Seems he may have gotten those numbers from this post in 2009:
If you google Raleigh water Report it will take you here:
There are a few different reports to click on, but there are essentially 2 treatment plants in Raleigh.
Here are the various numbers...scattered in abt 4different places on that site.
EM Johnson - Raleigh, NC (Falls of Neuse Rd)
Chloride: 14ppm(winter), 21ppm(summer)
Avg ph 8.4
DE Benton - Garner, NC
Avg ph ?
The use of 3-4ppm is accurate.
I have no idea how/if they are mixing them together. The Garner plant went online ~2 years ago Could always make a phone call or two, contacts are listed on that page as well.