San Francisco Stormwater Design Guidelines
based BMPs need not always be eliminated based upon this information. Rather, a modified design solution can make a BMP feasible. Vegetated swales can be used for stormwater treatment in areas with poor infiltration or contaminated soils provided that they are lined with an impermeable liner, underdrained, and constructed with clean import soil. See the BMP Fact Sheets in Appendix A for information on liners and underdrains. Steep slopes can limit the range of appropriate BMPs for a given site because they can cause high flow rates and instability. Terracing the site is one design solution that could allow the implementation of slope-dependent BMPs on a steep site. Check dams can also be used to mitigate problems caused by steep slopes. El Monte Sagrado Spa in Taos, New Mexico uses wetlands to treat stormwater so that it can be used to fill spa pools.
After all of the information has been evaluated, the BMP Decision Tree will indicate one of three outcomes for a given site: All BMPs are feasible; A subset of BMPs is feasible for unconditional
implementation; or A subset of BMPs is feasible with conditions.
The resulting list of BMPs can then be evaluated for their effectiveness in treating the pollutants of concern for the project. Project applicants should include the results of the Decision Tree process in their SCP.
Permeable pavement can be integrated into a variety of hardscapes such as roads and sidewalks, plazas, terraces and patios. 84
The Stormwater Control Plan