Nebraska Grout Study

Posted: February 17, 2012

Initiated by a "see through" casing, the study revealed some surprises. All grouts work as expected below the water table. Above the water table grouts vary in their ability to keep surface contaminants from penetrating the aquifer. The two most successful grouts to date were cement-sand and chip bentonite. The study is continuing.
Grouting a well

Grouting a well

The study was commissioned as a result of a plastic well. In 1999 the “ultimate well” was drilled at the University of Nebraska.  Clear PVC casing and well screen was installed and grouted. A video camera recorded the conditions after installation and again 16 months later. The second video showed that the grout had separated leaving voids and cracks in the grout along the casing above the water table. Enough pathways existed to create a potential for surface water contamination. A grout study was launched.

The first thought was to prove that the “ultimate well” result was just an anomaly, that properly placed grout does not develop voids after placement. It wasn’t. Several other wells showed the same result.

Next, eleven different grout recipes (all grouts approved for use in Nebraska) were tested through visual comparison and also by submitting the well head to a dye test, a total of 63 wells at five locations. One encouraging result was that grouts behaved as expected in saturated conditions i.e. below the water table. Voids and cracks only developed in the unsaturated part of the well. Chipped bentonite and cement-sand grout allowed the least penetration of dye and visually, the chipped bentonite showed the least void space. In contrast slurried bentonite grouts developed the most voids and also allowed the greatest penetration of dye. One finding of importance was that grouts containing cement did not bond to the plastic casing so that upon curing the grout pulled away from the casing providing a pathway for surface contaminant travel. An expected future result will be a regulation requiring steel casing when using cement based grouts.

This study was supported by several manufacturers of grout material and they are seeking to improve their grouts based on the findings. You can find more details in the November 2010 issue of the Water Well Journal, The Nebraska Grout Study by Jill Ross.