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

1 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: (3) Minimize the amount of soil exposed during construction activity.

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(1) M inimizing soil exposed controls or minimizes the discharge of stormwater from the

site

.

This requirement addresses two interrelated concepts

– minimizing how much of the site is disturbed (both at one time and the total amount of the site during the entire project) and minimizing the duration that soils are exposed. Soil erosion rates are a function of a number of parameters, including soil particle size distri bution, soil texture, cohesiveness, rainfall energy, slope, slope length, and the type and quantity of cover. Exposed soils are much more prone to erosion than covered or stabilized soils. Generally, projects with more land exposed and/or with soils expose d for longer durations would generate greater quantities of sediment, turbidity and other pollutants than those with lesser quantities exposed and/or exposure for shorter durations. Therefore, minimizing both the quantity and the duration of exposure would be expected to reduce the amount of pollutants contained in stormwater discharges. Even when down

- slope sediment controls are used, such as sediment basins or silt fence s , it is necessary to control up

slope soil erosion. (See Supplemental Explanation in Support of 450.21(a)(1) and example provided there.) This is because sediment controls are not 100% effective in removing pollutants. Therefore, if the total quantity of sediment reaching sediment controls is higher because up

- slope areas are exposed, the n the amount of sediment discharged from the sediment controls will be higher. M inimizing up

- slope disturbances will reduce the amount of sediment and other pollutants discharged from the site. The requirement to minimize the amount of soil exposed during construction activity can be accomplished through a number of practices. These include practices related to how much soil is exposed, such as phasing land disturbing activities, and soil stabilization practices, such as use of mulches, rolled erosion

contr ol products and vegetation. Permittees have flexibility to select appropriate controls to minimize the amount of soil exposed at their individual sites. Permittees also have flexibility to schedule and phase construction activities so as to limit the amoun t of land disturbed at one time and the duration of exposure.

See also the following websites for further support for this principle :

NRC Report http://www.epa.gov/owow/NPS/MMGI/Chapter4/index.html

Runoff Characteristics for Construction Site Erosion Control Practices, J. Irrig. Drain Eng. 136, 405 (2010); doi:10.1061/(ASCE)IR.1943

- 4774.0000202 (9 pages) http:/ /ascelibrary.org/iro/resource/1/jidedh/v136/i6/p405_s1?isAuthorized=no (Eleven erosion control BMPs were evaluated at a slope of 2H:1V, three at 3H:1V, and three at 4H:1V. The variations in slope were used to assess the effects of slope and CECB thickness on runoff. The results from this study provide new insight regarding the runoff characteristics from bare soil and erosion control BMPs that can be used to improve construction

- site storm water design. The

results show that 2.5

- and 5.0

- cm

- thick CECBs on top of netting or an excelsior fiber blanket provided a significant reduction in runoff relative to the bare soil and the other BMPs (e.g., 1.3

- cm CECBs, other blankets) due to water storage within the CECB, the mass of the CECBSupplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

2 providing a strong bond bet ween the soil surface and the bottom of the blanket reducing the potential for flowing water from coming in contact with the soil surface, and the netting/blanket under the CECB providing additional friction that helps keep the CECB from sliding down slope .)

In addition, it is commonly recommended as appropriate to minimize the amount of soil exposed during construction activity. Cities and states across the country recommend this for control of discharges. For example, see the following websites:

http://www.mdt.mt.gov/pubinvolve/stormwater/construction.shtml (Montana) http://www.deq.state.or.us/wq/storm water/docs/indswbmps.pdf (Oregon) http://www.belaireks.org/stormwater.cfm (Bel Aire, Kansas) http://www.centervilleut. net/downloads/publicworks/dc_bmp_manual.pdf (Davis County, Utah)

(2) What EPA does not mean by this requirement

.

Generally, permittees should minimize the amount of land disturbed at one time, the duration of exposure, and should promptly implement appropriate cover as soon as practicable or designated by the permitting authority . Permitting authorities may develop explicit criteria all or some projects, such as placing limitations on the amount of land exposed at one time, the duration of exposure, limiting disturbance in certain areas (e.g., steep slopes, on highly erodible soils), limiting disturbance during certain time periods (e.g., during spring thaw or during seasonally wet periods)

, and may also require specific types and quantities of soil c over or stabilization measures.

( 3 ) In its comments on the proposed C&D ELG/NSPS, NAHB expressed support for non

numeric 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 th at 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 stormwa ter 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 envi

ronmental 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 BMP

only ELG, NAHB suggeste d a revision to proposed 450.21(a)(3) to make that provision read asSupplemental Explanation in Support of BMPs in C&D ELG and NSPS February 15, 2012

3 follows: “Minimize the amount of exposed soil during the construction activity.” EPA had proposed the following: “Minimize the amount of soil exposed for the duration of the constructio n activity as well as at any one time.” Thus, while NAHB suggested edits to this BMP, it did not suggest deleting the requirement, thereby acknowledging, consistent with its overall comments in support of a BMP

- only ELG, that minimizing the amount of expo sed soil during the construction activity 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 will have an opportunity to pr ovide 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 speci ficity, 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 limita tions 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 CG P

, EPA has implemented this provision by r equiring that permittees minimize the amount of soil exposed during construction activities

. In the final permit fact sheet, EPA elaborates that soil exposure can be minimized by maintaining or preserving natural v egetation

on

- site, by phasing construction activities, or by implementing soil stabilization practices on

disturbed areas.

(5 ) A ppropriate time for implementation of this BMP in the construction process

.

This requirement a pplies to the entire duration of active construction. During certain time periods in certain climates, permitting authorities may provide some flexibility, e.g. during seasonally arid periods where little to no precipitation (and hence little erosion risk) exists.