Seeing the irrigation leak reminded me of how a plumber I've worked with told me to use the meter to check for a leak. On the meters here in San Diego they have the numbers in an odometer like window and below that there is a small triangle. The small triangle measures really small amounts.
He would shut off the water, mark right next to one of the triangle points and then come back a little later and see if it had moved. If it had there was a leak somewhere.
Anywhoo, congratulations on finding the likely culprit!