FEIS Summary - Knik Arm Bridge and Toll Authority

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Knik Arm Crossing Final EIS Summary Exhibit S-23 Environmental Impacts Associated with Construction and Operation of the Recommended Alternative (continued) Impact category Impacts on the Natural Environment Impacts on Surface Water Resources Direct impacts Construction impacts Indirect impacts Cumulative impacts Impacts on Wetlands Direct impacts Northern Access Alternative (Mat-Su Side) None Water Bodies and Water Quality Two unnamed lakes north of Lake Lorraine may be adversely affected due to stormwater runoff. Increased sediment runoff. Temporary increases in suspended solids, turbidity, and pollutants from construction equipment. Water Bodies and Water Quality Increased development near water bodies will result in encroachment on riparian areas, additional runoff, increased nutrient loading, fecal coliform contamination, increases in hydrocarbons, and increases in the extent of the area’s impervious surfaces. Fill in wetlands would result in loss of the following wetland types: Forested: 9.7 acres Sedge and grass: 15.5 acres Scrub/shrub: 3.3 acres Total: 28.5 acres Recommended Alternative Southern Alignment Crossing with 8,200-Foot Bridge and Connecting Roadways on Gravel Fill (The Crossing) Fill in estuarine shores and mud flats: 82 acres Fill in subtidal waters: 8 acres Placement of 33 piers Hydrology Impacts mostly related to erosion and accretion of sediment (total area of sediment accumulation will be approximately 60 acres on the west and 200 acres on the east side of Knik Arm): • minimal tidal-phase lags • impedance of flow (delay in high tide of less than 1 minute) • lag in ebb tide (delay in low tide of less than 6 minutes) • mid-channel current speeds will increase approximately 0.5 foot per second • central portion of channel’s average depth could increase 1–2 feet • constriction scour could increase to 5–6 feet next to abutments Water Quality There will be few direct impacts to water quality from the 8,200-foot bridge. Due to fast currents and assimilative capacity of Knik Arm, the impacts of stormwater runoff will be negligible. Water Bodies and Water Quality Increased sediment runoff Temporary increases in suspended solids, turbidity, and pollutants from construction equipment. Water Quality Increased development and access could adversely affect water quality by wastewater outfalls, additional nonpoint stormwater outfalls, and marine vessel or watercraft fuel spills. Fill in estuarine shores and mud flats: 82 acres Fill in subtidal waters: 8 acres Placement of 33 piers Erickson Alternative (Anchorage Side) Water Bodies and Water Quality Installation of culverts and the placement of fill will directly affect numerous drainages along the bluff north of the POA and Cherry Hill Ditch. Ship Creek will be crossed during Phase 2; neither phase, however, will adversely affect the creek. Water Bodies and Water Quality Increase in traffic will cause an increase in pollutant contributions. Increases of nonpoint sources of pollution from reasonably foreseeable future actions in the vicinity of the POA. Fill in wetlands would result in loss of the following wetland types: Forested: 1.3 acres Sedge and grass: 2.2 acres Scrub/shrub: 7.6 acres Total: 11.1 acres (continued on next page) Exhibit S-23 Environmental Impacts Associated with Construction and Operation S-44
Knik Arm Crossing Final EIS Summary Exhibit S-23 Environmental Impacts Associated with Construction and Operation of the Recommended Alternative (continued) Impact category Construction impacts Indirect impacts Cumulative impacts Impacts on Floodplains Direct impacts Construction impacts Indirect impacts Cumulative impacts Impacts on Wild and Scenic Rivers Direct impacts Construction impacts Indirect impacts Cumulative impacts Impacts on Coastal Barriers Direct impacts Construction impacts Indirect impacts Cumulative impacts Northern Access Alternative (Mat-Su Side) Four acres of forested, scrub/shrub, and sedge or grass wetlands will be affected. Soil will be disturbed, deposition of sediments and other pollutants will increase, and vegetation will be permanently altered by such disturbance. Wildlife use of the areas of vegetation disturbance will be temporarily adversely affected. Recommended Alternative Southern Alignment Crossing with 8,200-Foot Bridge and Connecting Roadways on Gravel Fill (The Crossing) Additional wetland area eliminated by 2030 due to development in the Mat-Su, relative to loss under the No-Action Alternative: Forested: 70 acres Sedge and grass: 260 acres Scrub/shrub: 120 acres Total: 450 acres None Erickson Alternative (Anchorage Side) Two acres of forested, scrub/shrub, and sedge or grass wetlands will be affected. Soil will be disturbed, deposition of sediments and other pollutants will increase, and vegetation will be permanently altered by such disturbance. Wildlife use of the areas of vegetation disturbance will be temporarily displaced. The total cumulative reduction of 819.6 acres includes 808.5 acres (0.9% reduction) in total Mat-Su Project Area wetlands which would not alter Mat-Su regional wetland functions and values. None Stream crossings by roads caused by indirect growth will have the potential to adversely affect floodplains unless unrestricted flow will be maintained. Development pressure in the Mat-Su Borough would be more aggressive, increasing the cumulative impact potential of residential and commercial development on marginal floodplain areas. There are no designated Wild and Scenic Rivers located within the Project Area. A 0.3 inch decrease in the extreme high-tide level north of the bridge could occur during extreme high-tide events. None As identified under the Coastal Barriers Resource Act, there are no coastal barriers in the Project Area. N/A None Development pressure in the Anchorage Bowl would be less aggressive, alleviating the cumulative impact potential of residential and commercial development on marginal floodplain areas. (continued on next page) Exhibit S-23 Environmental Impacts Associated with Construction and Operation S-45
Page 1 and 2: Knik Arm Crossing Final Environment
Page 3 and 4: Exhibit S‐1. Final EIS Document O
Page 5 and 6: Knik Arm Crossing Final EIS Summary
Page 15 and 16: Exhibit S‐22. Reasons for Preferr
Page 17 and 18: Findings, Compliance, and Permits E
Page 25 and 26: ! ! ! ! ! ! ! ! ! ! ! ! Knik Arm Cr
Page 33 and 34: The preliminary design includes pla
Page 35 and 36: Summary Initial Construction (Phase
Page 43: Knik Arm Crossing Final EIS Summary

FEIS Summary - Knik Arm Bridge and Toll Authority

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