We own a property management business in the Roaring Fork Valley and we also own a Welding Company- so we know remodels and all the joy it can bring!

They'll be welded onto cylindrical foundations. 

Let say a handyman does some welding and starts a fire.

If the roof is leaking it is because one of the seams wasn't welded properly and is allowing water in.

here are a few more contacts.....we have a local guy that buys old shipping containers & makes them into smaller dumpsters but that's a lot of do you yourself welding etchttp://www.bearicuda.com/enclosures/Industrial-plastic-cubic-yard-waste-dumpsters-receptacle-trash-bins.phphttp://www.ameri-kan.com/ http://www.par-kan.com/http://www.poynetteironworks.com/index.asp

I would worry about going under the sidewalk cuz you might create a pocket that might collapse.If it was me I would take a piece of oil feild pipe and weld a pointy cap on the end, slege it under the dirt sidewalk section, cut the cap off the end, and fish the new waterline through that way you don't risk your sidewalk caving in from the hole you would have dug. saves the sidewalk, time, and money...If you do but a new sewer line in, i would just pull up the sidewalk...

There were some metal bed frames and staircase railings that needed welding. 

They all needed a couple of quick spot welds in places and half a can of gloss black spray paint, and they looked and performed like new.

@Steve Kontos ; Truer words have never been spoken, I'm a fairly handy person when it comes to mechanical things (painting cars, welding panels, fabrication) but had never done construction work.

The local "hackerspace" (like learning how to weld and do carpentry and stuff) moved there and a lot of art studios and other hip things were all developing down there.