(1) The applicant shall meet the following requirements relating to the design and construction of nonpublic water supply systems:

(a) individual and shared wells must be constructed in accordance with ARM Title 36, chapter 21, subchapter 6, unless the requirements of this subchapter are more stringent;

(b) multiple-user water supply systems must be designed and constructed in accordance with department Circular DEQ-3, and ARM Title 36, chapter 21, subchapter 6, unless the requirements of this subchapter are more stringent;

(i) multiple user water supply systems with six or more connections, including connections outside of a proposed subdivision, must be designed by a registered professional engineer and as-built plans must be submitted to the department within 90 days after completion of the system. If an existing system is expanded to serve six or more connections, the expansion must be designed by a registered professional engineer. The reviewing authority may require smaller systems that it determines to be complex (e.g., a water supply system with substantial pressure difference through the distribution system) to be designed by a registered professional engineer;

(ii) if more than one multiple user water system is proposed for a subdivision, the systems must be tied together to ensure greater system reliability. The department may grant a waiver, pursuant to ARM 17.36.601, of this provision if the applicant demonstrates that interconnection of the systems is physically or economically impractical or would create an environmental or public health concern;

(c) the reviewing authority may require additional well construction and/or testing requirements not required in ARM Title 36, chapter 21, subchapter 6 or in department Circular DEQ-3, to ensure that wells within a particular subdivision will provide an adequate water supply.