Systems and methods for co-enhancing contaminant degradation such as LNAPL and DNAPL degradation. Embodiments of the inventive technology may relate to assuring adequate amounts (e.g., concentrations) of certain substances (e.g., nitrogen, electron acceptor, bacteria, microbial substrate) so that degradation of LNAPL and DNAPL is enhanced as intended. Any of the inventive methods may involve the amendment of groundwater with one or more particular substance (uric acid, electron acceptors, microbial substrate, as but a few examples) in order to enhance DNAPL, and perhaps also, LNAPL degradation.