Protection of Ground-Water Monitoring Wells Against Frost Heave

Abstract

Frost heave damage to grout seals around ground-water monitoring wells for hazardous and solid waste treatment, storage and disposal facilities can present severe environmental as well as expensive remedial problems. For instance, influent surface drainage along the annular well space can contaminate the ground water and mask the actual water quality that the engineering geologist or hydrogeologist is attempting to monitor. Moreover, repairing damaged wells or reinstallation of new wells can be very expensive. Therefore, protection of the grout integrity around the monitoring wells is of paramount importance! Predisposing conditions which promote frost heave include the following: Depth and duration of frost penetration affect the degree of frost activity. The soils must be susceptible to frost action, primarily clayey fine sands and silts. There must be a source of moisture close enough to supply capillary water to the frost line. When these conditions are right, monitoring wells, grouted with concrete, can be subject to damage from frost heave. Frost damage is not a new phenomenon, however, many workers have not immediately recognized the problem in the past. The author has observed frost damage around wells installed in the northern tier States and mountainous areas. The damage noted was crumbling, shearing and separation of the concrete apron and annular seal around the well casing. The steel protective casings and sometimes the wells themselves were dislodged vertically, destroying the integrity of the well which promoted influent drainage of potentially contaminated runoff to the ground water. The standard well design recommended by the U.S. Environmental Protection Agency and employed by most engineers and hydrogeologists, works well under conditions not subject to frost heave. However, the concrete apron which mantles the ground surface and forms a pile around the casing is the focal point of the full force of the heaving soil. To prevent frost heave damage of the monitoring wells, consider abandonment of the concrete aprons in frost susceptible areas. As an alternative to the traditional concrete mixtures, bentonite has proved successful as a grout seal around monitoring wells. Therefore, before the project officer installs ground-water monitoring wells, he should consider the following: Evaluate monitoring well sites for history and/or geologic conditions which promote frost heave. Be sure the design for the monitoring wells accounts for measures to prevent frost heave. Consider the use of bentonite clay for grout seals in frost susceptible areas.