A mercury leak containment device for removable attachment to an existing natural gas meter valve includes a container having a top opening for enclosing the fittings at which mercury may leak from the gas meter valve, a top cap for closing the top opening of the container when it is installed on an existing gas meter valve to deflect precipitation from entering the container, and a removable support for holding the mercury leak containment device in place with the fittings of the valve which are most likely to leak mercury fully enclosed.