Cook pasta to package. Drain and rinse with cold water. Set pasta to the side make sure all water is removed.
In a big bowl combine mayo, buttermilk, dill, garlic powder, salt and pepper. Stir to combine. Stir in Pasta, celery, cucumber, scallions and sweet pepper.
Cover and chill for 2 - 24hours.
If a little dry just before serving add SMALL amount of buttermilk.