Correction: This story has been updated to reflect that the cost of expanding the reservoir includes an estimated $8 million in interest.
When Lake Orange started running low on water in 1993, Hillsborough officials were forced to turn to Durham for help.
Seven years later, the town opened its West Fork Eno Reservoir west of Lake Orange, which provides the town with up to 1.8 million gallons a day. Hillsborough utilities inspector Nathan Cates credits the lake with saving the town from a crisis in 2007, when drought left most Triangle cities scrounging for water.
"I know it cost a lot of money to build the first phase, but it paid for itself, because people had water, Orange County Schools had water," Cates said. "We were in water restrictions because of the depth of the lake, but there was still water there, and we were able to ride out that drought."
Since then, the town has grown to roughly 6,500 residents, and Orange County planning estimates show that number could double by 2030. Like other Triangle communities, Hillsborough also has had a residential construction boom, with over 2,500 new homes built or in the pipeline since the recession.
But that's not why a long-planned reservoir expansion began Monday, March 19, Town Manager Eric Peterson said.
Instead, it's the pending expiration of a 20-year Army Corps of Engineers construction permit that allows the expansion, and which would be very difficult to get now, Peterson said. And, there's also the cost of increasing the reservoir's daily capacity to 3 million gallons.
Since 2015, that cost has doubled to $16 million, plus an estimated $8 million in interest on bonds. Engineers have warned the cost could double again or even triple in the future, Peterson said.
"Moving forward gives us the security of having a reservoir of water — literally and figuratively — and saving a lot of money for the community going forward," Peterson said.
Together, the 43-foot-deep reservoir and Lake Orange provide roughly 7,000 businesses and homes with up to 1.4 million gallons of daily water. Regional plans estimate the town's need could exceed its existing water supply by 2030.
Thalle Construction is leading the expansion project, which will clear 100 acres of trees around the reservoir. Crews will add access roads, plus a thicker base and taller chute walls to the earthen dam's auxiliary spillway. The main spillway runs from a box culvert, under the dam and into the river, as remotely controlled valves release the water.
A new "piano key" weir — the second one built in the United States — will be installed atop the auxiliary spillway, cutting the water's force as it spills into the river. The expansion will raise the water level by 10 feet.
The highest water level he's ever seen in the reservoir is 45 feet, Cates said. That much water moves "with a purpose," he said.
"When there is 45 feet of water in here after a major rain event, a tropical storm, that is a raging river coming down through (the spillway)," Cates said. "So when it gets down here at the bottom, it's water like you see at a waterfall, it's spinning and churning."
The expansion project also will involve some roadwork.
The N.C. Department of Transportation will detour traffic on Efland-Cedar Grove Road, beginning April 2, to straighten a curve and to raise and rebuild the roadbed. Carr Store Road also will be raised and a new bridge built to accommodate the higher reservoir level.
All three projects should be finished within a year, said Peterson, who acknowledged the town will have to raise its water and sewer rates to pay for the work. Those rates — among some of the Triangle's highest — are now $50.51 a month for in-town customers using up to 5,000 gallons of water, and $98.48 for out-of-town customers.
There are multiple reasons for the high fees, Peterson said, including the loss of big water customers like Flynt Fabrics, which closed in 2000; the town's small size; and strict Falls Lake wastewater rules that require costly water treatment plant upgrades.
The Town Board will decide how much to raise rates and over how many years during this year's budget talks, Peterson said.