I'd be surprised if it was alkaline. A RIS grist is typically fairly acidic due to the roast and other accessory grains. I see that you are in Chicago and their lake water has relatively modest alkalinity. If anything, I suspect that a beer made with that water might end up a little more acidic than desirable.
I could also imagine that overly roasty or tannic could be a descriptor under this situation. A sign of an overly alkaline (high pH) condition would be a dulling of the malt flavor and a coarseness of the hop bitterness and flavor.