The Montana Department of Natural Resources and Conservation (DNRC) has adopted rules governing the installation and abandonment of monitoring wells in Montana. Construction standards for monitoring wells are found in Administrative Rule of Montana (ARM) 36.21.801 et seq. and includes requirements for construction materials, installation of seals, prevention of contamination by equipment, and site protection and security. The regulations also require that a monitoring well constructor licensed by the Montana Board of Water Well Contractors prepare a monitoring well report form for each monitoring well drilled. The monitoring well constructor must supply copies of the report to the monitoring well owner and DNRC within 60 days of completing the well and must also retain a copy as a record in the constructor's files.
In addition, Montana Code Annotated (MCA) § 85-2-516 requires that, within 60 days after any well is completed, the driller must file a well log report with the Montana State Bureau of Mines and Geology. The well log report must be filed on a form specified by DNRC, which includes identifying a location for the well using at least two methods as specified on the form.
An initial survey of groundwater monitoring well elevations must be completed by a licensed surveyor or professional engineer registered in the State of Montana in accordance with MCA § 37-67-301 et seq. and ARM 24.183.101 et seq. Survey results must provide an accuracy of plus or minus 0.1 foot horizontally and plus or minus 0.01 foot vertically. The vertical control datum used to determine the elevation of the well must be the North American Vertical Datum of 1988 (NAVD 88), which should be referenced to a nearby United States Geological Survey (USGS), or equivalent, benchmark.
At CECRA facilities, latitude and longitude coordinates reference the State Plane NAD83 HARN Coordinate System, which should also be referenced to a nearby USGS, or equivalent, horizontal control mark.
ARM 36.21.810 provides that “[w]ells which have not been monitored for more than 3 years shall be deemed abandoned unless written permission is obtained from the board [of water well contractors] to maintain the well.” Standards for abandoning monitoring wells is also provided in this regulation.
Additional regulation regarding Monitoring Well Construction Standards can be found in the ARM 36.21.8.