Using Combined Remedial Design Saves Money, Improves Outcomes

Contaminated sites, particularly those impacted with dense, non-aqueous phase liquids (DNAPLs), pose significant challenges due to these contaminants’ persistence, distribution, and migration in soil and groundwater, making a one-size-fits-all solution nearly impossible to come by. This is why our approach at these types of sites is to rely on the full range of cutting edge, innovative site investigation tools and remediation technologies available, allowing us to streamline schedules, reduce costs, and improve a program’s effectiveness for our clients.

There are many types of remediation technologies to choose from today, and each has their own strengths and weaknesses as well as ranges of applicability, depending on site-specific characteristics. A common DNAPL remedy paradigm is to deploy a single technology and expect that technology to carry a site to remedy completion. A more powerful approach, however, is to combine multiple technologies in both time and space to provide more holistic, protective, rapid, and cost-effective site remedies. This requires a deep understanding of how to evaluate site characteristics, how to design and integrate technologies, and how those technologies’ design and implementation are affected by each other and evolving site conditions as a remedy progresses. Our experts put that understanding to good use to deploy an integrated DNAPL site remedy that addressed one of our client’s needs where other firms and isolated remedies had been ineffective for years.

Understanding the site to create a better solution

A project of ours that took place at a former manufacturing facility in New Jersey is a great example of how our team approaches DNAPL remedy integration. The site was used for light industrial manufacturing from the 1940s through the early 1980s, which resulted in DNAPL contamination. We were brought on board after our client came into ownership of the site, which other firms had been working on for nearly three decades without success in completing a full delineation or developing a meaningful solution.

Our solution began with an in-situ thermal remedy for the onsite DNAPL source area to destroy the onsite DNAPL source very quickly; however, we recognized that contaminants underlying the directly adjacent, downgradient property may continue to support a dissolved VOC plume if not also addressed. It was therefore important to incorporate a remedy for the adjacent property, which in this case consisted of injecting a reagent that combines bioremediation (with a solid organic carbon substrate) and chemical reduction (with zero-valent iron) degradation processes. The reagent is injected to create two treatment barrier zones, which will destroy contaminants as groundwater passes through each zone.

Integrated approach effectively addresses decades-long issue

This approach takes advantage of elevated groundwater temperatures from the source area thermal remedy to enhance natural biodegradation processes already occurring at the adjacent property. It was also easily constructed in accessible areas at the site, is expected to last 5-10 years with a single injection event, and combines multiple synergistic degradation processes. The natural microbial activity is increased by the presence of a fermentable organic carbon substrate and is further enhanced by more strongly reducing conditions and dissolved hydrogen produced by the zero-valent iron. The zero-valent iron also directly destroys the contaminants via abiotic reactions. This remedy is complemented by a carefully designed monitoring and contingency plan to ensure the groundwater remedies operate successfully.

These projects do tend to be complex and vary widely from one another, which means developing a customized solution is often the only way to see real results without breaking the bank. Our team of geologists, chemists, engineers, and hydrologists consistently achieve the best outcomes for owners of contaminated sites by relying on thorough investigation techniques and making the effort to think “outside the box” to develop innovative, effective integrated solutions to the unique challenges every DNAPL site presents.


Dan Bryant Director of Practices Environmental Remediation

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