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A Tracer Test for Detecting Cross Contamination Along a Monitoring Well Column |
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| Authors: | David Meiri |
| Institution: | David Meiri is a principal hydrogeologist at EBASCO Services Inc. (111 North Canal St., Ste. 915, Chicago, IL 60606-7204.) He is a certified ground water professional Prior to joining EBASCO in 1988, he was with Woodward-Clyde Consultants, Chicago, as a senior project engineer. He received his B.Sc. in mechanical engineering from Ben-Gurion University, Israel in 1974, and his M.Sc. in mechanics and a doctorate in civil engineering from the University of Wisconsin in 1976 and 1979, respectively. His prime interests are ground water flow and contaminant transport analysis, aquifer restoration, ground water modeling, and field aquifer testing. |
| Abstract: | A tracer test was used to evaluate whether cross contamination exists along a monitoring well completed through a shallow ground water system in fractured clay and screened in a sand and gravel aquifer. The fractured clay is separated from the sand and gravel deposit by a layer of highly plastic unfractured clay. A natural vertical downward hydraulic gradient of approximately 0.5 exists between the shallow system and the sand and gravel aquifer. Ground water contamination was detected in an adjacent monitoring well screened in the fractured clay and in the monitoring well screened in the sand and gravel deposit. No ground water contamination was apparent in an intermediate well screened in the unfractured clay layer. A tracer of sodium bromide was injected into a shallow boring near the monitoring wells. The tracer was detected in the monitoring well in the sand and gravel aquifer after three to seven days. The bromide concentration continued to increase in this well with time while the concentration in the shallow boring declined. This trend of tracer concentration indicates the tracer has in fact migrated downward and possibly traveled along the well column. |
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