1. GROUNDWATER QUALITY ASSESSMENT OF THE PINEY POINT AQUIFER
Elizabeth Keily1, Arif M. Sikder2, Mohammad Alauddin3, S. Leigh McCallister1 2, Daniel Boehling2
1 Biology Department, VCU 2 Center for Environmental Studies, VCU 3 Physical Sciences Department, Wagner College
Introduction
The rural population of the Virginia coastal plain is dependent mostly on groundwater as a drinking water supply. There are four main aquifers in the Virginia coastal plain: Potomac, Aquia, Piney Point, and Yorktown (Figure 1). The present study will focus on the Piney Point aquifer, which accounts for roughly 5 percent of the groundwater supply to the Virginia coastal plain. Piney Point aquifer sediments are early Eocene to early Miocene in age and were deposited relatively uniformly on the marine continental shelf. They are medium to coarse grained, glauconitic, fossiliferous sands. Since trace element concentrations in groundwater typically reflect the solid phases of the aquifer, groundwater samples and aquifer sediments were analyzed for trace elements side by side to understand the groundwater quality.
The objective of this study is to assess the vulnerability of the Piney Point aquifer for trace elements released from its sediments and, ultimately, to understand the release mechanisms of trace elements from the solid phases of the aquifer under varying pH within natural limitations.
Methods
Groundwater samples were collected from public wells sourced from the Piney Point aquifer. Water samples were obtained from spigots as close to directly from the well as possible. Sample containers were triple rinsed with well water before collecting and field filtering samples through a 0.2 um filter. One 40ml vial was collected at each site and acidified with 40uL of nitric acid. The groundwater temperature, pH, and conductivity was also collected.
Water samples were analyzed for trace element concentration with ICP-MS. Sediment samples were collected from the USGS Banbury Cross core and were analyzed for trace element oxides with X-ray Fluorescence (XRF).
Conclusions
Arsenic and chromium were higher than maximum contaminant levels in both the sediment and groundwater samples; this could be evidence of these elements are leaching from sediments to groundwater. Since arsenic was higher than EPA standards in all groundwater samples collected, concentrations may be high enough to have associated public health issues; however, more samples will be collected to replicate results.
Future Work
Leaching experiments will be performed on the bulk sediments in order to observe the trace element concentrations that are released into leachate solutions at differing pH found naturally in aquifer. As a study of this kind has not been performed in the Virginia coastal plain, this will provide a baseline of trace element concentrations for the Piney Point aquifer, as well as potential of release of toxic elements in the event of pH change within the aquifer.
Results
Table 1 shows trace element concentrations for 7 Piney Point aquifer groundwater samples with EPA drinking water standards in terms of maximum contaminant level listed at the bottom. Table 2 shows trace element oxide concentrations of 9 Piney Point sediment samples.
Arsenic, chromium, and lead were present in sediment samples, though no lead was present in water samples.
Arsenic was higher than the maximum contaminant levels for all water samples and all sediment samples it was detected in.
Barium was below the maximum contaminant level for all water samples.
Chromium was higher than the maximum contaminant levels for all water and sediment samples.
Lead was below maximum recommended level for all sediment samples.
Selenium was above maximum contaminant level in 3 water samples.
Table 2. Trace element oxide concentrations for Piney Point aquifer sediments from XRF analysis and Maximum Recommended Levels in sediments from U.S. EPA and Environment Canada. Samples are arranged by depth with youngest sediments at the top.
Table 1. Trace element concentrations for Piney Point aquifer groundwater samples from ICP-MS analysis and U.S. EPA Drinking Water Standards.
Acknowledgements
We would like to thank Dr. Greg Garman, Director of VCU Rice River Center and Dr. Rodney Dyer, Director of the Center for Environmental Studies, for making this research possible. We would also like to thank Dr. Joseph Turner for running the ICP-MS analysis and Xin-Chen Liu for running XRF analysis.
And we would like to thank the residents and owners of the wells that allowed us sample their water.
Figure 1. Hydrogeology of the Virginia Coastal Plain. (Source: The Virginia Coastal Plain Hydrologic Framework, USGS)