Environmental Tracers: An Underutilized Tool in Environmental Consulting?

I consider myself lucky to have come to environmental consulting through a couple of academic research detours; first at Columbia University in NYC then Southern Methodist University in Dallas. During my time at Columbia I worked with the Environmental Tracer Group within the Geochemistry department a Lamont Doherty Earth Observatory (LDEO).  This was a great preparation for environmental consulting as our work at LDEO was directly related to understanding many of the same environmental fate and transport problems that we deal with nearly every day.  Working in the environmental tracer group at LDEO provided an opportunity to use state of the art tools for quantifying many environmental processes. We explored atmospheric transport, unsaturated zone processes, groundwater recharge and flow rates and surface water mixing and gas exchange. So why is it that, during a decade of working on Superfund and remediation sites and on litigation matters, I do not see tracers used more widely?

While there are some technical and financial considerations, a big part of the reason may be that these tools just aren’t that well known in the consulting community.  It may simply be that the “bang for the buck” or overall benefit of these methods is not clearly understood. So in my next blog posts on BSTI’s website, I’m planning to provide an overview of some environmental tracers and their uses:

Deliberate Tracers in Groundwater: Injection of tracers to track movement in fast moving groundwater systems.

  • Evaluating flow patterns in karst or other complex environments where travel times are short.
  • Injection of a tracer at an up gradient location during a pump test to determine aquifer and fate and transport properties.
  • Tracers injected during pilot testing of in-site remedies to evaluate distribution of treatment.

Deliberate Tracers in Surface water: Release of tracers to measure flow, mixing and gas exchange in surface waters.

  • Measure flow and mixing, for example in rivers or estuaries with complex tidal flow.
  • When using gas tracers, the loss to the atmosphere over time allows for determination of gas exchange rates. This is important which is of interest because the rate at which oxygen enters determines the quantity of oxidizable compounds which can be discharged to a water body without resulting in low oxygen conditions harmful to aquatic life.
  • Measurement of interaction with groundwater.

Transient Tracers for Recent Groundwater:  Measures the date at which groundwater entered the aquifer to within a few years.

  • Measurement of low levels of manmade dissolved gases and some radionuclides, allows you to determine when groundwater was last in contact with the atmosphere, or groundwater age.
  • With measurements at several locations or depths, you can then directly measure groundwater flow and recharge rates.
  • Useful to calibrate groundwater models.

Stable Isotope Tracers: Differentiate the same chemicals from different sources based on isotope composition.

  • Evaluate the sources of water, for example rainwater will have a different ratio of oxygen and hydrogen isotopes than melted snow.
  • Differentiate merged plumes of same chemical, for example two difference sources of PCE may have different chlorine or carbon isotope ratios.
  • Likewise, the same metals released into the environment by two different processes may have different isotopic signatures allowing the origin to be distinguished.

What else peaks your interest? Tracers for quantifying groundwater/surface water interaction, sediment dating, unsaturated zone transport or bubble mediated gas exchange? The tools are out there and I’d love to hear about the applications that are of interest.

Nick Santella is BSTI’s Principal Geochemist. He may be reached for questions or comments at (nsantella@bstiweb.com) or by phone at 610-593-5500.

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What Might Site-Specific Soil Standards for PFOA Look Like?

 

The State of New Jersey recently adopted what is currently the lowest drinking water quality criteria (maximum contaminant level or MCL) in the country for perfluorooctanoic acid (PFOA) at 0.014 µg/l or 14 parts per trillion (ppt). This MCL is a health-based value developed by the New Jersey Drinking Water Quality Institute and is significantly lower than the 70 ppt health advisory level for PFOA put forward by EPA in 2016.  Developers of the NJ MCL considered both cancer and non-cancer toxicological effects (in studies looking at exposure of rats and mice) and came up with the same result from both effects.

In accordance with NJAC 7:9C-1.7, NJ MCLs become the groundwater quality standards. All aquifers are assumed to be used for drinking water unless specifically classified otherwise. This raises the question, with such low allowable levels in water/groundwater, what does this mean for cleanup of PFOA or other similar compounds in soils? New Jersey and many other states set soil to groundwater cleanup criteria for soils based on partitioning equations. Consequently, soluble/mobile compound cleanup levels in soil can be quite low. While criteria has not yet been adopted for PFOAs for site remediation, development of such a standard would be a necessary component of soil remediation. Using the partition equation and a conservative partition coefficient value of 115 l/kg, the generic soil remediation standard for PFOA in NJ would be 0.7 µg/kg (700 ppt). It’s easy to foresee the practical incompatibilities with soil cleanup levels in the part per trillion range. Even the much higher 5 ppb soil to groundwater cleanup levels for many mobile VOCs in NJ are difficult to achieve in many remediation scenarios.

If achieving generic cleanup standards is not practicable or comes with excessive costs, we can use one or more NJDEP-approved ways to develop site-specific soil to groundwater cleanup criteria. So the question of PFOA cleanup levels in soil make for an interesting test case to look at how site-specific conditions might (or might not) affect soil cleanup levels developed by different methods.

The simplest method is to use the same partitioning equations NJ uses to develop its criteria but with the addition of site-specific data, most importantly the total organic content (TOC) of the soils. TOC is the primary controller of partitioning of organic chemicals between the solid and liquid phase. If, for example, you increased TOC from the default 0.1% to 1%, typical of a topsoil, the soil to groundwater remediation standard for PFOA would increase by almost an order of magnitude of 3 µg/kg.

It’s also possible to directly measure partitioning in site soils using the Synthetic Precipitation Leaching Procedure (SPLP). This method is most often used with less mobile compounds, but even for mobile compounds, like chlorinated solvents, it can provide documentation of a site-specific standard an order of magnitude or so above generic levels; provided you can find soils in appropriate concentration ranges. Obviously, we can’t perform SPLP tests as part of a desktop exercise; however, it’s worth noting here since PFOA is typically present as an anion; other factors beyond organic carbon concentration can have some impact on partitioning. While some studies indicate that TOC is the dominant factor in partitioning, literature values for PFOA partition coefficient vary by several orders of magnitude. This suggests that performing SPLP testing may be a productive option to obtain site-specific information on partitioning behavior, which may demonstrate higher soil to groundwater cleanup criteria.

Lastly, there is guidance for developing alternate standards with modeling software. Modeling methods can incorporate the widest variety of site-specific considerations and so may produce the highest values for site-specific standards. In NJ, modelers can either use SESOIL on its own to estimate transport through the unsaturated zone and the resulting maximum aqueous concentration of a compound present in leachate, or modelers can use AT123D to model groundwater transport to define the area that will exceed groundwater criteria and how long it will take to achieve water quality standards.

Starting with SESOIL, let’s look at a simple scenario with a 0.1 mg/kg concentration of PFOA in surface soils. This could represent a variety of scenarios such as atmospheric deposition or application of bio solids containing PFOA. Simply using the partition equation, assuming a typical conservative 0.1% TOC would suggest an aqueous concentration of around 0.4 mg/l PFOA in the unsaturated zone. Using SESOIL in a site-specific scenario with 20 ft sandy soil column results in a lower maximum leachate concentration than indicated by the partition equation; around 0.1 mg/l as shown in green in the plot below. A loamy soil texture and 1% TOC at the top of the soil column slows down unsaturated zone transport even more, spreading leaching of PFOA out over the course of several years and brings the peak leachate concentration down further to about 0.05 mg/l (as shown in blue). This consideration would increase the allowable soil concentration and decrease remediation efforts.

 

Leachate Concentration PFOA

 

Once entering the saturated zone, there will be further dilution due to mixing which is dependent on the size of the source area and aquifer properties. Just as an example, let’s use AT123D to model groundwater transport for a 300 ft by 300 ft source area, a receptor 300 ft from the source and relatively high hydraulic conductivity and gradient. For the two scenarios presented above, dispersion dilutes the leachate concentrations down to around 0.02 mg/l in both cases. Groundwater concentrations are similar in both cases because contaminant mass flux remains the same in both scenarios and the mass loading is just spread out over a slightly longer time frame when unsaturated zone transport is slower.

 

Downgradient Groundwater Concentration PFOA
When the partition equation, or SESOIL alone, is used to derive soil to groundwater standards, dilution in the saturated zone is accounted for using a Dilution Attenuation Factor (DAF). In NJ, the accepted default DAF value is 20. For the scenarios above, the AT123D model predicts less dilution of the starting leachate values. So in this case where distance to a receptor is similar to the source size, the modeling performed with AT123D does not provide a higher soil to groundwater remediation standard; although it may serve other regulatory purposes.

So how can we know when site-specific modeling will result in soil to groundwater standards that are substantially higher than those provided by partition equations? If site TOC is unusually high, or SPLP analysis indicates a higher partition coefficient, higher cleanup levels may be justified. Likewise, distances to receptors (or in NJ the down gradient edge of a Classification Exception Area (CEA)), which are large in proportion to the source size, may experience greater than the 20x dilution provided by the DAF.

In summary, under some site conditions a more detailed analysis may move the decimal point to the right on the generic soil to groundwater cleanup standards that would be predicted for PFOA. If you are trying to protect groundwater quality close to a source area, as is most often the case in NJ, the soil to groundwater cleanup levels provided by partition equations are a pretty good place to start. And unfortunately, it’s likely that the soil to groundwater cleanup levels for PFOA really are going to be that low.

 

 


If you have any questions, please feel free to contact either Nick Santella (nsantella@bstiweb.com) or Tripp Fischer (tfischer@bstiweb.com).

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Help It or Hurt It: How are Environmental Matters Going to Affect Your Growth or Exit Strategy?

 

How can foresight and management of environmental matters be leveraged for better outcomes in business mergers, acquisitions and facility divestitures?

Gain useful insight in the slideshow below from our presentation at the Eastern Energy Expo:

 

If you have any questions, please feel free to contact either John Kollmeier of BSTI (610.593.5500 or jkollmeier@bstiweb.com) or Grant E. Nichols of JLT (720.501.2800 or Grant.Nichols@jltus.com).

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Who, What, When, Where & Why: Environmental Forensics

 

Questions regarding environmental forensics will come up at some level in almost every environmental project.

Cross Section Plume Map - Environmental Forensics
Site Conceptual Model – Cross Section of a Plume Map

This can range from drawing conclusions about a release from a UST system to sophisticated analysis of large environmental datasets collected specifically to identify contributions from multiple sources. The purpose of forensic interpretation is to tell a story. The story becomes most interesting when some or all responsibility shifts from one party to another. In many ways, this is a natural extension of developing a site conceptual model (SCM), and much of the data required for telling the story is collected as part of most primary environmental investigations. Do you need forensic data interpretation or interpretation of forensic data?

To get the most value for your dollars spent, it might be helpful to think of forensic techniques as a specialized way in which environmental data is evaluated rather than as a series of analytical techniques. Commonly collected data can have significant forensic implications, boring logs, slug tests, GC chromatograms and tentatively identified compounds (TICs) all have a story to tell. Prior to investing in the collection of dedicated forensic data, a good consultant will fully understand what answers you need and evaluate how close you are to those answers using data you already have. It may be, for example, that the data required to delineate and characterize the basic fate and transport of a chlorinated compound in groundwater, for regulatory purposes, is also sufficient to constrain the potential release date with the required precision. Or, the presence or absence of various gasoline oxygenates in a BTEX plume may be enough to identify the decade in which the release occurred.

 

 

A number of specialized analytical techniques can provide specific data useful for environmental forensics.

Chromatogram - Environmental Forensics
TPH Chromatogram

Only after reviewing existing data in light of the SCM can you start looking at the analytical techniques people usually associate with environmental forensics. The most basic may be petroleum fingerprinting, looking at the composition of LNAPL or petroleum in soil or water to identify the type of product present and degree of weathering. Like everything else in life, this can be done quick and inexpensive with moderate precision or slower and at greater cost for greater precision and defensibility. There are no foolproof analytical methods to date petroleum releases. However, the Christensen and Larsen (1993) method is often used to estimate the date of diesel/#2 fuel oil releases. This method is based on observed changes in the ratio of compounds over time due to biodegradation. While used with success in many cases, the further your site conditions are from those on which the method is based, the greater the caution should be exercised in interpreting results.

 

Moving beyond petroleum, a wide range of forensic techniques are available for different circumstances with an equally wider range in cost. With the right circumstances, specific tools like PCB congener analysis, stable isotope measurements, extended PAH analysis or sediment and groundwater age dating can provide key information to distinguish multiple sources or refine the understanding of contaminant fate and transport. As always, there is a tradeoff between the cost of sample collection and analysis and the need to document results with sufficient certainty to stand up to hostile scrutiny.

 

 

Leveraging existing data can ensure your environmental forensic efforts get you the answers you need.

You hope that you know (and like) what results you get from a forensic investigation. But even starting with a well-developed SCM, expect some surprises when the analysis and data evaluation are performed. The real life messiness of even the best environmental data is, on its own, a good reason to develop specific and realistic goals for a forensic evaluation before data collection. Developing those goals is easier when you are making the best use of the data you already have.

 

 

 

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Tales from Academia: Ryan Hupfer on the R/V Roger Revelle

ryan blog filled

Recently, I read about the christening of the R/V (Research Vessel) Neil Armstrong at the famous Woods Hole Oceanographic Institute (WHOI). In 2010, the U.S. Navy announced the construction of two new research vessels. After working with the scientific community to design the ship, the competition to operate the new vessel began. Later that year, the Navy awarded the job to WHOI. Outfitted with a modern array of oceanographic instruments, the ship is dedicated to studying climate change and the chemistry, physics and biology of our oceans.

 

This news made me reminisce of my own experiences in academia. Before working at BSTI, I attended graduate school at Rutgers University – New Brunswick, an R1 school where the oceanography and geology departments were closely knit. After establishing myself at Rutgers, I was fortunate to be in the right place at the right time when an opportunity to sail and sample ocean sediment arose.

 

RV Roger Revelle
The Research Vessel Roger Revelle

The R/V Roger Revelle planned to sail from Alotau, Papua New Guinea, to Manila, Philippines, making stops to collect ocean sediment cores and geophysical data. The cores and data collected from this expedition would later go on to be used to study climate change and ocean dynamics in a region known as the Western Pacific Warm Pool. Not only would I be able to take part in gathering the climate data that many take for granted in textbooks, I would get to go to an exotic location to do so! With the encouragement of my advisor (even though I would miss a month of classes), I applied to take part in a month-long oceanographic cruise in the western Pacific Ocean.

 

I was elated when I found out that I was selected. I packed my bags, and before my first semester of graduate school I boarded my flight from New York’s John F. Kennedy Airport to begin my journey half way around the world.

 

Papua New Guinea Coast - RV Roger Revelle
Coast of Papua New Guinea

 

Alotau, Papua New Guinea – September 4th, 2013

Airport and wallaby - RV Roger Revelle
(Top) The bustling Alotau airport
(Bottom) A wallaby!

I finally arrived in Alotau after what felt like three days. We had two days in Alotau, so I met up with the primary investigators and other graduate students, explored the town, took in the sights, swam at the local beaches and sampled the local suds. I took a liking to South Pacific Lager (aka SP to the locals), a crisp, refreshing lager that will quench your thirst and make you forget about even the muggiest Alotau nights; it had an iconic logo as well. I kept my eyes peeled for wallabies and birds of paradise, but unfortunately I only saw the former. Before I knew it, we boarded the ship and were on our way to Manila.

 

Ocean core extraction - RV Roger Revelle
Core coming up from the abyss

Once we became acquainted with the ship and I got over my initial seasickness, the science began. I was assigned to the night crew, working midnight to noon. This seems like a nightmare when you first think about it, but in hindsight I preferred it to working during the day. With temperatures in the mid 80’s and the humidity being high as can be, sweating through your clothes was common; within an hour it would appear as if you had fallen overboard.
It was much better to be in the cooler temperatures of the night. Adjusting to working at night was easy since the local time was 12 to 13 hours ahead of the U.S. East Coast. This made 1 AM out there the same as 1 PM back home. It also felt pretty cool to say “I’m on the night crew;” but I digress.

 

Over the next four weeks, I helped collect ocean sediment cores, seismic data and surface water samples along with the three other grad students and the post-doctoral researcher on my shift. Obtaining the sediment cores took up most of our time, the process taking all five of us to hoist the sections of the core overboard as they came up from the abyss. Imagine lifting an eight-foot section of PVC pipe filled with wet sand and mud; it was hard and at most times dirty work. Needless to say, my arms were toned by the end of the trip.

 

Retrieving Core and working - RV Roger Revelle
(Top) Team retrieving ocean sediment core
(Bottom) Hard at work on the R/V Revelle
Multicore and core - RV Roger Revelle
(Top) The multi-core
(Bottom) An extracted core

A second method of collecting ocean sediment cores involved loading and unloading a machine called a multi-core. This arachnid-esque device could collect eight 3-foot cores at once. The device was lowered then pulled up with the cores rigged to snap shut and collect a sample at the sediment-water interface. While these were much lighter than the long cores from the ocean floor, they were often half filled with water and therefore much more cumbersome when it came to packing them.

 

Once we had a substantial backlog of cores and started travelling, our focus switched. With the cores aboard, we analyzed the sediment with a gamma logger to quantitatively differentiate clay from sand and silt.

 

We continued collecting seismic data (which only took one person) and spent time splitting the cores in half, describing the contents and photographing them. After the qualitative descriptions, we packaged the cores so they could be shipped back to the U.S. where they would eventually be sampled and analyzed.

 

 

 

 

Manila, Philippines – October 3, 2013

After about a month, the science team departed the R/V Revelle in Manila, Philippines. While Manila was much more urban and developed than Papua New Guinea, it was still an interesting experience. Despite sleeping only a handful of hours, I wandered the streets around the hotel in which I was staying. I ate Filipino food from a roadside shack, which seemed intimidating at first but ended up being delicious. I ordered a chili oil noodle stir fry, which had a good kick to it, and sautéed kangkong (known as water spinach in English) with tofu, which satisfied my umami taste buds and my desire for fresh greens after being restricted to long-lasting boat food for the past month. I also drank coconut water straight from a coconut which was husked right before my eyes, and developed a love for rambutan and lychee while feeling the stares of many Manilans.

 

I stuck out like a sore thumb; I towered over almost all passersby, and my long hair and beard gave me a unique look. Despite the staring, the trip ended with a great dinner for all of the scientists that was hosted by a researcher at the local university. After a few hours of sleep, I woke, gathered my things and made my way to Ninoy Aquino International Airport for the long trip home.

 

Mayon Volcano - RV Roger Revelle
View of the Mayon Volcano

 

Home – September 4th 2013

Going on an oceanographic cruise was a great experience. Not only did I get to visit exotic places, I gained some great skills and learned some great lessons that I still use at BSTI today. Logging so many cores on the ship made me confident in my abilities and helped me realize what is useful to describe in a log. Like scientific investigations, soil boring investigations (which are similar to sediment core investigations except smaller) almost always involve something to be done, whether it be screening the boring with a PID, describing the core, collecting a sample or just taking legible notes and keeping them in order. I realized I must make good use of the time I have in between borings to get everything done, even when the time in between is minutes rather than hours or days. The work on the cruise may have been different from what I do now, but I will always cherish the skills and good habits I developed on that great adventure.

 

 

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