PURPOSE: This rule sets standards for the plugging of monitoring wells.

1. (1) A monitoring well that is abandoned as defined in 10 CSR 23-1.010(1) must be plugged. If a monitoring well has been determined to present a threat to groundwater, or determined to be in such a state of disrepair that the well cannot be used for its intended purpose, the division may order that the well be permanently plugged.

2. (2) When plugging a monitoring well, the following minimum requirements shall be met:

   1. (A) All pumps, sampling equipment, debris, or other substances must be removed;
   2. (B) All surface completion and permanent casing, riser pipe, and well screen must be removed from the borehole. If, when removing the casing, the borehole begins to collapse, grout must be simultaneously emplaced while the casing is removed to ensure a proper seal;
   3. (C) The well must be filled from bottom to top with grout. 10 CSR 23-4.060(9) sets standards for grout types that may be used when plugging monitoring wells;
   4. (D) If bentonite grout is used, after the grout is fully cured, check for settlement and top off if necessary. Fill with soil and compact the upper two feet (2') of hole or pave. The purpose of the compacted soil is to ensure that dehydration of the bentonite grout does not occur over time. If cement-slurry grout is used, fill the upper two feet (2') with soil or pave; and
   5. (E) A monitoring well that is less than twenty-four feet (24') in total depth may be completely excavated as opposed to being plugged with grout. If the remaining hole is ten feet (10') or more in depth, it must be filled with clean replacement material that is compactable to a permeability less than, or equal to, the minimum permeability of the encompassing native materials. A monitoring well installation contractor must be on site at all times during the excavation and filling operations.
3. (3) The plugging or complete excavation of a monitoring well must be reported on a registration report form supplied by the division.
4. (4) Monitoring wells must be plugged by a nonrestricted monitoring well installation contractor.
5. (5) Temporary monitoring wells ten feet (10') or greater in depth must be plugged by removing any temporary pipe and filling the well from total depth to three feet (3') from the surface with approved grout, with the remainder of the well filled with compacted uncontaminated native material or grout.

AUTHORITY: sections 256.606, 256.615, and 256.623, RSMo 2000.* Emergency rule filed Nov. 16, 1993, effective Dec. 11, 1993, expired April 9, 1994. Original rule filed Aug. 17, 1993, effective March 10, 1994. Amended: Filed July 13, 1994, effective Jan. 29, 1995. Amended: Filed Nov. 1, 1995, effective June 30, 1996. Amended: Filed Nov. 18, 2010, effective July 30, 2011. *Original authority: 256.606, RSMo 1991; 256.615, RSMo 1991; and 256.623, RSMo 1985, amended 1991.