5:15 PM - 6:45 PM
[AHW24-P03] Factors Affecting Ammonium Contamination in Deep Groundwater of Yokohama City, Japan
Keywords:Groundwater, Ammonium, Nitrogen isotope, Clay
As a city with second-highest population in Japan, it is expected to give the best facilities including the cleanliness of water. However, several deep groundwaters wells in Yokohama City are contaminated by ammonium-nitrogen. Groundwater contaminants include iron, arsenic, microorganisms such as Escherichia coli, and nitrogen contamination such as nitrate nitrogen and ammonia nitrogen, which have been reported around the world and have become an issue in the use of water resources. The purpose of this research is to investigate the factors affecting ammonia nitrogen pollution found in deep groundwater. We will understand the causes of ammonia nitrogen pollution by observing stable isotopes of ammonia nitrogen used for estimation and analyzing existing geological data. 20 samples were taken in 2022 and 2023 and more than half of the samples’ ammonium-nitrogen concentration exceeded the drinking water guideline value of 1.2mg/L. Based on ammonium-nitrogen isotope (δ15N NH4) values; the isotope value has a range from -2.2‰ to 5.7‰. The result suggests that the main source of ammonium contamination is from soil. Geological data provided by Mitsubishi Chemical Aqua Solution Co., Ltd. Shows that Yokohama City has a thick clay layer in several high ammonium contamination areas. This suggests that clay layer with potentially high organic matter contents might be the source of high level of ammonium. Furthermore, water isotope value also being observed and the value ranges from -58.7 ‰ to -47.7 ‰ with lower water isotope value tends to have lower ammonium-nitrogen concentration. With water isotope value, it is possible to find the source of groundwater and the find the possibility of groundwater being diluted by light isotope water. Thus, this study found a possible relationship between ammonium-nitrogen concentration in deep groundwater with clay in soil and dilution of groundwater by surface water. However, in order to understand the source of ammonium contamination in the groundwater, there require a detailed study on hydrogeochemical and biogeochemicalprocesses within the aquifer and aquitards.