INVESTIGATION OF A NOVEL TRACER, SODIUM 2-NAPHTHALENE SULFONATE, FOR SORPTION TO ORGANIC CARBON IN NATIVE SEDIMENTS

Uranium contamination in groundwater remains a cause for concern in many communities in the Western United States. Site conceptual models have been created that attempt to characterize the local hydrogeologic setting as well as model uranium fate and transport at contaminated locations. Among the most important variables to account for is the fraction of organic carbon (OC) in the contaminated zone of interest. OC plays a key role in redox geochemistry and uranium mobility, as uranium has been shown to adsorb to OC directly, retarding its movement downgradient (Bone et al., 2020). Preliminary data from both field scale tracer tests and batch microcosm experiments show that a novel tracer, sodium 2-naphthalene sulfonate (2-NS), might be suitable for estimating the fraction of OC in the aquifer matrix. Batch microcosm tests with 2-NS, quartz sand, and various fractions of granular activated carbon (GAC) showed linear equilibrium sorption with a ranging from 1240-1875 L/kg for the 0.1% and 1% GAC mass fractions; this compares well with the theoretical of 1000 L/kg (EPA, 2020). A new phase of batch microcosm tests with four native sediments with an OC content ranging from <0.01% - 2.67% will be used to develop sorption isotherms for 2-NS. 1-D flow-through column tests will also be conducted to investigate 2-NS sorption. These results will be presented in the hopes that 2-NS will be used in field-scale tracer tests to characterize the fraction of OC in the saturated subsurface.