Engineering Infrastructure & Subdivisions

• A Certificate of Subdivision Approval otherwise known as a COSA is sanitation approval from the Montana Department of Environmental Quality. The COSA outlines what the use of the property is, such as residential or commercial. It also describes what the potable water source will be (well, municipal water system, cistern, etc) and where wastewater will be disposed (drainfield/septic system, municipal wastewater facility). Finally, the COSA describes how stormwater must be mitigated for the site.

• By definition (MCA 76-4-102(23) a subdivision "means a division of land or land so divided that creates one or more parcels containing less than 20 acres, exclusive of public roadways, in order that the title to or possession of the parcels may be sold, rented, leased, or otherwise conveyed and includes any resubdivision, any condominium, townhome, or townhouse, or any parcel, regardless of size, that provides two or more permanent spaces for recreational camping vehicles or mobile homes.
  
  In most situations, if your lot was created after 1961 and it is less than 20 acres in size, your property will either have a COSA or it will have sanitary restrictions placed on it. See the FAQ on Sanitary Restrictions. Your local health department is well suited to help you determine if your property has a COSA or sanitary restrictions.

• Well locations are typically shown on the DEQ Approved Lot Layout and have a 100 foot radius well-isolation zone around them.
  
  In some cases, an "Approved Well Drilling Area" may be illustrated on the lot layout. This drilling area allows the parcel owner to drill the well anywhere within the "Approved Well Drilling Area". The area will be labeled specifically on the Lot Layout and will have a 100 foot well-isolation zone offset from it.
  
  The well must be drilled in the exact location shown on the Lot Layout or within the "Approved Well Drilling Area" unless a rewrite or modified lot layout is completed. See the FAQ on Rewrites and FAQ on Modified Lot Layouts

• The mixing zone is the area in which dilution of the wastewater is assumed to take place. It is defined in 75-5-103 and further defined in 17.30.502(6). As long as setbacks to the drainfield are met, buildings, roads, landscaping, etc. can be constructed in a mixing zone. Drinking water wells may not be installed within 100 feet of a mixing zone, unless previously approved on the DEQ Approved Lot Layout.

• DEQ tries to have digital copies of the COSA and Lot Layouts available, however, local county environmental health departments are the best resource for obtaining copies of these documents.

• 17.36.320(4) specifically states that there must be four feet of natural soil between the infiltrative surface and a limiting layer such as groundwater. Therefore, an elevated sand mound can not be used on a lot being reviewed under 76-4 MCA to create the 4 feet of separation.
  
  17.36.320(4) For subsurface systems, a minimum separation of at least four feet of natural soil must exist between the infiltrative surface or the liner of a lined system and a limiting layer. Exceptions to this rule are:
  1. at least six feet of natural soil must exist between the infiltrative surface or the liner of a lined system and a limiting layer on a slope of greater than 15 percent; and
  2. for elevated sand mounds constructed in accordance with Department Circular DEQ 4, the depth of the key may be included as part of the separation distance between the infiltrative surface and a limiting layer.

• In many cases, the house site illustrated on the lot layout is not the only location that the house can be built. Property owners should work with their local environmental health department and planning department to determine home sites that meet all applicable setbacks.

• Yes, even thought you have a COSA, a drainfield permit is still required by the local health department.

• Many local health departments have the ability to make minor changes to the drainfield and it's location. A Modified Lot Layout or rewrite is required if the drainfield location is greater than 25.0 feet from the soil profile used for siting the approved drainfield location. See the FAQ on Modified Lot Layouts and/or Rewrites.

• A rewrite of the COSA will be required to add a second living unit because it changes language in the COSA. See the FAQ on Rewrites.

• A modified lot layout/revised lot layout is used when changes are needed on the lot layout and the changes do not affect the language in the COSA. Common examples of modified lot layouts are moving a well location or changing the drainfield position.

• Sanitary Restrictions were allowed to be placed on subdivision lots prior to July 1, 1973. These restrictions were placed on the property in order to exempt the property from sanitation review. In some cases, sanitary restrictions were placed automatically on a lot(s) because the lot was required to go through sanitation review at the time the survey was filed but did not receive a COSA prior to filing.
  
  Finally, after July 1, 1973 many lots were excluded from sanitation review through the use of "no facilities" exemptions. These exemptions are listed on the front of the survey and state something like "Parcel A is excluded from sanitation review by the Department of Environmental Quality pursuant to 17.36.605(2)(a) as a parcel that has no facilities for water supply, wastewater disposal, storm drainage, or solid waste disposal, if no facilities will be constructed on the parcel;"
  
  In either case, a COSA must be issued for the lot(s) prior to developing facilities that require sewer or water.

• A COSA Rewrite is used to change specific requirements outlined in the COSA. For example, a rewrite is required to change the use of a parcel from one living unit to two living units, or from one living unit to one commercial unit. Changing the location of a well or drainfield may not require a rewrite but rather a Modified Lot Layout may be requested. See the FAQ on Modified Lot Layouts.

On February 14, 2024, Montana’s First Judicial District Court issued an order in Upper Missouri Waterkeeper, et al v. DNRC, in which it ruled that the Montana Department of Natural Resources and Conservation (DNRC) incorrectly applied the law when it determined that a developer was entitled to appropriate up to 10 acre-feet of water for each phase of a four-phased subdivision under the permit exception. The Court concluded that DNRC is required to treat all phases of a multi-phased development as part of the same combined appropriation. The Court also called into question other aspects of DNRC’s authority and evaluation of combined appropriations in the context of the subdivision review conducted by DEQ and local governments.

In the wake of the Court's order, DNRC and DEQ reevaluated their processes, resulting in a few changes:

• DEQ and DNRC terminated the Memorandum of Understanding between the two agencies that formally set forth the predetermination process for water rights. DNRC will no longer issue predetermination letters.
• DEQ must comply with ARM 17.36.103 (n) and (o). However, DEQ has begun the process of amending these rules to no longer require a predetermination letter for subdivision approval. While the rules are in the process of being amended, DEQ will deny subdivision applications submitted without a predetermination letter. If proposed rule amendments to ARM 17.36.103 (n) and (o) are effectuated, a Certificate of Subdivision Approval (COSA) may be issued without a predetermination letter upon final adoption.
• DNRC rescinded the Combined Appropriation Guidance that was last updated on March 23, 2022. DNRC will analyze groundwater development to determine whether it constitutes a “combined appropriation” with other existing groundwater developments pursuant to § 85-2-306, MCA, ARM 36.12.101(12), and any other law applicable at the time the Notice of Completion of Groundwater Development (Form 602) is filed. A groundwater development serving a lot in a single-phase subdivision or multi-phased subdivision will be treated as a combined appropriation with other groundwater developments in the respective subdivision for purposes of compliance with the 10 acre-feet volume limit of the permit exception in 85-2-306(3), MCA.  The cumulative volume of water appropriated by groundwater developments used in a multiphase subdivision may not exceed 10-acre feet annually when the exception under §85-2-306 is used to acquire water rights

Click the button below to read the Frequently Asked Questions on DNRC's website to learn how these changes may impact pending development, as well as what's on the horizon to ensure long-term clarity and coordination in the subdivision approval process.

Exempt Well FAQs

• Complete Application Package (Print- Updated August 23, 2024)
• Complete Application Package (Fillable- Updated August 23, 2024)
• Guidance & Instructions
• Pre-Application Form (Print) Pre-Application Form (Fillable)
• Application Part I - General Description & Information (Print) General Description & Information (Fillable)
• Application Part II - Required for Approval under Sanitation in Subdivisions Laws
• Application Part III - Required for Environmental Assessment under the  Subdivision & Platting Act
• Application Part IV (Print) Application Part IV (Fillable) - Subdivision Checklist -Updated December 22.2023
• Attachment A (Print) Attachment A (Fillable) - Waiver Request (Professional Engineer)
• Attachment B (Print) Attachment B (Fillable)- Waiver Request (Non-Engineer)
• Stormwater Certification (Fillable) - Sanitation in Subdivisions Act, ARM 17.36.310(5)

• Significance Determination Checklist
• Subdivision Review Fee Calculation - Effective December 22, 2023
• Environmental Assessment Checklist
• Mixing Zone (MZ) & Well Isolation Zone (WIZ) Flow Chart
• Element Checklist

• DEQ Circulars and Regulations

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 AdvanTex (AX model )
• Orenco AdvanTex (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)
• StreamStats Guidance

• Municipal Facilities Exclusion Checklist(MFE)
• Fillable MFE Checklist
• County Water and Sewer District Facilities Exclusion
• County Water and Sewer District Facilities Exclusion Fillable
• Fillable Notice of Change to Municipal or District Water & Sewer Checklist

Circular DEQ-8 and Stormwater Spreadsheets

• ARM 17.36.310(5) Certification
• DEQ-8 Subdivision Stormwater Drainage
• DEQ-8 Simplified Plan Spreadsheet
• DEQ-8 Standard Plan Spreadsheet

The public water and wastewater engineering review program reviews plans and specifications for new systems and alterations to existing systems. Approval from DEQ is required to construct, alter or extend a public sewer system serving 15 or more families or 25 or more persons daily for any 60 or more days in a calendar year.

1. Prior to operating, constructing, altering or extending a public water supply, the applicant must submit an engineering report along with the necessary plans and specifications to DEQ or a delegated division of local government for review and written approval.
2. The engineering report, plans, and specifications for a community public water supply must be prepared and designed by a professional engineer according to specific engineering criteria. An engineer may be required to prepare plans and specifications for a noncommunity public water supply when the complexity of the proposed system warrants that level of involvement by an engineer.
3. The applicant must identify the legal entity responsible for the ownership, operation, maintenance, and perpetuation of the public water supply system. If a change of ownership occurs, DEQ must receive written notice within 30 days.
4. The department has 60 days to approve, approve with conditions, deny the application, or to request more information. The DEQ or a delegated division of local government will issue a written approval for a public water supply system if it determines that the design report, plans, and specifications are complete and the applicant has complied with department rules.
5. If construction, alteration, or extension of the community public water supply system has not been completed within three years after approval, the applicant must resubmit all of the information required in items one through three above.
6. Within 90 days after the construction, alteration, or extension of the public water supply system, the project engineer must certify to DEQ that the required work was completed according to the approved plans and specifications.

Plan Review Fee Record Design Criteria

• Environment Assessment Business Process Flowchart
• DEQ Montana Environmental Policy Act (MEPA) Procedural Rule and Guidelines

Environmental Assessments

• Major Facility Siting Act Amendment for Talen Energy to utilize non-Rosebud Mine Seam Coal
• Rescission of Major Facility Siting Act Amendment for Talen Energy to utilize non-Rosebud Mine Seam Coal

Water/Sewer Main and Water Supply Well Checklists

• Plan Review Fee Record
• Deviation Form A - Request for deviations submitted by a professional engineer
• Fillable Deviation Form A - Request for deviations submitted by a professional engineer
• Deviation Form B
• Fillable Deviation Form B
• Sample Easement Language
• Preliminary Assessment Form - Preliminary Assessment of Groundwater Sources that may be Under the Direct Influence of Surface Water
• Well Grout Form - Supplemental for PWS wells
• 2018 Community Water Supply Well Checklist DEQ-1
• 2018 Non-Community Water Supply Well Checklist DEQ-3
• 2014 Water Main Extension and Replacement Checklist
• 2014 Sewer Main Certified Checklist

The Drinking Water State Revolving Fund (DWSRF) program is a federal-state partnership to help ensure safe drinking water. The program provides financial support to water systems and to state safe water programs.

Types of Financial Assistance

Types of assistance currently provided are direct loans and purchase or refinancing of existing debit.

Financial Requirements

• Financial capability to properly operate the system and to repay the loan
• Loan secured by a Bond or Note
• Different bonding & security options exist (Revenue, general obligation, SID, RSID, tax increment)
• Revenue Bond requires debt service reserve and coverage of 110%.
• Maintain financial records

Terms

The current interest rate is 2.5 percent with payment schedules not to exceed 20 years. Drinking Water Projects qualifying as disadvantaged may extend term up to 30 years.

Funds Available

The SRF loan programs are designed to provide a perpetual source of financial assistance to Montana communities.

The Water Pollution Control State Revolving Fund (WPCSRF) Program was established for water pollution control projects. The program provides at or below market interest rate loans to eligible Montana entities.

Examples of Eligible Water Quality Projects

Wastewater Projects

• Wastewater treatment plant improvements
• Interceptors, collectors, and lift stations
• Lagoon construction & rehabilitation
• Engineering & project inspection
• Land used for disposal purposes

Non-Point Source Projects

• Agricultural BMPs
• Urban storm water /construction runoff
• Animal feed operations (AFOs)
• Wetlands/Stream bank restoration
• Underground storage tanks
• Septic system removal or upgrade

Types of Financial Assistance

Types of assistance currently provided are: direct loans and purchase or refinancing of existing debt.

Financial Requirements

• Financial capability to properly operate the system and to repay the loan
• Loan secured by a Bond or Note
• Different bonding & security options exist (Revenue, general obligation, SID, RSID, tax increment)
• Revenue Bond requires debt service reserve and coverage of 110 percent
• Maintain financial records

Terms

The current interest rate is 2.5 percent with payment schedules not to exceed 30 years for certain projects.

Funds Available

The SRF loan programs are designed to provide a perpetual source of financial assistance to Montana communities.

To begin the application process, all entities must request that their project(s) be added to the Priority List contained in the Intended Use Plan. Early notification by the applicant is essential to get on the priority list and a project remains on the list until it has been completed regardless of the funding source(s) used to finance the project. This annual process begins in the Spring to identify projects which may need SRF funding for their project in the upcoming year.

The WPCSRF Survey Form or the DWSRF Survey Form is required to be placed on the Project Priority List. If your project is to address an emerging contaminant related to drinking water, use the DWSRF EC Survey Form. If your project is to address replacement of lead service lines use the DWSRF LSL Survey Form. Please COMPLETE and submit to DEQ Engineering Bureau with supporting information.

Once ready to begin the project, applicants must submit the Uniform Application Form For Montana Public Facility Projects to request SRF loan funding. These applications are accepted year round. After the application is evaluated and approved, funds can be committed to a project. The SRF loan program cooperates with the other funding programs to ensure project funding is available when it is needed.

Loans will be offered on a first-come basis until the demand exceed the available funds. Lower ranked projects may be funded before higher ranked projects (if the higher ranked project is not ready to proceed) as long as the funds are available. Ranking on the priority list is based on water quality and/or public health impacts and financial needs.

2025 Intended Use Plans and Project Priority Lists

Drinking Water | 2025 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2025 Intended Use Plan and Projecty Priority List (Final)

2024 Intended Use Plans and Project Priority Lists

Drinking Water | 2024 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2024 Intended Use Plan and Projecty Priority List (Final)

2023 Intended Use Plans and Project Priority Lists

Drinking Water | 2023 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2023 Intended Use Plan and Projecty Priority List (Final)

2022 Intended Use Plans and Project Priority Lists

Drinking Water | 2022 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2022 Intended Use Plan and Project Priority List (Final)

2021 Intended Use Plans and Project Priority Lists

Drinking Water | 2021 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2021 Intended Use Plan and Project Priority List (Final)

2020 Intended Use Plans and Project Priority Lists

Drinking Water | 2020 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2020 Intended Use Plan and Project Priority List (Final)

2019 Intended Use Plans and Project Priority Lists

Drinking Water | 2019 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2019 Intended Use Plan and Project Priority List (Final)

2018 Intended Use Plans and Project Priority Lists

Drinking Water | 2018 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2018 Intended Use Plan and Project Priority List (Final)

2017 Intended Use Plans and Project Priority Lists

Drinking Water | 2017 Intended Use Plan and Project Priority List (Final)
Water Pollution Control | 2017 Intended Use Plan and Project Priority List (Final)

• Lead Service Line Intended Use Plan and Priority List 2023 - Amended (Final)
• Lead Service Line Intended Use Plan and Priority List 2023 (Final)

• Emerging Contaminant Intended Use Plans and Project Priority List DWSRF 2024-2025 (Final)
• Emerging Contaminant Intended Use Plans and Project Priority List DWSRF 2023 - Amended (Final)
• Emerging Contaminant Intended Use Plans and Project Priority List WPCSRF 2024 (Final)
• Emerging Contaminant Intended Use Plans and Project Priority List WPCSRF 2023 (Final)

• Drinking Water State Revolving Fund 2023 Annual Report
• Drinking Water State Revolving Fund 2022 Annual Report
• Drinking Water State Revolving Fund 2021 Annual Report 
• Drinking Water State Revolving Fund 2020 Annual Report
• Drinking Water State Revolving Fund 2019 Annual Report
• Drinking Water State Revolving Fund 2018 Annual Report
• Water Pollution Control State Revolving Fund 2023 Annual Report
• Water Pollution Control State Revolving Fund 2022 Annual Report
• Water Pollution Control State Revolving Fund 2021 Annual Report
• Water Pollution Control State Revolving Fund 2020 Annual Report
• Water Pollution Control State Revolving Fund 2019 Annual Report
• Water Pollution Control State Revolving Fund 2018 Annual Report
• Letter to the Governor
• 2020 Triennial Report
• Montana's Report on Four Years of Wastewater Optimization