NMR relaxation measurements to quantify immiscible organic contaminants in sediments

Abstract

Laboratory NMR relaxation time (T2) measurements at 2 MHz were used to quantify the amount of toluene and bis(2‐ethylhexyl)phthalate (BEHP) in the presence of water in sand‐clay mixtures. NMR measurements were made on water, toluene, or BEHP in each sand‐clay mixture to understand the role of clay and iron content on the T2 of each fluid; we then made NMR measurements on mixtures of water and the contaminants in each sand‐clay mixture. Our ability to resolve the NMR response of the contaminant from that of water and to quantify the amount of the contaminant varied significantly with the clay and iron content of the sand‐clay mixtures. Detection limits as low as 3% contaminant (i.e., percent of the pore fluid, by weight) were observed in some sand‐clay mixtures. Our results suggest that NMR measurements could quantify toluene if some clay is present but are unlikely to be useful for quantifying BEHP.