Section R. 560.421 - Soil suitability for conventional systemsRule 421.
(1) The department shall ensure that soil texture and permeability conforms to the types and ranges specified in Table 3. Table 3
Suitable Soil Texture and Permeabilities
| Soil Texture | Permeability* (minutes/inch) |
| Sand, loamy sand | 1 - 15 |
| Sandy loam | 16 - 30 |
| Sandy clay loam, light loam | 31 - 60 |
| Clay loam, silty clay loam, clay | Above 60 |
* soil structure shall also be considered when evaluating permeabilUitnys. uitable
(2) To provide for adequate soil treatment capability, a minimum of 3 feet of unsaturated soil shall exist between high groundwater elevation or bedrock and the bottom of the infiltrative surface. Greater vertical separation may be required in accordance with the regulations of the city, county, or district health department having jurisdiction under the authority granted by Act No. 368 of the Public Acts of 1978, as amended, being §325.1101 et seq. of the Michigan Compiled Laws. Greater vertical separation may also be required where groundwater mounding underneath the soil absorption system or other factors would limit the treatment to protect on-site water supplies or surface waters. For lots or development sites less than 1 acre, the soil below the infiltrative surface of the absorption system shall meet the texture and permeability requirements of Table 3.(3) If the required 3 feet of unsaturated soils cannot be provided naturally, then the department will consider proposals for fill. Fill is acceptable only if the depth to high groundwater elevation or bedrock, or both, is a minimum of 2 feet below the natural, unaltered ground surface. Fill is only acceptable over soils specified in Table 3 as suitable by texture and permeability.(4) Fill materials shall consist of medium to coarse sands in accordance with the USDA classification system without excessive fines. Fill materials may be required to be placed for both the initial and reserve sewage disposal system areas 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.(5) If filling is required, any of the following persons may be required to submit a detailed development plan as the basis for approval: (a) A licensed professional engineer.(b) A professional surveyor.(c) A registered sanitarian.(d) A professional approved by the department. The person shall draw the detailed plan to scale showing both existing and proposed contours that have a maximum 2-foot interval and shall indicate the area for the initial and replacement sewage disposal system at locations that will be accessible for maintenance or replacement, or both.
Mich. Admin. Code R. 560.421