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REGIONAL BOARD RESPONSE(SWRCB/DCC FILE A-1524(A)) -3- PETITION FOR REVIEW OF WASTE DISCHARG$REQUIREMENTS ORDER NO. R5-2002-0181 CITY OF STOCKTON AND SAN JOAQUIN COUNTY PHASE I MUNICIPAL SEPARATE STORM SEWER SYSTEM inclusion of numeric effluent limitations. In DeltaKeepers' Comment Nos. 2(f)(1) and 3(b) (See A.R.,Item 13),DeltaKeeper asserts that: "There is no evidence in the record that supports the claims in Finding Nos. 33 and 34 that it is not feasible to establish numeric effluent limits. There is sufficient data to support development of numeric limits using long-establlished EPA methodologies. There is no evidence in the record that supports the claims in Finding Nos. 33, 34 and 50 that `[i]mplementation of performance standards and BMPs [best management practices] in accordance with the Permittees' SWMP [Storm Water Management Plan] and their schedules constitutes compliance with MEP requirements,and with requirements to achieve water quality objectives.' The BMPs fail to meet minimum BMP standards and will not achieve water quality objectives." Regional Board staff recognizes that the Regional Board has the authority to establish numeric effluent limitations for MS4 permits. However, we have concluded that establishing these effluent limits is technically infeasible at this time. To support our conclusion we cited USEPA's guidance document entitled, "Interim Permitting Approach for Water Quality-Based Effluent Limitations in Storm Water Permits" (EPA 833-D-96-001, September 1996) in Finding No. 35. This document states that, "[a]lthough [NPDES] permits must contain conditions to ensure that water quality standards are met, this does not require the use of numeric water quality-based effluent limitations." USEPA therefore acknowledges that these limits are optional for MS4 permits. On the subject of the feasibility of numeric effluent limits, the USEPA guidance document states that, "EPA has found that numeric limitations for storm water permits can be very difficult to develop at this time because of the existing state of knowledge about the intermittent and variable nature of these types of discharges and their effects on receiving waters." Indeed, it is important to note that, to date,neither USEPA nor the State Board has provided guidance on a methodology for deriving numeric water quality-based effluent limitations for MS4 permits. Because numeric effluent limitations require strict enforcement, the establishment of these limits in the WDRs would compel the Permittees to treat their MS4 discharges. This is the only way they could assure compliance with numeric limits. The process for developing these limits is: (1)to characterize MS4 discharges; (2)to evaluate treatment technologies for effectiveness and compliance with the MEP standard; and (3) to identify the achievable treatment standards that would become numeric effluent limitations. Accomplishing the first task is technically infeasible at this time because, as stated in the USEPA guidance document, "[s]torm water discharges are highly variable both in terms of flow and pollutant concentrations, and the relationships between discharges and water quality can be complex." This statement alludes to the fact that storm water quantity and quality are functions of an area's geology,topography,land use, and individual storm characteristics (i.e., duration,intensity, and number of dry days prior to the storm). The application of ill-conceived numeric effluent limits can have serious consequences. As stated in the USEPA guidance document,"[d]eriving numeric water quality-based effluent limitations for any