GREENSBORO, N.C. -- The Greensboro Water Resources Department is working to track down where two drinking water contaminants are coming from.

Officials say the levels of PFOS and PFOA spiked in 2015 to above the notification line, and now they're below half of that.

The department is testing lakes, rivers and the watershed to build data that they can use to develop a solution.

"In the drinking water business you always want to remove contaminants at the source if we can. But at the same time we're doing some pilot testing with our research partners, our water science partners at the Mitchell water plant in particular so that we may be able to build in some treatment techniques in a few years, should we need to reduce PFOS at the plant,” said Water Resources Director Steve Drew.

One of the "hot spots" the department identified was Horse Pen Creek, near PTI Airport.

Officials are working with the airport to find out what could've caused it and how to move forward.