7 Closing

Understanding basic microbiology and chemistry supports the work of groundwater professionals because the interaction of microorganisms and chemical compounds in groundwater flow systems can be used to modify subsurface conditions. Such modification can mitigate contamination in groundwater systems, enhance or decrease the transmissibility of groundwater, and strengthen or weaken the subsurface structure. Relying on microbial activity for these modifications is generally a cost-effective engineering approach to managing the subsurface. The simplest, least expensive option, is to allow natural processes to accomplish the work, but when those processes progress slower than is acceptable for the problem at hand, the natural pace and type of microbial activity can be increased by adding nutrients or additional microbial species along with the nutrients. Research with the aim of improving microbiologic solutions to groundwater problems continues through efforts to genetically engineer microorganisms with improved catabolic activity (Janssen and Stucki, 2020).