Denitrifying permeable reactive barriers (PRBs) installed in proximity to impaired waterbodies can help mitigate coastal eutrophication. We monitored the hydro-biogeochemical conditions and assessed nitrogen removal performance of a tidally influenced pilot PRB installed behind a perforated marine bulkhead. The pilot was installed in an area with appreciable submarine groundwater discharge (SGD) and elevated nitrogen concentration likely due to medium – high density residential septic input to the local watershed. The bulkhead PRB reduced groundwater nitrate concentrations from 285 to 429 μM to <1 μM. Data from the pilot PRB was used to inform a laboratory column experiment in which twelve columns filled with aged media retrieved from the pilot PRB received artificial groundwater and seawater mixtures (0, 1, and 11 ppt) at representative hydraulic loading rates (HLR) and influent nitrate concentrations. Nitrate removal was not affected by salinity nor by the presence of hydrogen sulfide that was produced in the 1 and 11 ppt treatments. Significantly less dissolved methane was observed in 1 and 11 ppt treatments compared to the 0 ppt treatment, indicating that the tidally driven supply of sulfate rich porewater can suppress the onset of methanogenesis. Extrapolating column experiment results, bulkhead PRBs have the potential to reduce nitrogen loading to adjacent water bodies by 1.6–3.2 kg N m−1 shoreline year−1 over a range of relevant groundwater nitrate concentrations and hydraulic settings. Integration of PRBs during bulkhead replacement is a promising strategy to remove legacy nitrate from groundwater to improve coastal water quality, and site-specific PRB design is critical to maximize nitrogen removal while minimizing the risk of pollution swapping.