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    State of Idaho

    Excerpts from The Catalog of Stormwater Best Management Practices for Idaho Cities and Counties

    Section 1 - Introduction

    The Catalog of Stormwater Best Management Practices for Idaho Cities and Counties provides technical guidance for construction site design and the selection of stormwater best management practices (BMPs). The catalog is a guidance document containing voluntary controls that could be formally adopted by a jurisdiction to establish standards, if desired. Measures, such as those described and other recognized equivalents, should be used to manage the quantity and quality of stormwater runoff from land development.

    In general, there are two types of BMPs for stormwater pollution control:

    1. Source control BMPs focus on minimizing or eliminating the source of the pollution so that pollutants are prevented from contacting runoff or entering the drainage system.
    2. Treatment control BMPs which tend to be more expensive to implement than source control BMPs, are designed to remove pollutants after they have entered runoff. Examples of source control BMPs include spill controls and employee education, while treatment control BMPs include detention ponds and oil/water separators. Most source control BMPs tend to be non-structural, and most treatment control BMPs tend to be structural in nature, although there can be exceptions. For example, a roof over a materials storage area at an industrial site would be considered a structural source control.

    The majority of the practices focus on controlling pollution at its source, before runoff enters a drainage conveyance such as a sewer system or river. However, some BMPs are also included that can be used to treat runoff and remove pollutants that have already entered the drainage conveyance. The structural measures will reduce pollutant loads in postconstruction site runoff, provided that the facilities are properly designed, installed, and maintained on a periodic basis.

    The catalog presents general technical guidelines. Specific conditions or local regulations may require modification of the recommended BMPs, and alternative practices that are approved by a local permitting authority may also require modification or replacement of recommended BMPs. The BMP selection matrices should be used as screening tools to assist the design professional, landowner, or reviewer in selecting the most appropriate or suitable measure based on site-specific conditions.

    Section 3 - Responsibility for Stormwater Management and Permitting

    This chapter introduces an overview of current federal, state, and local government agency stormwater plans, programs, and regulations. Design professionals may have to work closely with some government agencies more than others when planning a development project. As a result, those government agencies and their requirements have been included in more detail.

    Responsibility for stormwater management is often held collectively by landowners and several agencies and special districts. Persons wishing to discharge stormwater runoff into a drainage facility should contact the appropriate agency or special district about conditions or permitting requirements that may apply.

    Landowners are principally responsible for stormwater runoff from their property. In subdivisions with a stormwater facility (e.g., detention pond) that collects runoff from the entire development, the developer or local homeowners’ association may assume responsibility for maintenance. Alternately, the facility could have an easement to allow for maintenance by the city, county, or local highway jurisdiction. In this case, the local agency may charge the developer or homeowners’ association for the cost of such maintenance.

    Idaho adopts water quality standards to protect public health and welfare, enhance the quality of water, and serve the purposes of the Clean Water Act. These standards are the benchmarks DEQ uses to know if it is doing its job to protect Idaho's surface water. Nonpoint source pollution management includes the use of Best Management Practices (BMPs) which should be designed, implemented and maintained to provide full protection or maintenance of beneficial uses (IDAPA 58.01.02, § 350.02).

    Any project that requires a federal permit or license under the Clean Water Act, such as a National Pollutant Discharge Elimination System permit, or a Clean Water Act Section 404 dredge and fill permit, requires a Clean Water Act Section 401 certification. The certification states that the project will not cause a violation of state water quality standards.

    IDEQ is also responsible for protecting the quality of ground water in Idaho and relies on a combination of programs to protect ground water from pollution, clean up degraded ground water, and monitor and assess ground water quality. The IDEQ’s authority for nonpoint source control of ground water pollution includes the Ground Water Quality Protection Act (Chapter 1, Title 39, Sections 120 through 127, Idaho Code), the Idaho Ground Water Quality Plan, and the Ground Water Quality Rule (IDAPA 16.01.11).

    The EPA, Region 10 (Seattle) is also the National Pollutant Discharge Elimination System (NPDES) permitting authority for the State of Idaho. As such, the agency is responsible for permitting all point source discharges to waters of the United States, including stormwater discharges. The 1987 Amendments to the Clean Water Act (CWA) prohibit the discharge of any pollutant to waters of the U.S. from nonagricultural sources unless authorized by a NPDES permit. These requirements are being implemented in two phases through the EPA’s Stormwater Program. The federal stormwater regulations require permits for entities that own and operate municipal separate storm sewer systems (MS4s) that meet certain criteria, certain classifications of industrial facilities, and construction sites larger than one acre.

    Boise City, Garden City, the Ada County Highway District, Ada County Drainage District 3, District 3 of ITD, and Boise State University are the only entities in Idaho subject to Phase I municipal separate storm sewer system requirements. Owners or operators of MS4s in Idaho within “urbanized areas” (UAs), based on 2000 Census data, are regulated entities under Phase II requirements. Owners or operators of MS4s outside UAs could also be regulated as more information becomes available or through petition to EPA.

    Operators of Phase II-designated small MS4s are required to apply for NPDES permit coverage and develop, implement and enforce a stormwater management program designed to reduce the discharge of pollutants to the “maximum extent practicable,” to protect water quality, and to satisfy the requirements of the CWA. The stormwater management program must address six minimum control measures, including public education and outreach, public participation/involvement, illicit discharge detection and elimination, construction site runoff control, postconstruction runoff control, and pollution prevention/good housekeeping for municipal operations.

    Industrial facilities identified by EPA as needing an NPDES industrial stormwater permit must obtain an NPDES permit if they discharge stormwater either directly to surface waters or indirectly through separate municipal storm drains.

    Construction activities that disturb an area of one acre or more or that are part of a larger common plan of development (such as lots in subdivisions created since 1987) are required to submit a Notice of Intent (NOI) and prepare and implement a Stormwater Pollution Prevention Plan (SWPPP). These permit requirements are in addition to local regulations.


    Catalog of Stormwater Best Management Practices

    The Catalog of Stormwater Best Management Practices for Idaho Cities and Counties