BEDROCK AND GROUNDWATER INTERACTION: TRACING THE POTENTIAL FOR CATION CONTAMINANTS IN GROUNDWATER, SMALL POINT, MAINE

Contamination of groundwater due to the leaching of cations from bedrock can be a serious threat to public health. It is therefore important for geologists to identify potential hazards to bedrock groundwater systems. Small Point, a peninsula located in mid-coast Maine, is an important study location as there is no municipal water supply; residents must rely either on groundwater or a rainwater cistern for drinking water. The objectives of my study are to determine the: (1) relationship between groundwater and leached cations from bedrock, (2) mineral phases where cations are present and the likelihood of mobilization, and (3) implications on the public, namely where are the best and worst places to extract groundwater. For this analysis 10 different sample lithologies, determined from extensive mapping of the Small Point peninsula were studied. These lithologies include Fe-S and Al bearing schists, amphibolites, calc-silicates, and a graphitic phyllite. Using leaching experiments, where each unit was crushed and exposed to slightly acidified rainwater (pH 5.5), it was determined which of the cations found in each rock unit may actually become mobilized within the groundwater system. Inductively coupled plasma atomic emission spectroscopy (ICP-AES), was used to complete this analysis. Preliminary data from leaching indicates the most mobile cations are found in the schists and calc-silicate samples. Lithologies that did not mobilize cations easily include the graphitic phyllite, granofels, and amphibolite samples. Of the samples that easily leached cations, a rusty schist sample shows an increase in concentrations of Fe, Mg, and some Pb. A mica schist exhibited an increases in As, Mg, and Mn. The calc-silicate easily released Al, As, and Ca. Analyses in progress include x-ray diffraction and x-ray fluorescence on samples, where the mineralogic assemblage and weight percent oxide for each lithologic unit will be determined, before and after leaching. Additionally units will be analyzed in thin section using SEM/EDS to determine the major elemental constituents of each unit, through x-ray mapping. Through this work I can construct polygons in ArcGIS using the overall bedrock geology map developed by Sive et al. (2012, this meeting) and fracture patterns to show the public the best and worst places to drill for water.