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ON-LINE TOOLS FOR PROPER VERTICAL POSITIONING OF VERTICAL SAMPLING INTERVALS DURING SITE ASSESSMENT
Citation:
WEAVER, J. W. AND V. GOROKHOVSKI. ON-LINE TOOLS FOR PROPER VERTICAL POSITIONING OF VERTICAL SAMPLING INTERVALS DURING SITE ASSESSMENT. Presented at 18th Annual National Tanks Conference, Memphis, TN, March 20 - 22, 2006.
Impact/Purpose:
To assist decision-making by improving approaches to subsurface contaminant transport modeling based on evaluation of field observations and subsequent development of appropriate modeling approaches and tools.
Description:
This presentation presents on-line tools for proper vertical positioning of vertical sampling intervals during site assessment. Proper vertical sample interval selection is critical for generate data on the vertical distribution of contamination. Without vertical delineation, there is the possibility of underestimating the length of a contaminant plume. Tools are needed to plan proper vertical sampling, because of the expense of characterization. EPA developed an on-line calculator to estimate plume diving that uses estimates of hydraulic conductivity and aquifer recharge to estimate the minimum depth to collect a meaningful sample. This calculator has provided a useful tool for improved site assessment and raised awareness of recharge-driven plume diving. The method is limited, however, by the need to estimate the recharge rate, a parameter that is difficult to estimate in practice. Consequently, the resulting plume diving calculation results might be too uncertain for practical use. To avoid this problem, modifications to the procedure have been developed. Here the model fits the solution to water levels to avoid the need to estimate recharge rates. Additional work to overcome limitations in the methodology involves numerical solution for sloping aquifer bottoms.