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

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) Evaluationwould be completely avoided. The greatest single impact area (2.8 acres) would occur in Wetland A13 directlysouth of the runway end to construct the enhanced RSA. This represents a 0.2 acres reduction in impactreported in the DEIS and nearly two thirds of this impact (1.8 acres) would be to emergent wetland dominatedby the invasive common reed (Phragmites australis). The remaining 1.0 acres consists of shrub wetlandperiodically maintained by cutting to remove obstructions from Part 77 airspace.Impacts to Wetland A8 have been reduced to 0.1 acres along the fringe of the existing Runway 34 fill sectionfrom the 1.8 acres reported in the DEIS. The revised design largely avoids impact to this scrub-shrub andforested wetland which provides flood storage and water quality functions at the principal level in the formerimpact area. Impacts to Wetland A6 have been reduced from 1.8 acres to 1.5 acres. This wetland was largelycreated as the result of past sand and gravel removal and has low plant community diversity and provides fewfunctions aside from groundwater discharge. Finally, impacts to Wetland A11 have been reduced from 0.7 acresreported in the DEIS to 0.6 acres. Wetland A11 has a linear form as much of this wetland’s southern part wascreated by excavation through uplands to divert flows around Taxiway C and the Runway 34 End into WetlandA13. Prior to the extension of Runway 16-34 in 1967 much of this flow entered Wetland A8.Approximately 5.0 acres of federal-regulated vegetated wetland, an additional 6.5 acres of state-regulatedperimeter and riverbank wetland, and 0.2 acres of state-regulated floodplain outside of the limits of otherfreshwater wetlands would be altered by the Runway 34 safety enhancements (Tables 5-106 and 5-107).Significant Impacts: Under Alternative B4, approximately 5.0 acres of federal jurisdictional vegetated wetlandand 843 linear feet of intermittent stream would be altered by fill placement, affecting wetlands that providethree principal functions. Principal wetlands functions that would be impacted include nutrientremoval/retention/transformation, floodflow alteration, and sediment/toxicant/pathogen retention. Thisimpact would meet the FAA standard of significance as the filled wetland areas would be substantiallymodified and would not sustain the existing wetland functions and values. These losses would be mitigatedthrough a compensatory wetland mitigation program involving wetland restoration, creation, and preservationas described in Chapter 6, Mitigation.Indirect ImpactsIndirect impacts associated with Alternative B4 could include increased flood heights in Buckeye Brookassociated with the loss of flood storage in Wetland A13 associated with the fill placement for the enhancedRSA. This indirect impact would be mitigated by the construction of wetland Mitigation Site 1, described inChapter 6, Mitigation. The mitigation area would be constructed prior to fill placement for the RSA to minimizethe opportunity for short-term impacts.Fill placement in Wetland A13 could reduce the water quality function provided by the wetland by shorteningthe residence time of water passing through the wetland. Mitigation Site 1 would be designed to replace thiswetland function.Chapter 5 - Environmental Consequences 5-200 July 2011\\mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH05_Environmental_Cons_JUL_2011.doc