Trace Metal Characterization and Ion Exchange Capacity of Devonian to Pennsylvanian Age Bedrock in New York and Pennsylvania in Relation to Drinking Water Quality
Date of Award
Master of Science (MS)
Donald I. Siegel
Drinking Water Hazards, Ion Exchange, Natural Water Hazards, Trace Metals
Physical Sciences and Mathematics
I report the results of an evaluation on the factors that control the quality of potable water produced in domestic and other wells in the shallow sedimentary rock formations of the Appalachian Basin. I collected 49 samples from the upper 120 meters of Devonian to Pennsylvanian aged bedrock between Marcellus, NY and State College, PA and analyzed their bulk geochemical composition. In particular, I quantified the mobile and total metals for which there are health concerns related to unconventional gas exploitation in the Appalachian Basin; Fe, Mn, Sr, Ba, As, and Pb. Measured bulk concentrations for several formations reached maximum concentrations of 65 ppm As, 4,900 ppm Ba, 63,000 ppm Fe, 130 ppm Ni, and 68 ppm Pb.
To assess the mobility of these metals in the subsurface I used a variation of the U.S. Geological Survey Field Leaching Test. Metals such as Al, Zn, and U potentially can be leached from aquifer rocks naturally under acidic conditions, such as where pyrite might oxidize, to above current allowable regulatory values for these metals (2 mg/L, 5 mg/L, and 0.03 mg/L respectively) from some of the clay-rich formations. Small percentages (typically <1%) of the bulk concentrations were mobilized into solution but were still sufficient to exceed current EPA drinking water maximum contaminant levels (MCL) in many of the samples. In total, 74% of our samples exceeded MCL values for Al, 18% for As, 6% for Fe, 12% for Mn, 98% for Pb (above MCL Goal of 0 ppb), and 70% for U (above MCL Goal of 0 ppb).
Groundwater analyses from both New York and Pennsylvania show that natural ion exchange occurs along flow paths from ridge tops to valleys. I measured the total cation exchange capacity (CEC) of the samples and observed that they do not span the expected values for illite-rich clays (typically 10-40 milliequivalents/100g) commonly found in the Appalachian Basin. Instead, 88% of the samples had CEC values below 10 meq/100g with only 1 sample above 20 meq/100g. I quantified the hypothetical ground water flow path lengths necessary for the observed cation exchange to occur along fracture planes by combining CEC values with surface area measurements on three samples which ranged from 10.32-13.59 m2/g. These three estimates resulted in plausible flow path lengths of 2 km, 3 km, and 30 km.
Many state and federal regulations do not require water from domestic wells or groundwater samples collected for metal analysis to be filtered. I argue that these regulations expose residents to drinking water with turbidity caused by suspended minerals that have metals attached leading to total concentrations at or above the Environmental Protection Agency’s (EPA) MCL levels. I quantified the effects of turbid water at the EPA MCL of 5 NTU and improper filtration of turbid groundwater samples at the EPA MCL of 10 NTU on total metal concentrations used to trigger regulatory compliance related to possible contamination and health effects.
Along with this broad scale study area I compared my geochemical results to the Fiorentino II (2015) study on a Devonian outcrop 4 miles North of Cortland, NY to evaluate small-scale trace metal heterogeneity within a single stratigraphic section. My regional collection of single data points at outcrops plotted within the 10th and 90th percentiles of the small-scale outcrop study. Together these two studies provide important information to determine the extent to which ground water might be naturally high in trace metal composition, either because of geochemical conditions or entrainment of suspended material not removed prior to sampling.
Spradlin, Jeffrey Dale, "Trace Metal Characterization and Ion Exchange Capacity of Devonian to Pennsylvanian Age Bedrock in New York and Pennsylvania in Relation to Drinking Water Quality" (2015). Dissertations - ALL. 296.