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Improved Monitoring Methods for Performance Assessment During Remediation of DNAPL Source Zones

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Technical rept.

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The effective remediation of sites contaminated with chlorinated solvents continues to be extremely difficult and can be complicated by questions concerning the validity of the monitoring data used to assess a site and judge the performance of a remediation project. Standard practices for characterization and performance assessment, which commonly rely on sampling of subsurface porous media and groundwater, can be error-prone due to loss of volatile contaminants of concern COCs during sample collection and handling as well as the unaccounted-for effects that treatment agents can have on organic contaminant partitioning behavior. This report describes the methods and results of a project carried out to determine 1 the effects that sampling methods can have on the accuracy of measurements made for chlorinated solvents in samples of porous media collected from intact cores, and 2 the effects that remediation agents can have on the ability to infer chlorinated solvent mass levels in the subsurface based on groundwater concentration data. The results were intended to help delineate the limitations of current standard practices and help guide development of improved monitoring and assessment methods. In this project, the accuracy of VOC measurements was investigated using an experimental apparatus packed with sandy porous media and contaminated with known levels of VOCs, which could be sampled using different methods under variable, but controlled, conditions. Five sampling methods were examined representing different degrees of porous media disaggregation and duration of atmospheric exposure MDE that can occur during sample acquisition and preservation in the field. The results demonstrated that sampling method attributes can impact the accuracy of VOC measurements in porous media by causing negative bias in VOC concentration data ranging from near 0 to 90 or more. The magnitude of the negative bias is highly dependent on the attributes of the sampling method.

Subject Categories:

  • Organic Chemistry
  • Test Facilities, Equipment and Methods
  • Water Pollution and Control

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