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.

Return to Blogs >

Share This:
Facebooktwittergoogle_pluslinkedin

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).

Return to Blogs >

Share This:
Facebooktwittergoogle_pluslinkedin

Plastic Free July Challenge:
Reduce. Reuse. Rehydrate.

Happy Plastic Free July!
Will you take the challenge?

This month, we’re reminded of the importance of taking care of our world by reducing our use of disposable plastics. Did you know that over the last ten years we have produced more plastic than during the whole of the last century? According to EcoWatch, this massive amount of plastic production contributes to the billions of pounds of plastic that are taking up about 40% of the world’s ocean surfaces. Not only has our plastic waste contributed to the deaths of over one million seabirds and 100,000 marine mammals, it’s getting into our bodies as well.

 

Plastic Free July Challenge 2017 - Reduce Reuse Rehydrate

This Plastic Free July, we challenge you to help us work towards a healthier world through “Reduce. Reuse. Rehydrate.”

 

Plastic Free July Challenge 2017 - BSTI bottle Corfu, GreeceReduce your contribution to the growing plastic pollution issue by choosing to use less plastic. Ways to do this include buying in bulk at grocery stores or choosing products packaged in cardboard or glass instead of plastic.

 

Reuse products when you can. Our lives already include common reusable products like forks, knives, spoons and dishware. What about expanding that usefulness to include reusable snack bags instead of plastic bags?

 

Rehydrate with a reusable water bottle. It’s no secret that at BSTI we love our reusable water bottles. We love them so much, we want to give some away for free!

 

Tell us your story for a chance to win a BSTI water bottle!

Let us know how you have helped prevent plastics from entering our environment by sharing your story with us.

Submit your story as a comment below, and on August 1st, 2017, we’ll pick 5 winners to receive a stylish BSTI reusable water bottle!

 

Up to the challenge but need tips on how you can reduce your plastic footprint? Connect with us on social media for ideas:

Plastic Free July Challenge 2017 - Facebook link  Plastic Free July Challenge 2017 - Twitter Link      Plastic Free July Challenge 2017 - Google+ Link

 

Return to Blogs >

Share This:
Facebooktwittergoogle_pluslinkedin

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).

Return to Blogs >

Share This:
Facebooktwittergoogle_pluslinkedin

Groundwater and Your Business: Learn Why You Should Be Celebrating Protect Your Groundwater Day

Co-written by:

 

Prezi Screenshot - protect your groundwater day
How can we help? Click the image above to learn more.

September 6, 2016, just happens to be “Protect Your Groundwater Day!” Created by the National Groundwater Association (NGWA), Protect Your Groundwater Day is a day for everyone to celebrate the importance of groundwater and the impact it has on our everyday lives. So just what is groundwater and why is it important to you and more specifically your business?

 

Groundwater is the water found underground within the cracks and crevices of rocks and sand or within the soil. It is common to assume that there is an endless amount of groundwater/freshwater available to us, however only 1% of all the water on Earth is usable by humans. With that in mind, it is important for us not only to conserve water but also protect it from contaminants – especially when impacting groundwater from production can result in a costly cleanup project.

 

 

Why should a business pay attention to groundwater?

 

Like everyday people, industry is also dependent on groundwater. Groundwater provides about 18% of an industry’s fresh water (an economic value estimated at $2.7 billion), so the importance of clean groundwater to businesses is hard to overestimate. Inefficient use of groundwater costs money in terms of energy for pumping it and costs for treating and disposing of it after use. Likewise, accidental contamination of groundwater threatens a vital business resource. Many of our commercial and industrial clients only become aware of groundwater quality issues when they showed up in their own potable wells. When that happens, treatment of potable water becomes an additional expense on top of the environmental liabilities associated with remediation.

 

 

What can you do to protect your groundwater?

 

As noted on the NGWA website, you can protect groundwater by preventing its contamination by human activities and using it wisely. Complying with current State and Federal regulations on use and storage of chemicals, petroleum products and fertilizers goes a long way towards reducing the risk of groundwater contamination. Beyond legal requirements, it’s helpful to develop good housekeeping practices and a workplace culture that avoids shortcuts; especially with chemical handling. Water conservation is a vast topic, but it all starts with tracking your existing usage then developing practical and realistic goals for improvement.

 

Happy Protect Your Groundwater Day!

 

Return to Blogs >

Share This:
Facebooktwittergoogle_pluslinkedin