the wireless requirement is really interesting .. it will require a decent wifi signal at the valve, which is likely not above ground ..
You could get 5V DC from the AC power for the valve.. but this will require some AC-> DC and as mentioned waterproof box ..
To test, I would put a basic ESP8622 setup into the underground valve box with a long power cable and check if you can setup / ping the ESP through WiFi before I would go further.
Karl