I have been asked several times now as to whether our filter holders meet the specifications for Method 25. The answer is a simple, yes they do. Some have questioned whether we have actual Gelman filters or just an equivalent by another manufacturer because they did not look like the current model of Gelman filter being sold. For the sample consoles we produced, the filter holders were purchased through Fisher Scientific over two decades ago and were referenced as Gelman filter holders. We not only purchased the holders for our consoles, but also purchased a few which were modified to be used as an in stack filter and spare units for repairs. Since these are fairly robust filter holders with few points of failure, the last of the units were purchased in 1998. I cannot speak as clearly for the Nutech sample consoles as they were purchased as completed units, along with a few spare filter holders from Research Triangle Laboratories in the early 1990s. There are filters using the older Gelman design which are also currently available, such as the Advantec MFS holder.
We have posted a large picture of the inside of the filter box of the sample consoles we constructed on our website for reference. It shows the filter holder and the thermocouples to measure the gas temperatures as specified in Method 25. I have included the web address for the equipment page. The picture is at the bottom of the page. You can see the tee where the probe attaches with the exposed probe
thermocouple pointing to the left. The thermocouple for measuring the gas temperature going into the filter is a little harder to see as it is perpendicular to the camera in the tee attached directly to the filter housing inlet. As both of these measure the gas temperature, the temperature of the exterior of the probe and the surfaces of the filter box will be much higher in order to attain the correct temperature in the gas flowing through.
This situation has brought about other questions concerning compliance with the method requirements and modifications to the method. Most of the modifications we have enacted are tightened QA/QC measures.
For example, we increased the size of the oxidation catalyst and slowed the flow to increase residence time for the sample because we were seeing incomplete conversion of the NMOC in sources where Method 25 had been used but which were not the initial target sources. The intent of the method was better met by this modification as the EMC agreed at the time. The lowered rate of flow does increase the time required to perform the trap recovery, but as there is already a substantial amount of time required to recover the trap following the method guidelines, this increase is not that significant and the resulting benefits far outweigh the added time. The procedures we saw at Research Triangle Laboratories when it was still in operation focused on the minimal amount of time for recovery and, I believe, as a result more potential errors were introduced than benefits. The use of the “warm purge” during the trap recovery to transfer some of the sample from the sample trap at ambient temperature to a second trap on dry ice seemed to introduce carryover between samples at times. Considering the specified flows would require hours for the sample tank and the Intermediate Collection Vessel (ICV) to reach the pressure required to perform an analysis this did not introduce a significant time saving process. Of course, there could be other modifications in addition which could reduce the time, but more and more such modifications make for more and more concerns considering the number of various sources for which Method 25 is used and more for which it could be used. We opted to have multiple recovery systems which allowed for an increased throughput and more efficient labor usage without more modifications.
We also bake out the traps and individually analyze each and every one at a higher temperature than is used for recovery to help insure there is less chance of carry over. The method only requires a completed recovery of the trap at 200 C to be used for later sampling, where we additionally bake them at 300 C and then QC them at 250 C.
We perform a QC analysis on each and every tank prior to use, which is not addressed in the method at all. We clean them with multiple series of evacuation and filling with air prior to being evacuated to <10 mmHg and leak checked, usually over night, to ensure they are not leaking. We have had tanks sent out at <10 mmHg and ~325 mmHg absolute pressures kept by clients for over six months with no change in the pressure by most of the tanks. A very small percentage will leak over that time, which is why we still encourage the tanks to be sent to the site under positive pressure to ensure any contamination possibility is a low as possible. Even though our leak check procedure is much more comprehensive, a field leak check is also suggested because we are dealing with mechanical seals which can fail without notice.
We perform a QC analysis of each and every sample console after we have cleaned and leak checked them to much more stringent requirements than the method requires. This helps to ensure they are more easily used in the field but also allows us to provide a Chain of Custody (COC) for the equipment to document the levels to which they were checked prior to shipment into the field. This COC can be retained and included in the field testing report if required.
These additional measures to the method are part of how we were able to pass the EPA audit at the lowest documented level, which was 50.2 ppmC. This was before the program was shut down in the hopes it could be privatized, which unfortunately still has not happened. Total audits are the best way to determine if there are problems with the sampling, analysis, or both as the pass/fail data has indicated in the past. From what I was told by the people following the audits, our record showed a marked improvement over prior audits, which resulted in a request to visit our facility to see what we were doing differently. The difference was just that we had returned to the method requirements and eliminated the modifications which had been introduced as undocumented improvements over time. I cannot speak to our audit statistics as I never monitored them due to the way the audit program reused some of the audit cylinders and my desire to eliminate even the suspicion that we could guesstimate the concentration. It is always possible to cheat if one desires, so we try to ensure there is ample documentation and cross checking to eliminate any question concerning our results. Our company reputation, the reputation of our employees, and my personal reputation is far too important for me to risk, which is why we take every effort possible to provide the best quality results possible.
I do not have any information on the 301 validation for the changes as that is being handled internally by the proponent of those changes. To my knowledge, he is handling all of the sampling and analysis comparisons to be turned over to the EMC for review.
Triangle Environmental Services, Inc.
P.O. Box 13294 122 US Hwy 70 E
Research Triangle Park, NC 27709 Hillsborough, NC 27278
(919) 361-2890 (800) 367-4862 Fax: (919) 361-3474