We have used VLBI data and resulting images from two epochs separated by 15 months to study the radio supernovae and compact masers in the two colliding nuclei of Arp 220 (IC 4553), an Ultra-Luminous Infrared Galaxy (ULIRG) located at a distance of 76 Mpc (z = 0.018). Arp 220 has 49 confirmed radio supernovae in the two nuclei, and we have discovered OH absorption and maser amplification of the pointlike supernova continuum emission in both the 1665 and 1667 MHz lines. A question we seek to investigate is whether such features originate in material local to and associated with the supernovae, or whether they are due to chance lines of sight through an unrelated diffuse foreground OH medium. We look at these possibilities by analyzing the time variability and spectral properties of the features. We interpret our results in the context of the broader OH megamaser galaxy phenomenon.