Electrode noise for induced polarization measurements: Insights of contaminant interference

The induced polarization (IP) method has significant potential for characterizing and monitoring groundwater contamination, particularly given recent advances in extracting rich spectral information from time domain IP (TDIP) data. However, its effectiveness depends on the quality of full-waveform data, and the impact of electrode noise remains insufficiently understood in field applications, especially at contaminated sites. Sandbox experiments were designed to evaluate electrode durability and IP data errors under field relevant combinations of contaminant type and conductivity at sampling rates of 0.1, 10, and 10,000 Hz. An error assessment method combining probability distributions, Fourier transforms, and the signal to noise ratio was proposed. It reveals the frequency ranges of amplitude and phase spectral information inherent in TD data. Pb-PbCl₂ electrodes remained stable across the contaminant and conductivity range. For stainless steel electrodes, low-frequency noise decreased with increasing conductivity. Differences among contaminated media at same target conductivity are interpreted as combined responses to conductivity and ionic composition rather than as isolated contaminant effects. Organic contaminants may cause anomalous trends in electrode noise. Amplitude spectra were reliable across most of the 0.001-1000 Hz range, but for weaker signal, the SNR of stainless steel electrodes fell below 10 dB at <0.004 Hz. Reliable phase ranges were 0.01-1000 Hz (Pb-PbCl₂) and 0.042-1000 Hz (stainless steel) for Sample A, and significantly narrowed for Samples B and C. These findings provide insights into electrode noise, thereby improving the reliable extraction of IP information.