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 must be plugged immediately. If a monitoring well has been determined to present a threat to groundwater, the division may order that the well be permanently plugged. 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 that would interfere with the proper plugging of the well;
   2. (B) All protective casing, riser pipe and well screen must be removed from the borehole, if possible, unless approved by the division. Because the primary purpose of well plugging is to eliminate vertical fluid migration along the borehole, the preferred method of plugging involves casing and riser pipe removal. 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. In certain situations, the casing or riser pipe must be drilled out if it cannot be removed before the well is plugged. These situations will be determined on a case-by-case basis by the division. When casing is not required to be removed or if after attempting to remove the casing, it is not possible to remove it, then a hole must be dug around the casing three feet (3') deep and the casing and riser pipe cut off at that depth;
   3. (C) The well must be filled from bottom to top with grout. 10 CSR 23-4.060(11) sets standards for grout types that may be used when plugging monitoring wells; and
   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. Slight mounding over the well is recommended to prevent water from standing in the immediate area of the well.
2. (2) The plugging or complete excavation of all monitoring wells must be reported on a registration report form supplied by the division. These forms must be submitted, along with the fee, within sixty (60) days of the plugging (see 10 CSR 23-2 for applicable fees). If the review of the registration report form shows that the well has been plugged according to the rules, a registration number will be issued and sent to the well owner. The registration number indicates that the well was plugged according to the standards set out in the rules. When field screening type of temporary wells are drilled, usually multiple installations per monitoring site are used. All temporary wells per monitoring site may be reported on one (1) registration report form if they are all plugged the same way and only one (1) registration fee is required per site.
3. (3) Monitoring wells must be plugged by a permitted monitoring well installation contractor.
4. (4) Material used to plug monitoring wells must be compatible with any contaminants in the well so that the plugging action of the grout is not destroyed by any chemical reactions that may take place in the borehole environment.
5. (5) Monitoring wells less than ten feet (10') in depth must be plugged by returning uncontaminated native material or grout into the hole it was taken from. No reporting is required for these wells.
6. (6) Temporary monitoring wells greater than ten feet (10') in depth must be plugged by removing any temporary pipe and filling the well from total depth to ten feet (10') 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 (1994).* 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. *Original authority: 256.606 and 256.615, RSMo (1991) and 256.623, RSMo (1985), amended 1991.