Misleading Potentiometric Analysis from Groundwater Hydrographs (4/21/22) Mark Eisner, P.G.

Presentation Summary: Potentiometric water levels in the confined aquifers of the Mid-Atlantic Coastal Plain have been declining for decades; anthropogenic withdrawals probably loom large as a major contributing factor. Future projections of such hydrographs illustrate the possibility for various undesirable outcomes including, but not restricted to, increased risk of seawater intrusion, accelerated land subsidence in shoreline areas and even the “mining” of the aquifer should water levels decline to the stratigraphic top of the aquifer.

Mid-Atlantic states monitor potentiometric declines and use permitted water allocations to manage the risk of overuse. Regulatory agency efforts toward sustainable groundwater supply management use permit conditions to limit the pace of potentiometric decline, which often appears linear downward when plotted against time. Limiting permitted groundwater withdrawals from certain confined aquifers in areas of more rapid decline is a tool for such management efforts.

In the late 20th century, hydrographic data from one aquifer reflected a parabolic downward (i.e., ever-steepening) trend, rather than a linear one. Trend analyses suggested that a circumstance of aquifer dewatering could occur before the year 2100. Applicable statutes prohibited the local water management agency from issuing new permits for groundwater uses causing such a trend. In a 2006 hearing about a pending groundwater use, litigants came to dispute the utility of long-term USGS Groundwater Hydrograph data for (1) predicting future potentiometric trends and (2) forming the basis for local and regional aquifer use management decisions.

A key technical issue that governed the outcome is whether the apparently parabolic hydrographic trend was an irrevocable consequence of existing groundwater overuse and thus evidenced unsustainable groundwater uses, or whether it merely reflected a decades-long yet reversible trend of increases in permitted over-use. The judge allowed permitting practices to continue, but better data might have indicated that a differing groundwater management strategy needed to be applied without delay.

Speaker Bio: Mr. Mark W. Eisner, P.G. is a Vice President of Barton and Loguidice D.P.C. (B&L). Possessing 36 years of experience in environmental and hydrogeological consulting, Mr. Eisner directs hydrogeologic and hydrologic investigations for both private and public sector clients throughout the Mid-Atlantic region. Mr. Eisner’s foremost technical expertise is in matters relating to water resources, including the occurrence, movement, use and management of both groundwater and surface water as a natural resource, its susceptibility and properties when contaminated, and in methods for its safe and sustainable development, and when necessary, its remediation. He is a licensed Professional Geologist in all Mid-Atlantic States that have licensure and certification programs (DE, PA and VA).