Plume Mapping Requires Consideration of Unique Groundwater Conditions and Chemical Properties

Mercer, James

Plume Mapping Requires Consideration of Unique Groundwater Conditions and Chemical Properties

Thursday, November 7, 2013: 1:45 p.m.

James Mercer , Tetra Tech GEO, Sterling, VA

Complex site hydrogeology results in variations in chemical distributions at hazardous waste sites. Different permeable units have different unique plumes due, in part, to different flow directions and properties. Plumes in these different hydrologic units should not be aggregated. Different chemical properties prevent uniform distribution of chemicals. The transport properties of chemicals such as sorption and degradation determine how rapidly and how far each individual chemical will migrate. Different chemical release locations and dates further contribute to unique chemical migration extent and distribution. Consequently, combining multiple chemicals with different properties and distributions a priori is technically inappropriate. Combining multiple measurements of different chemicals over an extended time period (1) prevents interpretation of individual chemical plumes, (2) can result in connecting outlier data points that would otherwise be excluded, (3) combines data of different quality, and (4) does not consider active or passive remediation that will have an effect on older data, often lowering concentrations. The selected contouring method also has an impact on the shape and size of plumes. Further, selection of the numerical value of the outer contour will determine the size of plumes and may incorporate uncertain data.

James Mercer, Tetra Tech GEO, Sterling, VA

James Mercer is a hydrogeologist with Tetra Tech Inc. He received a B.S. from Florida State University and an M.S. and Ph.D. from the University of Illinois; all of his degrees are in geology. He spent eight years with the U.S. Geological Survey in the Northeastern Research Group working on contaminant and heat transport issues, including multiphase flow. He co-founded GeoTrans (now part of Tetra Tech) in 1979, and in 1980 began working on hazardous waste issues at Love Canal. In 1985, Mercer received the Wesley W. Horner Award of the American Society of Civil Engineers for the work performed at Love Canal. He continued to work on contamination issues and co-authored the book DNAPL Site Evaluation in 1993. In 1994, he received the American Institutes of Hydrology’s Theis Award for contributions to groundwater hydrology. Mercer has served on the National Research Council’s Water Science and Technology Board and was a member of the U.S. EPA Science Advisory Board. He is currently on the Scientific Advisory Board of SERDP.