Frequently Asked Questions

 

What advantages does Surfactant-Enhanced Chemical Oxidation have over conventional ISCO?

 

a. Greater contaminant contact with oxidants, through desorption of contaminants from soil pores and emulsification of residual free phase oils, which greatly increases the contaminant surface area, thereby increasing oxidative efficiency.

 

b. Source zone destruction of NAPL/recalcitrant compounds and rebound avoidance.  

 

c. Reduction in total oxidant needed over project lifetime compared to conventional chemical oxidation ongoing maintenance treatments (due to rebound). S-ISCO addresses the source of contamination, thereby eliminating rebound and the need for multiple treatments.

 

d. EthicalChem’s proprietary surfactant E-Mulse (Formerly VeruSOL) added to hydrogen peroxide decreases the rate of decomposition of peroxide resulting in safer, less exothermic reactions during implementation.

 

 

Can S-ISCO be applied at sites with roadways, utilities, and structures?

 

An advantage of a S-ISCO implementation is the ability to be applied under roadways and structures with minimal disruption and no impact to structures.

 

 

When underground utilities are present, S-ISCO implementations are designed to ensure compatibility with underlying piping and structures.

 

 

How long is a typical treatment period?

 

Treatment length varies based on site conditions but typically injection periods last between 1 week at small sites and 6 months for large sites.

 

 

How does the cost of S-ISCO compare to ISCO treatments, thermal treatments, and excavation?

 

S-ISCO treatment is generally the most cost effective solution at sites with source zone contamination from NAPLs or hydrophobic organic contaminants and/or sites where contamination is at depths greater than 15 ft or under structures. The ability to reduce source contamination eliminates the possibility of rebound and therefore multiple follow up treatments are not necessary. The cost of S-ISCO is similar to the cost of ISCO for a single treatment. EthicalChem is able to use lower doses of oxidant due to the improved oxidant efficiency by increased contaminant surface area created by surfactant emulsification. The surfactant cost is therefore offset by the lower oxidant requirement for S-ISCO.

 

 

Some examples of cost comparisons include a $5 million (>50%) cost savings in comparison to excavation at a MGP site in Queens NY, and a cost saving of  $2.5 million (70%)at a creosote site in DE compared to  the cost estimate for the alternative of thermal desorption followed  by bioremediation.

 

 

When is it best to use S-ISCO instead of ISCO?

 

S-ISCO is best when hydrophobic source contamination (residual NAPL) is present, soil contaminant concentrations are high, and/or the site objective is permanent contaminant destruction (ie clean soil). ISCO can be effective in treating groundwater contamination after the source or NAPL has been removed or destroyed, and is effective for more water soluble contamination i.e. nitrophenols, acetone.

 

 

Can S-ISCO address any amount of NAPL?

 

Free phase NAPL contamination is a technically challenging problem to address in the subsurface, and is typically a key element of treatment for achieving cleanup goals at sites. Oxidizing pure phase contaminant can require a significant amount of oxidant to meet cleanup goals. Attempting to oxidize bulk free phase plumes of NAPL is not cost effective. Therefore, when significant NAPL is present EthicalChem implements a sequential treatment approach beginning with Surfactant Enhanced Product Recovery (SEPR) followed by S-ISCO. SEPR applications utilize plant based surfactants along with low doses of hydrogen peroxide to loosen and desorb bulk NAPL plumes and help facilitate movement toward recovery wells. Once the majority of NAPL is removed from the subsurface, S-ISCO is implemented to chemically oxidize the residual NAPL and contaminants in place.

 

 

Does S-ISCO lead to contaminant mobilization?

 

During S-ISCO injections the surfactant and activated oxidant travel together in the subsurface. The surfactant desorbs and emulsifies contaminants from the soil while free radicals (generated from a catalyzed oxidant) simultaneously destroy the contaminant. The emulsification and oxidation processes take place continuously over several weeks. As soon as contaminants are emulsified they are more susceptible to oxidation, and will not travel far in the presence of typical groundwater speeds before being destroyed when an oxidant is present. Groundwater typically does not carry the emulsion off site prior to contaminant destruction.

 

 

Monitoring wells are appropriately placed on and off site in order to track potential movement of S-ISCO chemicals and/or contaminants. In the event a chemical detection is made outside of the targeted treatment zone, in the proximity of sensitive receptors, such as bodies of waters or underground utilities contingency measures, such as extraction, would be implemented. EthicalChem has not had to utilize contingency measures at any site to date.

 

 

Is the surfactant oxidized by the oxidant therefore increasing the amount of oxidant required?

 

The plant-based surfactants used by EthicalChem do not directly compete with the contaminants for reaction with the oxidant during oxidation. The surfactant molecules are relatively stable, with a larger molecular structure than most organic contaminants, making them less susceptible to oxidation than the contaminants.  Once most/all contaminants have been emulsified and destroyed, the remaining surfactant will be oxidized as well. If an oxidant is no longer present, the surfactants will eventually biodegrade.

 

 

When surfactant, oxidant, and contaminant, are all present within a system, the contaminant is subject to oxidation first, before the surfactant. Lab tests have been conducted to evaluate the oxidant -surfactant interaction with and without a contaminant (NAPL) present, in an aqueous system.

 

 

In the graph below the presence of surfactant is indicated by interfacial tension (IFT) measurements through time both in the presence and absence of NAPL. The IFT of pure water is about 72 mN/m, and a decrease in IFT (to a minimum of approximately 32 mN/m) signifies the presence of surfactant. The graph below shows that after 81 days (2/28) the surfactant is still present (therefore not oxidized) in both the system with NAPL and without NAPL. The next data point, collected at day 152, shows that the surfactant has been oxidized in the reaction without NAPL, however it is still present, stable, and effective in the reaction with NAPL. Note, this lab test is a comparison of oxidant/surfactant with and without NAPL in an aqueous solution only and the oxidant dosing was not designed for rapid destruction of the NAPL present. Additionally, in the subsurface, in the presence of many other factors such as soil type, pH, inorganics, etc, the actual destruction rates will typically be faster, however the relative relationships are expected to be the same; surfactant will exist longer in the presence of contaminants versus without contaminants.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What approach would EthicalChem recommend for chlorinated solvents such as TCE and PCE?

 

S-ISCO using potassium permanganate (KMnO4) is our preferred approach for TCE and PCE contaminated sites. Cost effectiveness of the treatment can be maximized by using a very low surfactant dose in the area surrounding the source zone. In cases where there is free phase TCE or PCE NAPL, SEPR would be implemented using a blend of hydrogen peroxide along with higher concentrations of surfactant, preceding the S-ISCO implementation.

 

 

Can S-ISCO be applied to treat PCB or pesticide contaminated soil?

 

Surfactants have been successfully used to remove PCB contaminated oil from soil in flushing applications.

 

PCBs and pesticides are difficult to address with in-situ chemical oxidation because of their low solubility and tight sorption to soil.  While surfactants have been identified that desorb many insoluble compounds, we have not yet identified a biodegradable surfactant that can effectively desorb >95% PCBs from soil.   

 

 

Do you regularly provide bench-scale treatability test services?

 

EthicalChem typically conducts surfactant screening tests along with the conventional chemical oxidation studies (batch tests or column tests) to determine the best S-ISCO treatment for the site. We will also provide products and guidance to third party laboratories.   

 

 

Is it safe to use S-ISCO to remediate near a river or shoreline?

 

S-ISCO has been implemented at several sites adjacent to major bodies of water without incident. At these sites groundwater monitoring was used throughout the injection process to validate that no chemicals or NAPL were transported off site. No contaminant mobilization has been experienced which has created issues near a body of water. For avoidance of risk, monitoring plans are typically put in place, along with contingency measures, such as extraction, when injecting near sensitive receptors.