If you do not have a shutoff below the dirt level or at the house you can pack dry ice around a short section of pipe and that will freeze the water and make a plug .
I have done this with galvanized and copper never tried plastic . Only an inch or 2 being frozen will plug the pipe and not break it. I have had to do this when I had to replace the main shutoff valve.
The blue cap is just the cover over the meter glass where the useage reading is. It looks like you have a meter riser installed. It is used when the city needs to raise the height of the meter. If you dig around on the City side you should find the city shut off. There is one there for sure. You will find a brass bar about 1.25 inch long and about 1/2 inch wide. If you want to shut it off, get a large cresent wrench and adjust it to fit the brass bar. Stand the wrench up and put a large screw driver through the hole in the wrench handle and carefully turn clockwise. Should turn about 180 degrees. Don't force it too much as it is brass and you can snap it off. And yes you are not supposed to be turning it, If you break it, you pay for the repairs. 27 yr's working for city water dept