Chloride is also often used to determine if groundwater samples are from the same groundwater flow system. In developing multiple lines of evidence for intrinsic biodegradation processes, biological monitoring data can provide strong evidence for microbiological activity. Biological monitoring can also provide more direct evidence for natural attenuation as opposed to chemical indicators of biological activity. There are several means of determining general or total populations of bacteria at a site. These assays will also provide evidence for microbial activity, and can indicate zones of microbial inhibition.
Direct Counts use microscopy to more accurately determine total bacteria in a sample.
These groups will have different biodegradative activities and rates and are active in the absence of oxygen. Assays Direct evidence for populations of contaminant-degrading bacteria can be obtained with specialized enumeration assays. More advanced genetic and biochemical methods, such as PCR, fatty acid analyses, and genetic probes , have also been developed for characterizing bacteria capable of specific contaminant degradation activities. In cases such as these, the EPA recommends laboratory microcosm studies in order to demonstrate site specific biodegradation activity. These microcosm studies are usually performed on a research basis, and are developed using the information gained from initial monitoring events.