127.29 Storm Water

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127.29.1 Definitions

Best Management Practice (BMP) – From MDNR’s 10 CSR20-6.200: Schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the pollution of waters of the state. BMPs also include treatment requirements, operating procedures and practices to control plant site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.

Illegal connection - a pipe or other conveyance that has illegally been connected to MoDOT’s MS4.

Illicit discharge - is defined by MDNR's 10 CSR 20-6.200 as a discharge of pollutants to a Municipal Separate Storm Sewer System (MS4) that is not comprised entirely of storm water and is not authorized under the NPDES permit.

Major outfall – MDNR defines as “a municipal separate storm sewer outfall that discharges from a single pipe with an inside diameter of thirty-six inches (36") or more (or its equivalent)”. Reference: 10 CSR 20-6.

MoDOT Community – MoDOT staff and external partners including contractor’s and consultants.

MoDOT’s MS4 area – MDNR designated MS4/urban areas, outstanding state and national waters, Total Maximum Daily Load (TMDL) effective watersheds.

MS4 – Municipal Separate Storm Sewer System.

New development – MoDOT defines new development for purposes of the MS4 permit, to mean projects (with land disturbance greater than or equal to 1 acre) that are constructed where there was previously no transportation facility.

Non-structural practices/controls - operational BMPs that prevent or reduce pollutants from entering storm water. Examples include preventative maintenance procedures, minimizing impervious surfaces, and spill prevention and cleanup.

Outfall – MoDOT defines an outfall as intentionally collected stormwater that is “A point source as defined by 10 CSR 20-2.010 at the point where a municipal separate storm sewer discharges and does not include open conveyances connecting two (2) municipal separate storm sewers, pipes, tunnels, or other conveyances which connect segments of waters of the state and are used to convey waters of the state.” Reference: 10 CSR 20-6.

Permanent BMP – a best management practice designed to be permanently left in place after construction to treat or contain stormwater.

Pollutant - Dredged spoil, solid waste, incinerator residue, sewage, garbage, sewer sludge, munitions, chemical waste, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, filter backwash or industrial,municipal or agricultural waste discharged into water. Reference: Reference: 10 CSR 20-2.

Redevelopment - MoDOT defines redevelopment for purposes of the MS4 permit with respect to transportation facilities, to mean non-maintenance work performed to or on an existing public transportation facility which provides for an increased number of thru lanes of travel unless the work can be accommodated without increasing the width of the existing pavement. Widening of an existing road that does not result in an additional thru lane does not constitute redevelopment. Widening to add shoulders does not constitute a thru lane unless the total widening is greater than or equal to 10 feet.

Run-on – storm water from adjacent landowners or development that is combined with MoDOT’s storm water.

Storm water outfall – a point source where intentionally collected storm water exits the right of way (ROW) and enters a “water of the state”. For example, roadside ditch.

Structural practices/controls - physical, structural or mechanical devices or facilities intended to prevent pollutants from entering storm water. Examples include building berms around potential pollutant source areas, roofs over outside truck wash bays, etc.

waters of the state – MDNR defines as “all rivers, streams, lakes and other bodies of surface and subsurface water lying within or forming a part of the boundaries of the state which are not entirely confined and located completely upon lands owned, leased or otherwise controlled by a single person or by two or more persons jointly or as tenants in common and includes waters of the United States lying within the state.” Reference: Missouri Revised Statutes 644.016.

Acronyms and Abbreviations

BMP Best Management Practice
CWA Clean Water Act
EPA Environmental Protection Agency
FHWA Federal Highway Administration
GI Green Infrastructure
IDDE Illicit Discharge Detection and Elimination
LID Low Impact Development
MCM Minimum Control Measure
MEP Maximum Extent Practicable
MDNR Missouri Department of Natural Resources
MoDOT Missouri Department of Transportation
MS4 Municipal Separate Storm Sewer System
NPDES National Pollutant Discharge Elimination System
ROW Right of way
SPCC Spill Prevention Control and Countermeasure
SWMP Storm Water Management Plan
SWPPP Storm Water Pollution Prevention Plan
TMDL Total Maximum Daily Load
UA Urbanized Area as defined by US Census

127.29.2 Purpose

Missouri Department of Transportation (MoDOT) is regulated under a National Pollutant Discharge Elimination System (NPDES) general, statewide storm water permit that requires MoDOT to develop and implement a comprehensive program to prevent pollution of surface waters resulting from storm water runoff. EPG 127.29.2 is intended to serve as general guidance to assist MoDOT staff and consultants in the selection, design, and maintenance of post-construction (i.e., permanent) best management practices (BMPs) in order to comply with water quality regulatory requirements. It is intended to achieve the following goals:

  • Comply with storm water permit
  • Provide an overview of important factors to be considered
  • Offer guidance in the consideration of physical, operational, and cost (capital and maintenance) characteristics of post-construction best management practices (BMPs) for water quality.

Provisions of the Federal Clean Water Act and related state rules and regulations require a municipal separate storm sewer system (MS4) permit when the facility serves a population of 1,000 or more within an urbanized area or are located outside an urbanized area serving a jurisdiction with a population of at least 10,000 and a population density of 1,000 people per square mile or more. Furthermore, a municipal separate storm sewer means a conveyance or system of conveyances including roads and highways with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, paved or unpaved channels, or storm drains designated and utilized for routing of storm water. MoDOT has an MS4 general permit, obtained from the Missouri Department of Natural Resources (MDNR), delegated by the Environmental Protection Agency (EPA). It requires MoDOT to develop and adhere to a Storm Water Management Plan (SWMP) comprised of six minimum control measures (MCMs) listed below.

127.29.3 MCM 1: Public Education and Outreach

Permit requirement. The permittee shall implement a public education program to distribute educational materials to the community or conduct equivalent outreach activities about the impacts of storm water discharges on water bodies and steps the public can take to reduce pollutants in storm water runoff. As part of the SWMP, the public education and outreach program shall include the following information, at a minimum:

  • The target pollutant sources the permittee's public education program is designed to address;
  • Identification of target audiences for the permittee's education program who are likely to have significant storm water impacts (including commercial, industrial and institutional entities);
  • A plan to inform individuals and households about steps they can take to reduce storm water pollution;
  • A plan to inform individuals and groups on how to become involved in the SWMP (with activities such as local stream and lake restoration activities);
  • The permittee's outreach strategy, including the mechanisms (e.g., printed brochures, newspapers, media, workshops, etc.) to reach target audiences, and the projected number of how many people expected to be reached over the permit term; and
  • A plan to evaluate the success of this minimum control measure.

127.29.4 MCM 2: Public Participation and Involvement

Permit requirement. The permittee shall implement a public involvement/participation program that complies with State and local public notice requirements, and involve the public in the development and oversight of the SWMP, policies and procedures. As part of the SWMP document, the public involvement/participation program shall include the following information, at a minimum:

  • How the permittee has involved the public in the development and submittal of the application and SWMP document;
  • The target audiences for the permittees public involvement program, including a description of the types of ethnic and economic groups engaged. The permittee is encouraged to actively involve all potentially affected stakeholder groups, including commercial and industrial businesses, trade associations, environmental groups, homeowners associations, and educational organizations, among others; and
  • The types of public involvement activities included in the permittees program. Where appropriate, the permittee must consider the following types of public involvement activities:
  • Citizen representatives on a storm water management panel;
  • Public hearings;
  • Working with citizen volunteers willing to educate others about the program; and
  • Volunteer monitoring or stream/lake clean-up activities.
  • The permittee's plan to actively involve the public in the development and implementation of their program; and
  • The method for evaluating success of this minimum control measure.

127.29.5 MCM 3: Illicit Discharge Detection and Elimination

MDNR’s general permit requires the MoDOT to develop, implement and enforce a program to detect and eliminate illicit discharges (as defined in 10 CSR 20-6.200) MoDOT’s system. This includes:

  • A map showing the location of all outfalls and the names and location of all receiving waters of the state that receive discharges from those outfalls.
  • A policy to effectively prohibit non-storm water discharges into the permittee's storm sewer system and implement appropriate enforcement procedures and actions.

MoDOT’s policy regarding illegal connections and discharges into MoDOT’s system is described at EPG System Attachments by Others and EPG Industrial and Domestic Waste Waters on Right of Way.

  • A plan and implementation schedule to detect and address non-storm water discharges, including discharges from illegal dumping and spills, to the permittee's system. The permittee's plan shaIl include dry weather field screening for non-storm water flows and field tests of selected chemical parameters as indicators of discharge sources. The permittee's description shall address the following, at a minimum:
• Procedures for locating priority areas which include areas with higher likelihood of illicit connections (areas with older sanitary sewer lines, for example);
• Procedures for tracing the source of an illicit discharge, including the specific techniques the permittee will use to detect the location of the source;
• Procedures for removing the source of the illicit discharge.

Private homeowners are regulated by the Missouri Department of Health and Senior Services. The Missouri Department of Health and Senior Services is to be contacted when wastewater discharge from a private homeowner is found on the right of way. Commercial businesses and industries are regulated by MDNR. When wastewater discharge from a regulated entity is discovered on MoDOT right of way, the Environmental Specialist will contact MDNR to determine if the commercial business or industry has a valid operating permit issued by MDNR to discharge effluent.

The Environmental Specialist will request MDNR to take whatever legal action necessary concerning any business or industry that does not have a valid permit from MDNR to discharge effluent to the highway right of way.

For additional information see EPG Rest Area Lagoon, EPG Sewage Disposal System, and EPG System Attachments by Others.

  • A plan to inform employees, businesses, and the general public of hazards associated with illegal discharges and improper disposal of waste. The permittee shall describe how this plan will coordinate with their public education minimum measure and the pollution prevention and good housekeeping minimum measure programs; and
  • The permittee should inventory, inspect and have enforcement authority for industries and commercial enterprises within their boundary that may contribute pollutants via storm water to the MS4.

Sources of illicit discharges are spills from roadway accidents, sanitary wastewater, effluent from septic tanks, improper oil disposal, laundry wastewaters, improper disposal of auto and household toxics, etc. See EPG Industrial and Domestic Waste Waters on Right of Way and EPG System Attachments by Others.

MoDOT is authorized to discharge the following non-storm water sources provided that the permitting authority has not determined these sources to be substantial contributors of pollutants to the permittee’s MS4 that require a separate permit:

Landscape irrigation
Rising ground waters
Uncontaminated ground water infiltration
Uncontaminated pumped ground water
Discharges from potable water sources
Foundation drains
Air conditioning condensation
Water from crawl space pumps
Footing drains
Lawn watering
Flows from riparian habitats and wetlands
Street wash water
Bridge wash water
Discharges or flows from emergency firefighting activities
Individual residential car washing
Dechlorinated residential swimming pool discharges

127.29.6 MCM 4: Construction Site Runoff Control

This measure covers our existing policy in EPG 806 Pollution, Erosion and Sediment Control Program.

Additionally, this measure is also covered within EPG 173 Erosion Control for Maintenance Operations.

127.29.7 MCM 5: Post Construction Runoff Control

The post construction runoff control MCM requires MS4 permit holders to develop, implement, and enforce a program to reduce pollutants in post-construction runoff to their MS4 from new development and redevelopment projects that result in the land disturbance of greater than or equal to 1 acre. Specifically, MDNR requires MoDOT to have a program that “shall ensure that controls are in place that have been designed and implemented to prevent or minimize water quality impacts by reasonably mimicking pre-construction runoff conditions on all affected new development projects and by effectively utilizing water quality strategies and technologies on a11 affected redevelopment projects, to the maximum extent practicable” (MO-R040000). This control includes developing and implementing strategies which include structural and/or non-structural best management practices (BMPs) and ensuring long term operation and maintenance of those BMPs.

Structural vs Non-structural Practices and Controls

Non-structural practices/controls are BMPs that are planning procedures or site-specific BMPs such as riparian zone preservation, minimization of disturbance and imperviousness, and maximization of open space. Structural BMPs fall into three categories (EPA Fact Sheet) or three main types of treatment BMPs. These three types are not mutually exclusive, but one BMP may fit into more than one type.

Retention/Detention BMPs: These types of BMPs gather runoff and hold it while slowly releasing it into drainage systems or receiving waters. These can be designed to control storm water volume and settle out particulates. Examples include: dry detention basins, wet detention basins, biodetention, stormwater wetland, wet ponds, etc.

Photo of dry detention basin designed to temporarily detain runoff during storm events.

Infiltration BMPs: These types of BMPs encourage filtration through soil to groundwater which results in reduced storm water runoff quantity and therefore pollutants. Examples include infiltration trenches/ditches/basins, grassy swales, pervious pavement, and infiltration basins or trenches.

Grassed swales can be used along roadsides and parking lots to collect and treat storm water runoff

Vegetative BMPs: These types of BMPs are landscape features that remove pollutants and facilitate percolation of runoff by maintaining natural site hydrology. Examples include grassy swales, filter strips, rain gardens, and wetlands.

Wetland as post-construction BMP. (ODOT photo)
Potential Storm water Controls
BMP Definition Function
Filtration Basin A shallow basin with engineered media or soil and an underdrain. Filtration, sorption, biological uptake, microbially mediated transportations.
Bioretention Basin A type of filtration basin with engineered media, an underdrain and landscaped vegetation. Filtration, sorption, biological uptake, microbially mediated transportations.
Dry Detention Basin A shallow, dry basin with an outlet pipe near the invert of the basin. Detention, sedimentation, sorption.
Filter Strip A linear section of land, either grassed or forested that physically infiltrates storm water. Filtration, infiltration, sorption, microbially mediated transformation, biological uptake.
Swale A broad and shallow channel with dense vegetation. Filtration, infiltration, sedimentation, microbially mediated transformation, biological uptake.
Infiltration Basin A shallow basin in permeable soils that detains and infiltrates storm water runoff. Infiltration, sorption.
Level Spreader A trough and level lip used to redistribute concentrated storm water as diffuse flow and sometimes combined with a filter strip. Energy dissipation, infiltration.
Wet Detention Basin A shallow basin that maintains a permanent pool of water using a control structure. Detention, sedimentation, biological uptake, microbially mediated transformations.
Preformed Scour Hole A riprap lined basin formed at the outlet of a pipe. Energy dissipation, infiltration.
Forebay A small basin located upstream of another storm water control. Detention, sedimentation.
Storm Water Wetland An engineered wetland with wetland vegetation. Detention, sedimentation, sorption, biological uptake, microbially mediated transformations.
Modified from NCDOT BMP Toolbox.

Fig. Structural and Non-Structural Controls

FHWA provides a good overview of BMPs and the expected treatment and maintenance of each.

Project Delivery Process

The projects will be reviewed using the request for environmental services (RES) process to screen projects for compliance with this requirement. The RES “Storm water/Water Quality” section should be addressed beginning at the initial/scoping phase for all projects that have greater than or equal to 1 acre of land disturbance and meeting the criteria of redevelopment or new development. See Fig. Storm Water Post-Construction BMP Consideration. The storm water specialist will review RESs that meet these minimum requirements.

  • Is the project within an MS4 area, TMDL watershed or cross an Outstanding State or National Resource water as identified in Tables D and E in CSR 20-7.031? (Refer to MS4 area map).
  • Does the project disturb ≥ 1 acre?
  • Does the project meet the definition of redevelopment or new development?

MoDOT has defined redevelopment, for purposes of the MS4 permit with respect to transportation facilities, to mean non-maintenance work performed to or on an existing public transportation facility which provides for an increased number of thru lanes of travel unless the work can be accommodated without increasing the width of the existing pavement (with land disturbance greater than or equal to 1 acre). Widening of an existing road that does not result in an additional thru lane does not constitute redevelopment. Widening to add shoulders does not constitute a thru lane unless the total widening is greater than or equal to 10 feet.

Examples include adding a through lane, widening a bridge by a lane width or widening shoulders that cumulatively add up to the addition of a lane width, etc.

MoDOT has defined new development (new construction), for purposes of the MS4 permit, to mean projects (with land disturbance greater than or equal to 1 acre) that are constructed where there was previously no transportation facility.

Examples include a new interchange on existing facility, adding an outer road where none existed previously, new facility where none existed previously, etc.

MoDOT has defined maintenance, for purposes of the MS4 permit, to mean projects that do not meet the criteria of redevelopment or development.

Examples include ramp widening or extending (less than a lane width), signal installation, intersection improvements, retrofitting an existing interchange (for example, typical to a DDI), slide repair, adding shoulders that is less than a lane width, guardrail replacement, resurfacing, and overlay projects.

If a project meets the criteria listed above for development or redevelopment, permanent post construction BMPs must be considered that treat the new impervious runoff in redevelopment and mimic the pre-existing runoff condition in new development. The district designer shall work with the stormwater specialist to consider site constraints and opportunities. If part of a project is determined to be “new development” the entire project is captured under those requirements. General design philosophy will seek to mimic natural hydrology through dispersal and infiltration of runoff.

The district designer shall determine new runoff storage for redevelopment and pre-existing runoff in new development. Treatment BMPs are engineered storm water treatment facilities and should be designated on all phases of plan sheets. Many of these measures will capture and hold water and potentially develop wetland characteristics over time. If these are designated as storm water treatment facilities, they will not be under the US Army Corps of Engineers jurisdiction as wetlands. Conversely, storm water BMPs should not be sited within an existing jurisdictional wetland or its natural vegetated buffer except by permit or as part of a wetland mitigation plan. Wetlands may be considered for runoff treatment by passive means of dispersal.

In areas where the drainage is not captured via curb and gutter, open-bottom, grassy ditches will serve as permanent BMPs. Grassy swales (i.e., ditches), while an important BMP, will not be tracked and inspected in MoDOT’s database of stormwater BMPs and therefore not inspected under that program. Grassy swales are defined as a flat-bottomed or U-shaped ditch. If a flat-bottomed or U-shaped ditch cannot be achieved due to other site constraints, ditch blocks/checks can be used in conjunction with V-shaped ditches to achieve infiltration and absorption goals. Additionally, grassy medians that capture drainage are also included as a post-construction BMP but not tracked and inspected.

127.29.7 bioswale.jpg

Example List of Commonly Used Post-Construction Control Practices:

  • Infiltration basins
  • Detention/retention
  • Vegetated strips and/or swales
  • Biofilters
  • Permanent erosion control, seeding and planting
  • Outlet protection/velocity dissipation devices
  • Earth dikes, drainage swales and lined ditches
  • Bridge slope protection
  • Rock slope protection
  • Mulching
  • Verification that interior drains are not connected to a storm sewer system

Special Watersheds with TMDLs in Effect

In project areas where a TMDL is in effect, it is feasible to tailor a permanent BMP to the pollutant identified. The American Association of State Highway Transportation Organization’s (AASHTO) Drainage Manual 2014 provides a table (Table 7-2) with the “Effectiveness and Applicability of Management Measures” for various permanent BMP control measures’ ability to remove specific pollutant types such as particulates, heavy metals, pesticides and organics. An example in table shows that curb elimination (promoting sheet flows) is highly effective at removing particulates, heavy metals and organics.

By the final RES stage submittal, the project shall include the location of the permanent BMP(s) on the plan sheets and noted under Water Quality/Stormwater section, for entry into the BMP database.

Detention Basin at I-64 and McKnight in St. Louis, MO.
FocalPoint filter in Columbia, MO.

General Exemptions

Once a project has met the qualifying criteria of redevelopment or new development, post construction BMPs must be considered during the project delivery process. If it is not feasible to place permanent post construction BMPs in the project area due to constraints such as utilities, right-of-way, safety, environmental or cost, written justification must be documented in the project file. While permanent BMPs may not be feasible, the projects must still adhere, at a minimum, to MCM 4 Construction Site Runoff Control and MCM 6 Pollution Prevention and Good Housekeeping measures. Below are some general exemptions:

  • Projects where the only work involved is the addition or rehabilitation of paved surfaces not intended for use by motor vehicles (such as sidewalks or bicycle/pedestrian trails).
  • Removing and replacing a concrete or asphalt roadway to base course, or subgrade or lower, without expanding the impervious surfaces.
  • Permit projects where MoDOT is not building/letting and the project is not on MoDOT right of way (designed by MoDOT but let by others).

Coordination with Adjacent MS4 Community

During the scoping phase of the project delivery process, if a project is located within another MS4 regulated area, it is recommended the community be contacted by district staff or environmental staff to determine whether the community has post construction requirements under their permit program. Another option is to investigate the community’s website or other resource to determine if they have specific requirements. A general review of the MS4 community’s MCM 5 Post Construction Runoff Control requirements shall be conducted. The district shall use all pertinent BMP information to determine the preferred treatment BMPs or other BMP opportunities in the watershed. Since MoDOT is regulated by MDNR under a MS4 permit, MoDOT is not required to comply with another MS4 regulated community’s requirements. However, the district should make an effort to coordinate with the community in an effort to share responsibilities.

If the MS4 community can provide a storm water treatment option off MoDOT right-of-way, it is most beneficial to pursue that opportunity. Working with MS4 communities to partner for long-term management and maintenance is preferred.

Projects that are Located Partially Inside an MS4 Community

If a MoDOT project is partially within the MS4 coverage area, but partially outside of the MS4 coverage area, permanent BMPs shall only be considered within the MS4 coverage area. The entire project description shall be used to determine the type of project, redevelopment or development, and therefore type of treatment.

If is not feasible to include permanent BMPs in the project and there are opportunities within the portion of the project outside the MS4 area, a swap is acceptable.

Cost-Share Projects and Unique Funding Projects

For cost-share projects within the MS4 area, permanent BMPs shall be applied using the flow chart to areas on MoDOT right of way that is applicable.

If it is not feasible and there are opportunities within the adjacent MS4 community, a swap is acceptable. An agreement for long-term maintenance must be agreed to by both entities.

If funding is through the community or county and MoDOT is only providing engineering services, post-construction BMPs are not required to be considered by MoDOT but may be required by the community or county under their stormwater permit.

Cost-Share projects that are entirely specific to a design element, such as railroad grade separations, sidewalks, etc. may be exempt if no other work is involved in that MS4 project area.

Projects as a Result of Adjacent Development

If a project is a result of an adjacent development and would not have otherwise been constructed by MoDOT, the water quality and/or quantity features shall be included in that development.

Traffic permits

If adjacent developments require an access permit and are within the MS4 coverage area, runoff from adjacent development must be treated prior to entering MoDOT right of way or directed away from MoDOT right of way.

Adjacent development that drains to MoDOT right of way cannot increase flows from the pre-construction condition.

Fig., Storm Water Post-Construction BMP Consideration

127.29.8 MCM 6: Pollution Prevention/Good Housekeeping

Permit requirement. The permittee shall develop and implement an operation and maintenance program that includes a training component and has the ultimate goal of preventing or reducing pollutant runoff from municipal operations. As part of the SWMP, the pollution prevention/good housekeeping program shall include the following information, at a minimum:

  • A list of all operations that are impacted by this operation and maintenance program;
  • Maintenance BMPs, maintenance schedules, and long-term inspection procedures for controls to reduce floatables and other pollutants to the permittee's regulated small MS4;
  • Controls for reducing or eliminating the discharge of pollutants from streets, roads, highways, municipal parking lots, maintenance and storage yards, waste transfer stations, fleet or maintenance shops with outdoor storage areas, and salt/sand storage locations and snow disposal areas the permittee operates;
  • Procedures for the proper disposal of waste removed from the permittee's MS4 and area of jurisdiction, including dredged material, accumulated sediments, floatables, and other debris;
  • Procedures to ensure that new flood management projects are assessed for impacts on water quality and existing projects are assessed for incorporation of additional water quality protection devices or practices;
  • An employee training program to prevent and reduce storm water pollution from activities such as park and open space maintenance, fleet and building maintenance, new construction and land disturbances, and storm water system maintenance. The permittee shall describe any existing, available materials the permittee plans to use such as those available from EPA, State or other organizations. The permittee shall describe how this training program will be coordinated with the outreach programs developed for the public information minimum measure and the illicit discharge minimum measure.

See 10 CSR 20-6.200.

MoDOT’s Coverage Area

127.29.8 map.jpg


EPA guidance on minimum control measures, National Menu of Stormwater BMPs.

EPA SWMM model for stormwater BMPs.

AASHTO, 2014, AASHTO Drainage Manual, 1st Edition, American Association of State Highway and Transportation Officials.