Stable Isotope Probing (SIP) to Assess the Feasibility of Monitored Natural Attenuation (MNA)
The study site was a former retail gasoline station with dissolved benzene concentrations exceeding risk based closure levels. Historical groundwater monitoring generally indicated a stable or decreasing benzene concentrations. Monitored natural attenuation (MNA) can be an effective remediation strategy at sites impacted by petroleum hydrocarbons but is sometimes viewed as a “do nothing” solution in which decreases in contaminant concentrations result from physical processes (e.g. dilution) rather than biodegradation. Ultimately, acceptance of MNA as a remediation strategy rested upon demonstrating contaminant biodegradation under existing site conditions.
- Is benzene biodegradation occurring under existing site conditions?
- Is MNA feasible?
Stable Isotope Probing Study
A stable isotope probing (SIP) was conducted to conclusively determine whether benzene biodegradation was occurring at the site. Briefly, Bio-Traps® amended with 13C labeled benzene were deployed in select monitoring wells within the BTEX plume for 45 days. Following field deployment, the Bio-Traps® were recovered and two methods were used to conclusively demonstrate biodegradation of the contaminant of concern:
- Quantification of 13C enriched phospholipid fatty acids (PLFA) which indicates contaminant incorporation into microbial biomass.
- Quantification of 13C enriched dissolved inorganic carbon (DIC) which indicates contaminant mineralization.