Rain, Flood, Contaminated Soils Can’t Stop Gator Drilling

By Jeff Griffin, Senior Editor | June 2013, Vol. 68, No. 6

Horizontal directional drilling (HDD) continues to solve problems for utility owners and operators by completing difficult installations of underground infrastructure that many times can be addressed by no other method of construction.

Very often, environmental factors are involved in the decision to use directional drilling. A good example is a Florida project when the city of Pensacola faced the challenge of constructing storm water structures and relocating storm outflow lines which passed through a plume of contaminated soil related to a U.S. Environmental Protection Agency (EPA) Super Fund project. The contamination was left by a creosote plant that operated from 1902 to 1981 and released volatile organic compounds into the soil.

The outflow lines carry storm water into Pensacola Bay. The EPA prohibited the pipes from being buried by open-cut construction because of the high level of contaminated ground water. Excavation would require extensive groundwater de-watering of the contaminated area and no nearby treatment facility could accept such a high volume of pumped groundwater for treatment and disposal of contaminants. Pensacola City Engineer Derrik Owens discussed the feasibility of using directional drilling on the project with EPA and representatives of Pensacola contractor Gator Boing & Trenching Inc.

Ultimately HDD was chosen as the most viable option for installing the conveyance pipes because the process would result in lower volume of returns which could be quantified, containerized and disposed of properly.

Roads Inc. was prime contractor for the project. “Finding a good HDD subcontractor was key to building this project,” said Robby Williams, Roads vice president. “Gator Boring met all of the project specifications for HAZMAT certification, equipment requirements and gravity experience in on-grade gravity flow pipe installation experience.”

Tight tolerance

The project called for installing three, parallel, 26-inch diameters HDPE pipes with four feet of cover and two feet of separation between the pipes. The fall in grade of the pipes was precisely 0.28 percent.

“This was a very challenging situation that required us to apply technology that is not typically utilized for this type of application,” said the city’s Owens.

Gator Boring used a 160,000-pound pullback Universal HDD 160x240 drill model for the installations. Pilot holes were drilled with an 8.75 Radius HDD rock head through sandy clay.