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The Patuxent River off Point Patience is a deep body of water. Deeper still are two tunnels being drilled underneath the river to provide a more powerful loop to keep electricity running in Calvert and St. Mary’s counties.

An existing line carrying 69 kilovolts lying at the bottom of the Patuxent failed in January 2005 “on the coldest day of the year. Once we lost that cable it was very difficult to get the lights on in Calvert County,” said Tom Dennison, public affairs manager for the Southern Maryland Electric Cooperative.

The need for a more reliable, looped electrical system was evident and SMECO embarked on a $110 million reliability project for its 154,000 customers in Southern Maryland.

“There’s never been a project of this size and this complex in our history,” Dennison said. The cooperative was established in 1937.

New poles are being installed through Calvert to carry a new 230-kilovolt system over to St. Mary’s. It was not practical to carry the lines over the Patuxent River, so SMECO is digging underneath it to extend the lines.

Between the Navy Recreation Center in Solomons and North Patuxent Beach Road, the Patuxent River is 105 to 110 feet deep, said Ted Aggeler, project manager for Black & Veatch, which is drilling the tunnels 50 feet below the river’s bottom.

One tunnel has been dug and its five conduits have been installed. That work started on Sept. 6 from the St. Mary’s County side. On the first day, the drill made 1,200 feet of the 4,500-foot crossing. It took six days for the drilling to come up on the Solomons side, Aggeler said.

The first tunnel was 12 inches across. It was then reamed first to 26 inches and then to 38 inches. All the while, the drill bit is assisted by water jetting. A mixture of water and bentonite clay is pumped down the hollow drill pipe and rushes out ahead of the drill bit, doing most of the work to clear the way, he said.

The mixture is denser than the salt water above and keeps the tunnel intact.

The mixture also travels back up to the surface carrying clay, sand, silt and sometimes pieces of wood. The mixture is recycled back down into the tunnel after the spoils are sorted. The spoil material is hauled off to a landfill.

The first tunnel was completed in mid-October. Last week, crews were finishing the 26-inch reaming on the second tunnel, 50 feet away from the other one.

Meanwhile thousands of feet of conduits were being fused at the Navy Recreation Center, taking up almost the length of the facility as each 40-foot section was added. The blue PVC pipes will hold the actual electric lines under the river.

There will be five conduits each in the two tunnels. Three carry the electric lines, one is fiber optics and the other is a spare, Dennison said.

The conduits are filled with ballast water to keep them in place, Aggeler said, so they don’t rise under the river bed, like a beach ball under water.

The second set of conduits is scheduled to be pulled under the river in the first week of December. All together there are 25 to 30 subcontractors working 11-hour days on the project.

The actual electric cables will be installed by another contractor next fall, Dennison said.

In Calvert County from Holland Cliff to Sollers Wharf, 186 new and taller power poles were erected with another 66 poles to be installed from Sollers Wharf to Buck Hewitt Road in St. Mary’s. The first 18 miles of line in Calvert are complete and energized, Dennison said. The new poles range in height from 110 to 160 feet.

The entire project should be completed by the end of 2014.

jbabcock@somdnews.com