Dumpsite Rehabilitation

Introduction Land filling is the most common and environmentally safe method of disposal for the fractions of municipal solid waste (MSW) that cannot be reduced, recycled, composted, combusted or processed. Open dumping of MSW, which is practiced by about three-fourths of the countries and territories in the world is a primitive stage of landfill development (Rushbrook, 2001). The open dumps or dumpsites cause degradation of the environment since they are susceptible to open burning and exposed to scavengers and disease vectors. Most often dumpsites are poorly sited and operated by technically inexperienced staff. Dumpsites in Asian countries are similar and characterized by indiscriminately disposed heaps of uncovered waste. Open burning, stagnant pools of polluted water, infestations by rats and flies, scavenging by domestic animals and rag picking through the wastes by scavenging community are a common sight. The presence of waste pickers has a major impact on the operation of the dumpsite as they pose a safety hazard not only to the scavengers but to the dumpsite employees as well. It reduces the efficiency of waste disposal due to the interference with operations at the tipping face and starting of fires by the scavengers, which cause air pollution problems. There are a number of major risks and impacts of the dumpsites on the environment. The leachate generated as a result of decomposition of waste contaminates surface and groundwater sources which become unfit for human consumption. Air pollution from open burning, fire hazards and explosions cause public health risks as well as add to the emission of greenhouse gases (methane and carbon dioxide). Scattering of wastes by wind and scavenging by birds, animals and waste pickers creates aesthetic nuisance. Malodour emanating due to the degradation of the waste in the dumpsite restricts land use development as it decreases the economic and social values in surrounding areas. The absence of daily cover on the dumped waste attracts the animal and human scavengers alike. The environmental and health impact of improper MSW disposal practices in open dumps can be reduced by dumpsite rehabilitation. This may be defined as a process by which disposed wastes in an existing dumpsite is excavated and either reused or disposed in an environmentally friendly manner. Excavated waste may require to be moved or relocated to higher portions of the site or placed in appropriate areas to enable an adequate gradient for the closed site. Dumpsite rehabilitation projects are initiated due to one of the following reasons:

(i)                Presence of marketable material in the dumpsite that can be excavated for sale or use;

(ii)              Reduction in the closure and post operation monitoring costs of the site;

(iii)           Stipulated requirement by the owner/regulator of the landfill to close and rehabilitate the site; and

(iv)            presence of toxic wastes within the dump site that poses public health risks.

The process of rehabilitating a dumpsite to a sustainable landfill may be done in a phased manner depending on the risk posed by the dump and its financial aspects as well. The key to enable such a change depends on today's scientific knowledge and the introduction of incremental improvements in the standards of disposal in line with the available financial resources (Rushbrook, 1999, 2001). The following sections of this chapter present a phased approach to the rehabilitation of dumpsites with a few case studies in India to highlight the progress in this direction.

Phased Approach to Dumpsite Rehabilitation

Developing countries suffer from limited available resources for upgrading or relocating open dumps. They also do not have adequate funds and technical competence to operate and maintain engineered solid waste disposal sites. It may not be possible for these countries to immediately attain a level of highly complex landfill design and construction as practiced by the developed countries. Therefore, the improvement of disposal practices could only be achieved by a step-by-step approach (Rushbrook, 1999, 2001) from open dumps to controlled dump, engineered landfills and sustainable landfills.

Controlled Dumps

The first step in upgrading open dumps involves reduction of environmental nuisances like odor, dust and infestation by vermins and birds. Controlled dumps are operated with basic inspection and recording of incoming wastes, monitoring of the tipping front, compaction of waste and application of soil cover. It is one step better than open dumping with certain basic control measures that include designating an authorized person at the site who controls the accessibility of vehicles and the type of waste being disposed at the site. Supervisors designate specific sites for tipping of wastes in a controlled pattern. Basic handling techniques are used to consolidate the waste and eliminate open burning, foraging by animals and controlled salvaging operations by waste pickers. Preliminary drainage control measures are used to manage leachate flows and storm-water runoffs from the sites. In order to achieve these improvements from open dumping system to controlled dumps, an appropriate combination of simple techniques is used. This may be accomplished by fencing of the site and provision of security personnel to control scavenging, monitor vehicles, control entry of stray animals and prevent open burning. Other methods used are provision/improvement of access roads, diversion of runoff with adequate drains, provision of sign and direction boards, monitoring of incoming vehicles and waste characteristics, planning of the tipping sites, and zoning for special waste disposal. Certain appropriate equipments and machinery are required for effectual operation. The management would maintain an office with records of waste disposal and monitor the safety aspects of the workers by providing adequate gears.

Fencing

The main purposes of fencing a dumpsite are to control access to the disposal site and curtail open dumping, manage uncontrolled scavenging by waste pickers and to protect the vegetated sites. As a minimum requirement all open dumpsites within 500 metres of communities should be fenced. Perimeter fencing is desirable around all rehabilitated open dumpsites though it may not be practical. It helps delineate the site boundary, discourages unauthorized vehicular access and prevents entry of stray animals. However, simple fencing will not deter scavengers from entering a site. The perimeter at both sides of the site entrance should be fenced sufficiently to prevent vehicles bypassing the official entry point. The minimum form of fencing to control vehicular access and larger animals would be a stake-and-wire strand (barbed-wire) fence or an excavated perimeter ditch and bund planted with fast growing hedge-forming shrubs. After closing the site to public access, the facility and the surrounding areas should be cleaned up so that any waste pile and windblown paper/plastic are collected and placed in a final disposal cell for covering. Particular attention should be given to any environmentally sensitive areas where waste might have been placed in or next to wetlands, piled with a steeper slope or placed in areas of natural drainage or impede surface water flow. The requirements are relatively simple and inexpensive for which local enforcement agencies should consider enacting appropriate ordinances and legislative provisions that prohibit unauthorized disposals.

Scavenging control

Scavenging is practiced in all municipal dumpsites by economically backward communities who collect valuables from the waste and make a living. This activity hampers controlled and safe operation of solid waste disposal sites and should be banned ideally due to the deleterious circumstances to the scavengers. Complete banning of scavenging would require additional site security measures, increased landfill volume, and loss of recyclables as well as it would be economically damaging to the scavenging community. To accommodate the scavenging activities without interfering with the waste emplacement operations, a policy is required. Where controlled scavenging activities are tolerated, the scavengers should be separated so that the work of the mechanical equipments used for emplacing waste would not be hindered. A temporary scavenging area could be set up near the waste disposal area where trucks discharge their loads. Once the scavengers have finished retrieving the valuables, the waste is bulldozed to the emplacement area. At larger dumpsites, a permanent scavenging area (raised platform) could be established and after their operation, the residues could then be transferred for transport to the emplacement area. One common method is to arrange a scavenging licence for families or groups of scavengers to enter the dumpsite for picking the valuables.

Access road

A sufficiently wide access road to a disposal site from the highway is essential to enable the passing of two trucks travelling in opposite direction. The road should be upgraded to service the dumpsite in all seasons to a standard that enables easy passage of trucks carrying waste to the site. At the same time, dumping of the waste on the road side should be banned and the callously dumped waste on the road sides need to be cleared. A minimum standard for the road surface is compacted earth or similar material with a top dressing of gravel to enable a firm running surface. A durable asphalt surface would be preferred if resources are available.

Fire control

Dumpsite fires are commonly set by the scavengers to recover metallic wastes. To eliminate this hazard, a plan would be required to extinguish fires and prevent future occurrences as the rehabilitation work progresses across the site. Use of water to extinguish fires should be avoided while isolation and rapid natural burnout or smothering with soil is preferred.

Lay out

The layout of the controlled dump is strongly influenced by the site’s geology. The potential for gas and leachate migration and the suitability of the soil for landfill base and cover material are crucial. Site layout relates closely to the geotechnical information - data on stratigraphy, hydrology and soil structure. These data are usually collected during the siteselection and investigations as these are required for the design and functioning of the dumpsite.

Slope stability

The slope of waste filled portions is a primary concern as adequate gradient is required to promote surface water runoff without ponding or water-logging or erosion of the final cover. The grade of the land and the length affects slope erosion. The final slopes of the filled portions of the site should be 2 - 8% in grade and should not exceed the upper limit. Over-steepened waste slopes should be identified for regrading with estimations of the quantity of waste to be removed. Unless local geotechnical reasons prevail in the site and cannot be adjusted, the waste side slope should not be steeper than 1 in 3 and top slopes should not be more than 1 in 20 (Rushbrook, 2001). Slope stabilization activities should seek to redistribute waste within the confines of the existing dumpsite without extending the external boundaries of the fill.

Surface Drainage

It is important to promote surface drainage in landfills to keep off the surface runoff from percolating through the garbage and solubalising the wastes to form leachate, which degrades surface and ground water quality. If leachate accumulation is identified in an open dumpsite, a plan should be made to either drain or pump it into a constructed lagoon (not liable to flooding) or even can be recirculated back into the waste. Leachate source should be determined to carry out remedial works that help to prevent future leachate accumulations.

Mechanical equipment

During the preparations for dumpsite rehabilitation, mechanical equipments should be provided in order to serve three basic functions that are essential for a controlled disposal which are related to soil, waste and support activities. The functions at the site include excavation, handling, spreading and compaction for soil and wastes, maintenance of on-site haul roads, pumping of water or leachate, making of drainage ditches and removal of trapped lorries from the landfill working area. The required number and type of equipment varies and depends on the quantity of waste handled daily together with the available resources to operate and maintain the equipment. The most essential equipment for the full-scale operation of the disposal site are:

(i)                one bulldozer of adequate capacity to handle the daily quantity of waste arriving at the site for spreading and compacting it and providing it soil cover; and

(ii)              one tractor with trailer to haul cover soil to the work zone and undertake other support activities. To facilitate the smooth operation and maintenance of the machinery, a supply of spare parts and consumable items are necessary while a supply of hand tools such as shovels, brooms, wheelbarrows and rakes are required for any manual work.

Soil cover

Once the landfilled areas have been sloped and all the waste compacted and covered, the site should be covered with at least 60 cm of clay-rich soil. This final cover of clay-rich soil should have an inner layer (about 30 cm for inert waste landfills or 45 cm for municipal solid waste landfills) compacted in lifts of 15 cm to minimize surface water infiltration. Compaction testing of this barrier layer may be required to ensure proper placing of the soil. An additional 30 - 45 cm of soil should be placed over the compacted clay layer to protect it from erosion, plant roots, vehicular traffic, etc. This buffer layer also provides a rooting depth for the final foliage cover. Compared to the benefits of a better-controlled operation and improved compaction of waste, soil cover is expensive and may not be significantly beneficial for a dumpsite located in a remote area. For a limited dumpsite volume, use of soil-cover decreases the available site volume for waste disposal. In the event of a decision to use cover material, the daily quantity should be estimated (based on 5 cm of daily cover, 25 cm intermediate cover and 50 cm final cover). Controlled dumps have only limited measures to mitigate environmental impacts. There exists unmanaged release of contaminants due to inadequate precautionary measures for leachate and landfill gas management. This is relevant where the produced leachate cannot be retained by the underlying permeable rock layer or fissured stratigraphy. This concern may be less critical in semi-arid and arid climates where leachate is not generated from dumpsites in measurable quantities and can be controlled in an engineered landfill.