Soil and groundwater contamination by an open dump: the case study of Tatuí (SP, Brazil)

Abstract

This study evaluates the extent of contamination of soil and groundwater impacted by the inappropriate deposition of municipal solid waste, as well as investigates the location of buried material, using electrical resistivity and electromagnetic geophysical methods, and groundwater monitoring data from 12 wells drilled in the open dump of the city of Tatuí (SP, Brazil). From 1991 to 2014, 40 tons/day of solid waste from the city residences and services was disposed of in the open dump, which comprises an area of 14.87 ha. Based on the chemical analysis of groundwater samples from monitoring wells in six campaigns, from June 2000 to January 2001, it was possible to determine that the groundwater contaminant plume is restricted to the area of the dump or extended to an area very close to it. Vertical electrical sounding method identified a resistive layer that was interpreted as an aquitard, and electromagnetic tomography detected anomalies related to the buried waste. However, it was not possible to obtain a good characterization of contamination of groundwater from depths greater than 8 m using Geonics EM34. The aquifer potentiometry is influenced by rainfall and physiographic characteristics of the dump area, where it is clearly seen that the waste is more permeable to the rainfall infiltration than the soil. Notably, non-contaminated groundwater has a Na-Ca-HCO3 geochemical signature, whereas contaminated groundwater has a Na-Cl-(NO3) signature. The main conclusion of this study is that although indirect methods were easier to use, they could not provide a good characterization of the contamination of the saturated zone, especially in areas of low permeability and heterogeneous and dispersed deposition of masses of waste. Thus, the simultaneous use of both techniques seems to be useful for similar case studies.