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Evaluation of Visual Methods to Detect NAPL in Soil and Water
Author(s) -
Cohen Robert M.,
Bryda Anthony P.,
Shaw Scott T.,
Spalding Charles P.
Publication year - 1992
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/j.1745-6592.1992.tb00072.x
Subject(s) - soil water , environmental chemistry , contamination , environmental science , groundwater , soil test , chemistry , soil science , geology , geotechnical engineering , ecology , biology
Non‐aqueous phase liquids (NAPLs), such as chlorinated solvents and petroleum products, are present in the subsurface at numerous contamination sites in North America. Determination of NAPL presence should be an early investigation goal to guide site characterization and control efforts. Indirect methods for assessing NAPL presence rely on comparing measured chemical concentrations to effective solubility limits for ground water and to calculated equilibrium partitioning concentrations for soil. Under ideal conditions, NAPL presence can be identified by visual examination of soil or ground water samples. Direct visual detection may be difficult, however, where the NAPL is clear and colorless, present at low saturation, or distributed heterogeneously. There appears to be little documentation of practical, simple methods for direct identification of NAPL in soil or water. For this study, a series of experiments was conducted to test the hypothesis that simple and inexpensive methods can be used to visually identify clear, colorless NAPL in soil and water samples. Specific methods evaluated include direct visual examination, ultraviolet (UV) fluorescence analysis, a soil‐water shake test, adding hydrophobic dye to the shake test, and centrifugation. Additionally, the utility of organic vapor analysis was examined as an NAPL screening tool. Of the methods investigated, the hydrophobic dye methods, followed by UV fluorescence, offer the most simple, practical, and effective means for direct visual identification of clear, colorless NAPL in contaminated soil samples. These methods can be utilized in the field or in a lab with minimal time and material expense. For volatile NAPLs, analysis of organic vapors in soil sample headspace can be used to screen samples for further examination and, possibly, to infer NAPL presence. The NAPL in water experiments demonstrate that very small quantities of clear, colorless NAPL in water can be quickly identified by mixing in a tiny amount of hydrophobic dye.