TMDL GP

3. NPDES Impaired Stormwater Total Maximum Daily Load General Permit (TMDL GP)

Under Section 303(d) of the Federal Clean Water Act, states, territories, and authorized tribes are required to develop lists of impaired waters. These are waters that are too polluted or otherwise degraded to meet the water quality standards set by states, territories, or authorized tribes. The law requires that these jurisdictions establish priority rankings for waters on the lists and develop a Total Maximum Daily Load (TMDL) for each of these waters. A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards. See related links at end of document for more information.

In the State of Vermont, the Agency of Natural Resources – Department of Environmental Conservation (Vermont DEC) is the permitting authority and administers the TMDL GP on behalf of the U.S. Environmental Protection Agency (EPA). The Vermont DEC recognizes the importance of managing the quantity and quality of stormwater runoff, especially within Vermont’s stormwater impaired waters. The Vermont DEC has successfully obtained EPA approval designating a number of waterways as impaired statewide.

A number of Vermont’s waters are listed as “impaired” primarily due to urban stormwater runoff. These waters fail to meet the Vermont Water Quality Standards based primarily on biological monitoring data. These impaired waters are listed on an EPA approved list under Part A, prepared pursuant to Section 303(d) of the Federal Clean Water Act. See related links at end of document for more information.

Once a waterway and its watershed are listed as impaired, it is scheduled for the development of a Total Maximum Daily Load (TMDL) and ultimately a TMDL General Permit which implements the TMDL. A TMDL is an EPA approved watershed restoration plan that attempts to limit and allocate discharge loads among the various dischargers to impaired waters in order to assure attainment of water quality standards.

VTrans operates systems to varying degrees in every one of the impaired watersheds. As such, VTrans is required to comply with the conditions of the TMDL General Permits on State Highways, other transportation facilities, and VTrans maintenance facilities that are located in these watersheds of waters that are principally impaired by collected stormwater runoff.

There have not yet been any General Permits developed yet to implement the Impaired Stream TMDLs. In lieu of this, and at the direction of Vermont DEC, MS4s are required to show that the BMPs selected to be implemented in the MS4 SWMP will reduce to the maximum extent practicable the identified pollutant(s) of concern. Addressing this issue in the MS4 NOI and SWMP satisfactorily meets the requirements for the stormwater impaired streams at this time.

Note: the permit states that consistency with the TMDL will be based on the implementation of specific practices and not on estimates of pollutant loading. When the General Permits implementing the TMDLs are issued, then compliance with the TMDL will be based on specific reductions of stormwater volume to the stream based on loading.

The Lake Champlain Phosphorus TMDL has been approved by the EPA. VTrans strives to ensure consistency with the Lake Champlain Phosphorous TMDL through adoption of the BMPs defined in the MS4 SWMP. Responses by VTrans to the specific Lake Champlain TMDL recommendations are:

  1. Adoption of erosion controls:
    VTrans has invested in our ongoing commitment to manage construction site runoff in many ways. Refer to NPDES Construction Activity Stormwater Permitting Program for more detailed information.
  2. Improved construction and maintenance practices for gravel backroads: There are no State “gravel back roads” in the VTrans MS4, however, VTrans does support the Vermont Local Roads and Better Back Roads Programs. See related links at end of document for more information.
  3. Promotion of riparian buffers and setbacks: Historically, roads were built in or near riparian buffers and in many cases the road’s right-of-way (ROW) contains the riparian buffer. VTrans has adopted a Riparian Buffer BMP, offering guidance to Operations Maintenance Personnel regarding the importance of maintaining riparian buffers in their undisturbed natural state. See related links at end of document for more information.

The Vermont Small Municipal Separate Storm Sewer Systems (MS4s) General Permit Requirements under the Agency’s General Permit 3-9014 were affirmed, but modified via Water Resource Board Dockets WQ-03-08 and WQ-04-03 (Consolidated) under a Memorandum of Decision (July 21, 2005 MOD) to clarify and add conditions to the General Permit. VTrans’ response to the two conditions relating to riparian buffers is evidence of our commitment to promote riparian corridor preservation and management as a water quality enhancement BMP. These BMP’s are noted under other Sections of the MS4 SWMP.

Related links

EPA TMDL

EPA Surf your Watershed

EPA Cleanwater Act

Vermont Water Quality Division

For maps of Vermont stormwater impaired watersheds

Vermont Local Roads

Better Back Roads

Riparian BMP

Other MS4 related Documents