In doing some research on this topic, I came across a majority of questionable sites who were obviously pushing an activist agenda for one reason or another and whose claims were largely unverifiable or contradictory. Apparently this is an issue where a lot of ideologies converge (animal rights, vegetarianism, anti-corporate, natural foods proponents, anti-chemical/preservative, etc) It was indeed difficult to come up with verifiable, credible information, but I did manage to find some sources.
From what I have managed to find, this question is mainly directed toward the practices of one company known as BPI (Beef Products Inc) which utilizes a controversial procedure to extract lean beef protein from slaughterhouse/meat packing scraps and render it fit for human consumption. This is then sold as filler to beef distributors around the world and is mostly used in ground beef and hamburger. A short breakdown of that process is here. That is all I'm going to say regarding that process, because it could quickly get off topic, this question pertains to the ammonia levels.
During this process, BPI exposes the surface area of its meat to a pH raising gas, which is typically ammonia (but does not have to be). This is done in order to kill microbes or slow their growth. Again, we could go into whether ir not this is an effective process, but that is not the question here.
After some searching I found the actual patenet filed for the process of applying ammonia gas to beef. This is the process apparently used by BPI, the company in question and done apparently to raise the pH of the meat in order to prevent or slow growth of bacteria. The process has also been summarized on a previous version of BPI's web site.
I may be missing something, but I see no way that this process could account for 30% ammonia content of the beef that comes through the process, let alone 30% of the weight of the finished ground beef products with which it is mixed.
Regarding the USDA testing process for ammoniated beef, I have found some links which may prove helpful. Here is one that outlines some of the process, taken directly from the USDA, it includes steps for testing of both ammoniated and non-ammoniated beef. I could not find a definitive limit for how much would be "allowable" and I assume that this is probably due to the fact that ammonia occurs naturally in most meats and proteins, and ammonia levels will change as the meat ages during storage and especially as it spoils due to deamination of amino acids.
However, the most commonly used figures I have found tend to hover around 30mg per 100g of beef