Montana’s Water Quality Act requires the Department of Environmental Quality to protect high quality waters from degradation. Nondegradation rules apply to all Montana Pollutant Discharge Elimination System (MPDES) permits, Montana Ground Water Pollution Control System (MGWPC) permits, and any activities that may affect the quality of surface or ground water.
Nondegradation determinations are typically associated with “mixing zones.” A mixing zone is defined by law and by rules as an area of wastewater discharge as it enters either receiving surface water or ground water. The zone is established in the wastewater permit or by final decision by DEQ on nondegradation. Water quality standards may be exceeded within the zone; however, the mixing zone must have: a definable boundary; be of the smallest practicable size; and a minimum effect on water uses. Water quality standards must be met at the end of a mixing zone. A mixing zone cannot be granted for a surface water discharge permit if it would threaten or impair existing beneficial uses. For ground water, human health-based standards must not be exceeded beyond the boundaries of the mixing zone. A proposed activity may not begin until DEQ has issued a nondegradation determination. Certain exemptions may apply to the nondegradation requirements. More information about mixing zones and nondegradation can be found in Water Quality Standards and in the Mixing Zone Rules
List of Subsurface Wastewater Treatment Systems (SWTS) that are approved as a Nitrogen-Reducing System
Orenco AdvenTex (AX model )
Orenco AdvenTex (AX20RT model )
Bio-Microbics MBR
Bio-Microbics Micro-FAST
ECOPOD-N
Fluidyne Eliminite
Fluidyne ISAM Sequencing Batch Reactor (SBR)
E-Z Treat Model 600 and 1200
HDR Engineering Activted Sludge / Biological Nutrient Reduction
HDR Engineering Membrane Filtration
International Wastewater Systems Model 6000 (SBR) with methanol
International Wastewater Systems Model 6000 (SBR)
Jet Model J-500CF
Norweco Hydro-Kinetic Model 600 FEU
Norweco Singular Green TNT
Norweco Singular TNT
Northwest Water Systems Model 2400 SBR
Northwest Water Systems Model 7500 SBR
Quanics Bio-COIR
Santec Extended Aeration Process
SepticNet
SeptiTech MD
How to Perform a Nondegradation Analysis for Subsurface Wastewater Treatment Facilities
- Appendix A: SWTS - Nondegradation Checklist (xls)
- Appendix B: SWTS - Significance Determination Checklist (pdf)
- Appendix C: SWTS - Ground Water Mixing Zone Determination Checklist (pdf)
- Appendix D: SWTS - Surface Water Mixing Zone Determination Checklist (pdf)
- Appendix E: Nitrate Sensitivity Analysis Spreadsheet (xls)
- Appendix E: Nitrate Sensitivity Analysis Spreadsheet - Cumulative Effects (xls)
- Appendix F: Bauman and Schafer Paper (pdf)
- Appendix G: Calculating Hydraulic Conductivity from Well Log Pumping Test Data (pdf)
- Appendix H: Hydraulic Gradient Three Point Solution Worksheet (pdf)
- Appendix I: Hydraulic Gradient Example (gif)
- Appendix J: Allowed Nitrate Concentrations (ARM 17.30.715) (pdf)
- Appendix K: Examples of Accepted Methods for Drawing Mixing Zones (pdf)
- Appendix L: Nitrate Sensitivity Analysis: Cumulative Effects Example (pdf)
- Appendix M: Identification of Confined Aquifers (1/3) (pdf)
- Appendix M: Identification of Confined Aquifers (2/3)(pdf)
- Appendix M: Identification of Confined Aquifers (3/3) (pdf)
- Appendix N: Phosphorus Breakthrough Analysis Spreadsheet (xls)
- Appendix O: Calculation of Cumulative Phosphorus Impacts (pdf)
- Appendix O: Calculation of Cumulative Phosphorus Impacts Figure (jpg)
- Appendix P: Summary of Categorical Exemptions (pdf)
- Appendix Q: Adjacent to Surface Water Dilution Analysis (xls)
- Appendix R: Darcy's Law for Calculating Ground Water Flow Volumes (pdf)
- Appendix S: Estimating 7Q10 on an Ungauged Stream (pdf)
- Appendix T: Trigger Value Calculations for Impacts of Nitrates to Surface Water (pdf)
- Appendix U: Pathogen Transport (xlsx)