Biodegradation of Petroleum Hydrocarbons: What Should be Monitored? by Bart Simmons In October, 1995, a team from the Lawrence Livermore National Laboratory (LLNL) and the University of California reported to the State Water Resources Control Board (SWRCB) on recommendations for changes to California’s Leaking Underground Fuel Tank (LUFT) Program. The report included a recommendation to utilize bioremediation whenever feasible for the remediation of LUFT sites. The Air Force Center for Environmental Excellence (AFCEE) has developed a protocol1 for the bioremediation of petroleum contamination which includes the water measurements listed in Table 1. The AFCEE guidance includes similar lists for soil and soil-gas. It includes some standard measurements; some which would require modification of standard procedures, e.g., including trimethylbenzene isomers with BTEX analysis; plus some non-standard measurements, e.g., ethane and ethene in groundwater. Clearly, if something like the AFCEE protocol were implemented, there would be a need for some additional standardization of sampling and analytical methods. The AFCEE protocol basically includes measurement of contaminants, electron acceptors (oxygen, nitrate, and sulfate), and metabolic products (ethane, ethene, carbon dioxide, and sulfide). Table 1 AFCEE Protocol for Water Measurements at Petroleum Contaminated Sites Being Bioremediated Aromatic hydrocarbons (BTEX, trimethyl benzene isomers) Total hydrocarbons, volatile and extractable Polycyclic aromatic hydrocarbons (PAHs) (optional) Total fuel carbon (optional) Dissolved organic carbon (optional) Dissolved oxygen Oxidation -reduction potential Nitrate Sulfate Ferrous iron Dissolved sulfide Ethane, ethene Carbon dioxide pH Conductivity Alkalinity Chloride AFCEE Analytical Protocols for Ground Water1 LUFT monitoring may require tests in addition to the AFCEE protocol. For example, as discussed in the last column, MTBE is now required for monitoring at LUFT investigations in some regions of California, and may serve as a conservative tracer of contamination during bioremediation monitoring. An unresolved question is whether bioremediation monitoring should include monitoring for additional metabolites. For example, benzylsuccinic acid, benzylfumaric acid and related compounds have been proposed for monitoring anaerobic bioremediation.2 These compounds are not measured by traditional methods. LLNL/UC and the Department of Defense (DoD) are planning a Petroleum Hydrocarbon Cleanup Demonstration Program, which would demonstrate a tiered risk-based corrective action process based on the American Society for Testing and Materials (ASTM) risk-based corrective action (RBCA) framework. This RBCA framework would also support a risk management strategy which depends heavily on passive microbial degradation of petroleum hydrocarbons. Meanwhile, the SWRCB SB1764 Advisory Committee has also addressed the issue of biodegradation of petroleum hydrocarbons. They found that current sampling and analysis is inadequate to assess the potential for intrinsic bioremediation. They recognized the AFCEE protocol, and also recognized the utility of biochemical markers such as benzoic acid or succinic acid derivatives. The proposed LLNL/UC/DoD Demonstration Program would help to translate the preference for bioremediation and risk-based cleanup into practical protocols. A future column will address the risk-based corrective action process and the question of what risk-based measurements should be. 1 Technical Protocol for Implementing the Intrinsic Remediation with Long-Term Monitoring Option for Natural Attenuation of Dissolved-Phase Fuel Contamination in Ground Water, AFCEE, Brooks Air Force Base, Draft, 1994. 2 Beller, HR, W-H Ding and M Reinhard, Byproducts of Anaerobic Alkylbenzene Metabolism Useful as Indicators of in Situ Bioremediation, Environ. Sci. Technol., 1995, 29, 2864-2870.