Leachate is produced as:

Rainwater absorbs water-soluble compounds in layers of trash
Plastic flows into ponds and streams
Toxic waste is emptied into ponds and streams
Metal comes into contact with water

Leachate is typically produced as rainwater percolates through layers of trash and other waste material, absorbing water-soluble compounds along the way. This leachate can contain a range of chemical contaminants, depending on the type of waste it has come into contact with. So, the correct answer to your question is "Rainwater absorbs water-soluble compounds in layers of trash".