Artificial groundwater recharge, by any method, is subject to limitations caused by some mechanism degrading the hydraulic conductivity of the porous media through which the recharge water is being infiltered or injected. Reduction of hydraulic conductivity may be caused by suspended solids, bacterial growth, chemical reactions of dissolved solids with the porous media or

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existing native water, and air entrainment or dissolution of gases in interstices of the porous medium.

A comprehensive study of factors affecting artificial groundwater recharge should include laboratory determinations of the relation of the various causes of hydraulic-conductivity reduction. Problems pertaining to the effect of water quality in relation to the lithologic environment of a recharge system also should be studied in the laboratory.

A laboratory facility has been designed and equipped to provide means of testing flow through porous media columns. Any quality of recharge water from distilled water to activated sludge, can be constituted in quantities providing for indefinite term tests. Flow can be through repacked or field cores under constant flow or constant pressure.

A flow-test data acquisition and computation system provides punched tape data storage and real time computation and plotting of intrinsic permeability changes with column depth and time.

Water quality data are taken during the test, and characteristics of the porous media and suspended solids are determined. Accumulation of material in porous media interstices is visually observed with scanning electron microscopy.

The data are analyzed to relate the physical, biologic, and chemical effects in the porous media flow system with the objective of obtaining data that can be transferred to field situations and thus develop more economical artificial-recharge systems.

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