For each Interval/Score achievement you will need to maximize your points gain. This is easier without a partner as your individual score is needed to earn this achievement. Interval 03 is a little different from the first two intervals, since there are only a few places you can effectively use cover. Once you reach the meat locker you can earn the "Yo, Adrian!" achievement. Exit the meat locker and into another warehouse room, you can use active cover on a ground freezer to your left. Camp there and let enemies come to you to earn the Kill from Cover challenges. Other than that be sure to shoot (and kill) the psycho's with suicide vests. You can get 6 weapon challenges here (Strader, SMG, CAS, Frag/Flash, 970's).