A Device for In Situ Determination of Geochemical Transport Parameters 1. Retardation

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Abstract
The retardation factor for dissolved chemicals in ground water is an important parameter in predicting the rate of migration of contaminants and in the design of remediation schemes for contaminated aquifers. Conventional methods for evaluating retardation factors include laboratory batch and column tests, and in the case of nonpolar organic contaminants, correlations with the organic carbon content of the aquifer material. In these procedures it is difficult to insure the geochemical integrity of the sediment material and the solutions used in the tests, leading to uncertainties concerning the applicability of the results. Alternatively, large‐scale tracer tests can be conducted; however, because of the time and cost requirements, these procedures have generally been limited to research applications. This paper describes an in situ column procedure for measuring retardation factors. The column is installed in advance of the cutting head of hollow‐stem augers, minimizing geochemical disturbance of the sediment, and the sediment within the column is exposed only to natural ground water from the immediate vicinity of the test device. By maintaining geochemical integrity, the method has considerable advantages over laboratory procedures, while being substantially less costly than conventional field tracer tests. Two tests are described in which retardation factors for strontium and for five halogenated organic compounds, obtained using the in situ device, were found to be in good agreement with results obtained by conventional methods.

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