Investigation of pollution and depth profiles of heavy metals in sediments around Arak landfill

It produced millions of tons of solid waste annually during Iranchr('39')s household, mineral, agricultural, and industrial activities that are heavy metal-rich. Solid waste generation is the most important environmental and health problem in the world, especially in developing societies. The rapid growth of urban, agricultural, and industrial activities, along with population growth, produces a wealth of waste. Open landfills are the oldest and most abundant solid waste landfill in the world. Uncontrolled landfills can have an adverse effect on the environment and human health. The most important risk of landfill on human health is sediment contamination by waste leachate. Municipal waste landfills can be associated with the release of contaminants due to leachate infiltration into sediments and surface and groundwater of the surrounding environment. The purpose of the present study was to determine the heavy metals contaminants of Arak landfill in comparison with the upper crust reference, to evaluate landfill pollutant indices at different depths, to determine the sources of Arak landfill and to determine the role of Arak landfill in the production of all types of heavy metals.  

Arak landfill is located in Amanabad plain and upstream of 14 drinking water wells in the Arak city. Annually, 350 tons of Arakchr('39')s garbage is brought to the landfill, 30% of which is dry waste (paper, glass, metals) and the rest more waste (kitchen waste, food, fruits).Thirty one sediment samples were collected from three boreholes in Arak landfill in 1396 (borehole with 22.5 m depth, 13 samples, borehole with 17.5 m depth, 10 samples and borehole with 13 m depth, 8 samples). It was determined texture, physical and chemical composition and heavy metals(Pb, Cr, Ni, Cu, Zn, As and Hg) of the sediments.  

The mean concentrations of Pb, Ni, Cu, Zn, As and Hg were 32, 64, 25, 73, 15 and 6.90 mg / kg in Arak landfill sediments, respectively, and greater from their mean concentrations in the upper crust (17, 18,13, 47, 5 and 0.05 mg / kg). The average concentration of Cr (39 mg / kg) is lower than the mean concentration in the crust (92 mg / kg). The enrichment coefficients of Pb, Cr, Ni, Cu and Zn vary from low to medium, for As from low to very high, and extremely high for Hg. The geo-accumulation coefficient is low for all elements except for Hg. The geo-accumulation coefficient is medium for Hg. Evaluation of the concentrations of Pb, Cr,Ni, Cu, Zn, As in three boreholes showed that their concentration did not show a specific trend towards depth. The enrichment coefficient and geo-accumulation coefficient for Pb, Cr,Ni, Cu, Zn, As were also absent trend. There is a great concentration of elements in specific  zones in depths. The amount of Hg as well as the enrichment coefficient and its geo-accumulation coefficient increase with increasing depth. In general, the degree of contamination of all elements increases with the depth in boreholes. In factor analysis, Cu, Mn, Ni, Zn and Pb were positively correlated in one group. As, Hg and organic matter are in another group. The correlation of As with Hg and organic matter is reversed. Also, the variables of mud, sand and gravel were in the other group, in which gravels were inversely correlated with mud and sand. The study showed that heavy metal concentrations of Cu, Ni, Zn and Pb occurred in an environment with high Mn. It was also enriched Hg in organic matter environments. In contrast, arsenic enrichment is in a separate phase that has no relation to organic matter. In addition, it was found that sediment texture (mud, sand and gravel) did not play a role in the concentration of heavy metals in surface and deep sediment of Arak landfill.

The analysis of dry and wet waste in long-term landfill accumulation in direct contact with precipitation and the runoff has involved the decomposition of heavy metals into deep sediment. Organic matter and manganese compounds play the most important role in the distribution of heavy metals at different depths in the sediments. Therefore, monitoring heavy metals in landfill leachate and downstream drinking water wells is essential. Since landfill is old and not engineering landfills, therefore, new landfills must be designed on the principles of landfill engineering. In addition, hydrological removal can prevent water from being exposed to landfill