The details of the RMZ at Hawarden are in the AIRAC which becomes valid on March 30th 2017.
The zone will also be shown on the next chart update. users will find that it appears on the next chart download.
If you are flying in that area you can comply with the requirements of the RMZ by either
speaking to them on 123.350, squawking 4607 and listening out on 123.350,
telephoning them beforehand
or have a letter of agreement between your airfield and Hawarden.
EGNR AD 2.22 will give chapter and verse.
Many thanks to the Flyer GA Forum for the heads-up