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Frequently Asked Questions - Soil Oxidant Demand

 


FAQs

General

How many samples should be analyzed from my site?

Should duplicate the Soil Oxidant Demand analysis be conducted on samples?

Should a laboratory test of Soil Oxidant Demand be conducted in addition to this screening analysis?

How can I interpret the SOD test results?

What do the SOD test results mean?

What is the EPA or Standard test method used in the Soil Oxidant Demand test kits?

Is there a laboratory report that goes with the Soil Oxidant Demand test kits?

Does Oxidation Systems offer Soil Oxidant Demand test kits that use other oxidants like hydrogen peroxide, Fenton’s Reagent, or persulfate?

Testing Related

What can I do if the 10-mL syringe breaks before I transfer all of the supernatant to the clear test tubes?

What do I do if the filter clogs before all 10 milliliters of the supernatant solution is transferred to the viewing tube?

I accidently let the SOD test run longer than 48 hours. Are the results still valid?

Should I composite my soil sample?

If I composite the soil sample, won’t the volatile constituents in the sample be lost and will the SOD test results still be valid?

The oxidant demand of my soil sample is greater than the maximum test range of 20 g/kg. What should I do?

All of the Reaction Tubes have a dark color, including the blank. Is something wrong?

All of the filtered samples have a dark color, including the blank. Is something wrong?

 

Sample Collection and Preservation

How much sample is required for the Soil Oxidant Demand Test?

How long can soil samples be held before conducting the Soil Oxidant Demand test?

What preservation methods are required for the Soil Oxidant Demand test?

Should site groundwater be used instead of distilled or de-ionized water for the Soil Oxidant Demand test?

How many samples should be analyzed from my site?

This question is a matter of professional judgment and depends on a number of site-specific factors. In general, the more samples that are analyzed for Soil Oxidant Demand, the more accurate and reliable the evaluation of the suitability and cost for implementing in-situ chemical oxidation. For a small to medium sized site, a good rule-of-thumb is to collect two to five samples from each geologic unit present. If varying contaminants are present in different areas of the site, several samples should be collected and analyzed from each region. Larger sites require more samples.

Should duplicate the Soil Oxidant Demand analysis be conducted on samples?

The need for duplicate analysis for a given site should be assessed relative to the planned use of the Soil Oxidant Demand test results. If the SOD tests are being conducted to determine if further evaluation of in-situ chemical oxidation is warranted (i.e. a “go / no-go” decision), then duplicate sample analysis may not be required. However, if the SOD test results are the principle method of evaluating ISCO, then duplicate sample analysis should be used to evaluate the accuracy and repeatability of the results.

 

Should a laboratory test of Soil Oxidant Demand be conducted in addition to this screening analysis?

Yes. The Soil Oxidant Demand test method developed by Oxidation Systems is intended to be a screening level analysis to evaluate the suitability of in-situ chemical oxidation for a particular site. Although the results are accurate and the test uses the same chemicals and many of the analytical procedures used in the laboratory SOD test method, it is not intended to be a substitute for the laboratory SOD method. However, the results are often identical to the laboratory method, and the SOD test kits offer rapid results with lower cost.

How can I interpret the SOD test results?

The results of the Soil Oxidant Demand test for permanganate (SOD series) are presented in units of grams of permanganate per kilogram of soil (g/kg). This means that for every 1 kilogram of site soil, there is enough reactive material (e.g. metals, organic compounds, contaminants, etc.) to “consume” or react with 1 gram of potassium permanganate.  Similarly, the test results for the persulfate test are presented in grams of persulfate per kilogram of soil.

What do the SOD test results mean?
The results of the Soil Oxidant Demand test for permanganate are presented in units of grams of permanganate per kilogram of soil (g/kg). If the SOD test results indicate 1 g/kg and the mass of soil requiring treatment at the site is 10,000 kilograms, then the amount of potassium permanganate required to satisfy the soil oxidant demand (also known as natural oxidant demand is 10,000 grams (1 g/kg x 10,000 kg).
Similarly, the test results for the persulfate test are presented in grams of persulfate per kilogram of soil.

What is the EPA or Standard test method used in the Soil Oxidant Demand test kits?

Oxidation Systems developed the Soil Oxidant Demand test kits using a modified version of the USEPA Soil Oxidant Demand screening test method for permanganate (PSOD-1). The Oxidation Systems test method is more quantitative than the USEPA method and includes more oxidant demand ranges (1, 5, 10, and 20 grams per kilogram).

Is there a laboratory report that goes with the Soil Oxidant Demand test kits?

Yes, Oxidation Systems has developed a Soil Oxidant Demand report that can be used to summarize the analytical method and the results. It is available on the CD provided with SOD-Starter Kit, or it can be downloaded from our website.

Does Oxidation Systems offer Soil Oxidant Demand test kits that use other oxidants like hydrogen peroxide, Fenton’s Reagent, or persulfate?

Yes, we now have test kits for sodium persulfate (sold by FMC as Klozur) in addition to our permanganate test kits. We are also actively developing test kits for other oxidants and expect to have them available soon. Sign up for our newsletter to be informed of new oxidant test methods and other innovative developments with Oxidation Systems.

Testing Related

What can I do if the 10-mL syringe breaks before I transfer all of the supernatant to the clear test tubes?

If one of the 10-mL syringes breaks, you can use one of the syringes from one of the other tests. If you do not have any syringes left, you can pour the supernatant out of the Reaction Tube into a container and filter it through a paper towel. The intent of the filtration step is to remove suspended particles that interfere with evaluating the color of the supernatant solution.

What do I do if the filter clogs before all 10 milliliters of the supernatant solution is transferred to the viewing tube?

It is not necessary to have a full 10 milliliters of the filtered supernatant. You only need enough liquid to compare the color of the remaining permanganate solution to the color comparator. If you do not have enough liquid to evaluate, you can filter the supernatant with a previously used filter.

I accidently let the SOD test run longer than 48 hours. Are the results still valid?

Yes, the results are still valid and can be used to evaluate the efficacy of using ISCO at your site. However, the SOD value will likely be higher than it would be if you had terminated the test at 48 hours.  Generally, most of the oxidant reacts within the first 48 hours, but the reactions continue until either all of the oxidant is consumed or all of the reactive materials in the sample have been oxidized.

Should I composite my soil sample?

Yes. It is extremely important to have soil samples that are representative of site conditions, and compositing the sample ensures that the 10 gram soil specimen is as close to those conditions as possible.  If the soil sample has a high degree of heterogeneity, you should thoroughly mix it. In addition, it is highly recommended that you conduct duplicate tests on this type of sample to account for the non-uniformity of the soil matrix.

If I composite the soil sample, won’t the volatile constituents in the sample be lost and will the SOD test results still be valid?

Although mixing soil samples that contain volatile organic compounds will result in the volatilization of some of the constituents, the oxidant demand associated with the mass of VOCs that are lost is small relative to the oxidant demand of the soil matrix. It is common for the oxidant demand for the soil matrix to be 1 to 3 orders of magnitude greater than the oxidant demand for the VOCs in the soil sample. (The presence of NAPL is an exception to this guide.)

The oxidant demand of my soil sample is greater than the maximum test range of 20 g/kg. What should I do?

You can modify the oxidant demand ranges on the permanganate SOD test kits by changing the mass of soil sample used. The standard method requires 10 grams of soil. To double the oxidant demand ranges, reduce the mass of soil to 5 grams. This will result in oxidant ranges of 2 g/kg, 10 g/kg, 20 g/kg, and 40 g/kg. Write the new oxidant demand ranges on the Reaction Tubes and note the change in soil mass on the worksheet. If the oxidant demand of the soil sample is greater than 40 g/kg, contact Oxidation Systems.

All of the permanganate Reaction Tubes have a dark color, including the blank. Is something wrong?

It is common for suspended particles to cloud the water in the Reaction Tubes, especially if the soil contains silt or clay. These suspended particles will be removed during the filtration step as the supernatant is removed from the Reaction Tubes and transferred to the clear Viewing Tubes.

All of the filtered samples have a dark color, including the blank. Is something wrong?

The permanganate SOD test kits rely on color changes to determine the oxidant demand of the soil sample. Some soil samples leach color, especially in the presence of an oxidizer. If the blank sample also has a color, it may not be possible to evaluate the amount of permanganate remaining in the samples. Hold the Viewing Tubes next to the color comparator chart in bright light (preferably sunlight) and try to determine if any pink or purple color is present. It may be possible to assess the presence or absence of permanganate in this manner which will allow you to obtain a range for the oxidant demand of the sample (e.g. between 5 and 10 g/kg). In some cases, the SOD test kits cannot be used and a laboratory SOD test is the only option.

 

Sample Collection and Preservation

How much sample is required for the Soil Oxidant Demand Test?

Each Soil Oxidant Demand test requires a minimum of 50 grams of soil. If you use site groundwater (distilled or de-ionized water can be used instead), you will need 250 milliliters (0.25 liters).  Refer to the Sample Collection and Handling Protocol for SOD Testing guidance document for additional information.

How long can soil samples be held before conducting the Soil Oxidant Demand test?

Although there is no hold time restriction for the Soil Oxidant Demand test, it is highly recommended that the SOD analysis be conducted within two weeks of collection. It is important to understand that oxidation and reduction conditions can change quickly for soil samples exposed to air and drying conditions. Therefore, samples should be analyzed as quickly as possible.  ).  Refer to the Sample Collection and Handling Protocol for SOD Testing guidance document for additional information.

What preservation methods are required for the Soil Oxidant Demand test?

For the Soil Oxidant Demand test, cooling at 4° C is the only sample preservation required during transport and storage. Refer to the Sample Collection and Handling Protocol for SOD Testing guidance document for additional information.

Should site groundwater be used instead of distilled or de-ionized water for the Soil Oxidant Demand test?

The effects of contaminants in the site groundwater usually will not significantly impact the test results because the concentrations of materials in the soil that react with permanganate are the major contributing factors. If site groundwater is not provided or available, de-ionized (DI) or distilled water can be substituted and should be noted in the report.  Refer to the Sample Collection and Handling Protocol for SOD Testing guidance document for additional information.




 

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