Triangle NoTES - May 2011

It seems that not everyone has heard the news about Tedlar bags, so I thought this would make a good subject for the newsletter. Dupont has stopped manufacturing the Tedlar material so the inventory of the bags will be limited to what the manufacturers have on hand. There are some materials which are claimed to be a replacement, but there seems to be none which are as popular as the old material for various reasons. Tedlar had many uses other than sampling bags, so the replacement material may not have been compared with the same application, so there may be a bit of a learning curve to follow.

I asked the EMC about their position on the replacements, but they have not finished looking at the stability data on the various possible replacement materials. I was told the recovery study data for any Method 18 work would determine whether that material was acceptable or not. I suppose a similar review would be in line for any other use, if the current supply is exhausted prior to any official guidance being issued. If there is any reason for concern, you may want to stock up on the bags while you can, which may allow time for all of the options to be better examined before you have to decide.

A secondary point I wanted to share was the stability of the vacuum in the canisters, especially with the landfill gas projects where any leakage may be an issue. We had a client who had one of those projects which keeps getting put back a few days as we have all seen so often. This case, however, was a bit worse than most and the project waffled for six months. The client had the sample canisters for the whole period and I was concerned over the potential for leakage. We do an extended leak check of the canisters that far exceeds the requirements of any of the methods, but still six months is a very long time even for a minuscule leak. After we had the client return the canisters and checked them out it turned out that I should not have been so worried. Out of ten canisters, one showed no change from the ~325 mmHg absolute pressure we had previously recorded prior to the six month wait. Three of the canisters showed a difference of 1 mmHg, four showed a difference of 2 mmHg, and one showed a difference of 3 mmHg after the six months. All of these would be considered equivalent as there was some potential for a similar pressure change in connecting and disconnecting from the pressure measuring devices. The only canister with a real issue had leaked 426 mmHg over the six month period, but was still not quite to atmospheric pressure. That is a change of ~2.33 mmHg a day, which would still pass both our internal leak check criteria and the criteria set forth in the methods. It seems to indicate about 90% of the canisters should be fine with long term storage, and all should work for more normal shipping and storage time frames.

Wayne Stollings

Triangle Environmental Services, Inc.