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In a contour plot, a contour line.represents the slr elevation along a line A closed contour therefore indicates either.a depression or a moun The-presence of closec contours representing a deep depression is an unacceptable condition-in ��. the design of a liner system. The deformed I Urface elevations in each grid point are calculated by the computer Program. The deforined surface contours on the 7 percent sloping surface arc then plotted for each case, as shown On Figures EX—1 - EX 4. Where the this ess-of the soil/waste layer is 1.8 m (6 feet), as shown on Figure EX 1, the presence of the Void will create a depression 9 cm (0.3 feet) deep. This depression could trap and accumulate liquids, hindering the free flow of leachate towards a collection point. When the thickn s of the soil-/waste layer above the void is increased to-2.25 m (7.5 feet), the depression is uced to less than 3 cm (0.1 foot), as shown on Figure EX 2.' With a 2.7 m (9 foot) thick so waste layer over the void, the-depression disappears. The disturbance in the liner surface dem ases as the depth to the void increases, as seen when the thickness of the soil/waste layer is in eased to 3.6 m (12 feet) (Figure EX 3 and EX 4). To evaluate the potential for grade.reversal, a characteristic curve of required soil/waste thicknesses M over a 0-9 m (3 feet) wide by 0.9 m (3 feet) deep by 1.8 m (6 feet) long void versus liner surfacegra des (a} is illustrated on Figure 3. s.o — E N 4.0 O ,D N - C 3.0 `O c s 0 r 00 O. cam`, 2:o O-O o \ _ C O�_O 1.0 O 0.0 0 5 10 15 20 25 30 35 40 Containment Liner Grade (degree) Figure 3 Required can oiled fill thickness to prevent grade reversal (T} versus containment liner grade (a) on 0.9m x 0.9m x 1.8m (3'x3'x6') void Goosyndrtics'93-Vancouver,Canada- 1505