Principal Component Analysis to Assess Remediation Progress at Two TCE-impacted Bioremediation Sites

ABSTRACT: Chlorinated solvents are one of the most prevalent groundwater contaminants in North America. Many of these contaminants are very difficult to clean up due to their physical properties and can pollute drinking water aquifers for decades to centuries. In-situ bioremediation (ISB) of tetrachloroethene (PCE) and trichloroethene (TCE) is as a popular remediation technology due to its inexpensiveness and flexibility for low-strength remediation applications. A typical ISB implementation involves the collection of large amounts of data to address the many possible problems and optimization remediation decisions. Currently, rather primitive tools and techniques are used to analyse these data, and the large amount being collected limits site-wide analysis efforts. Computer science algorithms for dimensionality reduction are common in research and certain industries that use "big data", however these techniques have yet to be adapted for environmental industry needs or performance monitoring of ISB applications. In this study a principal component analysis (PCA)-based method was applied to two TCE-impacted ISB site datasets, with the purpose of increasing the number of analytes and intermediate sampling times included in a single analysis method. The method connected each monitoring well's sample-scores through PCA space, thus combining spatial and temporal evolution and allowing a viewer to understand the well's overall behaviour. The method was able to separate monitoring wells into categories such as "Successful", "On-Track", "Rebound", and "Unsuccessful", and effectively summarize 1000s of data points to facilitate site-wide analysis. The results generally agreed with practitioner intuition that used traditional methods of analysis such as timeseries plots, isopleth plots, and general domain knowledge. The main benefits demonstrated by the technique were the speed and ease of analysis, and it is a potential screening tool for use by practitioners to expedite ISB analysis.