Yeah, the .51 ppm is the correct number.
As BigEd said chlorine will evaporate from standing water and be driven off quicker by boiling.
The water quality report is a quick look to see where you are at in contaminates. The water quality analysis, which is often not posted for smaller cities, gives you all the secondary levels of minerals in the water. You can often request this from your water authority.
If your water is similiar to Portland, and even Seattle for that matter, you have very soft water that can benefit from mineral additions for certain styles. I wouldn't worry too much starting out, but when you are ready read chapter 15 of the online version of how to brew. It can get a little technical.
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