According to various aspects and embodiments, a system and method for treated contaminated groundwater is provided. The groundwater is contaminated with an initial concentration of recalcitrant organic contaminant. According to some embodiments, the contaminated groundwater is treated by introducing a persulfate to produce a first treated aqueous solution and then exposing the first treated aqueous solution to ultraviolet light to produce a second treated aqueous solution. The second treated aqueous solution may have a concentration of the recalcitrant organic contaminant that is at least 50% less than the initial concentration of recalcitrant organic contaminant.