No need for evacuation but continue groundwater monitoring due to lower dose of toxic substance.
No need for evacuation, continue groundwater monitoring because the dose of toxic substance in a normal or safe range. In this range the toxic substance can't affect the health of people who drink that water.
If the dose of toxic substance increases more than 10 mg/ kg then the toxic substance killed people who drink that water. According to the graph, we can see that the dose is in a normal range so we can conclude that no need of evacuation for the people.