SAN JUAN, Puerto Rico - Power restoration workers in Puerto Rico continually overcome challenges presented to them by narrow roads, rugged terrain and dense vegetation in outlying mountainous areas.

The Puerto Rico Electric Power Authority (PREPA) reports that over one million customers now have power, but the work continues with over 400,000 customers still needing service.

Crews continue to work long hours, seven days a week, to insure the mission accomplishment of restoring power to the people of Puerto Rico.

"We've seen dense vegetation before and we've seen mountainous terrain, but combining the two makes the situation very challenging," stated Jerry A. Robinson, Quality Assurance Lead from the Seattle District. "The vegetation grows so fast here it presents new challenges for us."

Some areas of the operation have required helicopter support to airlift poles, materials and personnel.

In regions where dense vegetation and steep vertical terrain is present, helicopters have actually been used to string cable between poles.

"The crews out here are doing a fantastic job overcoming the obstacles and doing it as quickly as they can," stated Robinson.

Crews have found themselves digging four foot deep holes by hand in some cases just to be able to set power poles.

The United States Army Corps of Engineers is partnered with the PREPA, the Department of Energy and FEMA to restore safe and reliable power to the people of Puerto Rico.

"USACE is committed to the restoration of power for the people of Puerto Rico and we will continue to press forward until the mission is complete." said TF Power Restoration Commander Col. John Lloyd.

The island of Puerto Rico has 2,400 miles of transmission lines across the island and 30,000 miles of distribution lines with 300 sub-stations.

It is estimated that 80 percent of the grid has been affected by Hurricane Maria.