How to get crap out of underground water (laymen terms)

Hydraulic Gradient Control for Groundwater Contaminant Removal
Dorothy Fisher Atwood and Steven M. Gorelick
Journal of Hydrology, 76 (1985) 85-106

Summary

As its title implies, the focus of Atwood and Gorelick’s paper is how to control the hydraulic gradient of an unconfined aquifer as a means of containing a contaminant plume for save and effective removal. Although the research is a hypothetical test, the aquifer that is modeled is a real aquifer under the Rocky Mountain Arsenal near Denver, Colorado.

The authors chose to use a two-stage approach in modeling the problem so to avoid nonlinearities that would otherwise prohibit the use of linear optimization technique. The two-stage planning procedure successfully selects the best wells and their optimal pumping/recharge schedules to contain the plume while a well or system of wells within the plume removes the contaminated water (Atwood 85). The first stage of the test involved determining the plume boundary location as a function of time by combining a groundwater flow and solute transport model. The second stage used a linear program to determine the optimal (as defined by minimal pumping and recharge) well selection and pumping/recharge rates.

Two different optimization strategies were used: 1) Sequential optimization, which relies primarily on the previous pumping period for its initial conditions and 2) Global optimization, which optimizes the system over the entire 32 pumping periods. The total pumping/recharge rates are comparable for the two optimization strategies; however, the well selection and pumping schedules are very different (Atwood 102). The research shows that the cumulative pumping/recharge rates of the global solution are approximately 10% better (as deemed by pumping/recharge volumes) than the sequential solution. However, the authors urge that although the global optimization produces a better solution than the sequential strategy, the solutions are similar enough that other factors such as economic or social conditions should be considered.



Discussion

The number of groundwater contaminant incidents will continue to increase over the next several decades as we begin to reap some of the pitfalls of industrialization and ineffective environmental safeguards. This article is not only interesting but also useful because it gives an effective and generalized method for handling groundwater contaminant plumes. With that being said, I would have liked to seen the author extend the scope of the research and model the impacts of having multiple wells that remove the plume. To be quite candid, I know little about groundwater contaminant removal but my intuition tells me that 16 years of pumping to remove the groundwater pollutants is not only an extremely long period but very expensive – something that most communities who would be paying for this would not appreciate. I would like to see further research that would optimize the pumping cost and time with multiple wells removing the contaminate plume.