SDOT will be drilling under the Duwamish to move communications cables
The Seattle Department of Transportation is preparing to drill a hole horizontally under the Duwamish River to enable the installation of a telecommunications conduit. The project is being done said SDOT because the existing systems need an upgrade to prepare for the future and to "remove long term interdependencies between the Spokane Street Swing Bridge and the future bridge repair work."
The project is set to start in June 2021 and be completed by September.
CITY OF SEATTLE NOTICE OF SEPA DETERMINATION
The City of Seattle Department of Transportation (SDOT) has issued a Determination of Non-Significance (DNS) in accordance with the State Environmental Policy Act (SEPA) for the Spokane St Swing Bridge Horizontal Directional Drill (HDD) Project. Currently, moveable bridge telecommunications systems cross the Duwamish Waterway via the West Seattle Bridge. While SDOT intends to repair the West Seattle Bridge, an alternate route is needed for new planned communications systems due to the quality of the existing systems and the need to remove long term interdependencies between the Spokane St Swing Bridge functions and the future bridge repair work. This project would construct a new telecommunications conduit beneath the bed of Duwamish Waterway using HDD technology on the north side of the Spokane St Swing Bridge. The project would install new telecommunications systems (fiber and copper) within the new conduit for use in operating the bridge and for public/private fiber optic network connections between Harbor Island and West Seattle. These new communications would connect to the bridge and existing telecommunications networks via aerial and underground trenching improvements in uplands.
Comment Deadline: 5 PM, January 25, 2021.
Appeal Deadline: 5 PM, February 1, 2021. The DNS, SEPA Checklist, and supporting information may be examined at https://www.seattle.gov/transportation/projects-and-programs/programs/bridges-stairs-and-other-structures/bridges/west-seattle-high-rise-bridge-safety-program/low-bridge-projects. Agency Contact: Joel Darnell, SDOT, P.O. Box 34996, Seattle, WA 98124; 206-684-5065; Joel.Darnell@seattle.gov.
Spokane St Swing Bridge Horizontal Directional Drill Project
November 24, 2020 Spokane St Swing Bridge Horizontal Directional Drill Project SEPA Checklist Page 2 of 20
STATE ENVIRONMENTAL POLICY ACT (SEPA) ENVIRONMENTAL CHECKLIST
- A. BACKGROUND
1. Name of proposed project, if applicable:
Spokane St Swing Bridge Horizontal Directional Drill (HDD) Project
2. Name of applicant:
Seattle Department of Transportation (SDOT)
3. Address and phone number of applicant and contact person:
Joel Darnell, Project Manager Seattle Department of Transportation Capital Projects Division 700 Fifth Avenue, Suite 3900 P.O. Box 34996 Seattle, WA 98124 206-684-5065
4. Date checklist prepared:
November 24, 2020
5. Agency requesting checklist:
City of Seattle Department of Transportation (SDOT)
6. Proposed timing or schedule (including phasing, if applicable):
Construction is anticipated to begin in June 2021 with completion in September 2021 pending approvals and permits.
7. Do you have any plans for future additions, expansion, or further activity related to or connected with this proposal? If yes, explain.
There are concurrent project activities to repair/stabilize the Spokane St Swing Bridge and replace the control systems.
8. List any environmental information you know about that has been prepared, or will be prepared, directly related to this proposal.
A HDD feasibility study was completed for the project in November 2020.
9. Do you know whether applications are pending for governmental approvals of other proposals directly affecting the property covered by your proposal? If yes, explain.
There are concurrent nonproject activities to repair/stabilize the bridge and replace the control systems that require separate government approvals. There is also a concurrent nonproject activity to repair the adjacent West Seattle Bridge and construct a quiet zone at Terminal 5.
10. List any government approvals or permits that will be needed for your proposal, if known.
The following applications are pending for government approvals:
- ▪ Seattle Department of Construction and Inspections (SDCI) Shoreline Permit
- ▪ Washington Department of Fish and Wildlife (WDFW) Hydraulic Project Approval
- ▪ United State Army Corps of Engineers (USACE) Section 10 and 408 Permits
SDOT will be coordinating with the Elliott Bay Natural Resource Damage Assessment (NRDA) Trustees for work in the vicinity of Bluefield’s Wetland Mitigation Site 1.
11. Give brief, complete description of your proposal, including the proposed uses and the size of the project and site. There are several questions later in this checklist that ask you to describe certain aspects of your proposal. You do not need to repeat those answers on this page.
Currently, moveable bridge telecommunications systems cross the Duwamish Waterway via the West Seattle Bridge. While SDOT intends to repair the West Seattle Bridge, an alternate route is needed for new planned communications systems due to the quality of the existing systems and the need to remove long term interdependencies between the Spokane St Swing Bridge functions and the future bridge repair work. This project would construct a new telecommunications conduit (up to three in approximately 4-inch high-density polyethylene [HDPE]) beneath the bed of Duwamish Waterway using HDD technology on the north side of the Spokane St Swing Bridge. This project would start on Harbor Island within the existing pedestrian path located on the north side of the bridge access and approximately 550 feet east of the eastern shoreline. The HDD borehole would be drilled downward to get below surface utilities, foundations, streets and rail lines to cross the waterway and would curve back up to the ground surface on the north side of the bridge to a point approximately 450 feet west of the shoreline within right-of-way. The project would install new telecommunications systems (fiber and copper) within the new conduit for use in operating the bridge and for public/private fiber optic network connections between Harbor Island and West Seattle. These new communications would connect to the bridge and existing telecommunications networks via aerial and underground trenching improvements in uplands.
12. Location of the proposal. Give sufficient information for a person to understand the precise location of your proposed project, including a street address, if any, and section, township, and range, if known. If a proposal would occur over a range of area, provide the range or boundaries of the site(s). Provide a legal description, site plan, vicinity map, and topographic map, if reasonably available. While you should submit any plans required by the agency, you are not required to duplicate maps or detailed plans submitted with any permit applications related to this checklist.
The project is located below the Spokane St Swing Bridge in the Industrial District area (see Plans). Township 23N, Range 3E, Section 13 and Township 24N, Range 4E, Section 18.
- B. ENVIRONMENTAL ELEMENTS
- a. General description of the site: [Check the applicable boxes]
Flat Rolling Hilly Steep Slopes Mountainous
- b. What is the steepest slope on the site (approximate percent slope)?
Slopes along the project area are less than 5 percent and slope toward the Duwamish Waterway. There are adjacent steep slopes to the west and along the waterway.
- c. What general types of soils are found on the site (for example, clay, sand, gravel, peat, muck)? If you know the classification of agricultural soils, specify them and note any agricultural land of long-term commercial significance and whether the proposal results in removing any of these soils.
Soils on site are composed of dredged material used as fill, including gravelly loamy sand. The project would construct the HDD borehole below the sediment in the Duwamish Waterway. Subsurface conditions below the waterway include fill deposits, recent organic deposits, younger alluvium, older alluvium, and glacial deposits. Agricultural lands are not located near the project. There would be minor ground disturbance for staging, drilling, and removal of soil from borehole during construction.
- d. Are there surface indications or history of unstable soils in the immediate vicinity? If so, describe.
The project is located in a potential liquefaction area underneath historic fill. There are no known surface indications of instability.
- e. Describe the purpose, type, total area, and approximate quantities and total affected area of any filling, excavation, and grading proposed. Indicate the source of fill.
The project would require temporary workspace at the entry HDD location within right-of-way. The configuration of the temporary workspace would be about 40-feet of width, centered on the HDD entry location, with a length of approximately 100 feet. The proposed entry and exit locations within right-of-way are approximately 450 to 550 feet back from the shoreline of the waterway. Both the entry and exit locations would require a small mud pit (approximately, 4 feet deep by 4 feet square). Telecommunication trenches would be excavated and backfilled. Excavation quantities would not exceed 175 cubic yards. The purpose of the mud pit is to contain the drilling mud at either end of the crossing for ease of reuse and disposal. Pits and trenches would be restored to existing grade using fill material.
- f. Could erosion occur as a result of clearing, construction, or use? If so, generally describe.
Disturbed portions of the temporary workspace areas could be susceptible to erosion. However, as previously described the entry and exit locations would be buffered from the shoreline. Clearing would be minimal to establish the HDD entry and exit pits and trenches.
- g. About what percent of the site will be covered with impervious surfaces after project construction (for example, asphalt or buildings)?
The project would add two new handholes/vaults at each end of the HDD. Net increase in percent impervious surfaces would be negligible. Disturbed paved and natural areas in workspace areas would be restored after construction.
- h. Proposed measures to reduce or control erosion, or other impacts to the earth, if any:
The contractor will be required to follow the 2020 edition of Seattle Standard Plans and Standard Specifications for Road, Bridge and Municipal Construction and the Seattle Stormwater Code to control erosion in the project area.
The following general conservation measures and best management practices (BMP) are applicable at the construction site:
- ▪ The contractor will provide a construction stormwater and erosion control plan (CSECP) for City review and approval before beginning construction activities;
- ▪ The contractor will provide a construction BMP plan and a Spill Prevention Plan for city review and approval before beginning construction;
- ▪ All utility work will be performed in accordance with City requirements and the requirements of the utilities involved;
- ▪ Catch basin filters will be used in catch basins located downgradient of the site if necessary to prevent sediments from entering the storm drainage system during construction; and
- ▪ All permitting conditions required by local, state, and federal agencies will be followed during construction.
- a. What types of emissions to the air would result from the proposal during construction, operation, and maintenance when the project is completed? If any, generally describe and give approximate quantities if known.
Sources of emissions during construction would include:
- ▪ Negligible fugitive dust generated during limited excavation, drilling and other construction activities;
- ▪ Engine exhaust emissions from construction vehicles, work vehicles, and construction equipment; and
- ▪ Increased motor vehicle emissions associated with increased traffic congestion during construction.
The project would not result in new air emissions after construction is completed.
- b. Are there any off-site sources of emissions or odor that may affect your proposal? If so, generally describe.
There are no off-site sources of emissions or odor that would affect the project.
- c. Proposed measures to reduce or control emissions or other impacts to air, if any:
During construction, impacts to air quality would be reduced and controlled through implementing standard federal, state, and local emission control criteria according to the 2020 edition of Seattle Standard Plans and Standard Specifications for Road, Bridge and Municipal Construction. The standard specifications require that contractors maintain air quality to comply with the national emission standards for hazardous air pollutants.
Minimizing air quality impacts during construction may include such measures as spraying areas of exposed soil with water for dust control and minimizing vehicle and equipment idling to limit exhaust emissions.
- a. Surface:
1) Is there any surface water body on or in the immediate vicinity of the site (including year-round and seasonal streams, saltwater, lakes, ponds, wetlands)? If yes, describe type and provide names. If appropriate, state what stream or river it flows into.
The project would be adjacent to and below the Duwamish Waterway and a wetland. The wetland complex is part of the Bluefield wetland mitigation site with an easement in right-of-way and associated environmental covenant and access agreement that allows for transportation maintenance and improvements.
2) Will the project require any work over, in, or adjacent to (within 200 feet) the described waters? If yes, please describe and attach available plans.
3) Estimate the amount of fill and dredge material that would be placed in or removed from surface water or wetlands and indicate the area of the site that would be affected. Indicate the source of fill material.
4) Will the proposal require surface water withdrawals or diversions? Give general description, purpose, and approximate quantities if known.
5) Does the proposal lie within a 100-year floodplain? If so, note location on the site plan.
6) Does the proposal involve any discharges of waste materials to surface waters? If so, describe the type of waste and anticipated volume of discharge.
The project will avoid and minimize impacts to the wetland and Duwamish Waterway through proximity of entry/exit locations and drilling below the water bodies. The project would not likely affect an adjacent wetland mitigation site and buffer nearer to the west shoreline. The HDD borehole would be approximately 150 feet from the wetland mitigation site and the pipe would cross between approximately 25 to 50 feet below the wetland surface. SDOT will coordinate with Bluefield and the holders of the environmental covenant and access agreement prior to construction.
The proposed HDD installation depth for the portion of the bore under the waterway was evaluated based on anticipated soil conditions, existing infrastructure, risk of inadvertent drilling fluid returns, USACE dredge depths, and long-term loading on the HDPE pipe from soil and groundwater pressure. At the proposed crossing location in the channel (Sta. 16+90), the federal authorized project depth is 30 feet Mean Lower Low Water (MLLW). According to survey conducted by USACE in January 2020, actual depths exceed 41 feet MLLW at the proposed crossing location. The proposed HDD crossing has been designed to cross at approximate elevation -60 feet NAVD88 (-57.7 MLLW), more than 25 feet below the authorized channel depth and 20 feet below the actual depth.
The HDD would be below the waterway and within the associated floodplain.
1) Will ground water be withdrawn from a well for drinking water or other purposes? If so, give a general description of the well, proposed uses and approximate quantities withdrawn from the well. Will water be discharged to groundwater? Give general description, purpose, and approximate quantities if known.
2) Describe waste material that will be discharged into the ground from septic tanks or other sources, if any (for example: Domestic sewage; industrial, containing the following chemicals . . . ; agricultural; etc.). Describe the general size of the system, the number of such systems, the number of houses to be served (if applicable), or the number of animals or humans the system(s) are expected to serve.
- c. Water runoff (including stormwater):
1) Describe the source of runoff (including storm water) and method of collection and disposal, if any (include quantities, if known). Where will this water flow? Will this water flow into other waters? If so, describe.
2) Could waste materials enter ground or surface waters? If so, generally describe.
3) Does the proposal alter or otherwise affect drainage patterns in the vicinity of the site? If so, describe.
Stormwater in the project area drains to the Duwamish Waterway.
BMPs will be implemented during project staging and construction to avoid to the extent possible waste materials from entering ground water or surface water. Drilling fluid (bentonite) and native soils will be recovered from the borehole, removed, and disposed offsite at an appropriate facility.
No. Proposed work would require temporary workspace that would be restored after construction.
- d. Proposed measures to reduce or control surface, ground, and runoff water, and drainage pattern impacts, if any:
The project will be designed to avoid impacts to the wetland, waterway, and associated riparian areas. See Section B.1.h for proposed measures related to BMPs. SDOT will coordinate and follow recommendations from federal, state and local permits and with Bluefield and the holders of the environmental covenant and access agreement for Wetland Mitigation Site 1 adjacent and below the project.
- a. Types of vegetation found on the site: [Check the applicable boxes]
Deciduous trees: Alder Maple Aspen Other: (identify)
Evergreen trees: Fir Cedar Pine Other: (identify)
Crop or grain
Orchards, vineyards, or other permanent crops
Wet soil plants: Cattail Buttercup Bulrush Skunk cabbage
Water plants: water lily eelgrass milfoil Other: (identify)
Other types of vegetation: (identify)