According to CV Times on July 9th:

Striking a single line can render 911 emergency lines ineffective, cause significant injury and result in repair costs, fines and inconvenient outages. 

“The cleanup process from the floods will be daunting but, before any work begins, utility companies must first mark sites where important lines exist,” explains Marcy Fox, local manager, Frontier Communications. “Depths of utility lines may vary and there may be multiple utility lines in the same area, so it’s important to wait for the line locations to be marked before digging begins.

The depth of utility lines can vary due to erosion, previous digging projects and uneven surfaces. Utility lines must be properly marked because even digging only a few inches carries the risk of striking an underground utility line.