The curve below shows the percentage of population of aquatic species that die in response to doses of pollutant A, a toxic substance. A local manufacturing plant reports a spill that released pollutant A into the local watershed. Local officials must determine if the residents should be evacuated from the area. Initial groundwater samples show pollutant levels at 20 mg/kg of water. Which decision is supported by the empirical evidence provided by the dose-response curve?

- Evacuation is not needed; continue groundwater monitoring.
- Residents should be evacuated until levels decrease.
- The spill no longer needs to be monitored.
- Residents should only evacuate above LD50.