Strange combination of questions. :)

did the workers ever find anything intersting while digging?
I'm sure they did sometimes.

how deep in the ground do residential streets go?
Why do you ask?
And it probably varies greatly depending on the soil type in the area and the weather (ie. whether freezing/thawing is a factor)

Looking to bury someone? ;) lol

I started digging for a 6x10 ft. small garden & removed sod & went down about 15 inches where it gets kind of sandy. I found small pieces of course concrete, rather poor quality but few pieces like a small corner piece & some pieces like it had been a foundation for a small building. Several pieces of clay reddish pottery too heavy & not like what you get today. I've been here about 46 yrs so wonder who was here before me. Aunt lived in area & it had always been huge vacant lot until builder came in & built some houses. Streets can be different thicknesses depending on weight of vehicles that travel on them also. Weather would also factor in. In other states I've known of friends digging on their property & digging up bodies ( which they put deeper or moved so wouldn't be under building.(Indians) My dad found many artifacts as a kid in Midwest. GF found the barrel where they burned garbage & kept digging & found all kinds of glass objects & ceramics from Japan before the war.On news not long ago a couple found a treasure on their property, don't know if they got to keep it or not. From a robbery or something yrs ago & gold coins & things like that.

We found some dinosaur bones.

I never find good stuff :(

but I keep hoping!

I was planting an apple tree in the former pasture behind my house and found several dozen pieces of spent ammunition. It's been several years, and I no longer remember exactly what they were identified as: small and rusty.

When I was a teenager in Connecticut (many more years ago), a 3' area of our gravel driveway turnaround suddenly sank a foot or two. My brother and I thought it would be worth investigating, but my father wouldn't let us look to see if we could find treasure -- or a reason for the subsidence.

I don't know about under the basement; it was dug long before 1952. I do know the sewer and water mains are 6 feet, or more, deep.

When the workers dug the hole to install an egress window in the basement, they dug down 12 ft. We didn't see anything except topsoil and sand all the way down. As they were filling it in I made a joke about my MIL, and then remembered I had the earthy remains of my pet budgies (hermetically sealed) in the game freezer. They died while we lived on base; we wanted to wait to bury them at the new home.

I brought them out and buried them at about the 5' mark. They are in a plastic box with their favorite toys, treats, and a note just in case someone every "finds" them.