Accelerating permafrost thaw and changes in subsurface hydrology are occurring as a result of a rapidly changing Arctic climate. These changes have major implications for the mobility and reactivity of solutes, including carbon cycling. Simulating such processes requires numerical tools that couple water, energy, and solute transport with dynamic freeze-thaw processes and variably saturated conditions. We present SUTRA-solice, a new version of the USGS SUTRA code, developed to simulate variably saturated groundwater flow, advective-conductive heat transport with phase change, and reactive transport of multiple solute species, with additional functionality to support temperature- and saturation-dependent reaction rates. We illustrate the application of SUTRA-solice by simulating the fate and transport of dissolved organic carbon mobilized by permafrost thaw along an Arctic hillslope. The synthetic model captures key processes such as organic matter decomposition, microbial mineralization and lateral export, which depend strongly on soil temperature and moisture. These simulations help quantify the balance between vertical carbon release as greenhouse gases and lateral transport to surface waters. Continued model development and testing with field data will support improved understanding of hydro-biogeochemical feedbacks to climate change and their implications for Arctic carbon cycling.