In a blender, combine water, salt, brown sugar, orange juice concentrate, cumin and oregano. Blend until smooth, about 30 seconds. Transfer mixture to a large bowl.

Add ice and stir until water temperature reads no more than 45° on an instant-read thermometer. Add pork roast, then cover and refrigerate for 12 to 24 hours.

Preheat oven to 375°.

Remove pork from brine and pat dry with a paper towel; discard brine.

Rub olive oil onto surface of meat, then season it with pepper. Roast on a rack in a roasting pan until internal temperature reads 150° on an instant-read thermometer inserted at the center, about 1 to 1¼ hours.

Remove roast from oven, cover loosely with foil, and let stand for 10 minutes before slicing.