DETERMINING THE SOIL ORGANIC CARBON PARTITION COEFFICIENT (KOC) FOR THE NOVEL GROUNDWATER TRACER 2-NAPHTHALENE SULFONATE (2-NS)

Organic carbon-rich zones along groundwater flow paths serve a key role in the fate and transport of groundwater contaminants. Understanding the discontinuous distribution of organic-rich matrix material is therefore imperative in creating a site-specific model for contaminant transport. Typically, this is conducted by sampling sediment cores from discrete points in space downgradient from the known contaminant plume or source of contamination. Data must then be interpolated between these points to understand the subsurface geometry with respect to organic carbon. A groundwater tracer injection, however, would be more effective at capturing heterogeneity in organic carbon distribution within the saturated zone. 2-naphthalene sulfonate (2-NS), a poly-aromatic hydrocarbon, is proposed here as a possible sorptive groundwater tracer for investigating the composition of aquifer sediments with respect to the fraction of organic carbon. Batch sorption experiments were conducted with groundwater and sediment from a uranium contaminated surficial aquifer in Riverton, Wyoming, along with an organic carbon-rich peaty soil. 2-NS sorption was observed to be linear and easily reversible with all the sediments used and the calculated log organic carbon partition coefficients, or K_OC, were 1.53 ± 0.23 and 1.46 ± 0.04 L/kg in the aquifer materials and peaty soil, respectively. The results of these experiments supported the hypothesis that 2-NS would sorb to organic carbon in natural porous media according to linear equilibrium sorption, potentially providing a future groundwater tracer for investigating the mass fraction of organic carbon in aquifer matrix material.