**5. MSW sanitary landfill in Bauru, SP, Brazil**

The MSW disposal site in Bauru, São Paulo State, Brazil, is the biggest disposal site presented in this chapter, occupying an area of 270,000 m2 . It is a concept like a landfill, and the wastes are disposed in three layers of, approximately, 4 m height. Its bottom has an asphalt emulsion layer above compacted local soil. Digital topographical models show that wastes are disposed over an old valley.

The local geology consists of alluvium, colluvium, alteration soils, and sandstones (Bauru Group). The alluvium is characterized by silt-clayey fine sand and the colluvium by clayey sands. The landfill soil is fine to medium clayey sands. Groundwater flow is from east to northwest, reaching shallow water table depth of 5 m at the base of the landfill [15].

Ustra et al. [16] conducted a geophysical survey over the landfill area and suggested the formation of a contamination plume, based on the resistivity imaging. To investigate the contamination plume, the authors conducted a geophysical survey in the area downstream from the landfill, shown in **Figure 17**.

Chemical analysis data of groundwater sampling from monitoring wells (locations shown in **Figure 17**) showed that the downstream wells (P1, P2, P3, P5A, P5B, P7, P8, and P9) have the highest chloride concentration (12.5–30.5 mg/L, except P9), which is a clear sign of waste disposal leachate contamination. Anomalous sulfate, nitrate, nitrite, and iron (Fe) concentrations in some well downstream groundwater flow are below their maximum permitted value, established by the National Environment Council from Brazil, suggesting that this contamination is in its initial state (low contaminant concentration) and diluted into the aquifer. These parameters, when compared with the natural aquifer values, are considered anomalous even though.

#### **Figure 17.**

*Topographical map of the landfill with the location of monitoring wells, soundings, and the 3D geophysical survey mesh.* 

The 3D resistivity model (**Figure 18a**) show resistivity values lower than 100 ohm.m at 10 m deep, known to be n the saturated zone. A conductive feature is observed to start in the landfill (ρ < 20 ohm.m), propagating along the groundwater flow direction. Resistivity values lower than 20 ohm m observed outside landfill are interpreted as contamination plume supported by P2, P7, and P8 chloride anomalous values (mostly in conductive anomaly). However, according to chemical analysis of groundwater contamination, it can only be considered as low contaminant concentration plume. Highest chargeability (~33 mV/V) values are observed in the wastes but also at other regions in the saturated zone (**Figure 18b**). This feature is interpreted as a low salinity contamination plume. Despite low chargeabilities are usually associated with inorganic contamination plumes, the results from this study are in good agreement with Griffiths et al. [17], who observed the increase of chargeability with salinity, over a certain salinity range. The salinity range investigated by Griffiths is exactly the salinity range found in the monitoring well water conductivity. The groundwater flow is best marked by normalized chargeability (mn > 0.3 mS/m) as shown in **Figure 18c**.

 Ustra et al. [16] suggest that the increase of normalized chargeability outside the wastes is a signature of the local contamination plume. This interpretation is in good agreement with Viezzoli and Cull [18] who suggested that in high salinity environments, normalized chargeability is enhanced by clay content. In the case of the landfill, the distribution of the clay content is homogeneous (according with direct sampling), and there is no clay enrichment zone. Ustra et al. argued that in this case, salinity enhancement could highlight the clay content, enhancing the polarization in higher salinity zones that is the contamination plume.

#### **Figure 18.**

*(a) Resistivity, (b) chargeability, and (c) normalized chargeability models at the depth of 10 m, downstream the landfill.* 

*Resistivity and Induced Polarization Application for Urban Waste Disposal Site Studies DOI: http://dx.doi.org/10.5772/intechopen.81225* 
