How long does the Ebola virus remain infectious on contaminated items or surfaces?
This really depends on the environment, one study (listed below as reference 1) found that the Ebola virus can survive under ideal conditions on flat surfaces in the dark for up to six days - see the figure from the same publication. 



However, the virus is quite sensitive to UV radiation (see reference 2 for all the details) and most viral particles are likely to get inactivated within relatively short time. It might still be possible to get positive tests for Ebola from really sensitive PCR-based tests, but these are most likely not infectious anymore. The CDC lists common bleach (or any other routinely used disinfected) as a good way to get rid of Ebola viruses.

References:


Persistence in darkness of virulent alphaviruses, Ebola virus, and
Lassa virus deposited on solid surfaces
Sensitivity to ultraviolet radiation of Lassa, vaccinia, and Ebola
viruses dried on surfaces