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State Water Resources Control Board Releases Storm Water Panel Recommendations Regarding Feasibility of Numeric Effluent Limits

By: Mary Lynn K. Coffee

On June 19, 2006, the State Water Resources Control Board (SWRCB) released the recommendations of a panel of storm water experts convened to examine the feasibility of incorporating numeric limits into permits issued under the National Pollutant Discharge Elimination System (NPDES) program pursuant to the Clean Water Act.  The report entitled "Storm Water Panel Recommendations to the California State Water Resources Control Board: The Feasibility of Numeric Effluent Limits Applicable to Dischargers of Storm Water Associated with Municipal, Industrial and Construction Activities" sets forth a number of recommendations regarding numeric limits, and notably comes to different conclusions with regard to the different types of storm water discharges regulated by the SWRCB and the Regional Water Quality Control Boards. 


The recommendations of this panel are important because they are likely to be incorporated, to some extent, into the various NPDES permits issued by the SWRCB and the Regional Boards for storm water discharges, including municipal separate storm sewer system permits (MS4 permits), construction permits, including the SWRCB's General Construction Permit which applies to construction sites of one acre or more, and industrial storm water permits.  Thus, the panel's recommendations regarding the incorporation of numeric limits into NPDES permits are likely to impact a wide variety of dischargers.  Therefore, we encourage you to understand and, if appropriate, to submit comments on the way in which the SWRCB and Regional Boards should use the recommendations of the panel.  Comments are due to the SWRCB by July 28, 2006.


The storm water panel was convened by the SWRCB to:


·       "examine the feasibility of developing numeric limits for storm water pollution";[1]  and

·       Determine how to implement numeric limits or objective standards in NPDES permits, and the information, data, and technologies required to do so.


The panel was composed of a number of experts in the field of storm water pollution and control from the academic and scientific communities. 


With regard to municipal storm drain permits, important recommendations from the panel are:


·       Numeric effluent criteria are not feasible for municipal BMPs and in particular for urban discharges; however, with more rigorous design and an enforceable maintenance program it can be presumed that the facilities will continue to deliver close to the design level of treatment.

·       Although enforceable numeric limits are not feasible in municipal storm drain permits, the panel recommended the use of "upset" values or "action levels," which are levels that should trigger BMP operation review and assessment.[2]  The Report recommends that these values or levels should be set at a level above the treatment standard for the facilities, adjusted to account for normal observed treatment variability, but still at a level that "most all could agree [indicates] that some action should be taken."[3]  The Report then recommends that exceedences of these "upset values" should trigger "an appropriate management response."[4] 


With regard to construction activities, important recommendations from the panel are:


·       Active treatment technologies make numeric limits technically feasible at large construction sites (generally five acres or greater) for pollutants commonly associated with storm water discharges from construction sites; however, if the use of chemicals for water quality, and particularly sediment control is not permitted, then the Report concludes that numeric limits for even large construction sites is likely infeasible.  Further, technical practicalities and cost-effectiveness make the technologies less feasible at smaller construction sites. 

·       Even though numeric limits are technically feasible for construction activities, action levels are likely to be more commonly feasible and are more appropriate.

·       Although the panel concludes that numeric limits or action levels are technically feasible at construction sites, the panel expressed a number of reservations and concerns that the SWRCB should investigate and address to determine if it is prudent, practical and necessary to more effectively achieve nonpoint pollution control before mandating compliance with numeric limits at construction sites.  To determine if numeric limits are prudent, practical and best suited to more effectively control nonpoint source pollution at construction sites, the Report recommends evaluating, considering and establishing policies with respect to:

Ø       the costs of requiring compliance with numeric limits, which are anticipated to be high, versus the water quality benefits;

Ø       the minimum size of the construction site to which the limits will be applicable;

Ø       the pros, cons, limitations and appropriate applications of available active treatment technologies and advanced treatment systems;

Ø       the pros and cons of use of chemicals to control water quality in runoff discharges;

Ø       the benefits of active treatment technologies in light of the quality of receiving waters;

Ø       the use of numeric limits on a seasonal basis in light of seasonality of flows in semi-arid regions of the State;

Ø        the application of numeric limits to only a portion of any construction site (e.g. active grading areas, un-vegetated and/or un-stabilized soils);

Ø       development of numeric limits and action levels based only on average discharge concentrations determined based upon an appropriate minimum number of individual samples;

Ø        adoption of numeric limits that are different for different sites, taking into account the climate region, soil conditions, and natural background conditions for the site (e.g., vegetative cover) and for receiving waters (e.g., active treatment system should not be mandated when they could result in turbidity and TSS levels well below natural levels, which could adversely affect receiving waters); and

Ø        exemption from numeric limits for unusually large storms, or for storms that occur in an unusual rainfall pattern.


With regard to industrial activities, important recommendations from the panel are:


·       Numeric limits are feasible for some industrial categories and action levels are more appropriate for other industrial categories. 

·       The applicability of numeric limits and action levels would depend on a number of factors, including industry type, whether or not the facility is new or existing, whether the discharge from the facility is more similar to discharges and activities covered by public storm drain permits than industrial point source permits, and other factors such as available data for typical discharges. 


The SWRCB has hearings scheduled for July 21 in Sacramento and July 28 in Los Angeles, where oral comments on the recommendations will be accepted.  In addition, written comments will be accepted until July 28, 2006.

To view the full text of the storm water panel's recommendations to the SWRCB, click here.

Mary Lynn K. Coffee is a Partner in Nossaman's Irvine office.  She has extensive experience in compliance with, and permitting and approvals for development projects under local, state and federal resource protection laws, including the federal Clean Water Act (Sections 401, 402 and 404), the California Porter-Cologne Water Quality Act and the state streambed alteration provisions of the California Fish and Game Code.  In this role, she has particular expertise in the development of construction and post-construction surface water quality compliance programs for existing and new real estate developments.  She can be reached at (949) 833-7800 or


[1] The Feasibility of Numeric Effluent Limits Applicable to Discharges of Storm Water Associated with Municipal, Industrial and Construction Activities, Storm Water Panel Recommendations to the California State Water Resources Control Board (June 19, 2006), p. 2-3. 

[2] Id. at 8.

[3] Ibid.

[4] Ibid.  

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