Vision Directional Drilling Devises Innovative Approach for Installing Geothermal System at George Washington Birthplace
January 19, 2012George Washington is considered one of the most visionary men in American history. Heralded by presidential historians as the father of our country, the nation’s first president is often remembered as a forward-thinking man, with a passion for progress and a relentless spirit of innovation.
Born in 1732 at the Washington family home — known then as “Wakefield” — Washington’s uncanny vision had become apparent as a young man and later demonstrated by his leadership as a statesman. Among his greatest pursuits: to build a powerful nation using the federal government’s resources to build infrastructure, open western lands and promote commerce. His belief in the importance of creating a solid infrastructure was most insightful, especially given the times in which he lived.
Now, more than two centuries after his death in 1799, visitors to his birthplace will experience another innovative achievement while strolling comfortably through the cozy confines of this historic site and likely not even be aware, thanks to a new geothermal heat pump system installed by Vision Directional Drilling, based in Burlington, N.C. While the system installed is now not all that unique given the recent growth in popularity and the increase in the number of geothermal heat pump installations. But the approach for this job, conceived by Michael Strasburg of On-Site Energy, based in Alexandria, Va., and Mark Hall, owner and president of Vision Directional Drilling, along with his team of horizontal directional drilling (HDD) experts, is certainly visionary in its own right.
“When we get to a jobsite, I try to look ahead to identify any potential problems that would give us difficulty before we start the project,” Hall says. “We were aware of several restrictions at the George Washington birthplace that forced us to approach this job differently than most horizontal loop installations we’ve done in the past … which is hundreds.”
Replacing an Antiquated System
The original Washington birthplace was destroyed by fire on Christmas Day, 1779, and never rebuilt. Nearly a century and a half later, at the direction of the Wakefield National Memorial Association, formed in 1923, a replica was constructed and opened by the National Park Service on the 200th anniversary of Washington’s birth.
The structure had been heated by an inefficient, antiquated boiler system since being completed in 1932, and the home was never air conditioned. On-Site Energy, a leading design, engineering and consulting company that specializes in alternative energy solutions, was selected by the National Park Service to design the geothermal heat pump system for the Washington birthplace project.
According to an official with the National Park Service, the project is one of many examples that demonstrate the agency’s commitment to adopting more sustainable energy practices. The challenge is to incorporate alternative energy options that are cost-efficient without jeopardizing the historic integrity of the sites. The selection of geothermal for the Washington birthplace was an effective option because, unlike solar panels, the geothermal system is installed and contained underground, leaving the surface areas relatively undisturbed.
Maintaining Archaeological and Environmental Integrity
Among the many stipulations placed on Hall and his crew by the National Park Service was strict adherence to maintaining the archaeological integrity of the site, while minimizing the installation footprint so not to disrupt the aesthetics and appearance of this historic place. In addition — and likely the condition that presented the greatest installation challenge for the drilling crew — the property is situated along the volatile and highly protected ecosystem of the Chesapeake Bay. Given the shallow water table beneath the site and extremely tight work space (the Park Service allocated only a 30 sq ft launch area for the installation), a vertical installation approach was not an option. Yet Hall also faced challenges with horizontal.
“We only had a certain area that we could work in, because it was the only area that had been historically excavated and cleared to install the underground loops,” Hall explains. “There were also restrictions on where we could exit a bore due to environmental sensitivities of the Chesapeake Bay. The drill plan called for bores to extend 185 ft from the point of entry, but that length was outside of the historically excavated perimeter. This prevented us from exiting the ground like we normally do when installing geothermal loops using HDD.”
A Visionary Solution
The restrictions for installing the five horizontal loops that were to comprise the geothermal heat pump system would likely have intimidated many HDD contractors, but Hall, his crew and his local Vermeer dealer — Vermeer Mid Atlantic — embraced the challenges. They devised an alternative approach using HDD — given the restriction that prevented exiting the bore on the opposite end — pulling the drill stem back out and inserting the loop systems using a 1.5-in. piece of rigid pipe and then grouting the loop as it was pulled back out.
Hall used a Vermeer D36x50 Series II Navigator horizontal directional drill (HDD) to navigate the challenging soil conditions, that ranged from a 2- to 3-ft topsoil crust, to what Hall refers to as sugar sand, followed by a sand/rock mix with a fair amount of running sugar sand down to about 20 ft. Beyond the depth of 20 ft to about 22 ft, the crew encountered a layer of river rock, followed by swelling river clay.
“We chose the Vermeer D36x50 HDD model because of its high power-to-size ratio and light footprint,” Hall says. “The drill has the ability to bore through just about any ground conditions, and we certainly faced several on this site. We used a standard carbide tooth bit, to drill a 6.5-in. bore. We did this because we wanted plenty of room to shore up the grout after the loops were inserted. We were also grouting the system, so we knew we had 100 percent contact with the earth.”
Given the variation and quickly changing soil conditions, the right recipe of drill fluid was critical for maintaining the integrity of the bore and keeping the spoil of varying soil compositions flowing out so the bore path would remain open. To accomplish this, Hall used a heavy polymer bentonite mix with rail pack.
Stay Inside the Box
The 30-by-30 ft surface area relegated to the Vision Directional Drilling crew for setup, launch and surface disruption by the Park Service also required that the archeological integrity of the space be maintained at a specified depth. This meant that at the point where the bores extended beyond the specified range, the depth of the bore had to extend beyond the specified depth. Any area below this depth in the excavation zone was considered outside the historically protected area. To accomplish this, however, took yet another visionary move on the part of Hall and his crew.
“We were installing five loops connecting to a 10-ft wide header, all from the same launch position, and each loop required a minimum of a 10-ft separation,” says Hall. ”We rotated the drill position ever so slightly with each subsequent shot so by the time each bore had reached the 20-ft mark we had also achieved a 10-ft separation. The best way to visualize how this would appear beneath the ground is to picture five segments of a hand-held fan from above, like an aerial shot.”
Hall inserted the loops into the ground and, using the Vermeer GM30 grouting system, grouted as they pulled the drill stem back. The whole process worked beautifully.
Upon completing each of the five 185-ft loop installations, the D36x50 Series II HDD was rotated a full 180 degrees to complete the 120-ft bore back to the house for connecting the header line to the heat pump in a corner of the structure’s basement.
“We had a 12-by-12-in. area that we wanted to hit in the corner of the basement room,” Hall says. “That was kind of tough to shoot under, with the elevation change and all, but we hit it within probably a half an inch of what we were aiming for. It went really well.”
As a result, visitors who journey to the Wakefield replica today to pay homage to the nation’s first President, and visionary in his own right, can thank the HDD experts from Vision Directional Drilling for installing a system that not only makes their tour more comfortable, but is highly efficient and a prudent use of their tax dollars.
Randy Happel is a features writer for Two Rivers Marketing, Des Moines, Iowa.
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