An overview of arsenic in Maine ground water

Presentation (pdf document)

Robert G. Marvinney, Maine Geological Survey

Over the past several decades, many institutions have investigated aspects of arsenic in Maine ground water. In the early 1990s, the Maine Center for Disease Control and the Maine Geological Survey investigated elevated arsenic in several towns in southern Maine. This work showed that more than 10% of the sampled wells had arsenic concentrations above the MCL, 50 ppb at the time, and no clear relationship to geology. Review of available water analyses from MCDC suggested the same statistic for wells statewide. However, later work in NH indicated sampling bias in the Maine datasets from volunteered wells. Subsequent analysis of randomly selected wells in Maine suggested 2-3% at 50 ppb As. However, in the intervening time, the MCL was lowered to 10 ppb, and 10% of the randomly selected wells exceed this level. Work by the USGS during this time suggested a spatial correlation with carbonate rocks.

In the 21st Century, work has focused on the mechanisms of arsenic transport in ground water. Investigators at the University of Maine researched elevated arsenic in ground water at Northport. This conveniently small watershed with exceptionally high arsenic levels provided an excellent laboratory for studying the evolution of arsenic-rich ground water. The mechanism of arsenic mobility there is multiphase, involving primary sulfide minerals, iron-oxyhydroxide mineralization on fracture walls, and changing pH-Eh conditions. Current work with Columbia University focuses on elevated arsenic in ground water of the Augusta area, and its relationship to geology.