Tests to see how a train tunnel can be built through Singapore's largest nature reserve would have a "moderate" impact on plants and animals there, but only if measures to reduce impact are strictly implemented.
Otherwise, the soil investigation works for the upcoming Cross Island Line could have a large impact on the highly sensitive parts of the Central Catchment Nature Reserve. The mitigation strategies to prevent this include the use of enclosures to reduce engine noise and tanks to collect discharge.
This was one of the findings of an independent environmental study commissioned by the Land Transport Authority (LTA) to assess the impact of the line on the reserve, which includes reservoirs like MacRitchie, Upper Seletar, Upper Peirce and Lower Peirce.
Although gazetted by the LTA last Friday, the first viewings of the roughly 1,000-page report started only yesterday.
"The significance of residual impacts is mainly moderate (moderate to major), with the possibility of escalating to major only if the mitigating measures are not observed," said the report by consultancy Environmental Resources Management.
Last Friday, the LTA committed to some of these mitigation measures, like getting contractors to work closely with the National Parks Board (NParks) when venturing off-trail or encountering wildlife, and applying a 30m buffer zone around streams or marshes.
While environmental groups here acknowledged efforts to minimise impacts on the reserve, which is home to critically endangered species of wildlife such as the Sunda pangolin, they maintained that an "acceptable impact is no impact".
Mr David Tan, a biologist from the National University of Singapore and a member of the Save Our MacRitchie Forest volunteer group, opposes the idea of running an MRT line through the Central Catchment Nature Reserve. Despite the mitigating measures, he noted that the works will continue to have a "moderate to major" impact on the forest.
"Lapses in safety and vigilance can and will occur no matter how many mitigation measures are in place," Mr Tan added.
An LTA spokesman said measures proposed in the environmental impact assessment (EIA) Phase 1 study will be part of the contract requirements for the site investigation contractors. "No works can start until LTA is sufficiently assured that the measures are in place. LTA will closely supervise the contractors during the works. In addition, both NParks and the consultants, as well as representatives from nature groups where appropriate, will monitor the mitigation measures," she added.
Professor Peter Ng, head of the Lee Kong Chian Natural History Museum, said that although building an MRT line that cuts through the nature reserve would cause considerable impact, it is still too early to say whether that decision will be made.
"Soil investigation works is just part of the EIA. After all the data has been collected, it would be up to the authorities to study the information objectively, and decide if the line will still cut through."