Renewing calls for the Government to rethink possible plans to build an MRT tunnel under Singapore's largest nature reserve, several green groups are banding together to ensure their message gets across loud and clear.
Next month, the Love Our MacRitchie Forest volunteer group and the Herpetological Society of Singapore are among those hoping to raise awareness about the issue through a "March for MacRitchie" campaign.
The moves come even as engineers say that contractors have the tools to moderate harmful impacts on the environment.
The month-long series of events, which includes free guided walks to the reserve, school talks and an exhibition at the National Library, aims to inspire Singaporeans to speak up for the forest and support calls for the Cross Island Line to go around, instead of through, the Central Catchment Nature Reserve.
These plans come in the wake of last week's release of an environmental impact assessment report, which found that there will be "moderate" impact on the Central Catchment Nature Reserve when work on preliminary soil tests for the Cross Island Line start in the third quarter of the year. The tests will determine the soil and rock profile, which will help the authorities decide how a train tunnel can be built through the reserve.
The report also said the impact will only be kept to "moderate" levels if mitigating measures, such as the use of enclosures to reduce engine noise and tanks to collect discharge, are effectively carried out.
Engineers who spoke to The Sunday Times said that minimising negative impacts on the environment is well within contractors' capabilities.
In all, the report highlighted nine mitigation measures, which the Land Transport Authority (LTA) said will be part of requirements for contractors doing the site investigations. These measures include having 30m buffer zones around streams and marshes, and using enclosures to minimise noise and tanks to hold discharge, such as drilling fluid.
Contractors must also work closely with National Parks Board (NParks) staff when venturing off-trail or encountering wildlife.
Professor Chu Jian from the Nanyang Technological University's school of civil and environmental engineering, said that while these measures "will certainly increase cost", they were the best that can be offered without compromising engineering design standards.
Mr Chong Kee Sen, president of The Institution of Engineers, Singapore, said the measures could "effectively mitigate noise, soil, water and other impacts to the environment".
LTA has said it will also cut the number of 10cm-wide boreholes up to 70m deep needed to test the soil from 72 to 16. They will be drilled only on existing trails and clearings.
"Locating boreholes near existing trails is a good measure that reduces the effects of having additional access into the nature reserve," said Mr Chong.
Assistant Professor Chian Siau Chen, from the department of civil and environmental engineering at the National University of Singapore, added: "Some of these measures are well over and beyond what is required. All these mitigation strategies are very helpful from an engineering perspective.
"The key factor in ensuring effectiveness of these strategies is the monitoring and control."
But green groups say there are no guarantees whether contractors will stick to these mitigation measures fully. Biologist David Tan from Love Our MacRitchie Forest highlighted a 2013 incident in which a stream at the Venus Drive forest - just outside the reserve - was polluted by contractors despite mitigation measures in place. Similar lapses could affect the rich biodiversity in the reserve, he said.
If discharge from the soil investigation works is not contained properly and seeps into freshwater streams and other aquatic habitats, for instance, sediment could get trapped in the gills of fish and other aquatic organisms.
"The pollution could also affect visibility in the stream, which will have adverse effects on aquatic visual predators," he said.
Ecologists believe it would be hard to prevent negative effects spreading to other parts of the reserve.
Commenting on the 30m buffer zone, Dr Nanthinee Jevanandam, a sustainability specialist from Earthys Sustainability Consulting, said: "In general, increasing the buffer protects the immediate area, but there are interactions that can extend beyond the vicinity." For instance, animals roam the forests in search of food and mates, and may live in different parts of the forest at different stages of their life cycles.
Ms Natalia Huang, principal ecologist at environmental consultancy firm Ecology Matters, added: "The degree of how much of the impact is mitigated cannot be guaranteed and may not be measured either."
Green groups insist there should be zero impact on the reserve, highlighting the importance of the area. It comprises pristine freshwater streams and Singapore's largest patch of primary lowland rainforest. At least 413 species of plants, 218 species of birds, 30 mammals, 24 freshwater fish species and 17 species of amphibians can be found there, including a species of crab found nowhere else on Earth.
Mr Tony O' Dempsey of the Nature Society (Singapore) said: "During the Nature Society's deliberations with LTA, we determined that the impact on animals is high and remained high after mitigation.
"The Nature Society remains of the opinion that no impact is acceptable in the nature reserve."
For the alternative route around the reserve, the impact of soil investigation works along Lornie Road was deemed to be "negligible", and "minor" for areas near Venus Drive and a golf course, according to last week's report, which ST saw.
The decision on whether to build through or around the reserve is still being considered.
"The Central Catchment Nature Reserve is a national treasure," said business owner and former NParks conservation manager Joey Gan, 33, who has joined the March for MacRitchie movement. "Transport may be a key issue for the country but in this case, there is an alternative. If we don't take it, the damage to our national natural heritage could be irreversible ."