T.F. Green Airport Improvement Program - FEIS Chapters - PVD

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) EvaluationTable 6-13LocationAlternative B4: Potential Stormwater Control MeasuresStormwater Control MeasuresAirport Infi eldCargo and Fueling AreasVegetated swales, vegetated buffers, soi l modificati ons, subsurface and surface infiltration/detenti on systemsSecondary containment, oil/water separatorsMain Avenue Vegetated swales, vegetated buffers, bioretenti onStormwater Drainage SystemOil/water separators, sedimentation chambers, hoods and deep sumps in catch basins, subsurfaceinfiltration/detention,Partially and Fully Relocated Ai rport Road Vegetated swales, vegetated buffers, subsurface infiltration/detention, surface infiltration/detention, bioretenti onOutfall sSource: VHB, Inc.Engineered gravel wetlands, aeration structures, stone check damsA HydroCAD model was developed using Technical Release 20 (TR-20) to determine the resultant increase instormwater runoff for the 100-year storm event between the 2004 existing conditions and the Alternatives B2and B4 (see Appendix K, Water Quality). The HydroCAD preliminary basin sizing analysis was then used todetermine the maximum volume of stormwater retention required to mitigate any increases in stormwaterrunoff. The stormwater management report for the Improvement Program projects would include a moredetailed analysis that would include an evaluation of the smaller storm events and could also redistribute thesubsurface and surface infiltration/detention systems within smaller sub-watersheds. This analysis would alsoinclude design of the outlet control structures to increase the efficiency of these systems resulting in smallersystems than those determined in the FEIS analysis.The Improvement Program was evaluated for the five watersheds that discharge to one of five design pointswhere peak discharge rates were evaluated in the environmental consequences analysis. Table 6-14 shows thenet change in the peak flow rate requiring mitigation for the 100-year storm event and the maximum requiredstormwater storage volume for Alternative B4.Although there would be no significant water quality impacts, the Improvement Program would mitigate forincreases in impervious surfaces through compliance with RIDEM standards. Alternative B4 would be designedto meet the requirements of the SWDM.Chapter 6 – Mitigation 6-34 July 2011\\Mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH06_Mitigation_JUL_2011.doc