Sampling Help and FAQs

This page provides assistance and explanation for Method 3C/25C and Method 25. These videos show how to connect the equipment for sampling. A list of FAQs for each method is below the corresponding video. If you need further assistance please contact us.

Method 25 Heated Filter Assembly exploded view

Method 3C/25C

Method 3c/25c assembly video

Method 3C/25C FAQs

method/results

Equipment

Potential Issues

Shipping

Documentation


If the Method 3-C analysis fails the oxygen/nitrogen requirement do I still have to pay for a Method 25-C analysis?

  • No, you only are billed for the analyses performed. We perform the Method 3-C analysis first and if there are any concerns we postpone the following analyses to ensure you will be getting data you can use. If the failure of the Method 3-C means you cannot use the Method 25-C, the Method 3-C is all that will be performed. In some cases, such as a slight failure or if the sampling is not for compliance, you may request the Method 25-C analysis still be performed and for those cases you will be billed for only those analyses performed. (back to the Method/Results FAQs section)

If the Method 3-C analysis is only slightly outside of the oxygen/nitrogen requirement is the sample still invalid?

  • Technically the sample is invalid based on the specifications, however, since those specifications have changed so much over time, some regulatory groups may accept such a failure. The initial requirement was for less than 1% N2, which was changed to less than 5% and then less than 10%. The latest requirement is less than 20% N2 or 5% O2. The results are corrected to an air free basis per the formula in the method and guidance issued by the U.S. EPA. Because of this correction, the valid and invalid samples will be reported as essentially the same concentration as long as there is sufficient LFG in the sample. I believe anything with 50% or more of air in the sample is generally too questionable. I say air because there are some LFG sources where there is a very high concentration of N2 and with even a slight failure of O2 can show less than 50% combined CH4 and CO2. This is why we contact you to determine the best course of action for your samples before we proceed with the Method 25-C analysis. (back to the Method/Results FAQs section)

Can you get an additional speciation analysis after the Method 25-C analysis?

  • Yes, since the canister fraction is not converted to CO2 during the recovery process there is still sample available which may be analyzed as any other whole gas sample. There may be some restrictions on detection limits and recovery depending on the compounds of interest. (back to the Method/Results FAQs section)

Do you always correct for the nitrogen concentration reported in the Method 3-C analysis when calculating the Method 25-C concentrations?

  • No, with the new requirement allowing for N2 to exceed 20% if the O2 concentration is less than 5% the correction for N2 would bias the reported concentrations. Per guidance we requested from the U.S. EPA, we correct for either O2 or N2 depending upon the ratio of the compounds in the sample compared to ambient air. We use whichever of the two that will give the most accurate correction for air and adjust the formula in the method accordingly. This is automatically performed by the program used to generate the reported concentrations and which of the two is used is indicated on the data page for that sample. (back to the Method/Results FAQs section)

Why do you use a Calibration Limit instead of a Method Detection Limit in the determination of the cut off for reporting of the Method 25-C results?

  • We use the CL for the entire report because the MDL does not work for the NMOC fraction in the tank and we extend the use to the rest of the analysis for consistency. The reason the MDL does not work is that even though we are calibrating with only one compound, propane, there are many compounds which are classified as NMOC by the method. These compounds elute at different times so there is a large section of the chromatogram included unlike the usual specific area in which the injection of a standard would indicate the elution of a specific compound. Thus, the MDL for propane is lower than the combined MDL of propane and these other compounds. If there were a few compounds we could multiply the MDL of the calibration compound and have a reasonable and accurate MDL for them all. Much like reporting BETX using only benzene for the response factor, where you could reasonably multiply the MDL of benzene by four and have an MDL for this type of BETX analysis. However, there can be tens or hundreds of compounds which could be classified as NMOC in this manner. Since there are no specific numbers which could be used and even if there were, the MDL would be biased high for every source, we had to develop an alternative approach for our accreditation. We switched to a low calibration standard and now only report what we can identify over that concentration. The accreditation auditor agreed that was the more reasonable approach to a complex issue and thus it became the standard for us. (back to the Method/Results FAQs section)

Do you provide manometers for measuring the pre-test and post-test pressures?

  • No, we do not. This is because the Method specifies a resolution of 1 mmHg for the measurement, which limits the types of usable devices. The mercury manometers previously used are not easily shipped and the concerns over having mercury on site are significant. The choices in electronic manometers are limited due to that required level of resolution and there is a concern over how to determine if the electronic manometer is still accurate after being shipped. The inability to ensure the operation of anything we provide makes this an unsupportable option. (back to Equipment FAQs section)

Are the rotameters and gauges on the sample train calibrated?

  • No, they are not. In order to calibrate a rotameter one side must be at a constant pressure, which is the same pressure for which it is calibrated. Since the sources are under different pressures and the canister is under a decreasing vacuum, there can be no calibration. The vacuum gauge does not have the resolution to be used for anything other than an indicator, which is its purpose. To ensure proper sample volumes the rotameter is set to the approximate flow rate and the vacuum gauge is monitored for a corresponding drop in vacuum. The combination of the two prevents the need for more site specific procedures. (back to Equipment FAQs section)

To what level is the equipment checked prior to shipment?

  • Each tank, sample console, or pump is checked for operation prior to shipment to the client. Each tank and sample console is individually cleaned, leak checked, and analyzed to ensure there is no detectable carry over contamination from previous sampling. This is detailed in the report and also on the Supplies COC sent with every shipment. (back to Equipment FAQs section)

Should Teflon pipe tape be used on the connections?

  • Only those few connections which are pipe thread should have Teflon tape applied. The rest of the connections are swage fittings and those can be defeated by the use of tape, which can prevent the proper seal from being formed and cause leakage. (back to Equipment FAQs section)

What type of connections do I need to provide?

  • The sample console has a 1/8” OD tube with a Swagelok type nut and ferrule. If you can connect to a 1/8” nut and ferrule and to whatever connection the source has, everything else will connect with the console. (back to Equipment FAQs section)

Are there potential problems with barbed fittings and Tygon tubing?

  • It has been documented that Tygon tubing can lose the seal without any external indication of the event. This is generally not discovered until the Method 3-C analysis indicates the O2/N2 requirements fail and the sample is determined to be mostly or entirely ambient air. One way to fight this is to place a wire tie or some other type of clamping mechanism after the barbs to help keep the seal. You can also see this being discussed in the newsletters section. (back to Potential Issues FAQs section)

Do the landfill gas samples have to be shipped as a flammable gas?

  • Yes, unless the sample is sufficiently diluted by filling either the canister to the proper level with an inert gas prior to sampling or sufficiently pressurizing that sample with an inert gas prior to shipment. The use of a container larger than 5 L cannot legally be shipped with a flammable gas sample. (back to Shipping FAQs section)

What is the problem if we measure 5 liters of gas into a larger sized container?

  • The difference is that of a gas and a liquid. A liquid retains its volume regardless of the size container in which it may be introduced. A gas, however, expands until it fills the entire container regardless of the measured volume of gas. The pressure of the gas changes in relation to the volume of the container in which it is contained. That is why we can use the formula P1V1=P2V2 to calculate such changes.

That measured 5 L of gas introduced into a 5 L container at standard pressure and temperature would indicate a pressure of 760 mmHg. But if that same measured 5 L of gas had been introduced into a 10 L container the pressure would only be 380 mmHg because the gas would now be 10 L in volume. I know it seems a little counter intuitive that a measured 5 L of sample is not 5 L in another sized container, but that is what the DOT uses for the determination of gas volume for their regulations. (back to Shipping FAQs section)

What is the purpose of the Supplies COC?

  • This is to document the condition of the supplies being shipped, which can be added to the field sampling data if needed. This is the result of requests from auditing and compliance agencies and indicates the nominal pressure under which the canisters were shipped and the QA/QC procedures which have been applied to the supplies received. This is also detailed in the various areas of the report for those who do not choose to include this COC with the field data package. (back to Documentation FAQs section)

Do we need to take the pressure/temperature measurements in the field?

  •  As we have to take a pressure/temperature measurement when the canisters are prepared for shipment, many clients just want the same system to be used for the post-test measurements. We make the same readings, which we would compare to the field data in any case. Generally the specification for a 1 mmHg resolution for all pressure measurements proves difficult to achieve in the field, but that is standard in the laboratory. The laboratory data is generally more usable than the less precise field data. However, while not critical, field pressure/temperature data can be helpful in some instances. (back to Documentation FAQs section)

Method 25

method 25 assembly video

Method 25 FAQs

Method/Results

Equipment

Potential Issues

Shipping

Documentation


What is the difference between the Method 25 and Method 25C analysis?

  • The analysis of the canister fraction is the same, but the calculations are slightly different. The biggest difference is the trap fraction which contains all of the higher molecular weight compounds and is recovered separately. The potential is greater for these higher molecular weight compounds to be lost in the tank only sampling. (back to the Method/Results FAQs section)

Can you get an additional speciation analysis after the Method 25 analysis?

  • It is possible to perform such an analysis, but only on the canister fraction. The compounds in the trap fraction are converted to CO2 during the recovery process and cannot be identified afterward. (back to the Method/Results FAQs section)

What are the reporting limits for the Method?

  • The EPA guidance is to use Method 25 in sources greater than 50 ppmC, but in practice it can be used for lower concentrations. The analytical limits are going to be tied to the size of the sample taken and the size of the canister used. Since there are two fractions, each has different impacts. Generally, the larger the sample in the trap fraction the better the detection for that fraction due to the increased loading of organics in the trap. This is similar to the way the TO-15 sample is concentrated, but this concentration of sample is performed in the field. The canister fraction will depend on the ratio of sample to volume of the canister which will dictate the minimum dilution. For an “average” sample, a calculated concentration of <5ppmC in each fraction would be the lowest limit expected. However, collected blanks often have some reported concentration which indicate an uncertainty. These collected blanks are generally in the 20 ppmC range or lower. (back to the Method/Results FAQs section)

Why do you use a Calibration Limit (CL) instead of a Method Detection Limit (MDL) in the determination of the cut off for reporting the Method 25 results?

  • We use the CL for the entire report because the MDL does not work for the NMOC fraction in the tank and we extend the use to the rest of the analysis for consistency. The reason the MDL does not work is that even though we are calibrating with only one compound, propane, there are many compounds which are classified as NMOC by the method. These compounds elute at different times so there is a large section of the chromatogram included, unlike the usual specific area in which the injection of a standard would indicate the elution of a specific compound. Thus, the MDL for propane is lower than the combined MDL of propane and these other compounds. If there were a few compounds we could multiply the MDL of the calibration compound and have a reasonable and accurate MDL for them all. Much like reporting BETX using only benzene for the response factor, where you could reasonably multiply the MDL of benzene by four and have an MDL for this type of BETX analysis. However, there can be tens or hundreds of compounds which could be classified as NMOC in this manner. Since there are no specific numbers which could be used and even if there were, the MDL would be biased high for every source, we had to develop an alternative approach for our accreditation. We switched to a low calibration standard and only reported what we could identify over that concentration. The accreditation auditor agreed that was the more reasonable approach to a complex issue and thus it became the standard for us. (back to the Method/Results FAQs section)

Do you provide manometers for measuring the pre-test and post-test pressures?

  • No, we do not. This is because the Method specifies a resolution of 1 mmHg for the measurement, which limits the types of usable devices. The mercury manometers previously used are not easily shipped and the concerns over having mercury on site are significant. The electronic manometers are limited due to that level of resolution and there is a concern over how to determine if the electronic manometer is still accurate after being shipped. The inability to ensure the operation of anything electronic we provide makes this an unsupportable option. (back to Equipment FAQs section)

Are the rotameters and gauges on the sample train calibrated?

  • No, they are not. In order to calibrate a rotameter one side must be at a constant pressure, which is the same pressure for which it is calibrated. Since the sources are under different pressures and the canister is under a decreasing vacuum, there can be no calibration. The vacuum gauge does not have the resolution to be used for anything other than an indicator, which is its purpose. To ensure proper sample volumes the rotameter is set to the approximate flow rate and the vacuum gauge is monitored for a corresponding drop in vacuum. The combination of the two prevents the need for more site specific procedures. (back to Equipment FAQs section)

To what level is the equipment checked prior to shipment?

  • Each tank, trap, sample console, or pump is checked for operation prior to shipment to the client. Each tank and sample console is individually cleaned, leak checked, and analyzed to ensure there is no detectable carry over contamination from previous sampling. Each trap is cleaned and analyzed at a higher temperature than that used during the sample recovery process to ensure there is no detectable carry over from previous sampling. This is detailed in the report and also on the Supplies COC sent with every shipment. (back to Equipment FAQs section)

Do you always have to use a heated probe and heated filter?

  • No, in fact in cases where the gases being sampled are flammable you would specifically not want to use either the heated probe or the heated filter. There are allowances in the method for such modifications for legitimate safety issues. In the case of flammable gas sampling a more simple train is often used and without a filter as particulates are not generally an issue in these situations. (back to Equipment FAQs section)

Should Teflon pipe tape be used on the connections?

  • Only those very few connections which are pipe thread should have Teflon tape applied. The rest of the connections are swage fittings and those can be defeated by the use of tape, which can prevent sealing and cause leakage. (back to Equipment FAQs section)

What happens if I tighten the swage fittings more than ¼ turn past finger tight?

  • In the case of Teflon tubing, continued tightening can actually sever the tubing and in the case of stainless steel, it can actually cause a leak by deforming the ferrule and preventing the correct seal from forming. The best case scenario is that it will require any subsequent tightening to be similar to the worst previous instance. (back to Equipment FAQs section)

What if the pump outlet “smokes” or seems to have oil coming out?

  • That is common when large amounts of gas are pulled through the pump. This is generally only if the pump is left on and pulling ambient air through the pump down unit. If the pump remains on, closing the valve on the pump down unit will prevent this from happening. However, if the pump is turned off while under a vacuum some pump oil may be pulled into the pump down unit which can be transferred to anything else to which it is connected. Open the valve to release the vacuum when turning the pump off. (back to Equipment FAQs section)

What are the issues with filters in the inlet analysis?

  • The original requirement for the 25 mm glass fiber filter did not specify a specific level of filtration. There was an assumption that the Method 5 type filter would be used, but that was not specified. For an outlet test this concept works as expected since everything in the emission stream outside of what is classified as particulates is considered TGNMOC. For the inlet, there can be a problem in certain instances because the loading for a control device includes everything, but if the particulates are excluded the calculated loading is biased low. This would not be an issue if that which is classified as a particulate in the inlet is not modified in any way during the process, such as being made smaller, converted to a gas, or any combination thereof. In these cases the outlet may reflect a passing DRE based on the total loading, but the inlet analysis, which is excluding a significant portion of that loading, causes the appearance of a failure. We have seen evidence of this in several sources to date. As a result we provide a different filter for inlet sampling especially for those sources known to have such a problem. (back to Potential Issues FAQs section)

How significant is the bias created by CO2 in the condensate trap during sampling?

  • According the the researchers who worked on the studies, there is not a very significant bias at all. We have calculated the bias created by the trapping of different volumes of the gas stream based on the analyzed CO2 concentrations and those calculations indicate even less of a potential bias. (back to Potential Issues FAQs section)

When is it required to use a wet ice trap in conjunction with the dry ice trap?

  • Other than in the case of some of the regulatory agencies, there is no requirement to use the dual trap system, however there are instances where the use is helpful. When there are high concentrations of moisture in the source there is often a problem with ice plugs forming in the dry ice trap and stopping the flow of sample. In these cases the use of the wet ice trap to remove a large portion of the moisture will allow the sampling to continue without interruption. This also may have some effect on the trapping of CO2 by the ice crystals, which is the basis for the bias concern listed in the method. Without the formation of the ice plugs there is less chance of trapping CO2 which cannot be easily flushed from the trap prior to recovery of the sample. (back to Potential Issues FAQs section)

Are the samples considered hazardous?

  • The traps with samples should be packed with dry ice when returned and dry ice is technically a hazardous shipment. Federal Express seems to be the better choice for shipping traps in our experience, both for on time delivery and for ease in shipping dry ice. The canisters are usually not a hazardous shipment, but if the gas stream being sampled is hazardous, the canister fraction of the sample may also be hazardous. For example, the canister for a Method 25 sampling landfill gas will have to be treated exactly like a Method 25-C canister for shipping. If a canister smaller than 5 L is used, it can be shipped as a hazardous gas shipment, but all other sizes above 5 L must be diluted to the point they are no longer classified as hazardous. (back to Shipping FAQs section)

How are the pumps shipped to the customer?

  • The pumps are shipped in a cooler with separate containers of oil. Prior to use, the pump must be filled with oil to the proper level, which may leave oil in one container. If the oil is not added, the pump may seize or shatter, resulting in repair or replacement costs in addition to the need for shipping another pump for sampling. If sufficient oil is not added the pump may not operate correctly. The oil level needs to be monitored to ensure proper operation throughout the project. (back to Shipping FAQs section)

How do I ship the pump back?

  • As much of the oil in the pump as possible should be drained back into the containers used for shipping the oil to you. The pump can then be sealed in the plastic bag included in the shipment prior to being placed into the shipping cooler. This will help prevent oil from spilling onto other equipment, especially those containing samples for analysis. (back to Shipping FAQs section)

What is the purpose of the Supplies COC?

  • This is to document the condition of the supplies being shipped, which can be added to the field sampling data if needed. This is the result of requests from auditing and compliance agencies and indicates the nominal pressure under which the canisters were shipped and the QA/QC procedures which have been applied to the supplies received. This is also detailed in the various areas of the report for those who do not choose to include this COC with the field data package. (back to Documentation FAQs section)

What should the field crew record for the calculations?

  • For the calculations, the laboratory only needs the pre-test and post-test canister pressure and temperature. If you are reading a vacuum in the canister, we will also need the barometric pressure. The method requires the resolution for the pressure measurements to be to the nearest 1 mmHg. (back to Documentation FAQs section)