(1) The applicant shall demonstrate that ground water quantity is sufficient for the proposed subdivision. The applicant shall show that the following minimum flows are available:

(a) a single-family water system must provide a sustained yield of at least 10 gallons per minute over a one-hour period, six gallons per minute over a two-hour period, or four gallons per minute over a four-hour period. For purposes of the minimum flows identified in this rule, sustained yield must be based on water that is supplied from the aquifer, not from well bore storage; and

(b) a shared water system must provide a sustained yield of at least 15 gallons per minute over a one-hour period or 10 gallons per minute over a two-hour period.

(2) The minimum flows required in (1) (a) and (b) must be demonstrated through one or more of the following:

(a) test wells within the proposed subdivision;

(b) well logs and testing of nearby wells;

(c) hydrogeological reports; or

(d) ground water modeling.

(3) Multiple-user water supply systems must comply with department Circular DEQ-3. For individual and shared water supply systems, the reviewing authority may require pumping tests for one or more wells to demonstrate sufficient quantity and dependability. The tests must be conducted pursuant to department Circular DEQ-3.

(4) When the proposed water supply is an unconfined aquifer and a significant recharge source is from irrigation ditches or irrigated fields, the reviewing authority may require the applicant to demonstrate that the source will produce a water supply that is sufficient in terms of water quality, quantity and dependability for the proposed subdivision if all irrigation-related recharge to the aquifer is eliminated.

(5) The department may allow, pursuant to a waiver under ARM 17.36.601, a lesser flow than those set out in (1) (a) and (b) if the applicant demonstrates that the water supply system provides a sufficient quantity of water to meet demands and that adequate storage is provided to meet peak demand.

(6) The reviewing authority may require the applicant to submit information in addition to that required in (1) through (5) to demonstrate the dependability of the ground water supply if the reviewing authority believes that dependability is questionable. At a minimum, the applicant shall provide evidence that the aquifer can supply, by itself or through recharge from surrounding geologic units, water to wells in an amount equal to the proposed ground water withdrawals.

(7) If water is to be supplied by means other than individual on-site wells, the reviewing authority shall review the applicant's information about water right ownership and water use agreements to determine the quantity and dependability of the water supply.