请教:买lot䢖房刚签完合同几天却发现地基里有underground storage tank (UST)

Near tank soil has VOC contamination。UST contain oil film in liquid-VOCs, such as benzene, toluene and more. The 7 VOC are those presented in gasoline and paint.

Builder will hire enironmental firm to remove the tank and clear up due to leaking.
Should we still keep this deal? Or swhich a lot? Or back off?

If back off, can we get our deposit (几万）back?

It is safety concern, long term.
应该怎么对待此事？
谢谢。