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When Digging a Ditch the Old-Fashioned Way Won’t Work

Tue January 22, 2013 - Southeast Edition
Construction Equipment Guide

Loudoun Water in Loudoun County, Va., is a non-profit, public utility that is finding more cost effective ways to meet the needs of its customers. Loudoun Water has a unique and growing customer base of data centers that are using reclaimed water from the Broad Run Water Reclamation Facility to more economically cool their facilities. Increasing demand for reclaimed water has led the utility to lay additional pipe to meet customer needs. But, how do you put a 16 in. (40.6 cm) carrier pipe into a 20 in. (50.8 cm) casing pipe in 870 ft. (265 m) of solid rock, with limited accessibility, around a crowded intersection of busy Loudoun County, and without disturbing a historic biking trail when digging a ditch or trenching won’t work? The underground trenchless solution: the right pipe, the right contractor and the right machine.

Woodlawn Construction began directionally drilling rock with the help of Ditch Witch of Virginia in 1999 through installing telecommunication systems. Woodlawn Construction owner Phillip Staples purchased a third Ditch Witch rock directional drill from Ditch Witch of Virginia in early 2012 for a difficult project outside Leesburg, Va. This 860 ft. (262 m) bore went under Goose Creek in solid blue stone rock, but was not a problem for the Ditch Witch JT4020 all terrain (AT) directional drill or the experienced Woodlawn Construction crew led by drill foreman Matt Martin. After the Goose Creek job, Woodlawn Construction searched for bores in increased length and diameter to utilize the JT4020 AT to full potential. The dual pipe, water reclaim rock job for Loudoun Water presented the ideal challenge.

The Job

The 870 ft. (265 m) bore by Woodlawn Construction is part of an ongoing initiative by Loudoun Water to build a reuse water distribution system. To date, some 21,000 ft. (6,400 m) of 12 and 16 in. (30.5 and 40.6 cm) reclaimed water mains are in place. Other existing pieces of the system were installed by traditional trench excavation with road crossings by jack and bore.

Loudoun Water faced challenges with this particular stretch of pipe, including limited work area, a bike trail crossing, an active roadway, solid rock and the difficult task of pulling two pipes. The Ditch Witch JT4020 AT “machine sealed the deal with trenchless feasibility,” said Ralph Welliver, project engineer of Loudoun Water.

Normally 80,000-100,000 lb. pull back class drills bore for waterlines, but the small footprint and the 40,000 lb. pull back of the JT4020 AT was ideal for the narrow job site. With high drilling torque and unique rod within rod technology, the Ditch Witch JT4020 AT drills and steers simultaneously through rock, performing the same bores as larger class drills, according to the manufacturer.

“Reclaimed water is interesting, yet it has the same constructability properties as any pressure utility, such as sewer or water,” Welliver explained. However, reclaim water jobs are relatively new to Virginia since the enabling regulation went into effect in October of 2008. A total of seven utilities are pursuing reclaimed water at this time in Virginia, while other water-sensitive areas have been using reclaimed water for some years.

“It has taken a while for municipalities to get geared up for these projects. It takes the right customer base to make reclaimed water cost effective,“ said Liz Sitter, project engineer at Loudoun Water.

The Broad Run Water Reclamation Facility is an advanced treatment plant, placed into service in 2008 with the objective of producing the cleanest water possible. Broad Run, like many wastewater plants in Virginia, must follow nutrient restrictions in discharged water to avoid overloading the Chesapeake Bay and degrading the ecosystem. The reclaimed water system is a way to manage the “nutrient budget of wastewater. It also functions as a demand management tool for drinking water,” said Welliver.

“One gallon we don’t put back is one gallon we don’t pull from the Potomac River,” Welliver stated.

Reclaimed water is not to be confused with grey water. Grey water is the practice of collecting non-potable water, typically from sink drains, and using it at the same building for irrigation or flushing of commodes. The quality of reclaimed water is much higher because it is treated to specific quality levels in the wastewater plant.

Savings in the Pipe

Data centers in Loudoun County make an ideal customer base for a reclaimed water project as connections to potable and reclaimed water mains provide valuable redundancy and reliability of supply. Currently, an average of 60,000 gal./day from the completed reclaim water mains is used for irrigation, flushing and cooling. The bored section of the project loop Woodlawn Construction completed will bring approximately 1 million gal./day to serve more prospective customers. Significant savings are realized in reclaimed water as the cost per gallon is substantially less than the cost per gallon of potable water, according to the company.

Two pipes at 870 ft. each would appear as an added expense to the job, but actually were an important part of the cost savings. Underground Solutions Inc. became an integral part of the project because the company not only made fusible, gasket-free and leak-free PVC pipe, but also offered the reclaimed waterline in purple, the mandated pipe color for reclaim water in Virginia. Add to the mix the bore was “going through solid rock and would have been cost prohibitive with larger diameter HDPE,” commented Gary Shepherd, southeast regional sales manager of Underground Solutions Inc. Pulling a PVC carrier pipe with a 17.4 in. (44 cm) outer diameter and a PVC casing pipe of 22 in. (56 cm) outer diameter incurred less expense per foot, and less fluid and material costs than pulling HDPE pipes of 22 in. outer diameter and 30 in. (76 cm) outer diameter, respectively.

On Budget, and on Time

The 190 hp (141.6 kW) Cummins diesel engine JT4020 AT pulled back the two pipes with ease. The 20 in. casing pipe pullback through solid rock took approximately 6 hours while the 16 in. carrier pipe pullback inside the casing pipe was finished in 2 hours. For the small footprint, “the power of the machine is outstanding. The show of muscle was its ability to go through the rock,” Shepherd said.

“Woodlawn Construction stayed on schedule and performed within budget,” said Welliver.

The installation was deemed a notable success in Virginia given the length and use of both casing and carrier pipes.

“We’re proud of the job from our pipe standpoint. That’s for sure,” Shepherd said.

Woodlawn Construction “having this [Ditch Witch JT4020 AT] machine made it possible,” Welliver supported.

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