Permeable Reactive Barriers (PRBs) are placed along beachfront and marsh-edges to intercept groundwater flow as it enters coastal waters. Their function is to filter out nitrogen caused by fertilizer runoff, septic waste, and other sources before it causes pollution, eutrophication, algae blooms and other problems. Geochemical analysis suggests that the barriers effectively remove nitrogen, but slight differences in location appear to have a profound effect on their function. The investigator will use genetic sequencing tests on the microbes present in the PRBs to see whether the difference in effectiveness has to do with the presence of salt water in the PRB. There is some evidence that barriers regularly inundated by seawater foster microbes that enhances nitrogen removal. Understanding what environmental conditions help denitrifying bacteria thrive will help to guide future barrier design, construction and placement.