  We present analysis of high spectral resolution NIR spectra of CO and H$_2$O
in comet C/2009 P1 (Garradd) taken during its 2011-2012 apparition with the
CSHELL instrument on NASA's Infrared Telescope Facility (IRTF). We also present
analysis of observations of atomic oxygen in comet Garradd obtained with the
ARCES echelle spectrometer mounted on the ARC 3.5-meter telescope at Apache
Point Observatory and the Tull Coude spectrograph on the Harlan J. Smith
2.7-meter telescope at McDonald Observatory. The observations of atomic oxygen
serve as a proxy for H$_2$O and CO$_2$. We confirm the high CO abundance in
comet Garradd and the asymmetry in the CO/H$_2$O ratio with respect to
perihelion reported by previous studies. From the oxygen observations, we infer
that the CO$_2$/H$_2$O ratio decreased as the comet moved towards the Sun,
which is expected based on current sublimation models. We also infer that the
CO$_2$/H$_2$O ratio was higher pre-perihelion than post-perihelion. We observe
evidence for the icy grain source of H$_2$O reported by several studies
pre-perihelion, and argue that this source is significantly less abundant
post-perihelion. Since H$_2$O, CO$_2$, and CO are the primary ices in comets,
they drive the activity. We use our measurements of these important volatiles
in an attempt to explain the evolution of Garradd's activity over the
apparition.
