TABLE 1/Per-unit control values Figures based on managing 80% to 90% of annual runoff volume in well-drained soils or poorly drained soils with underdrains .
TABLE 2/Installation unit costs Based on data from 29 suburban, urban, and green space retrofits in Indianapolis and Columbus, Ohio; the Center for Watershed Protection's Urban Stormwater Retrofit Practices Manual v1.0; Water Environment Research Foundation's BMP and LID Whole Life Cost Models v2.0 report; the Center for Neighborhood Technology's Green Values Calculator; and RS Means Site Work & Landscape Cost Data 2009, 28th Ed. Visit www.pwmag.com for direct links to these tools.
TABLE 3/Costs per square foot of impervious surface managed Dividing the installation cost (Table 2) by the area managed (Table 1) yields the budget manager's Holy Grail: C/I.
Figure 1. BMP annual runoff removal effeciencies for varying soil infiltration rates