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THE SMELL OF SUCCESS
In building Singapore’s newest reservoirs, PUB transformed part of a 30-year-old rubbish dump into an idyllic park for all
By Cheong Suk-Wai
WHEN Mr Lee How Hay was a child, his evenings were redolent of an acrid odour. The stench was from the eastern bank of the Serangoon River, right across from his father ‘s Punggol chicken farm.
That part of the riverbank is known as Lorong Halus, which became a dumping ground in 1970. Rubbish trucks tipped tonnes of raw household waste there daily. By the time the Government closed it down in 1999, the dump spanned 234ha, or more than 100 football fields.
Mr Lee, now 57, and the assistant director of national water agency PUB’s best sourcing department, recalls: “We really got to smell Lorong Halus even though we weren’t exactly living at the river’s edge. The smouldering smell came from methane gas building up in the piles of rubbish.”
Relief came in the late 1970s when his family moved to Ang Mo Kio. But little did Mr Lee know that 30 years later, he would be responsible for transforming a 9ha corner of that dump into one of Singapore ‘s most idyllic spots, and one clean enough for a reservoir to be next to.
This transformation is just one of many innovations by PUB which have made it a giant among water managers globally. From July 1 to 5, PUB will again host and share its expertise at Singapore International Water Week, which draws delegates from around the world to share and learn ways to ensure clean water for all. It takes place at the same time as the World Cities Summit.
The makeover of Lorong Halus began in 2006 , when PUB decided to dam Singapore’s last two main rivers, Punggol and Serangoon, to form the 16th and 17th reservoirs. If PUB pulled it off, those two new reservoirs and Marina Reservoir at Marina Bay would increase water catchment areas from half to two-thirds of Singapore. That is massive for a city-state which relies primarily on rainfall for its water.
Now, living across a dump is one thing, but having one’s drinking water mixed with leachate, or water leaching from a waste dump, is quite another. To that, Mr Tan Nguan Sen, 56, director of PUB’s catchment and waterways department, says : “If it were a fresh dump, we wouldn’t dare do such a thing. But because it has been around for more than 30 years, the waste there has become inert.”
PUB sampled the leachate assiduously before transforming the dump, and found “negligible levels” of the most worrying contaminants, that is, heavy metals such as mercury, lead and cadmium.
So it was all systems go for the reservoir, but PUB went one better: Why not transform the dump into wetlands for everyone to enjoy as a park?
As Mr Tan puts it: “We wanted to turn our challenge into an opportunity, and so we found a way to treat the leachate as well as create an attraction for everyone and a habitat for birds and butterflies too.”
So PUB got its contractor Koon Construction to dig shallow earth basins at a flat part of that 9ha corner of Lorong Halus. Koon then lined these basins with waterproof membranes. Tall grasses, or reeds , and water lilies – plants which are long known as natural super – filters – would be grown in these basins to purify the leachate that would soon be pumped out of the ground and into these basins. The leachate- and reed-filled basins are the wetlands you see today.
PUB roped in wetlands ecologist Michelle Sim, 41, to work with local engineering design firm CPG Consultants to identify nine species of plants in all that were reliable enough to purify the leachate by sucking all the nitrogen and phosphorus out of it. Otherwise, Dr Sim says, these substances would encourage algae to bloom and turn water a sickly green.
Dr Sim previously helped Malaysia set up the 200ha wetlands in its administrative capital Putrajaya.
PUB could easily have used chemical instead of plant filters, but chose the natural way, which was cheaper to boot.
“The only reservation we had, ” Mr Tan admits , “was how effective the plants would be in filtering the leachate because we’d never tried out such filtering in Singapore.”
Today, the wetlands are so safe that PUB has even turned them into an educational destination for students from surrounding schools, such as North Vista Secondary. They trim the thriving reeds.
This haven of flora and fauna is also a new haunt for anglers hoping to reel in snakeskin gourami, perch and fighting fish.
PUB made all that happen in 2 ½ years.
Work to safeguard the Serangoon Reservoir first from the leachate began slightly earlier, in july 2007, with Mr Lee, his boss Koh Boon Aik , and their team “bashing through” jungle-like thickets of tall grass, including lots of lallang.
The entire dump was overgrown because over the years, truckloads of soil would be dumped regularly on the raw waste to tamp it down into the ground, which was soon overrun by weeds.
After slashing their way through metre by metre, PUB contractors Downer EDI and Ryobi-Kiso used a machine with a giant vertical chain saw to cut into the riverbank like a serrated knife through bread. Concurrently, that same machine broke up the cleared land while mixing cement and clay-like bentonite with the loosened soil.
This blitzed mixture dried fast to form a wall which was 0.8m thick, 18m deep and 6.4km long. This underground wall is what is keeping the leachate out of the reservoir today.
There was high drama at one point when the river had to be dredged to accommodate the wall. The dredged riverbed had to be dumped at a granite bund out at sea, but Indonesia suddenly stopped exporting granite to Singapore then. With no bund, Mr Lee had to halt work for almost half a year.
Another contractor, Swee Builders , built 125 wells with pumps and pipes all along the riverbank, to suck water out of the ground every time it rained. Otherwise the pooling rain would put pressure on the wall.
The pumps and pipes direct the rain-cum-leachate uphill to five tanks nearby, which sit on a grassy old rubbish mound. These deep tanks are off-limits to the public and are used to remove ammonia and particles from the leachate. The leachate is then piped downhill into waiting reed beds of cattails, papyrus and vetivers. These total 160,000 clumps in all and come from Thailand.
Of the three reeds, vetivers are usually the most effective filters, but more drama ensued when Dr Sim found them wilting from too much salt and too little phosphorus in the leachate. Luckily, planting more cattails saved the day.
After a final filtering by water lilies, the leachate is discharged into Singapore’s sewage , not potable water, system.
If you worry that some leachate will still find its way into Serangoon Reservoir, Mr Tan stresses that water from the reservoir is pumped out to Upper Peirce Reservoir and monitored for quality before it is tapped for drinking.
In any case, says PUB director George Madhavan, 51, who oversees public communications and community relations, “the reservoir actually starts outside your house. If you litter your surroundings, rain might wash your litter into the drains and carry it right into the reservoir” .
Today, Lorong Halus has left its fetid past behind.
Mr Lee says: “What is meaningful to me is not so much the wetlands as it is that I was involved in starting two new reservoirs to increase water supply for Singaporeans.”