Service Line Coverage, also called underground utility coverage, pays to repair/replace your water, sewer or electrical power lines. This would include the digging up of the ground to get to the affected line.
Typically, this covers rot, collapse, corrosion or decay, which is unique to a homeowner policy. It can also be added on the a landlord that has a 1-4 unit property. It must be an endorsement to the main policy and is not a separate policy.
For $20-$40 per year, you get $10,000 of coverage, which is a great deal. If you don not have Service line or Underground Utility coverage, it is one of the best insurance bargains to own.