AT&T Inc. says less than 10% of its nationwide copper-wire telecom network has lead-clad cables, addressing investor concerns over the extent of a potentially massive contamination situation and costly cleanup.

The Dallas-based phone giant said lead-clad cables make up a “small part” of its network of about 2 million miles of cable. Of that, about two-thirds are “either buried or in conduit” followed by aerial lines on poles and a “very small portion” running underwater, according to a filing with the US District Court for the Eastern District of California.

Read more from Bloomberg