of the 34 polluted waterside 34 12 this excavation can be done by conventional trenching machines with the actual digging being done under the biodegradable slurry 25 to a depth where an impervious stratum or acuaclude 17 exists a liner 24 of synthetic material is next installed in the slurry 25 adjacent the side of the trench 18 opposite the side 20 next to the 34 polluted waterside 34 12 as shown in fig3 the liner extends downward to a point near the bottom 22 of the trench 16 next a resin emulsion pelletized bentonite expansive clay or the like is poured through the slurry 25 to the bottom 22 of the trench 16 to form the plug 32 as shown in fig4 the plug material surrounds a portion 34 of the liner 24 and seals and anchors it in the slurry 25 at the bottom of the trench the next step the installation of a drain pipe 36 and riser pipes 40 in the slurry 25 as shown in fig5 is optional depending on whether it is desired to remove the leachate collected in the final step shown in fig6 gravel 42 is backfilled into the slurry 25 if a drain pipe and riser pipes 40 were previously installed as shown in fig5 the gravel 42 used would be pervious in nature if no drain was installed the gravel 42 used could be impervious in nature and together with the liner 24 and plug 32 form a totally impervious barrier to the migration of leachate from area 12 to area 14 if leachate collection becomes the sole purpose of the trench as may be the case for cross lot collection drainage within the boundary of the contaminated.