Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

6 Treatment Control MeasuresThe stormwater quality treatment control measures profiled in this chapter are themore common ones being implemented throughout the state and the rest of thecountry. Studies have shown these measures to be effective if properly installed andmaintained. Alternative technologies that provide equivalent treatment may beproposed and will be considered by the permitting agencies, but may result inadditional time for agency review and approval unless coordinated well in advancewith the appropriate agency staff.Treatment Control PrinciplesStormwater quality treatment control measures are engineered technologiesdesigned to remove pollutants from site runoff. They can have a higher cost andrequire more space than the runoff reduction measures discussed in Chapter 5. Alldevelopment and redevelopment projects meeting the size thresholds on Table 3-2require treatment control measures, but the required treatment volume or flow canbe reduced (potentially to zero) through the use of runoff reduction measures. Thetreatment control methods suitable for a given project depend on a number of factorsincluding: type of pollutants to remove, amount of stormwater runoff to be treated,site conditions, and state industrial permit requirements, when applicable. Landrequirements, and costs to design, construct and maintain treatment controlmeasures vary by measure and locale.Unlike flood control measures that are designed to handle peak flows from largestorm events, stormwater quality treatment control measures are designed to treatthe more frequent, lower flow storm events, or the “first flush” portions of runofffrom larger storm events (sometimes referred to as “first flush events”). Smallfrequent storm events (0.5 inches of rain and less) on the average represent over80% of the total average annual rainfall for the Sacramento area. The “first flush”flow and volume (referred to as the water quality flow or volume in this manual) istargeted for treatment in order to reduce pollutants to the maximum extentpracticable. There is no incremental water quality benefit to size treatment facilitiesto handle flows or volumes greater than these values.Selecting Treatment Control MeasuresIf stormwater quality treatment control measures are required for your project, theanswers to the following questions will help you determine the appropriate controlmeasure(s) for your unique conditions:Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007 6-1