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Biologic activity can clog waste injection wells and produce gas in aquifers. Beneficial effects such as solubilization of particulate matter are also possible.
Some organisms, particularly Protozoa, fungi, and bacteria of the biotic kingdom Protista, thrive under extreme conditions. Therefore, the potential for problems of biologic origin must be evaluated carefully in every situation. Exclusion of biota is to be expected only under the most hostile conditions.
Versatility in adaptation to unusual environments and size limitations imposed by typical aquifer materials suggest that Protista will be the predominant biota in the waste injection regime. The composition, size, and activity of a protistan population depends upon many factors. These include temperature, pH, salt content, concentration and types of nutrients and micronutrients available, oxygen concentration, and aquifer lithology among other things. All chemical elements necessary for cell building such as carbon, nitrogen, phosphorous, sulfur, and numerous trace elements must be present.
Past experience with artificial recharge wells suggests that public-health jeopardy by microorganisms introduced by injection of certain types of waste is not great. Bacterial travel in confined aquifers is negligible and survival time is short. Exceptions may exist in highly permeable strata.
Microbial growth supported by nutrients in the injectant occurs near the well screen. Addition of disinfectants to control microbial growth may be useful but certain biocides may become nutrients under some circumstances. The biocide may be ineffective in the waste injection regime. Slime control measures must be carefully selected.
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