(1) The reviewing authority may require that percolation tests, conducted in accordance with department Circular DEQ-4, be performed within the boundary of each proposed subsurface sewage treatment system. Percolation tests must be keyed by a number on the lot layout to the results in the report form.

(2) If the applicant or the department has reason to believe that ground water will be within seven feet of the surface at any time of the year within the boundaries of the treatment system, the applicant shall install ground water level observation pipes to a depth of at least eight feet to determine the seasonally high ground water level. The applicant shall monitor the observation pipes through the seasonally high ground water period.

(3) The applicant shall provide descriptions of the soils within 25 feet of the boundaries of each proposed drainfield. Soil descriptions must address the characteristics used in the U.S. Department of Agriculture's National Soil Survey Handbook (USDA, NRCS, September 1999) , and the Soil Survey Manual (USDA, October 1993) . These characteristics include, but are not limited to, soil texture, soil structure, soil consistence, and indicators of redoximorphic features. Soil descriptions must meet the following requirements:

(a) Soil descriptions for the proposed subdivision must be based on data obtained from test holes. Test holes must be at least eight feet in depth;

(b) At least one test hole must be dug for each individual drainfield and for each shared (two-user) drainfield, unless a waiver is approved by the department pursuant to ARM 17.36.601. Before a waiver is requested and granted, the applicant must complete test holes for 25% of the proposed drainfield locations in the subdivision, demonstrate that the soils are consistent throughout the area requested for a waiver, and must obtain the approval of the local reviewing authority for reduction in number of test holes. At least three test holes must be dug for each multiple-user and public drainfield, unless a waiver is approved by the department pursuant to ARM 17.36.601. At least one test hole must be dug in each zone of a pressure-dosed drainfield, unless a waiver is approved by the department pursuant to ARM 17.36.601. The department shall require additional test holes if it determines that there is significant variability of the soils in the proposed drainfield area;

(c) Test holes must be located within 25 feet of the boundaries of the proposed drainfield. The locations must be established by a person qualified to evaluate and identify soil in accordance with ASTM standard D5921-96el (Standard Practice for Subsurface Site Characterization of Test Pits for On-Site Septic Systems) ;

(d) If the applicant or the department has reason to believe that a limiting layer is within seven feet of the ground surface at the site of proposed subsurface sewage treatment systems, additional test pits and soil descriptions sufficient to describe the suitability of the soil must be provided; and

(e) Each test hole must be keyed by a number on a copy of the lot layout or map with the information provided in the report.