The McCook Fire Department and the Hazmat team from the Red Willow Western Rural Fire Department were called to the Walmart in McCook Sunday on the report of a chemical spill.
Crews arrived on scene around 2 p.m. to a mixture of bleach and ammonia near the front of the store.
Customers and employees were evacuated and the building was ventilated.
Three people were transported to the local hospital with minor injuries and 10 others were treated on scene.
The store was able to reopen around 5:30 p.m.
The incident is under investigation.