But today, a mere eight years after the last rubbish truck tipped its smelly load there, link houses have sprouted on the site, together with a 23-storey block of low-cost flats. And towering apartment blocks and shoplots will be built soon. And on the land next to the Taman Beringin landfill in Kepong, the largest in the country as it cater to Klang Valley dwellers' garbage, a five-storey apartment block is coming up.

These developments have gotten solid waste experts cringing - many feel landfill sites are just not suitable for human habitation as these dumps can leak foul liquids as well as combustible and explosive gases for years as waste slowly decays. And as decomposition gradually shrinks the waste volume, the land will sink.

"Closed landfills will continue to pose a threat to public and environmental health as waste decomposition can last for as long as 50 years," says Dr Mohd Nasir Hassan, an associate professor in environmental management at Universiti Putra Malaysia.

"Redevelopment of landfills is risky as there are no records of these sites. So their exact boundaries are usually unknown, as are the volume and types of waste," adds Nasir, who had monitored landfill leach ate (polluted wastewater) and gases in the Kelana Jaya dump in the 1990s. He reckons construction on landfills can be considered only after a lapse of 10 to 30 years - and provided the landfill is an engineered one featuring pollution controls and was properly closed with stabilised slopes, drains to collect leach ate and pipes to collect landfill gases.

Unfortunately, this is not the case in Malaysia. Almost all landfills here are essentially mountains of trash and simply abandoned when no longer used, which hardly makes them suitable for placing structures. But urban sprawl means that many disused landfills sit on what is now considered prime land. And so residential estates, commercial sites, factories, parks, golf courses and football fields have come up on many old landfills, and some of these have served to demonstrate the foolishness of building atop contaminated sites without taking safety measures.

Cracks have developed in houses in one residential site in Ipoh and in Taman Kota Laksamana in Malacca as well as low-cost flats in Bukit Kecil in Kuala Terengganu. Ground settlement left a golf course in Kuala Terengganu and a football field in Kuantan with undulating ground. Land subsidence of up to 2m in some spots caused the watchtower of the Fire Services Department in Setapak, Kuala Lumpur, to collapse in the late 1990s and left huge gaps between the ground and the foundation of the firemen's apartments.

High risks

Explosions seen in landfills of some countries have yet to occur here but Japan International Co-operation agency (Jica) consultant Hisashi Yamauchi warns of such a likelihood. "Landfill gases are known to migrate as far as 1km to an adjacent site. The state government should be careful with the development at the Kelana Jaya and Taman Beringin landfills as there is no proper closure," says Yamauchi, who heads the Jica team which recently completed a two­year project on landfill closure.

He says new guidelines on safe closure of landfills in Malaysia, prepared by Jica, recommend that landfills not be developed for at least 10 years after closure and should meet these conditions: the leachate must meet Department of Environment standards, have methane production of less than 1% and land settlement of below 2cm a year.

Dr Yasushi Matsufuji, a professor in landfill management at Fukuoka University in Japan, warns that there will always be risks and danger in and around landfills. "In open dumps, waste layers are in anaerobic (lacking oxygen) condition. Therefore, waste decomposition is much slower than that of well-designed semi-aerobic landfills. Landfills are stabilised only when the decomposition is completed. Therefore, any major reuse on or around landfills is not recommended (as long as) the landfills do not reach the stabilisation point which can take over 10 years from their closure," says Matsufuji, who is advisor to the Jica project.

He says government agencies must identify and register all landfills so that land authorities will have the right information when vetting development proposals.

In many instances, however, Malaysian house buyers purchase properties while unaware of the history of the sites.

Furthermore, the law is silent on the redevelopment of landfills. The Street, Drainage and Building Act 1974 prohibits buildings on unsanitary land where faecal matter, animal waste and vegetable waste have been dumped until the site has been rehabilitated and the waste removed.

Oddly enough, the Act makes no mention of municipal landfills despite the threat posed by such lands which may well contain illegally-dumped chemicals. There are also no guide­lines on how landfills should be rehabilitated and how much of the waste should be removed before development.

Safety steps

Developers of projects at the Kelana Jaya landfill, however, insist that all precautions have been or will be taken to render the land safe for structures.

One of the projects, launched two years ago, is on 4.8ha of the landfill. It consists of 120 units of link houses and 120 units of shoplot­cum-apartments, and was developed by Selaman Sdn Bhd, a subsididary of the Selangor State Development Corporation.

Mohd Faizal Othman, a civil engineer with Perunding PKJP, the consulting engineer for the development, insists that most of the buried waste had been extracted and disposed of at the Ayer Hitam landfill in Puchong. He says a 5m-thick layer of landfill waste was removed, leaving behind 1m which "posed no threat."

"We have used reinforced concrete piling to get a stable foundation. House buyers need not worry about settlement of houses as we have tied all the slabs (house foundation) to beams instead of the usual method where the slabs just sit on the earth."

He says the site was topped up with a layer of soil and, beneath each house, a layer of geo-textile material separates the waste layer from the top soil to prevent seepages. He says pipes were laid in the ground to tap gases and leachate, and these pipes are channelled towards a river bank.

Despite these measures, it is evident that the land was a rubbish dump as heaps of partially-decomposed rubbish can be seen at the project site. A cut slope behind a row of the, almost-completed link houses reveals partially-decayed waste inside. In the backlanes, trenches dug for drainage pipes show that the ground still contains landfill waste and no top layer of soil cover was evident.

Another development at the Kelana Jaya landfill consists of 118 shops and office units as well as a 15-storey block of serviced apartments. Waste is currently being excavated from the site. A staff member of the developer, Puncak Dana, says that only some of the waste will be removed and the site will be covered with 1m of earth. "We will use a strong piling system that is designed to be end-bearing, and will pile 12m to 20m deep until the piles reach a hard layer in the earth."

UPM's Nasir points out that piling will only support the houses; since there is no piling for roads and drains, such infrastructure may be affected by land subsidence. Nasir says landfill mining (the extraction of buried landfill waste), although technically possible, is a ridiculous idea because of the cost of excavation and proper disposal. He says the waste removal should be monitored to ensure the dug material goes to another landfill.

Urging for more scrutiny on development on closed landfills, he says the activity should undergo environmental impact assessment which currently is not the case. For Nasir, the two most favoured options for old landfills are recreational and non-food farming, such as tree plantations.

Noor Mohamed Mohamed Haniba, project executive at Worldwide Landfills Sdn Bhd which operates the Ayer Hitam landfill, concurs: "I will always say, go for parks."

He says the Ayer Hitam landfill, due to close in December, will be returned to the state government seven to 10 years later. "We have advised the state that it should then wait a further five to 10 years before doing anything structurally. In the meantime, the site can be turned into a park."

He cautions that landfill mining does not render a landfill suitable for development Geo-technical studies are still needed to deter­mine the exact boundaries of the landfill and the extent of pollution at the site. Landfill mining, he says, is not merely digging out the waste but should be done with care to prevent explosion risks.