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C RITICAL A REAS R EPORT
THUNDER HILLS SANITARY SEWER LINE – RENTON, WA
Prepared for:
Stantec Consulting Services Inc.
11130 NE 33rd Place
Suite 200
Bellevue, WA 98004
Prepared by:
April 2018
The Watershed Company Contact Person:
Tess Brandon, AICP
The Watershed Company Reference Number:
131113
Cite this document as:
The Watershed Company. April 2018. Critical Areas Report: Thunder Hills
Sanitary Sewer Line – Renton, WA. Prepared for Stantec Consulting Services Inc.,
Bellevue, WA.
1
T ABLE OF C ONTENTS
Page #
1 Introduction ........................................................................................................ 1
2 Methods.............................................................................................................. 2
3 Existing Conditions .............................................................................................. 2
3.1 Setting ....................................................................................................................2
3.2 Streams ..................................................................................................................3
3.3 Wetlands ................................................................................................................5
3.4 Habitat ...................................................................................................................5
3.4.1 Vegetation .................................................................................................................. 5
3.4.2 Fish and Wildlife ......................................................................................................... 6
4 Project Description .............................................................................................. 6
5 Relevant Critical Area Standards .......................................................................... 7
6 Impacts and Mitigation ...................................................................................... 10
6.1 Proposed Project Impacts ...................................................................................... 10
6.2 Proposed Mitigation Approach .............................................................................. 11
7 Summary ........................................................................................................... 13
8 Limitations ........................................................................................................ 13
References ................................................................................................................ 14
L IST OF E XHIBITS
Figure 1. Approximate project area and vicinity in Renton, WA. .................................................... 1
Figure 2. Access trail adjacent to Thunder Hills Creek. ................................................................... 3
Figure 3. Gabions along stream bank facing downstream toward the Interstate 405 culvert inlet.
............................................................................................................................... 4
Figure 4. Placed rock approximately 500 feet upstream of Interstate 405 forms a falls and
cascades which constitute a clear fish migration barrier. ..................................... 4
Figure 5. Non-native ivy along the channel mid-project. ................................................................ 6
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C RITICAL A REAS R EPORT
T HUNDER H ILLS S ANITARY S EWER L INE – R ENTON, WA
1 I NTRODUCTION
The City of Renton seeks to rehabilitate and partially relocate the Thunder Hills Sanitary Sewer
Interceptor and repair maintenance access. The purpose of this report is to document potential
critical area impacts and mitigation associated with the project. The proposed work is located in
the Thunder Hills Creek corridor from Grant Avenue South at its upstream end to Interstate 405
(Figure 1). The applicant proposes to improve system components and access for the sanitary
sewer interceptor through a combination of Cured-In-Place-Pipe (CIPP) technologies and
relocation of existing sewer line segments away from the creek.
Figure 1. Approximate project area and vicinity in Renton, WA.
Renton Municipal Code (RMC) Chapters 4-3-050 and 4-8-120 require compliance with specific
criteria as part of any modification to a critical area. This report discusses project compliance
with those criteria. The report presents a discussion of critical areas, habitat, and vegetation on-
site and how the proposed project can be achieved with no net loss of critical area functions and
values.
Project area
2
2 METHODS
Public-domain information was reviewed for this critical areas study. Sources include U.S.
Department of Agriculture’s (USDA) Natural Resources Conservation Service Soil maps, U.S.
Fish and Wildlife Service (USFWS) National Wetland Inventory maps, Washington Department
of Fish and Wildlife’s (WDFW) interactive mapping programs (SalmonScape, PHS on the Web),
City of Renton’s Mapping Applications (COR Maps), and King County’s GIS mapping website
(iMAP).
Ecologists Katy Crandall and Mike Foster, PWS, visited the project area on April 23 and 29 and
May 1 and 12, 2014 and delineated wetlands and streams on site. Boundaries and classifications
were verified in the field by senior ecologist Hugh Mortensen, PWS. Wetland areas were
evaluated and delineated using methodology from the Regional Supplement to the Corps of
Engineers Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region Version 2.0
(Regional Supplement) (Corps 2010). Delineated wetlands were initially classified using the
Washington State wetland rating system for Western Washington (Hruby 2004), and were then
updated based on the 2014 rating system (Hruby 2014).
The ordinary high water mark (OHWM) of streams within the project area was determined
based on the definition provided by WAC 173-22-030(11). The OHWM is located by examining
the bed and bank physical characteristics and vegetation to determine the water elevation for
mean annual floods. Field observations and published information were used to classify
streams according to Renton Municipal Code RMC 4-3-050, adopted June 1, 2015.
Detailed wetland and stream delineation and classification information is provided in Stream &
Wetland Delineation Report: Thunder Hills Sanitary Sewer Interceptor Alternatives Analysis, Renton,
WA (The Watershed Company 2015).
Additional site visits were conducted to assess current site conditions by Fisheries Biologist
Greg Johnston on January 24, 2017, and again accompanied by Water Resources Engineers Ed
McCarthy and Logan McClish on May 30, 2017.
3 E XISTING C ONDITIONS
3.1 Setting
The project area is located along approximately 3,600 lineal feet of Thunder Hills Creek in
Renton, WA, in the Black River sub-basin of the Duwamish-Green Watershed. The project area
is mostly a forested ravine, through which Thunder Hills Creek flows. Power line corridors
transect the project area in four locations. Vegetation in these corridors is disturbed grass or
scrub-shrub often containing significant amounts of invasive plant species. There is a trail used
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by pedestrians adjacent to the creek through most of the project area (Figure 2). Land uses along
and adjacent to the wooded Thunder Hills Creek ravine consist primarily of multifamily
residential development, but the ravine is also crossed by two Puget Sound Energy
transmission line corridors. While various property easements are in place, the entire corridor is
in multiple private ownerships.
Figure 2. Access trail adjacent to Thunder Hills Creek.
3.2 Streams
Thunder Hills Creek is a perennial stream that flows north-northwest through the entire project
area. Bed and bank armoring have been placed along significant portions of the stream channel
in an effort to prevent erosion. Large, loose riprap occurs throughout the channel, and gabion
baskets armor sections in the northern (downstream) portion of the project area (Figure 3).
According to City of Renton Maps, SalmonScape, and PHS online mapping and data sources,
this section of Thunder Hills Creek is not used by salmonid fish species. A total fish passage
barrier is located at the downstream end of the project area due to an impassable culvert under
Interstate 405. Additional barriers occur within the project area, most notably a series of
historically-manipulated falls and cascades resulting from large amounts of rock placed along
the ravine bottom approximately 500-600 feet upstream of Interstate 405 (Figure 4).
Seven small tributary streams join Thunder Hills Creek along its course through the project
area. All are presumed seasonally flowing streams. It is also presumed that all tributary streams
do not contain salmonid fish species due to a combination of narrow channels, steep grades, a
lack of connectivity with salmon-bearing streams downstream and a lack of resident fish habitat
upstream.
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Detailed information on streams delineated in the project area, and a map of all delineated
features, are provided in the Stream & Wetland Delineation Report (The Watershed Company
2015).
Figure 3. Gabions along stream bank facing downstream toward the
Interstate 405 culvert inlet.
Figure 4. Placed rock approximately 500 feet upstream of Interstate 405
forms a falls and cascades which constitute a clear fish migration barrier.
5
3.3 Wetlands
Six small wetlands were delineated in the project area and were named alphabetically based on
location along the creek, from upstream to downstream. A summary of these wetlands is
provided in Table 1. All wetlands are located adjacent to Thunder Hills Creek, with the
exception of Wetland A, which is collocated with the tributary stream (Stream E) at the
upstream end of the project area.
Table 1. Summary of wetlands delineated in the project area*
Name Rating HGM Class Habitat Score Total Score
Wetland A Category III Slope/depressional 4 17
Wetland B Category III Riverine 6 19
Wetland C Category IV Slope 5 14
Wetland D Category III Riverine 5 18
Wetland E Category III Depressional 5 17
Wetland F Category III Slope 5 16
* Wetlands rated using the Washington State Department of Ecology Western Washington Wetland Rating System
(2014).
Detailed information on wetlands delineated in the project area, and a map of all delineated
features, are provided in the Stream & Wetland Delineation Report (The Watershed Company
2015).
Two additional, unconfirmed wetlands were mapped by the project surveyor. Both are outside
the immediate project area, will not incur direct impacts, and share portions of some buffers
with Thunder Hills Creek and other project-area wetlands. For these reasons, these wetland
areas will not be discussed further in this report.
3.4 Habitat
3.4.1 Vegetation
Non-wetland areas are dominated mainly by a native deciduous forest with a few coniferous
trees. The forest has an understory that includes typical shade-tolerant native shrubs and
groundcovers. Patches of locally-dominant invasive weeds such as Himalayan blackberry and
English ivy are also present throughout the forest (Figure 5). Dense monoculture of Himalayan
blackberry and Japanese knotweed predominate where power transmission lines cross the
stream and along forested edges.
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Figure 5. Non-native ivy along the channel mid-project.
3.4.2 Fish and Wildlife
No priority habitats or species have been mapped or field identified within the project area.
Thunder Hills Creek within the project area does not include suitable habitat for salmonids.
This lack of suitable habitat for these species is due to its small size and headwater location, the
presence of migration barriers and obstacles within and downstream of the project area
(including several extensive piped stream sections), and its location upstream of the Black River
Pump Station where fish passage facilities are present but are of questionable effectiveness.
The project area does not include any designated or proposed critical habitat for any species
listed under the Endangered Species Act (ESA). Information on potential site use by ESA-listed
species and potential project impacts is provided in more detail in the No Effect Letter Report for
ESA-Listed Species: Thunder Hills Sewer Interceptor Rehabilitation (The Watershed Company
2017a).
4 P ROJECT D ESCRIPTION
Thunder Hills Sanitary Sewer Interceptor was installed in 1965 and, like many sewer projects of
that time, was installed in a stream valley to take advantage of favorable gravity-flow
conditions. It consists of approximately 3,600 lineal feet of 10-inch to 18-inch concrete pipe that
runs beneath or adjacent to Thunder Hills Creek. The depth of the pipe varies, and may be
greater than 30 feet in some areas. Access to the existing sewer has deteriorated and the ability
to inspect, maintain, and repair the line is hampered. Erosion along the creek has compromised
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the sewer interceptor in the past; portions of the stream bank were stabilized with gabion
baskets in the early 1980s, and emergency repairs that used large quantities of rip-rap armoring
were done in 2008 and 2009.
The project area is located along the sewer interceptor between stations 1+00 at the north to
30+83.82 at the south. Along this corridor, the City proposes to improve system components
and access for the sanitary sewer interceptor through a combination of Cured-In-Place-Pipe
(CIPP) technologies and construction of replacement sewer line segments. From the northern
end of the project area south, proposed improvements include enlarging an equipment
turnaround at Station 6+50 1 and improvements to access paths along the project alignment. A
new parallel sewer will be installed from approximately Station 3+28 to 11+20 and 13+08 to
15+44 underneath the new/improved access roads. The remaining portion of the existing sewer
will be rehabilitated in place using CIPP technology. Rockeries will be rebuilt, as well as new
rockeries constructed to protect the existing/new sewer and access road.
5 RELEVANT C RITICAL AREA S TANDARDS
This section identifies standards within the RMC that apply to the proposed project, and
discusses how the project meets or addresses those standards, as appropriate.
Stream and Wetland Buffers (RMC 4-3-050.G)
Streams in the City of Renton are classified using the State’s Permanent Water Typing System
(WAC 222-16-030) (RMC 4-3-050.G.7.a). Using this classification system, Thunder Hills Creek is
classified as a Type Np stream and has a standard buffer of 75 feet (RMC 4-3-050.G.2). The
seven tributary streams in the project area are all designated as Type Ns streams and have
standard buffers of 50 feet (RMC 4-3-050.G.2).
Wetland buffer widths are determined based on wetland category, habitat score, and land use
intensity (RMC 4-3-050.G.2). Of the six wetlands delineated in the project area, four (Wetlands
B, D, E, and F) have a standard buffer of 100 feet. Wetland A has a standard buffer of 75 feet,
and Wetland C has a standard buffer of 50 feet.
The existing sanitary sewer interceptor is located parallel to Thunder Hills Creek and is entirely
within the combined wetland and stream buffers in the project area. As such, it is classified as a
nonconforming structure under RMC 4-3-050.C.6 and is subject to the provisions of RMC 4-10-
090, “Critical Areas Regulations – Nonconforming Activities and Structures.” That section states
that a legally nonconforming, regulated activity or structure may continue, provided that any
expansion or alteration to the activity or structure that increases the extent of its nonconformity
obtain a permit pursuant to the provisions of RMC 4-3-050.
1 Station numbers refer to location markers found on project site plan drawings.
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Where new pipe segments are proposed, they will be located within the footprint of access
roads. In some areas vegetation has encroached upon these existing access roads/trails. As a
result, some new, unavoidable impacts to the combined wetland and stream buffers will occur.
These impacts, and the proposed mitigation approach, are discussed in more detail in Chapter
6.
Criteria for Permit Approval – Type F, Np, and Ns Streams (RMC 4-3-050.G.7.e)
RMC 4-3-050.G.7.e defines conditions for permit approval for projects on or near regulated
Type F, Np, and Ns water bodies, including the following condition applicable to the proposed
project:
ii. A proposed action meets alternative administrative standards pursuant to this Section and the
proposed activity results in no net loss of regulated riparian area or shoreline ecological function in the
drainage basin where the site is located.
Thunder Hills Creek is not a shoreline of the state, therefore the relevant standard in this
case is “no net loss of regulated riparian area.” Section 6.2 of this report describes the
project approach to mitigation in order to achieve no net loss of critical area functions and
values, including riparian area.
Alterations to Critical Areas (RMC 4-3-050.J)
RMC 4-3-050.J.2.b provides the following criteria for administrative approval of new utilities in
streams, lakes, and buffers with an approved critical area study:
i. Fish and wildlife habitat areas shall be avoided to the maximum extent possible;
As described in Section 3.4.2, the project area does not contain any mapped priority
habitat or critical habitat for sensitive species. Due to their existing location within
combined wetland and stream buffers, improvements to the interceptor and access roads
cannot avoid these buffer areas entirely. However, sections of the existing sewer main will
be rehabilitated using CIPP technologies where the interceptor crosses the stream in order
to avoid direct stream impacts. Where new pipe segments are proposed, they will be
located within the footprint of and beneath the access roads.
ii. The utility is designed consistent with one or more of the following methods:
(a) Installation shall be accomplished by boring beneath the scour depth and hyporheic zone of the water
body and channel migration zone; or
(b) The utilities shall cross at an angle greater than sixty (60) degrees to the centerline of the channel in
streams or perpendicular to the channel centerline; or
(c) Crossings shall be contained within the footprint of an existing road or utility crossing;
The proposed improvements will not affect the existing Thunder Hills Creek crossing
location or orientation of the sanitary sewer interceptor. Where the interceptor crosses the
stream, repairs will be conducted using CIPP technologies and will take place entirely
within the existing interceptor. The proposed improvements therefore comply with
provision (c), and are contained within the footprint of an existing utility crossing.
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iii. New utility routes shall avoid paralleling the stream or following a down-valley course near the
channel;
Due to the alignment of the existing sewer main and the necessity to maintain connectivity
and gravity flow, the proposed improvements and new pipe segments cannot entirely
avoid an alignment parallel to Thunder Hills Creek. To minimize impacts from these new
pipe segments where they are proposed, the segments are located farther from the stream
than the existing pipe and within the footprint of the improved access.
iv. The utility installation shall not increase or decrease the natural rate of shore migration or channel
migration;
Much of the length of the stream is already topographically constrained within a narrow
valley. As described in Chapter 3, bed and bank armoring have been placed along
significant portions of the Thunder Hills Creek stream channel in an effort to prevent
erosion. Large, loose riprap occurs throughout the channel, and gabion baskets armor
sections in the northern (downstream) portion of the project area. No new armoring will
be constructed on unarmored segments of the stream bank, and overall the proposed
improvements will not affect the natural rate of channel migration.
v. Seasonal work windows are determined and made a condition of approval;
The standard Army Corps of Engineers (Corps) construction work window for King
County streams is July 1 to September 30. A Hydraulic Project Approval (HPA) from the
Washington Department of Fish and Wildlife (WDFW) will include a similar timing
restriction. The City of Renton plans to comply with both the Corps and WDFW work
windows by completing construction work between July 1 and September 30, or as
allowed or further restricted by permitting conditions including City of Renton permits.
vi. Mitigation criteria of subsection L of this Section are met.
Section 6.2 of this report describes the project approach to mitigation, including mitigation
sequencing.
RMC 4-3-050.J.4 provides the following criteria for approval of alterations to wetlands, and
details mitigation procedures for impacts to wetlands:
a. No Net Loss: Activities that adversely affect wetlands and/or wetland buffers shall include mitigation
sufficient to achieve no net loss of wetland function and acreage and to achieve, where practicable, a net
resource gain in wetlands over present conditions. The concept of “no net loss” means to create, restore
and/or enhance a wetland so that there is no reduction to total wetland acreage and/or function.
Section 6.2 of this report describes the project approach to mitigation, including mitigation
of wetland impacts.
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6 I MPACTS AND M ITIGATION
6.1 Proposed Project Impacts
Construction associated with the proposed sewer interceptor rehabilitation will result in some
disturbance to streams, wetlands, and their associated buffers. Impacts from proposed project
activities include temporary impacts from construction, direct wetland impacts from access
road improvements, and impacts to the combined wetland/stream buffers from access. Impact
areas are shown on project site plan drawings submitted with this report.
The sewer interceptor rehabilitation work itself does not include in-water work and will not
result in adverse stream impacts. Habitat enhancement work requested by WDFW and the
Muckleshoot Tribe includes the placement of in-stream large woody debris, discussed in more
detail in Section 6.2.
Temporary Impacts
Temporary impacts include vegetation clearing associated with construction work areas,
including equipment staging and access. Temporary combined wetland and stream buffer
impacts will occur adjacent to the access roads throughout the project area, for a total of 20,703
square feet.
Direct Wetland Impacts
Direct wetland impacts include placement of a gravel access road within Wetland F, and
construction of a new gravel turnaround that extends partially into Wetland E at the
southernmost extent of the project area. These direct wetland impacts total 1,332 square feet.
Combined Buffer Impacts
Permanent buffer impacts will occur as a result of the new gravel access roads that extend
parallel to Thunder Hills Creek throughout the project area. Impacts are limited to the footprint
of the new roads and total 41,000 square feet.
Tree Removal
The impacts described above, including temporary, direct wetland, and combined buffer
impacts, will involve tree removal where trees are located within proposed clearing and
grading limits. A total of 36 trees are proposed for removal (Table 2). Please refer to the site plan
drawings for the location of each individual tree within the project area.
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Table 2. Summary of trees proposed for removal.
Common Name Species Name
Deciduous (D) /
Coniferous (C)
Diameter
at Breast
Height (in.) Count
Bigleaf maple Acer macrophyllum D 12 3
16 2
18 6
20 1
24 1
Cottonwood Populus balsamifera D 12 2
20 1
22 1
24 1
36 1
44 1
Douglas fir Pseudotsuga menziesii C 30 1
36 1
Red alder Alnus rubra D 12 1
14 1
Western red cedar Thuja plicata C 12 1
16 4
20 2
Unknown deciduous Unknown D 8 1
10 3
12 1
6.2 Proposed Mitigation Approach
RMC 4-3-050.L.1.b requires an analysis of mitigation sequencing for proposed non-exempt
alterations to critical areas. The following describes the proposed mitigation approach,
including avoidance, minimization, rectification, compensation, and monitoring of adverse
impacts. Details of this approach are provided on the mitigation plan drawing set.
Avoid
Proposed avoidance measures for this project include:
• Using existing access points to avoid the need for new stream crossings; and
• Using CIPP technologies to rehabilitate the existing sewer interceptor where it crosses
Thunder Hills Creek.
Minimize
Proposed minimization measures for this project include:
• Where replacement pipe segments are proposed, construction those segments under the
access road to minimize the footprint of construction and maintenance impacts;
• Locating the improved access roads over the existing overgrown access road to
minimize impacts to vegetation in the combined wetland and stream buffer;
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• Locating the improved access roads as far from the stream as possible, given
topographic constraints;
• Using specialized maintenance vehicles and equipment on the northern portion of the
project area, which allows a narrower width path (seven feet compared to 12-foot road)
for maintenance access;
• Implementing a Temporary Erosion and Sediment Control plan, provided with the
project site plan drawings; and
• Timing construction to avoid the wet season when sedimentation and erosion would be
anticipated.
Rectify
All temporary impacts, including direct wetland impacts and buffer impacts, will be mitigated
in-place through planting of native vegetation in order to restore those areas to pre-project
conditions.
Compensate
RMC 4-3-050(L)(1)(d) requires that unavoidable impacts be compensated on site unless
demonstrated to be scientifically infeasible due to physical features of the property. When
mitigation cannot be provided on site, it must be provided “in the immediate vicinity of the
permitted activity on property owned or controlled by the applicant” (RMC 4-3-050(L)(1)(d)(ii)).
Permanent impacts to combined stream/wetland buffers will therefore be compensated within
the project area at a ratio of approximately one-to-one. 42,945 square feet of existing buffer will
be enhanced through removal of invasive vegetation, planting of native vegetation, and
monitoring and maintenance of planted vegetation until establishment.
Given the steep nature of the project site and the lack of public ownership, on-site compensation
for direct wetland impacts is not feasible. Use of a wetland mitigation bank is allowed for
wetland impacts under RMC 4-3-050(G)(9)(e) where on-site compensation is not feasible, and
where the bank better meets established reginal goals for wetland functions. Direct wetland
impacts from the project will therefore be compensated through the purchase of credits from
the City of Renton’s approved mitigation bank on Springbrook Creek. The details of this
purchase and mitigation approach are provided in Thunder Hills Creek Sanitary Sewer
Rehabilitation Mitigation Bank Use Plan (The Watershed Company 2017b).
Although no direct stream impacts are proposed and the project area does not include fish-
bearing streams, the project area is within the designated Usual and Accustomed fishing
grounds of the Muckleshoot Tribe. As a result of input from the Muckleshoot Tribe and agency
consultation, the project proposes placement of large wood in Thunder Hills Creek to enhance
fish habitat should the existing fish passage barriers be corrected and fish use in the creek
resumed in the future. Large wood will include nine logs, rootwad, and treetop sections along
the lower section of creek, extending approximately 250 feet upstream from the Interstate 405
culvert inlet.
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Monitor
A five-year monitoring plan is proposed to ensure success of all required planting that was
installed to rectify or mitigate adverse impacts. Maintenance and corrective actions will be
conducted as necessary based on monitoring results over time.
7 S UMMARY
The City of Renton proposes to rehabilitate an existing sanitary sewer interceptor along
Thunder Hills Creek. Improvements to the sewer will include a combination of CIPP
technologies and construction of replacement sewer line segments, as well as repair of the
existing access roads. The project area is located in a forested ravine that contains the creek as
well as several tributary streams and wetlands. Proposed replacement sewer line segments will
be located farther from the creek than the existing line and directly beneath new/improved
access roads, which will utilize the footprint of existing disturbed access routes. Where the
sewer line crosses the creek, CIPP technologies will be used for sewer rehabilitation in order to
ensure no direct stream impacts. The project will result in both temporary and permanent
impacts to wetlands and combined wetland/stream buffers. Temporary impacts will be
mitigated on-site. Permanent buffer impacts will be mitigated on-site at a one-to-one ratio
through buffer enhancement, while permanent wetland impacts will be mitigated through
purchase of credits from the City of Renton’s Springbrook Creek mitigation bank. Additionally,
large wood will be installed in the creek bed to enhance fish habitat should fish use be restored
in the future. As a whole, the proposed project avoids, minimizes, and compensates for adverse
impacts to on-site critical areas to the extent feasible, while enhancing wetland functions in the
City through use of the mitigation bank. On balance, the project is consistent with the City of
Renton’s goal to achieve no net loss of on-site or off-site critical area functions and values.
8 LIMITATIONS
The information contained in this report is based on the application of technical guidelines
currently accepted as the best available science and in conjunction with the manuals and criteria
outlined in this document. All discussions, conclusions, and recommendations reflect the best
professional judgment of the author(s) and are based upon information available to us at the
time the study was conducted. All work was completed within the constraints of budget, scope,
and timing. The findings of this report are subject to verification and agreement by the
appropriate local, State, and Federal regulatory authorities. No other warranty, expressed or
implied, is made.
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REFERENCES
City of Renton. City of Renton Mapping Applications.
(http://rentonwa.gov/government/default.aspx?id=29886) 12 October 2015.
Hruby, T. 2014. Washington State Wetland Rating System for Western Washington: 2014
Update. Washington Department of Ecology Publication #14-06-029, Olympia, WA.
King County iMAP: Interactive Property Mapping Tool.
(http://www.kingcounty.gov/operations/GIS/Maps/iMAP.aspx) 28 July 2017.
The Watershed Company. October 12, 2015. Wetland and Stream Delineation Report for
Thunder Hills Sanitary Sewer Interceptor Alternatives Analysis. October 12, 2015, Renton,
WA.
The Watershed Company 2017a. No Effect Letter Report for ESA-Listed Species: Thunder Hills
Sewer Interceptor Rehabilitation. August 15, 2017.
The Watershed Company. 2017b. Thunder Hills Sewer Interceptor Rehabilitation: Springbrook
Creek Mitigation Bank Use Plan. August 17, 2017.
USDA (United States Department of Agriculture) Natural Resources Conservation Service.
2017. Web Soil Survey. (http://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx)
28 July 2017.
USFWS (United States Fish and Wildlife Service) Wetlands Mapper.
(http://www.fws.gov/wetlands/data/Mapper.html) 12 October 2015.
WDFW (Washington Department of Fish and Wildlife). Priority Habitats and Species, PHS on
the Web. (http://wdfw.wa.gov/mapping/phs/) 12 October 2015.
WDFW, King County, Esri, HERE, DeLorme, Intermap, USGS, METI/NASA, USDA, EPA. 2014.
Salmonscape viewer. (http://apps.wdfw.wa.gov/salmonscape) 12 October 2015.