Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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40 CFR 450.21(a) Erosion and Sediment Controls. Design, install and maintain effective 

erosion controls and sediment controls to minimize the discharge of pollutants. At a 

minimum, such controls must be designed, installed and maintained to: (6) Provide and 

maintain natural buffers around surface waters, direct stormwater to vegetated areas to 

increase sediment removal and maximize stormwater infiltration, unless infeasible. 

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(1) Providing and maintaining natural buffers around surface waters, and directing 

stormwater to vegetated areas to increase sediment removal and maximize stormwater 

infiltration, controls or minimizes the discharge of stormwater from the site. 

This requirement reduces the discharge of sediment and other pollutants from construction 

activities. As described by Muñoz-Carpena et al. (Modeling Hydrology and Sediment Transport 

in vegetative filter strips, Journal of Hydrology, Volume 214 (1999), pg. 111-129), vegetative 

areas, including vegetated filter strips, remove pollutants through “filtration, deposition, 

infiltration, absorption, adsorption, decomposition and volatilization.” This paper further 

described the mechanisms of pollutant removal as follows:

“Vegetation at the downstream edge of disturbed areas may effectively reduce 

runoff volume and peak velocity primarily because of the filter’s hydraulic roughness, 

and subsequent augmentation of infiltration. Decreasing flow volume and velocity 

translates into sediment deposition in the filter as a result of a decrease in transport 

capacity (Wilson, 1967). Barfield et al. (1979) and Dillaha et al., (1986) reported that 

grass filter strips have high sediment trapping efficiencies as long as the flow is shallow 

and uniform and the filter is not submerged. 

As sediment is deposited from runoff in these vegetated zones, sediment-bound 

nutrients are also removed (Bolton et al., 1991; Flanagan et al., 1989). For nutrients 

attached to sediment (i.e. organic phosphorous, ammonium and organic N) the 

deposition process largely controls the effectiveness of the filter area, whereas infiltration 

is the controlling factor for soluble nutrients (such as nitrates and inorganic 

orthophosphates).”

Therefore, buffers and vegetated areas provide removal of sediment and other pollutants 

through filtration and other mechanisms. In addition, infiltrating stormwater reduces the amount 

of water being discharged, thereby potentially reducing the amount of erosion the discharge will 

produce. Directing stormwater to vegetated areas to allow for filtration and infiltration can be a 

highly effective means of managing stormwater on construction sites because this will reduce 

the amount of pollutants contained in the discharge through filtration and other removal 

mechanisms, and infiltration will reduce the volume of the discharge and the associated 

dissolved pollutants in the infiltrated volume. This can be accomplished in a number of ways. 

Examples include directing sheet flow leaving silt fences, filter berms or other perimeter controls

to vegetated buffers adjacent to streams. EPA notes that this is common practice on many 

linear projects where dispersion of stormwater to adjacent vegetated areas can be preferred 

over designing and constructing conveyances. Other examples include directing stormwater 

exiting sediment basins to vegetated areas such as vegetated buffers adjacent to streams or 

other vegetated areas on or adjacent to the site through the use of corrugated pipes and level 

spreaders. EPA notes that this technique is highly appropriate on sites incorporating low-impact 

development and environmental site design, since sites constructed using these principles will 

typically have areas of vegetation preservation that may be appropriate for dispersion of treated 

stormwater during the construction phase. However, permittees need to consider the total 

volume of stormwater and the amount of sediment in the stormwater when selecting appropriate 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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mechanisms and locations for dispersion, filtration and infiltration in vegetated areas. Using

these techniques is not a substitute for up-slope erosion and sediment controls. In addition, 

concentrated points of discharge, such as discharge from sediment basins, should incorporate 

appropriate energy dissipation devices if necessary to prevent erosion when directing these 

flows to vegetated areas. These techniques will help to prevent the formation of gulleys and 

associated erosion. 

(2) What EPA does not mean by this requirement.

This requirement only applies during the active phase of construction. This requirement does 

not mandate providing or maintenance of the buffer in the post-developed condition. This 

requirement is also not intended for the operator to have to create vegetated buffers in areas 

that would not be appropriate for vegetative buffers (e.g., in areas where the existing, natural 

area adjacent to a stream is not comprised of vegetation but rather consists of rocks, gravel, 

sand, cobble, etc.). In these cases, the existing, natural area could be considered the 

appropriate buffer and preservation of that area in its natural state could constitute compliance 

with this requirement, as any setback between the areas of disturbance and the surface water 

will provide some attenuation of pollutants and stormwater flows.

(3) In its comments on the proposed C&D ELG/NSPS, NAHB expressed support for nonnumeric effluent limitations in the form of BMPs like this provision.

In its cover comment letter on the proposed C&D ELG/NSPS, NAHB stated that it “has 

consistently advocated for an ELG that allows for site-specific selection of BMPs, appropriate 

sediment basin sizing criteria and the implementation of pollution prevention practices.” NAHB 

comment cover letter at 2. NAHB stated that EPA’s proposed Option 1, a BMP-only ELG, 

“would build upon the significant environmental progress made to date by ensuring that all 

construction sites meet a minimum standard of excellence by adopting those erosion and 

sediment controls that have evolved and are now accepted across the country.” Id. NAHB 

urged EPA to broaden “best management practices and pollution prevention to ensure these 

practices can be implemented at every permitted construction site, in all circumstances across 

the country.” Id. at 3. 

In its detailed comments attached to its cover letter, NAHB continued to support a BMP-only 

ELG to control stormwater discharges from active construction sites. NAHB urged EPA “to 

remove any requirements to meet numeric effluent limits and proceed with a BMP-based ELG to 

control stormwater discharge.” NAHB detailed comments at 38. NAHB claimed that “[i]n the 

case of EPA's proposed C&D ELGs, the combination of ELG precedent and the fact that EPA is 

focusing exclusively on stormwater provides irrefutable support for a BMP-based ELG 

approach.” Id. at 42. NAHB concluded that “[t]here is substantial authority for and evidence 

regarding the success associated with permitting authorities relying on BMP-based approaches 

to achieve environmental objectives. EPA also should rely on a BMP-based approach for the 

C&D ELG rulemaking.” Id. at 46 (emphasis in original).

In addition, in its redline/strikeout “precisely crafted edits” of EPA’s proposed Option 1, the BMPonly ELG, NAHB suggested a revision to proposed 450.21(a)(7) to make that provision read as 

follows: “Provide and preserve natural buffers around surface waters.” EPA had proposed 

“Provide and maintain natural buffers around surface waters.” Thus, while NAHB suggested 

changing “maintain” to “preserve”, it did not suggest deleting the requirement, thereby 

acknowledging, consistent with its overall comments in support of a BMP-only ELG, that 

providing and, at a minimum, preserving natural buffers around surface waters is key to 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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controlling and minimizing the discharge of stormwater from active construction sites. See 

reference to “precisely crafted edits” on page 144 of NAHB’s detailed comments on the 

proposed ELG/NSPS, as well as the attachment to EPA-HQ-OW-2008-0465-1360. See also 

NAHB’s reasoning for changing “maintain” to “preserve” on page 147 of its detailed comment 

letter.

(4) Implementation of this provision in NPDES permits.

The construction stormwater ELG will be implemented in NPDES permits as the applicable 

technology-based effluent limitations in those NPDES permits. The ELG is not directly 

applicable to any regulated entity. If the permitting authority chooses to copy the ELG verbatim 

into its draft proposed NPDES permit as the technology-based effluent limitation, dischargers 

will have an opportunity to provide comment on the need for more specificity if they are 

concerned that the narrative nature of the limit could unfairly subject them to arbitrary 

enforcement. Furthermore, in the event that the permitting authority does not provide any 

additional specificity, it is typical in stormwater permits for active construction for the permitting 

authorities to include a requirement to prepare a storm water pollution prevention plan (SWPPP) 

in the permit. While the provisions of the SWPPP are not effluent limitations themselves, they 

indicate how the discharger intends to meet the narrative effluent limitations in the permit. As 

such, SWPPPs can be helpful to the regulated entity in demonstrating how they are meeting 

their effluent limitations. 

In the 2012 CGP, EPA has included a provision requiring permittees discharging to a surface 

water within 50 feet of their site to implement one of three compliance alternatives:

1. Provide and maintain a 50-foot buffer of undisturbed natural vegetation; or

2. Provide and maintain an undisturbed naturally vegetated buffer that is less than 50 feet 

and is supplemented by additional erosion and sediment controls, which in combination 

achieves the sediment load reduction equivalent to a 50-foot buffer of undisturbed 

natural vegetation; or

3. If it is infeasible to provide and maintain an undisturbed naturally vegetated buffer of any 

size, you must implement erosion and sediment controls that achieve the sediment load 

reduction equivalent to a 50-foot buffer of undisturbed natural vegetation.

 

EPA believes that the compliance alternatives provide permittees with needed flexibility to meet 

this requirement.

(5) Appropriate time for implementation of this BMP in the construction process.

Preservation of buffers adjacent to water bodies should be done at the beginning of 

construction. The use of temporary exclusion fencing or silt fences are examples of appropriate 

means of delineating the buffer boundaries. The use of fencing allows equipment operators and 

others working on site to clearly see the buffer areas and other areas of no disturbance. As 

sediment controls (such as basins) are brought on-line, provisions for directing treated 

stormwater to vegetated areas and buffers can be implemented. 

(6) Where a buffer boundary starts and ends.

The final rule does not establish a minimum buffer width. However, in implementing the buffer 

requirements in NPDES permits, permitting authorities may establish minimum buffer widths so 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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that the permit requirements are more transparent, environmentally effective, and enforceable.

EPA does not believe that there is one appropriate minimum buffer width that should apply to all 

sites nationwide. EPA believes that the establishment of a minimum buffer width is best 

determined through consideration of several factors by the permitting authority. Some of the

factors that a permitting authority may evaluate in developing a minimum buffer width include:

How effective are buffers at removing sediment and other pollutants in the areas

covered under the permit?

What size buffers are necessary to provide high levels of pollutant removal?

What types of state and local regulations already affect the buffer area?

Is a uniform buffer width requirement appropriate?

Permitting authorities may consider providing flexibility to any minimum buffer width 

requirements for sites that may have difficulty implementing a minimum buffer width on their 

site, and to provide flexibility for situations in which buffer disturbances are necessary. 

(7) Circumstances that make buffer controls “infeasible”.

EPA does not intend for this requirement to conflict with state water right law, and thus the 

Agency believes that it would be infeasible to provide and maintain natural buffers around 

surface waters where doing so would conflict with state water right law. In addition, for some 

projects that are in close proximity to surface waters (such as streams and lakes), there may not 

be preexisting buffers between the new construction project and the surface water or the 

vegetation quality may be poor. In these cases, the permitting authority should exercise 

discretion in establishing appropriate requirements. For example, the permitting authority may 

authorize disturbance within the buffer in order to allow removal of existing vegetation and 

installation of new vegetation. Another example of where this standard may require discretion by 

the permitting authority is reclamation or stream stabilization/improvement projects. In these 

cases, disturbance within the buffer may be an integral part of the construction project. EPA 

does not intend this requirement to limit activities within buffers necessary to complete 

restoration or stabilization projects, or other projects where removal, replacement or alteration of 

vegetation is a necessary component of the project.

For certain locations within projects, such as locations where stream crossings or other wateroriented features are constructed, EPA would not expect that buffers would be maintained since 

this would be infeasible. Additionally, EPA recognizes that it may not be feasible to provide a 

buffer if space constraints require disturbances within the buffer, or if the nature of the 

development requires it to occur within the buffer (e.g., a waterfront marina). EPA also notes 

that it does not expect permittees to provide buffers around constructed conveyances on site, 

such as channels that are constructed on site to convey stormwater. 

EPA also recognizes that certain linear projects may have difficulty in complying with a minimum 

fixed buffer width requirement due to space constraints. If you are subject to the requirements 

in this Part of the final CGP for “linear construction projects” (see Appendix A of the final CGP), 

you are not required to comply with this requirement if site constraints (e.g., limited right-of-way) 

prevent you from meeting the requirements of the compliance alternatives in Part 2.1.2.1a, 

provided that you retain as much natural vegetation as is feasible and/or to the extent feasible 

provide supplemental erosion and sediment controls in the buffer area. You must also 

document in your SWPPP your rationale as to why it is infeasible for you to comply with the 

requirements in Part 2.1.2.1a, and describe any buffer width retained and/or supplemental 

erosion and sediment controls installed. 
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EPA notes that individual permitting authorities can develop appropriate criteria for determining 

feasibility and infeasibility criteria for these types of situations. EPA also notes that permitting 

authorities may consider alternative erosion and sediment control requirements to provide 

flexibility for sites that are unable to implement buffers in order to minimize pollutant discharges 

to surface waters.

(8) Circumstances that make directing stormwater to vegetated areas to increase 

sediment removal and maximize stormwater infiltration “infeasible”.

EPA does not intend for this requirement to conflict with state water right law, and thus the 

Agency believes that it would be infeasible to direct stormwater to vegetated areas to increase 

sediment removal and maximize stormwater infiltration where doing so would conflict with state 

water right law. In addition, EPA notes that dispersion to vegetated areas may not be 

appropriate in some arid and semi-arid areas where little or no vegetation exists and slow or 

non-infiltrating soils are present. However, in arid and semi-arid areas with soils that will readily 

infiltrate (e.g., hydrologic soil group A or B soils), dispersion and infiltration techniques may still 

be feasible and appropriate and can accomplish significant volume (i.e., pollutant) reductions. 

These techniques may also not be appropriate for certain projects, such as trench excavations 

in urban areas where pervious or vegetated areas within the project footprint are non-existent.

For some highly developed projects, there may not be available land that can be used as a 

discharge area for stormwater or the available land may be very small in relation to the volume 

of stormwater requiring management. In these cases, this requirement may not be feasible for 

managing all of the stormwater, but management of some of the stormwater through dispersion 

and infiltration may be feasible.