DOI: 10.5593/SGEM2016/B21/S08.083


C. Boente, J. Gallego, E.Rodriguez-Valdis, C. Sierra, J.Menendez-Aguado
Friday 9 September 2016 by Libadmin2016

References: 16th International Multidisciplinary Scientific GeoConference SGEM 2016, www.sgem.org, SGEM2016 Conference Proceedings, ISBN 978-619-7105-58-2 / ISSN 1314-2704, June 28 - July 6, 2016, Book2 Vol. 1, 665-674 pp

This study presents a three-dimensional characterization of soil and subsoil affected by hazardous waste filling and soil pollution. The study site is a brownfield which was active as a fertilizer plant until its closure in 1997 (Nitrastur in Asturias, NW Spain). It has an extension of almost 20 ha and it presents both in surface and depth, several fillers of pyrite ashes and other waste mixed with layers of polluted and non-polluted soils. In this sense, numerous characterization campaigns including soil samples, test pits and monitoring wells, have been done in the last decade and they have revealed high concentrations of As and Pb, among other heavy metal(loid)s, at many different hot points.
Given that contamination within the site is very heterogeneous, there are several zones where the waste is mixed with natural soil. In addition, after more than 20 years of abandonment, natural attenuation and weathering processes have to be taking into account to understand the current distribution of polluted soil and waste (i.e. mechanical dispersion, groundwater affection, etc.). Therefore, a first challenge was to distinguish accurately between pure waste disposal areas (pyrite ashes mainly) and polluted soils. In this sense, several criteria based on the physical properties of the waste (color, texture, etc.) and on their chemical composition (higher or lower contaminant concentration) have been considered and discussed. On the other hand, in order to estimate the distribution of the different layers of pyrite ashes scattered in the whole parcel, common geostatistical & geospatial techniques (such as kriging, IDW interpolation and splines) have been carried out by means of GIS techniques, including the development of specific algorithms for the calculation of volumes.
As a main result, a 3D model of the distribution of pyrite ashes (more than 80.000 m3) throughout the site has been obtained, and volumes, both of the affected soil areas and the top layers to be excavated, have been also estimated. In this context, the total site area has been divided in 20 different subareas, in which different batches of soil and waste can be distinguished. As a consequence, an estimation of yields for soil remediation techniques and for waste potential revalorization has been also obtained, again with the help of GIS tools.

Keywords: hazardous waste, soil pollution, geostatistics, GIS, brownfield

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