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Kennydale Lakeline Sewer System Replacement Project
PROJECT NARRATIVE – GEOTECHNICAL
EXPLORATIONS
Prepared for:
Carollo Engineers, Inc.
May 2024
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
Kennydale Lakeline Sewer System Replacement Project
PROJECT NARRATIVE – GEOTECHNICAL EXPLORATIONS
Prepared for:
Carollo Engineers, Inc.
1200 Fifth Ave, Suite 900
Seattle, WA 98101
Prepared by:
Confluence Environmental Company
Marlene Meaders
Audrey Michniak
Chris Cziesla
May 2024
This report should be cited as:
Confluence (Confluence Environmental Company). 2023. Kennydale lakeline sewer system replacement project: Project
narrative – geotechnical explorations. Prepared for Carollo, Seattle, Washington, by Confluence, Seattle, Washington.
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
May 2024 Page i
TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................................................................... 1
2.0 EXISTING CONDITIONS ...................................................................................................................................... 3
2.1 Wetlands ................................................................................................................................................... 3
2.2 Streams and Lakes ................................................................................................................................... 3
2.3 Flood Hazard Areas .................................................................................................................................. 4
2.4 Steep Slopes ............................................................................................................................................ 4
2.5 Habitat Conservation Areas ...................................................................................................................... 4
2.6 Shorelines ................................................................................................................................................. 4
3.0 SCOPE OF WORK ................................................................................................................................................ 6
3.1 Geotech Best Management Practices ...................................................................................................... 8
3.2 Groundwater Monitoring Wells ................................................................................................................. 8
3.3 Timing ....................................................................................................................................................... 9
4.0 REFERENCES .................................................................................................................................................... 10
TABLES
Table 1. Proposed geotechnical boring locations and the type of surface present. ................................................. 5
Table 2. Proposed geotechnical boring locations and the depth of the boring. ........................................................ 6
FIGURES
Figure 1. Kennydale lakeline sewer system location. ................................................................................................ 2
Figure 2. Proposed Kennydale lakeline geotechnical exploration locations. ............................................................. 7
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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1.0 INTRODUCTION
The Kennydale Lakeline Sewer System (lakeline system) was constructed in 1972 to provide
sanitary sewer service to approximately 57 lakefront homes along Lake Washington from the
north end of Gene Coulon Memorial Beach Park to just south of May Creek (Figure 1). The
lakeline system consists of a flush station, an 8-inch cast iron sewer pipe buried offshore in Lake
Washington, a system of side sewer laterals connecting customers to the lakeline system, and
the Lake Washington No. 2 lift station that pumps the flow to the King County regional system.
The Kennydale lakeline system is aging and needs to be replaced to ensure long-term service
and to protect Lake Washington. In 2016, the City of Renton (the City) hired a consultant team,
led by Carollo Engineers, to evaluate the condition of the lakeline system in two phases. This
project team developed alternatives to address operation, maintenance, and reliability.
From 2016-2018, the City conducted an assessment of the Kennydale lakeline system, which
included an attempt to clean and video inspect the entire lakeline system in 2018. Due to its
location, varying water depth, and the original construction methods used, the City was only
successful in cleaning and inspecting approximately 80% of the lakeline system. As part of the
hydraulic assessment, it was concluded that the hydraulic capacity of the lakeline system is
reduced, indicative of partial blockages in two general areas. These partial blockages are likely
the result of solids settlement caused by velocities below those needed for self-cleaning, and
settlement of the lakeline over time resulting in undulating slope. Current access from the
shoreline for cleaning is limited, and settled solids cannot effectively be removed using the
shore-based cleaning protocol.
The City has come to the conclusion that a land-based grinder pump sewer system is needed
based on results from the 2018 assessment, cleaning and maintenance attempts, participation in
the in-water sewer workgroup, environmental and permitting considerations, and evaluation of
numerous alternatives. 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.
Confirming the feasibility and designing the land-based grinder pump sewer system
replacement requires geotechnical explorations and testing. Five borings are proposed along the
shoreline (Figure 2). This document provides information for geotechnical exploration of the
project site to design the lakeline system replacement.
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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Figure 1. Kennydale lakeline sewer system location.
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2.0 EXISTING CONDITIONS
The following information includes existing conditions based on a desktop analysis and
background research on the project site to understand existing conditions and location of critical
areas in relation to the proposed geotechnical explorations. The methods used to identify critical
areas satisfy the information needs identified under Renton Municipal Code (RMC) 4-3-050B
and RMC 4-3-090B.
2.1 Wetlands
Based on global information system (GIS) data, no wetlands are within 300 feet of the lakeline
system (King County 2024; Renton 2024; USFWS 2024; WDFW 2024a).
2.2 Streams and Lakes
No streams are located within the lakeline system. However, May Creek is located just 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 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 and discharges into Lake Washington just north of
the Lake Washington #2 Lift Station. May Creek provides high quality tributary habitat to Lake
Washington. However, 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). Fall Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch),
sockeye salmon (O. nerka), resident costal cutthroat (O. clarki), and steelhead (O. mykiss) are
known to use May Creek (WDFW 2024b).
Lake Washington provides habitat for a wide variety of fish life, including Endangered Species
Act (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 2024b, 2024a). A distinct population
of sockeye salmon spawn on Lake Washington beaches. Spawning takes place in Lake
Washington wherever suitable gravel beaches with upwelling are available (Gustafson et al.
1997; WDFW 2024c). A majority of the lakeline system has been mapped as sockeye spawning
habitat based on suitable gravels and historical spawning activity (WDFW unknown date), but
the geotechnical explorations will all be above the ordinary high water mark (OHWM) of Lake
Washington and will not overlap with salmonid habitat.
Water quality within Lake Washington along the areas that overlaps with the lakeline system is
not on the Washington State Department of Ecology (Ecology) 303(d) list (Ecology 2024a).
However, just offshore of Coleman Point, a portion of Lake Washington is classified as
Category 1 for bacteria and total phosphorus and a Category 2 for 4,4’-DDD, 4,4’-DDE, methyl
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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mercury, and polychlorinated biphenyls (PCBs) (Ecology 2024a). A Category 1 is designated
when an area meets the standards for clean waters. Placement of a waterbody in Category 1
does not necessarily mean that a water body is free of all pollutants, just that it meets the
standards for all the pollutants for which it was tested. A Category 2 is designated when an area
is of concern. These areas have some evidence of water quality problems but not enough to
require production of a water quality improvement project.
Just north of lakeline system (north of May Creek), a portion of Lake Washington is classified as
Category 2 for PCBs and as a Category 1 for bacteria and total phosphorus. The same area north
of May Creek is on the 303(d) list for sediment because sediment bioassays, arsenic, high
molecular weight polycyclic aromatic hydrocarbons (HPAHs), low molecular weight polycyclic
aromatic hydrocarbons (LPAHs), and phenol failed to meet the standards. Category 5 is
designated when polluted waters/sediments are present (i.e., on the 303(d) list).
2.3 Flood Hazard Areas
Based Renton (2024) GIS data, no flood hazard areas are within 300 feet of the lakeline system.
2.4 Steep Slopes
Slopes along the shoreline 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 (Renton 2024).
2.5 Habitat Conservation Areas
No wildlife habitat corridors or priority species sites were identified along the lakeline system
(WDFW 2024a).
2.6 Shorelines
The shoreline of Lake Washington is designated as a Shoreline of the State as defined by RMC
4-3-090B(1a). As such, the shoreline is defined as 200 feet landward of the OHWM of Lake
Washington. The OHWM of Lake Washington is 18.6 feet elevation according to North
American Vertical Datum of 1988 (NAVD 88).
There is approximately 4,670 linear feet of shoreline along the lakeline system. The shoreline in
this area is highly modified with approximately 4,370 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. There are also overwater structures are present throughout the shoreline
along the lakeline system corridor (Ecology 2024b). Overwater structures consist primarily of
docks associated with single-family residences. A log boom delineating the designated
swimming area at Kennydale Beach Park is also present.
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Riparian vegetation along the lakeline system is primarily lawn and ornamental shrubs, with
scatted trees. The riparian vegetation provides little shading over the nearshore waters. The
exception to this are the riparian areas just north of the house at 3307 Lake Washington
Boulevard and the shoreline associated with 3827 Lake Washington Boulevard. On these lots,
there are existing mature trees and shrubs that extend over the nearshore water, providing
shade, cover, and insect drop into the lake.
Proposed geotechnical borings are located in upland areas either in the City ROW, King County
ROW, or other public property (Table 1). All proposed geotechnical boring locations and access
routes are located on asphalt or graveled surfaces and no vegetation overlaps with where the
borings are proposed.
Table 1. Proposed geotechnical boring locations and the type of surface present.
Exploration Parcel Location Surface Present
B-1 King County Parcel Access Road Asphalt
B-2 King County Parcel Access Road Asphalt
B-3 City of Renton ROW City ROW near 3500 Burnett Ave N Asphalt
B-4 City of Renton ROW Lake Washington Blvd Asphalt
B-5 King County Parcel Mt. View Ave Parking Area Compacted Gravel
Source: Shannon & Wilson 2024
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3.0 SCOPE OF WORK
The proposed work includes geotechnical exploration using borings to aid design of the project.
There would be a total of 5 borings located along the shoreline (Figure 2). The equipment, work
area, access considerations, and duration of drilling for each boring location is described below.
The proposed borings avoid work below the OHWM of Lake Washington (i.e., no in-water
work). Aside from overlapping with the shoreline zone, no other critical areas will be impacted
during geotechnical explorations. All borings are proposed through asphalt or gravel and no
vegetation will be disturbed.
Proposed geotechnical borings will be advanced using a track-mounted Acker Recon drill rig
and mud-rotary drilling methods to a depth of 15 feet to 25 feet below ground surface (Table 2).
Soil samples will be obtained in conjunction with standard penetration tests at 2.5-foot intervals.
Each boring will include an observation well for measuring groundwater depths. A vibrating
wire piezometer will be installed at each boring location to monitor water levels continuously
for the duration of the project.
Table 2. Proposed geotechnical boring locations and the depth of the boring.
Exploration Parcel Location Purpose Total Depth Below
Ground (feet)
B-1 King County Parcel Access Road Force main trench 15
B-2 King County Parcel Access Road Grinder pumps 15
B-3 City of Renton ROW City Parcel at 3500 Burnett Ave N Retaining wall 25
B-4 City of Renton ROW Lake Washington Blvd Force main trench 15
B-5 King County ROW Mt. View Ave Parking Area Force main trench 15
Source: Shannon & Wilson 2024
Access to the boring locations will be via City- or King County-owned parcels and public ROW
(refer to Site Plan Fig. 2-6). Most staging areas will be at the same location as the borings. Due to
the location of nearby residences, B-1 will likely be staged from the B-2 location. The boring will
require a work area that is approximately 20 feet wide by 50 feet long (~1,000 square feet). In
addition to the work area for the boring, the following will be needed:
▪ Blocking to protect the curb during mobilization and to level the drill rig.
▪ Mats or plywood to protect the ground from rutting,
▪ Plastic sheeting beneath the mud tank to protect from mud leakage.
▪ Straw wattles around the mud tank to protect from mud leakage.
▪ Absorbent pads beneath the drill rig to protect from oil and hydraulic fluid leakage.
▪ Four (4) 50-gallon barrels to contain drill cuttings and drilling mud.
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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Figure 2. Proposed Kennydale lakeline geotechnical exploration locations.
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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3.1 Geotech Best Management Practices
Best management practices (BMPs) that will be implemented to protect critical areas and buffers
include:
▪ Project staging and storage areas will be located in currently developed areas, such as
City ROWs adjacent to each boring location.
▪ All equipment to be used for construction activities will be cleaned and inspected prior
to arriving at the project site to ensure no potentially hazardous materials are exposed,
no leaks are present, and the equipment is functioning properly.
▪ Construction equipment will be inspected daily to ensure there are no leaks of hydraulic
fluids, fuel, lubricants, or other petroleum products. Absorbent pads will be placed
beneath equipment to catch any leakage. Should a leak be detected on heavy equipment
used for the project, the work will immediately cease and will not be used again until
repaired.
▪ Construction equipment will not enter Lake Washington below the OHWM.
▪ The contractor will designate at least one employee as the erosion and spill control (ESC)
lead. The ESC lead will be responsible for the installation and monitoring of erosion
control measures and maintaining spill containment and control equipment. The ESC
lead will also be responsible for ensuring compliance with all local, state, and federal
erosion and sediment control requirements.
▪ Plastic sheeting and straw wattles will be utilized along the downslope edge of ground
disturbing activities and around the mud tank to intercept sediment transported by
water runoff prior to entering surface waters.
▪ All temporary erosion and sedimentation control measures will be inspected,
maintained, and repaired for the duration of the field investigation program to ensure
continued performance of their intended function. Straw wattles will be inspected
immediately after each rainfall, and at least daily during prolonged rainfall. Sediment
will be removed as it collects behind the straw wattles.
▪ Should any BMPs not function as intended, additional actions will be made to minimize
erosion, maintain water quality, and achieve the intended environmental performance.
▪ Thinners and solvents will not be used to wash oil, grease, or similar substances from
heavy machinery or machine parts.
▪ All fueling and maintenance of equipment will occur more than 300 feet from the
nearest wetland, ditches, flowing or standing water unless it is within an existing
parking lot.
3.2 Groundwater Monitoring Wells
Five wells will be installed in the boring locations. Each well will have a vibrating wire
piezometer installed to monitor water levels continuously for the project duration. During
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
May 2024 Page 9
design, the wells will be accessed for monitoring once every 3 months (seasonally). The wells
will be decommissioned by the contractor. The wells will be decommissioned in accordance
with the requirements of Washington Administrative Code (WAC) 173-160 by backfilling with
either bentonite chips or bentonite slurry.
3.3 Timing
Geotechnical explorations will occur as soon as the permits are obtained. A King County Special
Use Permit is concurrently under review. This work is anticipated to take approximately 2 days
to complete.
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4.0 REFERENCES
DNR (Washington Department of Natural Resources). 2024. Forest practices application
mapping tool, water type maps | Online Data. DNR, Olympia, Washington. Available at
https://fpamt.dnr.wa.gov/2d-view#activity?-13605823,-
13601237,6026033,6028228?WADNR_PUBLIC_FP_Trans!1!2!,WADNR_PUBLIC_FP_Hydro!
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! (accessed April 9, 2024).
Ecology (Washington State Department of Ecology). 2024a. Water Quality Atlas - Map | Online
Data. Ecology, Olympia, Washington. Available at
https://apps.ecology.wa.gov/waterqualityatlas/wqa/map?CustomMap=y&BBox=-
14338616,5395963,-12562831,6503994&RT=0&Layers=27&Filters=y,n,n,n,n,n (accessed April
9, 2024).
Ecology. 2024b. Coastal Atlas - Map | Online Data. Ecology, Olympia, Washington. Available at
https://apps.ecology.wa.gov/coastalatlasmap (accessed April 9, 2024).
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.
King County and City of Renton. 2001. Final Adopted: May Creek Basin action plan. King
County, Seattle, Washington. Contributions from the City of Renton. Available at
https://your.kingcounty.gov/dnrp/library/2001/kcr726.pdf (accessed April 9, 2024).
King County. 2024. iMAP | Online Data. King County, Seattle, Washington. Available at
http://gismaps.kingcounty.gov/iMap/?center=-13603640%2C6028724&scale=2256.994353&
(accessed April 9, 2024).
Renton (City of Renton). 2024. COR Maps | Online Data. City of Renton, Renton, Washington.
Available at https://maps.rentonwa.gov/Html5viewer/Index.html?viewer=cormaps
(accessed April 9, 2024).
Shannon & Wilson. 2024. Revised Proposed Exploration Plan. Kennydale Lakeline Replacement,
Renton, Washington.
USFWS (US Fish and Wildlife Service). 2024. National wetland inventory: Surface waters and
wetlands | Online Data. USFWS, Washington, D.C. Available at
https://fwsprimary.wim.usgs.gov/wetlands/apps/wetlands-mapper/ (accessed April 9,
2024).
Kennydale Lakeline Sewer System Replacement Project: Project narrative – Geotechnical Explorations
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WDFW (Washington Department of Fish and Wildlife). 2024a. PHS on the web | Online Data.
WDFW, Olympia, Washington. Available at https://geodataservices.wdfw.wa.gov/hp/phs/
(accessed April 9, 2024).
WDFW (Washington Department of Fish and Wildlife). 2024b. SalmonScape | Online Data.
WDFW, Olympia, Washington. Available at
https://apps.wdfw.wa.gov/salmonscape/map.html (accessed April 9, 2024).
WDFW (Washington Department of Fish and Wildlife). 2024c. Lake Washington beach
spawning sockeye | Online Data. WDFW, Olympia, Washington. Available at https://
https://fortress.wa.gov/dfw/score/score/species/population_details.jsp?stockId=5300
(accessed April 9, 2024).