Source separation is the other extreme, where each material is cleaned and sorted prior to collection. This method requires the least post-collection sorting and produces the purest recyclates, but incurs additional operating costs for collection of each separate material. An extensive public education program is also required, which must be successful if recyclate contamination is to be avoided. In Oregon, USA, its environmental authority Oregon DEQ surveyed multi-family property managers and about half of them reported problems including contamination of recyclables due to trespassers such as transients gaining access to the collection areas.