Technical guidance used by MPCA to develop guidelines for setting TMDL WLAs for regulated stormwater

Introduction

Successful implementation of stormwater requirements in a Total Maximum Daily Load (TMDL) requires integration of three components:

• The permit must contain language that links the TMDL language to Stormwater Pollution Prevention Program (SWPPP) requirements.
• There must be a procedure for incorporating TMDL requirements into the SWPPP.
• A TMDL must contain clear language that can be linked to the permit and SWPPP.

MPCA is preparing a series of modules designed to address a variety of stormwater topics. Modules 4.1, 4.2 and 4.3 address the 3rd requirement stated above.

Modules 4.1, 4.2 and 4.3 are for stormwater staff, TMDL staff, or stakeholders involved in development of TMDLs that involve a permitted stormwater component. The modules present information on a variety of policy issues that impact development of a TMDL and subsequent activities by regulated stormwater entities in response to the TMDL. Prior to viewing the material in this module, material in Stormwater module 1, Stormwater Overview, and TMDL module 1, TMDL Overview, should be understood.

The learning objectives for Modules 4.1, 4.2 and 4.3 include the following:

• Understand the basics of MPCA’s Stormwater Program;
• Understand language in stormwater permits; and
• Understand TMDL-stormwater issues, including potential solutions and problems.

The following document provides a discussion of issues related to setting wasteload allocations for permitted stormwater and to implementing activities to address a stormwater wasteload allocation. Several recommendations are presented. In some cases, these recommendations are developed as policy to be implemented in developing TMDLs that include a stormwater component.

Stormwater program

The Federal National Pollutant Discharge Elimination System (NPDES) was mandated by Congress under the Clean Water Act. Many activities are regulated under the NPDES Program, including confined animal feeding operations (CAFO), combined sewer overflows (CSO), sanitary sewer overflows (SSO), and stormwater. Stormwater can further be divided into three permit areas – construction activities, industrial activities, and municipal activities. Minnesota regulates the disposal of stormwater through State Disposal System (SDS) permits. The MPCA issues combined NPDES/SDS permits for construction sites, industrial facilities and municipal separate storm sewer systems (MS4s).

Each of the three stormwater permitting programs has a general permit. Individual permits may also be issued within each program.

Under the Phase I construction permit, operators of large construction activity resulting in the disturbance of five or more acres of land are required to obtain general permit coverage. Phase II includes small construction activity that results in the disturbance of equal to or greater than one acre, or less than one acre if that activity is part of a "larger common plan of development or sale". Owners and operators of projects meeting the above criteria must obtain permit coverage and implement practices to minimize pollutant runoff from construction sites. Permits may also be required for activity disturbing less than one acre but deemed by MPCA to represent a risk to water resources. The current general construction permit was issued August 1, 2003. The construction permit is applied statewide, except for Tribal areas. For example, some feedlot activities require permit coverage. For more information, see [1].

Public and private operators of industrial facilities included in one of the 11 categories of industrial activity defined in the federal regulations by an industry's Standard Industrial Classification (SIC) code or a narrative description of the activity found at the industrial site are required to apply for a permit. A facility may be eligible for a conditional no-exposure exclusion from permitting provided their industrial materials and activities are entirely sheltered from storm water. The federal regulations can be found at 40 CFR 122.26 (b)(14)(i)-(xi). For more information, see [2].

A municipal separate storm sewer system is a conveyance or system of conveyances (roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, storm drains):

• Owned or operated by a state, city, town, borough, county, parish, district, association, or other public body (created by or pursuant to State law) having jurisdiction over disposal of sewage, industrial wastes, stormwater, or other wastes, including special districts under State law such as a sewer district, flood control district or drainage districts, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the federal Clean Water Act, United States Code, title 33, section 1288, that discharges to waters of the United States;
• Designed or used for collecting or conveying stormwater;
• Which is not a combined sewer; and
• That is not part of a publicly owned treatment works.

Not all MS4s require permit coverage. The cities of Minneapolis and St. Paul are Phase 1 permittees and require individual permits. The remaining regulated MS4s are Phase 2 permittees and are either mandatory or designated. Mandatory MS4s occur in urbanized areas as defined by the 2010 Census. An "urbanized area" is a land area comprising one or more places (“central places”) and the adjacent densely settled surrounding area (“urban fringe”) that together have a residential population of at least 50,000 and a density of at least 1,000 people per square mile. The definition also includes any other public storm sewer system located fully or partially within an urbanized area. For example, the University of Minnesota Twin City campus is a mandatory MS4 because it operates a conveyance system and is part of an urban area. There are 212 mandatory MS4s in eight urban areas in Minnesota.

MS4s outside of urbanized areas that have been designated by the MPCA for permit coverage include cities and townships with a population of at least 10,000 and cities and townships with a population of at least 5,000 and discharging or the potential to discharge to valuable or polluted waters. These designated MS4s are required to obtain permit coverage by February 15, 2007. For more information see [3].

Permit language for impaired waters

Although this document focuses on TMDL language, it is important to understand permit language that pertains to impaired waters and TMDLs. TMDL language must be written in a manner that is consistent with permit language and requirements. This section provides a summary of permit language. Permits can be found on MPCA’s Stormwater website ([4]).