(1) Wells which have not been monitored for more than three years shall be deemed abandoned unless written permission is obtained from the board to maintain the well.
(2) Monitoring wells that have outlived their useful purpose shall be abandoned by one of the following methods:
(a) if the casing and screen are left in place, the casing and screen shall be sealed from the bottom up by the following methods:
(i) using a pump and hose or tremie pipe to conduct the sealing material to the bottom of the well; or
(ii) by filling the casing and screen with bentonite pellets or chips placed in a manner that will prevent bridging. Metal casings shall be cut off three feet below the ground surface and the last three feet backfilled with naturally occurring soils;
(b) the department recommends that the casing be removed in all possible instances. If the casing and/or screen are removed, the hole shall be filled with sealing material, concrete, or bentonite pellets or chips from the bottom up, as the casing and/or screen is removed. From six to three feet from the surface, bentonite shall be added to the well. The last three feet shall be filled with naturally occurring soils;
(c) the sealing material shall be bentonite pellets or chips, bentonite clay grout, neat cement grout, or concrete. The material may contain nonbiodegradeable fluidizing admixtures, provided they will not contaminate the groundwater. Sealing materials which settle shall be topped to provide a continuous column of grout to within three feet of the surface; or
(d) other methods for abandonment with prior board approval.
(3) For flowing wells, the abandonment procedures outlined in ARM 36.21.671 shall apply.
(4) A properly abandoned well shall not produce water nor serve as a channel for movement of water.
(5) A water well log report, fully describing all abandonment procedures, shall be submitted to the Ground Water Information Center (GWIC) of the MBMG within 60 days of abandoning the well.