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

1

40 CFR 450.21(b) Soil Stabilization. Stabilization of disturbed areas must, at a minimum, 

be initiated immediately whenever any clearing, grading, excavating or other earth 

disturbing activities have permanently ceased on any portion of the site, or temporarily 

ceased on any portion of the site and will not resume for a period exceeding 14 calendar 

days. Stabilization must be completed within a period of time determined by the 

permitting authority. In arid, semiarid, and drought-stricken areas where initiating 

vegetative stabilization measures immediately is infeasible, alternative stabilization 

measures must be employed as specified by the permitting authority.

___________________________________________________________________________

(1) This non-numeric effluent limitation controls or minimizes the discharge of 

stormwater from the site. 

Exposed soils erode at a much higher rate than stabilized soils. Erosion is caused by 

detachment of soil particles by rainfall, by flowing water and by wind. Stabilization measures, 

including mulches, vegetation and rolled erosion control products, will reduce raindrop impact 

energy and reduce soil detachment and transport. This is because the raindrops will hit the 

cover material, as opposed to the soil particles. When the raindrop hits the cover material, the 

energy of the falling raindrop is dispersed. If the cover material were not there, then the raindrop 

would strike the soil particles and may cause detachment. Flowing water would then transport 

the soil particles downslope. Stabilization also reduces erosion because the plant root material 

anchors the soil particles in-place. This reduces detachment by raindrops as well as transport 

by flowing water. Stabilization also reduces erosion by wind. Soil eroded by wind can be 

transported and deposited to other areas of the site (or off-site), where rainfall and flowing water 

can mobilize the deposited soil and transport it to receiving waters. Stabilization of exposed soil 

areas is the most important and effective means of reducing erosion and discharge of sediment 

from construction sites. Allowing disturbed areas that have reached final grade or that will not be 

disturbed in the near future to stay disturbed for 14 additional days would significantly increase 

the amount of time available for erosion to occur. While mobilized sediment can be removed, to 

some extent, in downslope sediment controls, these controls will not remove all sediment, 

turbidity and other pollutants because their performance is variable. See example of sediment 

basin provided in Supplemental Explanation in Support of 450.21(a)(1). Therefore, a pollutionprevention approach will reduce the amount of sediment mobilized in the first place and reduce 

the quantity of pollutants discharged from construction sites.

Both vegetative and non-vegetative stabilization measures may be used as both temporary and 

permanent stabilization measures in all areas, depending on the nature of the construction 

activity. In arid, semi-arid or drought-stricken areas, vegetative stabilization may not be feasible. 

In these cases, the use of non-vegetative stabilization, both as temporary or permanent 

measures, may be appropriate.

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

EPA acknowledges that some portions of some projects are intended to be left unvegetated or 

unstabilized following construction. An example would be a dirt access road or a utility pole pad 

where the final plan calls for the area to remain a dirt road or an unstabilized pad. EPA does not 

expect temporary or permanent stabilization measures to be applied to these areas unless 

required by the permitting authority. EPA also notes that re-disturbance of some stabilized areas 

may be necessary during construction projects. For example, equipment may need to drive over 

stabilized areas to access portions of the site. In addition, some portions of a site that may not 

be undergoing clearing, grading, excavating or other earth disturbing activities may need to 
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

2

remain disturbed. An example might be a dirt access road that has reached final grade, but may 

not be paved until later in the project. In these cases, compaction of the soil, covering with 

gravel and/or application of a soil binder may be considered adequate temporary stabilization 

measures.

(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)(1) to make that provision read as 

follows: “Stabilize disturbed soils when earth disturbing work has been stopped on that portion 

of the site and will not resume for a period exceeding 14 calendar days, weather permitting.” 

EPA had proposed “Stabilize disturbed soils immediately when earth disturbing work has 

temporarily or permanently ceased. Stabilization measures must be implemented immediately 

on any portion of the site whenever final grade is reached or when earth disturbing work has 

been stopped on that portion of the site and will not resume for a period exceeding 14 calendar 

days.” Thus, while NAHB suggested changes to EPA’s proposed provision, it did not suggest 

deleting the provision, thereby acknowledging, consistent with its overall comments in support of 

a BMP-only ELG, that stabilizing disturbed soils is 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. 

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

3

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. 

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

The provision, as stated, requires initiation immediately whenever any clearing, grading, 

excavating or other earth disturbing activities have permanently ceased on any portion of the 

site, or temporarily ceased on any portion of the site and will not resume for a period exceeding 

14 calendar days. Stabilization must be completed within a period of time determined by the 

permitting authority. Additional flexibility is provided in arid, semi-arid and drought-stricken 

areas.

(6) What EPA means by terms “initiated”, “immediately”, and “period of time”. 

The term “initiated” in this context of this requirement means that the permittee must 

take some action towards stabilization. The rule provides some flexibility in terms of what 

constitutes initiation of stabilization that may be further defined by the permitting 

authority. EPA intends that optimally, the actions taken to initiate stabilization include 

those that involve changes to the disturbed land area, such as the physical preparation 

of the exposed area for seeding, planting, or the installation of other erosion control 

products. However, EPA acknowledges that other types of actions may be considered 

as having initiated stabilization as well, such as finalizing arrangements to have 

stabilization product fully installed by the deadline for completing stabilization. The 

permitting authority has flexibility to specify in the permit what series of actions it 

considers to constitute the initiation of stabilization. 

The term “immediately” in the context of this requirement means that the permittee must,

as soon as possible and generally not later than the same day, take some action 

towards stabilization as soon as any clearing, grading, excavating or other earth 

disturbing activities have ceased. The use of the term “immediately” is not meant to 

create a liability for a violation because stabilization is not initiated the second, the 

minute or hour after disturbance. The term is used to define a reasonable deadline for 

initiating stabilization measures. In this context, the provision requires construction 

operators to initiate stabilization measures immediately whenever earth-disturbing 

activities on any portion of the site have temporarily ceased and will not resume for a 

period of 14 or more days, or whenever such activities have permanently ceased. 

Therefore, where construction activities have temporarily or permanently ceased in an 

area of the site, initiation of stabilization generally must begin on the same day as the 

work has stopped so that the period of soil exposure is minimized. If an operator 

completes grading of an area at the end of a work day, then “immediately” could 

reasonably be interpreted to mean that the operator must initiate stabilization activities 

on the next work day.
Supplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

4

In most instances, the operator should know when construction is scheduled to cease in 

an area, and therefore the requirement to initiate stabilization work immediately is 

something that should fit within the construction project’s overall schedule of activities on 

the site. EPA acknowledges, however, that there may be some instances in which it is 

not possible to know at first whether work has temporarily ceased for a period of 14 or 

more days, and therefore whether the requirement to stabilize applies. For instance, 

where an operator experiences an unplanned or unanticipated delay in construction due 

to circumstances beyond its control (e.g., sudden work stoppage due to unanticipated 

problems associated with construction labor, funding, or other issues related to the 

ability to work on the site, weather conditions rendering the site unsuitable for the 

continuation of construction work), and it is not known at first how long the work will be 

delayed, the permitting authority may find that it is reasonable to allow for the immediate 

initiation of stabilization as soon as the operator knows with reasonable certainty that 

work will be stopped for 14 or more days.

The phrase “period of time” as used in the provision means the amount or duration of 

time (for example, a number of days) that the permittee has from the initiation of 

stabilization activities until the stabilization activities must be complete. This gives the 

permitting authority the discretion to define what period of time it considers appropriate 

for requiring the construction operator to complete stabilization activities after having 

initiated them. EPA believes the permitting authority is in the best position to define this 

period of time based on such factors as prevalent soil conditions, vegetative types, 

precipitation patterns, etc.

(7) Whether temporary cessation that exceeds 14 calendar days through no fault of the 

operator would trigger a permit violation. 

EPA acknowledges that there may be some instances in which it is not possible to know at first 

whether work has temporarily ceased for a period of 14 or more days, and therefore whether the 

requirement to stabilize applies. For instance, and as mentioned above, where an operator 

experiences an unplanned or unanticipated delay in construction due to circumstances beyond 

its control (e.g., sudden work stoppage due to unanticipated problems associated with 

construction labor, funding, or other issues related to the ability to work on the site, weather 

conditions rendering the site unsuitable for the continuation of construction work), and it is not 

known at first how long the work will be delayed, the permitting authority may reasonably 

determine that it is allowable for the operator to immediately initiate stabilization as soon as the 

operator knows with reasonable certainty that work will be stopped for 14 or more days.