My grandson who is 6 weeks old and passes very foul smelling gas very often on a daily basis. what is causing this and should we be concerned?

Not particularly : The gas a kid passes is a combination of air they swallow during feeds and that created by gut germs acting on their gut debris. Gut germs feed on debris not fully absorbed by the kid & varies with the feed and the type of gut germs. They do make probiotics that infants can take which may alter the smell, but it has no importance beyond the offensive nature of the smell.