There are several factors to consider in making sure you grout a well system properly.
By William Wagner
Water, ironically, can be a well’s worst enemy. That’s why a meticulous grouting job is so important.
“Water tends to flow horizontally by a lot,” says Marvin F. Glotfelty, RG, principal hydrogeologist at Clear Creek
Associates in Phoenix, Arizona. “That’s a good thing, not a bad thing. It means we can isolate the bad stuff from the good stuff.
“While we’re doing that, out in the aquifer, it’s not going to move vertically, but when it gets to the borehole that you’ve drilled into the earth, now you have the annulus, which will allow water to move vertically just fine. There’s nothing stopping it unless you put a seal in there. The cement seal is what shields off the bad stuff from the good stuff. In almost every well, you control the water quality to the layers, to the strata, you intend. That’s what (grouting) does.”
Unfortunately, grouting hasn’t always been undertaken with the care that is required.
Over the course of his career, Jeff Blinn, now an industry consultant in Spring, Texas, who used to work for Baroid Industrial Drilling Products, has seen his share of grouting-related horrors.
“It’s more common than you think,” says Blinn, who’s next installment of “Clear as Mud” will appear in the August 2021 issue of Water Well Journal.
“I’ve seen things go bad. I’ve seen people try to cheat the grouting of the well even when it’s in the specifications. They do it to the point where they take a bunch of empty sacks and push them around the upper part of the casing and then just cement in the top 5 or 10 feet and say they grouted the entire well. That’s not a best practice by any stretch of the imagination. You’re not achieving a seal that way.”
The lesson in all of this? Don’t cut corners when it comes to grouting. Here are some factors to consider to achieve that optimal seal, courtesy of two industry experts.
The Well Design Matters
How you approach grouting often depends on the specifications of the well system. And as we know, each well has its own quirks. Thus, you need to strategize before you begin piling in cement. Glotfelty calls any given plan a “domino effect.”
“(The grouting method) is driven by the well design,” he says. “We start with, ‘Well, what’s this well for? Is this a 1000-gallon-a-minute well? Is it a 10-gallon-a-minute well? Is it a well that won’t be pumped very hard?’ There are a lot of different ‘what ifs.’
Then what kind of pump? And you need to think about your geology too. Are you in hard rock or alluvial? Those will make a difference. Is the aquifer good quality everywhere, or is there a problem somewhere, like contaminated water?”
Just Dump the Cement in There
As primitive as this sounds—and it is indeed a primitive method—it’s relatively common for shallower wells. Says Blinn, “The first thing people usually think of is just pouring some sort of grout into place. That works mostly for shallow wells rather than deeper wells. Where you have very shallow aquifers, a well might only be 40 feet deep. A lot of times, they’ll pour chipped bentonite seal around their casings. It’s simple, it’s quick, and it does the job in those circumstances. It is used in a lot of areas (around the country).”
Blinn cautions, however, that there are certain drawbacks to the dump-and-run approach, regardless of the well’s depth.
“There’s no guarantee that you’ll get a great seal by doing it that way,” he adds. “And the amount of water might limit how far the grout will fall before the bentonite swells up and starts to stick, so you might not get a full seal all the way around your casing. It’s the simplest way, but it’s not always the best. It has its limitations.”
If You’re Going Deeper . . .
With deeper wells, a more common—and more certain—method is to, as Blinn puts it, “tremie some sort of grout into place.” This, he says, is “the only way you can be assured to get grout from the bottom to the top. Grouting from the bottom to the top is the preferred method to be sure you fill your annular space.”
But a tremie pipe isn’t foolproof, either. It takes a skilled hand to use one properly.
“Unless you want to leave your tremie in place forever, you pull the tremie line out (as you’re going),” Blinn says. “But you always keep the end submerged in fresh grout, so that you don’t end up with gaps in your grout. If I was only doing a 40-foot well, I probably wouldn’t tremie it; I’d probably pour a chipped bentonite into place. But anything deeper, then, yes, I would definitely use a tremie line to guarantee I’ve got my grout from bottom to top. This probably is used more often than not. It’s pretty much well accepted in the community these days that it’s the only way you can truly get a seal.”
The Halliburton Method
Though the Halliburton method isn’t commonly used, Blinn cites it as an option for particularly deep wells.
“It’s where you pump grout down inside the casing and out the bottom, out the annular space,” Blinn says. “But that takes a lot more equipment to do it properly. In some larger jobs—municipal work or commercial wells that are done—sometimes the engineers just spec it in. At least I’ve seen it that way. It’s not as common as a tremie line. Your average well driller is much more familiar with just using a tremie and a grout pump and pumping it that way.”
No matter how you go about grouting, use this rule of thumb: Think before you pour. The stakes, after all, are extremely high.
“It’s very critical to the final result of the well,” Glotfelty says. “In many aquifers, the water quality, as well as the water quantity, is stratified—it comes in different layers. The layers of water quality can be independent from the layers of sediment.
“So, that means you might have—just as an example—nitrate in the upper part of the aquifer, high arsenic in the lower part, and perfectly good water in the middle. There are ways to measure that, but if you don’t put in a good cement seal, problems will occur.”
William Wagner is an award-wining writer, editor, and project manager for Wagner Communications. He has written for magazines, newspapers, books, and websites. He lives in the Chicago area, and can be reached at firstname.lastname@example.org.