You don't really need a memory hole to make people forget about these leak events. The Aliso Canyon leak in LA in 2015 (https://en.wikipedia.org/wiki/Aliso_Can

You don't really need a memory hole to make people forget about these leak events. The Aliso Canyon leak in LA in 2015 (https://en.wikipedia.org/wiki/Aliso_Canyon_gas_leak https://en.wikipedia.org/wiki/Aliso_Canyon_gas_leak) was comparable size (~100,000 tonnes CH4) and is also dimly recalled.