Water Well Journal
Issue link: http://read.dmtmag.com/i/740475
I wrote about grouting and mixing and placing both neat cement grouts and bentonite-based grouts in the September edition of Drawing from the Well. I received a couple of email inquiries from readers and their feedback made me realize we need to explore the issue of grouting more. In fact, we're going to turn the subject into a multi-part series. There is a picture behind the desk in my office where I used to work. It shows a path winding through a beautiful for- est. Below the image are the words: "Integrity—A Path on Which You Will Never Get Lost." It's a motivational picture I acquired to keep our employees as well as myself focused on the right path. I mention this because everything a water well contractor does, for the most part, is out of the sight of the customer. Therefore, there is a lot of integrity that goes into what we do. Grouting is just one phase of that integrity, but it's one of the most important too. While you can televise the well if there is a problem, you can't televise the grout job. So the grout integrity is of vital importance to the success and usabil- ity of the water well to the customer. The Early Days The emails I received was one asking "What is graded ben- tonite?" and another from a regulator who expressed concerns that the bare minimum standard in his state for grouting wasn't enough. You might recall I wrote in the September column about looking back at some of the early grouting done on domestic water wells. I mentioned the practice of using cuttings from a bailer and dumping them around the casing. This was just one example among others. As I was getting my feet on the ground in the industry in the late 1970s and early 1980s, grouting was making advances in the industry. As I was struggling with how to do it, making sure it was done right and trying to figure out how to be effi- cient, I came across an article in the February 1988 issue of Water Well Journal. It was titled "Sealing Well Casing: An Idea Whose Time Has Come" and was written by Donald E. Calhoun III, a hydrologist for the Ohio Department of Natural Resources. The email from the regulator made me recall that article. If you have time, I encourage you to look it up. It can be found at the National Ground Water Association's website. Extremely well written, it outlines the specific problems Calhoun encountered. It was written at a time when new bentonite grouts were making their way onto the scene in the water well industry. The article came at an ideal time for me. By that point in my career, my company was well on its way to full length grout- ing of all domestic water wells. But as with any process, things always continue to evolve and usually for the better. We also evolved. Graded Bentonite Graded bentonite is a product bentonite suppliers have pro- duced, initially for plugging abandoned wells. It is a raw ben- tonite product that is crushed, dried, and graded typically into two sizes—either ⅜ inches or ¾ inches. It is designed to be dumped down an existing well to aban- don it. Some contractors use it as a barrier on top of a gravel pack in screened wells prior to pumping a grout to prevent the grout from migrating into the pack itself. Other contractors use it on shallow grouting and dump it down the annulus to seal the annulus. There is, however, an inherent danger in dumping graded bentonite down a wellbore and using it as a grout. The danger is premature bridging of the product either in the wellbore or the annulus. This is especially true for the smaller diameter wells and wells with a narrow annulus. Our firm has used only ⅜-inch graded bentonite as we have found it works well in all sizes of water wells as well as the annulus. The danger comes from the fines found in the bags of the graded bentonite. While all manufacturers take care to keep the fines out during processing and bagging, loading and moving of the bags will result in more fines being produced. Those fines, if not filtered out while pouring the bags, will allow the fines to build up either on the static water level of the borehole being abandoned or the annulus of the well that is being grouted. The fines then cause the static to thicken and, ultimately, a bridge to develop. If this occurs in the grouting of an annulus, there is really not much way of removing the bridge. So your grout job is not complete and leaves room for a potential path- way from the surface to open up. Filtering of the fines is typically done by dumping the bag of graded bentonite over a piece of hardware cloth or coarse screen that is fashioned into a trough or funnel. By allowing the bentonite to tumble so to speak across the hardware cloth, GROUTING ISN'T "JUST GROUTING" Part 2: Working with graded bentonite. DRAWING FROM THE WELL GARY SHAWVER, MGWC waterwelljournal.com 50 November 2016 WWJ To read part one of this series on grouting, check out the September issue or go to www.WaterWellJournal.com.