Contaminated Ground — ruling 1

The enchanted land loses its existing land types and any abilities printed on it. It now has the land type Swamp and has the ability to tap to add {B}. Contaminated Ground doesn't change the enchanted land's name or whether it's legendary, basic, or snow.

Contaminated Ground — ruling 2

Contaminated Ground's last ability triggers whenever the enchanted land becomes tapped for any reason, not just when it's tapped for mana.

Contaminated Ground — ruling 3

If, while casting a spell or activating an ability, the enchanted land's controller taps the land for mana to pay for it, Contaminated Ground's ability triggers and goes on the stack on top of that spell or ability. Contaminated Ground's ability will resolve first.

Contaminated Ground — ruling 4

On the other hand, the enchanted land's controller may tap the land for mana, let Contaminated Ground's ability trigger and go on the stack, then spend that mana to cast an instant or activate an ability in response. In that case, that instant or ability will resolve first.

Contaminated Ground : règles, fonctionnement et interactions (MTG)

Contaminated Ground is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Enchant land Enchanted land is a Swamp. Whenever enchanted land becomes tapped, its controller loses 2 life.

How it works : Contaminated Ground

Original English text — Wizards of the Coast / Scryfall

#1June 15, 2010· Wizards of the Coast
The enchanted land loses its existing land types and any abilities printed on it. It now has the land type Swamp and has the ability to tap to add . Contaminated Ground doesn't change the enchanted land's name or whether it's legendary, basic, or snow.
No other card is named in this ruling.
#2June 15, 2010· Wizards of the Coast
Contaminated Ground's last ability triggers whenever the enchanted land becomes tapped for any reason, not just when it's tapped for mana.
No other card is named in this ruling.
#3June 15, 2010· Wizards of the Coast
If, while casting a spell or activating an ability, the enchanted land's controller taps the land for mana to pay for it, Contaminated Ground's ability triggers and goes on the stack on top of that spell or ability. Contaminated Ground's ability will resolve first.
No other card is named in this ruling.
#4June 15, 2010· Wizards of the Coast
On the other hand, the enchanted land's controller may tap the land for mana, let Contaminated Ground's ability trigger and go on the stack, then spend that mana to cast an instant or activate an ability in response. In that case, that instant or ability will resolve first.
No other card is named in this ruling.