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Project elements we will study during NEPA

What is the NEPA process?

The National Environmental Policy Act (NEPA) process evaluates how a proposed project will affect the environment. WSDOT will analyze a range of topics to understand the project’s effects on the natural, cultural and built resources in the area.

We are currently in the scoping stage of the process, when WSDOT will determine what will be studied in the EA. This stage includes opportunities for project partners and the public to provide input. This input will help to inform what should be included in the EA.

Once WSDOT completes the EA, there will be an opportunity to provide feedback on the results. This feedback will help inform the final design of the project and planning for construction.

A flowchart titled “NEPA Process Flow Chart.” It outlines steps from PEL Study to prepare Environmental Impact Statement or Environmental Assessment. There are decision points for significance of impact. Prepare Environmental Assessment is highlighted with, “we are here.”
As part of the NEPA process, WSDOT will analyze a range of topics to understand the project’s effects
on the natural, cultural and built resources in the area.

What WSDOT will study during the Environmental Assessment

During the EA, WSDOT will assess the potential benefits, impacts and mitigation strategies for these primary project elements:

  • Widen I-5 by adding one high-occupancy vehicle lane in each direction from approximately Marvin Road in Thurston County to Mounts Road in Pierce County.
  • Replace existing bridges and construct new bridges across the Nisqually Delta to increase the resiliency of I-5 to flooding and sea level rise and support habitat enhancements.
  • Construct a new grade-separated crossing of the BNSF railroad east of the Nisqually River.
  • Realign McAllister Creek where it crosses I-5 to improve tidal exchange, water quality and fish habitat.
  • Build a shared-use path adjacent to I-5, providing a nonmotorized connection between Lacey and DuPont, and improve access to the Billy Frank Jr. Nisqually National Wildlife Refuge.
  • Remove two existing fish passage barriers under I-5 in the Red Salmon Creek drainage.
  • Install new storm water treatment areas to treat runoff from I-5 within the project.
  • Improve surrounding habitat and allow for the creation of new habitat where existing I-5 embankment would be removed.

The list below includes environmental categories that could experience impacts or benefits from the project. WSDOT identified these categories during the PEL by studying existing conditions. These environmental categories will be studied in detail during the EA.

  • Stormwater and water quality
  • Wetlands and other waters
  • Fish, wildlife and vegetation
  • Floodplains and sea level rise
  • Geology and soils
  • Visual quality
  • Air quality, greenhouse gases and energy
  • Cultural resources
  • Noise
  • Hazardous materials
  • Land use, farmlands and Section 6(f) – Land and Water Conservation Fund outdoor recreation areas
  • Section 4(f) – Parks, recreation areas, refuges, and historic sites
  • Social, economic and Environmental Justice

For more information on each of these topics, see the Final PEL Study Report (PDF 4.8MB).

No Build Alternative

NEPA also requires the evaluation of a No Build Alternative. The No Build Alternative would maintain the highway in its existing configuration. The EA will study what the effects would be if the project is not built, including studying the risk of not updating aging structures. The No Build Alternative serves as the baseline to compare to the Build Alternative.

Narrowing down bridge length options

The PEL Study identified three potential bridge length options for the project area. Since the PEL Study ended, WSDOT narrowed these options through further analysis:

  • The 6,000-foot Bridge Length Option would replace the Nisqually River bridges. This option would remove someof the soil and dirt that supports I-5 through the delta. It would also add approximately 6,000 feet of new bridge structure on the eastern side of the delta.
    • This option would realign McAllister Creek to provide a more natural stream channel.
  • The 12,000-foot Bridge Length Option would replace the Nisqually River bridges. This option would remove all of the soil and dirt supporting I-5 through the delta. It would also add approximately 12,000 feet of new bridge structure to span the entire width of the delta.
    • This option would realign McAllister Creek and would include a new elevated I-5 interchange at Exit 114.
A map showing bridge length options for the proposed project. Two options are illustrated: the 12,000-foot option and the 6,000-foot option. The map highlights BNSF Crossing, Billy Frank Jr. Nisqually National Wildlife Refuge and Joint Base Lewis-McChord.
WSDOT is studying two bridge length options during the NEPA EA.

WSDOT is not carrying forward the 3,000-foot Bridge Length Option into the NEPA analysis. The 3,000-foot Bridge Option would not fully span the Nisqually River’s historical channels. This means it would not restore the natural water flow in the delta as much as the 6,000- and 12,000-foot options. It would also potentially be vulnerable to future channel erosion.

Constructing a new crossing of the BNSF Railway tracks

I-5 currently crosses under the BNSF Railway mainline that connects Tacoma and Portland. This railway serves approximately 40 freight trains per day. The existing BNSF bridges over I-5 are not long enough for the proposed I-5 HOV lanes and the shared-use path. WSDOT is studying two options for the I-5 crossing of the BNSF rail line.

Option 1: I-5 Over BNSF – Proposed concept

A conceptual image illustrates the proposed design for I-5 over the BNSF Railroad. The proposed design includes northbound and southbound I-5 bridges passing over the existing BNSF railway. Labels indicate directions for southbound I-5, northbound I-5, a shared-use path, and Nisqually Road SW. A forested area is in the background, and marshland is visible below.

This option would construct an I-5 bridge in each direction over the BNSF rail line. The highway structure would be about 1,700 feet long. The high point would be nearly 60 feet above the existing surface. That would provide 23.5 feet of clearance above the BNSF tracks. After crossing the tracks, the structure would slope down to the west to connect with the new bridge. The slope would allow for stormwater runoff to flow to treatment areas without affecting sensitive habitat.

Option 2: I-5 Under BNSF

A conceptual image illustrates the design for I-5 under the BNSF Railroad. The proposed design includes northbound and southbound I-5 bridges passing under the existing BNSF railway, which is the existing condition. Labels indicate directions for southbound I-5, northbound I-5, a shared-use path, and Nisqually Road SW. A forested area is in the background, and marshland is visible below.

This option would reconstruct the existing railroad bridges as a single bridge that would span the length of I-5. There would be permanent impacts to wetlands and floodplain areas to make room for new stormwater sites. This configuration would need to build temporary railroad trestles and retaining walls. It would also need to move some railroad tracks to maintain rail operations during construction.  The railroad detour during construction would require clearing trees and temporarily working in wetlands near the existing track.

Realigning McAllister Creek

A map shows the current McAllister Creek alignment. The creek runs south from the wildlife refuge and under I-5. The alignment has a sharp bend to the east.
The current alignment of McAllister Creek has a sharp bend. The creek is steep and narrow in certain areas. The project proposes realigning McAllister Creek to a more natural alignment.

The project proposes realigning McAllister Creek where it crosses below I-5 to improve water quality and habitat.

The realignment would remove the sharp bend where I-5 currently crosses the creek. This would reconfigure the steep and narrow channel. This will allow the creek to move more naturally and support the growth of native wetland and plants. WSDOT is working with the Nisqually Indian Tribe to develop proposed enhancements.

A conceptual cross-section diagram of McAllister Creek shows I-5 above the stream channel. The channel and floodplain width is approximately 300 feet. The stream channel is labeled as looking downstream.
The project proposes a new alignment for McAllister Creek. The bridge would allow for
about 300 feet of width for the creek channel and floodplain.

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