2013م - 1444هـ
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This book has described and hopefully demonstrated that the single-well, push-pull

test, in all its various manifestations, is a useful tool for site characterization, pilot

testing of various remediation strategies, and so on. The advantages of in situ

testing are clear, and the push-pull format makes it possible to perform field

experiments at relevant scales for a modest cost and with no more logistical

complexity than a laboratory experiment. Often in the biogeochemical sciences,

we think of research as a linear process from small-scale laboratory development to

ultimate (usually at a date a long way off) full-scale field application. However,

using the push-pull test it is possible to conduct field experiments in parallel with

laboratory experiments and this should lead to better synergy between the two.

Simple field experiments have the remarkable ability to sharpen experimental

design by identifying the most important parameters to control in laboratory

experiments and to quickly select the most promising small-scale procedures and

techniques to further develop in the laboratory. Nevertheless, much developmental

work on the push-pull test format remains to be done. Additional numerical and

analytical methods for interpreting push-pull test breakthrough curves for the ever

more complicated biogeochemical systems being studied are needed. The design of

push-pull tests can be refined to incorporate valuable auxiliary data such as isotopic

composition of test solutions, microbial community dynamics, surface chemistry

reactions, and so on. To date, only a limited number of push-pull tests have been

conducted (using gas phase tracers) in the vadose zone and these have focused on a

single microbial process (methane oxidation). Most push-pull tests have been

conducted in the near surface (<100 m deep), but the test is potentially most

valuable in deep subsurface environments where the costs of drilling for sample

collection are very high. Thus, push-pull tests in deep boreholes on land and

beneath the seafloor hold great potential in elucidating important biogeochemical

processes in those environments. Combining push-pull tests with various geophysical imaging techniques also holds great promise because of the ability to modify

the subsurface environment (e.g., by injecting electrolytes that can be detected by

electrical conductivity arrays) in defined ways and thus identify preferential flow

paths, reactive surface areas, etc.