Although it is the focus of decades of environmental cleanup, petroleum hydrocarbons (PHC) remain a significant focus of remediation efforts across the globe. PHC sites span a full spectrum of size, scale and complexity, ranging from a corner gas station to a large refinery, marine terminal or abandoned former industrial site.
The wide assortment of sites using petroleum products over long histories has ensured that petroleum contaminated sites remain among the most prevalent type of contaminated sites worldwide. The Canadian Federal Contaminated Site Inventory (FCSI) lists over 6,000 suspected or active sites contaminated with PHCs. It is estimated that there are more than 250,000 brownfield sites in the US, with PHCs as the primary focus of cleanup.
Conventional remedies may no longer be the most effective approach
For many years, petroleum-contaminated site management has primarily leveraged (and required) excavation and/or the implementation of active engineered remedies that are both power and resource intensive. With the evolving focus on sustainable solutions and the value of nature-based solutions, biological systems continue to gain momentum. This is partly due to their reduced environmental footprint. It is also due to their effectiveness in depleting residual contaminant mass that would be largely inaccessible by many of our historically go-to conventional options such as skimming, total fluids pumping and multi-phase extraction. Along with a limited potential benefit at many sites, these conventional options are often associated with significant environmental costs/footprints.
Our challenge today is to determine how we can balance our remedies to achieve the greatest result with the smallest environmental footprint.
Enhancing more sustainable and cost-effective outcomes
Natural source zone depletion (NSZD) is already a big part of this shift in perspective. It is a nature-based approach to petroleum hydrocarbon remediation facilitated by the growing recognition of the ubiquity and significance of natural microbial NAPL depletion processes. On its own, NSZD leads to more sustainable and cost-effective outcomes that are equally protective of human health and the environment at many low-risk petroleum NAPL sites. Enhanced NSZD (eNSZD) will increasingly be part of the conversation in the future, where reduced remedial timeframes and/or quicker transitions to nature-based solutions are required or desirable to return sites to beneficial use faster.
We are developing approaches allowing NSZD to be enhanced in a manner that will be low maintenance/self-sustaining while maintaining the reduced environmental footprint that makes NSZD a more sustainable remedial strategy. Raising subsurface temperatures by 10-15 degrees Celsius can double to triple biological activity, thereby increasing NSZD rates. Sustainably increasing oxygen to the subsurface can further enhance NSZD. We are exploring different approaches to eNSZD using both sustainable sources of heat and air/oxygen delivery to enhance what is happening naturally. We have several sites where we’re implementing these approaches and are excited to see how much NSZD degradation rates can be enhanced using simple sustainable techniques.
To learn more about how NSZD can positively impact the management of your petroleum-contaminated sites, please contact:
Stay connected to our expert insights
References
CRC CARE 2020, The role of natural source zone depletion in the management of light non-aqueous phase liquid (LNAPL) contaminated sites, CRC CARE Technical Report no. 46,
Kamath, R, Connor, JA, McHugh, TE, Nemir, A, Le, MP & Ryan, AJ 2011, ‘Use of longterm monitoring data to evaluate benzene, MTBE, and TBA plume behavior in groundwater at retail gasoline sites’, Journal of Environmental Engineering, vol. 138, no. 4, pp 458–469.
Mace, RE, Fisher, RS, Welch, DM & Parra, SP 1997, Extent, mass, and duration of hydrocarbon plumes from leaking petroleum storage tank sites in Texas, Bureau of Economic Geology, Geologic Circular 97-1, University of Texas at Austin, Austin, Texas, USA.
Newell, CJ & Connor, JA 1998, Characteristics of dissolved petroleum hydrocarbon plumes: Results from four studies, American Petroleum Institute Soil and Groundwater Bulletin, Washington DC, USA.
Rayner, JJ, Bekele, E, Donn, M, Bastow, T, Davis, GB, Woodbury, R, Furness, A & Geste, Y 2020, Australian case studies of light non-aqueous phase liquid (LNAPL) natural source zone depletion rates compared with conventional active recovery efforts, CRC CARE Technical Report no. 47, CRC for Contamination Assessment and Remediation of the Environment, Newcastle, Australia.