Handful of bentonite chips/Photo by ISWS staff
Grouting is the process of filling the space between the borehole wall and the casing. This space is called the annulus and needs to be properly sealed to prevent the migration of contaminants from the surface into the drinking water aquifer. By grouting a water well, you ensure the integrity and safety of the well.
A well can be grouted using materials such as neat cement, concrete grout, bentonite chips, bentonite pellets, and bentonite grout. The geology and the depth of the well will determine what grouting material is used.
It is important to follow the state or local well construction codes when choosing and applying grout for well sealing.
Bentonite is a clay that swells when it encounters moisture. Once moistened, the pieces fuses together create a water-proof seal in the annulus. It is commercially available in different sizes and can be used as a slurry making it a versatile product. It does have limitations due to its low shear strength, which makes it unsuitable for high hydraulic gradient sealing locations where strength is important.
Neat cement is a specific type of cement-based grout that finds application in various contexts, particularly in well construction and repair. Compared to bentonite grouts, neat cement grouts have a higher slurry density, making it suitable for flowing well construction or repair.
A slurry is a mixture of a liquid, typically water, and denser solid particles. The solid particles remain suspended in the liquid. Both bentonite and neat cement can be used as a slurry and can be injected in the well using a tremie pipe. A tremie pipe is a tool used in the process of grouting. It is inserted all the way down to the bottom of the well and pumps grout into the well. The tremie pipe is slowly removed as the annulus is filled from the bottom up ensuring a thorough seal.
Are all wells grouted?
Not all water wells are grouted. The grouting of water wells depends on various factors such as regulations, geology, and construction requirements. In some cases, grouting may not be necessary or may be done differently based on specific circumstances. It is important to consult local regulations and guidelines to determine the grouting requirements for water wells in a specific area.
References
Gaber, Michael S. Michigan Flowing Well Handbook, March 2005, Michigan DEQ.
Well Owner’s Handbook, Environmental Health Division, Minnesota Department of Health.
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