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The single-well, push-pull test has been used in previous field studies to measure in situ zero- and first-order rates for aerobic and anaerobic microbial respiration in the saturated zone. In this paper we demonstrate that the test can also be used to obtain more generalized descriptions of the kinetics of microbially mediated enzymatic reactions. Laboratory and field tests were performed with the model enzyme substrate p-nitrophenyl-β-D-glucopyranoside (PNG). During a push-pull test, injected PNG is hydrolyzed in situ to p-nitrophenol (PNP); the rate of PNP production is taken as a measure of the β-glucosidase activity expressed by indigenous microorganisms. Laboratory tests were performed in physical aquifer models packed with natural aquifer sediment; field tests were performed in a shallow unconfined alluvial aquifer at a petroleum contaminated site. The laboratory and field tests demonstrate that it is possible to compute the in situ rate of PNP production as a function of PNG concentration u sing only data from a single push-pull test. These data can then be used to estimate the Michaelis-Menton kinetic parameters [V.sub.max] and [K.sub.m] for the hydrolysis reaction. This approach potentially extends the range of applicability of the push-pull test approach for use in determining kinetic parameters for a wide range of microbial processes in situ. These could include the broad class of substituted nitrophenyl substrates used to assay other enzyme systems, as well as microbially mediated redox reactions that occur during contaminant transformations., J.D. Istok (l,4) J.A. Field (2) M.H. Schroth (3) Introduction Quantitative information on subsurface microbial metabolic activity is needed: (1) to improve our understanding of flows of energy, carbon, and [...]

Introduction The single-well, 'push-pull' test method (Istok et al. 1997) is useful for obtaining quantitative information on a wide variety of aquifer physical, chemical, and microbiological characteristics in situ. The [...]

J.D. Istok [a] J.A. Field [b] M.H. Schroth [a] T.E. Sawyer [b] M.D. Humphrey [a] Abstract Sorption to aquifer sediments can limit the effectiveness of surfactants injected to solubilize residual [...]

J.A. Field [a] J.D. Istok [b] M.H. Schroth [b] T.E. Sawyer [a] M.D. Humphrey [b] Abstract The objective of this study was to evaluate the ability of the single-well, 'push-pull' [...]

Introduction Quantitative information on subsurface microbial metabolic activities is needed (1) to improve our understanding of microbiological processes in pristine and contaminated environments; (2) to predict rates of natural microbial [...]

Provides a simplified method of `push-pull' test data analysis to determine in situ reaction rate coefficients in aquifers. Use of a numerical flow and transport code; Method for estimating microbiological process reaction rate coefficients; Derivation of a semi-analytical solution; Application of a sensitivity analysis.