CORRELATIONS BETWEEN BEDROCK LITHOLOGIES AND ARSENIC CONTENT OF DRINKING WATER WELLS ON MATINICUS ISLAND, MAINE

Matinicus is a two square mile island 23 miles off the coast of Penobscot Bay, Maine and is populated by ~50 year round residents. The island lithologies are largely divided into two regions. The east side of the island is mostly coarse-grained biotite-granite. Foliated metamorphic lithologies including biotite - quartzite, quartz - plagioclase - biotite ± andalusite ± garnet schist, and amphibolite ± garnetite, are mapped along the western coast. The contact between the metasedimentary units and the granite is characterized by a moderately rusty zone with angular inclusions of metasedimentary units ranging in size from 5 - 150 cm wide rafted in the granite. This zone may be the source for arsenic found in high concentrations in some residents’ wells on Matinicus. Recent geologic mapping correlated with the residents’ water quality results from state and independent laboratories suggests that wells drilled to depths of 100-260 ft along the contact zone have higher concentrations of arsenic than the other wells on the island. To test this hypothesis the depth, type, and arsenic concentration of the residents’ wells will be compiled and compared to the results of a companion study (Downey, et al., 2012) focusing on documentation of arsenic-bearing minerals in the various lithologies of Matinicus Island. The results of this study will have important implications for Matinicus’ permanent residents’ access to safe drinking water.