In the first half of 2012, the City of Napa replaced a 7.400-foot section of water main on the west side of Highway 221 from Napa Valley College south to Kaiser Road, resulting in a major improvement in how water moves through our distribution system.  Project construction activities included the use of two horizontal directional drilling rigs operating at sites along the project area.  The project was featured in a Napa Valley Register article on February 3, 2012.

Project highlights, including photos and video clips, are posted below in reverse chronological order:

April 26, 2012

New 24" transmission main was placed in operation with all valves open.

February 28, 2012

pipe pulling-endOn Monday, February 27, the fifth length of pipeline (about 1,100 feet) was pulled through the hole and is now successfully in place, leaving only a little more than 1,000 feet remaining to install.  Once all of the pipe is installed, the drilling portion of the work will be complete and the contractor will start connecting the sections of pipeline.  Each connection is slightly different from the next based on existing facilities that need to connect to the water main (including several water services and fire hydrants) as well as new valves needed to optimize the operation of the water main.

Click the photo for video of the end of the pipe pulling process.  The large equipment in the background (a track hoe) is used to guide the new water main into the hole by lifting the middle so that the pipe can curve into the drilled hole without any unnecessary strain on the pipeline.  Once the pipeline has only a small amount of length left to be pulled into the hole, the equipment is no longer needed.

February 14, 2012

On Tuesday, February 14, the second length of pipeline (about 1,500 feet) was pulled through the drilled hole that runs under the Napa Valley Memorial Park and is now successfully in place.  The ends of each section of new pipeline are kept protected (before, during, and after installation) to ensure that the interior remains clean until the pipeline is ready to be placed in service.

When a hole is drilled and ready for new pipeline to be installed, the hole remains filled with a mixture of the drilling fluid and soil cuttings (from the drilling process).  Known as "mud," this mixture helps the drilled hole stay open and intact so that the new pipeline can be pulled in.  In order to pull the new pipeline through the hole, the drilling rig drill pipe is bolted to one end of the pipeline and pulled through the hole, toward the drilling rig.  As the new pipeline is pulled, the volume of the pipeline displaces the "mud" causing it to pour out into a receiving pit where it can be pumped to a truck and hauled away from the site.  When the pipe is completely pulled through, a portion of the "mud" remains in the hole filling in the voids around the pipeline, becoming the new backfill for the pipe.

Click on the left photo for closeup video of the pipe pulling process.  The fluid seen in the video is the "mud" from the hole.  Click on the right photo for video illustrating how gently and quietly the pipeline is able to glide through the hole, the only noise coming from the pump that removes the excess "mud" from the site.

pipe pull closeup     pipe pull

February 7, 2012

On Friday, February 3, the first length of pipeline (about 1,700 feet) was pulled through the drilled hole in front of the College and is now successfully in place (see photo on left).  By the end of the week, the 36" hole for another 1,500 feet of pipeline is expected to be completed.  Most of this section of pipeline was drilled with the drill head being pushed from the drilling equipment toward its intended destination.  However, a portion of the second hole was switched from forward progression to a reverse direction, where the drilling equipment pulls the drill toward the machine.  This is known as "back reaming."  Click the photo on the right for video of the "back reaming" of the second half of the 36" hole.

pipe pullbackbackreaming

The fluid seen in the video is the drilling fluid mixing with the earth cuttings.  As the fluid then enters the trench pit, the fluid is removed and returned back to the mud treatment system. 

January 24, 2012

Starting Friday, January 20, sections of pipeline were delivered to the site to prepare for the fusion process.  Over just a few days, more than 1,000 feet of pipeline was fused together and laid out in preparation for installation after completion of the first bore hole.  The photo shows a portion of the length that has been fused together.

fused pipeThe fusion process in general is simple, but requires sophisticated machinery to ensure a continuous even bond between the pipe sections and an even heating of the ends.  Before fusing each joint, the pipe alignment is tested to ensure the pipe ends will joint flush with one another.  Once the ends are confirmed to be even, each end is cleaned and the heating plate is wiped down.  The heating plate is temperature-tested to ensure it is heating evenly.  Once all of this is completed, the heating plate moves into position and each end of the pipe is pressed against it.  After several minutes, the plate is removed from position and the pipe ends are pressed together to form the bond.  The pipe ends are held tightly pressed together until the bond cools and the fusion is complete.

For this project, each pipe section is 40 feet in length, which results in more than 180 fusion bonds required to make the length of pipe continuous.  Click for videos of the pipe fusion process:

January 19, 2012

Drilling operations commenced, with two drilling teams starting their initial drill (known as the "pilot hole").  This is the preliminary drill that sets the final alignment of the pipeline.

Here you can see one of the project's several drill sites, along with the drilling mud treatment assembly.  As the drill contiinues through its path, the drilling mud (an essential part of the operation) is collected and treated through a three-phase process that allows the material to be recycled back into the drilling operation.  Click on the images to see videos of the drill rig and treatment assembly in operation.

drill operation

mud filtering