I'm also buying at Pulte, and have done a lot of research, including talking to an independent practicing California environmental engineer with a focus on intrusion barriers. Here's what I determined. The entire Great Mall area (and many sites in the bay area including parts of Mountain View) are on SuperFund sites. All the new construction around there (including Dr Horton Center pointe and KB etc.) all have vapor barriers (I've asked them).
The spill was VOC/PCE in the 80s and the chemicals are still evaporating now and the next couple decades. It is being monitored regularly (documents available at the water board site) and all readings show it is decaying. Each home is protected with Geo-Seal, which is a sandwich of vapor barriers under the foundation that'll stop vapors dead in it's track. Read up on it and watch youtube videos. This stuff is used in hospitals, military complexes, etc. The vapors could be 1000x times stronger than the current readings and geo-seal wouldn't even break a sweat. The only way vapors can get in the home is if there is a building defect in the barrier.
I asked the PE (engineer) about seismic activity and he said this: "Geoseal bonds very strongly to the underside of the concrete slab that gets poured onto it. It is also a flexible enough material (it can stretch before breaking) so we generally do not consider it a risk to break in an earthquake. Personally I think the only way it tears is if the slab itself breaks and in that case you would have bigger structural problems and not be living in the structure anyway." And by the way, Pulte has post tension slab which is apparently pretty amazing.
Again, there are many homes in the Bay Area on superfund sites with none of this protection!
The city of Milpitas is putting a school K-6 in the vicinity that'll open up in 2018. Would they do that if the vapor was a concern?
I asked my agent what he thought about the disclosures and he said that tons of homes come with disclosures. What's important is what the disclosure is, not that it exists. The disclosure is for all future buyers and renters, everyone living there should know not to dig holes through the foundation! That is a good thing.
I was very concerned with the vapor stuff but now not at all. You're near BART, VTA, a new school, the Great Mall, The Fields (new Santana Row wanna-be).