36.12.121 AQUIFER TESTING REQUIREMENTS

(1) Aquifer testing design and procedures must follow standard procedures that are discussed in hydrogeology textbooks and professional literature.

(2) Minimum information that must be submitted with applications:

(a) a map with labeled location of production and observation wells;

(b) well logs of production and observation wells; and

(3) Minimum testing procedures are as follows:

(a) Pumping must be maintained throughout the duration of the test. The rate may not depart from the average pumping rate by more than 5%.

(b) The average pumping rate must be equal to or greater than the proposed flow rate if the application is for one well or if the total proposed rate for multiple wells can be obtained from a single well.

(c) The proposed pumping rate may be demonstrated by testing multiple wells as long as (e) is met by one well and the remaining flow rate is demonstrated by eight-hour drawdown and yield tests on additional production wells under (e)(ii) and (e)(iii).

(d) Pumping rate must be measured with a reliable measuring device and recorded with clock time according to the schedule on Form No. 633.

(e) Minimum duration of pumping during an aquifer test must be 24 hours for a proposed pumping rate and volume equal to or less than 150 GPM or 50 acre-feet, or 72 hours for a proposed pumping rate and volume greater than 150 GPM or 50 acre-feet.

(i) At a minimum, an eight-hour drawdown and yield test is required on all new production wells.

(ii) In addition to (e), if more than one new production well is proposed, at a minimum an eight-hour drawdown and yield test is required on all subsequent new production wells.

(iii) The testing procedures for a minimum eight-hour drawdown and yield test performed on any production well must follow (a), (d), and (h).

(f) One or more observation wells must be completed in the same source 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.

(g) Background groundwater levels in the production well and observation well(s) must be monitored at frequent intervals for at least two days prior to beginning the aquifer test according to Form No. 633.

(h) Water levels in the production well and/or observation well(s) must be reported with 0.01-foot precision according to the schedule specified on Form No. 633.

(4) An applicant may make a written request for a variance from the aquifer testing requirements in (2) and (3). The variance process is provided for in ARM 36.12.123.

History: 85-2-113, 85-2-370, MCA; IMP, 85-2-302, 85-2-311, 85-2-330, 85-2-341, 85-2-343, 85-2-344, 85-2-360, 85-2-361, 85-2-362, 85-2-402, 85-2-506, 85-2-508, MCA; NEW, 2004 MAR p. 3036, Eff. 1/1/05; AMD, 2012 MAR p. 2071, Eff. 10/12/12; AMD, 2018 MAR p. 451, Eff. 2/24/18; AMD, 2023 MAR p. 1872, Eff. 1/1/24.