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May 2006

Going Underground

If new snowmaking pipe is on the agenda this summer, forget those trenches-directional drilling may be the better solution.

Written by Jim Buckingham | 0 comment

For most snowmaking systems, the water pipelines are buried in the ground. Installing those pipelines has always meant digging trenches, laying the pipe and then backfilling the trenches. But a small ski area in Alberta recently used a (new to skiing) technique known as directional drilling that can make the process easier and less environmentally disruptive.

There are several undesirable side effects of digging trenches to install snowmaking pipe. While the trenches are open, they create a serious potential for water erosion, both within the trench and from the windrows of excavated material sitting beside the trenches. When trenches run through wooded areas, trenching damages trees and roots, and some trees must be removed entirely. Even trenches that run close to islands of trees may damage the roots. Plus, the trenches and windrows can disrupt other work around the installation.

After backfilling the trenches, the restoration begins. Areas must restore vegetation and surface drainage. It can take a few years to fully stabilize the restored areas.

Directional Drilling
Directional drilling is much less disruptive of the ground and vegetation. The technique was developed to place pipelines under roads and railways without disrupting them. It involved drilling a hole more or less horizontally under a road or other obstacle, so pipe or cable could be pulled through the hole.

Oil, gas and other kinds of pipelines have adopted the technique; it’s also used to lay communication cables and optical fibers. As its uses expanded, the technology became very sophisticated. Directional drilling can now be done for any size of pipe from two-inch to 36- inch, and it is possible to accurately control the direction of the drill bit—up, down, left, right—as it cuts the hole. For example, it’s possible to start a hole on a gentle down-slope into the ground, then run it horizontally at a set depth, and finally angle up to the surface at an exact location. Directional changes can be made only in long sweeping curves, but in most cases, sharp curves in pipelines are undesirable anyway. And developments in drill bits and techniques make it possible to penetrate all kinds of soils, from clay to solid rock.

One Area’s Experience
Last summer, Long Lake Ski Area, a community ski hill about 90 miles northeast of Edmonton, Alberta, installed its snowmaking system using this technique. Long Lake is owned by Thorhild county. The area was built in the 1970s and operated with some success when snowfalls were good. However, by the early ‘90s it became obvious that the area was not viable without snowmaking. After a few years of not operating, the county, along with Athabaska county and nearby municipalities, financed a snowmaking system so the area could reopen.

Ray Sauer, a former area manager, came back as project manager to oversee the snowmaking installation. He asked for bids from several pipeline companies—with a great deal of oil and gas activity in Alberta, pipeline companies are readily available. Sauer specified that the contract would include returning the ground surface and vegetation to their original condition. The work included a 450-foot six-inch line from the snowmaking pond pump house to the hill, a 4,200-foot loop of four-inch pipe, and about 2,000 feet of two-inch lateral lines for 14 hydrants. Bids ranged from about C$110,000 to C$130,000.

D-Line Construction of Leduc, Alberta, a company that does both conventional trenching and directional drilling, won the bid. D-line sought the quickest and most economical method to lay the pipe and do the reclamation. They chose directional drilling, for two reasons. First, the subsoil was mostly clay, which is easy to drill. Second, directional drilling greatly reduces the amount of erosion control and revegetation work. It proved a wise choice, as the work went quickly, with minimal disruption of surface terrain.

Installing Snowmaking Pipe
The placement of each section of pipe follows a simple routine. With a backhoe, D-Line dug a series of small excavations about 600 feet apart along the proposed pipeline, and then “connected the dots.” The drill rig (see illustration and Fig. 1) bored a hole from one excavation to another.

The technology is very precise. The drill bit contains a radio transmitter, and a person on the ground surface approximately above the bit carries a special radio receiver (Fig. 2) that relays the exact location of the bit and its depth to the drill operator, who can control the direction the bit will travel. The two-man crew works together to direct the bit and control its depth below the surface. If the bit strikes a boulder or bedrock (signaled by a lack of progress and the sound of the drill) the operator can pull the drill stem back 20 or 30 feet and redirect the bit to pass around the obstacle. Then the team can bring the bit into the next excavation at the exact place and depth they want.

Once the drill bit penetrates the next excavation (Fig. 3), the crew replaces the bit with a swivel coupling attached to a string of pipe of the proper length for the hole (Fig. 4). The drill operator then pulls the drill stem and the attached pipe back through the hole to the excavation at the start of the section. At that point, a welder can join the pipe to the end of the previously laid section. Each section matches the points where the system designers specified junction boxes or valves. The work can progress quickly; it’s possible to drill the hole and lay 600 feet of pipe in two hours.

Crews install laterals from the main pipeline out to each hydrant in much the same way. In many cases, the laterals connect to the main line at the excavation points. Where they don’t, the crew makes an excavation for a hydrant and chooses a location for the junction on the main line. A hydrovac excavation system (Fig. 5) makes an 18-inch circular hole down to the main line at this point, using high-pressure water to cut the earth and a vacuum hose to extract the water and mud. This eliminates the danger of hitting the mainline while digging blind with an excavator. Once the hydrovac exposes the mainline pipe, a backhoe can safely enlarge the excavation to accommodate a welder.

The hole for each lateral starts at the excavation on the mainline and the crew drills a hole to the hydrant excavation. They then pull the lateral into the hole and join it to the mainline at one end, and to the hydrant at the other. Then they backfill the excavations at the mainline and hydrant.

The obvious advantages of this system are the speed of installation and the minimal disruption of the surface ground, which greatly reduces the need for reclamation and restoration. Trees can be left standing; the pipeline just passes below or through the roots. Similarly, pipelines can pass under roads and stream beds without disturbing them. And sewer, water, and power lines can remain unscathed with little effort.

There are a few disadvantages to directional drilling. While the process can be less expensive than conventional trenching in easy-to-work soil, in rocky ground, it may be considerably more expensive. In areas where little pipelining is done, this type of equipment may not be readily available. However, for many ski areas, even if they install most of a pipeline project with conventional trenching, directional drilling may be the most economical and practical way to place pipelines under wooded areas, streams or environmentally sensitive areas such as wetlands.

Jim Buckingham is a ski area consultant and a former manager of Mt. Norquay, Can.