# Contaminant Arrival Times at Wells G and H

Simulated concentrations of TCE from Ph.D. dissertation of Maura Metheny (2005)

Another major difference in the testimony of the three expert hydrogeologists in the trial was the arrival times of TCE and PCE in wells G and H. The plaintiffs' expert stated that these contaminants would reach wells G and H in less than 3 years. The Beatrice expert claimed that the contaminants would never flow to the municipal wells because the Aberjona was a groundwater divide preventing flow under the river to the wells. The W.R. Grace expert stated that the contaminants could not have reached wells G and H by May of 1979.

Each expert had at his disposal the same water-level, streamflow, and permeability data upon which to make these calculations. Each expert, however, used a different approach to making the calculations. One expert relied on the results of a 1-dimensional model that assumed steady-state conditions within the flow system and spatially uniform values of permeability, porosity, and hydraulic gradient. One expert used the water-level and streamflow data to construct potentiometric surface maps and a potentiometric profile to show that groundwater could not flow under the Aberjona River. The third expert incorporated all the site-specific water-level, streamflow, and permeability data into a 3-dimensional computer model that accounted for the transient character of the flow system due to temporal variations in recharge from precipitation, and changes in the pumping rates of wells G and H and their periodic use (Bair, 2001 (Acrobat (PDF) 4MB Jun18 09)). Excerpts from the trial testimony of these three experts can be found in Resource Collections under the **Trial Testimony** section.

Jury box for the eight jurists in the Woburn Toxic Trial

The jury listened to 78 days of testimony, much of it highly technical in nature dealing with geology, hydrology, contaminant movement, and computer modeling. None of the testimony dealing with the crucial issues of if and when did the contaminants reach wells G and H was consistent. By design, a jury learns passively. Jurists cannot talk to one another during the trial, only after closing arguments are made and their deliberations begin. Jurists cannot read textbooks to help them understand concepts and principals. Jurists, as in the Woburn Toxic Trial, usually cannot take notes to help them recall facts and opinions. None of the jurists in the Woburn Toxic Trial had a degree beyond high school, yet as a group, they were asked by our society to analyze and evaluate an inordinate volume of highly technical information

(Bair, 2001) (Acrobat (PDF) 4MB Jun18 09). The crux of the case came down to which expert did they understand and/or believe in terms of his calculation of contaminant arrival times at wells G and H.

**Learning Modules 3, 5, and 8** involve constructing the maps and performing the calculations to make (simplistic) estimates of contaminant arrival times in wells G and H.