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: (7) Minimize soil 

compaction and, unless infeasible, preserve topsoil. 

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(1) Minimizing soil compaction and, unless infeasible, preserving topsoil controls or 

minimizes the discharge of stormwater from the site. 

This requirement is designed to reduce the amount of soil eroded and discharged from the site 

by reducing the amount of runoff generated and by providing conditions conducive to 

establishing vegetative stabilization. Compacting soil increases the amount of runoff produced. 

This is because compacted soil does not allow water to infiltrate as rapidly as loose soil. 

Minimizing soil compaction allows for infiltration and retention of stormwater within the soil, 

which reduces the amount of runoff. Reducing the amount of runoff will reduce erosion, and 

therefore reduce the amount of sediment and other pollutants that can be transported within the 

site and to sediment controls and through perimeter controls. Since sediment controls and 

perimeter controls are not 100% effective in removing sediment and other pollutants, reducing 

the amount of sediment and runoff directed to these controls will reduce the amount of 

pollutants discharged from these controls.

Topsoil improves soil structure and provides a favorable growing medium for temporary and 

permanent vegetative stabilization measures. Preserving topsoil allows for better vegetative 

stabilization. Better vegetative stabilization reduces erosion rates of the underlying soil and also 

increases the infiltrative capacity of the soil. Reducing erosion rates and reducing the runoff 

volume will reduce the amount of sediment transported to downslope sediment and perimeter 

controls. Since sediment controls and perimeter controls are not 100% effective in removing 

sediment and other pollutants, reducing the amount of sediment and runoff directed to these 

controls will reduce the amount of pollutants discharged from these controls.

Preservation of topsoil also means limiting disturbance and removal of the topsoil and 

associated vegetation. Limiting clearing and grading to only those areas where necessary to 

accommodate the building footprint is an example of topsoil preservation. Preserving topsoil in 

this manner would reduce the volume of stormwater as well as the quantity of sediment and 

other pollutants mobilized from these areas of preservation, which would reduce the amount of 

pollutants discharged from the site.

Topsoil stockpile areas, if used, should be prevented from eroding, which can be accomplished 

by using various cover materials. Use of temporary vegetative stabilization measures for topsoil 

areas may also be considered if the stockpiles are to remain on-site for an extended period of 

time before being used.

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

EPA notes that the “minimize soil compaction” language is meant to apply to those areas of the 

site where soil compaction is not necessary for structural or stability concerns. For example, 

EPA would not expect permittees to minimize compaction in areas, such as where roads, 

foundations, footings or other structures are to be built, or on embankments, where soil 

compaction is necessary by design. Rather, this requirement is intended to apply to other areas 

of the site, such as those where vegetation is to be preserved. EPA notes that some projects 

may be designed to be highly impervious after construction, and therefore little or no vegetation 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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is intended to remain. In these cases (and perhaps others), preserving topsoil at the site would 

not be feasible since the topsoil would not be necessary for establishing vegetation. Another 

case where it may not be feasible to preserve topsoil would be if the topsoil is of poor quality or 

contaminated such that it would not be beneficial for establishing vegetation. Although poor 

topsoil may be improved through addition of soil amendments, there may be cases where this is 

not feasible or where keeping the topsoil on-site would conflict with other regulations or 

programs with respect to contaminated soils. Although not a requirement of this rule, minimizing 

soil compaction may be necessary in areas of the site where post-construction controls are to 

be designed to infiltrate stormwater. Examples of these areas would be areas underneath 

porous pavement systems or areas where infiltration basins are to be installed. Consideration of 

soil compaction during the construction phase would be critical to ensuring proper operation of 

these types of practices. 

For some projects where the construction envelope may encompass the entire land area, there 

may not be space available on-site to stockpile topsoil that is removed. In these cases, the use 

of off-site borrow or storage areas may be appropriate. In addition, topsoil may be sold for use 

on other projects where more topsoil is available than needed on-site. EPA considers diversion 

to other uses where not needed on site to be a situation where it is not feasible to preserve all 

topsoil. NAHB commented on page 147 of their detailed comment letter that EPA should add 

desirable topsoil to this requirement. While EPA has not changed the language of the rule, the 

term “unless infeasible” should provide sufficient flexibility for the permitting authority to require 

only preservation of topsoil that will foster vegetative stabilization.

(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)(5) and (6) to make those 

provisions read as follows: “Preserve desirable topsoil and natural vegetation consistent with 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

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project goals” and “Minimize soil compaction as appropriate and consistent with other applicable 

building codes and requirements.” EPA had proposed “Preserve topsoil and natural vegetation” 

and “Minimize soil compaction by construction equipment in areas that will not contain 

permanent structures or where compaction is not necessary for structural integrity. In disturbed 

areas that will not contain structures or where compaction is not necessary for structural 

integrity, utilize deep ripping and decompaction of soils and incorporate organic matter to 

restore infiltrative capacity.” Thus, while NAHB suggested some changes to EPA’s proposed 

provisions, it did not suggest deleting the provisions, thereby acknowledging, consistent with its 

overall comments in support of a BMP-only ELG, that minimizing soil compaction and 

preserving desirable topsoil and natural vegetation are key to 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. 

Note also that, on page 147 of its detailed comment letter, NAHB suggested that “EPA’s soil 

compaction BMP should be removed because there are other regulatory requirements that may 

address compaction associated with the type of construction, and this truly is a local issue 

related to land use planning and the natural hydrology of the area.” This comment is 

inconsistent with NAHB’s suggested edit in its redline/strikeout “precisely crafted edits” to the 

soil compaction BMP, where NAHB suggested edits to it but did not suggest removing it from 

the regulation. However, NAHB stated on page 146 of its detailed comment letter that “NAHB 

believes that its redlined submission [i.e., redline/strikeout “precisely crafted edits”] speaks for 

itself and does not wish to be bound by issues raised in this section of the comments.” 

(emphasis added) Thus, NAHB’s redline/strikeout “precisely crafted edits”, in which it merely 

suggested edits to this provision, take precedence over what NAHB stated in its detailed 

comment letter, in which it suggested deleting the soil compaction provision. 

In any event, EPA included the “minimize soil compaction” provision in the final ELG/NSPS to 

ensure that permitting authorities consider the issue, but are provided with flexibility in 

implementing the requirement by the use of the term “minimize”. 

(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 provisions requiring permittees to preserve native topsoil 

on their site, unless infeasible. The permit also requires that in areas of the site where final 

vegetative stabilization will occur or where infiltration practices will be installed, permittees must 

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

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Restrict vehicle / equipment use. Restrict vehicle and equipment use in these 

locations to avoid soil compaction; or

Use soil conditioning techniques. Prior to seeding or planting areas of exposed soil 

that have been compacted, use techniques that condition the soils to support vegetative 

growth, if necessary and feasible. 

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

This requirement is applicable during all phases of construction. During the initial clearing and 

grading phase, permittees should generally avoid the use of equipment and compaction of soils 

in those areas where soil compaction is not necessary for structural stability of design reasons. 

Compaction of soil in areas adjacent to structures is likely inevitable, due to the action of 

equipment. However, permittees can consider decompaction techniques, such as deep ripping, 

as a means of restoring infiltrative capacity in these areas. EPA notes that this concept is 

consistent with the concepts of Low Impact Development (LID), and minimization of soil 

compaction during construction will facilitate use of LID and stormwater retention practices in 

the post-developed condition. 

(6) When preservation of topsoil would be infeasible.

Preserving topsoil may be infeasible in certain situations. For example, if a site is to be highly 

developed in the post-developed condition such that a majority of the site will be covered with 

structures or paved, then preserving topsoil for use at this site may be infeasible. In addition, 

some sites may not have space to stockpile topsoil on site for later use. EPA is aware that 

stockpiling of topsoil in off-site locations or transfer of topsoil to other locations is frequently 

used in these situations and EPA would view this as acceptable practice. If off-site areas are not 

readily available, then this would be an example of where this requirement could be considered 

infeasible. Permitteees should consult permitting authorities for site-specific considerations such 

as these.