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Denny Substation Project
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Seattle City Light completed the environmental clean-up at the site of the future Denny Substation. City Light purchased the site, the former Greyhound Bus Maintenance Facility, in 2009, with the intention of building a new electrical substation in North Downtown to keep pace with Seattle's growing power needs. Due to historical leakages of gasoline, diesel and waste oil the site needed to be cleaned up prior to construction of the substation. City Light developed a plan to remediate the site to residential standards, which requires the removal of all contaminated soil that exceeds those standards.

City Light completed Phase 1 of the plan in late 2012, when it demolished the Maintenance Facility and removed underground storage tanks. Phase 2 began in early 2013 and included removal of all contaminated soils, installing a stormwater detention system and backfilling the site with clean dirt. The site is now ready for construction; however, the environmental review and design of the substation need to be completed before construction begins.

Prior to purchasing the property, the utility conducted a Phase I-II Environmental Assessment to determine environmental conditions and to evaluate the costs and potential risks associated with purchase. The environmental assessment found soil and groundwater contamination from gasoline, diesel, and waste oil products due to historical leakage from underground storage tanks. Some of these materials were found as deep as 35 feet below ground surface within areas of the property. Seattle City Light developed a voluntary clean-up plan to remediate the site to meet Model Toxics Control Act (MTCA) "Level A" clean-up standards as applied in close proximity to residences (see WAC-173-340-704 - Use of Method A). The clean-up plan included removal of all contaminated soil on the property that has been identified as exceeding these standards.

Seattle City Light published a SEPA Environmental Checklist and a Determination of Non-Significance in September 2011. The checklist contains additional information about the history of the site, the clean-up plan and construction work required to complete the clean-up. The utility has obtained permits required for this remedial construction including wastewater discharge, land use, demolition, grading, shoring, and street improvements.

Seattle City Light contracted with Glacier Environmental to implement the clean-up plan, which is being conducted in two phases. The first phase began in late August 2012 and consists of the following actions:
  • Abate and properly dispose of hazardous materials inside the building (asbestos and lead containing materials, and mercury and PCBs in light fixtures)
  • Salvage items with historical significance or architectural value (such as signage, windows, and doors)
  • Demolish the building and recycle or dispose of all demolition debris offsite
  • Remove four previously decommissioned underground storage tanks
  • Decommission and remove one underground storage tank
  • Backfill maintenance pits, install erosion controls, and secure the site over rainy months
  • Continue operation of an existing interim on-site treatment system to remove and dispose of contaminated groundwater
Phase 2 of the environmental clean-up began April 1, 2013 and was completed in January 2014, and consisted of the following actions:
  • Fence a larger site including adjacent parking lots, and a portion of Pontius Avenue for construction staging
  • Excavate, stockpile, separate and remove contaminated soils for proper disposal off-site
  • Install a shoring wall around two-thirds of the site to safely support soil excavation work
  • Use clean fill and clean excavated material to backfill excavated areas
  • Install a storm water detention system
  • Bring the site to a final grade and cover with crushed rock
  • Restore sidewalks and areas of the street right of way affected by construction
  • Utility relocations on John Street and Pontius Avenue requiring brief electrical and water service disruption for some customers
  • Partial closure of the alley behind the Colwell Building
  • Sidewalk closure on the east side of Minor Avenue between Denny Way and John Street>
  • Parking restrictions and sidewalk and lane closures on John Street between Pontius Avenue and Yale Avenue and along Pontius for the duration of the street closure.
  • Construction noise typical to the use of heavy equipment
  • Additional truck traffic on John Street, Denny Way, Fairview Avenue, Mercer and Westlake.

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    700 5th Avenue
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    P.O. Box 34023
    Seattle, WA 98124-4023

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