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Kennydale Lakeline Sewer System Replacement Project LAKE STUDY
Prepared for:
Carollo Engineers, Inc. May 2025
RECEIVED
07/30/2025
amorganroth
PLANNING DIVISION
Docusign Envelope ID: A6950DB9-F338-45C7-991A-0D2425171124
Kennydale Lakeline Sewer System Replacement Project LAKE STUDY
Prepared for:
Carollo Engineers, Inc. 1200 Fifth Ave, Suite 900 Seattle, WA 98101
Prepared by:
Confluence Environmental Company Marlene Meaders Audrey Michniak Margaret Wolf
May 2025
This report should be cited as: Confluence (Confluence Environmental Company). 2025. Kennydale lakeline sewer system replacement project: Lake study. Prepared for Carollo, Seattle, Washington, by Confluence, Seattle, Washington.
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Kennydale Lakeline Sewer System Replacement Project: Lake Study
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TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................................................................... 1
2.0 DESCRIPTION OF PROPOSED ACTION ............................................................................................................ 3
2.1 Phase 1: Upland Work .............................................................................................................................. 4
2.2 Phase 2: In-Water Work ........................................................................................................................... 4
3.0 LOCATION ............................................................................................................................................................ 6
3.1 Site Parcels .............................................................................................................................................. 6
3.2 Streams and Lakes ................................................................................................................................... 6
3.3 Geologically Hazardous Areas ................................................................................................................. 7
3.4 Floodplain and Floodway Boundaries ....................................................................................................... 7
3.5 Riparian Vegetation ................................................................................................................................ 11
3.6 Existing Structures .................................................................................................................................. 12
3.7 Site Access ............................................................................................................................................. 12
3.7.1 Phase 1: Upland Work ............................................................................................................ 12
3.7.2 Phase 2: In-Water Work .......................................................................................................... 14
4.0 LAKE ASSESSMENT ......................................................................................................................................... 14
4.1 Ecological Functions ............................................................................................................................... 14
4.2 Fish and Wildlife ..................................................................................................................................... 17
4.3 Trees and Vegetation Protection ............................................................................................................ 18
4.4 Slope Protection and Erosion Control ..................................................................................................... 19
5.0 NO NET LOSS OF ECOLOGICAL FUNCTIONS ............................................................................................... 21
5.1 Phase 1: Upland Work ............................................................................................................................ 21
5.2 Phase 2: In-Water Work ......................................................................................................................... 22
5.3 Summary ................................................................................................................................................ 22
6.0 REFERENCES .................................................................................................................................................... 23
TABLES Table 1. General information by phase .......................................................................................................................... 3
Table 2. Properties associated with Phase 2 in-water work ........................................................................................... 6
Table 3. Trees removed or impacted by the project. .................................................................................................... 11
FIGURES Figure 1. Kennydale project parcels and existing lakeline sewer system location ......................................................... 2
Figure 2. High erosion hazard area at the project site ................................................................................................... 8
Figure 3. Landslide hazard areas at the project site ...................................................................................................... 9
Figure 4. Sensitive and protected slope areas at the project site ................................................................................. 10
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Figure 5. Phase 1 example view of land-based sewer system design, site access, and staging ................................. 13
Figure 6. Phase 2 project site access and work areas ................................................................................................. 15
Figure 7. Sockeye spawning locations in the project site. ............................................................................................ 16
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1.0 INTRODUCTION
The Kennydale Lakeline Sewer System (Kennydale lakeline system or lakeline system) is owned
and operated by the City of Renton (City) and provides sanitary sewer service to Kennydale
Beach Park and 56 properties along Lake Washington from the north end of Gene Coulon
Memorial Beach Park to just south of May Creek (Figure 1). The 4,680-foot-long lakeline system
consists of a flush station, an 8-inch cast iron sewer pipe buried offshore in Lake Washington, 3
manholes, and a system of 37 gravity side sewer laterals connecting customers to sewer
treatment. The Lake Washington No. 2 lift station pumps the flow from the lakeline system and
the basin to the north to the King County Eastside Interceptor, the regional conveyance system,
and then to the King County South Plant where it is treated. The Kennydale lakeline system is a
low-pressure system that operates by collecting fresh lake water via an intake pipe at the flush
station located at the north end of Gene Coulon Park and pumping water through the line to
convey wastewater collected by the lateral connections to the Lake Washington No. 2 lift station
at the north end of the lakeline system near North 40th Street. The initial 300 feet of the lakeline
system is in upland habitat and the rest is predominantly buried below the lakebed, within
approximately 50 feet of the shoreline.
The City concluded that the Kennydale lakeline system needed to be replaced based on the
results of the 2016 to 2019 assessment. While technically feasible, in-lake alternatives were
anticipated to have significantly higher costs compared to an upland grinder pump system.
Additionally, state and federal permitting agencies require applicants to demonstrate that there
is no practical alternative prior to approving new construction in a regulated waterbody. After
participating in the in-water sewer workgroup, considering environmental and permitting
factors, and evaluating numerous alternatives, the City selected a land-based individual lift
station (ILS) with grinder pumps as the preferred alternative because an upland grinder pump
system significantly reduces the risk to the environment at a lower cost and because past
cleaning and maintenance attempts of an in-water system have partially failed.
The Kennydale Lakeline Sewer System Replacement Project (the project) is being designed and
permitted per applicable regulatory requirements. Once the replacement system is complete,
the existing lakeline system will be decommissioned.
This document is the Lake Study that is required because the project is in a regulated shoreline
area (Figure 1). The purpose of this document is to demonstrate compliance with the City
Shoreline Master Program (SMP) and development criteria found in the Critical Areas
Regulations per Renton Municipal Code (RMC) 4-3-090. This study will demonstrate that the
proposed project meets the criteria of no net loss of ecological functions as described in RMC 4-
3-090(D)(2). Project Drawings were developed by Carollo and are presented in the shoreline
application materials. Sheets from the Project Drawings will be referenced throughout this
document.
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Figure 1. Kennydale project parcels and existing lakeline sewer system location
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2.0 DESCRIPTION OF PROPOSED ACTION
The purpose of the project is to provide reliable and easily maintainable sewer service to Renton
shoreline residences that integrates with the existing sewer conveyance and pumping system
and that has the least aquatic environmental impact possible. This project is needed because the
existing Kennydale lakeline system that was installed in Lake Washington in 1972 is reaching
the end of its useful life and is unable to be maintained in its current location. The following is a
brief summary of the proposed project for context in the Lake Study. Details of the proposed
action and construction methods are provided in Confluence (2025).
There are two phases of the work: (1) upland, and (2) in-water. The general information for each
phase is identified in Table 1.
Table 1. General information by phase
Category Phase 1 Phase 2
Project Information
Name Upland Work In-Water Work
Length 4,950 LF 4,680 LF
Location City ROW, City property, private residences, and public parks Lake Washington (Lakeline) and just upland from Lake Washington (Flush Station, Lift Station)
Section/ Township/ Range
S32, T24N, R5E S31, T24N, R5E S6, T23N, R5E
S32, T24N, R5E S31, T24N, R5E S6, T23N, R5E
Zoning Residential-8, Residential-6 Aquatic (Lakeline), Residential-8 (Flush Station) Residential-6 (Lift Station)
Shoreline Designation Single Family Residential, Urban Conservancy Aquatic (Lakeline), Single Family Residential (Flush Station)
Project Cost $10.1 million $615,000
Materials Excavation 9,562 CY 33 CY
Fill 9,562 CY 39 CY
Distance from OHWM 5 to 200 feet from the shoreline (upland grinder pump stations)
~50 feet from the shoreline (in-water lakeline) 33 feet from the shoreline (upland flush station) 19 feet from the shoreline (upland lift station)
Water Depths N/A 6 to 20 feet (Lakeline)
CY = cubic yards; LF = linear feet; OHWM = ordinary high water mark; ROW = right-of-way
The proposed action is summarized below in Section 2.1 for the upland phase and Section 2.2
for the in-water phase. Additional details on construction methods, site access, operations and
maintenance of the replacement sewer system, and conservation measures used during
construction for both phases of the work can be found in the Project Narrative and Code
Consistency Analysis (Confluence 2025).
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2.1 Phase 1: Upland Work
Phase 1 of the project includes installing a new land-based sewer system that includes a low-
pressure sanitary sewer force main, discharge laterals, and grinder pumps. A total of 54 private
residences and the Kennydale Beach Park will connect to the new force main via discharge
laterals from the front, back, or side yards of each property and the park. There are 2 residences
that are currently served by the Kennydale lakeline system that will connect to a new gravity
system instead of a grinder pump. The new force main and discharge laterals will be at a
minimum of 3 feet deep. Each house will have its existing gravity sewer line rerouted to its own
grinder pump station with the 2 exceptions stated above. The discharge pipe (approximately 1
¼ inches in diameter) from the grinder pump stations will be routed to the new force main that
will be installed in the City right-of-way (ROW) or an access road owned by King County Parks
to the east and upland of the existing private residences.
The Phase 1 project site covers a total parcel area of approximately 1,681,600 square feet (SF), or
39 acres, which includes 62 parcels, a linear force main in the adjacent roadways that is
approximately 3,000 linear feet (LF), and discharge laterals that add up to approximately 5,000
LF. A total of 55 grinder pumps will be added to service the private residences and Kennydale
Beach Park. The total ground surface disturbance includes approximately 113,700 SF, which is a
small portion of the total parcel area. Note that the value for disturbance area adds 15% to the
anticipated impact values to account for potential changes during final design. Additionally,
impact areas assume that installation will be through open-trench excavation. Discharge laterals
may be installed using trenchless methods, which would reduce the amount of surface
disturbance.
A grading plan was prepared in accordance with RMC 4-8-120(D)(7), and showing contour
intervals of 2 feet where slopes are less than 10% and 5 feet where slopes are 10% or greater. The
grading plan is provided within Sheets C01 to C10 of the Project Drawings.
Temporarily affected areas will be restored in-kind to existing conditions. Vegetation will be
replaced at a 1:1 ratio using native species or replacing landscaped species. There are a total of 4
significant trees proposed to be removed outside of critical areas or buffers but within the
shoreline. Replacement of significant trees are based on Renton and King County codes (RMC
4-4-130H.1.b, RMC 9-13-8B, and KCC 16.82.156E.2.a,b). A Vegetation Management Plan
provides details on the location and type of restoration for each area that is disturbed
(Confluence and Tree Solutions 2025). This plan is provided under a separate cover with the
permit application package.
2.2 Phase 2: In-Water Work
Phase 2 includes decommissioning the existing lakeline system, which can occur after
completion of Phase 1. Before decommissioning activities begin, the lakeline will be cleaned.
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Lakeline cleaning will consist of flushing the line with water to remove accumulated materials.
The source of the flushing water will be the existing lake intake to the flush station. Water used
for flushing the line will be conveyed via the existing system to the King County regional
system and will not enter surface waters. Once the line is cleaned, the pipe is proposed to be
filled with lake water to avoid needing to pump controlled density fill (CDF) into the pipeline
and the potential for CDF to enter the water if there are leaks or breaks in the pipe.
In-water work includes removal of the 3 existing manholes, resulting in the removal of
approximately 33 cubic yards (CY) of material at 4 parcels that are either directly affected or
adjacent to the work (APN 3124059077, 3342103760, 3342700211, 3342700240). The areas where
manholes are removed will be backfilled to 6 inches below original grade and then top dressed
to original grade with spawning gravel mix (estimated as 11 CY of fill). An additional 2 CY of
gravels will be placed in locations where the pipe is exposed, which is estimated at 2 locations.
Finally, gravel will be placed at the flush station intake (~2 CY) located at APN 0523059010.
Gravel placement for all in-water work will provide habitat for juvenile salmonids as well as
support spawning for sockeye salmon (Oncorhynchus nerka). Gravel size range will be
determined by specific site conditions such as exposure, wave fetch, slope, and consultation
with the Washington Department of Fish and Wildlife. It is estimated that restoration will
include a total fill of 39 CY.
There is a limited amount of work in upland areas associated with decommissioning the flush
station (APN 0523059010) and upgrades to Lake Washington Lift Station 2 (APN 3342700011).
The primary work at the flush station will include removing the interior components and
adjacent appurtenances of the flush station (the shelter, antenna, light, etc.). The above-grade
electrical/controls shelter, electrical vault, antenna, and site lighting will be removed.
The Lake Washington Lift Station No. 2 is located on-land on the northern end of the lakeline
system (APN 3342700011). In addition to lakeline system flow, the lift station collects flow north
of the station from an upland gravity system and will remain with minor upgrades to its
Supervisory Control and Data Acquisition (SCADA) and electrical systems to allow for
connection to the new permanent generator. The area of the transformer and generator may
require a retaining wall or other slope stabilization method and appropriate screening as
required by code. These minor upgrades will result in approximately 500 SF of new impervious
surface area.
Site access for the upland work will occur from City ROW directly adjacent to the site.
Additional details for the Phase 2 work are provided in the Project Drawings (Sheets D01 to
D02).
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3.0 LOCATION
The following information includes a description of the project site based on a combination of a
desktop analysis, site visits, and background research. Information from other discipline reports
(e.g., Arborist Report, Geotechnical Engineering Report) will be included in this section and
referenced as appropriate.
3.1 Site Parcels
A total of 54 houses and the Kennydale Beach Park will be involved in the installation of ILS
with grinder pumps and new sewer lines connecting to the land-based sewer system
(Confluence 2025). In-water work is associated with a few residences to remove the manholes
and capping the flush station intake (Table 2). In-water work associated with the existing
lakeline system is located approximately 50 feet from ordinary high water mark (OHWM).
Table 2. Properties associated with Phase 2 in-water work
Parcel Number Address Use Proposed Construction Activities
0523059010 2725 Mountain View Ave N Flush Station and Public Park (Coulon Beach Park) Cap existing 8-inch intake in vault; place gravel at the flush station intake (~2 CY)
3342103760 N/A Aquatic/no use Remove manhole #5378 between House #3307 and #3233 (remove a 10-foot by 10-foot area to depth of 3 feet for a total of 11 cubic yards of material) 3124059077 3307 Mountain View Ave N Single Family Residence Remove manhole #5379 at the in-water edge of the property (remove a 10-foot by 10-foot area to depth of 3 feet for a total of 11 cubic yards of material)
3342700240 3713 Lake Washington Blvd N Single Family Residence Remove manhole #5380 between House #3715 and #3713 (remove a 10-foot by 10-foot area to depth of 3 feet for a total of 11 cubic yards of material) 3342700211 3715 Lake Washington Blvd N Single Family Residence Remove manhole #5380 (see above)
3.2 Streams and Lakes
No streams are located within the existing lakeline system or proposed land-based sewer
system. However, the mouth of May Creek is located approximately 350 feet north of the Lake
Washington #2 Lift Station. May Creek is a 7-mile long tributary to Lake Washington. It is
classified as a Type S stream, or a Shoreline Stream, within the vicinity of the Lake Washington
#2 Lift Station (DNR 2024). The creek originates in the steep forested slopes of Cougar and
Squak Mountains and in the highlands of the Renton Plateau.
The project is located along the Lake Washington shoreline and within the lake itself. Lake
Washington is classified as deepwater habitat that has been modified by a man-made barrier
and has an unconsolidated bottom made up of at least 25% small particles (<6-7cm) and with
less than 30% vegetative cover (USFWS 2025). The regions of Lake Washington along the
lakeline system are free from severe 303(d) listings, although there are areas of concern off
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Coleman Point for metabolites of DDT (Listing IDs 83696, 84429), Polychlorinated Biphenyls
(PCBs) (Listing ID 86672), and methyl mercury (Listing ID 88678).
The shoreline of Lake Washington is designated as a Shoreline of the State as defined by RMC
4-3-090(B)(1a). The shoreline is defined as 200 feet landward of the OHWM of Lake Washington
(refer to Figure 1). The OHWM of Lake Washington is 18.6 feet elevation according to North
American Vertical Datum of 1988 (NAVD 88). There is approximately 4,680 LF of shoreline
along the existing lakeline system. Note that, given the scope of this project and the fact that the
OHWM will not be affected, a formal delineation using methods described by Anderson et al.
(2016) was not conducted.
3.3 Geologically Hazardous Areas
Slopes along the shoreline at the project site range from flat (less than 15% slope) to gently or
moderately sloping (less than 40% slopes), with a majority of the shoreline having 15 to 25%
slopes within 200 feet of the OHWM. Renton (2025) identifies the shorelines associated with the
southern portion of the project as high erosion hazard areas (Figure 2), the entire project site as
medium and high landslide hazard areas (Figure 3), and several locations of the project site as
sensitive slope areas (Figure 4). The main overlap with geologically hazardous areas and the
project site is moderate and high landslide areas. These areas are primarily associated with
work to install the ILS with grinder pumps and discharge laterals within private property.
There is no overlap with protected slopes and high erosion areas other than within existing
roadways.
The shoreline along the project site overall is highly modified with approximately 4,500 linear
feet of the shoreline heavily armored with riprap, gabion walls, or other vertical bulkheads.
There are a few areas (approximately 300 linear feet in total) where bulkheads are absent and
gravel-dominated pocket beaches occur. Protection of these critical habitat areas during
construction are identified in the Geotechnical Engineering Report (Shannon and Wilson 2024).
3.4 Floodplain and Floodway Boundaries
The existing Kennydale lakeline system and proposed land-based sewer system do not fall in
floodplain or floodway boundaries. May Creek, directly north of the lakeline system, qualifies
as a Federal Emergency Management Agency (FEMA) floodway, with areas on either side of it
qualifying as FEMA 100-year floodplains with a 1% annual chance of flooding (King County
2025a). Lake Washington is a controlled system and not considered part of the FEMA floodway.
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Figure 2. High erosion hazard area at the project site
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Figure 3. Landslide hazard areas at the project site
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Figure 4. Sensitive and protected slope areas at the project site
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3.5 Riparian Vegetation
Based on available data and site visits, no wetlands are within 300 feet of the lakeline system
(King County 2025a; Renton 2025; USFWS 2025; WDFW 2025a). Riparian vegetation along the
waterside of the shoreline associated with the lakeline system is primarily lawn and ornamental
shrubs, with scattered trees (Tree Solutions 2025). The riparian vegetation provides little
shading over the nearshore waters. There are a few exceptions to this with larger sections of
existing mature trees such as Western red cedar (Thuja plicata), Coast redwood (Sequoia
sempervirens), black cottonwood (Populus trichocarpa), and bigleaf maple (Acer macrophyllum),
and shrubs that extend over the water, providing shade, cover, and insect drop into the lake.
There are also several black locust (Robinia pseudoacacia) along the water, which are considered a
weed of concern by King County (2025b).
The Arborist Report includes a full description of trees within and adjacent to the project site
(Tree Solutions 2025). A total of 308 trees were surveyed, 4 significant trees are proposed to be
removed, and 13 are proposed to be impacted as part of the proposed project activities using
trenchless construction methods(Table 3). Information related to tree protection measures are
identified in the Arborist Report. Additional details on replacement of vegetation and trees is
provided in the Vegetation Management Plan (Confluence and Tree Solutions 2025).
Table 3. Trees removed or impacted by the project.
Tree ID Tree Location by Parcel Scientific Name Common Name DSH Action
29 3124059004 Callitropsis nootkatensis Alaska yellow cedar 6.5 Impacted
30 3342104050 Callitropsis nootkatensis Alaska yellow cedar 7.8 Impacted
59 3124059004 X Cuprocyparis leylandii Leyland cypress 15.6 Impacted
66 3342104040 Salix babylonica ‘Pendula’ Weeping willow 42.8 Impacted
71 Shared 3342104010, 3342104009 Salix babylonica ‘Pendula’ Weeping willow 48.5 Impacted
83 3342103942 Magnolia grandiflora Southern magnolia 9.4 Impacted
190 3124059076 Acer macrophyllum Bigleaf maple 9.8 Impacted
191 3124059076 Alnus rubra Red alder 22.8 Impacted
192 3124059076 Acer macrophyllum Bigleaf maple 34.8 Impacted
193 3124059076 Fraxinus oxycarpa Raywood ash 9.9 Impacted
194 3124059076 Acer macrophyllum Bigleaf maple 17.8 Impacted
237 3342700250 Sequoia sempervirens Coast redwood 72.4 Impacted
272 3342700126 Magnolia grandiflora Southern magnolia 14.0 Remove
273 3342700126 Magnolia grandiflora Southern magnolia 10.4 Remove
275 3342700100 Robinia pseudoacacia Black locust 21.5 Remove
276 3342700100 Robinia pseudoacacia Black locust 39.2 Impacted
308 3342700176 Crataegus sp. Hawthorn 13.5 Remove
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3.6 Existing Structures
Overwater structures are present throughout the shoreline along the Kennydale lakeline system
corridor. Structures on the project site are primarily single family residences and auxiliary
structures (e.g., sheds, bulkheads, docks, boat lifts). Forty-nine of the 57 parcels where the
lakeline system would be decommissioned have small docks permanently mounted on pilings.
The shorelines of all properties are armored with either stone or concrete bulkheads. Several
residences also have retaining walls, fences, or other types of structures. There are 3 manholes
along the existing lakeline system. The flush station located at the south end of the Kennydale
lakeline system (APN 0523059010) includes a shelter, antenna, light, and other appurtenances.
There is also an above-grade electrical/controls shelter, electrical vault, antenna, and site
lighting. Finally, the Lake Washington Lift Station No. 2 is located on-land on the northern end
of the lakeline system (APN 3342700011). Lift Station No. 2 has a shed that includes the power
supply for the existing lakeline system and auxiliary equipment.
Proposed structures for the land-based sewer system are all underground or small electrical
panels in upland locations. The location, size, and number of these underground structures are
described above in the Project Drawings.
3.7 Site Access
Site access is different for the two phases of work.
3.7.1 Phase 1: Upland Work
Vehicular access to the project site is limited. There are 2 roadways that serve all properties
connected to the Kennydale lakeline system: (1) Mountain View Ave N and (2) an unnamed
access road own by King County Parks that parallels Lake Washington Blvd N (Figure 5). These
2 roadways cross the Eastside Rail Corridor (Eastrail), a public multi-use trail. The roadway and
adjacent parking is on land that includes City ROW and parcels owned by King County Parks
that includes Kennydale Beach Park and the Eastrail. The unnamed road paralleling Lake
Washington Blvd N is the access for the private properties in the project site. These properties
have addresses of Lake Washington Blvd N, but the unnamed roadway is separated from Lake
Washington Blvd N by the Eastrail.
Vehicular access to Mountain View Ave N is just west of the intersection of Lake Washington
Blvd N and N 33rd Street. Vehicular access to the access road owned by King County Parks
adjacent to Lake Washington Blvd N is just west of the intersection of Lake Washington Blvd N
and N 37th Street (Figure 5). Staging will be located on Mountain View Ave N, access road part
of King County Parks property, or the property directly adjacent to the area being constructed
(Figure 5). Sections of the roadways adjacent to the work areas and City-owned parcels will be
used in stages for the entire upland construction period (spring 2026 to fall 2027).
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Figure 5. Phase 1 example view of land-based sewer system design, site access, and staging
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3.7.2 Phase 2: In-Water Work
The location of work is shown in Figure 6. In-water work is proposed in 5 parcels that may
experience temporary construction impacts (APN 3124059077, 3342103760, 3342700211,
3342700240, 0523059010). The work includes in-water activities in Lake Washington to
decommission the existing lakeline system; there will not be any in-water construction of the
new system. The project locations for the decommissioning work are primarily aquatic and
work will be staged from a floating barge and/or boat.
There is a limited amount of work in upland areas associated with decommissioning the flush
station (APN 0523059010) and upgrades to Lake Washington Lift Station 2 (APN 3342700011).
Site access for the upland work will occur from City ROW directly adjacent to the site.
4.0 LAKE ASSESSMENT
The following information includes existing conditions and ecological functions provided by
Lake Washington in the project vicinity. The information in this section is intended to satisfy the
criteria identified under RMC 4-3-090.
4.1 Ecological Functions
No streams are located within the Kennydale lakeline system corridor. However, May Creek is
located just north of the Lake Washington #2 Lift Station and is a tributary to Lake Washington.
Use of May Creek by salmonids and other wildlife is declining due to habitat loss, erosion,
sedimentation, and deteriorating water quality (King County and City of Renton 2001).
Lake Washington provides habitat and foraging opportunities for a wide variety of fish and
wildlife species, including Endangered Species Act (ESA)-listed fish species. The nearshore
associated with the project site is highly modified by the presence of bulkheads and numerous
docks, which impact fish migration in freshwater systems (Carrasquero 2001). There is also a
distinct population of sockeye salmon that spawn on Lake Washington beaches. Spawning can
take place in Lake Washington wherever suitable gravel beaches with upwelling are available
(Gustafson et al. 1997), although beach surveys have not occurred in recent years to confirm use
of these areas (King County 2024). Most of the sockeye salmon that occur near the project site
are from the Cedar River and use Lake Washington for migration and rearing. A majority of the
lakeline system has been mapped as sockeye spawning habitat based on suitable gravels and
historical spawning activity (Figure 7).
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Figure 6. Phase 2 project site access and work areas
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Figure 7. Sockeye spawning locations in the project site.
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The project site and surrounding area include several significant trees, as defined in RMC 4-11,
and other non-significant trees (Tree Solutions 2025). A total 308 trees were surveyed within
and adjacent to the proposed project site. Trees surveyed are generally located along the
Eastrail, in a few backyards, and within parks. A total of 61 species were identified during the
arborist surveys. These trees are mostly in fair to good health and structural condition with a
few trees indicated as poor or excellent health. In general, the project site includes land uses
with moderate to high intensity development that have little to no habitat opportunity and are
dominated by single family residents and landscaped species. Areas with more dense
vegetation in public parks are dominated by invasive species such as Himalayan blackberry
(Rubus armeniacus), English ivy (Hedera helix), and reed canarygrass (Phalaris arundinacea).
Because these vegetated areas are either dominated by invasive vegetation or include only a
narrow area of native vegetation surrounded by paved areas and buildings, the associated
habitat functions and values are relatively low.
The riparian vegetation on the water side provides very little shading for Lake Washington. On
lots with overhanging vegetation, trees provide shade, cover, and insect drop into the lake
(Christensen et al. 1996; Tabor et al. 2011). It is notable that some of these overhanging trees
(e.g., black locust) are also considered a weed of concern by King County (2025b). There are also
several large weeping willows (Salix babylonica 'Pendula'), western redcedar (Thuja plicata), and
other native and non-native landscape species. The Arborist Report has a table of trees and
location of each species identified (Tree Solutions 2025). Trees provide habitat for terrestrial
species.
The shoreline associated with the project includes several areas with sensitive slopes, landslide
hazards, and high erosion hazard areas. Disruption to these areas can result in a degradation of
environmental quality and public safety. Stability of these geologically hazardous areas are an
important consideration for both construction methods and design of the structures being
installed.
4.2 Fish and Wildlife
Many bird species have been observed in and near the project site, including the following
species: osprey (Pandion haliaetus), bald eagle (Haliaeetus leucocephalus), red-tailed hawk (Buteo
jamaicensis), mallard (Anas platyrhynchos), common merganser (Mergus merganser), bufflehead
(Bucephala albeola), belted kingfisher (Megaceryle alcyon), great blue heron (Ardea herodias),
American goldfinch (Spinus tristis), Wilson’s warbler (Cardellina pusilla), and Northern flicker
(Colaptes auratus) (iNaturalist 2024). Birds will use the project site for foraging and migration.
An osprey nest was identified approximately 1,000 feet north of the mouth of May Creek, along
N 42nd Place, and bald eagle nests on the south end of Mercer Island. A bald eagle was
observed in a mature conifer at 3827 Mountain View Ave N and a land owner at 3009 Mountain
View Ave N observes regular use of the area by a foraging eagle.
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Mammals observed in and near the project site include mule deer (Odocoileus hemionus), eastern
cottontails (Sylvilagus floridanus), North American river otters (Lontra canadensis), and eastern
grey squirrels (Sciurus carolinensis) (iNaturalist 2024). Mammals will use the project site for
foraging either in riparian areas or in Lake Washington and May Creek.
May Creek provides tributary habitat to Lake Washington. Fall Chinook salmon (Oncorhynchus
tshawytscha), coho salmon (O. kisutch), sockeye salmon, resident costal cutthroat (O. clarki), and
steelhead (O. mykiss) are known to use May Creek (WDFW 2025b).
Lake Washington provides habitat for a wide variety of fish life, including ESA-listed species
Puget Sound Chinook salmon, Puget Sound steelhead, and Coastal-Puget Sound bull trout
(Salvelinus malma), as well as other salmonids such as coho salmon, sockeye salmon, and
resident costal cutthroat trout (WDFW 2025b, 2025a). Other native fish species that occur in the
area include freshwater sculpins (Cottus spp.) and threespine stickleback (Gasterosteus aculeatus).
Fish will use the area for foraging and migration.
Although specific surveys of the project site has not been conducted, common invasive and
non-native species known to occur in Lake Washington and/or its tributaries include New
Zealand mud snail (Potamopyrgus antipodarum), pond loach (Misgurnus anguillicaudatus),
common sunfishes (Lepomis spp.), yellow perch (Perca flavescens), largemouth bass (Micropterus
salmoides), smallmouth bass (M. dolomieu), and common carp (Cyprinus carpio carpio) (WDFW
2025c).
4.3 Trees and Vegetation Protection
Trees and vegetation will be protected using common best management practices (BMPs) as
defined in the 2024 Stormwater Management Manual for Western Washington (2024
SWMMWW) (Ecology 2024) to ensure that project work is confined to the approved work area.
Preserving Natural Vegetation (BMP C101): The purpose of preserving natural
vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the
single most effective method for reducing erosion. Natural vegetation should be
preserved on steep slopes, near perennial and intermittent watercourses or swales, and
on building sites in wooded areas. Trees and other vegetation within the work area to be
preserved during construction will be designated with high visibility fencing at a
sufficient distance to prevent soil compaction or root damage. Additionally, during
construction, the duff layer, native topsoil, and vegetation will be retained to the
maximum extent practicable.
High Visibility Fence (BMP C103): High-visibility fencing is intended to restrict
clearing and construction to the approved limits and prevent disturbance in those areas
that should be protected. Prior to beginning land disturbing activities, the work area
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limits will be clearly delineated with high visibility fencing. Additionally, any sensitive
areas and their buffers or significant trees to be retained will be marked for preservation.
Tree Protection during Construction (BMP T101): The tree protection procedures and
requirements as outlined under T101 will be completed, including:
- The submittal of a Tree Protection Plan by the project arborist outlines the location
and specifics of each significant tree (Tree Solutions 2025).
- The installation of tree protection fencing around the tree protection zone at a
sufficient distance to prevent both above- and below-ground impacts.
- The installation of mulch or woodchips in the tree protection zone.
- Long-term care and monitoring of preserved trees.
- The supervision of all tree protection activities by the Project arborist, as needed.
Additional measures to protect trees are provided in the Arborist Report (Tree Solutions 2025)
and RMC. For example, RMC 4-4-130.H.10 requires 6-foot-tall chain-link tree protection fencing
be installed at the dripline of retained trees and that the fencing be anchored in place with posts
anchored into the ground to a depth that will ensure fencing remains upright throughout the
project. Additional minimum protection measures can be found in RMC 4-4-130.H.10.
4.4 Slope Protection and Erosion Control
The project will adhere to the City’s development standards for slope protection and erosion
control. The following BMPs will be implemented as defined in the 2024 SWMMWW to ensure
that disturbed soils are stabilized:
Mulching (BMP C121): Mulching soils provides immediate temporary erosion
protection and additionally enhances plant establishment. Mulching may be used in
combination with seeding and planting.
Topsoiling/Composting (BMP C125): Topsoiling and composting provide a suitable
growth medium for final site stabilization with vegetation. Although the priority is to
retain existing native soils and duff layers, topsoil and compositing may be used where
project construction has resulted in poor soil quality.
Sodding (BMP C124): Sodding established turf for immediate erosion protection and to
stabilize drainage paths. Sod may be installed in combination with seeding and planting
to reestablish turf in the areas of existing lawn on the Project site.
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Nets and Blankets (BMP C122): Erosion control blankets will be installed on steep
slopes that are susceptible to erosion and where ground-disturbing activities have
occurred. This will prevent erosion and assist with establishment of native vegetation.
Temporary and Permanent Seeding (BMP C120): Seeding reduces erosion by
stabilizing exposed soils. Seeding may be used in combination with planting throughout
the project on disturbed areas that have reached final grade.
Plastic Covering (BMP C123): Plastic covering provides immediate, short-term erosion
protection to slopes and disturbed areas.
The following BMPs will be used during construction to reduce or control erosion and
sedimentation:
A Temporary Erosion and Sediment Control (TESC) Plan and a Source Control Plan will
be developed and implemented for all clearing, vegetation removal, grading, ditching,
filling, soil compaction, or excavation. The BMPs in the plans will be used to control
sediments from all vegetation removal or ground disturbing activities.
A Construction Stormwater Pollution Prevention Plan (CSWPPP) will be developed to
protect local water quality during construction.
The contractor will designate at least one employee as the erosion and spill control (ESC)
lead, also called a Certified Erosion and Sediment Control Lead (CESCL; BMP C160).
The CESCL will be responsible for the installation and monitoring of erosion control
measures and maintaining spill containment and control equipment. The CESCL will
also be responsible for ensuring compliance with all erosion and sediment control
requirements.
All exposed soils will be stabilized during the first available period, and no soils will
remain without stabilization for more than two days from October 1 to April 30 or for
more than seven days from May 1 to September 30.
Disturbed areas will be returned to existing or improved conditions (e.g., replanting or
repaving) as soon as practical after construction is completed.
With a limited storm drainage system along the alignment, construction site dewatering
discharge locations should be identified during the design process. Where catch basins
are not close to construction, dewatering volumes may need to be stored, removed, and
disposed of off-site.
Additional measures to protect slopes and control erosion are provided in the Geotechnical
Engineering Report (Shannon and Wilson 2024). One of the most important BMPs, particularly
during wet weather, is to immediately cover any bare soil to prevent accumulated water or
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runoff from the work area from becoming silty in the first place. In addition, the Geotechnical
Engineering Report indicates that water should not be allowed to flow uncontrolled over the
top of any temporary or permanent slope. All permanently exposed slopes should be seeded
with an appropriate species of vegetation to reduce erosion and improve the stability of the
surficial layer of soil.
Other recommendations include constructing ILS foundations on dense, unyielding native soils,
finishing excavation with a flat-nosed bucket, and replacing excavated materials with
Washington State Department of Transportation M41-10 gravel borrow material that is placed
and compacted to a dense and unyielding state (Shannon and Wilson 2024). Additional
recommendations and the results of the slope stability analysis are presented in the
Geotechnical Engineering Report. Future construction permits will include a TESC Plan
consistent with RMC 4-8.
5.0 NO NET LOSS OF ECOLOGICAL FUNCTIONS
The following information includes how the proposed project will meet the criteria of no net
loss of ecological functions as described in RMC 4-3-090(D)(2). Mitigation sequencing, as
outlined in RMC 4-3-090D(2.)(a)(iii), includes impact avoidance, minimization, mitigation, and
monitoring in that order.
The Project Narrative and Code Consistency Analysis provides information on avoidance and
minimization measures that will be used by the proposed project (Confluence 2025). Avoidance
of impacts are provided through design and proposed construction methods. The primary
avoidance measure is converting the existing Kennydale lakeline system to an upland system to
avoid potential discharge of wastewater into Lake Washington. Other BMPs, as detailed in the
Project Narrative and Code Consistency Analysis, will be used during construction to avoid or
minimize potential environmental impacts. Finally, site restoration and cleanup at the end of
construction will ensure that the project will result in primarily temporary impacts.
The following information provides additional details on no net loss of ecological functions for
each phase of the project.
5.1 Phase 1: Upland Work
Phase 1 project work will result in surface impacts, excavation of already impacted locations,
and fill to install the new land-based sewer system. Impacts are fully described in the Project
Narrative and Code Consistency Analysis (Confluence 2025). Impacts from Phase 1 in upland
areas are temporary and conditions will be restored to existing conditions post construction per
the Vegetation Management Plan (Confluence and Tree Solutions 2025). The land-based sewer
system will be installed using recommendations from the geotechnical engineers to protect
sensitive slopes and control erosion (Shannon and Wilson 2024). The only temporary loss of
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ecological functions from this work will be replacing trees, which will require time to reach full
maturity. Tree replacement will result in a temporal loss of organic matter input into the
system.
Shoreline processes such as water flow; erosion and accretion; infiltration; groundwater
recharge and discharge; sediment delivery, transport, and storage; large woody debris
recruitment; nutrient and pathogen removal; and stream channel formation/maintenance will
not be negatively impacted by Phase 1 of the project. Minor regrading of the City ROW and an
access road owned by King County Parks during installation of the sewer force main will
improve stormwater drainage and control. Overall, Phase 1 of the project will result in no net
loss of ecological functions.
5.2 Phase 2: In-Water Work
Phase 2 project work will result in minor excavation for the removal of existing manholes but
the decommissioned pipeline will be left in place to avoid excavation, disturbing sediment, and
adversely affecting sensitive habitats within the project vicinity. Impacts are fully described in
the Project Narrative and Code Consistency Analysis (Confluence 2025). The in-water locations
where there is excavation, exposed pipe, or the flush station intake pipe will receive a limited
amount of gravels to restore the area to better than existing conditions.
Upland impacts during Phase 1 include improvements at the flush station to remove the
interior components and adjacent appurtenances (the shelter, antenna, light, etc.). The above-
grade electrical/controls shelter, electrical vault, antenna, and site lighting will also be removed.
Improvement at Lift Station No. 2 include the installation of a new permanent generator and
small retaining wall. These impacts will have a net increase in impervious surface area of
approximately 500 SF.
Shoreline ecological functions such as fish and wildlife habitat, food chain support, and water
temperature maintenance will not be negatively impacted by Phase 2 of the project. The
addition of spawning gravels in small locations may enhance habitat for benthic invertebrates
and sockeye salmon spawning substrate in small 100 SF areas. The minor change in impervious
surface area at Lift Station No. 2 is associated with a location that is already surrounded by
impervious surface area and the change is considered negligible. Overall, Phase 2 of the project
will result in no net loss of ecological functions.
5.3 Summary
The Kennydale lakeline system is owned and operated by the City and provides sanitary sewer
service to Kennydale Beach Park and 56 properties along Lake Washington from the north end
of Gene Coulon Memorial Beach Park to just south of May Creek. The City concluded that the
lakeline system needs to be replaced by a land-based sewer system with grinder pumps to
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provide reliable and easily maintainable sewer service to Renton shoreline residences that
integrates with the existing sewer conveyance and pumping system and that has the least
aquatic environmental impact possible. The project is being designed and permitted per
applicable regulatory requirements, including the Renton SMP and development criteria found
in the Critical Areas Regulations per RMC 4-3-090. Once the replacement system is complete,
the existing lakeline system will be decommissioned.
This document, the Lake Study, demonstrated that the proposed project meets the criteria of no
net loss of ecological functions as described in RMC 4-3-090(D)(2). The lake assessment looked
at the ecological functions of critical areas at the project site. The project includes the use of
standard BMPs and recommendations from a certified geotechnical engineer and arborist to
protect trees, vegetation, and sensitive slopes. There are also several BMPs and
recommendations to control erosion during construction. While there are temporary changes,
the project will result in no net loss of ecological functions in the long-term.
6.0 REFERENCES
Anderson, P. S., S. Meyer, P. Olson, and E. Stockdale. 2016. Determining the Ordinary High
Water Mark for Shoreline Management Act Compliance in Washington State. Washington
State Department of Ecology. Publication Number 16-06-029.
Carrasquero, J. 2001. Over-water structures: Freshwater issues. Prepared for the Washington
Department of Fish and Wildlife, Washington Department of Ecology, and Washington
Department of Transportation. Prepared by Herrera Environmental Consultants.
Christensen, D. L., B. R. Herwig, D. E. Schindler, and S. R. Carpenter. 1996. Impacts of lakeshore
residential development on coarse woody debris in north temperate lakes. Ecological
Applications 6(4):1143–1149.
Confluence (Confluence Environmental Company). 2025. Kennydale lakeline sewer system
replacement project: Project narrative and code consistency analysis. Prepared for Carollo
Engineers, Seattle, Washington. Prepared by Confluence Environmental Company, Seattle,
Washington.
Confluence and Tree Solutions. 2025. Kennydale lakeline sewer system replacement project:
Vegetation management plan. Prepared for Carollo Engineers, Seattle, Washington.
Prepared by Confluence Environmental Company and Tree Solutions Inc., Seattle,
Washington.
DNR (Washington State Department of Natural Resources). 2024. Forest Practices Application
Mapping Tool (FPAMT) | Online Data. https://fpamt.dnr.wa.gov/2d-view#activity?-
13605823,-
13601237,6026033,6028228?WADNR_PUBLIC_FP_Trans!1!2!,WADNR_PUBLIC_FP_Hydro!
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3!1!,WADNR_PUBLIC_Public_Land_Survey!8!4!,WADNR_PUBLIC_FP_Misc!4!1!,WADNR_
PUBLIC_FP_Water_Type!1!,WADNR_PUBLIC_OCIO_Parcels!0!
Ecology (Washington State Department of Ecology). 2024. 2024 Stormwater Management
Manual for Western Washington.
Gustafson, R. G., T. C. Wainwright, G. A. Winans, F. W. Waknitz, L. T. Parker, and R. S. Waples.
1997. Status review of sockeye salmon from Washington and Oregon. NOAA Tech. Memo.
NMFS-NWFSC-33.
iNaturalist. 2024. Observations [online database with search boundary along Kennydale
Lakeline]. Available at: https://www.inaturalist.org/ (Accessed on December 10, 2024).
King County. 2024. Lake Union Monitoring Overview | On-line Information. King County,
Seattle, Washington. Available at: https://green2.kingcounty.gov/lakes/LakeUnion.aspx
(Accessed on February 28, 2024).
King County. 2025a. iMap | Online Data. King County, Seattle, Washington. Available at:
https://gismaps.kingcounty.gov/iMap/?center=-13603640%2C6028724&scale=2256.994353&
(Accessed on March 12, 2025).
King County. 2025b. Black locust identification and control - King County, Washington. King
County, Seattle, Washington. https://kingcounty.gov/en/dept/dnrp/nature-
recreation/environment-ecology-conservation/noxious-weeds/identification-control/black-
locust (Accessed on March 13, 2025).
King County and City of Renton. 2001. Final Adopted: May Creek Basin action plan. King
County, Seattle, Washington.
Renton (City of Renton). 2025. COR Maps | Online Data. City of Renton, Renton, Washington.
Available at: https://maps.rentonwa.gov/Html5viewer/Index.html?viewer=cormaps
(Accessed on March 12, 2025).
Shannon and Wilson. 2024. Draft geotechnical engineering report: Kennydale lakeline sewer
improvements, Renton, Washington. Prepared for Carollo Engineers, Seattle, Washington.
Prepared by Shannon & Wilson Inc., Seattle, Washington.
Tabor, R., K. Fresh, R. Piaskowski, H. Gearns, and D. Hayes. 2011. Habitat use by juvenile
Chinook salmon in the nearshore areas of Lake Washington: Effects of depth, lakeshore
development, substrate, and vegetation. North American Journal of Fisheries Management
31:700–713.
Tree Solutions. 2025. Arborist Report. Prepared for Carollo, Seattle, Washington, by Tree
Solutions, Seattle, Washington.
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USFWS (U.S. Fish and Wildlife Service). 2025. National Wetlands Inventory. Available at:
https://fwsprimary.wim.usgs.gov/wetlands/apps/wetlands-mapper/ (Accessed on March 12,
2025).
WDFW (Washington Department of Fish and Wildlife). 2025a. PHS on the Web. WDFW,
Olympia, Washington. Available at: https://geodataservices.wdfw.wa.gov/hp/phs-test/
(Accessed on March 12, 2025).
WDFW. 2025b. SalmonScape | Online Data. WDFW, Olympia, Washington. Available at:
https://apps.wdfw.wa.gov/salmonscape/map.html (Accessed on March 12, 2025).
WDFW. 2025c. Search for aquatic invasive species | Washington Department of Fish & Wildlife.
https://wdfw.wa.gov/species-habitats/invasive/species (Accessed on March 12, 2025).
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