My advice is to build your environment policy from the bottom up. Instead of starting with vague concepts, it is more meaningful to start with what is possible and cost of that. This prevents the inhibition of responsibility and creativity of your employees. This in turn leads to better and more cost-effective solutions, ensures that no promises are made that cannot be kept and that your environmental management plan is in alignment with the other business objectives.
Ultimately, it comes down to the delivery of your promises. You can’t do any more than that, and you won’t get away with any less.