São Carlos School of Engineering (EESC), University of São Paulo, Avenida Trabalhador São Carlense 400, São Carlos, SP 13566-590, Brazil.
São Carlos School of Engineering (EESC), University of São Paulo, Avenida Trabalhador São Carlense 400, São Carlos, SP 13566-590, Brazil.
J Contam Hydrol. 2020 Mar;230:103623. doi: 10.1016/j.jconhyd.2020.103623. Epub 2020 Feb 4.
Even though attenuation processes in the subsurface are known to reduce the impacts of contaminant plumes, their importance is significantly dependent on geological and climatic characteristics, as well as on the leachate quality. The knowledge of attenuation processes linked to different geological formations is therefore fundamental in predicting the impacts of waste disposal areas. Geophysical methods are useful tools for assessing and delineating contaminant plumes, as well as their changes with time, which enables their lower-cost monitoring and association with geological and environmental properties. This paper shows the results of geophysical surveys conducted in the years of 1996, 2005 and 2018 in a waste disposal area located at a Guarani Aquifer recharge zone in Brazil. The objective of this study was to show the evolution of the contamination plume, as well as discuss some possible transport and attenuation processes that the contaminants may undergo in similar areas. Five geophysical sections surveyed within a time span of 20 years were compared, and the information was integrated with physicochemical data from monitoring wells. The results show a horizontal plume spreading, reaching about 200 m from the deposit and about 60 m of depth, 20 years after the ending of disposal activities. The measured resistivities in 2018 are similar to the ones found in 1996 and 2005 in the same surveyed areas, showing that a significant temporal attenuation did not occur. Moreover, samples collected close to anomaly zones and within a distance of 200 m from the deposit presented concentrations of some heavy metals above the screening values according to the Brazilian legislation, showing a metals mobility higher than previously expected, which can be possibly explained by the aquifer's acidic conditions. The estimated plume velocity was about 7 m/yr, a plume deepening was observed until about 50 m and changes in water flow direction and/or diffusion processes made the plume spread to areas previously regarded as upgradient. Therefore, the present paper shows that the rehabilitation of sites neighboring waste disposal sites (less than 200 m from it) did not seem to be feasible through natural attenuation in sandy soils and that the plume spreading is significant in this geological formation. Thus, abandoned disposal areas, constantly considered to be closed after the ending of disposal activities in developing countries, generate plumes which move silently and may reach areas of concern in the future.
尽管地下物质衰减过程被认为可以降低污染物羽流的影响，但它们的重要性在很大程度上取决于地质和气候特征，以及渗滤液的质量。因此，了解与不同地质构造相关的衰减过程对于预测废物处置区的影响至关重要。地球物理方法是评估和划定污染物羽流及其随时间变化的有用工具，这使得它们可以进行低成本监测，并与地质和环境特性相关联。本文展示了在巴西瓜拉尼含水层补给区的一个废物处置区进行的地球物理调查的结果，这些调查分别于 1996 年、2005 年和 2018 年进行。本研究的目的是展示污染羽流的演化，并讨论污染物在类似地区可能经历的一些迁移和衰减过程。比较了在 20 年内进行的五条地球物理剖面，将信息与监测井的理化数据进行了整合。结果表明，在处置活动结束 20 年后，污染物羽流水平扩展，距离堆积物约 200 米，深度约 60 米。2018 年测量的电阻率与 1996 年和 2005 年在同一调查区域的电阻率相似，表明没有发生显著的时间衰减。此外，在异常区附近以及距离堆积物 200 米范围内采集的样本中，一些重金属的浓度超过了巴西法规规定的筛选值，表明金属的迁移性比预期的要高，这可能是由于含水层的酸性条件所致。估计的羽流速度约为 7 米/年，观察到羽流深度加深到约 50 米，水流方向的变化和/或扩散过程使羽流扩散到以前认为是上游的区域。因此，本文表明，在沙质土壤中，通过自然衰减来修复紧邻废物处置场（距离不到 200 米）的场地似乎是不可行的，而且在这种地质构造中，羽流的扩散是显著的。因此，在发展中国家，废弃的处置区在处置活动结束后通常被认为已经关闭，但它们会产生无声移动的羽流，并可能在未来对关注区域造成影响。
