Detecting and quantifying organic contaminants in sediments with nuclear magnetic resonance

Abstract

We have conducted proton nuclear magnetic resonance (NMR) measurements of relaxation times [Formula: see text] and [Formula: see text] as well as the diffusion coefficient [Formula: see text] to detect and quantify gasoline, diesel, crude oil, and trichloroethylene (TCE) in sediment samples containing water. The sediment samples were coarse sand, fine sand, and a sand-clay mixture. We found that water, gasoline, diesel, and crude oil all exhibited similar signal amplitudes per unit volume, whereas TCE exhibited one-tenth the signal. The ability to use [Formula: see text] measurements to distinguish the contaminant signal from the water signal depended on the bulk-fluid properties as well as the sediment texture and grain size. In the [Formula: see text] distributions for samples containing equal volumes of contaminant and water, the contaminant signal could be resolved for crude oil in sand and for gasoline and TCE in the sand-clay mixture. Adding the diffusion measurement, using either pulsed or static gradients, made it possible to distinguish diesel and crude oil in all of the samples due to the large differences between the [Formula: see text] of the contaminants and water. From the diffusion measurements, we were able to accurately quantify diesel and crude oil volumes ranging from 1% to 17% of the total sample volume. These methods could be applied in the field using NMR logging tools to quantify and monitor subsurface contamination.

Quantifying Crude Oil Contamination in Sand and Soil by EPR Spectroscopy

“…While this is an established laboratory method and has been used repeatedly, it is not feasible under in situ conditions where relaxation contrast may be too small. Two-dimensional studies, correlating T 2 relaxation time and diffusion coefficient, succeed in separating oil from water and other fluids [24]. While such experiments can be carried out even on mobile NMR systems such as the NMR-MOUSE, depending on the range of parameters, they can be time-consuming and problematic in terms of quantification.…”

Modelling the Transport and Export of Sediments in Macrotidal Estuaries with Eroding Salt Marsh

“…The potential of salt marshes to trap fine sediments, and consequently particle-bound pollutants, is especially relevant when dealing with highly contaminated waters coming from industrial and agricultural discharges (Ullrich et al 2001;Soto-Jiménez and Páez-Osuna 2010;Wallschläger et al 2000;Caborn et al 2016;Fay and Knight 2016). Nutrient-rich waters…”

Low‐Field Borehole NMR Applications in the Near‐Surface Environment

“…The correlation of relaxation behavior with diffusion properties allows the separation of some of the effects that combine to influence T 2 relaxation (Song, 2010). The ability to collect D – T 2 correlations improves the feasibility of using borehole NMR tools to detect degradation of organic contaminants by allowing the separation of the water and hydrocarbon signal, for example, since water and hydrocarbons have different self‐diffusion coefficients (Fay and Knight, 2016). The latest versions of the Javelin and Dart borehole NMR probes can now encode for effective self‐diffusion and record D – T 2 correlations, although the corroborating research is not yet published.…”