The report details out the status of landfill and waste disposal technologies in India & abroad and reviews the scientific studies undertaken to support its design for long-lasting performance. Hydrological considerations play a major role in the selection of landfill sites and in the design and performance of landfills for hazardous waste management. A landfill is a form of a biochemical reactor where the municipal solid waste (MSW) comes into contact with moisture, a catalyst, and gets decomposed into solid waste, gases and liquid contaminants (leachate) resulting in the release of heat. The design of the control and recovery systems requires the estimation of amount and composition of gas and leachate accurately, as also the changes in these with time. Lysimeters are used to simulate the landfill performance.
Landfill leachate contaminant concentrations are of primary importance from the point of view of the study. These include organic matter, nitrogen compounds, anions, metals and volatile organic compounds. Chemical and biological reactions modify the compound composition with age of the landfill, and are of concern in environmental hydrology studies. Permeability and hydraulic conductivity measurements for the liners and natural barriers provide basic parameters for the landfill design. Various field and laboratory experiment methods are available for estimating these. These, along with the estimation of various soil parameters like porosity, field capacity, wilting point, saturated hydraulic conductivity and soil retention capacities are a valuable input in studying hydrology.
Besides, hydrological parameters like weather, topography, surface storage, snowmelt runoff, infiltration, evapotranspiration, soil storage, lateral drainage, leakage through linear and geo-membrane may possibly be monitored in the selected sites. These parameters could also be employed in the water balance method to estimate the percolation of the exact quantity of leachate. Hydro-geological investigations could be carried out, by fixing and monitoring of observation wells. Resistivity surveys could be used for collecting the necessary lithological information.
In case of groundwater, only mathematical modeling of flow and contaminant transport can ensure the degree of risk involved with selection of a landfill site. Proper use of models like HELP and CHRONO along with numerical flow and contaminant transport models like MODFLOW, SWIFT, MT3D and MODPATH may serve the purpose. Soil erosion models like WEPP and RUSLE can be used to estimate the degree of soil erosion and runoff. In conclusion, the Environmental Impact Assessment of landfill and waste disposal sites requires extensive hydrological investigations to safeguard the natural resources from pollution.
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