Tuesday, August 26, 2008

drain snakes and slug tests

In a previous post, toolkit, I mentioned a couple essential items that I try to always have with me:

Drain snake

You might notice a connection…

Yep, they’re all things that you use to retrieve stuff you’ve lost down a well or borehole. In all honesty, I’ve never gotten a magnet to retrieve anything.

The drain snake, though has gotten me out of a couple iffy situations. You see, sometimes we do slug tests - we drop a solid mass, called a slug, into the well, and see how fast the water returns to its original level after it’s been disturbed. Usually, you have a transducer sitting at the bottom of the well to measure the water level changes.

That’s where the problems happen. The transducer is a rather expensive little piece of equipment that is usually retrievable by a power/data cord and string…or just the string. The problem is you’re dropping a solid mass as quickly as possible into a well already occupied by this other stuff. Ideally, you’d drop it in a controllable manner, and have enough water in the well not to let it get too close to the transducer. Sometimes you don’t.

So, the slug I’ve used has generally been a solid piece of PVC with a hole drilled in it. You don’t have things you can try and snag with a hook, so if the slug gets tangled up in the transducer line or wedged in there, you don’t want to tug too hard because the last thing you want to do is break the string holding the slug. And it goes without saying that you don’t want to start yanking on the transducer cable.

This is where the drain snake comes in handy. It’s stiff enough to be forced to the bottom of the well, and flexible enough to get by obstructions. All you do is rig the end so that it has a good “lip” to catch the bottom of the slug, and it’s sturdy enough that you can yank the slug loose. It can also be modified to remove dead critters, used to probe for possible damage to the well, costs less than $15, and even your smallest local hardware store will carry it.

Slugs don't even need transducer cable to get stuck. The first time I bought a drain snake, it was a day I'd planned to just take manual water level readings because we had a tight budget. I had someone standing by, reading to start collecting readings as fast as possible, and I hurled the slug into the well and it got wedged inside about 5 feet down, short of the water and easily visible, but out of reach. The well had gotten bent, and PVC well + PVC slug + me throwing it down too fast = severely stuck slug. I was convinced we'd permanently blocked the well. We went to the tiny hardware store about 20 minutes away (there's never a home depot when you really need one) and raided it for anything that looked remotely useful, came back, and popped the slug out in one try.

So if you've got a toolkit that you're dragging into a remote area and you need to pare down the stuff you're bringing, leave the big magnet and take the drain snake.

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