Please list the zip_codes of all the residential areas in Huntingdon county with over 30 employees.
over 30 employees refers to employee > 30; 'HUNTINGDON' is the county
SELECT DISTINCT T1.zip_code FROM zip_data AS T1 INNER JOIN country AS T2 ON T1.zip_code = T2.zip_code WHERE T2.county = 'HUNTINGDON' AND T1.employees > 30