Monitored Natural Attenuation in Qualitative Geochemical Assessments

Jake Gossen Presents at ESAA WaterTech

Monitored Natural Attenuation (MNA) has become a proven and viable approach to treat dissolved metals contamination at former industrial facilities. Following Hemmera’s recent development of a conceptual site model for metal release and attenuation, analytical results from sentinel wells indicate attenuation mechanisms are functioning and this model is consistent with field observations, offering significant time and cost savings during site closures. Thanks to MNA, multi-million-dollar remedial programs have been reduced to budgets in the order of $50,000.

At one confidential site where Hemmera’s geochemical assessment teams recently applied MNA, a dissolved-phase plume comprising several different metals was situated adjacent to a tidally influenced river, where water quality periodically fluctuates between fresh and saline conditions. A large industrial complex is located at this site, which was historically used for steel processing and manufacturing. Site investigations identified dissolved metal plumes (Al, B, Cd, Cu, Ni, Zn) related to a metal cleaning process utilizing sequential sulphuric acid, zinc phosphate, and borax dip baths. Analytical results indicated groundwater metal concentrations at the site were greater than federal and provincial guidelines and standards for freshwater and marine aquatic life.

Hemmera proposed a risk-based approach to achieve site closure. Following a review of historical analytical results, a fate and transport assessment was conducted involving a geochemical desktop study of the behaviour and mobility of the metals identified in groundwater at the site. Groundwater concentration contour figures indicated that the extent of cadmium, copper, nickel, and zinc coincided with the extent of the dissolved aluminum plume. Field parameters collected during groundwater sampling also indicated a zone of low pH that coincided with the dissolved aluminum plume, which appeared to originate at the metal cleaning baths. In addition, the floor below the metal cleaning baths was cracked, and sulphuric acid had infiltrated into groundwater, reducing the pH considerably (~7 to less than 4); gibbsite had dissolved and an aluminum plume had formed. Gibbsite is an adsorbent and its dissolution released the adsorbed divalent cations into the solution (cadmium, copper, and nickel).

Advection, dispersion, and rainwater infiltration subsequently diluted the groundwater and pH began to rebound back to neutral conditions. In addition, tidal fluctuations in river elevation periodically recharged the river bank at the site, creating a physical and geochemical barrier for further down-gradient migration of dissolved metals. Hemmera’s successful implementation of an MNA solution addressed site contamination issues at a fraction of the cost of conventional site remediation practices.


For more information about this project, contact Jake Gossen (jgossen@hemmera.com), an engineering hydrogeologist at Hemmera. This story was developed from a presentation for the 2015 ESAA Watertech Conference that took place on April 20 to 22 in Kananaskis, Alberta.

Hemmera Contributes to the Success of Inaugural BCEIA BEST Conference

The British Columbia Environment Industry Association (BCEIA) hosted their inaugural Bettering Environmental Stewardship and Technology (BEST) Conference in Whistler, May 29-30, 2014. More than 180 delegates attended sessions and panel discussions on topics that ranged from trends in remediation and Brownfields renewal, to fostering First Nations relationships and recent changes in environmental assessment policy, regulations, and practices.

Hemmera has a strong presence in BCEIA – two senior Hemmera staff members sit on the BCEIA Board of Directors for 2014-2015. Jason Wilkins, Director of Land Development, and Anju Wicke, Business Leader for BC/Yukon, were also members of the BEST Organizing Committee. In addition, Jason moderated various sessions, including one that focused on Brownfields, and other Hemmera experts gave presentations during the conference.

On the first day of the conference, Business Leader Mike Choi led off the Trends in Remediation stream with his presentation on Site Groundwater Management Strategies: Groundwater Remediation Using Permeable Reactive Barriers. Permeable reactive barriers (PRBs) are developed according to a site’s unique characteristics to treat a diverse range of inorganic and organic contaminants, and are a successful tool for remediating groundwater contamination. Utilizing natural biological and chemical treatment approaches, PRBs intercept and passively treat dissolved contaminant plumes, thereby reducing risks to downstream receiving environments and receptors. Mike’s presentation explored potential design and installation strategies for PRBs, and provided information on their remediation performance.

In addition to this professional presentations, Hemmera was a proud sponsor of the event, and was honoured to play a part in BCEIA BEST 2014.

For more information on any of the topics discussed above, please contact our experts: