If Highway 221 is part of your commute, you may be fearing for the worst.
The west side of the highway, stretching for more than a mile from Napa Valley College south to Kaiser Road is lined with 24-inch wide segments of water pipe waiting to be placed underground.
But to the surprise and relief of many, this project may have no impact on drivers or adjacent properties.
Since mid-January, crews have been working to replace a 7,400-foot stretch of pipe using a technique known as directional drilling. Unlike traditional pipe-replacement methods, it does not require a wide trench to be dug.
Instead, a horizontal hole is made from an above-ground point, flushed with mud and drilling fluid and then filled with a semi-flexible piece of fusible polyvinyl chloride (PVC) pipe. The new pipe will be laid 40 feet below ground at its deepest point to avoid utilities and other barriers.
“Imagine a needle going through a piece of fabric,” said Megan Thomas, a city engineer. “The ground is the fabric.”
The technique is far less invasive than trench-digging, Thomas said. Had traditional pipe-replacement methods been used, all the trees in front of Napa Valley Memorial Park would have been removed, along with landscaping and signs in around Napa Valley College and the municipal golf course at Kennedy Park.
Additionally, a lane on south-bound Highway 221 would likely have been closed for the space required to dig a 12-foot-wide trench, Thomas said.
“You don’t have excavators and equipment going through (the area),” said Rob Craw, regional manager of Underground Solutions, the company behind the fusible pipe used in the project. “It eliminates excavation and restoration costs.”
While two crews drill space for the pipe, a third fuses long pieces of PVC pipe together.
“There are no gaskets,” Craw said. “The weak point of a segmented pipe are the joints.”
In 2011, the city saw four major water lines break, all at the joints or collars that connect one segment of pipe to another. Water General Manager Joy Eldredge said because the PVC pipes are fused together using precise temperatures and measurements from a computer, there is far less room for error than with concrete pipes bound together using a crew and a backhoe.
“It’s like a computer versus us doing math,” she said.
In November, the City Council awarded a $3.1 million contract to HDD Company, Inc., of Cameron Park, to do the work.
Thomas said it’s hard to quantify how much the project would have cost using traditional methods, but directional drilling certainly is the cheaper method because it does not require buying easements and unexpected costs are far less likely to arise.
“We look at this as what we’re not affecting,” she said.
The new pipe will replace a 16-inch wide segment of pipe that currently restricts water flow between two 24-inch pipes, Eldredge said. According to the construction contract, the new pipe should be finished by May, before the summer increase in water demand.
The old pipe will be filled with concrete to prevent sinkholes and left in the ground, Eldredge said.
The city tried out the method on two smaller projects, one in 2008 and another in 2010, Thomas said. In some cases where there are narrow easements, utilities, trees and varied topography, directional drilling can replace traditional replacement methods in Napa.
“It’s definitely a technology that’s getting a lot of momentum,” Eldredge said.
Fusible PVC also holds promise because Napa soils are known to be particularly corrosive to concrete and cast-iron pipes. The PVC has a life expectancy of 50 to 100 years, officials said.
“The true data will be in about 70 to 80 years,” Eldredge said. Seeing the corrosion issues we see, it sure leads us to believe this is the right direction to go.”