R 560.422 Deep cut excavations.

Rule 422. (1) If suitable soils, as specified in Table 3, are not present within the upper 6 feet of the soil profile and alternative methods of sewage treatment and disposal have been considered under R 560.424, then the department may approve the use of deep cut excavations to expose acceptable underlying soils that exist within 20 feet of the natural grade. (2) Acceptable underlying soils shall consist of a minimum of 4 feet of soils which have a permeability of greater than 30 minutes per inch and which are not permanently or seasonally saturated as confirmed by soil profile evaluations. (3) Deep cut excavations are not allowed if the soils that are cut through are seasonally or permanently saturated. Exceptions may be considered where drainage of groundwater from overlying soils would not be expected to adversely impact the function of the sewage disposal system. (4) Deep cut excavations are not allowed unless hydrogeologic information confirms that the underlying soils being exposed have no direct hydraulic connection to a useable aquifer intended for drinking or household purposes. (5) For deep cut excavations the department may require alternative methods of sewage treatment. The department may require such excavations to be completed and filled with medium to coarse sands in accord with the USDA classification system before final recording of the plat or approval for on-site sewage disposal of a development site that is less than 1 acre in size. Any of the following persons demonstrating competence shall provide certification of fill materials and placement to the department: (a) A licensed professional engineer. (b) A professional surveyor. (c) A registered sanitarian. (d) A certified professional geologist. (e) A certified professional soil scientist. (f) A professional approved by the department. (6) The owner or owner's designated representative shall complete deep cut excavations over 100% of the required initial and reserve absorption system area for the upper 6 feet; however, excavations may be reduced to a minimum of 50% of the required absorption system area between 6 and 20 feet deep.