NAC534.4365. Monitoring wells: Plugging.

     1. Except as otherwise provided in this section, a monitoring well must be plugged within 30 days after monitoring is no longer required.

     2. If the casing cannot be removed, a monitoring well must be plugged by placing neat cement by tremie pipe in an upward direction from the bottom of the well to the surface of the well. Alternatively, the appropriate volume of bentonite chips may be used from the bottom of the monitoring well to within 20 feet below the surface of the well. The well driller shall place a surface plug consisting of neat cement, cement grout or concrete grout in the well from a depth of at least 20 feet to the surface of the well.

     3. If the casing in the monitoring well can be removed from the well bore, the bottom end of the casing in the monitoring well must be removed or perforated and neat cement or bentonite chips must be placed by tremie pipe in an upward direction from the bottom of the well to within 20 feet of the surface of the well as the casing is removed from the well bore. The well driller shall place a surface plug consisting of neat cement, cement grout or concrete grout in the well from a depth of at least 20 feet to the surface of the well.

     4. If the integrity of the borehole remains intact as the casing is removed from the well bore, the well may be plugged as a borehole as provided in NAC 534.4371.

     5. If there is evidence that water-draining formations, or water-bearing formations of different water quality or hydraulic head were encountered during the original monitoring well construction and the casing does not break free, and if bentonite chips are used as the plugging material, the driller must, in addition to the requirements of this section, perforate the casing as needed and place neat cement across each confining formation so that the plugging fluid penetrates the annular space and the geologic formation in that interval.

     6. If the water-bearing formations are unknown and any casing does not break free, bentonite chips must not be used as the plugging material. The driller must perforate the casing as needed and plug the monitor well with neat cement so that the plugging fluid penetrates the annular space and the geologic formation.

     (Added to NAC by St. Engineer, eff. 12-30-97; A by R009-06, 6-1-2006; R039-12, 6-29-2012)