Assessment of Heavy Metal Contamination in Sand and Water Using Time Domain Reflectometry

Detecting and quantifying heavy metal contamination in soil and groundwater is one of the many geoenvironmental challenges that demand a robust, noninvasive, and real-time monitoring scheme. The current study underscores the potential of dielectric measurements in achieving this objective. The dielectric response of deionised (DI) water and sand contaminated with six heavy metals—lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), iron (Fe), and chromium (Cr)—was investigated using time domain reflectometry (TDR) with a specific focus on the TDR trace parameters, i.e., apparent dielectric permittivity (ka) and return pulse voltage (Vf). The impact of volumetric water content (θv) on the dielectric behavior of contaminated sand was also examined. The results revealed a consistent decrease in both ka and Vf with increasing contaminant concentration in DI water and sand, indicating a significant influence of ionic interactions and polarization effects on the dielectric properties. Among the studied contaminants, Pb exhibited the highest ka, while Cu showed the lowest, highlighting contaminant-specific variations in dielectric response. For all the sand samples contaminated with heavy metals, ka increased while Vf decreased with an increase in θv. Predictive models were developed to estimate heavy metal concentrations in contaminated sand based on Vf, ka, and θv, with coefficients of determination (R2) exceeding 0.9 for all cases.