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T •'ZV:stty!C•wY'1�'r.s+ � 4.=• s'T^w yN,-uC�7^'• ...n�a • ._ye•ag1-..._".-�"�.!' elevation clan. In a contour plot, a contour �Cine.repre. "nts thy' S . A closed contour therefore indicates either a depression ora artoun The presence of closedcontours representing a deep depression is r- unacceptable condition i,. the design of a liners stem. The deformed surface -elevations in each d point am calculated by the Program. The deform surface contours on the percent loping surface are thento computer each case, as shown o Figures EX 1 - EX 4. P fled for ' Where the Chic ess-of the soil waste layer's 1.8 m (6 feet), as shown on Figure EX I, the presence of the vol will create a depression 9 cm ({3.3 feet) deep. This depression could trap and accumulate liquids, hindering the free flow of leachate towards a collection point. When the thiakn s of the soil/waste layer above the void is increased to•2. feet), the depression is ueed to less than 3 cm - m (7.h • (Q.1 foot); as shown on Figure EX 2. With a 2.7 rn•(9 foot) thick so !waste layer over the void, the depression disappem. The disturbance in the liner surface deca== as the depth to the void increases, as seen when the thickness of the soil/waste l-aYer is iln creased to 3.6 m (12 Abet) (Figure EX 3 and 0X_4). To evaluate the potential for grade reversal, a characteristic curve of required soil/waste thicknesses U) over a 0 9 m (3 feet) wide by 0.9 rn (3 feet) deep by 1.8 m (6 feet) long void versus liner surface grad (a) is illustrated on Figure 3. 5.0 E z H 4.0 0 d C & c c U f- 0 1171, 0 O.2.0 o` O CD v -- O 0-O 0 S 10 15 A"20 25 30 35 40 Confo_inm-enf Liner Grade (degree) _ Figure 3 Required con 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 GeasyndrAjr-s*93-Vancouver,Canada-1505