What material is recommended for sealing the annular space in an unperforated well casing?

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The recommended material for sealing the annular space in an unperforated well casing is cement grout or bentonite slurry. This choice is preferred because both materials are effective at creating a strong seal that prevents surface contaminants from entering the well. Cement grout offers a solid barrier that can withstand pressure and resist erosion, while bentonite slurry expands when wet, forming a gelatinous barrier that effectively fills voids and keeps water from above from infiltrating into the well.

Cement grout is robust and can provide structural support, reducing the chances of casing deformation over time. Bentonite slurry is particularly useful in areas where the geology is variable since it adapts to different soil types and moisture conditions.

Other materials, such as sandy soil or air and water mixtures, do not offer the same level of protection against contamination. Sandy soil may allow for the movement of water and contaminants through the voids, while an air and water mixture lacks the physical properties needed to create an effective seal. Plastic foam also does not exhibit the durability or sealing characteristics essential for protecting the well from pollutants. Thus, cement grout or bentonite slurry stands out as the best option for securing the integrity of an unperforated well casing.

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