This is knee jerk fear mongering.
The bill states that the law wouldn't supersede any statutory requirement (such as protection of PII).
The bill also specifies that the data should be presented so that "substantial reproduction" of the study is possible. It doesn't specify that reproduction needs to be done. It doesn't specify "100% independently verified."
These guys are asking the EPA to follow similar guidelines the FDA imposes on companies in evaluating a new drug or device. The FDA maintains a public database of filings, it's really interesting to go through. The bill is even closer to NIH publication guidelines. This is not just an anti-EPA thing here (granted, I'm sure there's some of that going on), this is getting the EPA in line with other health oriented agencies.
As for de-identification of the government owned part of the data, the Republicans are right. That should take an expert a couple of days, but it does cost money (there are many businesses who specialize in this kind of thing). The CDC doesn't leave money sitting around (I'm kind of shocked they leave PII medical records sitting around though, my company can't do that). They probably just can't pay to de-identify the data, and don't know if they can legally trust a Congressional committee to handle the data properly (probably they can't). So they're stuck without funding. The bill specifies $1M to do this, but given all the government offices involved, that's probably not enough.
Here's the real issue: The government doesn't actually own all the data the EPA is referencing, so the EPA can't publish it or share it. This is all to put pressure on the EPA to ask Harvard and ACS to share the data.
The data the government makes decisions on should be public. It shouldn't be acceptable for a scientist to say "trust me, I did the analysis correctly." We're not perfect, we make mistakes. Peer review is broken, we can't rely on that to catch errors. Open things up a bit more, and we'll get better conclusions.