How Bukit Batok BTO site will prevent water pollution
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Earth control measures are in place at the West Glades @ Bukit Batok BTO site to prevent the contamination of public drains.
PHOTO: ST FILE
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The Housing Board is putting in place measures at the West Glades @ Bukit Batok Build-To-Order (BTO) site
Stage 1: Inspection before tree felling
aqbto09 Tree pre-felling inspection. This is to check for presence of wildlife, e.g. nesting birds, and ensure that trees that are meant to be conserved will not be felled.
PHOTO: HDB
This is to check for wildlife, for example, nesting birds, and to ensure trees that are meant to be conserved will not be cut down.
All sections of the site that have been cleared have progressed from this stage.
Stage 2: Site clearance
aqbto09 Some land is cleared to form a path for the construction of the drain, including working space. Credit: HDB
PHOTO: HDB
Some land is cleared to form a path for building the drain, including working space.
Certain sections of the site, mainly the eastern and northern edges, are at this stage.
Stage 3: Trench excavation for drain construction
aqbto09 A trench is dug for the installation of the precast concrete drain segments.
PHOTO: HDB
A trench is dug to install precast concrete drain segments.
Certain sections of the site, mainly the western and eastern edges, are at this stage.
Stage 4: Installation of precast drain segments and earth control blanket
aqbto09 The precast drain segments are installed piece by piece. The exposed earth surfaces are installed with ECBs. Credit: HDB
PHOTO: HDB
The segments are set up piece by piece. The exposed earth surfaces are covered with earth control blankets to minimise soil erosion.
Certain sections of the site, mainly the southern and western edges, are at this stage.
Stage 5: Installation of silt fence between drain and earth work area
This is to minimise silt flowing into the cut-off drain.
None of the sections has reached this stage.
National water agency PUB requires this to be in place before site clearance works can continue.
How the breaches occurred
Due to the hilly terrain, HDB set out to construct the drains to collect silty water in two stages.
In the first stage, an interim drain is built at the top of the lower slope to facilitate earthworks above it. This is necessary because if the drains were to be first constructed along the perimeter at the base of the slope, the slope may become unstable.
In the second stage, as the slope is cut back and the earth works progress towards the interim drain, the drain will be replaced with a similar one along the hoarding at the base of the slope.
Frequent rain in the past one to two weeks had hampered the progress of works on the drains.
Some parts of the earth were exposed due to earth works and the contractor progressively installed earth control blankets as a temporary measure to minimise soil erosion. But due to a temporary supply issue, the contractor was not able to cover some exposed areas within a day.
While the site’s environmental mitigation and monitoring plan stipulates that the blankets used should be 100 per cent biodegradable, the contractor temporarily used a different blanket for localised areas outside the hoarding due to the lack of supply. This has since been resolved.
Sources: HDB, Ministry of National Development
