GEOCHEMICAL EVALUATION OF SOURCES FOR ARSENIC IN GROUND WATER, NORTHPORT, MAINE

Forty-four domestic water wells were sampled in Northport, Maine and surrounding areas and analyzed for metals, acid anions, alkalinity, pH and specific conductance. Arsenic concentrations ranged from less than 1 ppb to 1940 ppb, with concentrations as high as 5500 ppb previously reported in this area. Water wells providing water with the highest concentrations of arsenic are clustered around the Kellys Cove area. Wells in this cluster were re-sampled and arsenic was speciated in the field using ion exchange resin. The pe calculated from the As(3)/As(5) redox couple ranged from -1.5 to about 4, with most samples clustering near a pe of 0.

The water chemistry data has been evaluated using principle component analysis and a variety of graphical methods. Arsenic is positively correlated with iron, manganese, and silica and negatively correlated with vanadium and copper. Samples with high arsenic concentrations plot in a calcium bicarbonate field on a piper plot.

Rock cuttings collected from a domestic water well installed in the study area were analyzed with an electron microprobe and reflected light microscopy. Extensive sulfide minerals, including pyrite, chalcopyrite and pyrrhotite, occurred in these samples. Arsenic minerals identified in these samples include arsenopyrite, gersdorffite, and loellingite.

This water well was sampled at 5 m intervals with arsenic concentration peaking near a fracture zone. Other chemical parameters follow this trend suggesting that the fracture zone is the source of the arsenic.