Works to see if a train tunnel for the Cross Island Line can be built under Singapore's largest nature reserve have been postponed again.
The investigation works to determine the soil and rock profile under the Central Catchment Nature Reserve were supposed to start last month, after an initial postponement from the third quarter of last year. However, they have not commenced to date.
A check by The Straits Times last Thursday showed that the Sime Track and Terentang Trail - on which 10 boreholes were supposed to be drilled - were still open to the public. There was also no sign of any works within the reserve.
In response to queries, the Land Transport Authority (LTA) would only say that work within the reserve is "expected to commence within these two months".
The LTA did not provide reasons for the delay, but The Straits Times understands that preparatory work ahead of the soil investigation works is still ongoing.
But site investigation works for the alternative route have commenced and are expected to be completed at end-2018, the LTA said.
At the central reserve, other than the drilling of the boreholes - each about 10cm wide to extract soil samples - the works also involve geophysical surveys, which will see surveyors going off-trail into the forest to collect data using handheld equipment.
It is less intrusive than the drilling, but nature groups have aired concerns that surveyors may trample on the sensitive vegetation in the reserve.
The latest delay is the second one so far. The works were initially supposed to start in the third quarter of last year, but were pushed back due to extensive talks between the LTA and nature groups.
Discussions then had resulted in the authorities agreeing to put in place 10 extra measures to reduce any negative impact on plants and animals there, on top of an earlier nine.
These include mandating that contractors use enclosures to reduce engine noise and tanks to collect discharge, scheduling at least one rest day in between surveys, and engaging a tree expert to ensure trees are not damaged.
The LTA said it would continue to work closely with the appointed contractors, the National Parks Board (NParks) and key representatives from the nature groups during the works to ensure compliance with the mitigation measures.
The LTA has also engaged an environmental adviser to monitor the process and conduct audits of an environmental management and monitoring plan, which was developed to ensure proper implementation, management and compliance with the mitigation measures.
Green groups, such as the Nature Society (Singapore) and the Love Our MacRitchie Forest volunteer group, are pushing for the 50km Cross Island Line to go around instead of through the reserve, where rare animals, such as the critically endangered Sunda pangolin, can be found.
Biologist David Tan, from the Love Our MacRitchie Forest group, said: "In a sense, it's good that LTA is taking things slowly rather than barrelling through at full speed.
"Mistakes are much more likely to occur when works are rushed, and we know from past incidents that the risk of environmental damage is not insignificant."
Last year, for example, Mr Tan said there were at least two cases at MacRitchie where mitigation measures were either not implemented or had failed entirely, resulting in siltation and damage to two separate streams in the forest.