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

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) EvaluationWhile Alternative B4 would increase impervious surfaces and the amount of glycol used for deicing departingaircraft, the proper design of a new stormwater management system and construction of the new DeicerManagement system would ensure that Alternative B4 would meet state stormwater standards.6.10.1 Mitigation for Water Quality Impacts for Alternative B4Alternative B4 includes mitigation for increases in impervious surfaces. Proposed mitigation measures focus oncompliance with federal regulatory standards and including RIDEM standards and the SWDM, adopted inDecember 2010, which are described in Section 5.11.1, Regulatory Context, of Chapter 5, EnvironmentalConsequences.6.10.1.1 Design Alternative B4 in Compliance with all Applicable State and Federal Regulatory StandardsAlternative B4 would incorporate three types of control measures to minimize changes to hydrology and waterquality:• Designed stormwater controls,• Operations and maintenance procedures, and• Construction-period control measures (presented in Section 6.19, Construction Period Mitigation).In addition, as a component of state environmental permitting and the T.F. Green Airport ImprovementProgram, RIAC would enhance the stormwater management system in accordance with state requirements andprepare a supporting stormwater management report that complies with the SWDM. The stormwatermanagement report developed for the Improvement Program would contain an analysis of existing andproposed stormwater conditions, a description of erosion and sedimentation controls to be used duringconstruction, plans for long-term operation and maintenance of the stormwater system, and documentation todemonstrate compliance with the current SWDM.Designed Stormwater ControlsA conceptual stormwater design (see Appendix K, Water Quality) was developed for the Alternative B4 todetermine the maximum size and suitable locations (Figure 5-43) for the larger stormwaterdetention/infiltration systems. The design could be developed to comply with the higher rainfall intensities andpeak runoff requirements from the SWDM. While these stormwater detention and infiltration systems could bedesigned to mitigate peak rates of runoff, additional smaller systems would also be required to supplementthese systems to provide additional groundwater recharge and water quality mitigation. Low-impactdevelopment (LID) best management practices (BMPs), such as bioretention basins, vegetated swales, andengineered gravel wetlands, and structural BMPs, such as sedimentation chambers, oil/water separators, stonecheck dams etc., would be installed to provide additional peak flow attenuation and address TSS removalrequirements. The LID BMPs would serve as pretreatment to the larger detention/infiltration systems wherepossible to provide additional opportunities for infiltration and satisfy the groundwater recharge requirementsfrom the SWDM to provide treatment of stormwater as close to the source as possible. Table 6-13 lists potentialstormwater control measures that could be included in the final design. These measures will be designed tomeet RIDEM stormwater requirements and RIPDES requirements.Chapter 6 – Mitigation 6-33 July 2011\\Mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH06_Mitigation_JUL_2011.doc