  Dwarf galaxies are found to have lost most of their metals via feedback
processes; however, there still lacks consistent assessment on the retention
rate of metals in their circumgalactic medium (CGM). Here we investigate the
metal content in the CGM of 45 isolated dwarf galaxies with
$M_*=10^{6.5-9.5}~M_\odot$ ($M_{\rm 200m}=10^{10.0-11.5}~M_\odot$) using {\it
HST}/COS. While H I (Ly$\alpha$) is ubiquitously detected ($89\%$) within the
CGM, we find low detection rates ($\approx5\%-22\%$) in C II, C IV, Si II, Si
III, and Si IV, largely consistent with literature values. Assuming these ions
form in the cool ($T\approx10^4$ K) CGM with photoionization equilibrium, the
observed H I and metal column density profiles can be best explained by an
empirical model with low gas density and high volume filling factor. For a
typical galaxy with $M_{\rm 200m}=10^{10.9}~M_\odot$ (median of the sample),
our model predicts a cool gas mass of $M_{\rm CGM,cool}\sim10^{8.4}~M_\odot$,
corresponding to $\sim2\%$ of the galaxy's baryonic budget. Assuming a
metallicity of $0.3Z_\odot$, we estimate that the dwarf galaxy's cool CGM
likely harbors $\sim10\%$ of the metals ever produced, with the rest either in
more ionized states in the CGM or transported to the intergalactic medium. We
further examine the EAGLE simulation and show that H I and low ions may arise
from a dense cool medium, while C IV arises from a diffuse warmer medium. Our
work provides the community with a uniform dataset on dwarf galaxies' CGM that
combines our recent observations, additional archival data and literature
compilation, which can be used to test various theoretical models of dwarf
galaxies.
