Use of Logarithmic-Scale Correlation Plots to Represent Contaminant Ratios for Evaluation of Subsurface Environmental Data

Abstract

Contaminant concentration ratios are used commonly to distinguish between different sources of contamination and to evaluate contaminant attenuation in groundwater, soil air, soil, and sediment. Logarithmic-scale correlation (log-log) plots provide special capabilities in representing contaminant ratios. Log-log plots can reflect the ranges in concentrations over many orders of magnitude, the magnitude and ranges of concentration ratios, and whether ratios are constant or change with declining concentration. Declines in contaminant concentrations due to dilution and dispersion processes will not change contaminant ratios, and such data should plot along isoratio lines. If contaminant concentrations are reduced also by other attenuation processes such as sorption or biodegradation that affect one of the contaminants to a greater degree than the other, the ratio will change and the data will deviate from the isoratio line trends. Examples are given to illustrate the use of log-log plots in the interpretation of chemical data from sites of groundwater, soil air, and sediment contamination.