HomeMy WebLinkAboutPN_Project_Narrative_180309_v1
King County South Plant Biogas and Heating System Improvements 1 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
Project Narrative
Project name, size and location of site
King County proposes to replace South Plant’s Biogas Upgrading System (BUS) and heating system to
improve the beneficial use of digester gas at King County Wastewater Treatment Division’s South
Treatment Plant (STP) while also reliably supplying heat to meet process and space heating demands. The
South Plant Biogas and Heating Systems Project includes construction of a Heat and Energy Recovery
Building (HERB), a new thermal oxidizer, heating system improvements within the existing Digester
Equipment Building, and utility connections.
The proposed project is located at 1200 Monster Road SW in Renton, Washington (King County Parcels
2423049097 and 2423049006). The 3.92 acres of the approximately 50-acre STP where the project will
be constructed is located in NE Quarter-Section, Section 24, Township 23 North, Range 9 East.
Land use permits required for proposed project
Land Use Permits required for the project include a Conditional Use Permit, Site Plan Review, Shoreline
Exemption, and a Street Frontage Improvements Waiver.
Zoning designation of the site and adjacent properties
The current zoning classification of the site, as well as adjacent properties, is Heavy Industrial (IH).
Current use of the site and any existing improvements
The current use of the site is a public utility (the King County South Treatment Plant).
Special site features (i.e. wetlands, water bodies, steep
slopes)
The project site has been mapped by the City of Renton with moderate Coal Mine Hazards and high
Seismic Hazards. These hazards were evaluated in geotechnical investigations completed by Shannon and
Wilson, Inc. and the results of these investigations are summarized in the Revised Geotechnical Report,
King County South Treatment Plant Biogas and Heat Systems Improvements (January 2017) and the
Geotechnical Report Addendum, Biogas and Heat Systems Improvements Projects, King County South
Treatment Plant, Renton, Washington (December 2017). On site and off site wetlands within 200 feet of
the project site were delineated by Environmental Science Associates and the result summarized in the
South Treatment Plant Biogas and Heat Systems Improvement Project Wetland Assessment Report
(January 2018). One Category IV wetland (Wetland A) was identified on the site. Wetland A is a small
(1,248 SF) depressional wetland that formed within a previously landscaped area at the south end of the
grassy slope where the proposed HERB building will be located. In addition, an off-site wetland mapped
north of the project area within Waterworks Gardens was delineated. No work will occur within either
wetland or their buffers.
Project Narrative
King County South Plant Biogas and Heating System Improvements 2 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
Springbrook Creek is located approximately 450 feet to the northeast of the limits of construction for the
HERB and approximately 250 feet to the east of the proposed spoils placement area. A flood hazard area
associated with Springbrook Creek is mapped on a portion of the project site. A portion of a temporary
construction entrance will be located within this area, but no permanent facilities or fill will be located
within the mapped flood hazard area.
Statement addressing soil type and drainage conditions
Soils were investigated in the geotechnical investigations completed by Shannon and Wilson, Inc. (see the
Revised Geotechnical Report, King County South Treatment Plant Biogas and Heat Systems
Improvements (January 2017); the Addendum to Geotechnical Report, King County South Treatment
Plant Biogas and Heat Systems Improvements, Renton, Washington (March 2017); and the Geotechnical
Report Addendum, Biogas and Heat Systems Improvements Projects, King County South Treatment Plant,
Renton, Washington (December 2017). In general, the site overlies previous fill consisting of silty sand
with gravel to a depth of approximately 25 feet. The fill layer is underlain by native sand, silt, and gravel
to a depth of approximately 80 feet. The existing storm drainage system at STP is described in the
Technical Information Report/Full Drainage Review (February 2018) completed by Davido Consulting
Group, Inc. The entire project site is within Drainage Basin 7, which drains to the stormwater sewer
system on the site and ultimately discharges to Springbrook Creek/Black River.
Proposed use of the property and scope of the proposed
development
Heat and Energy Recovery Building (HERB). The approximately 9,782 square foot (SF) HERB will be
located within an unused site, previously designated for plant expansion, currently comprised of lawn
overtopping a mound formed by previous previously-placed construction fill. The site slopes gradually to
the east towards the existing Solids Motor Control Center (MCC) Building and is maintained as lawn
grass over the mounded spoils. Previously placed spoils will be removed and the existing slope will be re-
graded as part of building construction. Spaces in the HERB will include gas compression rooms, a boiler
room, a control room, an electrical room, a bathroom, a gas analyzer room, and space for heating,
ventilation, and air conditioning (HVAC) equipment.
Site improvements include a new driveway around the west and south sides of the HERB, seven
uncovered parking stalls north of the HERB, and concrete walkways and equipment staging areas
surrounding the HERB on three sides. No changes to vehicular or pedestrian access to the site will occur
as a result of this project. No frontage improvements or work within the public rights-of-way are
proposed for this project.
Existing utility tunnels that run under the nearby Digester Equipment Building will be extended to
provide utilities to the new building. New low pressure sludge gas (LSG), waste gas, and high-pressure
sludge gas (HSSG) pipes will be routed underground along the plant’s driveway (Road N) between the
existing waste gas burners and the current BUS. All utilities in the road will be installed using open-cut
construction methods. New electrical equipment will be installed in the Solids MCC Building and the
new building. New effluent-source heat pumps (referred to as heat extractors, HXTs) will replace the
existing HXTs and will be located in the lower floor of the existing Digester Equipment Building.
Project Narrative
King County South Plant Biogas and Heating System Improvements 3 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
Thermal Oxidizer. The project will include installation of new thermal oxidizer equipment located
outside on a new concrete pad (approximately 2,437 SF) immediately south of the existing waste gas
burners and west of the proposed HERB. The thermal oxidizer will combust waste gas from the BUS. The
primary feature of the thermal oxidizer is an elevated stack alongside a horizontal oxidation chamber.
Spoils Placement. This project proposes to move the spoils excavated for the HERB and associated
facilities (approximately 17,000 CY) to a separate spoils placement location, located on an approximately
one-acre area south of the HERB and the existing digesters within an open lawn area of the STP site.
Spoils will be compacted and seeded to match existing grades and vegetation type.
Associated Stormwater Facilities and Landscaping. At present, the surface water in the project area
flows into STP’s stormwater conveyance and treatment system, which includes multiple biofiltration
swales, catch basins, pipes, a large pump station, and a series of wetponds and wetlands in Waterworks
Gardens.
As described in the Technical Information Report/Full Drainage Review, runoff from the building roof
and most of the impervious areas will be collected and routed to a detention vault before being discharged
to the existing stormwater system onsite. Runoff from a portion of the asphalt walkway will disperse via
sheet flow into new and existing landscaped areas where it will infiltrate.
The proposed landscape design includes plantings adjacent to the new building and new paved areas and
in stormwater treatment and detention facilities, and responds to grading of the eastern portion of the hill
in the center of the project site to provide a level area for the new building. The regraded hill will be
stabilized with a selection of drought-tolerant shrubs and groundcovers. Other areas of disturbance will be
restored with a grass and herbaceous plant seed mix similar to the existing groundcover found on the site.
Landscape plantings will be a combination of native Pacific Northwest species and drought-resistant
ornamentals. Plants will be selected for adaptation to the different growing conditions present across the
project site, including shaded areas within and adjacent to existing stands of mature trees, sunny areas
within new landscape buffers and plantings adjacent to paved areas, and seasonally wet areas within the
stormwater treatment and infiltration areas.
The number of trees requiring removal is within the City of Renton’s tree retention threshold for
industrial zones.
Access
The primary access to the northern portion of the Plant, where the project will be developed, is via SW
7thStreet. However, there are additional driveways located off of Monster Road SW, Longacres Dr SW,
and SW Grady Way.
Proposed off-site improvements (i.e. installation of
sidewalks, fire hydrants, sewer main, etc.)
No off-site improvements are proposed.
Project Narrative
King County South Plant Biogas and Heating System Improvements 4 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
Total estimated construction cost and estimated fair
market value of the proposed project
The value of the improvements is estimated at $5.5 million.
Estimated quantities and type of materials involved if any
fill or excavation is proposed
Approximately 17,000 cubic yards of soil will be excavated, all of which will be used on site. For all
excavation activities associated with the proposed facilities, subsequent backfill will consist of native soil
to the greatest extent possible, supplemented by clean fill when required by permit conditions or
engineering specifications.
Number, type and size of any trees to be removed
Of the 180 assessed trees, 42 trees with a Diameter at Breast Height (DBH) greater than 6” are proposed
for removal. Thirty-nine trees will be removed due to impacts of construction,3 trees will be removed due
to the poor condition of the trees which makes their location near construction and proposed facilities
high risk. Trees proposed for removal by species and size and listed in the table below (Table 1).
TABLE 1
TREES PROPOSED FOR REMOVAL
Scientific Name Common Name Size
Calocedrus decurrens Incense Cedar 11"
9’’
6’’
Fraxinus sp. Ash 13"
7"
Larix sp. Larch 6"
Liquidambar styraciflua Sweet Gum 8"
Malus sp. Crabapple 7"
7"
8"
8"
10"
10"
11"
Picea abies Norway Spruce 8"
8"
10"
11"
14"
Project Narrative
King County South Plant Biogas and Heating System Improvements 5 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
Scientific Name Common Name Size
16"
16"
17"
Populus nigra Cottonwood 8"
10"
Prunus laurocerasus Laurel 13"
Pseudotsuga menziesii Douglas Fir 6"
7"
8"
9"
9"
9"
9"
9"
10"
10"
10"
11"
11"
11"
11"
12"
12"
For more information, see the King County South Treatment Plant Biogas and Heat Systems
Improvements Tree Report (February 2018).
Distance in feet from the wetland or stream to the nearest
area of work for projects located within 100 feet of a stream
or wetland
For Wetland A, all work, including the proposed HERB, thermal oxidizer, and all associated grading, will
occur outside the standard 50-foot buffer. At its closest point, work will occur within 75 feet of the
offsite wetland, Wetland B, located within Waterworks Gardens. As described in the South Treatment
Plant Biogas and Heating Systems Improvement Project Wetland Assessment Report (January 2018), the
plant driveway (Road N) separates Wetland B from all project areas. In addition, an approximately 8-foot
wide paved path is located adjacent to the road. Given that any buffer functions from the project site to
the wetland are substantially prevented by the existing road and trail as described in the report, no impacts
to the wetland or wetland buffer are anticipated from any project actions.
Project Narrative
King County South Plant Biogas and Heating System Improvements 6 ESA / D150513.00
CUP / Site Plan Review Submittal February 2018
For projects within 200 feet of Black River, Cedar River,
Springbrook Creek, May Creek, and Lake Washington
please include the following info (see CUP specs)
Distance from closest area of work to the ordinary high water mark
The project site will be approximately 1,000 feet from the Black River and 450 feet from Springbrook
Creek for work related to the HERB, 250 feet for the proposed spoils placement site, and 128 feet for the
temporary construction entrance.
Description of the nature of existing shoreline
In the City of Renton, Springbrook Creek was extensively modified and straightened for agricultural
drainage in the 1920s by King County Drainage District No. 1. The channel area abutting the project was
improved in the 1980s and 1990s for flood control by the City in cooperation with the Natural Resource
Conservation Service. The stream is constrained and channelized throughout the shoreline (City of
Renton, 2010). Levees that define the streambank limit the width of the riparian corridor (Parametrix,
2010).
Springbrook Creek is classified as Shoreline High Intensity under City of Renton’s Shoreline
Management Program. Existing vegetation within the shoreline is primarily limited to the riparian area
adjacent to the creek, and is typical native riparian forest species and includes a mixture of red alder,
willow species, Himalayan blackberry and sedges (Carex spp.) along with some ornamental trees.
Conifers are almost exclusively absent and in those areas where shade was absent reed canary grass is
abundant. The Springbrook Creek vegetated riparian area is separated from the project site by the plant
driveway (Road N).
Chinook, chum, coho, steelhead trout, and cutthroat trout are found in Springbrook Creek, utilizing the
habitat primarily for migration (City of Renton, 2010; WDFW, 2017). Under the 2003 State water quality
standards, Springbrook Creek is categorized as “Spawning Rearing and Migration Habitat” for aquatic
life use and “Primary Contact” for recreational use. The Creek is on the 2012 Washington Department of
Ecology’s 303(d) list for violation of dissolved oxygen and fecal coliform bacteria standards (Category 5)
(King County, 2017).
References
City of Renton. 2010. Shoreline Master Program Update Draft Restoration Plan. March 2010. 552-1779-
031.
King County. 2017. Stream Report: Springbrook Creek – 0317. Accessed on 12/8/17. Available at:
http://green2.kingcounty.gov/streamsdata/watershedinfo.aspx?locator=0317
Washington Department of Fish and Wildlife (WDFW). 2017. SalmonScape. Accessed on 12/11/2017.
Available at: http://apps.wdfw.wa.gov/salmonscape/