Authors' reply

Dr. Crane raises a number of interesting points, but these serve to support not distract from, the conclusions of our paper. Without independent verification that the source inputs used are appropriate and sufficient, the results of EPA's Chemical Mass Balance Model (CMB) cannot be used to verify the contribution of a given source. Neither Van Metre and Mahler's (2010) nor Crane's (2014) use of CMB demonstrates whether refined tar sealers are actually a source in any urban sediment. When using the results of receptor models to promote source control policy, care must be taken to clarify the underlying assumptions and uncertainty.