EVALUATION OF POTENTIAL METHANE GENERATION IN THE INVESTIGATION OF AN ABANDONED CONTAMINATED LANDFILL IN SANTIAGO, CHILE

This study presents the environmental evaluation of an abandoned and potentially contaminated landfill using analyses for the presence of heavy metals and for methane generation potential. The site is located in the city of Santiago, Chile, and was used as a rural landfill for domestic, industrial and construction waste until 1978, but is now in a heavily urbanized area and surrounded by houses. Analyses performed on 24 samples taken in and around the site show Potential Methane Generation (PMG) values between 1.6% and 11.3% of maximum projected levels. These low values, compared to those of an active landfill, indicate that waste material stored in the site has a low capacity to generate methane. Concentrations of heavy metals in the surface and deep soil are similar to typical levels for these metals in normal soil, according to international USEPA standards, and do not present imminent risk to human health. The use of the PMG test technique for the study of the health risk of an abandoned landfill is a new contribution to the Chilean evaluation methodology and management program for Abandoned Sites with Potential Presence of Contaminants (SAPPC). As part of the environmental management strategy for the site, two of the five operable units studied were transformed into a park after this study.


INTRODUCTION
Studies related to the potential presence of contaminants in soils at a site are varied and usually develop as a prior and fundamental step in the evaluation of remedial alternatives, recovery of the site for different uses, or both, depending on the characteristics of the location.However, there is no definitive, common methodology applied to all situations.To deal with this limitation, several comparative models have been developed to establish the presence of abnormal levels of contaminants at a specific site under study (Aslibekian and Moles, 2003;Muhlba-chova et al., 2015;Rodríguez et al., 2015;Wen et al., 2015;Khan et al., 2008).For example, since 1995 in the United Kingdom it has been known that soils within 1 to 3 km of metal smelters may contain up to 15 times the natural values of Pb in the soil and also may present high concentrations of Cd at distances as far as 40 km from the originating industrial activity (Aslibekian and Moles, 2003).
In polluted soils, interactions between heavy metals, organic matter content and microorganisms have been correlated (Muhlbachova et al., 2015).Increasing concentrations of metals in the urban environment have been studied, wherein concentrations of Brazilian Journal of Chemical Engineering Cd, Ni and Cr measured in plant leaves in 2012 exceeded those reported in 1941 for the same species by factors of 10, 13 and 16, respectively (Rodríguez et al., 2015).The increase of these pollutants in the urban atmosphere was related to human activity changes during a period of more than 70 years.The anaerobic biodegradation of domestic and industrial waste in landfill sites goes through a complex process and therefore it is not easy to estimate the biological conversions involved.Measurements at these sites must be performed carefully taking into account different waste sources such as pharmaceutical residues, plastic products, antibiotics, and complex organic compounds (Wen et al., 2015;Khan et al., 2008;Kumar et al., 2004;Aguilar-Virgen et al., 2011;Aguilar-Virgen et al., 2012;Angelidaki and Sanders, 2004;Stergar and Zagorc, 2002;ISO 11734, 2012;Kolstad et al., 2012;Gartiser et al., 2007;El-Mashad et al., 2012;Angelidaki et al., 2006).
Human activities in Chile have generated locations known as Abandoned Sites with Potential Presence of Contaminants (SAPPC), such as old landfills, uncontrolled dumpsites, or industrial waste sites.When abandoned, these sites may be converted to new land uses without additional regulation.Studies of contaminants in soils at these and other sites have been performed considering the type and extent of pollutants in the involved area (Romero et al., 1999;Ginocchio et al., 2004;Molina et al., 2009;Escudey et al., 2007;Badilla-Ohlbaum et al., 2001;Palma-Fleming et al., 2000).The systematic evaluation of SAPPC in Chile began only 5 years ago, in 2010, and has targeted defined areas that have been environmentally impacted by one or more potentially polluting activities, which ended at some point without a proper site closure process.
In 2012, the Chilean Government began to apply a national methodology (Chilean Government, 2012) to identify and confirm the presence of contaminants at these sites.This methodology contains an ordered sequence of activities whose first step is the application of criteria to identify and prioritize SAPPC sites within each region.Subsequently, in step two, the Preliminary Investigation collects and analyses site historical information.In step three, the Confirmatory Investigation collects and analyses site samples.See Figure 1.
The Confirmatory Investigation of the SAPPC methodology, as shown in Figure 2, is designed to determine representative concentrations of pollutants present at the potentially contaminated site, which are then compared with reference criteria to confirm whether or not the suspected contaminant levels pose a preliminary risk to potential receptors.Suitable methods of analysis for this study were selected for quantifying the presence of heavy metal contaminants.To evaluate an abandoned landfill under the SAPPC methodology, it is crucial to establish the levels of landfill gas (biogas, consisting of CH

Figure 1 :
Figure 1: Illustration of the Chilean SAPPC.Evaluation Methodology developed and conducted by the Ministry of Environment.

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