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Municipal Wastewater Facility Planning

Wastewater facility plans shall be prepared for each reviewable project involving new or modified sewerage systems owned by municipal or other non-industrial entities pursuant to s. NR 110.08(1), Wis. Adm. Code. The basic purpose of facility planning is to assess the condition of a sewerage system, establish a need for improvement, evaluate options to address system needs and to identify the cost-effective alternative.

Design Flow

Planning Assumptions

In accordance with s. NR 110.09(1), Wis. Adm. Code, a 20-year planning period shall be used for wastewater facility planning. The 20-year period shall commence with the anticipated start-up of the proposed new facilities. A sewer service area shall be identified. If the facility is located in a NR 121, Wis. Adm. Code, designated planning area or in a community larger than 10,000 people, then the sewer service area must conform to the recommendations of the applicable area-wide water quality management plan as approved by the department. The Regional Planning Commission or other designated agency responsible for implementation of the area-wide plan must document that sewer service area and population projections conform to the area-wide plan.

As indicated in s. NR 110.09(2)(j)4, Wis. Adm. Code, it is possible to stage the construction of treatment facilities over time periods of less than 20 years. This must be justified, however, by a cost-effective analysis performed over a 20-year planning period. If a staged project is to be evaluated, the effluent limits should be obtained for both the 20-year design flow and the design flow for any lesser staged design period. Both sets of limits would be necessary in order to complete the cost-effectiveness comparison of the staged alternative and the normal 20-year design alternative.

Population Projections

Requirements for population projections are addressed in s. NR 110.09(2)(j)1, Wis. Adm. Code. Population projections for service areas within NR 121, Wis. Adm. Code, designated areas or in communities larger than 10,000 people must conform with area-wide water quality management plans and receive approval from the applicable Regional Planning Commission or other designated agency. All other projects must conform to the official Wisconsin Department of Administration population estimates and projections made in accordance with s. 16.96, Wis. Stats. If population projections for specific areas are not available, or need to be broken down into more detail, a linear extrapolation of trends from the recent past should be used. Any deviation from a linear projection method must be clearly justified.

Derivation of Design Flows

Many factors need to be considered to predict future wastewater facility flows and loadings in a manner that will ensure a cost-effective design and facility service life. Although ch. NR 110, Wis. Adm. Code, provides certain criteria for flow projection assumptions and procedures, it does appropriately allow for designer discretion, and the exercise of good professional judgment by a qualified professional engineer is important. The chapter NR 110 requirements for determinations of design flows are summarized in the remainder of this guidance.

The "average design flow" is defined in s. NR 110.03(12g)(b). Designers often use various types of dry weather flows and may refer to them as "average daily flows." Dry weather base flows may still be used as appropriate for design purposes, but the "average" flow that the DNR will use for effluent limit determinations and as the permit "design flow" must be the total annual average flow as described.

Facility design flows shall be developed according to the procedures of s. NR 110.09(2)(j). These procedures require design flow calculations to be based on existing wastewater flow data, when such data is available and is valid. The most recent flow data set covering a minimum three-year time period is recommended. Flow data may need to be adjusted to account for system bypassing events or inaccurate flow metering. The data set should be analyzed to identify a per capita average flow and various peaking factors. These can then be applied to projected population increases to obtain design flow estimates, including various maximum and peak design flows. Allowances for future increases of per capita flow over time are not allowed under s. NR 110.09(2)(j)2m.a.

Any maximum or peak design flow should normally be expressed as one of the following (exceptions may be acceptable based on specific design circumstances):

  • Maximum month design flow: The largest volume of flow anticipated to occur during a continuous 30-day period, expressed as a daily average.
  • Maximum week design flow: The largest volume of flow anticipated to occur during a continuous seven-day period, expressed as a daily average.
  • Maximum day design flow: The largest volume of flow anticipated to occur during a one-day period, expressed as a daily average.
  • Maximum hour design flow: The largest volume of flow anticipated to occur during a one-hour period, expressed as a daily or hourly average.
  • Peak instantaneous flow: The maximum anticipated instantaneous flow.

As required by s. NR 110.09(2)(j)2, flow estimates need to account for residential, commercial, institutional, industrial and infiltration and inflow (I/I) sources. Additional capacity for treatment of hauled septage wastes may also be approved where justified. If wastewater flow records are not available, water supply records may be used to estimate the "average daily base flow" (ADBF), which is the average flow excluding I/I. If adequate water supply records are not available, the ADBF may be estimated by using 60 to 70 gallons per capita per day (gpcd) for areas with populations of 5,000 or less. The ADBF may be estimated using 65 to 80 gpcd for other cities and towns. These figures account for commercial and institutional sources that would typically be associated with the residential population. Exceptions to these figures may be approved where large commercial and institutional flows exceed 25% of the total estimated ADBF.

A flow component for sewer system infiltration and inflow will need to be added to the ADBF to obtain the total "annual average design flow." NR 110 does not prescribe an exact method for estimating future I/I. Some designers have proposed use of the new sewer construction quality test leakage rate of 200 gallons per inch of pipe diameter per mile per day as a method to estimate future I/I. This criterion is a standard for new construction and is not intended to be a method of estimating future I/I. Non-excessive I/I quantities may be substantially greater than that associated with the 200 gpd/in./mi. criteria. The designer will need to consider characteristics of the specific collection system and its hydrogeological setting to estimate potential future infiltration flows.

In accordance with s. NR 110.09(2)(j)3, flow projections for industrial contributions should account for existing industrial and future documented industrial flows, and may include a nominal flow allowance for future unplanned industrial expansions. This allowance for unplanned industrial flow should normally not exceed 5% (or 10% for service areas less than 10,000 population) of the total non-industrial design flow. The unplanned industrial flow will be allowed only if area-wide management plans, land-use plans and local zoning provide for such industrial growth.

When flow records do not exist, certain flow peaking factors are prescribed in Table 2 of s. NR 110.15(4)(c). The specific language in this section indicates the peaking factors should be used to estimate the "maximum design flow rate." It is important to recognize that these peaking factors are actually intended to be used to derive the maximum hour design flow, not maximum day. The factors are based on the ratio of peak hour flows to annual average flows, and the factors apply to the entire annual average wastewater flow (i.e., not to a base flow component). It should also be noted that in s. NR 110.13(1)(b) and (c), a sewer design criterion of 100 gallons per capita per day and certain peaking factors are specified. These criteria are intended only for sewer design and should not be used in place of the s. NR 110.09(2)(j) procedures applicable to treatment facilities.

Planning Effluent Limits

Planning Effluent Limits

This guidance is provided for use by wastewater facility designers who need to request effluent discharge limits as part of a facility planning study for any new or modified sewerage system project subject to ch. NR 110, Wis. Adm. Code. Chapter NR 110 is applicable to all sewerage systems except systems treating industrial wastewater or "private sewage systems" regulated by the Department of Commerce. This guidance is not applicable to limit questions arising from routine Wisconsin Pollutant Discharge Elimination System (WPDES) permit reissuance or to requests for alternative phosphorus limits.

The DNR normally provides planning limits only for conventional pollutants for facility planning. The calculation of limits for toxic substances may occur separately through the WPDES permit issuance process. Conventional limits are normally sufficient for facility planning and design purposes, however, designers should be aware of and consider the impacts of other potential limits to the extent possible.

Although the methods for determining land application limits differ from the methods used for surface waters, the procedures in this guidance may also be used for planning limit requests for proposed discharges to groundwater via a land application system. Groundwater standards are in ch. NR 140, Wis. Adm. Code, and effluent limits for municipal and domestic wastewater land application systems are in ch. NR 206, Wis. Adm. Code. In general, these standards and limits do not vary for different discharge locations, but in some instances alternative limits may be established due to specific site circumstances. For example, if the land application site is located in an area where groundwater migrates a short distance and then emerges into surface waters, the department may impose alternative effluent limits.

When Planning Effluent Limits Should Be Requested

Identifying the effluent limits that will apply to various potential discharge points is essential to enable an analysis to determine the most cost-effective means of disposing of treated effluent as is required under s. NR 110.09(2)(g), Wis. Adm. Code. Requests for planning limits should be made early in the planning process, as soon as a reasonable design flow estimate and discharge locations can be identified. The department recognizes that initial design flow estimates may be subject to further refinement as a planning analysis proceeds, and that limits may also need corresponding revision. When numerous discharge locations are potentially viable, DNR staff should be consulted to screen the options to enable a more efficient focus on the most promising locations. The DNR routinely encourages "planning initiation meetings" with community officials and their engineering consultant when a planning effort is just beginning. The scope of an effluent limit request may be one of the primary topics at these meetings.

Submittal And DNR Review Procedures

Requests for planning limits should include a cover transmittal letter and a report addressing the information listed below. Requests should be sent to:

Jason Knutson
Wastewater Section Chief
Water Quality Program
Wisconsin DNR
PO Box 7921
Madison WI 53707-7921

The assigned plan review engineer will conduct a review of the proposed service area, population projection and design flows. Once these are determined to be acceptable, the request will be transferred to appropriate department staff for determination of applicable water quality standards and calculation of planning effluent limits. The planning limits determination will be documented in a memo and returned to the department plan reviewer, who will transmit the planning limit memo to the applicant along with any other pertinent comments.

Information Necessary For Planning Effluent Limit Requests

General information:

  • name of existing or proposed facility (include owner contact information);
  • county;
  • WPDES permit number (if existing facility);
  • summary of current limits (if existing facility); and
  • identify if proposal is for a new discharge or increase to an existing discharge. If the latter, identify the existing design flow and location.

Proposed discharge location: A map showing the proposed discharge location should be provided (7.5 minute quadrangle maps are recommended). If multiple receiving streams or discharge locations are being considered, each location should be identified on the map.

Proposed facility design flows: Wastewater facilities are normally designed to treat the maximum loading condition expected to occur within a 20-year planning period. Because flow rates into wastewater plants are variable, a design condition is defined by expressing average flow rates that will occur over different time periods, within the year of the maximum loading condition. These design flows are then used to design sewerage system components to provide compliance with WPDES permit limits and other performance objectives. Additional detailed information on design flow determinations is available from the Design Flow tab.

At a minimum, the "Annual Average Design Flow" must be provided to enable a limit determination under Chapter NR 210 for conventional limits for planning purposes. The other listed design flows do not necessarily need to be included for the initial limit request, but should be identified in the final facility plan report as necessary to evaluate alternatives in accordance with NR 110 requirements. Facility Plan reports should always identify the Maximum Month Design Flow because this will be used by the DNR for the Compliance Maintenance Annual Report (CMAR) assessment.

  1. Annual Average Design Flow: The average of the daily flow volumes anticipated to occur for a continuous 12-month period, expressed as a daily average. (NOTE: This is not a dry weather flow. It is the total yearly flow volume discharged, expressed as a daily average.)
  2. Maximum Month Design Flow: The largest volume of flow anticipated to occur during a continuous 30-day period, expressed as a daily average.
  3. Maximum Week Design Flow: The largest volume of flow anticipated to occur during a continuous seven-day period, expressed as a daily average.
  4. Maximum Day Design Flow: The largest volume of flow anticipated to occur during a one-day period, expressed as a daily average.
  5. Maximum Hour Design Flow: The largest volume of flow anticipated to occur during a one-hour period, expressed as a daily or hourly average.
  6. Peak Instantaneous Flow: The maximum anticipated instantaneous flow.

The maximum month, week and day design flows may be necessary to establish mass limits or limits for toxic or other "non-conventional" substances. The maximum hour flow or peak instantaneous flow are not normally necessary for limit calculations, but are typically necessary for design purposes and should be included in the facility plan report if applicable for the specific project design.

Although the above list does not include a dry weather flow, determining a dry weather flow ("base flow") is typically necessary as part of analyzing flow components (base flow, infiltration, and inflow), and it should normally be identified in a facility plan report. Any quantified flow used for facility design purposes must be identified and explained in a facility plan report.

The planning effluent limit request should contain the design flow calculations and an accompanying explanation of the assumptions and methods used to derive the design flows. Information on sewer service areas and population projections should also be included.

Potential effluent discharge options: In some cases it may be beneficial to consider effluent storage to enable improved control of discharge rates or the time periods of discharge. For example, storing flows such that discharge periods could be limited to one or two months of the year. Another discharge option could involve coupling a land application discharge with a surface water discharge such that the discharge rate to the stream could be reduced during the land application season.

Any proposal for a unique discharge scheme should be clearly explained and design flows adjusted accordingly. For any facility that does not discharge continuously, the average design flow during the discharge period should be provided.

Identification of Alternatives

Identification of Alternatives

The primary objective of facility planning is to identify and evaluate various potential solutions to address wastewater management needs. For new facilities or major upgrades, the alternatives analysis should consider the establishment of the sewer service area and possible connections to existing sewerage systems (regionalization). Facility plans must conform with approved sewer service areas contained in areawide water quality management plans. If a revision to a sewer service area is being proposed, the first step of the planning process will be to seek an amendment to the sewer service area.

Any proposal for a new or upgraded treatment plant may include consideration of different treatment technologies, facility sites and discharge locations. Discharge may be to surface waters or to groundwater via land application systems such as spray irrigation or rapid infiltration basins. The DNR encourages consideration of innovative as well as conventional technologies. If new or innovative methods of treatment are proposed, supplemental performance data may be required to support performance claims for the technology.

If a municipality is planning for a treatment facility upgrade that will result in a capacity increase of 20% or more, they are required to evaluate the need to include septage receiving facilities and additional treatment capacity specifically for septage. Please see the DNR program guidance for septage considerations in municipal wastewater facility planning and for application of 0% Clean Water Fund loans.

The alternatives analysis should include consideration of improving plant performance by improved operation and maintenance measures. In some cases, this may be addressed separately by an "Operation and Needs" study. Phased construction of upgrades may be considered, but all alternatives must still be compared on the basis of a 20-year planning period. When it is proposed to significantly upgrade any portion of an existing facility and to increase plant capacity, the facility planning analysis should also examine the condition of the other processes at the facility. If the other existing processes are not code compliant or do not perform adequately, the facility plan should examine whether it is necessary and cost-effective to improve them.

All alternatives must be feasible in terms of being implementable from legal, institutional, financial and management standpoints. In some circumstances, local annexation requirements may be associated with a regionalization alternative. Annexation requirements would be evaluated along with project costs and non-monetary factors. In general, the department does not accept annexation, by itself, as a factor that would necessarily prevent implementation of a project.

After identifying feasible alternatives, they may be systematically compared and screened to identify the principal alternatives to be subjected to the detailed cost analysis. The level of detail in the analysis will depend upon the size and complexity of the project and the range of cost differences among alternatives.

Cost-Effective Analysis

Cost-Effective Analysis Methodology

To provide valid monetary cost comparisons, all opportunity costs associated with an alternative over the 20-year planning period should be identified and presented on a total present worth or equivalent uniform annual cost basis. Sunk costs should not be included in the cost-effectiveness analysis because these costs have already been committed regardless of the alternative selected. Sunk costs include investments in existing wastewater facilities and associated lands, outstanding indebtedness and costs for preparing the facilities plan.

Costs should be based on market prices prevailing at the time of the study. Except for energy and land costs, the inflation of costs over the planning period is not allowed. The analysis should account for initial capital costs, future capital costs, annual operation and maintenance costs and salvage values. Salvage values are determined by assigning a design service life to various components and then calculating the remaining service life and associated value of the component at the end of the planning period.

Current Discount Rate

Present worth factors must be based on the current discount rate as established by the DNR in accordance with s. NR 110.09(1)(a), Wis. Adm. Code. [The discount rate for the Federal Fiscal year 2023, which applies to facility plans beginning on or after Oct. 1, 2022, is 2.625%.]

Connection fees or other charges should not be included in a cost-effective analysis if they are a method of cost recovery for a sunk cost, or if they only reflect a transfer of payments from one entity to another.

Costs for treatment capacity acquisition from an existing treatment plant may, or may not, be included in the cost-effectiveness analysis depending on specific circumstances. If an existing facility has planned (or excess) capacity to service an area, then no capacity acquisition cost should be included in a cost-effectiveness analysis conducted for connecting that area (the capacity is already available and cost is sunk). But if an existing treatment facility does not have planned (or excess) capacity to service a certain area, then serving that new area would reduce the plant's reserve capacity intended for its remaining service area, and thus shorten its design service life. As a result, the plant would need to be upgraded sooner than what would otherwise be necessary. This represents an actual future cost that should be accounted for in the cost-effective analysis if the plant upgrading would be expected to occur within the 20-year planning period.

Compare alternatives based on total present worth or equivalent uniform annual costs. The DNR typically considers alternative costs within 10% of each other to be essentially equal in monetary value due to normal cost estimating variability. In some situations, the department may require the provision of a sensitivity analysis to assess how project costs would vary based on a range of planning assumptions or circumstances.

The facility plan report should contain both a cost-effectiveness analysis and a fiscal impact cost analysis. The fiscal cost analysis will consider grant or loan assistance, financing arrangements, and provide estimates of expected user charges or fees (which should include any existing indebtedness).

The final determination on cost-effectiveness is made with consideration of monetary costs, fiscal impacts, environmental impacts and possibly other non-monetary considerations.

Environmental Impacts

Environmental Impacts

The facility plan report should include environmental impact information on all the alternatives. More specific environmental impact information should be provided for the recommended alternative.

Resources Impacts Summary

This summary provides a suggested format for preparation of an Environmental Assessment to be included with facility plan reports for proposals of new or modified sewerage system projects. The required content of an Environment Assessment for sewerage system projects is described in s. NR 110.09(3), Wis. Adm. Code. Depending on project specific circumstances, the scope and level of detail for an Environmental Assessment may be less than or greater than what is suggested by this outline.

  1. Project Identification
    Applicant: ___________________________________________________
    Address: ________________________________________________________
    Title of Proposal: ______________________________________________
    County: ______________ City/Town/Village ___________________
    Township: ______________ North, Range ____________ East, West
    Section: _________________________________________________
  2. Project Description
    1. Why is the project needed?
    2. What is to constructed and where?
    3. What area is to be served? (Service area, existing and projected populations)
    4. What is the design flow and loading?
    5. What is the applicable stream classification and effluent limits?
    6. How will the project be implemented? (Construction schedules, financing and user charge)
  3. Affected Environment
    1. Physical: Describe existing resource features (including wetlands, lakes, streams, shorelands, floodplains, groundwater, soils and topography) that may be affected by the proposed project.
    2. Biological: Identify plant and animal communities in the planning area with an emphasis upon those species likely to be impacted. Threatened or endangered status should be discussed if applicable.
    3. Cultural: Describe zoning and land use, ethnic and cultural groups, and archaeological and historic resources that may be affected by the proposed project. Describe the economic setting of the area.
    4. Other Resource Features: Identify parks, natural areas, prime agricultural land, etc.
  4. Project Impacts
    1. Primary:
      1. Describe expected changes in surface water or groundwater quality. List stream crossings and any required Chapter 30 permits.
      2. Describe construction-related impacts such as noise, traffic disruptions and air emissions.
      3. Describe impacts upon flora and fauna.
      4. Describe loss of prime agricultural land or disruption of agricultural activities.
      5. Describe project impacts on wetlands and floodplains. Explain why such resource impacts are necessary.
      6. Describe impacts upon scenic and other aesthetic resource features.
      7. Describe impacts on cultural, historic and archaeological features.
    2. Secondary: Describe the future environmental impacts resulting from increased urbanization and land use changes potentially induced by the availability of wastewater collection and treatment services. Special attention should be given to impacts upon wetlands and other surface waters including those resulting from storm water runoff and erosion. Other secondary impacts upon flora, fauna, air quality, agriculture, urban services, scenic values and cultural, historical and archaeological resources should also be addressed.
    3. Mitigative Measures: Describe measures proposed to minimize or mitigate adverse primary and secondary impacts noted above.
    4. Alternatives Considered
      1. Provide a description and cost comparison of alternatives considered. List the capital cost, annual O&M cost and total present worth cost for each alternative.
      2. Describe the environmental impacts of the non-selected alternatives identified above which differ from those expected for the selected alternative. Include the "No Action" alternative.
    5. Contacts: List agencies, environmental groups and individuals contacted regarding the proposed project. Provide the date of the contact, the person contacted and a summary of their comments.


    • Community and regional maps
    • Site map with topographic and other relevant resource features
    • Sewer service area map
    • Map locating stream crossings
    • Other attachments as necessary
Public Involvement

Public Involvement

Public involvement is an important aspect of any planning effort for a new or significantly modified sewerage system. Municipalities must conduct at least one public hearing as required by s. NR 110.09(4), Wis. Adm. Code. A copy of the facility plan report should be available for public review before the hearing and at the hearing. Exceptions to the public hearing requirement may be provided if the proposal is for a minor upgrade or if it is a revision to a previously approved project subject to a previous public hearing. Prior to issuing a facility plan approval letter, the DNR will issue a news release and typically allow a two-week time period for public comments.

For major projects, such as constructing both a new collection system and treatment facility, the DNR encourages public informational meetings in addition to the required public hearing. A newsletter may also be useful to keep residents informed of ongoing planning developments. It is critical that comprehensive and accurate user cost estimates, planning options, and associated environmental impact information are made available to the public. The DNR will consider all comments received as part of the decision-making process on a community's proposed cost-effective alternative.

Facility Plan Revisions

Facility Plan Revisions

After a facility plan report receives DNR approval, there are typically minor design refinements or project changes that occur as the final construction plans and specifications are developed. Minor changes from approved facility plan recommendations should be identified and justified as part of the construction plan and specification review. If the changes are significant, it may be necessary for the sewerage system owner to prepare and submit a facility plan amendment report to the DNR for review under the s. NR 110.09, Wis. Adm. Code, facility planning rules. The review of an amendment may include a requirement for an additional public hearing. Changes that are normally considered "significant" would involve proposed use of a new site, significant changes to project cost estimates, significant changes to effluent limits or other design parameters or the discovery of potential environmental impacts not previously identified.

Abbreviated Facility Plans

Abbreviated Facility Plans

An abbreviated facilities plan (sometimes called an "Engineering Report") can be used to satisfy the facilities planning requirements for minor modifications to municipal treatment plants.

The abbreviated form may be appropriate for modifications to existing treatment facilities where:

  • The assumptions of the most recent comprehensive facility plan still apply;
  • The construction is at the existing plant site;
  • The alterations would not change the overall treatment capacity;
  • The proposal does not involve new treatment technology or a change of outfall location; and
  • Construction will have no significant environmental effects.

The abbreviated facilities plan will include the following components:

  • A brief description of the treatment facilities;
  • A concise problem statement;
  • Relevant background information;
  • Description of any significant environmental issues. Any air permit requirements or encroachments on wetlands or floodplains should be addressed, along with impacts to archaeological resources (if outside the extents and depths of previous excavation) and endangered resources;
  • Alternatives Considered. The department recognizes that the number of feasible alternatives may be limited for some types of projects;
  • Cost-effectiveness Analysis. This must be done on a 20-year Total Present Worth or Equivalent Uniform Annual Cost basis. The plan must include an estimate of the effect of the project on user charges for a typical residential customer; and
  • Public Participation. The municipality is encouraged to keep the public informed. However, a formal public hearing will not be required if user charges are not anticipated to increase by more than 20%.

If the planning assumptions of the most recent facility plan, including populations, flows and loads, planning horizon, etc., no longer apply, please contact department staff to determine if an expanded abbreviate facility plan that addresses these inconsistencies may be appropriate, or if a comprehensive facility plan is necessary.

Department approval of a common construction or minor addition project is a minor action under ch. NR 150, Wis. Adm. Code.

Collection System Projects

Facility Planning for Collection System Projects

Any proposed reviewable project for a wastewater treatment facility is subject to the facility planning requirements of s. NR 110.09, Wis. Adm. Code, including a demonstration of project need and cost-effectiveness. The facility planning requirements for collection system projects will differ depending on the project type and funding. Any proposal for storage of wastewater, either within sewer lines or in remote storage facilities, is subject to s. NR 110.09 and a facility plan report must be submitted for DNR review. For conventional sewer or pump station projects, the facility planning requirement is dependent on whether a state Clean Water Fund (CWF) loan will be sought.

If no CWF loan is involved, the applicant must comply with the requirements of ss. NR110.10 (for sewers) and NR 110.11 (for lift stations). These requirements can be satisfied by completing the standard DNR forms for sewer and lift station construction plan and specification submittals. There is no need to submit a separate facility plan report. If the Clean Water Fund will be used to finance a collection system project a facilities plan is required. See below for projects that include sewer replacement and/or rehabilitation only.

The Clean Water Fund Program is intended to provide financial assistance for projects providing environmental benefits. A collection system project may be eligible if it is necessary to increase conveyance capacity to prevent bypassing, sanitary sewer overflows, or sewage treatment facility overflows, to eliminate excessive clearwater infiltration or inflow or to maintain the structural integrity of the system. The loan program is not intended to fund routine maintenance or sewer extensions to new development. Sewer extensions to existing development may be eligible for funding if the project will eliminate adverse environmental or public health impacts associated with the use of private onsite wastewater treatment systems and certain additional criteria are met. Information on these requirements is available on the Environmental Loans Unsewered Projects page.

Facilities Plans For Sanitary Sewer Replacement And Rehabilitation

A facilities plan is required if the Clean Water Fund is used to finance a sanitary sewer replacement or rehabilitation project. The abbreviated form of a facilities plan for sewer replacement and rehabilitation, as outlined below, may be used.

The report may be submitted concurrent with the construction plans and specifications. However, you must submit them sufficiently early to allow the DNR to review and approve the facilities plan prior to the Clean Water Fund Program application deadline. Please contact municipal wastewater plan review staff to determine an appropriate submittal timeline. This does not apply to new interceptor sewers or replacement sewers that provide capacity for growth in areas outside of the existing sewer service area. Construction plans and specifications for sewer replacement and/or rehabilitation should be submitted using the normal sewer plan submittal procedures.

Contents Of A Sanitary Sewer Replacement And Rehabilitation Facilities Plan

Use the following outline for an abbreviated "Engineering Report" format for the sewer replacement and rehabilitation plans when Clean Water Fund financing is anticipated. Allow at least six months for facilities plan approval prior to the CWFP application deadline. If not seeking Principal Forgiveness from the CWFP, allow time for plan approval prior to your expected CWF application submittal date. Please contact municipal wastewater plan review staff to determine an appropriate submittal timeline. A public hearing will generally not be required.

The elements to be included in the Engineering Report are as follows:

  1. Description of the proposed project and demonstration of need for the project.
    The age and condition of the sewer should be given. Documentation of the problem to be corrected may include inspection reports, flow monitoring or other information as appropriate. It is usually not necessary to submit copies of inspection reports or television logs but the source of the information should be provided.
    Justification for funding may include structural deficiency, inadequate capacity or removal of infiltration and inflow. Storm sewer replacement or rehabilitation is eligible for funding only if the work will prevent clear water flows from entering a sanitary sewer from a storm sewer. In those cases evidence of the connection between the storm and sanitary sewer (such as results of a dye-water flooding test) must be provided;
  2. A brief evaluation of alternatives to correct the problem.
    Generally it would be expected that rehabilitation would be considered as an alternative to replacement. Provide a brief discussion of alternatives considered and the reason for selecting the recommended alternative;
  3. Project cost and user charge estimate.
    An estimate of the cost of the project and expected effect, if any, on user charges to the typical residential customer should be provided if no change is expected that should be stated. If user charges will increase by more than 20% a public hearing should be held;
  4. Environmental effects.
    The environmental effects of sewer replacement and rehabilitation projects would be expected to include consumption of fuel and materials of construction, noise, dust, and odor and traffic disruption. It is not necessary to document such effects. Any impacts on floodplains, wetlands or other environmentally sensitive areas, however, should be discussed; and
  5. Parallel cost estimate.
    A parallel cost estimate must be included. In most cases the estimate would be 100%. However if a replacement sewer provides capacity for growth outside the existing sewer service area a parallel cost estimate must be prepared as described in NR 161.
I/I Analysis And SSES

Infiltration And Inflow Analysis And Sewer System Evaluation Survey

The design of any wastewater treatment plant must include consideration of "clear water" that may enter a sewage collection system under wet weather or wet soil conditions and be transported to the treatment facility. Depending on the scope of a facility planning effort and the extent of clear water flows, separate studies for an "Infiltration/Inflow Analysis" and a "Sewer System Evaluation Survey" (SSES) may be required. The content of these studies is addressed in ss. NR 110.09 (5) and (6), Wis. Adm. Code. A WPDES permit may require that a "System Evaluation and Capacity Assurance Plan" (s. NR 210.23 and ch. NR 110, Wis. Adm. Code) be conducted. A history of frequent sewage bypasses or overflows occurring in the sewerage system may result in a requirement to prepare one or more of these studies.

If infiltration/inflow can be demonstrated to be below certain threshold levels, the department will consider the I/I to be "non-excessive" and separate I/I or SSES studies will not be required. The infiltration threshold criterion is whether the dry weather flow (the highest base flow plus infiltration occurring for a seven- to 14-day dry weather period during a year) is less than or equal to 120 gallons per capita per day (gpcd). The inflow threshold criterion is whether the maximum daily flow during a storm is less than or equal to 275 gpcd. These criteria are guidelines, not code requirements, and different guidelines or supplemental information may be considered when warranted by specific circumstances.

Capacity Re-Rating

Requests for Re-Rating Capacity of Municipal Wastewater Treatment Facilities

In certain instances, the owner of a wastewater treatment facility may revise the design capacity that has been previously identified and approved by the DNR for an existing facility. The design capacity figures are used in WPDES permits, for effluent limit determinations (in some cases) and for facility evaluations conducted as part of the Compliance Maintenance Annual Report (CMAR). Design capacity is normally expressed in terms of a hydraulic loading (flow rate as gallons per day) and organic loading expressed in terms of Biochemical Oxygen Demand (pounds of BOD5 per day). A request to revise either one or both of these may be submitted.

The department approves the original design flows and loadings for wastewater treatment plants as part of plan reviews conducted under ch. NR 110, Wis. Adm. Code. A proposed capacity revision request should be submitted to:

Jason Knutson
Wastewater Section Chief
Water Quality Program
Wisconsin DNR
PO Box 7921
Madison WI 53707-7921

The request should include a transmittal letter and two copies of a detailed engineering report to explain and justify the proposed revision. The plan reviewer, the regional wastewater engineer and other DNR staff as necessary will review the request. A letter documenting the acceptance or denial of a revision will be sent to the facility owner.

Wastewater treatment plants are often designed by employing conservative empirical design methods and it may be justified to re-rate a plant's capacity based on actual performance data. Owners and designers should keep in mind, however, that there are good reasons for conservative design criteria that relate to accounting for the variability of influent flows and loadings that typically occur in any municipal sewerage system.

The "design flow" for municipal wastewater plants in Wisconsin (see the "Design Flow" tab above) is defined as the average annual flow expected in the design year (the design year is typically the 20th year after facility construction). But any design must also account for the normal variations in flows and loads, and consider the complete hydraulic regime expected in the design year (average flow, plus minimum and maximum flows expected over various time durations). This influent variability translates into a variable effluent quality that must be accounted for in assessing compliance with discharge limits.

For example, based on the typical distribution of effluent quality data associated with activated sludge plants, the long term arithmetic mean effluent BOD concentration must be about 20 mg/l in order to comply with a 30 mg/l BOD monthly average limit at a 95% compliance rate (95 months out of 100 months). This type of design conservatism is necessary to ensure substantial compliance with limits. This factor of conservatism may be inherently built-in as part of certain empirical design criteria, but designers must take care to account for this factor when relying on performance data or other design assessment methods.

The DNR plan reviewers will examine re-rating requests with the goal of ensuring that overall effluent limit compliance rates are maintained at acceptable levels. Each unit process in a treatment system will be examined and the overall plant design flow or loading will normally be determined by the one-unit process that is most restricting in terms of design capacity. This analysis should include sludge processing and storage units. The proposed new design flow criteria should normally include identification of the annual average design flow, plus the maximum month, maximum week and maximum day design flows. In some cases, the effluent limits will need to be recalculated when the design flow changes.

Design flow is defined in terms of the expected flows and loadings from a service area. This is normally, but not necessarily, the same as the actual capacity of the treatment facility. For example, a plant may have been originally designed with a large capacity allowance for an industrial facility, and then that industry subsequently ceased operations and discharge. In this situation, the design capacity could be re-rated based on the capacity necessary to serve the remaining community for a 20-year time period. The resultant re-rated capacity could then be less than the original rated capacity and less than the actual facility capacity.