Assignment #2

Review Article

1) Article Reference
ATWOOD, D., F. and GORELICK, S., M. (1985) “Hydraulic gradient control for groundwater contaminant removal” Journal of Hydrology 76 pp. 85 - 106

2) Summary
This paper presents a methodology for determining an optimal operation schedule for an aquifer restoration plan. The aquifer restoration plan consists of the use of wells for both cleaning up pollutants from the aquifer as well as stopping the flow of the contaminant plume to spread out.
A case study was developed in the Rocky Mountain Arsenal, which is a military facility design to manufacture and process toxic chemicals. This aquifer is located near Denver, Colorado. The study area was chosen due the high quantity of hydrological and geological data available.
The groundwater management plan for pollutant removal basically is consisted of wells for pollutant removal (those wells have to be located inside the pollutant plume) and hydraulic gradient control wells (which have to be located outside the plume area) that are used to control the flow of the groundwater (pumping on high elevations or recharging in low elevations). An optimization model is used to find the best operation plan for this purpose. Note that a pump can be inside the plume at the beginning of the operation, but after some clean up, become outside of the plume and could them be used for hydraulic gradient control.
The equations used to model this process were the finite difference model developed by Trescott et al. (1976) for the ground water movement and the solute transport combined with groundwater flow simulation in the computer code developed by Konikow and Bredehoeft (1978) for pollutant transport. The methodology is dived in two main stages. First the velocity field is assumed based on initial data. Within this stage the plume boundary is estimated. With this information the Contamination distribution is approximated. On Stage 2, the optimization for the best well selection and operation is developed. Based on the known velocity field the solution is checked and some interactive process back in Stage 1 can be developed.
For the optimization model, the objective is to minimize the sum of pumping and recharge rates. One constrain is to guarantee the flow to go inwards in the direction of the center of the plume. For this gradient control constraint detailed information is provided.
The results showed that a best selection of wells and operation schedule could be achieved. The two stage procedure allowed a single global optimization for all 32 pumping periods. A verification of the results is provided by running the model with the chosen conditions.

3) Discussion
I think this paper is very interesting and shows the utility of optimization procedures solving water resources problems. It seems to me that optimizations procedures are intrinsically related to modeling practices in the modern time. The application of models that represent a reality is followed by an optimization procedure that allows the decision makers to choose from a set of alternatives the one that best fits the desiring goals.
Still this paper is a little too advanced for me, as some of the constrains and the matrix operation were not very clear to me. But the good part is I can feel is getting much more easy to understand them and I hoping by the end of the semester we will be pretty close to develop applications such as this one.