San Francisco Stormwater Design Guidelines
diminishing returns: extraordinary effort yields little increased benefit treatment to the MEP
increase in effort yields increased water quality benefit effort
Figure 2. As the maximum extent practicable (MEP) standard is approached, additional investment in BMPs yields reduced benefit.
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Inspection, the Port of San Francisco Planning Division, or the Port Building Department by January 1, 2009. All new project applications, incomplete project applications, and amendments received thereafter will be subject to these Guidelines. Table 1 lists the types of projects that are excluded from the Guidelines. The RWQCB monitors San Francisco’s implementation of General Permit requirements. The Port and the SFPUC must submit ongoing reports on their respective development review efforts, the number and type of projects reviewed, and the stormwater control measures included in the projects. To assess the effectiveness of stormwater control measures, the Port and SFPUC must define criteria for compliance. The RWQCB and the EPA require that stormwater control measures be designed to reduce pollution in stormwater runoff to the Maximum Extent Practicable (MEP).
water quality benefit
Regulatory Context
The Maximum Extent Practicable Treatment Standard
MS4 permits require stormwater management strategies to “reduce the discharge of pollutants to the maximum extent practicable, including management practices, control techniques and system, design and engineering methods.” Treatment to the maximum extent practicable (MEP) can be achieved by applying the BMPs that are most effective at treating pollutants in stormwater runoff. The SWRCB has said of the MEP standard that there “must be a serious attempt to comply, and practical solutions may not be lightly rejected.” The SWRCB also states that if project applicants implement only a few of the least expensive stormwater BMPs, it is likely that the MEP standard has not been met. If, on the other hand, a project applicant implements all applicable and effective BMPs except those shown to be technically infeasible, or those whose cost would exceed any benefit to be derived, then the project applicant would have achieved treatment to the MEP. As technology and design innovation improve, stormwater BMPs become more effective. The definition of MEP continually evolves with the field to encourage innovation and improved water quality protection. Because of this, some end-of-pipe strategies such as vortex separators, which were considered to meet the MEP standard ten years ago, are no longer accepted as such. Similarly, in cases where just one BMP may have gained project approval in the past, today there are many cases where multiple BMPs will be required in order to achieve treatment to the MEP.