(1) Wells which have not been monitored for more than 3 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 using a pump and hose or tremie pipe to conduct the sealing material to the bottom of the well or 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 3 feet below the ground surface and the last 3 feet backfilled with naturally occurring soils;

(i) It is recommended that in all cases where possible the casing be pulled.

(b) 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 6 to 3 feet from the surface, bentonite shall be added to the well. The last 3 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. They may contain nonbiodegradeable fluidizing admixtures, provided they will not contaminate the ground water. Sealing materials which settle shall be topped to provide a continuous column of grout to within 3 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.