Friday, January 9, 2009

drilling methods and utilities

We have a whole bunch of ways to put holes in the ground, using anything from DPT rigs you can mount to a golf cart to air-rotary rigs that are a block long. But when you’re installing standard monitoring wells above bedrock, you tend to use either augers (claws that spin down) or casing (pipes you hammer down). Augers are faster, casing minimizes dragging contaminants to clean layers below; but what do you prefer (everything else being equal) if you’re afraid of hitting utilities?

Each has its own problem. When you punch through something with casing, you wish that you’d had the augers because the scratching of the claws might have alerted you to a problem. But there’s nothing quite like when the auger gets stuck, and you yank it up (if you can) to find a massive ball of wires wrapped around it. Then you get to play the “um, do you have power?” game with all the neighbors.

You may think, “why don’t you just go more carefully?” For the first couple feet, we do. But we may have all sorts of perfectly innocent boulders and other natural barriers that we need to power through, and determining which is natural and which is not can sometimes be difficult. Hence my extreme dislike of the first five feet.

1 comment:

GeologyJoe said...

oh yeah. you can really worry alot about the first 5-6 feet. dig safe is great but isn't super accurate. existing site plans are good too when they are available, which is about 1 every 8 years.

What I have done in a few cases where we had to put in wells very close to utilities was to use a vactor and suck out,excuse me vaccum extraction, the soil to a depth of to say 8-9 feet. Then come in with the hollow stem auger.