I believe the one who asked the question knew that, but was wondering how the Boulderbadge increases the attack stat, etc.
In the older pokemon games, they set a cap on the EVs a pokemon could aquire. Obtaining the corresponding badge removed that EV cap and makes the max EVs the normal 255, thus allowing the pokemon's full potential to be realized.
I do not know what the max EV for each stat would be without the badge that removes the cap. However, it's a common misconception that badges grant EVs; please know this is NOT the case. Also, this cap is removed in the 4th generation games (I guess they thought it annoying/unnecessary).