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The bacterial flora of three unpolluted saline aquifers were examined. Aerobic, anaerobic, and facultative microorganisms were isolated and classified to genus. The organisms isolated were those commonly found in surface water and soil. Methanogenic bacteria were present in all aquifers.

A pressure chamber for determining the effect of increased hydrostatic pressure on growth and metabolic activities of groundwater bacteria is described. The chamber was used to show that moderate increases in pressure (to about 100 atmospheres) result in increased growth of mixed cultures of industrial-injectionwell bacteria and in the more complete degradation of formate and nitrate by these bacteria, as compared with identical cultures at atmospheric pressure.

A model system was developed for the purpose of studying the biological compatibility of aqueous industrial waste and subterranean disposal zones for injected waste. The model design incorporated devices for; anaerobic, aseptic compositing of effluent samples; collection of gases generated in the model elements; isolation of model elements against downstream contamination; and imposition of a normally‐distributed waste concentration profile in the feed stream. The finished model was, with the exception of operating pressure, physically and chemically similar to an existing waste disposal aquifer, and waste degradation and population growth data obtained on the model correlated with observations of the same parameters made in the real aquifer.