(1) There are numerous tests that can be performed on wells and aquifers, with a variety of objectives and procedures. An adequate aquifer test will depend on factors such as whether the well is located in a basin closure area (see ARM 36.12.120) , the expected pumping schedule of the well, the potential interference with existing water rights and the characteristics of the aquifer in which the well is completed.

(2) Applicants are encouraged to confer with department staff prior to designing an aquifer test to ensure that the test will not have to be repeated, which may require additional expense.

(a) Department staff will provide guidance on testing procedures, monitoring, and reporting, but will not provide technical support or assistance.

(3) Aquifer testing must follow standard procedures that are discussed in hydrogeology textbooks and professional literature. The following are preferred aquifer testing procedures:

(a) A hydrogeologist, hydrologist, or engineer familiar with aquifer testing procedures must supervise the aquifer test, however, the supervisor does not need to be on site.

(b) Aquifer test data Form No. 633, or equivalent, must be used to record the data required for the test.

(c) Pumping must be maintained at a constant discharge rate equal to or greater than the proposed pumping rate for the entire duration of the test. If the discharge rate varies, the applicant must note the clock time and discharge rate.

(d) Minimum duration of pumping during an aquifer test must be 24 hours for a proposed use or discharge of 150 gpm or less and a proposed volume of 50 acre-feet or less.

(e) Minimum duration of pumping during an aquifer test must be 72 hours for a proposed use or discharge of greater than 150 gpm and proposed volume greater than 50 acre-feet.

(f) Discharge of the pumped well must be measured with a reliable measuring device, which can include a barrel, in-line flow meter, flume, or weir.

(g) Discharge rate must be monitored and recorded with clock time and adjusted if necessary at 15-minute intervals during the first three hours of the aquifer test and at frequent intervals until the end of the test to maintain a constant discharge.

(h) Discharged water must be conveyed a sufficient distance from the production and observation wells to prevent recharge to the aquifer during the test. Adequate water conveyance devices include pipe, large-diameter hose (e.g., fire hose) , lined ditch or canal, or an existing irrigation system.

(4) The following procedures are preferred to ensure monitoring is adequate:

(a) One or more observation wells must be completed in the same water-bearing zone(s) or aquifer as the proposed production well and close enough to the production well so that drawdown is measurable and far enough that well hydraulics do not affect the observation well.

(b) One or more observation wells must be completed in the overlying water-bearing zone(s) or aquifer if the proposed production well is purported to be completed in a hydraulically disconnected deeper aquifer.

(c) An observation well can be an existing well. An existing well should not be pumped, or if pumped should be monitored at a frequency necessary to separate the effects of its pumping.

(d) New observation wells must be constructed as described in ARM Title 36, chapter 21, subchapter 6. However, observation wells less than ten feet deep are not subject to those rules. In those cases, observation wells might be constructed by simple excavation, or installing PVC pipe, perforated black pipe, or a sand point.

(e) Electronic pressure transducer/data logger instrumentation, electric well probes, pressure gauges on turbine pumped wells, or graduated steel tapes are acceptable methods of measuring groundwater levels.

(f) Groundwater levels in the production, at least one of the observation wells in the source aquifer, and at least one observation well in the overlying water-bearing zone or aquifer must be monitored at frequent intervals for at least two days prior to beginning the aquifer test to evaluate background water-level trends and the prepumping hydraulic gradient. An applicant must evaluate and correct for background water-level trends.

(g) Groundwater-level drawdown in the production well and monitored observation well(s) during the pumping phase of the aquifer test must be measured with 0.01-foot precision according to the schedule specified on Form No. 633.

(h) Groundwater-level recovery in the production and monitored observation well(s) must be measured with 0.01-foot precision according to the schedule specified on Form No. 633 or at a minimum, according to the specified schedule on Form No. 633 for the first 24 hours of recovery and four times per day until end of the recovery test.

(5) A report describing the testing and monitoring procedures and presenting analyses, interpretations, and conclusions must be submitted with the application. The following reporting requirements are preferred:

(a) a topographic map with labeled locations of production and observation wells, discharge point, surface water monitoring sites, and a scale bar and north arrow;

(b) if available, a geologic map, stratigraphic, geomorphic, or lithologic descriptions, and drilling logs;

(c) distances between the pumping well and the observation well, and depths, dimensions, and perforated intervals of each well as specified on Form No. 633;

(d) surveyed wellhead elevations and staff gage elevations if basin closure testing is required;

(e) a narrative description or conceptual model that describes the aquifer system;

(f) a description of testing methods;

(g) groundwater level and surface water monitoring data;

(h) aquifer-testing data, transmissivity and storage coefficient determinations and effects to groundwater and surface water availability;

(i) analyses, interpretations, and conclusions; and

(j) all pumping schedules and drawdown and recovery data must be submitted in electronic format.