The Environmental Protection Agency is out collecting sedimentation samples and water samples from a stretch of canal in Donna and Donna Lake.
They are searching for Polychlorinated Biphenyl TMs also known as PCB TMs.
It TMs banned in the United States, but it was used in electric transformers, environmental scientist Rafael Casanova said.
PCB TMs are known to cause cancer and according to the Environmental Protection Agency, it has been found in a canal stretching from Arroyo Colorado and Valley View Road and in Donna Lake.
"The EPA found out about the site back in 1993-94," Casanova said.
Since then, several agencies have investigated the source of the contamination, but it TMs still a mystery.
The EPA is collecting the sediment samples through cores that are a foot deep and using a device that is left suspended in water that gathers sediment from the water.
"The EPA's purpose for this investigation is to determine first the source of contamination the extent of the contamination and then to determine a final cleanup plan," Casanova said.
Scientist hope to eliminate possible sources of the contamination through these samples.
The EPA did a survey of the canal a few months ago and detected metallic objects which could potentially be the source of the contamination.
"Yesterday some members of the EPA dive team were here trying to determine the feasibility of doing a dive to see what TMs actually down there," Casanova said.
In about two months scientist will be back to gather the samples from the devices left suspended in the water.
They are hoping the samples will provide clues that will help solve this 20-year mystery.