Molarity provides better clarity – using molar-based data when evaluating chlorinated volatile organic compound impacted sites

Abstract

Chlorinated volatile organic compounds are common constituents observed at many contaminated groundwater sites. Common industry practice has been to measure these constituents in groundwater on a weight concentration basis (e.g. µg/l, mg/l). This paper highlights the use of molar-based concentrations, especially in the case of parent-daughter degradation sequences commonly observed with the chloroethene, chloroethane, and chloromethane families of compounds. Converting to molar-based concentrations provides the practitioner greater insight into groundwater plume behavior including better evaluation of degradation processes, remedial progress, possible commingling, and/or sourcing. For example, this paper provides a tank analogy to evaluate whether the commonly misinterpreted observation of “DCE-stall” may be occurring at a site. Multiple examples of the benefits of using molar-based concentration data are also summarized in a project case study presented herein. As demonstrated in this paper, molarity does provide better clarity and can be a powerful evaluation tool in the groundwater practitioner’s toolbox.