We recently discovered that the National Workgroup on Leak Detection Evaluation (NWGLDE) moved their website over to NEIWPCC. See https://neiwpcc.org/nwglde/
You might want to make a note because the previous link of 20+ years did not leave a forwarding address.
As you may know, this group provides a catalog of all the third party certification standards for leak detection equipment that are governed by the underground storage tank rules nationwide.