07 mg/l (median) 0.20 mg/l (anytime) Nitrate as NO3- mg/l mg/l (median) 0.09 mg/l (anytime) Note: the actual concentration is below detection limit of APHA method * waivers will be obtained for the concerned parameters - ENVIRONMENTAL PROFESSIONALS Page 38

47 Chapter 3 - Water Pollution Property of discharged water The list of substances contained in the final effluent discharge is dependent on the presence and concentrations of matters in raw seawater and the inclusion of other chemical during the desalination process. Table shows the seawater condition upon which the desalination plant is designed. Table : Seawater content for design condition of desalination plant Description Unit Data Plant output (at design conditions, 100% production) ml/d MIGD 136, Seawater water design C temperature Seawater salinity design value g/kg ph Silt density index 7 (According to ASTM D4189) Total dissolved solids mg/l 35,000 Total suspended solids mg/l 60 Free carbon dioxide as CO2 mg/l 2.6 Total hardness as CaCO3 mg/l 6,260 Ammonium as NH3 mg/l 0.5 Bicarbonate as HCO3 mg/l Carbonate as CO3 mg/l 30 Chloride as Cl mg/l 20,000 Sulfate as SO4 mg/l 2,900 Nitrate as NO3 mg/l 1 Fluoride as F mg/l 2 Oil & Grease mg/l 10 Biochemical oxygen demand as O2 mg/l 2 Total organic carbon µg/l 2,500 Calcium mg/l 1100 Magnesium mg/l 1500 Sodium mg/l 10,000 Potassium mg/l 800 Barium mg/l 0.1 Strontium mg/l 8 Boron mg/l 5 Iron mg/l 2 Manganese mg/l 0.03 Copper mg/l 0.03 Zinc mg/l 1 Silica mg/l 5 Source: Hyflux Design Data, Seawater Content for Design Conditions, 2011 ENVIRONMENTAL PROFESSIONALS Page 39

48 Chapter 3 - Water Pollution The concentration of each water quality parameter in the effluent discharge will be affected by operational mode of both plants; 2 of 6 proposed potential operational scenarios were identified as potential worst case scenarios for the purpose of this study. The determining factor for the selection of scenarios is the discharge aspect: under scenario 1, the power plant cooling water will discharge directly to shoreline outfall; under scenario 2, the reject brine of elevated temperature (from power plant cooling water) will be discharged through offshore outfall diffuser. Table : Considered scenario for the purpose of this study Scenario ID Plant operation Remarks 1 Power Plant in service at 100% load Desalination Plant not in service Outfall temperature higher than incoming seawater temperature Cooling water from power plant will be discharged through shoreline outfall 2 Power Plant in service at 100% load Desalination Plant in service at 100% output Cooling water from power plant will be desalinated by desalination plant. Rejected brine of elevated temperature will be discharged through offshore outfall. Excess flow of cooling water from power plant will be discharged through shoreline outfall Note : see Table for complete list of potential operational mode of proposed plants The projected discharge characteristic will be as follows. Under scenario 1, the properties of incoming seawater will remain the same as properties of discharge cooling water, with the exception of the temperature aspect. Estimated temperature of the discharged of cooling water is 36.4 C, which is approximately 7 C above ambient condition. The warmer water will be discharged through shoreline outfall at flow rate of 990 MLD. Under scenario 2, the concentration of water quality parameters of intake seawater will increase in the reject brine through the RO process. In addition, temperatures of the brine discharge are predicted to be elevated by approximately 7 C at the offshore outfall, as cooling water from the power plant will be fed to the RO plant. The elevated temperature brine will be discharged through the offshore outfall diffuser at a flow rate of 509 MLD. Excess flow of cooling water from the power plant will be discharged through the shoreline outfall at a maximum rate of 162 MLD Detail of estimated properties of discharged water is presented on Table ENVIRONMENTAL PROFESSIONALS Page 40

49 Chapter 3 - Water Pollution Table : Properties of discharged water for Scenario 1 and 2 Description Units Scenario 1 Scenario 2 Calcium mg/l as Ca Magnesium mg/l as Mg 1,268 2,062 Sodium mg/l as Na 10,060 16,365 Potassium mg/l as K Ammonia mg/l as NH 3 ND ND Barium mg/l as Ba Strontium mg/l as Sr Bicarbonate mg/l as HCO Sulphate mg/l as Ca 2,537 4, Chloride mg/l as SO 4 18,255 29, Fluoride mg/l as F Nitrate mg/l as NO Boron mg/l as B 4.5* 7.32* Silica mg/l as SiO TDS mg/l 33,000 53,679 ph Temperature Suspended solids Scale inhibitor Source: Hyflux design, Potential impact during construction stage Impact of the increased surface water run-off Any increase of surface water or stormwater over the construction site, may lead to reduced light penetration and smothering of sessile benthic organisms, which in turn may result in reduced photosynthesis activities. This is expected to be an impact of temporary nature on the marine life and will cease after construction is completed. Given the small footprint of site (approximately 14 ha), the additional run off volume could be regarded as minimal and highly localized, thus the impact is deemed negligible. Off surface water run-off, only 50% will be discharge directly to the sea, the remaining half will be discharge to the PUB surface water drainage system in Tuas South Avenue 3. Implementation of erosion control measure specified in section will mitigate the risk of unnecessary erosion. ENVIRONMENTAL PROFESSIONALS Page 41

50 Chapter 3 - Water Pollution Impact of accidental spill from vessel construction Vessel spill during marine construction could occur and may affect marine biota and ecosystems, water column, nearby SingSpring desalination plant, reservoirs in the region (3.5km) and the intertidal community of neighbouring country (3.1km). The level of impact is dependent on the types of chemical used and their toxicity. However, the effects are likely to be temporary and localised on any communities or ecosystems because quantities of chemicals stored and used would generally be small. Medium or significant spills are considered unlikely to occur. The risk of an accidental spill affecting the neighbouring reservoirs and intertidal community of neighbouring country were rated as low because the quantity of any spill is likely to be small and the reservoirs and nearest shore are located at a sufficient distance from the Project area to minimise the impact. The risk of an accidental spill affecting the SingSpring desalination plant were rated high because of the close distance between SingSpring desalination plant and Project area. Implementation of vessel spill measure, explained in section3.3.1, will mitigate the risk of unnecessary vessel spill Impact of Dredging for Intake and Outfall Structures The proposed project requires dredging to place the intake and outfall pipeline at the desired levels into the seabed. Dredging work is estimated to excavate the seafloor material at the volume of 2,400 m 3 and 2,160 m 3 from intake area and the outfall area respectively. Dredging will be carried by clamshell bucket or long arm excavator mounted on barge. It has been estimated that the dredging work would require, in a longest stretch, continuous dredging-covering work of 2 weeks duration. This would likely disturb some biological habitats and affect the associated biological communities, although disturbance would likely be localized to around the SEPs. Benthic communities are most likely to be affected by seabed clearing. There may be localized damage to the seabed and the plants and animals that inhabit the affected areas. Generally, marine mammals are expected to avoid disturbed areas due to noise and vibration from construction activities, so it is unlikely that clearing activities would affect these species. The consequence of these activities are not considered to be significant as long arm excavator mounted on barge would be removed from the marine environment upon completion of construction of the marine outfall and it is expected that these communities would recover to their original state after construction activities are complete, provided no further disturbance takes place. Secondary impacts due to dredging (such as dispersal of sand from the seabed) would also only occur for a short period of time. An increase in turbidity of the seawater reduces light penetration and leads to reduce sunlight reaching benthic communities. ENVIRONMENTAL PROFESSIONALS Page 42

51 Chapter 3 - Water Pollution It is understood that the seabed material is one of course silty materials which is coarse, noncohesive when loosen, and settle readily in a water column. It is also known from past land reclamation and dredging activities in the vicinity of the project area that such dredging work could generate local higher concentration of suspended solids. The TSS concentration has been known to be in the range of ppt which is assumed at the sustained rate, generated in the dredging zone for the duration of the works..i.e. 2 weeks. After that the TSS concentration will decrease and return to the ambient condition. The spreading of the TSS to the intakes in its vicinity, if any, will be most severe during that period of 2 weeks. As such, the following initial and boundary conditions are assumed as shown at Table Table : Assumed Initial Boundary Condition Parameter Assumed Initial Condition Ambient TSS 10 ppt TSS at source Scenario A ppt Scenario B 400 ppt Source: Report on Assessment of Dredging Effect. See Appendix F The tidal hydrodynamic package used is DELFT-3D and the period of simulation is set for 2 weeks (Feb 01 Feb 15, 2011), and the appropriate tidal harmonics are used as the boundary conditions to simulate the tidal flow in Singapore waters. ENVIRONMENTAL PROFESSIONALS Page 43

52 Chapter 3 - Water Pollution Scenario A: Source TSS 200 ppt Figure shows the TSS distribution corresponding to Scenario A over a typical tidal cycle (at 2 hours interval). The ambient TSS is 10 ppt. It can be seen that the TSS plume adheres to the shore and the TSS envelope of ( ppt) lies well within the Singapore waters. The high concentration TSS plume is not present. The TSS concentration in Singspring intake location does not rise beyond ppt. Figure 3.2-2: Distribution of TSS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2-hour interval Scenario A (source TSS 200 ppt). (Source: Dr. Tan Soon Keat, 2011) ENVIRONMENTAL PROFESSIONALS Page 44

53 Chapter 3 - Water Pollution Scenario B: Source TSS 400 ppt Figure shows the TSS distribution corresponding to Scenario A over a typical tidal cycle (at 2 hours interval). The ambient TSS is 10 ppt. It can be seen that the TSS plume adheres to the shore and the TSS envelope of ( ppt) lies well within the Singapore waters. The high concentration TSS plume is not present. The TSS concentration in Singspring intake location does not rise beyond ppt. Figure 3.2-3: Distribution of TSS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2-hour interval Scenario B (source TSS 400 ppt). (Source: Dr. Tan Soon Keat, 2011) The far field simulation studies of the dispersion of TSS (continuous sustain TSS concentration of 200 ppt and 400 ppt) show that the area covered by marginally higher TSS concentration is small despite the rather high TSS concentration at source. The plume has a marginally higher TSS concentration, i.e. 0,05 ppt above the ambient of 10 ppt. ENVIRONMENTAL PROFESSIONALS Page 45

54 Chapter 3 - Water Pollution It can be concluded that the TSS generated due to dredging operation has relatively little or negligible impact on the coastal waters around the project area. Any impact on seawater quality will be temporary and will cease when construction is completed. On the other side, there may be some beneficial effects of dredging. Locally, it can increase dissolved oxygen content of the water column, achieved through induced mixing by the dredging activities, thus reintroducing air into the seawater. The removal of the dredged sediments also helps to remove possible polluted sediments, which may induce adverse chemical reactions on the seabed if left alone Potential impact during operational stage At operational stage various impacts to the receiving watercourse were identified and summarized in the followings Impact of Increased Salinity RO concentrates are often denser then seawater of natural salinities, hence, plumes tend to extend further along the seafloor than at the surface. Therefore, macro-benthic organisms tend to be at greater risk of exposure to RO concentrate discharges as compared to pelagic and planktonic organism. Sedentary organism living on or in the seafloor in proximity to outfall diffuser, which are unable to move from the impact zone and are intolerant to high salinity, will be likely to be more affected. In addition, potential seawater quality impacts within a mixing zone from the outfall discharge point need to be considered. Depending on the design of the outfall, bathymetry at the outfall discharge point and marine ambient conditions (i.e currents and tides), the RO concentrate could lead to visible seawater quality impacts, which may extend to or beyond the marine border with Malaysia. A quantitative assessment of the potential seawater quality impacts by the brine discharge / RO concentrate from the proposed TuasSpring desalination plant was conducted. The proposed desalination plant makes use of the RO process for water treatment. Seawater is drawn in from the coastal intake and discharge at a higher reject concentration. As a result, the salinity-values of the source and discharge seawater are as follows: TDS (Salinity Water temperature Source (ambient) seawater 29.5 ppt 29.0 deg C Discharge seawater 54.6 ppt 36.4 deg C * * Caused by elevated temperature power plant cooling water as source water to desalination plant ENVIRONMENTAL PROFESSIONALS Page 46

55 Chapter 3 - Water Pollution A power plant will be built on site to provide power as well as warmer seawater to the desalination plant, either as source water or as dilution water in the reject stream. For evaluation purposes, focus was on the outfall discharge of the RO plant, including the scenarios when the desalination is operated at 10% and 100% capacity, and with and without using the cooling water from the power plant. There are 4 scenarios as summarised in Table Table : Test scenarios of outfall discharge (TDS and Temperature) Scenario Discharge rate (MLD) Total Dissolved Solids (ppt) Temperature (deg C) (ambient) (ambient) The design for the offshore outfall discharge is shown in the schematic sketch in Figure and Figure The outfall pipe conveys the discharge from the plant to the outfall diffuser, and terminated approximately 120 m away from the shore as shown in Figure The diffuser nozzles are located elevated at the top cap and are set at MRL, corresponding to below Chart Datum. There are 12 nozzles directed radially and horizontally outwards, issuing at 10 m/s at the nozzle (250 mm diameter). The nozzles are about 1 m above the seabed. Figure 3.2-4: A schematic sketch of the outfall pipe. (Source: Hyflux, 2011) ENVIRONMENTAL PROFESSIONALS Page 47

56 Chapter 3 - Water Pollution Figure 3.2-5: A schematic sketch of the outfall diffuser with discharge nozzle. (Source: Hyflux, 2011) Seabed Contour The seabed bathymetry nearer the shore (within ~150 m) is generally straight and parallel to the shoreline. However, the vertical gradient is generally steep reaching 8 m within 100 m from the shore. As the brine discharge is a negatively buoyant, i.e. the discharge stream is denser than the receiving water, the plume issued from the discharge outlet would sink to the bed and be carried by the momentum of the discharge into the deeper water, following the sloping terrain, and away from the shoreline. The plume mixes with the receiving water and is diluted in the process. In the case where the discharge water temperature is elevated at 36.4 deg C, the discharge plume is approximately neutrally buoyant. In any case, the design of the diffuser is to create turbulent mixing (by the jet impinging in the ambient water), whereby the discharged plume is diluted to close to ambient seawater salinity within a certain distance from the diffuser. While the interpretation is generally correct, the discharging flow actually sets up entrained flow along its trajectory. Figure shows a diagrammatic representation of the core flow and the entrained flow. Therefore, while the core of the plume exhibits the highest TDS (saline) concentration, part of the saline content is also being spread radially from the core. ENVIRONMENTAL PROFESSIONALS Page 48

57 Chapter 3 - Water Pollution Depending on its distance from the core flow, the salinity could be elevated. It follows that there is an optimum distance from the outlet location beyond which the plume s influence is insignificant. Core flow Plan view Elevation Figure 3.2-6: A diagrammatic representation of the core flow and the secondary flow as a result of flow entrainment in the receiving water body. (Source: Dr. Tan Soon Keat, 2011) In the case of the neutrally buoyant plume, the trajectory will be one of horizontal distribution. It is to be noted that the above general assessment is based on still receiving water body such as an inland lake or an enclosed basin. The effect of tide and current/wave would modify the picture. The design for outfall discharge shown in the original drawings is a vertical-diffuser or vertical riser at the end of the transport pipe and 12 horizontal discharge ports/nozzles at the top cap, issuing the discharge radially and horizontally at 10 m/s at the nozzles, see Figure The nozzles are approximately 1 m above seabed and set at below the Chart Datum. In general, the longer the plume trajectory is designed, the better the initial mixing with the ambient seawater. Better initial mixing will reduce the salinity build-up near the discharge area and the return point, where the plume sinks back to the seafloor. Longer plume trajectories from the discharge ports can be designed through an inclined angle of the discharge nozzles. Research has shown that 60 degrees inclined dense jets for brine discharge from desalination plants achieve a maximum mixing efficiency. However, the terminal rise may be relatively high and thus not suitable for disposal in shallow coastal waters without the risk if the discharge plume rising to the surface. For this reason and the purpose of this assessment, a horizontal discharge direction has been assumed. ENVIRONMENTAL PROFESSIONALS Page 49

58 Chapter 3 - Water Pollution Figure 3.2-7: The trajectory at an inclined 60 degree angle with a terminal rise height (Zt) and return point (Xr). Zo indicates the height of the height of the discharge point above seafloor level. The shades in the plume are indicative of the brine dilution. (Source: Shao and Law, 2010.) Simulation study near field mixing of TDS and thermal plume Of the 4 scenarios, Scenarios 1 and 2 are less critical (10% capacity) as the mass of salinity (TDS) are much lower when the plant is operating at full capacity, Scenarios 2 and 4. The near field evaluation is carried out for Scenarios 2 and 4 first. If under these scenarios and the entrainment mixing near field could produce satisfactory dilution, then scenarios 1 and 3, being of lower TDS mass discharge, satisfactory dilution will also be achieved within the distance stipulated. The near field entrainment/mixing (in quiescent water) assessment is performed using CORMIX. The results of analysis for Scenarios 2 and 4, as well as the distribution of the thermal plume at near field (mixing) in quiescent water are presented below. Scenario 2: TDS of 54.6 ppt at 36.4 deg C, Q = MLD Figure shows the dilution profile of the salinity (TDS) for Scenario 2. The ordinate (vertical axis) shows the TDS expressed in part per thousand (ppt). The minimum TDS, based on minimum dilution, refers to the minimum dilution or largest ppt at the cross-section (distance from the nozzle). It can be seen from Figure that the dilution is rapid immediately after the flow leaves the nozzle, reducing to a minimum dilution to about 34 ppt (about 6 times dilution or 84% reduction in TDS concentration) within 10m from the nozzle. Mixing dilution reaches lower than 30.5 ppt at about 45 m from the nozzle. In terms of average dilution, the TDS plume could be viewed as completely mixed and diluted to ambient condition within 20 m from the nozzle. It is also noted that the plume would have touched the seabed about 8 m from the nozzle. ENVIRONMENTAL PROFESSIONALS Page 50

59 Chapter 3 - Water Pollution Figure 3.2-8: The dilution profile (minimum and averagetds concentration) Scenario 2. (Source: Dr. Tan Soon Keat, 2011) ENVIRONMENTAL PROFESSIONALS Page 51

60 Chapter 3 - Water Pollution Scenario 4: TDS of 54.6 ppt at 29 deg C, Q=509.8 MLD It is noted that the elevated temperature in Scenario 2 is not large, and the effect of buoyancy within the mixing zone with an exit speed of 10 m/s is relatively minor. This is shown by the result in for Figure For all intent and purposes, Figure and Figure could be considered identical. 29 Figure 3.2-9: The dilution profile (minimum and average TDS concentration) Scenario 4. (Source: Dr. Tan Soon Keat) ENVIRONMENTAL PROFESSIONALS Page 52

61 Temperature (deg C) 70 MGD Tuas Desalination and Power Plant (DBOO) Project Chapter 3 - Water Pollution Thermal Plume discharge of MLD and temperature of 36.4 deg C Figure shows the temperature distribution over longitudinal distance from the nozzle. It can be seen that the temperature of the plume decreases rapidly, dropping to within 1 deg C above ambient within 15m (minimum temperature). The temperature drops to less than 0.2 deg C above ambient within 70 m from the nozzle. Nearfield Dispersion of Thermal Plume Minimum Temperature Average temperature Distance from nozzle (m) Figure : The dilution profile (minimum and average temperature) Q = MLD at 36.4 deg C. (Source: Dr. Tan Soon Keat, 2011) The near field mixing assessment shows that the salinity/tds concentration and temperature plume will be diluted to close to ambient condition within 70 m from the nozzle based on the current outfall configuration design. ENVIRONMENTAL PROFESSIONALS Page 53

62 Chapter 3 - Water Pollution Dispersion of TDS and thermal plume Although it has been shown that the TDS and thermal plume could be diluted to close to ambient condition within 70 m from the nozzle, in quiescent water, it is of interest to evaluate the worst cases of non-mixing scenario at source, and the plume is advected and dispersed by the tidal currents. The simulation is performed using DELFT-3D. Scenario 2: TDS of 54.6 ppt at 36.4 deg C, Q = MLD Figure shows the TDS distribution corresponding to Scenario 2 over a typical tidal cycle (at 2 hours interval). The ambient TDS is 29.5 ppt. It can be seen that the plume adheres to the shore and the TDS envelope of ( ppt) lies well within the Singapore waters. Figure : Distribution of TDS plume in West Johore Strait over 1 tidal cycle (12 hours), at 2-hour interval Scenario 2. (Source: Dr. Tan Soon Keat, 2011) ENVIRONMENTAL PROFESSIONALS Page 54

63 Chapter 3 - Water Pollution Scenario 4: TDS of 54.6 ppt at 29 deg C, Q = MLD Figure shows the TDS distribution corresponding to Scenario 4 over a typical tidal cycle (at 2 hours interval). The ambient TDS is 29.5 ppt. It can be seen that the plume adheres to the shore and the TDS envelope of ( ppt) lies well within the Singapore waters. It can be seen that the results are consistent with that of scenario 2 and that the effect of temperature is insignificant in this case. Figure : Distribution of TDS plume in West Johor Strait over 1 tidal cycle (12 hours), at 2-hour interval Scenario 4. (Source: Dr. Tan Soon Keat, 2011) ENVIRONMENTAL PROFESSIONALS Page 55

64 Chapter 3 - Water Pollution Thermal Plume discharge of MLD and temperature of 36.4 deg C Figure shows the temperature distribution at the shore of the project area. The ambient temperature is taken as 29 deg C. It can be seen that the thermal plume adheres to the shore, dropping to within 0.1 deg C within a short distance from the shore and well within the international boundary. Figure : Distribution of thermal plume in West Johore Strait over 1 tidal cycle (12 hours), at 2-hour interval. The discharge rate is MLD. Source: Dr. Tan Soon Keat, 2011 ENVIRONMENTAL PROFESSIONALS Page 56

65 Chapter 3 - Water Pollution Overall, the findings of the far-field simulation are consistent with the findings of the near-field mixing. The plumes TDS diffuse and disperse to marginally higher levels than the ambient seawater within a short distance (~70m) from the discharge and has minor to negligible impact on the marine environment and the international boundary. The following summary statements are made: The intensity of mixing with the discharge port/nozzle (250 mm diameter) issuing the jets at 10 m/s produced rapid mixing and dilution of the TDS and temperature. Within 70 m of the nozzle, the concentration and temperature of the plume has been diluted / reduced to close to ambient conditions. The TDS and thermal plume, at full discharge (509 MLD, 54.6 ppt of TDS, and warmer temperature of 36.4 deg C) do not appear to cause significant changes to the TDS concentration and temperature at the international boundary. Neighbouring intake, if any, will not be affected as long as the structure is located more than 70 m away from the outfall diffuser. 3.3 Measures to ensure compliance with requirements in the Code of Practice Measure during construction stage Measure to mitigate the risk of accidental spills Periodic inspection of vessel condition Limit on-vessel storage and/or use of hazardous substances and dangerous goods Arrange mechanical containment such as booms, barrier and, skimmer as well as natural sorbent materials to capture and store the spilled oil until it can be disposed of properly around the vessel Desalination plant owner could prepare mechanical containment near intake port as a secondary protection Measure to minimize Erosion, Site Run-off and Water Quality Impacts Before Site Preparation can be done, Earth Control Measures (ECM) are proposed to be put in place throughout the duration of the construction activities to prevent silt from being washed into neighbouring water bodies during storm events. ENVIRONMENTAL PROFESSIONALS Page 57

66 Chapter 3 - Water Pollution The ECM includes an Erosion Control Plan, which is to minimize the formation of bare surfaces that can be exposed to rainfall to prevent erosion. The Sediment Control Plan is to capture sediments washed down from the construction site to minimize pollution to nearby waterways. The implementation of the ECM is to facilitate earthworks, which will generate large volumes of loose earth and will greatly increase the sediment particles in the runoffs when exposed to rain. Since the construction site is at a higher ground and is close to water bodies, any increase in sediment particles in the runoffs will eventually pollute the environment. An Environmental Control Officer (ECO) should be engaged throughout the construction activities to provide advice in the following: Control of disease-bearing vectors and rodents Proper management and disposal of solid and liquid waste Control of noise and dust pollution Drainage Control General Housekeeping Mitigation measures will be required during the construction to prevent unacceptable water quality impacts from storm-water runoff and other sources that could enter the marine environment during construction. Water pollution control will need to comply with requirements in Environmental Protection and Management Act and associated water regulations and standards, and be conducted in a manner to minimize on water quality within and outside the site. PUB s relevant regulations, codes and trade effluent standards need to be complied with. For instance, NEA s/pub s Trade Effluent Standards for Discharge into Watercourses and Controlled Watercourses prescribe a Total Suspended Solids (TSS) concentration of not more than 50mg/L (Watercourse) and 30mg/L (Controlled Watercourse). A number of mitigation measures are recommended to avoid unacceptable water quality impacts during the shaft construction phase. These include: No construction site runoff should be allowed to enter any public sewer, natural watercourse or canals adjacent to the site; Temporary perimeter surface water drainage channels and inert solid removal facilities should be constructed in advance of site formation and earth works to divert drainage to treatment areas and avoid unacceptable impacts on natural water courses and adjacent marshlands. Surface run-off sites should be directed into adequately designed sand and silt removal facilities such as sand traps, silt traps and sediment basins before discharge into any natural drainage channel. ENVIRONMENTAL PROFESSIONALS Page 58

67 Chapter 3 - Water Pollution Earthwork surfaces should be compacted and the subsequent surface protected (i.e. gravel) to prevent erosion caused by rainstorms. A temporary access road should have proper temporary side drainage systems installed. Temporary, open storage of excavated materials shall be covered with tarpaulin or similar fabric during storm events. Any washout of construction or excavated materials from excavation and site formation should be diverted to appropriate sediment traps, to achieve a controlled flow of storm flow and construction runoff. Any groundwater pumped out of boreholes, bored piles or any other subsurface structure should be discharged into sediment traps to enhance deposition rates and remove silt before discharge into adjacent watercourses. A wheel washing facility should be provided at every site exit. Wheel washing activities, which ensure that no earth, mud and debris is deposited on roads, shall be settled out and removed before discharging into storm drains. Wastewater discharged from the wash-down of trucks and drums should, wherever practicable, be recycled. To prevent pollution from wastewater overflow, the pump sump of any water recycling system should be provided with an on-line standby pump of adequate capacity. Oil interceptors should be provided in the construction site runoff drainage system, in addition to the silt removal facility, and be regularly (weekly) emptied to prevent the release of oils and grease into the storm-water drainage system after any accidental spillage. The interceptor should be provided with a bypass to prevent flushing during periods of rainfall. All generators, fuel and oil storage facilities on site should be adequately bunded for minimum containment of 1.5 times storage volume. Any drainage from these areas shall be connected to storm drains via an oil interceptor device. If any office, site canteen or toilet facilities is erected at the construction site, then foul water effluent shall be directed to a foul water sewer or to a sewage treatment and disposal facility either directly or indirectly by means of pumping or approved method. Vehicle and plant servicing areas, vehicle wash bays should be located under roofed structures. The drainage in these covered areas should be connected to foul sewers via an oil interceptor or be tinkered away for proper disposal. Oil spillage or leakage should be contained and cleaned up immediately. Waste oil should be collected and stored for recycling in accordance with the EPMA (Hazardous Substances) Regulations. Debris and rubbish shall be properly handled and disposed of to avoid entering watercourses and causing water quality impacts. ENVIRONMENTAL PROFESSIONALS Page 59

68 Chapter 3 - Water Pollution Measure to minimize the re-suspension of sediments from dredging Dredging of sand will be done from designated approved area of the river following MPA guidelines The dredging is carried out within the areas specified in the application and the dredging depth does not exceed 1.0m of the specified dredging depth. Dredging will be limited to a maximum of two weeks continuously. Minor dredging of the trench shall be carried by clamshell bucket or long arm excavator mounted on barge. Small bucket of size 3m 3 shall be deployed to minimise seabed disturbance. The seabed material to be removed from this dredging has been tested and found to be nontoxic. Random checks are required to ensure that the dredging activities are carried out in accordance with the application. The inverted trapezoidal trench of 4m x 14m x 2m height shall extend 120m seawards for outfall pipeline. The inverted trapezoidal trench of 7m x 25m x 3m height shall extend 50m seawards for Intake pipeline. The GRP pipes for Intake and Outfall are 2 x 2.5m diameter and 1.6m diameter respectively. A number of management techniques and mitigation measures have been developed, such as tidal dredging, physical barriers e.g. silt screens, which may be used to mitigate effects of dredging on sensitive organisms Measure to minimize impacts during operations To avoid the flow of chlorine into the sea from intake tank, the chlorine pump operates should only be operated when intake pumps are in operation. Continual monitoring of chlorine concentration at inlet of intake pipe, the monitoring system should be able to alert operator at control room or de-activates the chlorine pump. To avoid entrainment and entrapment of fish within intake, the flow velocity at the openings shall not exceed 10 cm/s for open intake and 30cm/s for opening connected to intake bay. Wastewater shall be directed to neutralization tank prior to disposal through outfall. Limiting the discharge velocity to maximum 10 m/s to ensure that the temperature will be diluted close to ambient condition within 50 m from the nozzle. ENVIRONMENTAL PROFESSIONALS Page 60

69 Chapter 3 - Water Pollution Measure to minimize water quality impacts during operations Iron oxide, boron and TSS concentrations exceed the NEA Trade Effluent Discharge Standards at the desalination outfall, due to the relatively high background levels and the concentration effect of the desalination process. A waiver has been requested in from NEA to allow for these exceedances within the mixing zone. Recommended Ambient Water Quality Guidelines for salinity and temperature are exceeded within the 70m outfall diffuser mixing zone. The concentrations for these parameters are brought back to compliant levels at the boundary of the mixing zone. As no exceedances of the recommended Ambient Water Quality Guidelines for is predicted outside the mixing zone for ammonia, nitrate, nitrite, phosphate, or chlorophyll-a, there is no additional measures needed. There are no significant adverse visual effects predicted from the outfall discharge stream. 3.4 Monitoring programme Parameters monitored, type of monitoring equipment, frequency of monitoring Continual monitoring of Chlorine concentration at the intake port and outfall diffuser. The system should be able to alert operator immediately or synchronized with intake pumps and chlorine pumps. Continual monitoring of seawater properties at the boundary of mixing zone near diffuser outfall Continual monitoring of seawater properties at points near power plant s shoreline outfall ENVIRONMENTAL PROFESSIONALS Page 61

70 Chapter 4 Noise Pollution Chapter 4 - NOISE POLLUTION 4.1 Sources of noise pollution There is potential noise and vibration during construction work from pile driver, loader, truck, and dredging and vessel movement. The sources of noise from the desalination plant have been identified. Noise may originate from high-energy pumps used to pressurize seawater during Reverse Osmosis process, the pumps are used to force seawater through the RO membranes. The other 2 potential sources of noise come from blowers and back-up generator. The potential sources of noise from the combine-cycle power plant are from main buildings and cooling towers. 4.2 Existing ambient noise During the course of the study, the Consultant conducted the ambient noise measurement at five points at the boundary of the proposed site; three of which were located along pedestrian way along the eastern perimeter; the remaining two were positioned at the corner at seaward direction from the site. Details of location can be found at Figure The measurement of existing ambient noise at the proposed site shows that the higher noises were received at the locations along pedestrian way than those at points near the sea. Along pedestrian lane, the measured range of noise level is dba at the mean value of 65.8 dba; The prominent source of which are trucks and other form of heavy vehicles. The summary graph and table are presented in Figure 4.2-1and Table ENVIRONMENTAL PROFESSIONALS Page 62

71 Chapter 4 Noise Pollution Figure 4.2-1: Ambient Noise at Proposed Site. Point N1 & N5 are located at seaward corner, N2, N3, N4 are located at pedestrian lane at eastern border of the site. The bar indicates the range of recorded value; the dot indicates mean value. Table 4.2-1: Summary of Ambient Noise at Proposed Site Point Time of measurement Noise Level, dba Min Max Mean Stdev N1 12:15:21-12:32: N2 11:24:54-11:44: N3 10:54:32-11:11: N4 10:15:01-10:32: N5 12:45:02-13:04: ENVIRONMENTAL PROFESSIONALS Page 63

72 Chapter 4 Noise Pollution Figure 4.2-2: Location of noise measurements at Tuas area Estimates of noise levels emitted during construction The noise emitted during construction work on land will be mainly from the pile driver, loader and trucks. The estimated noise level 15 meter from source is estimated to be in the range of 85dBA to 101dBA (refer to Appendix H) The implementation of noise control measures, explained in section 4.4, will mitigate the risk of noise pollution. The vibration emitted during construction work on land will be mainly from the same sources as mentioned above. The proposed site is an industrial area whith no presence of fragile buildings or hospitals or clinics. The construction period is expected to be 24 months. It is expected that there is no prolonged distrubance or damage from construction vibration. ENVIRONMENTAL PROFESSIONALS Page 64

73 Chapter 4 Noise Pollution No impacts are predicted at any aquaculture facility or any seagrass, coral or mangrove habitat due to the small scale of the marine component by noise and vibration during dredging and vessel movement. Reference to the noise level at desalination plant was obtained through measurement of noise at boundary of a similar operational plant, the SingSpring desalination plant, which is located at north to the proposed site as shown at Figure Based on field observation, two points (N6 and N8) were considered representative as the main source of noise is the process from within the plant. N6 was located at southern perimeter of the plant; N8 was located at northern perimeter. Of the two representative measurement points, noise at N8 point is the highest, yet it is still below the allowable limit of noise level stipulated by NEA. Figure 4.2-3: Noise level at the perimeter of SingSpring Desalination Plant. The measurement was conducted at day time for about 15 minutes at frequency of 1 reading per second. ENVIRONMENTAL PROFESSIONALS Page 65

74 Chapter 4 Noise Pollution Being closer to the main road, point N7 deemed inappropriate for the purpose of reference, as higher value of recorded noises at this point was primarily attributed to moving heavy vehicles. Summary at Figure suggest that existing plant emits less noise to pedestrian as compare to those traffic during the day. Table 4.2-2: Summary of ambient noise at Singspring perimeter Point Time of measurement Noise Level, dba Min Max Mean Stdev N6* 13:11:23-13:29: N7 13:58:00-14:17: N8 14:22:34-14:40: Source: Enviro Pro, Analysis of noise data. Note : * with noises attributed to the passing by fighter plane removed Noise emitted from the desalination plant s back-up generator is estimated to be 1.5 dba. However, as this is a back-up generator, no noise will be emitted from the generator during routine operation. Additional reference with regards to the noise levels at the proposed power plant was obtained through the measurement of ambient noise at the boundary of similar power plant s configuration, which is the Senoko power plant (See Figure 4.2-4). Four data points were obtained; Points S1 and S2 were collected at the south and southwest portion of the site while points S3 and S4 were located at the southeast and eastern perimeter of the plant. Based from the four representative measurement points, noise collected at S4 yields the highest reading and still remains below the allowable limit stipulated by NEA (see Figure 4.2-5). ENVIRONMENTAL PROFESSIONALS Page 66

75 Chapter 4 Noise Pollution Figure 4.2-4: Location of noise measurements at Senoko Power Plant Area ENVIRONMENTAL PROFESSIONALS Page 67