EASA provides in the NPA 2015-18, extensive guidance for SMS. The achievable level of risk (ALARP) is explained. " Showing that the safety risk is ALARP means that any further risk reduction is either impracticable or grossly outweighed by the cost".
That means that runway safety risk mitigations will have to be calculated in order to show the appropriate authority that further risk reduction would be grossly outweighed by the cost.