Background Fluorescence Analysis

A Powerful Subsurface Contaminant Transport Investigation Tool

Many dye tracing tests show that groundwater does not flow in the same direction inferred from site monitoring well networks.  Localized zones of higher permeability, such as former river/stream channels, faults and fractures, glacial features, or even a utility trench, may be present in the subsurface that form preferential groundwater flow paths that may not be detected using conventional monitoring methods.  At sites with contaminated groundwater, the presence of preferential flow paths can result in transporting contamination in unanticipated directions, which can result in poor characterization of the groundwater contaminant distribution and less-effective site groundwater remediation.

Background Fluorescence Analysis (BFA) is a powerful tool that can reveal these preferential groundwater flow paths and can improve site characterization and remedy effectiveness by identifying and then focusing site remediation on zones of the highest contaminant transport (flux).  BFA can be used to optimize the performance for remedial responses such as in-situ chemical oxidant injections, barrier wall placement, pump & treat system optimization, and NAPL recovery by focusing effort on the preferential groundwater flow paths, resulting in reduced project costs and shorter treatment times. 

BFA measures the fluorescence properties of dissolved organic carbon compounds present in groundwater at very high, parts per trillion resolution.  The high resolution allows us to identify small differences and similarities among site water samples.  Each water sample has a unique signature similar to a chemical fingerprint that helps scientists track the probable sample origin. 

BFA can be used in conjunction with non-toxic fluorescent dye injections to quantitate and verify identified preferential flow paths.  Fluorescent dye tracing (FDT) provides travel times for preferential pathways and reveals areas where flow is relatively stagnant. 

Aries has successfully used the BFA and FDT tools in both overburden and bedrock groundwater.  The BFA and FTD samples can be collected during a conventional groundwater monitoring event.  

January 23, 2018

Key Points

BFA can reveal the following:

  • Sample interconnections from various locations based on the sample fingerprints;
  • Well head capture zones;
  • Areas that petroleum or solvent product has flowed from and the extent of contaminant migration;
  • The presence and distinction of multiple contaminant sources (comingled plumes);
  • The likely preferential flow pathways and hydraulic connections within a monitoring well network;
  • Bedrock fracture preferential flow pathways; and
  • Groundwater – surface water interactions.

Contact

Peter J. McGlew, P.G., LSP
Principal Hydrogeologist
pmcglew@aries-eng.com

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