Robots are being increasingly used in the fight against highly-infectious diseases such as Ebola, MERS, and SARS-COV-2 . Many of the robots that are being used employ ultraviolet lights mounted on a mobile base to inactivate the pathogens . However, these lights are often mounted in a fixed configuration and do not provide adequate decontamination of horizontal surfaces, which can be a major source of cross-contamination . In the paper, we describe the design, implementation, and testing of an Ultraviolet Germicidal Irradiation (UVGI) system implemented on a mobile manipulation robot . A human supervisor designates a surface for disinfection, the robot autonomously plans and executes an end-effector trajectory to disinfect the surface to the required certainty, and then displays the results for the human supervisor to verify . We also provide some background information on UVGI and describe how we constructed and validated mathematical models of Ultraviolet (UV) radiation propagation and accumulation . Finally, we describe our implementation on a Fetch mobile manipulation platform, and discuss how the practicalities of implementation on a real robot affect our models.