WATER POLLUTION MANAGEMENT FOR SILT DISCHARGE IN LAND TRANSPORT AUTHORITY PROJECT SITES: CASE STUDY...

WATER POLLUTION MANAGEMENT FOR SILT DISCHARGE

IN LAND TRANSPORT AUTHORITY PROJECT SITES: CASE

STUDY OF DOWNTOWN LINE 2, CONTRACT 911

Jernice Kew Huiling, Executive Engineer (Environmental)

Alex Yip Jui Yong, Deputy Project Manager

Safety Division, Land Transport Authority, Singapore

Downtown Line 2 (Civil Construction Team 1), Land Transport Authority, Singapore

[email protected], [email protected]

ABSTRACT

With the rapid development and transformation of Singapore's urban landscape that boosted the

construction industry over the last decade, water pollution from the construction sites has become a major

concern. Construction projects could cause substantial environmental impacts if effective management

control is not put in place. When top soils are cleared for site preparation works, erosion will occur during

rainy days. The silt bearing runoffs will result in massive sediment pollution in our water catchments such

as the scenic reservoirs and Marina Barrage. Silt turns the waterway turbid, preventing sunlight infiltration

and destroys aquatic life. Not only is marine ecology devastated, the aesthetic beauty of the reservoirs will

be badly affected. Therefore, with the intensive and extensive construction activities currently going on,

effective earth control measures and management are necessary and essential for maintaining the

sustainability of our precious water resources.

Contract 911 (C911) - Design and Construction of Depot for Downtown Line 2 is one of the project with the

largest earthworks and excavation activities. Contract 911 (C911) involved the excavation of about 3.85

millions m3 of earth and with a large site area of 25 ha. It faces greater difficulties in terms of erosion

control as compare to its neighbouring sites along the developing rail transit line. Furthermore, the

existing site terrace (high slope area) stretches from north to south of the entire construction site has also

post greater challenges in controlling effective soil erosion and management. The overall erosion drainage

system, retention ponds, water treatment plants, erosion control measures, etc have to be carefully designed

and assessed. A holistic review of the ECM is thorough and precise. Hence, this paper aims to draw on

C911s unique characteristic as a platform to highlight the importance of controlling silt discharges, foster

greater awareness of our commitment and share our experiences on the challenges faced in the delivery of

our land transport infrastructure projects.

Keywords: Construction; sediment; erosion; land transport; water pollution; silt; water resource

management; road; rail

INTRODUCTION

Singapore, located at the Southern tip of Malaysia

Peninsular, is a country with a total land area of 707.1

m2. Despite being a small island, the Singapore

Government places great emphasis in water resource

management. Via the virtues of early land use

planning, 30% of the land has been allocated as water

catchment areas and the whole island wired up by a

huge network of storm water canals and drains, to

capture as much of its annual 2400mm rainfall as

possible, which eventually is diverted into these

catchment areas or reservoirs for water provision and

portability.

Given the large networks of canals and drains and the

high storm water catchment rate in Singapore, surface

runoffs from the construction sites will find their way

easily to the reservoirs. In addition, with the land

scarcity and large catchment areas, it is no surprise

that sites may be found within 1 or 2 kilometers of

these reservoirs, creating direct impact to the marine

lives and potentially turning water from blue to brown.

For example, Downtown Line 1 and Circle Line, one

of the many railway lines LTA is currently

developing, is located within the basin of one of

Singapores most important and new catchment area

known as the Marina Barrage. Other than the

intention of turning the Barrage into one of

Singapores water sources, there are also plans to

transform the area into a bustling recreational hub for

Proceedings of the World Urban Transit Conference 2010 (WUTC 2010)Copyright 2010 WUTC Organizers :: Published by Research PublishingISBN: 978-981-08-6396-8doi:10.3850/978-981-08-6396-8 P049 149

water activities. Economic repercussions will be huge

if the water is allowed to be silted overtime. Hence,

the Land Transport Authority being the largest

developer has a major role to play.

Land Transport Authority (LTA)

LTA is a statutory board under the Ministry of

Transport that spearheads land transport

developments in Singapore which includes roads,

rails (Rail Transit System), pedestrian facilities as

well as regulating vehicular and traffic matters. LTA

has till date developed almost 150km length of MRT

both above and below ground as well as a wide array

and network of expressways, arterial, collector and

local access roads which adds up to more than

3,300km and has currently continued to expand its

rail network system to include Downtown Line 1 and

2.

DOWNTOWN LINE 2 - CONTRACT 911

Contract 911 (C911) is managed by LTAs main

contractor: GS Engineering & Construction Hock

Lian Seng Infrastructure Ltd. Joint Venture (GS-JV-

HLS). It comprises the design, construction and

completion of the Depot and its connecting tunnels

between contract boundary C912. C911 is one of the

projects with the largest earthworks and excavation

activities. It has a land area of about 25 ha and an

estimated volume of 3.85 million m3 of earth to be

excavated.

The proposed Depot for Downtown line (DTL) is

located along Woodlands Road and stretch from the

junction of Kranji Expressway (KJE) to Kwong Hou

Sua Teochew Cemetery opposite of Sungei Kadut

Avenue. The proposed Depot as a self contained

operational unit which will be providing maintenance,

operations and support for the operation of

Downtown Line.

The proposed Depot is located at the northern end of

DTL and is designed to maintain an ultimate fleet of

108x3 car electric trains for operation of services

together with supporting service vehicles.

WATER POLLUTION MANAGEMENT AT

C911

Pre-Construction Stage

As required by Singapores Legislation, C911 GS-JV-

HLS had engaged a Qualified Erosion Control

Professional (QECP) to plan and design a system of

earth control measures (ECM). QECPs are registered

Professional Engineers who has satisfactorily

completed specialized professional course in erosion

and sediment control. The submission would have to

include design calculations and specifications such

that the discharge contains less than 50mg/l of total

suspended solids (TSS), the maximum allowable

legal limit stated in the code of practice. Due to its

sheer size, C911 site was segregated into 4 areas and

the ECM plan was initially developed separately for

each of the area before construction works start. As

work in the Depot progressed with increasing

complexity, the team saw that there was a need to

revise and combine all 4 ECM plans to ensure that the

ECM system remains effective and integrated.

Figure 1: Earth Control Plan

On top of the existing legislations, LTA has

developed internal manual and specifications that sets

the standards and system which are required to

establish during the construction phase they are the

Safety, Health & Environmental Management System

(SHEMS) Manual, and the General Specifications

(GS). The SHEMS Manual provides a guide for LTA

project teams to carry out construction work activities

on-site, with due considerations given to

environmental protection. The GS on the other hand,

stipulates contractors responsibilities and provides

details on the provisions that they must provide, with

some of the requirements being stricter than what is

legally required. For example, the Environmental

Control Officers (ECO) engaged by contractors must

have at least 3 years of practical experience relevant

to ECO scope of works and they must attend

professional courses on erosion control so that they

have required knowledge and expertise to manage silt

runoffs on site. Other effective requirements unique

to LTA will be mentioned in the following section.

150 Proceedings of the World Urban Transit Conference 2010 (WUTC 2010)

Construction Stage

Challenges

The concurrent massive excavation work post a great

challenge to the erosion control work. The measures

implemented have to be continuously monitored,

improved, enhanced and relocated. The terrains and

landscape of the entire work site is changing from

time to time. As such, the extensive drainage system

in Area 1 to 4 have to be diverted, adjusted or

relocated from stage to stage.

The nature of the excavation work such as large slope

excavation has again challenged the effectiveness of

the erosion control measure implemented. The runoff

is accelerated and has pick up more erosion before it

is channeled or diverted to the controlled drainage

system.

In addition, the natural location as such higher

platform level over the entire work site than to the

adjacent industrial estate has again constituted a

greater challenge. The design and implemented

erosion control system has to be effective, efficient

and flood protected. No over flow from the erosion

control system from the depot site to the Woodlands

Road and the adjacent industrial estate is allowed

Earth Control Measures on Site

C911 first started off with studies looking into the

feasibility of minimizing the formation of bare

surfaces by opening up the land in phases. Taking

into account the balance between economic

constraints and environmental protection, earthworks

are phased into 2 stages Area 3, 4 and 1 and Area

2. Area 2 (of about 10ha) had started 9 months later.

Another strategy that C911 had adopted is to

prioritize permanent turfing and road works so that

these designated bare slopes are quickly cut to the

required angles and shapes and turfed/paved up as

swiftly as possible.

Figure 2: Permanent Turf Works started in the early

phases

Whenever possible, bare surfaces are protected from

erosion at source by means of various types of covers.

Such covers include use of erosion control blanket,

LSS, hardcores and canvas sheets. In many

circumstances, there are limited areas where

protective covers can be used due to the many

continual on-going works that is carried out on site.

However, GS-JV-HLS does recognize the importance

of reducing runoffs at source. Hence, bare areas with

no activities at the time being (such as surcharging

areas) are identified and covered with either erosion

control blanket or LSS. Other areas where works are

more frequent are, whenever possible, covered with

canvas sheet.

Figure 3: Various Earth Control Measures on Site

Proceedings of the World Urban Transit Conference 2010 (WUTC 2010) 151

Topography of C911 shows that the site generally

slopes towards Woodlands Road. Given the large

amount of on-going construction activities and the

size of the site, effective sediment controls are one of

the key measures in preventing silty water from

flooding Woodlands Road and flowing out into the

stormwater canal. GS-JV-HLS employed the use of

the following measures to contain all runoffs within

the site and to set up a flow system that directs water

to be treated to a level of less than 50mg/l before

discharging:

Perimeter and Internal Drainage System

Pre-cast concrete perimeter drains coupled with

internal concrete-lined drainage system forms the

most important network for an effective sediment

control. This project site has by far one of the most

numbers and length of internal drains that mostly lie

along the bottom of the terraced slopes and

surcharging areas, thus capturing all laden runoffs

before directing them to the sedimentation/retention

ponds. These internal drains are necessary to reduce

potential floodings on the uneven grounds at low-

lying areas of the site and to reduce further erosion at

the bottom of the slope.

Figure 4: ECM plan showing the intricate network of

drainage system

Use of Surcharging Area

Despite the many challenges, C911 had their share of

good fortune. The designated 2m high surcharging

area is located between the slopes and Woodlands

Road, thus providing a much required obstacle to

prevent surface runoffs from discharging out from the

site.

Figure 5: Surcharging area preventing runoffs away

from site

Retention Ponds, Treatment Plants and Monitoring

Devices

A total of 4 giant retention ponds, 1 for each of the 4

areas, have been built to accommodate the maximum

volume of a once in 2 years rainfall. Each pond

measures as follows:

- Area 1 pond = 100m x 21m x 3m



- Area 4 pond = 80m x 15m x 2.5m

A treatment plant of 60m3/h capacity, situated next to

each pond has also been catered for all 4 areas.

Discharges are continuously monitored through

wireless TSS (total suspended solids) monitoring

system where TSS readings can be captured online at

the comfort of ones office. Such device comes with

an additional feature of SMS (short messaging system)

alerts where it sends an SMS to the relevant personnel

when the TSS readings reach above the legal

requirements of 50mg/l.

CCTV camera was also installed at the site of

discharge to monitor the quality of water output.


Figure 6: Retention ponds, treatment systems &

monitoring devices on site

Silt Fence and Silt Traps

While most other construction sites uses silt fence to

line the drains so as to reduce the amount of silt

flowing into the drainage system, C911 employs the

use of silt fence in other ways as well. Silt fences

were lined around material stockpiles to ensure that

the material are, as far as possible, retained within the

designated area. Silt trap have also been installed

along the perimeter drains.

Figure 7: Silt fence along perimeter drains

Figure 8: Silt fence surrounding stockpile

Figure 9: Silt Trap

Earth Control Measures Programmes

LTA had been very active in encouraging contractors,

including GS-JV-HLS, to perform above legal and in-

house requirements for environmental matters. Over

the years, a number of schemes and educational

programmes had been launched to ensure Singapores

environment is being protected while meeting the

developmental needs of the society.

One such effective scheme developed, and used in

C911 as well, is the Environmental, Safety and

Security (ESS) assessment. The purpose of such

scheme is to monitor the contractors EHS

performance on a monthly basis throughout the

contract duration. The assessment consists of a main

ESS form and an annex of ESS form. The annex

assessment form details areas, encompassing ECM,

solid waste management, noise control, water

pollution control, air pollution control and mosquito

control, to be assessed for comprehensive assessment

on Environmental Management. ECM and water

pollution control holds a high weightage of 27 out of

the total 80 marks. The score given in the annex will

be pro-rated to 5% of the main ESS form which

consist of mainly safety management and practices.

The LTA person-in-charge of contract, tasked as the

assessor, has to evaluate the contractors ECM and


water pollution control performance on the following

items:

Environmental Management

Items Max

Score

Actual

Score

Adequate protection of exposed earth

& material 5

Adequate & effective provision/

maintenance of silt traps, silt fence,

wash bays & perimeter cut-off drains

5

Concentration of total suspended

solids in discharge not greater than

50mg/L

5

Earth

Control

Measures

Prevention of earth or construction

wastes littering from construction

vehicles

2

No sign of oil leakages 5 Water

Pollution

Control No sign of chemical leakages 5

Figure 10: ESS Assessment on Earth Control

Measures and Water Pollution Control

The ESS assessment is made more effective by the

Safety Performance Scheme (SPS), a contractually

binding carrot-and-stick (with monetary reward and

penalty) scheme to motivate contractors to achieve

excellent EHS performance on their projects.

Contractors have to allocate 1.5% of the lump sum

stated in the Letter of Award for the provision of ESS

facilities and they are subjected to a total bonus or

penalty of 0.5% subjected to a cap of $1million as

shown in the figure below.

Figure 11: Safety Performance Scheme

Based on the ESS Assessment form where

environmental management accounts for 5% of the

total score, if the contractor achieves a score of 65, he

will be considered as performing up to the minimal

expectations and will not be awarded nor penalized. If

he achieves a score higher than 65, he will be paid an

increased adjustment as according to the graph. On

the other hand if he achieves a score of lower than 65,

the adjustments will be deducted up to 0.5% as

labeled under the poor performer category.

Other programmes LTA has in place includes

publicity materials and promotional events. Since

2006, a series publication have been release year after

year posters promoting effective water pollution,

erosion and sediment controls on site; LTA Safety

Newsletters with articles written on ECM on LTA

Sites and Technical Aspects of Earth Control;

pocket calendars that provides essential information;

and a guidebook on Best Environmental Practices:

Earth Control Measures.

This guidebook provides a good coverage (with

pictorial illustrations) of the relevant legislations, and

the planning and controls that should be in place

during the pre-construction and construction stages. It

also imparts a scoring assessment list to judge the

sites level of ECM implementation. The table below

provides a portion of the items in the list and the

recommended maximum scores. If the site achieved a

total score of less than 50, it indicates poor ECM on

site and further improvements are required. If the site

scores between 50 and 85, it indicates an average

implementation of ECM and there are rooms for

improvements. Achieving a score of above 85 would

indicate excellent ECM on site. LTA contractors are

strongly encouraged to make use of this detailed

assessment list to evaluate their level of ECM

implementation and to identify the area for

improvements.


Figure 12: ECM guidebook and recommended list of

Assessment Criteria

While materials such as the guidebook and

newsletters are meant for Supervisor levels and above,

other items were developed to ensure that the

message was brought across even to the construction

workers on site. For instance, the pocket calendar was

designed to be handy and easy to carry around in

construction sites by workers. It contains information

such as a simple colour comparison chart for

wastewater discharges which can be used to do an on-

site verification on the TSS discharge quality.

LTA also appreciates and recognizes individuals and

contractors who have demonstrated the most pro-

active attitude and has been successful in managing

and promoting environmental protection on their

worksite. Annual promotional and award events were

organized to serve as a platform for acknowledging

their exemplary efforts and for stakeholders to share

their best practices and experiences.

Figure 13: Environmental Excellence Award and

LTA Pocket Calendar

CONCLUSION

Over the years, LTA had developed numerous

national road and rail projects, and from time to time,

distinctive sites such as C911 would emerge and

provide upmost challenges to LTA. For this case, the

unique combination of its vast area of construction,

sloping terrains, high volume of earthworks and large

amount of rainfalls in the recent months, has made

managing the silty discharges from site an uphill task.

However, with an effective environmental

management system in place, continual supervision

by the LTA project teams together with a responsible

and diligent contractor, C911 has now became one of

the sites with the most extensive earth control

measures in place.

ACKNOWLEDGEMENT

Special thanks to LTA C911 Project Team and GS

Engineering & Construction Hock Lian Seng

Infrastructure Ltd. Joint Venture (GS-JV-HLS) for

their contribution and support in developing and

maintaining an environmentally friendly site.

REFERENCES

1. Best Environmental Practices: Earth Control Measures, Land Transport Authority,

Singapore

2. Code of Practice on Surface Water Drainage, Public Utilities Board, 5

th Edition,

March 2000 with amendments under

Addendum No.4 September 2006

3. Environmental Protection and Management Act, Chapter 94A, Singapore

4. Guidebook on Erosion and Sediment Control at Construction Sites, The Singapore

Contractors Association Ltd and Public

Utilities Board, 3rd

Edition, September 2006

5. http://www.singeo.com.sg/singeo/maps/mrtdtlmap.html

6. LTMaster Plan: A People-Centred Land Transport System, Land Transport Authority,

Singapore

7. Sewerage and Drainage Act, Chapter 294, Singapore

8. Singapore Land Transport Statistics in Brief 2008, Land Transport Authority, Singapore

9. Tan Yong Soon with Lee Tung Jean and Karen Tan, Clean, Green and Blue: Singapores

Journey Towards Environmental and Water

Sustainability, Singapore 2009

10. www.pub.gov.sg

11. www.lta.gov.sg


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WATER POLLUTION MANAGEMENT FOR SILT DISCHARGE IN LAND TRANSPORT AUTHORITY PROJECT SITES: CASE STUDY...

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