Landfill area must sink no matter how much pressure they flat the area. Like the concrete floor, it must crack, if it is on the landfill area, the crack will be more serious. The developer puts more $ to undergroud pipes to let waste water and methane gas release, or planting more trees to remove sting smell. You can know it is not short term problem.

It is normal for new development with higher methane gas as they dig up the ground and let the “aged” gas release. How much gas and waste water can be released in long term as the fresh trash+dirt keeps decaying underground?

If you buy the house there, surely the developer says it is not a problem. If the buyer knows it is landfill with dirt, the resale price ???

Power tower is a problem. It depends how big it is and the distance to your home. It is common sense that people live closed to high voltage power lines get cancer easier. Even your doctor won’t allow you to have x-ray too often. Do you want to pick a house to have “x-ray” everyday? It is up to your judgement.