Characterization of DNAPL Source Zone in Wisconsin (NSERC IRC Project)

G360 PROJECT TEAM: Dr. Jessica Meyer, Dr. Beth Parker & Brent Redmond (MASc Candidate)

A mixture of organic contaminants that occurs as a dense non-aqueous phase liquid (DNAPL) has accumulated in a fractured sandstone 45-55 meters below ground surface at the Hydrite site in south central Wisconsin. Between 1999 and 2002, sixteen boreholes were drilled to evaluate the vertical extent of mobile DNAPL. These boreholes were iteratively advanced 10 feet and then pumped until DNAPL was not recovered. The boreholes were left as open bedrock wells providing University Consortium researchers an opportunity to investigate current source zone conditions using high resolution sealed hole methods.  

Research funded by NSERC, Hydrite Chemical Company, and FLUTe™ is now underway  to help characterize this source zone.  FLUTe™ offers several products for characterizing the distribution of contaminants while at the same time sealing the entire length of the open borehole with a FLUTe™ liner. The FLUTe™ NAPL cover is hydrophobic, quickly wicking NAPL into the cover. The NAPL passes through the cover, staining the cover and dissolving the multicolored dye stripes (Figure 1). The FLUTe™ FACT uses strips of activated carbon felt to provide depth-discrete contaminant concentrations within a sealed borehole. FLUTe™ liners with NAPL covers and FACT strips were deployed by University Consortium researchers in four of the existing RW wells at the Hydrite site in September 2018.

FACT sample analysis and interpretation is still ongoing. The NAPL covers provided immediate insight. The ink was entirely removed (dissolved) from the bottom 2 feet and 16 feet of two of the NAPL covers (Figure 2). The complete removal of the ink is strongly suggestive of accumulation of DNAPL in the bottom of these two holes. However, interface probe measurements taken in the same holes about a week later did not provide an indication of free phase. Consequently, additional research is planned for the summer of 2019 to resolve the two sets of observations. In addition, there were relatively few examples of distinct staining that would be associated with DNAPL accumulated in individual fractures. The results from the FLUTe™ NAPL covers and FACT strips will be used to design temporary multilevel systems to perform targeted pumping of individual fractures/ beds in several of the boreholes. The data collected will provide important insight into the current day architecture of the DNAPL source zone.

Pictured Left: Example of NAPL cover with no staining (lines of ink are intact).
Pictured Right: Example of an extremely stained NAPL cover, in which all the ink has been removed.

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