Firstly, please turn your caps lock off.

Secondly, you need to get a copy of your local electrical standards and regulations relating to your particular site. The country and application-specific details are located within them (including the required earth resistance limits and acceptable pit construction, fill and termination methods which also depend on the soil composition and weather). There is no single magic formula or value, site design depends on a number of factors and site and country dependent requirements.

There is plenty of general information on the internet like the following, but you will still need to consult your local standards and regulations to ensure your site is legally compliant.

http://us.fluke.com/usen/Solutions/earthground/GroundingBasics.htm

Simple:

1. Turn off Caps Lock
2. Follow the local electrical codes.