Abstract

Arsenic was detected in the 29 water samples out of the 46 groundwaters located in the Ulsan metropolitan area and it's concentration ranges from <0.1 to 72㎍/L. Among them the arsenic concentrations of three samples are over domestic drinking-water requirements (50㎍/L), and those of 10 samples are more than WHO MCLs, 10㎍/L. High arsenic groundwater were recognized in the two region; one was the tectonic line, especially Ulsan iron mine at Dalcheunri and the other was around Hyomundong distributed Jeongja conglomerate. It is estimated that the former is originated from pyrite oxydation type, oxygenated redox, whilst the latter is resulted from oxidation of reducted FeOOH. The species of arsenic in groundwater is in pentavalent arsenic, H₂AsO₄^-, HAsO₄^-2 near tectonic line, and trivalentarsenic, H₃AsO₃ around Hyomundong.

Keywords Ulsan, arsenic, groundwater, WHO