In this activity, students play the roles of investigators attempting to determine the source of arsenic contamination in groundwater, which has sickened some people in a hypothetical community. They will analyze data to trace the flow of the contaminant and attempt to identify its source, which is suspected to be a local factory. They will understand that point sources of pollution may not necessarily be obvious, and that close examination of the data may be required to determine what is actually happening. They will also investigate how burial practices of the nineteenth and early twentieth centuries produced arsenic-laden areas that contribute significant groundwater contamination.