7.1 INTRODUCTION
There is various mitigation measures recommended to prevent, reduce or eliminate the adverse environmental impacts resulting from the proposed project. Most of the recommended mitigation measures are closely linked to good on-site practices during the various phases of the project development. The project proponent should take these measures into consideration during the detailed design and implementation stage of the project.
7.2 CONSTRUCTION PHASE
7.2.1 Erosion and Sediment Control Plan
During site clearing, it may be necessary to remove existing vegetation and turfing at areas next to the existing road. Consequently, the exposure of bare, exposed land to natural elements of erosion (rain and wind) will lead to soil erosion.
Various mitigation measures can be implemented at the construction phase for different work activities so that the potential impacts are minimized. The Erosion and Sediment Control Plan (ESCP) is prepared based on the requirement of Department of Environment and is to be submitted to the Department of Environment (DOE) for approval. The ESCP aims to:
Reduce and minimize soil erosion and water pollution of the waterways adjacent to the site.
Introduce suitable silt control measures and best management practices for the proposed Project.
Provide guidelines for the implementation of a continuous monitoring programme of the BMPs.
The ESCP is prepared based on the “Urban Stormwater Management Manual for Malaysia” (MSMA 2nd Edition) by the Department of Drainage and Irrigation (DID), 2011 and the “Guideline for Prevention and Control of Soil Erosion and Siltation in Malaysia” by the Department of Environment 1996. The
“Guideline for Erosion and Sediment Control in Malaysia” by DID, 2010 is also used as a reference.
During the construction phase, the proposed Project needs to comply with the relevant standards and legislation as given in the following table.
Table 7.1 : Relevant Standards and Legislation Environmental
DID Guideline for Erosion and Sediment Control in Malaysia, 2010
Drainage DID Guidelines (Urban Storm Water Management Manual for Malaysia, 2000)
Street, Drainage and Building Act, 1974
Table 7.1 : Relevant Standards and Legislation (cont’d) Environmental
Aspects Standards and Legislation
Water Quality Environmental Quality (Sewage) Regulations, 2009
Environmental Quality (Industrial Effluents) Regulations, 2009
In order to minimize erosion and sediment transport, it is necessary to introduce mitigation measures to control erosion and subsequent silt runoff from the site into the drains or water bodies such as:
limiting the extent of ground exposure,
limiting the size of stripped land,
surface stabilization treatment (turfing and temporary protective measures such as covering the soil surface with plastic sheets),
sediment trapping devices and runoff-control measures such as temporary interceptor drains.
These erosion and sedimentation control measures are to be carried out using the Best Management Practices (BMPs) and are described below.
7.2.1.1 Erosion Control Soil Surface Stabilization
After construction begins, soil surface stabilization should be applied to all disturbed areas that may not be at final grade but will remain undisturbed for periods longer than 14 days.
Where applicable and necessary, soil surface stabilization protects soil from the erosive forces of raindrop impact, flowing water and wind.
Other erosion control practices include surface roughening, mulching, and establishment of vegetative cover and the early application of gravel base on areas to be paved.
Effective erosion control will lessen the need for substantial and more costly sediment control measures.
The construction of the KIDEX alignment will have minimal land clearing and exposure as the entire alignment is elevated and mostly will be constructed over road medians and road shoulders which are already paved.
However cut and fill activities are still required for the construction of the at-grade section at the TUDM area (CH12400-12800).
Phasing of Construction Activities
Any land clearing at the road shoulder and road reserves should be carried out according to the development schedule to minimize the amount of land exposure.
Good coordination is vital between the teams responsible for any vegetation removal, paved ground breaking and construction and final turfing / landscaping or hard paving of the new road shoulders and reserves.
Once the area has been cleared, construction should be carried out as soon as possible.
Construction activities should take into consideration the prevailing climatic conditions at that time, particularly rainfall.
It is recommended that as far as possible site clearing be avoided during the wet season to minimize soil erosion.
Vegetation Buffer
Site clearing shall be limited to areas of the alignment for each stage of work.
Vegetation cover should not be cleared or paved surfaces broken up until site clearing and construction is ready to begin.
Buffer strips or corridors of vegetation can also be used to separate disturbed land from adjacent watercourses, as they control and filter sediments from surface runoff.
Buffer strip performance generally increases as buffer width increases or as the buffer slope decreases.
The minimum width of an effective buffer strip should be 10m.
Temporary Covers
If turfing cannot be carried out immediately at the exposed areas, temporary covers such as plastic sheets, geotextile or fibromats can be used instead.
The use of temporary covers, which is either made of natural or synthetic material, can be used to cover up the exposed soil to reduce erosion due to rainfall impact.
Drainage Control
Before commencement of earthworks (if any), temporary drains shall be constructed to channel surface runoff for control of sediment discharge where possible.
Perimeter drains are important to prevent any sediment laden runoff from the site exiting off-site and conversely also to prevent surface runoff from off-site entering into the site.
Drainage provisions within the site and downstream should be adequate to ensure that no flooding occurs. The sizes for the earth drains are as shown in Table 7.2.
Table 7.2 : Sizing of Earth Drains Earth Drain Length maintained to prevent collapse of the sidewalls.
If at all possible, temporary drains in the form of pre-cast concrete drains are recommended as they will not be subjected to erosion and generation of additional sediment.
Depth
Width
If site conditions and space permits, wider diversion drains and dykes should be constructed and where the water flow is greater than 0.6 m/s, check dams are to be constructed to slow down the velocity of the water flow.
The drainage system should be regularly inspected and maintained especially after heavy rainfall.
The temporary drainage should be altered as and when necessary to keep the site free of standing water.
All runoff from undisturbed areas should not be allowed to mix with runoff from disturbed areas.
This can be achieved by constructing contour banks at the downstream boundaries between every disturbed and undisturbed area.
Perimeter drains are recommended for all areas fronting rivers and these drains should be directed into silt traps to prevent direct ingress of silt into the rivers.
Due to the urban surroundings of KIDEX, most of the surface runoff during construction will flow into the existing drainage system before discharging into silt traps and then eventually into larger waterways such as monsoon drains, Sg. Kayu Ara, Sg. Penchala and Sg. Klang.
The temporary drainage systems at major waterway crossings and the design of temporary earth drains are shown in Appendix 8.
7.2.1.2 Sediment Control
Sediment controls must be constructed before land disturbance takes place or at the very least concurrent with the site clearing.
Sediment control will be site specific and can include vehicle tracking controls, sediment barriers, silt traps; or a combination of any or all of these measures to prevent the movement of eroded sediment from being transported off-site.
Some sediment controls can also be used for containment of the work site to prevent the inflow of off-site waters into the site and adding to the sediment load within the site.
For KIDEX, any possible soil discharges will be minimal due to the overall project site area being already impervious and any breaking of hard paved areas will only be necessary at the road shoulders or road medians for piling.
Areas of concern only involve cut and fill areas at the TUDM area (CH12400-12800).
Silt Trap
A total of 30 silt traps will be constructed for major waterway crossings of the KIDEX alignment and also at the cut and fill area at TUDM.
The locations of the silt traps and the proposed design of the silt traps are shown in Appendix 8.
Silt Fences
Silt fences are used to intercept drainage and surface flow prior to entering nearby waterways or rivers.
Silt fences will be installed where necessary at areas fronting the rivers to channel surface water runoff into the sediment basins/traps. The design of a silt fence is shown in Appendix 8.
Silt fences are only appropriate and suitable where surface water flow is not strong and should never be placed within runoff channels.
At the toe of slopes, they must be placed with an adequate distance to allow for maintenance and removal of accumulated sediment.
The construction of silt fences is based on an “as and where /when required” basis.
This means that the location of the silt fences may be shifted, increased or changed as construction site conditions changes.
Check Dam
Check dams are temporary dams constructed across diversion channels and temporary earth drains to reduce the velocity of the storm water flow.
As an example, where the gradient is 2% and the check dams are 0.5m high, the spacing intervals are a distance of 25m.
If the gradient is reduced to 1%, then the distance spacing increases to 50m.The design of the check dam is shown in Appendix 8.
Washing Bay and Stabilized Construction Access
The wheels and undercarriage of trucks exiting the construction site are to drive through a washing bay which is a sump covered with reinforced iron bars and with manual jet spraying to clean the wheels and undercarriage.
The wash water is to be recycled through the sediment settling sump and any overflows directed into the temporary drain that lead into the silt trap. The design of the wash trough is attached in Appendix 8.
The stabilized construction access for the exit should have a paved or concrete slab minimum 10m length or a gravel run of 15m with 15cm gravel depth and 5cm sized aggregate.
The stabilized construction access are to have bunds or drains to channel water back into the sump or sloped back towards the sump and a low bund or cut-back curb to prevent wash water from flowing onto the public roads and drains. The typical design of a stabilized construction access in shown in Appendix 8.
7.2.1.3 Best Management Practices (BMP) Stage 1 – Clearing and Paving for Lane Diversion
If necessary, to relocate existing storm water drain inlets at curbside to outside boundary RHS and LHS of work area and reconnect to existing storm water culvert.
Where practical or viable, protect storm water drain inlet with sandbags, fiber roll, block and gravel, gravel bags, filter fabric or stone (rock) collar. If drain inlets are to be sealed, no more than half to be sealed while at least half to remain open and protected with inlet protection so as not to cause localized flooding of existing roadway.
Temporary containment of cleared area with sandbags or gravel bags beneath safety hoarding prior to preparation of road surface.
Temporary diversion drains or bunds to divert surface runoff from work site into protected storm water inlet.
Stabilized construction access with wash bay at exit from work area.