Guide Book on Silt Control at

Construction Sites

Jointly produced by :

The Singapore Contractors Association Ltd Public Utilities Board

www.pub.gov.sg/ECM

CONTENTS

1. Preface o Message from SCAL o Message from PUB Director, Drainage Department

2. Why is there a need for ECM? 3. How can the Construction Industry help?

o Developer / Owner o Contractor o Professional Engineer

4. How to have an effective ECM? o Erosion Control o Sediment Control

5. What is the procedure to submit ECM? 6. Checklist of Erosion and Sediment Control 7. Bad & Good Practices at construction sites 8. Legislation against silty discharge into public drains 9. ECM products, services and technologies

10. Other useful links Annexes Annex 1 Sample specifications and itemised breakdown for

ECM Annex 2 Schematic drawing for ECM at construction sites

Preface Message from SCAL: The Singapore Contractors Association has been supporting the effort to promote a high level of environmental awareness in the construction industry and we should play a more proactive role to ensure the construction sites and related development works would not give rise to environmental hazard in the neighborhood. Together with the Drainage Department, SCAL has produced this guidebook, highlighting on the basic measures that the contractors should take to prevent or minimise water pollution by the wash down of silt and debris from the construction sites into the public drain. We hope that the guidebook on silt control at construction sites will serve its intended and meet the requirements of the contractors. Mr Tan Kian Hoon President Singapore Contractors Association Ltd

Message from PUB: This guidebook is the result of a joint effort between the Singapore Contractors Association Ltd and the Drainage Department. We are very grateful to the Association for its active participation in this publication, particularly its hardworking officials and committee members who, despite their busy schedules, found time to work on the guidebook. My sincere thanks to the President and Council Members of SCAL, and members who have contributed towards the publication of this guidebook. Unlike the rivers and canals of the past, we now have beautiful and clean watercourses that we can be proud of. Everyone of us plays a part in keeping our waters clean. As contractors, your role is important. Through the simple act of controlling earth and silt washdowns, you can prevent your site from becoming a source of muddy waters that taint our watercourses. This guidebook contains an overview of silt or earth control measures that can be implemented at construction sites. The measures described in the book are chosen because of their proven effectiveness and ease of installation. Other measures may be necessary for worksites with special needs. We hope that you will find this guidebook useful. With best wishes, Yap Kheng Guan Director, Drainage Department

Why is there a need for Earth Control Measures (ECM)?

Singapore is well respected for her clean and green environment as well as her resourcefulness in harnessing her scarce water resources.

Over the years, we have spent much effort to clean up and beautify our rivers. This has resulted in the clean and aesthetic waterways, like Singapore River and Kallang Basin which Singaporeans enjoy today.

Singapore River

Sungei Sembawang Sungei Api Api

While our rivers and canals are clean most of the time, we still see them turn brown during and after a rain. The silty brown water is spoiling our proud image of a green and clean Singapore.

More importantly, the silty water is hampering our effort to make every drop counts as the silt will make it more difficult and costly to treat. Over the next 5 to 10 years, more of our canals and rivers will be dammed up to increase Singapore's robustness in water resources. By 2008, a barrage will be built across Marina Bay which will impound water from 5 major urban river catchments.

Together we can definitely do more and better to improve the quality of the storm runoffs discharging into our rivers and canals.

What causes the river to turn brown? Silt and sediment control is a key element in our stormwater management strategy. Sediments introduced into our rivers cause environmental pollution and increase flood risk and turn our river water brown. Sediments can remain suspended for a very long time.

The major source of sediments is from construction sites. Construction activities disturb existing ground cover and vegetation, and expose much bare surfaces.

How can the Construction Industry help? Each sector of the construction industry plays a critical role in implementing an effective earth control measures (ECM) at construction sites, as follows:

Developer / Owner

to specify ECM requirements into the contract document and allow contractor to price the ECM works into the contract sum (see Annex 1 for sample specification and itemised BQ)

Contractor

to engage a Professional Engineer (PE) to design the ECM (see schematic drawing in Annex 2) and continuously review it for the whole duration of works to meet the changing site activities.

to install the ECM according to PE's design before the commencement of site works, and modify it as required by the PE during the course of the work.

to maintain the ECM until the end of the site works, and only remove the ECM until permanent rehabilitation of disturbed areas are put in place, and as advised by PE.

to submit a set of ECM proposal (and its updated revisions based on construction phases) to Director, Drainage Department for record.

to submit photos showing well-maintained perimeter cut-off drains, silt fence, sedimentation basins, discharge point and public drains downstream of the construction site to Director, Drainage Department by email on a weekly basis and after every rain.

Professional Engineer

to advise the developer / owner and contractor on the importance of ECM in Singapore's effort to remain clean and green, and to harness every drop of water.

to plan and design an effective ECM to be in place before the commencement of construction works.

to continuously review and improve the ECM in tandem with the changing site activities.

How to have an effective ECM?

An effective earth control measure (ECM) must comprise 2 aspects:

(a) Erosion Control - to minimise bare earth surfaces (b) Sediment Control - to capture sediment

and shall comply with Clause 6.3 of the Code of Practice on Surface Water Drainage.

Erosion Control It is much easier and more cost-effective to prevent erosion than to trap sediments after erosion has taken place. With proper planning, a site should not have more than 0.1 ha of bare surface at any one time.

The following are some good ECM management practices to minimise erosion by having minimum bare earth surfaces:

to sequence and schedule the earthworks / demolition works in stages and progressively with the subsequent construction activities and building works.

to minimise site disturbance by keeping site clearance works to a minimum by retaining as much of the existing vegetation as possible.

to pave up the bare surfaces and all construction access by concrete or milled waste or other suitable materials.

to turf up the bare surfaces immediately in an earthwork / demolition work if there is no subsequent construction activities.

to protect the bare slopes by close-turfing, cementitious spray / grouting, canvas sheet or erosion control blanket.

to protect the earth stockpiles by canvas sheet or erosion control blanket.

Sediment Control After achieving minimum bare earth surfaces, sediment control facilities must be put in place to capture the sediments washed down from the construction sites. Some of these sediment control measures and facilities which must be in place before the works start shall include the following:

to provide concrete-lined cut-off drains (minimum C7 precast channel) along the perimeter of the construction sites.

to provide silt fence properly installed and embedded onto the ground along the perimeter cut-off drains (between the construction site and the cut-off drains).

to provide sedimentation basins of adequate size and sufficient numbers along the perimeter cut-off drains and before the discharge points into public drain.

What is the procedure to submit ECM?

(I) During Planning and DC stage

Director, Drainage Department will include the standard clause when giving clearance / approval for the owner/ developer to take note of the ECM requirement or for the QP to advise the owner / developer :

The developer/owner shall provide effective erosion and sediment control measures and facilities (such as perimeter cut-off drain, silt traps, turfing/covering to bare areas) to control silt and mud from construction site, and shall desilt and clear all affected watercourses until completion of development work. The proposed erosion and sediment control measures are to be submitted by a Professional Engineer to Drainage Department for record before commencement of earthwork.

(II) During Construction Stage

The Contractor shall submit the ECM proposal duly endorsed by his PE to Director, Drainage Department and carbon copied to the owner / developer as follows:

Before Work Commences - to submit the ECM proposal indicating that:

o minimum bare surfaces will be ensured according to the construction activities in each phase.

o a system of ECM will be in place before work commences

During Work - to revise and resubmit the ECM proposals according to each phase of the construction activities indicating that:

o Minimum bare surfaces will be ensured.

o the system of ECM will be effective for each phase will be in place before each phase commences.

Upon Work Completion - to confirm that all the site activities have been completed and the ECM can be removed.

CHECKLIST OF EROSION CONTROL

To minimise bare earth surfaces to 0.1ha at

any one time To sequence and reschedule earthworks or

demolition works in stages and progressively with subsequent activities

To pave up all construction access and bare

surfaces with concrete, milled waste, etc To protect bare slopes and stockpiles with

canvas, close turfing or erosion control blankets

To establish final surface / turfing quickly

CHECKLIST OF SEDIMENT CONTROL

Provide perimeter lined cut-off drains Provide perimeter silt fences along perimeter

cut-off drains Provide adequate size and number of

sedimentation sumps before discharge and along the perimeter cit-off drain

Protect earth slopes/surfaces with closed turf,

milled waste, concrete, erosion control blankets, polythene sheets or other suitable materials

Maintain sediment control facilities at least

once a week and after every storm event Review ECM plan with PE as work

progresses Remove ECM only at the end of work and as

advised by PE

BAD & GOOD PRACTICES

AT CONSTRUCTION

SITES

r SILT FENCE NOT PROPERLY INSTALLED

Silt fence not properly embedded resulting in gaps below the fence

Silt fence is installed on the wrong side. It should be installed to trap the silt from the worksite

r INADEQUATE SILT TRAP/ SEDIMENTATION TANK

Inadequate silt trap resulted in silty water discharges onto adjacent footpath

Inadequate sedimentation tank resulted in silty water discharges into public drain

r BARE SLOPES/SURFACES

Uncovered earth slopes/ surfaces resulted in silt being washed down into public drains

r DISCHARGED OF SILTY WATER INTO PUBLIC DRAINS

Silty discharges at upstream, causing siltation of abstraction pond at downstream

a TYPICAL SILT FENCE & LINED PERIMETER CUT-OFF DRAINS

Silt fence firmly embedded in ground and installed in between cut-off drain and worksite

a COVERING BARE AREA

Earth slope protected with canvas sheets

Earth slope covered with closed turfing

Earth stockpile protected with erosion control blankets

LEGISLATION AGAINST SILTY DISCHARGE INTO

PUBLIC DRAINS

The following legislation and requirements pertaining to the control of erosion and sediment are highlighted: THE SEWERAGE AND DRAINAGE ACT, CAP. 294

Works affecting storm water drainage system

Section 26(1) - No person shall carry out or cause to be carried out any works which will affect any storm water drainage system, drain or drainage reserve, directly or indirectly, without obtaining in respect of those works, a clearance certificate or approval of the Director.

Section 26(2) - Where any work has been carried out in contravention of subsection 26(1), the Board may by Notice in writing require the person who carried out the works, the owner or occupier of any premises in respect of which the works were carried out to carry out such works as the Board thinks necessary within such time as may be specified in the Notice.

Default in compliance with notice

Section 41(1) - Where a person on whom a Notice under section 26 is served fails to comply with the notice within the time specified in the Notice, he shall be guilty of an offence and shall be liable on conviction to a fine not exceeding $20,000.

SEWERAGE AND DRAINAGE (SURFACE WATER DRAINAGE) REGULATIONS REVISED EDITION 2001 Prohibition of discharge of silt, etc. into storm water drainage system Regulation 4(1) - No person shall discharge or cause or permit the discharge into the storm water drainage system of Total Suspended Solids in concentrations greater than 50 milligrams per litre of the discharge.

Regulation 4(2) - Every person carrying out earthworks or construction works shall comply with the Code of Practice and in particular with the following requirements:

earth control measures shall be provided and maintained in accordance with the Code of Practice

runoff within, upstream of and adjacent to the work site shall be effectively drained away without causing flooding within or in the vicinity ofthe work site.

all earth slopes shall be set outside a drainage reserve;

all earth slopes adjacent to any drain shall be closed turfed; and

adequate measures shall be taken to prevent any earth, sand, topsoil, concrete, debris or any other material to fall or washed into the storm water drainage system from the stockpile thereof.

Penalty Regulation 6 - Any person who contravenes or fails to comply with any provision of these Regulations shall be guilty of an offence and shall be liable on conviction to a fine not exceeding $5,000 and, in the case of a continuing offence, to a further fine of $500 for every day or part thereof during which the offence continues after conviction.

ECM products, services and technologies Silt Fence

Silt fence is a sediment control practice. It is intended to be installed adjacent to critical areas where sediment-laden water can pond, thus allowing the sediment to fall out of suspension and separate from the runoff. It is not intended to be an erosion control practice. Improperly applied or installed silt fence will increase erosion. Suppliers: AbacusCorp , email : abetrad@Singnet.com.sg Mirafi Geosynthetics Products :

http://www.mirafi.com/products/products_index.html Permathere : http://www.permathene.co.nz/htm/silt.htm Southwest Environment Services, Inc :

http://www.southwestenvironment.com Sedimentation Tank

Environmental Management Division : http://www.hkpc.org/emd Hong Kong Productivity Council : http://www.hkpc.org

Silt fence is a temporary sediment barrier consisting of filter fabric entrenched into the soil and attached to supporting posts for efficient control of sediment run-off from construction sites.

AquaSed, a system specially designed by Hong Kong Productivity Council (HKPC), is capable of treating large volume of highly turbid silty water discharged from construction sites. This system can treat the silt water to comply with the discharge standards and ensure the construction work uninterrupted.

Erosion Control Blankets

Suppliers : North American Green : http://www.nagreen.com CHT-Natural Solutions, email : yufong@starhub.net.sg Mirafi Geosynthetics Products:

http://www.mirafi.com/products/products_index.html

Turbitiy Curtain

They are intended for construction work adjacent to a water resource to contain sediment within the work area. They allow suspended sediment at a dredging site to settle out of the water column in a controlled area, minimising the area that is affected by the increased suspended sediment usually present at a dredging site. However, turbidity curtains are limited to project locations with less than 1-2 knot currents.

Suppliers: Elastec American Marine Inc : http://www.elastec.com/curtains.html Permathene : http://www.permathene.co.nz/turbidity.htm Mentanza Pty Ltd : http://www.mentanzapl.com/silt_screens.htm

Turbidity curtains are impermeable barrier, constructed of a flexible reinforced thermoplastic material. The upper hem has floatation material and the lower hem has ballast material.

An alternative to canvas sheet and closed turfing, it is a machined-produce mat made of coconut or palm oil fibre which provides immediate erosion control once installed.

It is biodegradable and has different grades for different duration of protection, ranging from 2 months to 36 months.

Indirect Screening for Silt / Debris Control

Conventional direct screening Indirect screening technology

Suppliers: CDS Technologies : http://www.cdstech.com Stormceptor : http://www.rinkerstormceptor.com Rocla : http://www.pipe.rocla.com.au

Other useful links

International Erosion Control Association : http://www.ieca.org

US Environmental Protection Agency : http://www.epa.gov

A non-powered, low maintenance alternative to traditional screening systems. Its unique and non-blocking screen design is capable of deflecting silt / flotsam for removal while allowing clean water to flow back to the waterways.

Annex 1 SAMPLE SPECIFICATIONS FOR EARTH CONTROL MEASURES 1 The Contractor shall be responsible for preventing silt from being

washed into public drains by implementing an Earth Control Measure (ECM) for the construction site to meet the requirements under the latest Sewerage and Drainage Act Cap 294. (Information on ECM requirements can be found in PUB website www.pub.gov.sg/ECM)

2 In his tender submission, the Contractor shall submit his

schematic ECM plans of the construction site for the contract duration taking into account the different phases of construction activities. He shall also provide the name of the PE who will be endorsing the ECM plan after the tender is awarded. These schematic ECM plans shall make the Contractor aware of the ECM requirements and the cost to implement an effective ECM. Notwithstanding the submission of these schematic ECM plans the Contractor shall deem to have separately price for the ECM in the contract sum.

3 Before construction works commence on site, the Contractor

shall engage a Professional Engineer (PE) to plan and design the ECM, and he shall install the ECM according to the PE's design. The ECM plan and design shall be submitted 1 week after the award of the contract. During the course of the construction works, the PE shall review the ECM proposal regularly to meet the changing needs of the construction activities. The Contractor shall improve the ECM as advised by his PE. The planning and design of the ECM shall meet the minimum requirements stipulated and in accordance to the Code of Practice on Surface Water Drainage.

4 The Contractor shall maintain the ECM for the whole duration of

the contract to ensure that it is effective at all times. Proper records detailing the maintenance works, supported by dated photographs, shall be kept by the Contractor for verification.

5 The Contractor shall not remove the ECM until all works are

completed and upon the advice of his PE. 6 The Contractor shall submit the ECM proposal duly endorsed by

his PE to Director, Drainage Department for records. The proposed ECM shall consist of the following three parts:

I. Project Particulars

The following information shall be provided under the Project Particulars: (a) Project description (b) Name and address of site occupier; (c) Site area and contract period; (d) Location map and site plan.

II. Erosion Control Plan (described in 7)

III. Sediment Control Plan (described in 8) 7 During construction, the Contractor shall minimize the formation

of bare surfaces under the ECM's Erosion Control Plan. The Plan shall depict graphically the activities, including sequence of work, type and duration for each phase of construction activities to include the following measures to:

(a) sequence and schedule of the earthworks I demolition works

in stages and progressively with the subsequent construction activities and building works.

(b) minimise site disturbance by keeping site clearance works to

a minimum by retaining as much of the existing vegetation as possible.

(c) pave up the bare surfaces and all construction access by

concrete or milled waste or other suitable materials. (d) protect the bare slopes with close-turfing, concrete grouting,

canvas or erosion control blanket.

(e) protect the earth stockpiles with canvas or erosion control blanket.

(f) restore ground cover over disturbed areas, which are or have

become bare, as soon as possible.

8 The Contractor shall put in place the ECM's Sediment Control Plan, which aims to capture the sediments washed down from the construction sites. Some of these sediment control measures and facilities, which must be in place before the works start, shall include but not limited to the following:

(a) concrete-lined cut-off drains (minimum C7 precast channel)

along the perimeter of the construction sites. (b) silt fence properly installed and embedded onto the ground

along the perimeter cut-off drains (between the construction site and the cut-off drain).

(c) sedimentation basins or any other sediment filtering or

settling system of adequate size and sufficient numbers along the perimeter cut-off drain and before the discharge points into public drain.

9 The PE shall submit full basis of design back up with design

calculations to show clearly how the perimeter cut-off drains, silt fence and sedimentation basins are designed and sized as well as how such design will effectively filter off silt and allow only clean water to discharge into public drains. The discharge into the storm water drainage system shall not contain Total Suspended Solids in concentrations greater than the limit stipulated in the latest Surface Water Drainage Regulations and Code of Practice on Surface Water Drainage. The intensity of a one-in-two year storm should be adopted for the proposed design.

Sample Itemised Breakdown for Earth Control Measures S/No Description Qty Unit Rate Amount

($)

A Allow for engaging a Professional Engineer to design and submit an Earth Control Measures Proposal to the full satisfaction of the SO as well as Director, Drainage Department; all as specified.

- Item -

B Allow for the implementation

and maintenance of the Erosion Control Plan; all as specified.

- Item -

C Allow for the implementation

and maintenance of Sediment Control Plan; all as specified.

- Item -

TOTAL TO SUMMARY OF TENDER

Annex 2

Acknowledgement

1st edition - 2001

1. The Singapore Contractors Association Ltd

2. Drainage Department, Ministry of the

Environment

2nd edition Dec 2003