Use of Radiocarbon Dating to Evaluate Sustainability of Groundwater Pumping in Delaware
Monday, May 5, 2014: 1:00 p.m.
Curtis (Westin Denver Downtown)
A. Scott Andres
,
Delaware Geological Survey, Newark, DE
Zack Coppa
,
Delaware Geological Survey, University of Delaware, Newark, DE
New test data that show the presence of groundwaters with conventional radiocarbon ages between 9,600 and 16,200 years in test wells finished in the Piney Point, Rancocas, and Mt. Laurel aquifers in the Coastal Plain of southern New Castle and northern Kent Counties, Delaware. Sample depths range from 155 to 525 feet below land surface. Model corrections to radiocarbon ages, done to adjust for aquifer matrix effects, range from 10 to 30 percent.
Conceptual models and simulations both show that prior to onset of groundwater use, groundwater entered the system in the northwest and flowed to the southeast down the regional dip of the geologic units and toward the regional discharge areas in Delaware Bay or the Atlantic Ocean. Pumping has reduced the potentiometric surfaces in the aquifers by tens of feet. Though heads still exceed the tops of aquifers by significant amounts, there is concern for intrusion of deeper saline water.
Comparison of these ages with flow-model estimated ages for pre-pumping groundwater flow conditions indicates that observed ages are thousands of years older than expected suggesting that pumping has significantly altered both potentiometric surfaces and flow paths. Older water is now being pumped back from deeper, previously downflow sections of the aquifer. Regular salinity and monitoring and additional radiocarbon dating will continue to be done to evaluate trends.
A. Scott Andres, Delaware Geological Survey, Newark, DE
Scott Andres has worked as a hydrogeologist at the Delaware Geological Survey since 1984, and has a secondary faculty appointment in the Department of Geological Sciences at the University of Delaware. Recent research areas include watershed-scale assessments of nutrient loads, regional characterization and mapping of aquifers, integration of GIS tools into groundwater flow and transport models, and field studies and simulation of performance and groundwater impacts of soil aquifer treatment.
Zack Coppa, Delaware Geological Survey, University of Delaware, Newark, DE
Zack Coppa is a research associate with the Delaware Geological Survey, working on the southern New Castle–northern Kent Counties Groundwater Monitoring Network project.
