The Source and Transport of Arsenic in Northeastern Ohio Groundwaters

Abstract

Groundwaters in the Northwest School System area of Canal Fulton, Ohio were examined for their hydrologic and chemical properties. In general, the groundwaters in the study area were inter-connected by a complex system of aquifer and aquitards. Arsenic oncentrations were above EPA limits in two wells, but were elevated above the background value throughout much of the area. Two major aquifer systems exist within the study area: The Sharon Sandstone of the upland areas; and the outwash sand and gravel deposits of the buried valleys. Flow is generally from the north, but local variations are caused by the Tuscarawas River Valley on the south and west of the study area. Recharge to the local aquifer system may be occurring in the central portion of the study area from the chloride-contaminated Tuscarawas River. The areal distribution of arsenic within the study area indicates that the arsenic is not sourced from the Tuscarawas River and gives no indication of an outside source of arsenic. Within the study area, there is no evidence for an anthropogenic source of arsenic to the groundwaters. Agricultural soils, abandoned underground coal mines, industrial impoundments to the north, and an abandoned industrial dump site within the study area were all eliminated as possible sources for the arsenic. Theoretical and laboratory studies of arsenic in these groundwaters demonstrates that it is entirely of inorganic make-up, and consistsof about equal parts of arsenate and arsenite. Redox considerations suggest that arsenic is controlled by an adsorption equi1ibrium with ferric hydroxides, and that the reduction of the ferric hydroxides by a recent lowering of Eh and/or pH in the aquifer has liberated both iron and arsenic to solution. A high correlation between ferrous iron and total dissolved arsenic supports this model.