EOS® Related FAQs
EOS® Frequently Asked Questions
These frequently asked questions (FAQs) are a compilation of EOS®-oriented questions and answers that we have received over time. We hope you find this information useful. If you have further questions, please contact us.
How does EOS® work?
EOS® is engineered for effective distribution in the subsurface. Unlike some competitive products, EOS®' small droplets have a slight negative charge to prevent them from coalescing, simultaneously enhancing sorption onto slightly positively charged aquifer materials. The EOS® emulsion is designed to transport through the pore spaces and adhere to the sediment, providing a carbon source that will last for years.
Very simply, anaerobic bacteria required for reductive dechlorination need a food source. EOS® provides both quickly available carbon (lactate) and slow-release carbon (soybean oil) with nutrients required for biotic stimulation. In the presence of the available food and nutrients, the anaerobic bacteria "breathe" the chlorinated solvents resulting in harmless waste products and energy for growth.
More specifically, the biotic processes that remediate dissolved halogenated solvents involve a series of oxidation/reduction reactions. Oxidation is the removal of an electron from a compound; reduction is the addition of an electron. EOS®, like many additives used for the enhanced reductive dechlorination of hydrophobic chlorinated organic carbons, provides a source of electrons that ultimately benefit halorespiring bacteria. These bacteria require anaerobic conditions to metabolize dissolved chlorinated solvents, which are electron acceptors. Thus, EOS® is oxidized, while the chlorinated solvents are sequentially reduced.
The reductive dechlorination process requires the addition of a degradable organic compound, such as EOS®, into the aquifer to overcome the continuous electron acceptor supply, such as oxygen, nitrates and sulfates that are naturally present. Electron acceptors can enter the contaminated aquifer from upgradient regions or be delivered into the contaminated aquifer through recharge or gaseous oxygen diffusion from the vadose zone. The degradation process initially makes use of the available dissolved oxygen, followed by the nitrates and then the sulfates. Dechlorination of halogenated organic compounds works best under sulfate-reducing and methanogenic conditions.
The electron donor EOS® continues to biotically degrade through a fermentation process, which produces molecular hydrogen. Fermenting bacteria work especially well in anaerobic environments. The bacteria gain energy, which is necessary for life, by splitting the organic compounds in EOS® and generating chemically oxidized and reduced compounds.
Finally dechlorinating bacteria, such as Dehalococcoides, derive energy by using the molecular hydrogen as an electron donor and the chlorinated organic compounds as electron acceptors. The microbes substitute the chlorine atoms on the halogenated solvent with the molecular hydrogen in the dehalorespiration process. This results in the sequential chemical reduction of the chlorinated organic compounds eventually yielding harmless byproducts such as ethene and ethane.
Will EOS® float on the water table?
Unlike field-prepared emulsions and straight soybean oil and its derivatives, EOS® will not float on the water table. EOS® is engineered to prevent agglomeration or flocculation of the small oil droplets, allowing the emulsion to spread the designed distance in the subsurface while sorbing to soil surfaces.
Will emulsified oils mobilize contaminants?
EOS adheres to the aquifer sediments very quickly, so contaminants are not mobilized.
Will EOS clog the aquifer?
EOS is engineered to have droplet sizes significantly smaller than most pore spaces. The slight negative charges on the droplets repel the droplets from each other, while sorbing them onto the slightly positively charged aquifer soils.
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Does emulsification cause the soybean oil to biodegrade too rapidly?
EOS® will remain effective in the aquifer for at least three to five years. Emulsification absolutely increases biodegradation rates, which helps explain why EOS® is such an effective product. Without emulsification, soybean oil would degrade so slowly that it would not effectively stimulate biodegradation processes.
Do contaminants sorb to oil preventing biodegradation?
EOS® treatment results in a small temporary increase in sorption of the contaminants into the oil phase, a clearly beneficial effect. Biodegradation does not occur in the oil, but can retard migration of the contaminant, especially DNAPL. Years of laboratory and field research have proven that, over time, contaminants are eventually released back to aqueous phase as biodegradation proceeds. The contaminants are then more susceptible to degradation in the newly enhanced environment.
How long will EOS® last?
Extensive laboratory and field studies have shown that EOS® will support anaerobic biodegradation for three to five years depending on the amount of substrate injected and site conditions. In a laboratory column study, Long and Borden (2005) showed that a single injection of emulsified soybean oil can support complete reductive de-chlorination of 10,000 µg/L to PCE to ethene for up to seven years. Field tests of the emulsified oil technology by the Air Force Center for Environmental Excellence (AFCEE) have shown that emulsified edible oils have lasted over three and one-half years at Dover Air Force Base (AFB), over three years at Edwards AFB, and over two and one-half years at Altus AFB. A recent biobarrier project supported by the Environmental Security Technology Certification Program demonstrated that a single EOS injection lasted over one and one-half years while reducing influent perchlorate concentrations to below detection (over 99.9% reduction) with concurrent reduction of 1,1,1-TCA to non-toxic end-products (Zawtocki et al., 2004). Monitoring is continuing to evaluate the effective life of this barrier.
Based on bench scale and field studies, proper application of EOS® should last at least three to five years in the aquifer. As part of the engineering design criteria, you control the life expectancy of the remediation. Your EOS Remediation representative can assist you with designing sufficient substrate life for your project.
Can I use EOS® for source control?
Absolutely. For source control applications, EOS® is usually injected on a grid spacing or in a series of closely spaced barriers. Depending on the proximity of property boundaries, a recirculation system may be considered.
How do I determine my well spacing?
Field tests have shown that EOS® can be distributed large distances in the subsurface from just a few injection points. However, drilling costs are only one part of the total project cost. Using a larger well spacing can increase the total cost by increasing the time (i.e. labor cost) for injection.
The graph below illustrates the effect of drilling costs and injection well-flow rates on the least cost well spacing. When injection rates and drilling costs are low, it is actually less expensive to use closely spaced wells. However, as drilling costs and/or feasible injection rates increase, larger well spacings become more cost effective. For large projects, it is useful to generate cost estimates for several different well spacings to find the least cost alternative. A site-specific analysis should consider the available water supply, access restrictions, continuous versus intermittent injection, labor and drilling costs, etc.
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How do you inject EOS®?
EOS®, a low-viscosity fluid, requires no specialized material handling or pumping equipment. It is designed to migrate out into the aquifer away from the injection point at ambient temperature and low pressure. The ability to emplace the material into the aquifer at a considerable distance from the injection point is a major benefit of EOS®.
EOS® is delivered to a site in 55-gallon drums, totes or in bulk as a concentrate and must be diluted with a ratio of at least four parts of water to one part of EOS® before injection. Based on your specific design, either a "water chase" or an initial dilution ratio of 10:1 can be used for injection purposes. Both methods are equally effective and each has its advantages. The key consideration is to provide the correct amount of EOS® throughout the treatment zone.
A benefit of using EOS® at your site is employing your choice of injection methods. Our experience has shown that where direct push technology can be used, installation of micro wells (¾ to 1-inch PVC wells) can be very cost effective option. However, micro wells are neither better nor worse than conventionally installed wells. If multiple technologies are appropriate, cost factors normally determine the conveyance choice.
There are a variety of injection techniques, including injecting multiple wells simultaneously, to reduce injection costs. EOS® can be diluted in a holding tank and then injected or can be injected using a Dosatron. The Dosatron eliminates tank mixing and reduces injection labor costs. Your EOS Remediation representative can help recommend suitable injection methods.
Do we need to chase EOS® with water?
EOS® is designed to be easily emplaced throughout the aquifer treatment zone. We have found that using chase water reduces labor costs. Increasing the dilution rate of the concentrate has the same effect as water chase. Instead of diluting the concentrate 4:1 with water and using a water chase, you could simply increase the dilution with no follow-up water chase. By using chase water, the system can be automated to deliver potable water into the subsurface. A low-pressure feed of potable water does not require onsite supervision; an injected dilute emulsion, however, should be monitored. Either method meets the design requirement.
Can EOS be used in a recirculation system?
There are numerous sites where recirculation has been used during the injection of EOS®. Recirculation during injection offers the advantages of providing an on-site water supply and increasing groundwater flow gradients to draw EOS® through the aquifer.
Have regulators accepted EOS®?
Yes. EOS® is a natural, food-grade substrate that stimulates biodegradation.
Have regulators disallowed the use of any EOS® products?
No.
How do you prevent migration of EOS® outside (downgradient) of the intended remediation area?
We have found that EOS® does not migrate a significant distance away from the injection point. Once the injection process stops, the driving force ceases. EOS®, by design, sorbs to the aquifer materials and does not continue to migrate with groundwater. Downgradient monitoring using visual indicators combined with low injection pressures can be used to evaluate how far EOS® has moved through the aquifer. Recirculation is another way to provide hydraulic control during injection or to move EOS® in a particular direction or distance in the subsurface.
What groundwater parameters should we monitor after injection?
Your monitoring program may be specified for your site by the regulatory agency with site jurisdiction. At a minimum, your monitoring program should incorporate the contaminants of concern and reduction-oxidation (REDOX) potential. Field parameters of pH, conductivity and dissolved oxygen are also recommended. Apparent turbidity, observed as a faint white tint, can sometimes be used as a visual indicator of EOS® presence.
A more detailed monitoring program could include additional metals such as iron, manganese, arsenic, total organic carbon, light hydrocarbon gases (methane, ethane, ethene) and possibly volatile fatty acids. Increasingly complex sites could also monitor for phospholipids fatty acids and Dehalococcoides.
How do you measure the presence of EOS® in the aquifer?
The most obvious method is to visually examine a sample of groundwater. If EOS® is present, the sample will have a light whitish cast to milky appearance. If the concentration of EOS® is low and not discernable visually, then laboratory tests measuring total organic carbon or volatile fatty acids can be used.