De or het grondontsmetting?

The correct Dutch article is:

de grondontsmetting

Rule Words ending in -ing: almost always de. See the rule

How to use grondontsmetting

the grondontsmettingde grondontsmetting
this grondontsmettingdeze grondontsmetting
that grondontsmettingdie grondontsmetting
our grondontsmettingonze grondontsmetting
your grondontsmettingjouw grondontsmetting
every grondontsmettingelke grondontsmetting
which grondontsmetting?welke grondontsmetting?
a big grondontsmetting / the big grondontsmettingeen grote grondontsmetting, de grote grondontsmetting