Page 22 - TN811 2022 issue 4

The classic cross bore is a sewer line penetrated by a non-metallic (plastic) natural gas service line installed
by horizontal directional drilling or plowing. This creates a problem when the sewer line gets clogged, and the plastic natural gas line is punctured when the clog is removed. Natural
gas is a great fuel but when it is not properly contained, and it reaches a source of ignition it can explode. Even if the natural gas does not explode, it burns. Unintended explosions or fires are almost never good things.
The problem is that very few sewer lines (or, for that matter, water lines) are marked or easily located. New (or replacement) natural gas service lines in cities or suburbs = a pretty good chance that, sooner or later, cross bores may become a problem.
The Common Ground Alliance recently added “Cross Bore” to its Best Practices glossary: “An intrusion of an existing underground utility or underground structure by a second utility resulting in direct contact between the transactions of the utilities that compromises
the integrity of either the utility or underground structure.” Translation: Cross bores are a lot more than natural gas service lines and sewers.
What do I mean by that? We live in
an internet age. How do we access the internet? Originally, it was by hard wire – mostly hard wire phone lines strung from pole to pole. As technology advanced, more and more phone lines were buried along with more and
more electrical supply lines. With
the advent of cell phones, there are fewer and fewer “landlines” devoted to phone service, but landlines are still required to access the internet (and cable TV). Landlines used to be copper and relatively easily located. What is happening today? Copper landlines are being replaced by fiber optic lines that can carry a lot more data at far higher speeds.
Do you see where I am going? The trend is to install fiber optic lines using trenchless technology. This increases the potential for cross
bores for two reasons. First, any
time trenchless technology is used
to install underground utilities (gas, electric, water, sewer, fiber optic) and there are other underground utilities present, there is the potential for cross bores. Second, locating underground fiber optic cable is considerably
more difficult than locating metallic underground utilities. The potential for future cross bores is therefore increased.
Why do I mention this? The neighborhood I live in is (finally!!) getting high speed fiber optic
internet. The first hint was USIC (US Infrastructure Corporation) marking underground utilities all over the place. They had been in the neighborhood
for other projects and even a couple of my own projects. Their personnel have always been friendly and, as far as I can tell, they flag and mark everything they are supposed to mark. USIC is also a Gold Supporter of the Common Ground Alliance.
A few days later, the digging started. I had never seen moling - a trenchless method used to install small diameter underground utilities. During the moling process, a pneumatically driven machine known as a mole forces its way through the soil along the desired path of the pipe. Sort of a short range horizontal directional drilling process without any rotating tool. I did not
get to see an actual mole, but they dug small access pits every 20 or 30 feet
or so and apparently ran the mole
from pit to pit. They could go under sidewalks and streets with relatively little disturbance at the surface. One
of my neighbors did complain about not replacing the sod (he was the “Yard of the Month” and is known to be particular about such things), but the more significant problem was damage to sprinkler systems near and along sidewalks (can you say “Cross Bore”?). I was lucky – the work for my yard was in the easement behind my fence and my yard was not disturbed. My guess
is that the installation contractor came back and repaired the sprinklers, but I have not confirmed that.
The installation is not yet complete (i.e., our high-speed has not been connected), but it appears to be going well in the disruptions seem to be at a minimum.
When you get your fiber optic internet, I hope everything goes as well for you!!
Be safe out there!!
John Jacobi retired from PHMSA. For questions or comments, email: jjacobi@sbcglobal.net
20 • Tennessee811 2022, Issue 4
Cross Bores - a Recent Experience