Frequently Asked Questions ABOUT EDT
How does the Reterro Evaporative Desorption process extract contaminants from soil?
The Evaporative Desorption Technology (EDT) process is designed to deliver a uniform flow of heated air at high flow rate through a mass of soil (nominally 20 tons per batch) under light vacuum. The process is designed to be inherently safe and free of fugitive emissions. The heated input air accelerates the evaporation of the contaminants, and the uniform air flow assures that all of the soil is treated. Soil is excavated and loaded into specially designed containers. Two of these containers are loaded into the treatment chamber for each process batch. Nominal process time is 2 hours per 20-ton batch, and varies with soil type, soil moisture, contamination level, and treatment standard. EDT is suitable for treatment of a variety of volatile, semi-volatile, and chlorinated volatile organic compounds. Non-volatile contaminants, such as metals or other inorganic compounds are not affected by or removed by EDT, but may be treated after EDT to limit their leachability from soil.
How "green" is Reterro soil remediation process technology?
Reterro commissioned an independent consulting firm (WSP/Parsons Brinkerhoff) to compare Evaporative Desorption Technology (EDT) to its largest competitor, transportation & disposal, on a large project that was completed by Reterro in 2015. The results were compelling, and Reterro significantly outperformed the transport & dispose alternative in all impact categories: Global Warming Potential, Primary Non-Renewable Energy Demand, and Particulate Emissions. We found that, whether powered from a grid source or a portable diesel source of electricity, our on-site EDT treatment process had ten times less impact on global warming potential and energy demand, and also produced less than 1% of the particulate (PM2.5). This is largely due to the high rate of diesel consumption when contaminated soil is transported to a landfill. Empty trucks must travel to the project site and then make the trip to the landfill, which could be several hours away. Separate trucks carrying clean backfill material must also visit the project site, and they make an empty trip when they leave. Reterro EDT systems emit little or no contamination. When operating, the process chamber is under a slightly negative pressure and outside air is drawn into the chamber rather than allowing contaminants to leak out. At the outlet of our process, the catalytic oxidizer or carbon treatment pollution control devices are highly effective. In some cases, the process exhaust can be cleaner than the surrounding air.
How does the Reterro performance guarantee work?
After a very thorough evaluation of Reterro Evaporative Desorption Technology (EDT), a global leader in reinsurance with a balance sheet equivalent to a Fortune 10 company was able to provide Reterro with a policy that backs our performance guarantee. This policy provides price protection to clients of Reterro in the event that EDT fails to meet the agreed-upon treatment goals. It was possible for Reterro to obtain this coverage because Reterro has a proven record of project success, has the means to perform bench-scale testing that correlates well with full-scale performance, has multiple means of monitoring the performance of the process in real time, and can demonstrate process effectiveness very early in the execution phase of a project. In the event that an alternative method, such as transportation and disposal, must be employed, the alternative can be executed by Reterro at no additional cost to the client.
How is the Reterro performance guarantee different from a performance bond?
Unlike a performance bond, the Reterro process performance guarantee covers all Reterro Evaporative Desorption Technology (EDT) projects and does not need to be negotiated and vetted on a project-by-project basis. This means that there is no bonding or guarantee negotiation delays to the deployment schedule, and each Reterro EDT project is protected from issues that might arise on other Reterro EDT projects.
How is the Reterro Evaporative Desorption process powered?
On larger projects, where it becomes cost-effective, we can use a connection to the local power grid. Reterro has a transformer and electrical switch gear that can provide a connection for up to three EDT treatment systems. In many cases, the original activity at the project site leaves behind a suitable electrical infrastructure. For projects over 30,000 tons, it is almost always cost-effective to make a connection to the local grid. For smaller projects, we use a diesel-powered or natural gas-powered electrical generator. Suitable generators are available for local rental almost everywhere.
How does Reterro EDT compare to in-situ approaches to soil remediation?
There are several differences between Reterro ex-situ batch treatment and the various forms of in-situ continuous treatment approaches. The most significant differences have to do with the certainty of the treatment. When a site is excavated all of the hidden features are revealed. These include contamination missed during initial sampling, lithology variations, buried debris, perched water, and other subsurface interferences. It is extremely rare to find a site that has a uniform subsurface profile. Instead, there are a variety of subsurface features that interfere with the uniformity and overall effectiveness of in situ treatments. Whether the treatment uses injection of chemicals, bio-agents, steam or air; or whether it uses vacuum extraction with or without resistive, radio frequency, or other heating; the subsurface path(s) taken will be the path(s) of least resistance. Significant amounts of contamination can remain in pockets that received little treatment, or no treatment at all. In addition, in-situ approaches typically require very long treatment time, and often require multiple iterations of the treatments. The uncertainty inherent with in-situ approaches was tolerated at a time when ex-situ approaches were falling out of favor due to safety concerns and/or inability to be permitted in densely populated areas. Reterro technology was developed to allow more certain and higher rate treatment than is possible with an in-situ approach, while at the same time overcoming the limitations that made previous ex-situ thermal approaches too costly or unable to obtain an operating permit. In-situ approaches are useful when physical obstructions or excessive depth make excavation impractical, such as when treatment is required underneath an active roadway or a structure that must be preserved.
How does Reterro handle the contaminants after they have been removed from the soil?
If the contaminants are chlorinated volatile organic compounds (CVOC), Reterro uses activated carbon to capture them. Reterro operates the carbon capture in such a way as to keep stack emissions below detection limits, and far lower than regulatory standards require. When the carbon reaches its carrying capacity, it is replaced with clean carbon and the contaminated carbon is transported to a licensed disposal facility for recycling. The contaminant is completely destroyed and a certificate of destruction is issued. The regenerated activated carbon can be reused several times before it loses effectiveness. If the contaminants are fuel-based volatile organic compounds (VOC) such as gasoline, diesel, motor oil, BTEX*, or PAH**, Reterro uses a high flow rate catalytic oxidizer to break down the extracted hydrocarbon to CO2 and water vapor, with efficiency in excess of 99.5%. The catalytic oxidizers that Reterro uses are custom-built to our specification and are fully integrated into our control systems. Reterro has instrumented its equipment to continuously monitor every critical operating parameter, including temperatures, flow rates, pressures, VOC concentrations, humidity, valve states, interlocks, and alarms. All of that information is continuously recorded and email alerts are automatically generated to key personnel when a critical variable approaches its limit. All of this contributes to the relative ease that Reterro has when seeking an operating permit, especially in a non-attainment jurisdiction like SCAQMD***.
* BTEX is short for Benzene, Toluene, Ethylbenzene, and Xylene, which are highly volatile organic compounds
** PAH is short for polynuclear aromatic hydrocarbons, which are semi-volatile organic compounds
*** SCAQMD is the South Coast Air Quality Management District, which includes the Los Angeles metropolitan area
What types of industries generate the contamination that Reterro EDT can treat?
Reterro specializes in the removal of fuel range hydrocarbons (gasoline, diesel, and motor oils) and chlorinated solvents (chlorinated volatile organic compounds – or CVOC). Typical examples of CVOCs are:
• PCE (perchloroethylene or tetrachloroethylene) is a solvent used for dry cleaning and degreasing.
• TCE (trichloroethylene) is a solvent used for degreasing and is also a breakdown product of PCE in the environment.
• DCE (cis 1,2-dichloroethylene) is a breakdown product of TCE in the environment.
• Vinyl chloride is a breakdown product of DCE in the environment, and is also used in plastics manufacturing.
• Carbon tetrachloride is a degreasing solvent.
• DCA (1,2 dichloroethane)is a degreaser and paint remover. It is also used in the production of vinyl chloride for plastics manufacturing.
Fuel and oil contamination are typically the result of liquid transfer or storage failures of some type, and they are encountered most often at bulk fuel transfer facilities, service stations, and some industrial sites like refineries or large manufacturers. Treatment to a residual of a few hundred parts per million is typically required. CVOC spills occur at dry cleaners (retail or industrial scale), manufacturing facilities that use CVOC to degrease parts, auto repair shops, and other locations where large-scale degreasing is done. Treatment to a few parts per billion is typically required.
What are the other common contaminants that EDT cannot address, and what do you do if they are present on a site?
Reterro process and equipment works by evaporating contaminants from the soil, so non-volatile contaminants like metals (lead, arsenic, etc.), PCBs (polychlorinated biphenyls from transformer leaks), and very heavy hydrocarbons from manufactured gas plants cannot be treated effectively. In some cases, EDT can be used to treat volatile contaminants, and then another treatment technology can be applied to the remaining non-volatile contaminants.