Scott Bair

Ohio State University

The animation of induced infiltration from the Aberjona River to Woburn wells G and H contains is created in both plan view and cross section view. The animation can be viewed to address several concepts in an introductory hydrogeology course. It shows how induced infiltration waxes and wanes as pumping rates of wells change. It also shows in plan and cross section views how surface water induced into an unconfined aquifer can remain within the aquifer as a pod of river water for months until the natural discharge from the aquifer back to the Aberjona River flushes the pod of river water from aquifer. The animation also shows the effects of partially penetrating pumping wells on flow paths of water emanating from the Aberjona River.

The animation was created in TecPlot and can be viewed in the Windows Media Player, QuickTime Video, and Real Player. It is based on a calibrated groundwater flow model constructed using MODFLOW and a solute transport model constructed using MT3D by Maura Metheny for her Ph.D. dissertation.

To portray the movement of river water through the aquifer to the pumping wells, 100 ppb of an unretarded solute was placed in the model cells representing the Aberjona River. When normal hydraulic gradients near the river reverse and induced infiltration occurs due to well pumping, solute moves out into the unconfined aquifer toward the pumping wells, whereas when the wells stop pumping and hydraulic gradients revert back to normal, solute slowly moves back toward the river as it is flushed from the aquifer by groundwater discharge to the river.

Solute concentrations in the aquifer were computed monthly from 1960 to 1986. Municipal wells G and H operated periodically from October 1964 to May 1979. A well operated by the Riley Tannery, which was later bought by Beatrice Foods, was used from before 1960 to after 1986.

Because the animation shows the percentage of river water moving through the unconfined aquifer and does not show hydraulic heads, students must be familiar with the concepts of vertical hydraulic gradients, reversals of hydraulic gradients near rivers caused by pumping wells, cones of depression, groundwater divides, and the effects of partially penetrating well screens on flow paths.

I use this animation two times in my course. I use it after explaining induced infiltration of river water as a means to graphically portray the process and the temporal changes that occur when pumping rates and schedules vary and I use it again later in the course when I talk about groundwater contamination and remediation techniques, natural attenuation and flushing being one of them. I ask students to view the animation and write down four observations seen in the animation that portray concepts gone over in class.

My goals in having students view this animation are to have students become aware that:

1. temporal changes occur in almost all hydrologic processes—that flow systems are rarely steady state for long,
2. river water chemistry can have a major impact on groundwater chemistry when induced infiltration occurs,
3. mixing and filtration are important geochemical processes,
4. partially penetrating screens on pumping wells produce non-textbook flow paths, and
5. once contaminated, aquifers can take to years to flush contaminants.

Because changes in hydraulic heads are not shown in the animation, students are forced to visualize what an equipotential map and flow paths would look like when river water is induced into an aquifer. Forcing students to visualize situations when there is scant or no data requires a firm understanding of fundamental principals.

It is still unknown whether the cluster of childhood leukemia cases in east Woburn was caused by TCE and PCE contamination from five known sources of contamination within the capture zones of municipal wells G and H, or whether the leukemias were caused by induced infiltration of Aberjona River water, which may have contained dissolved concentrations of arsenic, chromium, and lead. Several papers have been written about the arsenic, chromium, and lead contamination in Woburn. These papers could be read, combined with a broad discussion about mobility of heavy metals under different oxidation states, hypotheses drawn by the class, and experiments designed by the students to ascertain whether contaminated river water could have reached wells G and H. Designing an experiment to test an hypothesis is a higher-order thinking skill needed by all scientists and engineers.

See the related activity in this collection, TCE Transport to Woburn Wells G and H.

Aurillo, A.C., R.P. Mason, and H.F. Hemond, 1994. Speciation and fate of arsenic in three lakes of the Aberjona watershed, Environmental Science and Technology, v. 28, no. 4, p. 577-585.

Bair, E.S., and M.A. Metheny, 2002. Remediation of the Wells G & H Superfund Site, Woburn, Massachusetts, Ground Water, vol. 40, no 6, p. 657-668.

Bair, E.S., 2001, Models in the Courtroom, Chapter 5, in Model Validation, Perspectives in Hydrological Science, M.G. Anderson and P.D. Bates, eds., John W. Wiley & Sons Ltd., West Sussex, England, 57-76.

Davis, A., J.H. Kempton, A. Nicholson, and B. Yare, 1994. Groundwater transport of arsenic and chromium at a historical tannery, Woburn, Massachusetts, U.S.A., Applied Geochemistry, v. 9, p. 569-582.

Harr, J., 1995, "A Civil Action," Random House, New York, 500 p.

Metheny, M.A., 2004, "Evaluation of Groundwater Flow and Contaminant Transport at the Wells G & H Superfund Site, Woburn, Massachusetts, from 1960 to 1986 and Estimation of TCE and PCE Concentrations Delivered to Woburn Residences," Ph.D. dissertation, Department of Geological Sciences, The Ohio State University, 346 pp.

Metheny, M.A., 1998, "Numerical Simulation of Groundwater Flow and Advective Transport at Woburn, Massachusetts, Based on a Sedimentological Model of Glacial and Glaciofluvial Deposition," M.S. thesis, Department of Geological Sciences, The Ohio State University, 197 pp.

Metheny, M.A., and E.S. Bair, 2001. The Science Behind A Civil Action—The Hydrogeology of the Aberjona River, Wetland and Woburn Wells G and H, West, D.P. and R.H. Bailey, eds., in Guidebook for the Geological Field Trips in New England, 2001 Annual Meeting of the Geological Society of America, p. D1-D25, Boston, Massachusetts.

Metheny, M.A., E.S. Bair, and D.K. Solomon, 2001. Applying variable recharge to a 19-year simulation of groundwater flow in Woburn, Massachusetts and comparing model results to 3H/3He ages, Seo, H.S., E. Poeter, C. Zheng, and O. Poeter, eds., in MODFLOW 2001 and Other Modeling Odysseys—Conference Proceedings, vol. 2, p. 783-789, International Ground Water Modeling Center, Colorado School of Mines, Golden, Colorado.

Myette, C.F., J.C. Olimpio, and D.G. Johnson, 1987, Area of influence and zone of contribution to Superfund-site Wells G and H, Woburn, Massachusetts; U. S. Geological Survey, Water-Resources Investigations Report 87-4100, 21 p.

Spliethoff, H.M., and H.F. Hemond, 1996. History of toxic metal discharge to surface waters of the Aberjona watershed, Environmental Science Technology, v. 30, no. 1, p. 121-128.