Lightning protection on heritage tree completely encircled by a concrete driveway

[PBrandt]

A client would like their 60 foot tall post oak to be protected with a tree lightning protection system. The problem is the tree is completely encircled by a concrete driveway and the drip line of the tree extends partway over the driveway. Here's a video of the area:

My main question is whether the grounding rod needs to be on the far side of the driveway (which would necessitate boring under the driveway). How would you approach this job? If you would bore under the driveway what is your favorite way to do that? Thanks for any suggestions.

 

[Nish]

Could a shallow groove be cut, or ground out, across the the driveway for the cable lay in, later covering it back over with whatever is used to patch a crack in concrete?

 

[treemonkee58]

Talk to the experts at Talonlp.com. The offer air terminals and expert advice for lightning protection.

 

[cerviarborist]

Dripline isn't a germaine measurement for anything other than calculating the number of aerial terminals for the system. If you can install the ground rod 10 feet away from the trunk or more, you're within standard. It looks as though you may have that much distance from your video. I just boxed up and moved my library, including BMP's in anticipation of surge flooding from Irma and haven't brought it home yet for reference, but if you can, search the Oct-2015 and Dec-2015 issues of Arborists' News on the ISA website to read two CEU articles which give a good overview of TLPS's. I'd also strongly suggest purchasing the BMP booklet on the topic.

 

[benfuest]

Hi, not sure of the connection between drip line and air terminals. Can you elaborate please. With the information available I would say you have the room for the earth termination without going into the concrete, just be prepared to go deep and be sure to install the ground rods before any work on above ground aspect of the system.

 

[cerviarborist]

Hi, not sure of the connection between drip line and air terminals. Can you elaborate please. With the information available I would say you have the room for the earth termination without going into the concrete, just be prepared to go deep and be sure to install the ground rods before any work on above ground aspect of the system.

Canopy diameter=drip line. BMP specifies air terminals spaced no more than 35 feet apart throughout the canopy.

 

[benfuest]

I see where your coming from. I prefer to look at the canopy and major limbs, its much the same.

 

[JD3000]

Here's part 1 of the arborist news articles Cervi is talking about

 

[guymayor]

For a tree with a strong central leader, I don't see that 35' *guideline* requiring 2 terminals.

Agree that it can go inside the concrete. and this might be useful: http://www.historictreecare.com/wp-content/uploads/2012/05/Lightning-TCIA-2008.pdf

 

[cerviarborist]

See what you want. I prefer to work to standards. I and my clients sleep better at night.

 

[PBrandt]

Thanks for all the great advice and links. I see now in the BMP that the minimum recommended distance for the grounding rod is 10 feet from the trunk. I'm not sure where I got the idea that the rod should be placed at the drip line.

 

[FreeFallin]

...which would necessitate boring under the driveway). How would you approach this job?

If you wind up needing to go under the driveway, an old trick I used to use installing water lines is to make a water pick by cutting a piece of 3/4 schedule 40 PVC at an angle on one end, and then put a garden hose adapter on the other. Trench enough outside that circle to lay the pipe flat, turn on the water and you should be able to jam it under the concrete by hand in 10-15 minutes. I have seen 20' runs done this way.

 

[Nish]

If you wind up needing to go under the driveway, an old trick I used to use installing water lines is to make a water pick by cutting a piece of 3/4 schedule 40 PVC at an angle on one end, and then put a garden hose adapter on the other. Trench enough outside that circle to lay the pipe flat, turn on the water and you should be able to jam it under the concrete by hand in 10-15 minutes. I have seen 20' runs done this way.

I wonder if this method could be used to lay utilities under trees and their structural roots.

I love this forum and the willingness of specialists to weigh in with their insights.

 

[guymayor]

Dripline is the favored location because...that is where water drips, and a moist environment makes for better grounding.

If your ground rod location is under the canopy, you might want to check the grounding considerations that Ben has on his site. If soil is not clay, grounding is all the more important. Ben tried to get A300 to pay more attention to grounding 10 years ago, but that fell on fairly deaf ears.

 

[benfuest]

Dripline is the favored location because...that is where water drips, and a moist environment makes for better grounding.

WRONG.

If your ground rod location is under the canopy, you might want to check the grounding considerations that Ben has on his site. If soil is not clay, grounding is all the more important.

WRONG.

Ben tried to get A300 to pay more attention to grounding 10 years ago, but that fell on fairly deaf ears.

ALSO WRONG.

 

[PBrandt]

Hi Ben,

Since I'm not sure I understand your post above, are you disagreeing with Guy's opinion that the dripline is the preferable location for the grounding rod? It seems that, within reason and whenever possible, it is best to place the ground rod as far from the primary roots as possible since roots are often damaged around the grounding rod after a successfully intercepted strike.

 

[benfuest]

No, I disagree with Guy's explanation re drip line. your explanation re primary root system is correct. Research conducted by myself over here and Dr Tom Smiley at Bartlett lab concluded that the soil affected around the ground rod, having intercepted a strike is approx 12-18 inches.