Environ. Sci. Technol. 1993, 27, 986-986
SIR: We thank D. G. Jewett and colleagues for their comments and extension of the statistical analysis of our data. Our strategy was to use an experimental approach developed for filtration work with nonmicrobial particles (e.g., latex beads, clays, and mineral oxide suspensions) and apply it to microbial particles to test the applicability of filtration theory. The extended statistical treatment presented by D. G. Jewett et al. helps to reinforce that experimental measurements with microbial particles typically have higher inherent uncertainty compared to measurements with nonbiological particles. It is clear that future investigations should use experimental systems better adapted to testing the filtration model. If the model is applicable, then longer columns and smaller media would indeed improve the demonstration of effects due to solution conditions, despite the inherent variability of viable counts. This is especially important when the value of a is much less than 1.0. Our conclusion that the filtration model appears to be predictive of bacterial transport in porous media was mainly based on the agreement between experiment and theory obtained for the high-salt case (0.19 I a I0.86). For this case, the measured breakthrough response overlaps with the new larger confidence interval put forth by D. G. Jewett et al. The suggested conclusions
of our paper do not change. The results are encouraging with regard to the basic approach, but they are not conclusive. We reiterate our recommendation for further experimental work to develop reliable measures of the filtration parameters and to validate the filtration model used in this work.
BE6 Envlron. Sci. Technoi., Vol. 27, No. 5, 1993
0013-936X/93/0927-0986$04.00/0
Robert E. Martin Lyonnaise des Eaux Dumez 72 Avenue de la Libert6 92022 Nanterre, France Edward J. Bouwer' Department of Geography and Environmental Engineering The Johns Hopkins University Baltimore, Maryland 2 1218 Linda M. Hanna BCM Engineers One Plymouth Meeting Plymouth Meeting, Pennsylvania 19462
0 1993 American Chemical Society
