Contamination,risk, and heterogeneity: on the effectiveness of aquifer remediation |
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| Authors: | Reed M Maxwell Steven F Carle Andrew F B Tompson |
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| Institution: | (1) Atmospheric, Earth, and Energy Sciences Department, Lawrence Livermore National Laboratory, 7000 East Ave. L-208, Livermore, CA 94550, USA |
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| Abstract: | The effectiveness of aquifer remediation is typically expressed in terms of a reduction in contaminant concentrations relative
to a regulated maximum contaminant level (MCL), and is usually confirmed by sparse monitoring data and/or simple model calculations.
Here, the effectiveness of remediation is re-examined from a more thorough risk-based perspective that goes beyond the traditional
MCL concept. A methodology is employed to evaluate the health risk to individuals exposed to contaminated household water
that is produced from groundwater. This approach explicitly accounts for differences in risk arising from variability in individual
physiology and water use, the uncertainty in estimating chemical carcinogenesis for different individuals, and the uncertainties
and variability in contaminant concentrations within groundwater as affected by transport through heterogeneous geologic media.
A hypothetical contamination scenario is developed as a case study in a saturated, alluvial aquifer underlying an actual Superfund
site. A baseline (unremediated) human exposure and health risk scenario, as induced by contaminated groundwater pumped from
this site, is predicted and compared with a similar estimate based upon pump-and-treat exposure intervention. The predicted
reduction in risk in the remediation scenario is not an equitable one—that is, it is not uniform to all individuals within
a population and varies according to the level of uncertainty in prediction. The importance of understanding the detailed
hydrogeologic connections that are established in the heterogeneous geologic regime between the contaminated source, municipal
receptors, and remediation wells, and its relationship to this uncertainty is demonstrated. Using two alternative pumping
rates, we develop cost-benefit curves based upon reduced exposure and risk to different individuals within the population,
under the presence of uncertainty. |
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