  We consider excitation spectrum near a twin boundary in an orthorhombic $d+s$
superconductor. The low-energy spectrum is highly sensitive to the presence of
the small amount of s-wave component. Robustness of the bound states at the
Fermi level with respect to impurities and an extra boundary potential is
investigated. The role of Andreev transmission process for the low-temperature
thermal conductivity across twin boundaries is studied for an impure
superconductors. At very low temperatures the bulk part and the twin boundaries
part of the thermal conductivity have similar linear-$T$ dependences, whereas
at intermediate temperatures the two contributions behave like $T^3$ and $T^2$,
respectively.
