HDPE Outfall
A 2,500-ft, 36-in. HDPE outfall in an affluent beach area of Port Hueneme, Calif., required the use of horizontal directional drilling for its installation. A big project in its own right, this bore was part of a massive water reclamation project for the Calleguas Municipal Water District that was a decade in the making.
The Calleguas Municipal Water District is a public agency created in 1953 to provide southeastern Ventura County, Calif., with a reliable supply of high quality water. Calleguas serves a 350-sq mile area and includes the cities of Oxnard, Camarillo, Moorpark, Thousand Oaks, Simi Valley and Port Hueneme, as well as surrounding unincorporated areas.
The Calleguas Regional Salinity Management Project (SMP) is a regional pipeline that will collect salty water generated by groundwater desalting facilities and excess recycled water and convey that water for re-use elsewhere. Any unused supplies will be safely discharged to the Pacific Ocean, where natural salt levels are much higher. The SMP is designed to bolster the region’s annual water supply by an estimated 40,000 acre ft.
According to the project description, the SMP is critical to the region’s water reliability as imported supplies from the State Water Project have become increasingly vulnerable to drought, catastrophic levee failures from flood and/or seismic events and regulatory shutdowns of pumping facilities to protect endangered species. The SMP will also improve water quality by moving salts out of the watershed.
The HDD Co., which has handled five sewer outfall projects on the West Coast over the last five years, was awarded the project in March 2009. The purpose of the $15 million Port Hueneme outfall line is to serve as the conduit to pump the brine water from the SMP pipeline into the Pacific Ocean.
Directional drilling played a crucial role as the project construction progressed — an outfall pipe needed to be installed at the end of the SMP pipe. Constructed of a combination of HDPE and steel pipe, the outfall is 36 in. in diameter and approximately 1 mile long, with about half the length installed using HDD from the Port Hueneme beach parking lot. Construction of the outfall began in earnest in September 2009, with the HDD portion beginning in October and wrapping up in November 2009.
Drilling operations were set up in the beach parking lot next to the beach under which the pilot bore would be drilled. From there, a 900,000-lb rig, built by The HDD Co., was set up, as well as three Gardner Denver mud pumps and a recycling unit.
Getting Started
The HDD Co. was established in 1998, but its president Neil Swope has roots in the directional drilling market that go back over 20 years. The contractor boasts a staff in which key members also have 20-plus years of experience in HDD and have completed more than 1,000 bores in a multitude of soil conditions. In 2009, The HDD Co. partnered with The Crossing Co., based out of Nisku, Alberta, Canada, to form one of the largest HDD operators in North America. The combined company now offers clients access to a fleet of 14 HDD drilling spreads. Crossing Company president Ryan MacLean notes that this new partnership has expanded its geographic reach and enhanced its ability to provide the equipment and qualified people necessary to complete multiple HDD projects for any type of utility in a short period of time.
In preparing for this project, The HDD Co. had a multitude of challenges in installing the outfall line — from environmental to manmade, with some expected and some that came out of the blue.
“Probably the most challenging thing about the project was the environmental concerns. The drilling itself was purported to be pretty routine,” said Rick Evans, vice president of engineering and estimating of The HDD Co. “We did have some problems that one could not have foreseen.”
Among the environmental issues The HDD Co. had to work around were concerns the sea life of the Pacific Ocean, specifically migrating whales that had to be continually monitored, as well as seals, which enjoyed laying on anything contractors put in the water, such as equipment.
Also, The HDD Co. was obligated to implement a sound mitigation program to comply with decibel level restrictions. A 24-ft high sound wall was constructed that surrounded the entire parking lot area to absorb the project noise, thus not disturbing the residents of the oceanfront condominiums and beach visitors.
“[The project owners] were very stringent about the noise levels and they were constantly monitored during the entire project,” said Evans.
Swope noted that sound walls such as the one built for this project are becoming much more commonplace on large construction sites as more work is being done within populated urban areas. “The noise is becoming much more of an issue than it has been in the past,” he said. “Contractors need to work hard to manage [the noise].”
Another challenge crews faced was drilling into the ocean. A Tensor steering system was used to navigate and TruTrack coils were laid out on the beach to the waterline, as well as in the water to track the bore. Crews also ran fluorescent dye in the drilling fluid to monitor for any frac-outs in the offshore section of the bore. A flourometer was used to monitor the dye.
“The marine crews had to traverse back and forth along the borepath as we were drilling to monitor for traces of the dye to check for frac-outs,” Evans said. “If the dye showed up on the ocean floor, it would show up on the flourometer and that would mean we had a frac-out and we would have to shut down the drilling operation, which fortunately we did not have to do.”
Drilling Time
Before drilling could commence, The HDD Co. needed to install a 54-in. steel conductor casing to stabilize the borehole and to keep the beach sand from sloughing. This was done using an American Augers auger boring machine
“We intended to install 115 ft of casing, but we could only get 80 ft of it in because it was getting difficult to install,” Evans explained. “We found out later that we had actually hit a layer of boulders under the beach.”
The discovery of the boulders wasn’t made until crews were pulling back the HDPE and crews could not pull the pipe into the conductor pipe. No one — The HDD Co., prime contractor Manson Construction or the Calleguas Municipal Water District — was aware the boulders existed, even though geotechnical work had been done prior to the project. The obstruction caught everyone by surprise, Evans said.
“When we were doing the pullback, [the pipe] pulled fine right up until it reached the end of the conductor casing,” Evans said. “We had to secure a permit and excavate from that point to the entry point in the parking lot and put in a new piece of pipe.”
Excavation of the boulders — some as large as 4 ½ ft in diameter and 30 ft underground — and other concrete debris added approximately 45 days to the project’s schedule.
Everything else about the project went according to plan. Manson Construction supplied the offshore support, working off a large derrick barge in the ocean as well as several other smaller vessels.
There wasn’t room at the project site to fuse the 2,500 ft of HDPE so that process was done at the nearby naval station at Point Mugu, about eight miles south of the project site. The fused pipe had to be launched over a sea wall and was towed to the project site and lined up with the bore. Divers were used to lift the pipe off the ocean floor (some 45 ft under water) and hook it to the drill pipe to do the pullback.
Evans and Swope credit the work of Manson Construction and the marine divers for the coordination to make this aspect of the project work.
Project Odds and Ends
The 9 7/8-in. pilot hole took eight days to drill and the hole was forward reamed to 27 in. and then back reamed to 52 in. Pullback went smoothly until it reached the conductor casing, where crews tried for 12 hours to get it into the casing.
Swope credits many facets of the project for its success, including the navigational plan, sound attenuation plan, coordination with the marine contractor, as well as the implementation of an annular pressure management plan using downhole pressure tooling.
Sharon M. Bueno is managing editor of Trenchless Technology.
