PURPOSE: To discharge the sewage leaching into a water shielding layer packed with drain materials between double water shielding sheets through filter media and to efficiently treat the leaking sewage by constituting a water shielding structure of this water shielding layer and a pressure receiving means for maintaining a reduced pressure state in the water shielding layer.

CONSTITUTION: The main part of a waste treatment plant 10 is composed of spring water collecting and draining equipment 11 for gathering and draining the underground water which is the spring water in a hollow reclaimed land, the double water shielding sheets 12 for preventing the leakage of the sewage, the pressure reducing pump 13 for reducing the pressure between the water shielding sheets 12 and sewage collecting and draining equipment 14 for collecting and draining the leaching water. The water shielding sheets 12 are constituted by packing the drain materials 12c between both the front and rear surface water shielding sheets 12a and 12b. The sheets are laid atop the filter media 11b placed on the periphery of a spring water collecting and draining pipe 11a. The pressure receiving pump 13 is installed in the outside part of the reclaimed land in communication with the inside of the water shielding sheets 12. The leaking sewage is drained to a sewage treatment plant in case of a water flowing state by rupture of the front surface sheet 12a.