  A single crystal niobium thin film was grown using molecular beam epitaxy on
a c-plane sapphire wafer. Several samples were fabricated into dc resistivity
test devices and coplanar waveguide resonator chips using the same
microfabrication procedures and solvent cleans. The samples were then subject
to different acid cleaning treatments using different combinations of piranha,
hydrofluoric acid, and buffered oxide etch solutions. The different samples
expressed changes in dc resistivity in the normal and superconducting states
such that the low temperature resistivities changed by more than 100\%, and the
residual resistivity ratio dropped by a factor of 2. The internal quality
factor of coplanar waveguide resonators measured near 5~GHz also showed
significant variation at single photon powers ranging from 1.4$\times 10^6$ to
less than 60$\times 10^3$. These changes correlate with the formation of
surface crystallites that appear to be hydrocarbons. All observations are
consistent with hydrogen diffusing into the niobium film at levels below the
saturation threshold that is needed to observe niobium hydrides.
