FREQUENTLY ASKED QUESTIONS

Treatment Application

How are temperatures and pressures encountered with aproposed process during treatment controlled? Will standard PVC injection wells be utilized or will special well casing be required?

As stated earlier, an ISOTEC reagent combination utilized at a site is first tested during a bench-scale lab study. The ISOTEC process utilizes low concentration reagents under a gravity or slight pressure injection with constant off-gas releases through a site-specific injection apparatus. Reagents utilized are stabilized and at a low concentration, with injection in a controlled manner to reduce the possibility of any hazard occurring. Pressure and temperature measurements are not typically collected due to ISOTEC’s non-aggressive reactions. Temperature rises of upto 10 degrees Celsius are noted for a short period (<24 hours), and slight applied pressure is used only within less permeable aquifers. Standard PVC injection points are sufficient with the ISOTEC process. Treatment program activities are limited to the specific areas within the known contaminant plume, with injection of treatment chemicals controlled at the surface during the application. A site engineered injection apparatus is used to control flow of treatment chemicals into the subsurface via the chosen injection pathway.

In the injection of reagent into the contaminated subsurface, what percentage of pore volume is necessary for making adequate contact with contaminants of concern? Is there a concern with the displacement/forced migration of contaminants associated with adding significant volume of liquid to the subsurface? If so, how is this displacement/forced migration controlled?

The first part of the question should be answered by the stoichiometric ratio determined in the bench-scale lab study, along with several other factors as discussed above. The ISOTEC process injection rate and volume of discharge are extremely complex and interrelated to the reaction rates of hydroxyl radicals with the contaminants, the contaminant distribution coefficients in the subsurface systems, and the rate of hydrogen peroxide decomposition within the subsurface. The rate at which any flow can be injected into the subsurface is determined by the soil/aquifer characteristics. The treating flow will be discharged under hydrostatic or an applied pressure based on the engineering and construction of the injection system and receiving aquifer. The volume of discharge varies based on the specific stoichiometry determined in the lab study, level of contamination, volume of area to be treated, and subsurface soil and ground water characteristics.

The following should address the requested information on the actual destruction of contaminants versus possible displacement/forced migration. The ISOTEC process is a contact treatment that actually changes the chemical composition of the compound in-situ and occurs instantaneously. When ISOTEC chemicals are injected into the subsurface, a reaction transpires which immediately produces free radicals (via modified Fenton’s reagent or activated persulfate). The free radicals are non-specific oxidants that react with most organic contaminants at diffusion controlled rates. As the free radical comes into contact with organic compounds, oxidation occurs. A complete oxidation of the organic compound results in the production of carbon dioxide and water. Therefore, no displacement/forced migration occurs, only the chemical oxidation of organic compounds within the area being treated. In addition, subsurface aquifers consist of large quantities of liquid totaling in the millions of gallons. The addition of a few hundred/thousand gallons of ISOTEC catalysts and oxidizers within a particular area would not cause any significant decrease in contaminant levels due to dilution.

How are such parameters as pH and alkalinity manipulated as part of the full-scale treatment process in order to optimize performance of the injected reagents? Provide details.

Laboratory treatability studies and corresponding field treatment programs can be performed at sites with varying subsurface conditions such as low acidic pH levels to higher alkaline levels. ISOTEC’s patented catalysts allow for the generation of free radicals and chemical oxidation to occur through most of the pH scale (i.e. pH = 2-10). ISOTEC’s 4000 series catalysts are designed to function under natural subsurface conditions (i.e. pH of 7) and are suitable for majority of the sites using modified Fenton's or persulfate. Therefore, no manipulation is required.

Are ISOTEC reagents prepared on site? What happens to these chemicals when injected into the subsurface?

ISOTEC catalysts consist of a site-specific chelated iron complex. ISOTEC typically uses H2O2 and sodium persulfate at a concentration of 5%-20% during injection activities. Permanganate is used at concentrations ranging from 1% to 10%. Typically, the H2O2 is shipped directly to the site and stored in DOT approved 55-gallon drums with an initial concentration of 50%. Sodium persulfate is shipped to the site in a dry form in 55 lb bags. Potassium permanganate is shipped in dry form in 100 kg pails while sodium permanganate is shipped in liquid form in DOT approved 55-gallon drums at an initial concentration of 40%.

Field dilution and addition of ISOTEC’s proprietary non-hazardous stabilizers and mobility control agents are performed as determined during our bench scale studies. All reagent components are premixed in a dry form and packaged prior to shipment to any site. The reagent additives will be mixed/ diluted on-site and added during dilution activities. The ISOTEC series catalysts consist of a chelated iron complex. The iron complex is similar and at levels comparable to that of naturally occurring metals within the soil matrix. ISOTEC catalysts include proprietary chelating agents, which keep the catalyst in dissolved form until adequate dispersion is completed and at levels to that of naturally occurring metals within the subsurface. The oxidizer slowly consumes the catalytic components before a gradual liberation of catalyst throughout the treatment area occurs. This process allows the catalyst to distribute evenly within subsurface before finally adsorbing to the soil particles. After a short period of time, the catalyst is oxidized to simple ferrous/ferric ions. For modified Fenton's, the hydrogen peroxide oxidizer is itself reduced to water and oxygen. For activated persulfate, the sodium persulfate oxidizer is reduced to sulfate. For permanganate, MnO2 formation occurs, which precipitates as a dark brown to black solid that adsorbs to the soil matrix.

Since the hydroxyl ions which are generated are not selective, some of them will be wasted on other carbon sources such as the peat layer beneath the site. Besides the PCE, there are other contaminants, such as waste oils (PAHs) and phthalates, which will react with the oxidants.

It is true that hydroxyl radicals generated during the reaction are non-specific and will react with any organic material including peat and free product. Our bench test will test low to high reagent concentrations to evaluate the reagent quantities needed for contaminant treatment for the site-specific soil and groundwater and will include volumes to offset scavenging losses. A pilot study is primarily conducted to obtain a better idea of the overall site-specific factors affecting the process efficacy. Typically, ISOTEC uses a conservative correction factor while estimating the reagent quantities in order to account for losses such as those caused by the scavenging materials (such as peat) in the native soil. The reaction with the free product results in its gradual depletion from the subsurface, which is beneficial for the site.

When injecting modified Fenton's reagent into DNAPL areas, a conversion from DNAPL into dissolved phase will occur. This raises an important question on how will this conversion take place. Do the reagents they will be adding to the groundwater will include surfactants to bring the DNAPL into solution.

ISOTEC modified Fenton's process does not utilize any surfactants as part of its reagents. The critical ingredients are hydrogen peroxide and chelated iron complex. The conversion of DNAPL into dissolved phase will occur because of DNAPL desorption from the soil matrix and subsequent transfer to groundwater phase when groundwater contacts desorbed DNAPLs. Desorption occurs because the hydroxyl radicals non-selectively attack the soil-based organic matter binding these contaminants to the soil. The extent of transfer will depend upon the solubility of contaminants and their associated distribution coefficient.

Fenton-reaction involves forced injection of air into the subsurface which may result in pressure buildup that may create hydraulic fracturing resulting in preferential pathways.

Air injection into the subsurface, forced or otherwise is not performed at majority of ISOTEC sites. At sites with extremely tight subsurface conditions (such as tight clayey soils), pneumatic fracturing of the subsurface using pressurized air/nitrogen injection may sometimes be performed to promote distribution of reagents but only after a thorough investigation of the feasibility and potential effects have been completed.

Safety is a priority with the ISOTEC Process, which uses relatively non-aggressive reaction chemistry. Possible side effects such as surface breakout or lateral migration of treatment reagents and/or off-gases occur with aggressive reaction type oxidative processes utilizing high concentration of reagents under a constant pressurized condition. ISOTEC does not utilize this approach. Reagents utilized by ISOTEC are stabilized and at a low concentration, with injection in a controlled manner to reduce the possibility of surface breakout or lateral migration. Furthermore, at sites with shallow depth of ground water, extreme caution is exercised while injecting reagents as the mounding effect created raises the ground water elevation to close proximity of the surface. This mounding effect will be monitored in the field by collection of continuous water levels shortly after injection of reagents. It should be noted that the mounding effect offers a potential benefit by treating contaminants present in the "smear" or vadose zone.

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