Wednesday, April 2, 2008 : 9:00 a.m.

A Case Study of Capture Zone Delineation in A Multi-Aquifer System Based on Inverse Modeling of Pump Test Data

Ioannis Benekos, Ph.D., Min-Ying Jacob Chu, Ph.D. and Christopher M. Stubbs, Ph.D., PE, ENVIRON International Corporation

Capture zone delineation is commonly used to assess remediation alternatives and pumping strategies at contaminated groundwater sites. The capture zone extent is a function of aquifer characteristics which are often estimated from aquifer tests.  Pump test analysis is typically performed using specialized commercial software based on analytical solutions to the groundwater flow equation.  Since these solutions cannot represent complex geological settings where multiple strata and heterogeneity prevail, a more accurate and computationally demanding procedure may be warranted. For example, inverse modeling using pilot points and a numerical forward model may provide a more representative spatial distribution of aquifer properties. We evaluate whether a more complex, computationally demanding analysis is necessary to accurately estimate the capture zone of a well screened across two geologic units.

To illustrate, we present a case study of aquifer test analysis using inverse modeling at a site in southern California. The saturated zone at the site consists of two different hydrostratigraphic units. The pumping well is screened across both units, but the monitoring wells are only screened in one of the units. The groundwater flow model MODFLOW and the parameter estimation package PEST were used for forward modeling and parameter estimation, respectively. The resulting hydraulic conductivity and storativity fields from inverse modeling are compared to the average aquifer properties obtained from a commercial aquifer test software package. Finally, we compare the capture zones resulting from the two approaches.

Ioannis Benekos, Ph.D., ENVIRON International Corporation Dr. Benekos is a Senior Associate at ENVIRON International Corporation. He has technical expertise in chemical fate and transport modeling in groundwater and vadose zones, in performing human health risk assessments for hazardous industrial waste disposal, agricultural or spill sites, and in providing probabilistic cost estimates for site remediation in mergers and acquisitions. Dr. Benekos has a Ph.D. in Civil and Environmental Engineering from Stanford University, an M.Sc. in Civil and Environmental Engineering from Cornell University, and a Diploma in Civil Engineering from the National Technical University of Athens, Greece. He is a Registered Professional Engineer (Civil) in Greece.

Min-Ying Jacob Chu, Ph.D., ENVIRON International Corporation Dr. Min-Ying Chu is a Senior Associate/Technical Adviser at ENVIRON International Corporation. His expertise includes remedial strategy and remedial performance evaluation, biological remedial system design, chemical fate and transport, groundwater modeling, and vadose zone transport processes. Dr. Chu has a Ph.D. in Environmental Science and Engineering from Stanford University.

Christopher M. Stubbs, Ph.D., PE, ENVIRON International Corporation Dr. Stubbs is a Manager at ENVIRON International Corporation. He has technical expertise in chemical fate and transport modeling to support site remediation and human health risk assessment. Dr. Stubbs has a Ph.D. in Hydrology and Water Resources Engineering from MIT, an M.S. in Environmental Engineering and an M.S. in Technology and Policy also from MIT, and a B.A. in Physics from UC Berkeley. He is a Registered Professional Engineer (Civil) in California.


2008 Ground Water Summit