טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShalem Shaham Tamar
SubjectMonitoring Soils Contaminated by Heavy Metals Using Induced
Polarization
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Alex Furman
Full Thesis textFull thesis text - English Version


Abstract

Soil and groundwater pollution in general, and by heavy metals in particular, is a major threat to human health. Heavy metals originate from non-point sources and their fate in the environment is determined by various interactions and is influenced by multiple factors. Accordingly, heavy metals contamination is often wide-spread and it is difficult to predict or monitor its scope and distribution. Fast, accurate and low-cost measurement of heavy metal contamination is therefore of high desire. Geophysical methods, specifically spectral induced polarization (SIP) may be an alternative to the tedious sampling techniques typically used. In the SIP method, an alternating current at a range of low frequencies is injected into the soil and the resultant potential is measured along the current’s path. SIP is a promising method for monitoring heavy metals, because it is sensitive to the chemical composition of both the ions absorbed on the soil minerals as well as the pore fluid and to the interface between the two.

The goal of this research is to examine SIP as a tool for identifying and monitoring heavy metals in soil, in static and dynamic transport and remediation processes. First, the influence of the concentration of copper, lead and zinc on the SIP signatures of saturated sandy and clayey soils was investigated, considering relatively high concentration ranges. Next, sandy soil was contaminated by copper and the saptio-temporal changes of the SIP signature were studied during the progress of the pollution and while the metal was extracted from the soil.

A clear distinction was observed between the electrical signatures at equilibrium state of clean soil and soil contaminated by heavy metals. However, there was no consistent correlation between the amount of pollution and the SIP response. The results also show evidence of electrodic polarization, related to the formation of metallic particles in the soil (especially in the high concentrations), as detected by XRD measurements.

Quadrature conductivity of sandy soil decreased during the progress of a copper pollution front, with apparent distinction between anions (chlorides) and cations (copper). Spatial analysis of the column during the pollution shows temporal delay in the progress of the SIP response along the column, consistent with retarded phenomena such as adsorption. Extraction of the metal from the soil through chelation to EDTA increased the conductivity above its original value. Progression of the SIP response along the column at that phase was approximately the same as the flow rate.

In conclusion, SIP is shown to be able to serve as a tool for identification and monitoring of heavy metals in soil. However, there is a need of a considerable extension of the database and a complete understanding of the mechanisms governing the SIP response of soil in the presence of heavy metals. Further work should be done in understanding how the chemo-physical properties of the solid and liquid phases affect the electrical signature of soils