How does SIP work?

In many ways, an SIP study is analogous to a tracer test to track the environmental fate of a “labeled” contaminant and conclusively demonstrate biodegradation as the treatment mechanism. For an SIP study, Bio-Traps are “baited” with a specially synthesized form of the contaminant containing “heavy” carbon (13C) as the label. Since 13C is rare, carbon originating from labeled contaminant can be readily distinguished from carbon (predominantly 12C) from other sources. When the baited Bio-Trap is deployed in a monitoring well, the 13C labeled contaminant is subject to the same physical, chemical, and microbiological processes as the unlabeled contaminant present at the site. For many contaminants of concern (e.g. benzene, MTBE, and others), biodegradation is a process whereby microorganisms use the contaminant as a carbon and energy source (food) producing new cells (biomass) and CO2. Thus, if biodegradation is occurring, the 13C label from the synthesized contaminant in the Bio-Trap will be incorporated into microbial biomass and dissolved inorganic carbon (CO2).

Following deployment, the Bio-Trap is recovered and two methods are used to conclusively demonstrate biodegradation of the contaminant: phospholipid fatty acids (PLFA) and dissolved inorganic carbon (DIC). PLFA are a main component of the membranes of all microbes, therefore, detection and enrichment of 13C in the PLFA unambiguously shows incorporation of the contaminant into biomass. Likewise, enrichment of 13C labeled DIC conclusively demonstrates contaminant mineralization.