Experts say the landfill needs an underlying layer of clay to prevent toxic materials seeping into the soil and polluting the groundwater. The waste also needs to be alternated with a layer of soil to allow it to decompose properly.

Tatva Global Deonar Environment Ltd., the contractor in charge of the Deonar dump, said [Mumbai's city government] had not provided the material necessary despite agreeing to do so.

The municipal body also dumped more than 6,000 tons of waste a day in the landfill, more than double the agreed amount, a spokesman for the contractor said in an email.