This is the email I received from Organic Valley:
The shelf stable milk products reports tree nut allergens on the same line and in the facility. It also appears a number of processing facilities which package the Half Gallons and quarts also have peanut and/or tree nuts allergens either present at the facility or present on the line at the facility.. They are as follows: 27-421, 36-8550, 51-4109, 06-01, 18-388,36-5631.
The above plant numbers can be found on the top of each carton of product-they may or may not be hyphenated.