Looks like Scottsdale has/had some areas where the Municipal sewers are combined and carry sewage waste and service storm drains, very common in the North East US. The thinking in those municipalities is/was that a building only needed one sewer when connecting to a combined sewer because if storm water was conveyed separately its ultimate destination would be the combined sanitary sewer. In many of these areas there has been a lot of municipal money spent separating sewers, and then homeowners are being forced to install separate storm or sanitary piping at the homeowners cost. (It is almost always better to install new sanitary piping, avoids foundation drains.) Looks like Scottsdale either separated or is thinking ahead.
Steve