2.1 Study area
The experimental plot was established on the solid waste dump of the Nalwa Steel and Power Limited (NSPL) located in the Raigarh district of Chhattisgarh, India (Figure 1). NSPL is an operating integrated steel plant that manufactures sponge iron by the direct reduction process. The aerial extent of the waste dump lies between 83º22’35”E to 83º23’27”E and 22º00’51”N to 22º02’10”N covering an area of approximately 7 hectares. The dump height ranged between 40-50 m with a slope of more than 60–70º inclination. The area experience subtropical climate with temperature ranged between 8–49oC and the mean annual precipitation was 750 mm. The waste materials were dumped externally at the outskirts of the steel plant surrounded by Shorea robustadominated forest.
The main stages involved in sustainable closure and subsequent reclamation of the waste dump were as follows (Figure 2): (a) leveling of the surface, compaction and maintaining slope of 1:3 for proper surface runoff, (b) re-grading of slopes and blanketed with coirmats followed by topsoil and seeded with grass-legumes seeds, (c) safety measures like stone pitching at the toe of the dump and construction of garland drain, (d) re-grading the surface before applying forest topsoil up to 0.6-1 m depth, (e) for stabilization of the slope and sidewalls coir mats of dimension (1m × 30m) were used, (f) for the development of green cover in the initial stage, seed mixture of grass (P. pedicellatum ) and legume (S. hamata ) in a 1:1 ratio was sown. the view of stabilized dumps after 5 years, with the development of mulch covers in lean season (summer), is shown in Figure 3. In the berm of dumps, tillers of lemongrass (Cymbopogon citratus ) were planted. Tree species like Azadirachta indica , Leucaena leucocephala , Acacia nilotica, Pongamia pinnata were also planted on the edges to increase dump stability.