Water Well Journal
Issue link: https://read.dmtmag.com/i/557876
"The industry rule of thumb has al- ways been the annular space has to be three times larger than the size of the particle you're putting in," Krause says. "So, if you're putting in three-quarter- inch chip . . . a two-inch minimum range is kind of the smallest we'd ever want to go." Dugan recommends using chips with no less than a 3-inch annular space, especially on deep holes. Otherwise, the chips will be too difficult to place. "Chips are going to plug up and bridge to the sides, so you're going to have a lot of problems getting chips all the way down the hole," Dugan says. "And you can't drop granular bentonite from the surface and expect to get that in there because it seals too quickly. It's going to set up before you get a complete seal of the hole." Bentonite grouts If annular space is an issue, pumpable bentonite grouts may be a good option, especially for monitoring wells. "On a domestic water well you don't have the annular space to get chips down it a lot of the time," Dugan says. "So a tremie line with a 20% solids grout is very convenient to use. One 50-pound bag mixed with 24 gallons of water makes 3.5 cubic feet of grout, so you have a good yield out of the product and it's easy to mix and pump. You can completely fill the well up and be done with it." But—like bentonite chips—a ben- tonite grout doesn't mix well with salt- water. It also may not be the best grout for the job if you require structural strength in the well. "If you need structural strength to maintain that stability of the borehole, or you want that casing anchored, these pumpable bentonite grouts don't exhibit good structural strength," Krause says. "They're not structural like a cement grout or a cementitious grout." With any pumpable grout, maintain- ing adequate pumping pressure is im- portant in keeping the grout pumpable throughout the process. "The clock is ticking whether it's a cement grout or a bentonite grout," Krause says. "You only have 'X' amount of time before it starts to set and cause plugging or pumping problems." Bentonite grouts are also temperature sensitive, so the temperature of the water you're mixing with it and the tem- perature of the tremie pipe you're using to pump it matters. If the water tank sits out on the job site all day or if the tremie pipe is coiled and lying in the sun, the grout may set up faster than you're expecting it to. "When using a tremie pipe, you should pump freshwater through it to cool it down," Dugan says. "Otherwise, if you pump that first batch of grout through it without cooling that line down, that grout is going to flash-set inside of the tremie line and complete- ly plug it off. You're going to be shut down trying to clean it out or get another tremie line." Cement grouts Like bentonite grouts, pumped ce- ment grouts do well in wells with tight annular spaces. Unlike bentonite grouts, cement grouts offer better structural strength—best for large municipal wells where you're hanging large multi-stage pumps. If not using chips, Schneider prefers cement grout because it's not only strong, but can help keep costs down. GROUT from page 31 DACUM Codes To help meet your professional needs, this article covers skills and competen- cies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOB-2, DOB-4, DOC-4, DOD-2, DOE-2, DOE-3, DOE-16 More information on DACUM and the charts are available at www.NGWA.org. Learn Grouting in Las Vegas The NGWA Groundwater Expo and Annual Meeting, December 15-17 in Las Vegas, Nevada, will have three workshops on grouting. Below is information about all of them. Get even more detail about the Expo at www.GroundwaterExpo.com. Grouts and Grouting Methods for Water Supply Wells Tuesday, December 15, at 10:30–11:30 a.m. Identify the types of grouts and additives most commonly used in water supply wells and learn their pros and cons. The session will also discuss grout placement methods and techniques, their appropriate applications, and precautions. Such methods, terms, and techniques include pouring, annular tremie pipe, Braden head, 'Halliburton', stab-in shoe, plugs, etc. Presenter: Steve Schneider, MGWC Grouting Challenges: How the Professionals Do It Wednesday, December 16, at 8:30–10 a.m. The secret of properly grouting on any job is detailed preplanning to accommodate the products, mechanics, conditions, and construction process. This panel will share insight on the limitations of engineered grouts, pour or pump decisions, multiple completions, annular size, and problem solving for completion and abandonment. Presenters: Jeff Blinn and Stewart Krause Grouting and Sealing: Matching Products' Properties to the Job Tuesday, December 15, at 8–9 a.m. Sealing materials such as granular bentonite, bentonite chips, and bentonite tablets will be discussed along with well plugging and abandonment procedures and recom- mendations. Also covered will be types of grouts, including a comparison between cement and bentonite grouts; causes of formation loss; high solids bentonite grouts; thermally-enhanced grouts; and grout mixing and pumping procedures and tips. Presenter: George M. Dugan waterwelljournal.com 32 September 2015 WWJ