Maybe? But you'd run into some difficulties
As screamline mentioned, there are some spells that could help you out (I especially agree that Hallow could be helpful). I'll add to them with a couple of other mentions:
Dispel Magic: If the contagion or poison in the area is a result of a spell or magical effect, then Dispel Magic may help remove it.
Purify Food and Drink: This spell can purify all (nonmagical) food and drink of disease or poison within a 5 foot radius, up to 10 feet away. If the contagion was entirely within a small (very small) body of water, a large number of low level casters could cast this spell simultaneously, each choosing a different part of the location. Most usefully, this is Ritual spell. So a single spellcaster could conceivably cast this spell again and again (taking ten minutes and six seconds each time) over the course of a day, diluting the poison so much that it was no longer harmful.
In spite of these spells being useful, I have to stress that there is one major element of magic that may impede any magical attempt to free an area of pollution:
Cover excludes area of effect
In the rules on area of effect, it is stated that (PHB, p. 204)
A spell’s effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn’t included in the spell’s area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.
Many DMs would consider the ground to give total cover to anything underground. So many spells which would remove disease, poison, or some other pollution from an area might only do so on a surface level. For example, if you were to cast "Purify food and drink" on an area suffused with poison, you might purify the plants growing there (since part of them are above ground, they do not have total cover), and any above ground water. But you would not necessarily purify the poison in water bellow the ground.
Many similar spells could have their effects blocked by the solid earth. Although there are some spells that explicitly penetrate barriers, most of those are divination spells, rather than ones which could heal or destroy something.