The Environmental Protection Agency is expanding its inquiry of the leading telecommunication providers in the United States after investigations found that their older cables contaminate water and soil across the country.

The agency sent a letter to AT&T and Verizon on Thursday requesting meetings with the companies as part of a monthslong inquiry into whether the companies’ old infrastructure was releasing lead into the environment. EPA investigators found more than 100 readings with lead above the safety guidelines for children at locations previously identified. Now, the agency is trying to determine what role the telecom providers played in these levels.