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(1) In installing and developing a monitoring well, care shall be taken to preserve the natural barriers to groundwater movement between aquifers. All sealing shall be performed by adding the mixture from the bottom of the space to be sealed toward the surface in one continuous operation, except for driven wells.

(2) The minimum sealing material thickness shall be 1 1/2 inches around the outside of the casing on all sides, except for driven wells.

(3) For driven wells, granular or powdered bentonite shall be fed alongside the casing.

(4) Seal material shall extend down to within five feet of the zone being monitored. In sand and gravel formations, a minimum of 10 feet of surface seal shall be used, except when the zone of monitoring is higher.

(5) If the borehole will be advanced through a confining bed immediately below a contaminated aquifer, a casing shall be sealed into the top of the confining bed prior to advancing the borehole through the confining bed. All contaminated tools, drilling fluids, and down-hole equipment shall be cleaned or treated prior to advancing the borehole through the confining bed.

(6) A monitoring well encountering an artesian condition shall be sealed and controlled in the same manner as an artesian water well (ARM 36.21.658) .

History: Sec. 37-43-202, MCA; IMP, Sec. 37-43-202, MCA; NEW, 1988 MAR p. 2503, Eff. 11/24/88; AMD, 1991 MAR p. 913, Eff. 6/14/91.

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