Knowing how to calculate the gallon-per-foot volume of a cylinder can save drillers money when it comes to grouting. Source: iStock

I drove over to Lansing in early February for the Michigan Ground Water Association’s annual Fundamentals course for well drillers. Good stuff, and a big thanks to the MGWA for the hospitality.

The training featured a lot of great information, and I could only make it to the first day, so I’m sure I just scratched the surface. I listened to lectures on well classification, isolation distances and sanitary best-practices, as well as basics on rotary, cable, jet and auger drilling. I learned a lot. Drilling 101 was just what I needed. Yes, I’ve soaked up plenty of information about the industry in my short time at National Driller. But the learning doesn’t stop and it only helps me serve you, the readers, better.

Great chance to take off my editor’s cap, and put on a student cap for a day.

I want to take a minute to pass on a basic tip-mainly for rotary drillers, but really for anyone who uses grout products. Steve Buer of Buer Well Drilling mentioned it, and it seemed like it was both simple and, based on the reaction from the class, not very well known. It’s a calculation for the number of gallons needed to fill an annular space.

The basic equation:

Diameter in inches squared x 0.0408 = gallons per foot

So, if a pipe has an interior diameter of 6 inches, that works out to 1.47 (rounded up) gallons per foot of space. If you have a 100-foot cylinder with a 6-inch interior diameter, that’s 147 gallons. Of course, that fills the entire borehole, so grouting around a casing you’d subtract that from the total. For simplicity’s sake, let’s say the casing has an exterior diameter of 4 inches. That casing would displace 0.65 gallons per foot, or 65 gallons over the 100-foot length. Subtract 65 from 147, and you need about 82 gallons of grout (and if you’re using much more than that, math isn’t your problem).

Figuring there was more than one way to grout a well, I also dug around and found this equation, which does the same thing:

 (Borehole interior diameter in inches squared – pipe exterior diameter in inches squared) ÷ 24.51 = gallons per foot

Using the same numbers: (36-16) ÷ 24.51 = 0.82

Again, multiply that by the 100 feet of well in the example and you get 82.

Now, I’ve never considered myself a math person. But I am a big fan of working smarter, not harder. Math has its uses, and in this case a little bit of it can save drillers a lot of money over time. So, write down one of these equations, plug it into your smartphone on the jobsite and stop wasting bentonite.

In Other News

On page 40, you’ll find our interview with Robert Bittner, P.E., the new president of the Deep Foundations Institute. That feature by freelance writer Holly Case originally appeared in The Foundations Report eNewsletter. If you’re interested in that sector, you can subscribe through our website. Go to, click on Home, and then click on eNewsletters. You can also subscribe to National Driller’s eNewsletter, and get the latest industry news between issues.

We’ll also roll out our Sourcebook 2013 soon, so be sure to update your listing. Don’t forget that, in addition to telephone, email, website and other contact details, Sourcebook entries can also include business logos and pictures of products. Look out for an email from us with more details.

Jeremy Verdusco, editor