This paper evaluates environmental conditions responsible for the high concentrations of trace metals in Indonesian coastal groundwater. Indramayu, which has significant potential groundwater resources, but for which limited information is available regarding its vulnerability, is selected as our study area. Results show that Fe²⁺ and Mn²⁺ are natural contaminants in the groundwater of the study site. The correlations of trace metals with salinity and redox-sensitive parameters verify that saline water has a significant impact upon the dissolution of Fe and Mn. Furthermore, reductive condition is confirmed to be responsible for Fe and Mn dissolution with a less significant correlation compared to salinity. Moreover, the high concentrations of trace metals are coupled with high dissolved organic carbon (DOC), which indicates that reductive environment may arise because of organic-matter decomposition. Finally, the impact of human activity upon Fe and Mn dissolution is identified at the northern tip of Indramayu, where trace-metal contents are significantly elevated. Further, in the southern part, the groundwater condition is relatively more natural; thus, the impact of human activity upon the presence of Fe and Mn is lesser in this region.