**3. MSW disposal site in São Carlos, SP, Brazil**

This study site located in the city of São Carlos, São Paulo State, Brazil is an example of how choosing a disposal are without any consideration for environmental impacts can have disastrous consequences. Wastes were disposed at a natural depression zone produced by intense erosion. There was a small river in this site

**Figure 8.** 

that was covered by the waste dump. The area received industrial, domestic, and hospital wastes over 7 years, and it was then closed with the material being covered by soil in 1996. From the site's topography, the water drain to NW direction is expected, as well as the contamination plume flow in this same direction. Parts of the wastes are deposited in dry soil (above saturated zone), and in the NW part, the trenched bottom is in direct contact with the aquifer.

The site location is at Paraná Basin's east board, where the sandstones of Botucatu Formation occupy most of the study area. Botucatu Formation is the main geological unit of the most important water reservoir in Brazil, the Guarani Aquifer. The sediments from the area are characterized predominantly as fine sand, punctually more clayey or silty.

For mapping this site were performed five resistivity/IP lines across the deposit and one external to it. Data were collected with Syscal Pro (Iris Instruments). Metallic electrodes were used for current injection, and nonpolarizing electrodes (Cu/CuSO4) for potential measurement. Current was injected in cycles of 2 s, and the IP measurements were recorded with 160 ms delay after current shut off. Data were inverted with the software RES2Dinv.

**Figure 8** shows the positions of monitoring wells and geoelectrical sessions in the site. The combination of resistivity and time-domain induced polarization (IP) *Resistivity and Induced Polarization Application for Urban Waste Disposal Site Studies DOI: http://dx.doi.org/10.5772/intechopen.81225* 

#### **Figure 9.**

*Resistivity (top), chargeability (middle), and normalized chargeability (bottom) sections of L3 with monitoring wells P25, P31, and P15.* 

improved the site investigation. We will present results from lines L3 (across the wastes trench), L1 (at the boundary of the trench), and L0 (outside the trench).

 Line L3 (**Figure 9**) identifies the area affected by the wastes and leachate, characterized by low resistivity values (<30 ohm m). The waste trench, the contaminated soil, and the contamination plumes are characterized by low resistivity values, and it is not possible to distinguish these different zones. The chargeability session shows the influence of the upper part of the trench (from 60 to 130 m) characterized by high values (>40 mV/V). The leachate attenuates chargeability values, due to its high salinity confirmed by groundwater well Pm31. The contamination plume dilution in the saturated zone produces higher chargeabilities. Normalized chargeability, a direct measurement of polarization, clearly marks the horizontal limits of the trenches and the contamination plume, by high Mn values (from 60 to 130 m, confirmed by visual inspection in the field). Both ρ and Mn show the horizontal spread of the contamination plume.

#### **Figure 10.**

*Resistivity (top), chargeability (middle), and normalized chargeability (bottom) sections of Line 1 and monitoring wells P27 and P28.* 

 **Figure 10** presents the results for L1. The resistivity session shows the trench, the contaminated soils, and the contamination plume. Chargeability can limit the wastes between 40 and 90 m and a leachate concentration zone detected by the groundwater well Pm28. Normalized chargeability also identifies the wastes and the contamination plume. In this session, the contamination plume does not spread laterally as L3, which is confirmed by chloride concentrations found in the groundwater well Pm27 (11 mg/l). In the groundwater well Pm25, located in a low ρ and high Mn at L3, the chloride concentration found was 133 mg/l. The line L0 (**Figure 11**) crosses a small river raised from the erosion where the wastes were deposited and the leachate tends to be lixiviated by surface water flow. For this reason, no groundwater wells were installed along this line. The resistivity session shows the water table level very close the surface and low resistivity (50–100 ohm m) in the stream region, characterizing the contamination zone. Normalized chargeability identifies the water table and shows the zones of higher Mn in the stream region. Water sample collected from a small river 50 m always showed a chloride concentration of 64.4 mg/l and an electrical conductivity of 102.8 mS/m. The background values from the stream are to be 0.6 mg/l for chloride concentration and 5.7 mS/m for electrical conductivity.

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

**Figure 11.**  *Resistivity (top), chargeability (middle), and normalized chargeability (bottom) sections of Line 0.* 

 Results from this study show that resistivity successfully identifies the wastes, the contaminated soil, and the contamination plume, being efficient in mapping the affected area. Chargeability is very sensitive to wastes and leachate, but its dependence upon salinity makes its interpretation sometimes complex. Normalized chargeability on the other hand was a more efficient parameter: it increases with fluid conductivity within the fluid conductivity range observed in this study.
