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`e v City of Stockton and County of San Joaquin Page 50 NPDES Permit CAS0083470 Response to Comments measurable number specifying the minimum acceptable outcome for a facility or practice."NR-151, pages 6 & 7. (Note: we disagree that the balancing of cost effectiveness and other competing issues with BAT meets the statutory definition of MEP. We quote it solely to show the connection between MEP and performance standards.) For example, Wisconsin establishes an MEP performance standard for new development as an 80% reduction in Total Suspended Solids (TSS). The standard for in-fill development under 5 acres is 40%reduction in TSS within ten years and an 80%reduction for development that occurs ten years after the effective date of the rule. NR-151,page 39. Construction sites must implement BMPs to reduce sediment loads by 80%. Id,page 37. Residential, commercial and industrial sites are required to implement BMPs to infiltrate specific volumes of runoff. Runoff control measures from roads,parking lots, commercial sites and industrial sites must include set-backs and pretreatment systems (including oil/grease separation,biofiltration, filtrations, swales or filter strips) before runoff is discharged to infiltration areas. Id.,pages 41 &42. There are even municipal-wide percentage reduction requirements. A municipal storm water program must achieve a 20% reduction in TSS by 2008 and a 40%reduction by 2013. Id.,pages 47 &48. The percentage reductions contained in the Wisconsin performance standards "are designed to meet state water quality standards." NR-151,page 9. If the Department of Natural Resources finds that water quality standards will not be attained using the performance standards, the Department"shall" promulgate site specific performance standards. Id. The Wisconsin approach mandates performance standards for all runoff including runoff from existing areas. This stands in stark contrast to the proposed Permit,which only includes performance standards for new development. Response: The Permittees' revised SWMP will contain BMPs that each Permittee will implement to reduce the discharge of pollutants from their respective MS4s to the MEP. The Permittees are required to establish performance standards for each proposed BMP. Pursuant to 40 CFR 122.26(d)(2)(iv)(A), the Permittees will provide estimates of the expected reduction of pollutant loads for structural and source control BMPs. These estimates may or may not be presented as a percentage of pollutant reduction, depending on the type of BMP employed. Where appropriate, these estimates will be used as performance standards. If these estimates do not provide appropriate performance standards, the Permittees will propose alternative performance standards in their SWMP. For non-structural BMPs (e.g.,business outreach and construction site inspection), the Permittees will propose performance standards that represent the designated level of effort required to comply with this Order and the federal MEP standard. The State Board, in its Water Quality Order 99-05, endorsed compliance with applicable water quality standards as a program-wide performance standard for SWMPs. This program-wide performance standard is preferable to one based on percent pollutant reduction in urban discharges because water quality standards are much easier to monitor. Determining a percent pollutant reduction in urban discharges is a complicated task that is monitoring intensive and fraught with uncertainty. This uncertainty, which must be addressed through statistical analysis, creates a margin of error that makes strict enforcement difficult, if not impossible.