Install a new double check backflow inside the closet where the sprinkler system is. This will help in multiple ways. The only current shut off to the sprinkler system is a PIV in the outside lawn that is currently leaking by and prevents routine work at the riser from being able to be completed. It will also be allow the sprinkler system to have better protection from cross contamination with the city which may be mandated in the near future anyways.