[en] In 1992, the US Postal Service (USPS) entered into an Interagency Agreement with the Department of Energy (DOE) whereby DOE would provide technical assistance in support of the USPS Radon Assessment and Mitigation Program. To aid in this effort, DOE tasked the Hazardous Waste Remedial Actions Program (HAZWRAP), which is managed by Martin Marietta Energy Systems, Inc., for DOE under contract AC05-84OR21400. Since that time, HAZWRAP has developed and finalized the sampling protocol, mitigation diagnostic protocol, and the quality assurance and quality control procedures. These procedures were validated during the Protocol Validation (1992-1993) and Pilot Study (1993-1994) phases of the program. To date, HAZWRAP has performed approximately 16,000 radon measurements in 250 USPS buildings. Mitigation diagnostics have been performed in 27 buildings. Thus far, 13% of the measurements have been above the Environmental Protection Agency action level of 4 pCi/L. This report summarizes the pilot program radon testing data and mitigation diagnostic data for 22 sites and contains recommendations for mitigation diagnostics