investigation of contamination of groundwater sources surrounding landfill sites; case study: takestan city landfill site

nonstop growth of urban population and concentration of industrial and agricultural activities in many parts of the world and iran have given rise to increased demand for water for different uses .furthermore, as one important factor of lack of exchange between human and environment resulting in wide exploitation from agricultural lands, mine extraction, and application of various industrial tools, increased population has no role except pollution and contamination. within this framework, one can view the issue of pollutions from two perspectives of natural resource destruction and development of waste stemming from various consumer goods. it might even have caused great transformations in quality and quantity of waste in response to rapid development of human artifacts and production of chemicals after industrial revolution .threat to groundwater by landfill sites has always existed in many parts of the world. in particular, in developing countries, as a result of industrial and household wastes, even when there is no hazardous waste at the landfill site, the resulting leachate is still a significant threat to groundwater. although through immuring waste, hygienic landfill sites have brought about beauty and cleanliness to the environment and provided people and environment with health and hygiene, they will cause potential adverse effects due to generation of two by products, gas and leachate. leachate consists of the extract from the passage of waters mainly ditch water through waste mass containing numerous contaminants. gas is also produced at the landfill site in response to chemical decomposition and decay of perishable waste and food. this gas mainly consists of methane, some carbon dioxide and volatile organic acids . although soil is the most important and widely used physical, chemical, and biological filter for waters, waste recycler, and a host for many substances, its capacity is limited and many toxins and materials added to soil may become more concentrated and in turn create serious threats to the environment . greenhouse effects of methane and carbon dioxide gases, development of global warming, suffocation caused by carbon dioxide gas, and explodability of methane are among the effects brought about by gases emitted from landfill sites. the influence of methane gas on world atmosphere and greenhouse conditions is about 21 times as large as the effect of carbon dioxide .takestan city is situated in southwest of ghazvin between 46° and 42’ east and 36° and 4’ northeast (fig. 1) with an altitude of 1265 m. except for northwest and west of the city with a relatively steep slope, other regions of the city have a moderate slope. the general slope of the region extends from west to east and gradual decrease of slope has resulted in subsidence of remaining water of abharrood and kharrood rivers in the southern part. the maximum slope extending from northwest toward takestan is around 3% and its average is 1.7% towards northwest. the general slopw of the region from takestan toward ghazvin northeastwards is approximately 0.3%. takestan city, located in the plain of ghavzin is restricted to alinaghieh, aghdagh, and abuhanifeh altitudes from northern, northwestern, and western fronts situated at 7-15 km distance from the city. regarding the limitation for development of the city in eastern and southeastern fronts, due to presence of vineyards and industrial lands at northeastern front of the city along with artificial barriers of development such as railways at the southern front, the only appropriate direction for urban development is the northwestern front limited by tehran-zanjan highway. on the other hand, since the region is earthquake prone and there are some known faults including parandak, ipek, shtehard, geshlagh, and abyek, vertical development of the city is only possible by following earthquake code 2800 in urban constructions. the general slope of the city is about 2% from northwest to southeast and is 0.3% from west to east. samples of groundwater and leachate were analyzed chemically in laboratory after sampling followed by measurement of heavy metal concentration together with bod5 and cod. according to the main objective of the research, 5 sampling stations were specified within the study area from which water samples were taken in mehr of 1393. in order to investigate the trend of qualitative variations, the obtained results were further compared with the results of 1393. four sampling stations were selected from takestan landfill downstream (a, b, c, d) and the fifth one (e) was selected from landfill upstream so that the potential effect of leachate on groundwater resource contamination within the study area be investigated more accurately. the leachate sample was further analyzed and the results were then compared with discharge standards. the studied parameters were electrical conductance, ph, tds, tss, bod, cod, na, ca, and some heavy metals (including copper, zinc, iron, lead, chromium, cadmium, molybdenum, manganese, nickel, and aluminum). in order to analyze water standards qualitatively, some valid standards presented by iranian institute of industrial research and standard, the standard of potable water in the country’s water industry, world health organization, and european :union: potable water standard were used for drinking usages. the qualitative parameters measured regarding water sampling included ph, ec, tds, tss, bod, cod, na, ca, and some heavy metals (including copper, zinc, iron, lead, chromium, cadmium, molybdenum, manganese, nickel, and aluminum). the comparison of qualitative parameters values in takestan landfill leachate in 1383 and 1393 indicated reduced value of most qualitative parameters particularly heavy metals in 1393 in response to alterations of landfill reactions (acidic conditions to methanogen). the comparison of qualitative parameters values in leachate with the national standard of discharge to surface waters and absorbent wells manifested that takestan landfill leachate both in 1383 and 1393 has had values (for most contaminants) over than national standard of discharge. therefore, it should not spread into the environment easily and with no proper management. the comparison of analysis results of groundwater qualitative parameters within the study area revealed a significant increase of some contaminants particularly heavy metals. the probable reason could be leachate leakage to the environment and permeation to groundwater resources in the vicinity of landfill. concentration of lead, cadmium, and nickel in water samples had the largest violation from national and international qualitative standards compared with other studied contaminants. regarding the ascending trend of many studied contaminants (especially heavy metals) in water samples next to takestan landfill, it can be stated that the leachate emitted from the landfill may have had a significant impact on the contamination of water resources around the landfill.