HomeMy WebLinkAboutThunder Hills Memo #8 FINAL 102115
CITY OF RENTON
Technical Memorandum No. 8
Alternative 1
Summary of Sensitive Area Impacts
Thunder Hills Sanitary Sewer Interceptor Alternative
Analysis
October 21, 2015
Prepared By:
Hugh Mortensen , Sarah Sandstrom, and Katy Crandall
750 6th Street South
Kirkland, WA 98033
425-822-5242
The Watershed Company Project No. 131113
Contents
1.0 INTRODUCTION ......................................................................................................................1
2.0 SENSITIVE AREAS ....................................................................................................................1
2.1 WETLANDS .................................................................................................................................... 1
2.2 STREAMS ....................................................................................................................................... 1
2.3 OTHER CRITICAL AREAS ................................................................................................................. 2
3.0 POTENTIAL IMPACTS ...............................................................................................................2
3.1 AVOIDANCE AND MINIMIZATION MEASURES .............................................................................. 4
3.2 ENDANGERED SPECIES AND HABITAT ........................................................................................... 5
3.3 IMPLICATIONS OF IMPACTS TO BUFFERS ..................................................................................... 5
3.4 IMPLICATIONS OF DIRECT IMPACTS TO STREAMS ........................................................................ 6
3.5 IMPLICATIONS OF DIRECT IMPACTS TO WETLANDS ..................................................................... 7
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
1
1.0 INTRODUCTION
The City of Renton seeks to repair and relocate the Thunder Hills Sanitary Sewer Interceptor and
reestablish maintenance access. The purpose of this memorandum is to document anticipated impacts
to wetlands, streams, and habitats and related implications for design and permitting. A separate
memorandum, Technical Memorandum No. 9, prepared by Stantec, discusses the permit needs and
required permit application materials. The findings discussed in this memorandum are based on the
attached plans, dated August 21, 2015. The findings of this report are subject to verification and
agreement by the appropriate local, state and federal regulatory authorities.
2.0 SENSITIVE AREAS
Wetlands and streams within the project study area were delineated and preliminarily documented in a
delineation memorandum dated May 12, 2014. That memorandum identified Thunder Hills Creek,
seven tributary streams, and six wetlands in the study area. In 2015, after the delineation memo was
completed, the City of Renton updated its critical areas regulations, resulting in changes to stream
classifications and wetland and stream buffers. Updated information relating to stream and wetland
classification and applicable standard buffer widths are presented below.
2.1 WETLANDS
The delineation memorandum initially rated wetlands using the Washington State Department of
Ecology’s (Ecology) Western Washington Wetland Rating System (2004), which was in effect at the time
and accepted by local, state and federal permitting agencies. Ecology’s rating system was updated in
2014 and all wetlands were re-rated to be consistent with local, state and federal requirements (2014
forms and figures attached). Updated wetland classifications, based on the 2014 rating system, and
buffers based on the City of Renton’s updated critical area regulations are reported in Table 1.
2.2 STREAMS
For the preparation of this memorandum, additional investigation of stream typing incorporated
information from the Forest Practices Application Mapping Tool (FPAMT)
(https://fortress.wa.gov/dnr/protectiongis/fpamt/index.html), Salmonscape
(http://apps.wdfw.wa.gov/salmonscape/map.html), and the City of Renton Maps Application
(http://rp.rentonwa.gov/SilverlightPublic/Viewer.html?Viewer=COR-Maps).
The stream typing reported in the May 12, 2014 memorandum is generally consistent with the findings
from the review of mapping, except that the city’s stream classification system has changed from Class
1-5 to Class S, F, Ns, and Np, consistent with the Washington Department of Natural Resources (WDNR)
permanent stream typing criteria. Thunder Hills Creek was previously described as a Class 3, non-
salmonid bearing, perennial stream. The FPAMT and the City of Renton Maps identify Thunder Hills
Creek as a Type N non-fish bearing stream. Salmonscape identifies the piped section of stream under
Interstate 405 as a total fish passage barrier. Whereas the City of Renton Maps classify Thunder Hills
TECHNICAL MEMORANDUM NO. 8
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
Creek as perennial, Salmonscape identifies the upper two-thirds of the project area as seasonal.
Downstream from Interstate 405, the City of Renton Maps and field observations indicate that Thunder
Hills Creek meets Rolling Hills Creek, which runs southwest through an open channel for approximately
1,000 feet before being piped through the stormwater infrastructure under the Renton Village Shopping
Center. Eventually, Rolling Hills Creek drains into the Black River and from there into the Duwamish
River. Based on the limited watershed area upstream of the project area, and the total fish passage
barriers downstream of the project area, the Type N classification for Thunder Hills Creek within the
project area is warranted. Based on field observations, Thunder Hills Creek is assumed to be perennial
in years of normal rainfall within the project area.
Stream C and Stream H were delineated in the field; however, these streams were not located by the
survey. These streams are on the opposite bank of Thunder Hills Creek from the proposed sewer work;
therefore, they do not affect the conclusion of this memorandum. Nevertheless, in the interest of
complete documentation the general location of these streams should be noted in project plans and
permit application documents.
2.3 OTHER CRITICAL AREAS
In addition to wetlands and streams, the project is located at the base of a ravine, and is mapped by the
City of Renton as a high severity erosion hazard area and a moderate severity landslide hazard area.
Geologically hazardous area standards will apply; a geotechnical report, and potentially an independent
review, will be required. Independent review can be administratively waived by the City Administrator.
No priority habitats or species have been mapped or field identified within the project area, therefore,
additional local standards for habitat conservation areas are not expected to apply. Floodplains are also
not mapped within the project area.
3.0 POTENTIAL IMPACTS
Potential permanent impacts to sensitive areas, including wetlands and streams have been generally
summarized in Table 1, and are based upon the attached project plans (Sewer Plan and Profile
Alternative No. 1) provided by Stantec and dated August 21, 2015 and a site visit meeting on July 2,
2015. The full extent of all temporary impacts, including construction entrances, staging areas, and
other temporary clearing areas have not been fully documented. For the purposes of this memorandum,
it is assumed that all temporary impacts will be limited to buffer areas and appropriately mitigated
following project completion. According to the preliminary site plans, the project will impact the buffers
of all wetland and stream critical areas identified in the study area. Additionally, direct impacts will
occur to portions of Thunder Hills Creek, Stream G, and Wetlands E and F. Stream F could also be
modified if Stream G is rerouted.
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
3
Table 1. Classifications of streams and wetlands along Thunder Hills Creek, per Renton Municipal
Code, and projected impacts to each feature and its associated buffer.
Critical Area Renton Municipal
Code Classification
(2014 Ecology rating –
wetlands only)
Standard
Buffer
Width (ft)
Direct Impact to
Feature
Impact to Buffer
Thunder Hills
Creek Class Np 75
Possible direct impact
from culvert work
associated with Stream
G drainage
Entire project within
buffer
Stream B Class Ns 50
None Gravel road in buffer Stream C Class Ns 50
Stream D Class Ns 50
Stream E Class Ns 50 None Gravel road, gravity
wall or rockery, and
parallel sewer in buffer Stream F Class Ns 50
Possible modifications
to banks if Stream G is
rerouted
Stream G Class Ns 50
Repair/replace culvert
or reroute stream; Cut
into portion of stream
Gravel road, slope cut,
and gravity wall or
rockery in buffer
Stream H Class Ns 50 None Gravel road and
parallel sewer in buffer
Wetland A
Category 3, Low
Habitat Function (4
points)
75 None
Gravel road and gravity
wall or rockery in
buffer
Wetland B
Category 3,
Moderate Habitat
Function (6 points)
100 None
Gravel road, parallel
sewer, slope cut, and
gravity wall or rockery
in buffer
Wetland C
Category 4,
Moderate Habitat
Function (5 points)
50 None
Gravel road, paved
road, and parallel
sewer in buffer
TECHNICAL MEMORANDUM NO. 8
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
Critical Area Renton Municipal
Code Classification
(2014 Ecology rating –
wetlands only)
Standard
Buffer
Width (ft)
Direct Impact to
Feature
Impact to Buffer
Wetland D
Category 3,
Moderate Habitat
Function (5 points)
100 None
Gravel road, parallel
sewer, slope cut, and
gravity wall or rockery
in buffer
Wetland E
Category 3,
Moderate Habitat
Function (5 points)
100 Small portion of gravel
road in wetland Gravel road in buffer
Wetland F
Category 3,
Moderate Habitat
Function (5 points)
100 Gravel road through
wetland
Gravel road and
parallel sewer in buffer
3.1 AVOIDANCE AND MINIMIZATION MEASURES
Permit applications will need to document unavoidable critical area impacts. This includes temporary
construction-related impacts, as well as permanent impacts from the project. As part of that
documentation, all available avoidance and minimization measures must be discussed and addressed.
Examples of proposed avoidance measures currently planned for this project include:
• Using existing access points to avoid the need for new stream crossings.
• Using a slip-line approach to repair the existing sewer line where it crosses Thunder Hills Creek.
Examples of proposed minimization measures include:
• Relocating the sewer line under the access road to minimize the footprint of construction and
maintenance impacts.
• Locating the proposed road over the existing unmaintained trail to minimize impacts to
vegetation in the buffer.
• Locating the road as far from the stream as possible, given topographic constraints.
• Using a narrower width path (7 feet compared to 12-foot road) for specialized equipment on the
northern portion of the project area.
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
5
• Implementation of a Temporary Erosion and Sediment Control plan.
• Timing construction to avoid the wet season when sedimentation and erosion would be
anticipated.
A mitigation plan will also be necessary to demonstrate that all unavoidable impacts to functions and
values will be appropriately compensated or replaced consistent with local, state, and federal guidance.
3.2 ENDANGERED SPECIES AND HABITAT
A review of online mapping resources and site visit observations indicate that no federally threatened or
endangered species are located in the project area. The project area is in an urban environment, where
available upland habitat is limited to isolated patches of forests that experience regular disturbance.
Listed birds, mammals, and amphibians are not likely to occur in the vicinity of the project area because
they are generally restricted to less developed areas with large areas of contiguous habitat. Similarly, as
discussed above, Thunder Hills Creek does not support listed salmonid fish, and the nearest salmon-
bearing stream is the Black River, 1.8 miles downstream of the project extent.
Because the project area is well-removed from the likely occurrence of a federally listed species, a
biological evaluation will not likely be required, but a no-effect letter is recommended to describe the
project area relative to the location of listed species. The no-effect letter would be submitted as an
attachment to the JARPA when applying for federal permits. This letter provides the Corps with
necessary documentation to evaluate and confirm that their consultation with National Marine Fisheries
Service and U.S. Fish and Wildlife Service is not necessary.
3.3 IMPLICATIONS OF IMPACTS TO BUFFERS
As described above and in Table 1, the entire project would be located within stream and wetland
buffers designated by the City of Renton. Renton Municipal Code (RMC) 4-3-050.C.3 exempts repair and
replacement of existing utilities within an existing improved public road right-of-way or easement from
critical area standards. Based on the plans, we assume that the proposed project would not qualify for
this exemption, as it would extend beyond the existing improved area and include instream work.
Renton Municipal Code (RMC) 4.3-050.J.2.b. also provides criteria for administrative approval of new
utilities in streams, lakes, and buffers with an approved critical area study, provided:
i. Fish and wildlife habitat areas are avoided to the maximum extent possible; and
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; and
TECHNICAL MEMORANDUM NO. 8
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
iii. New utility routes avoid paralleling the stream or following a down-valley course near the
channel; and
iv. The utility installation shall not increase or decrease the natural rate of shore migration or
channel migration; and
v. Seasonal work windows are determined and made a condition of approval; and
vi. Mitigation criteria are met.
Although the above standards are intended for new utilities, replacement of an existing utility line is
expected to qualify for the same administrative approval process.
The City of Renton allows for buffer averaging or reduction, provided that the selected approach meets
the city’s minimum width standards and maintains or improves ecological functions. Since the entire
project falls within the buffer of Thunder Creek (as well as numerous additional, overlapping wetland
and stream buffers) and since the project area is mainly on private property, there is likely no
opportunity for buffer expansion under an averaging plan. Therefore, buffer impacts are best mitigated
through enhancement of existing buffers (removing weeds, planting native plants, monitoring and
maintaining vegetation until established). There is ample opportunity for such enhancement
throughout much of the project site. The specific approach to buffer enhancement will need to be
discussed as a part of the critical areas report.
3.4 IMPLICATIONS OF DIRECT IMPACTS TO STREAMS
Direct impacts are those that alter the physical stream bed or banks. Such impacts would require
approval by the City of Renton, WDFW, and the Corps.
The applicant should anticipate that WDFW will require that any stream culverts modified as a part of
the project to be appropriately sized to accommodate transport of high flows (100-year event) and
debris. There is additional potential that WDFW will require that all culverts within the project area are
updated to pass high flows. Fish passage standards should not apply given the permanent status of the
complete fish passage barrier downstream (under Interstate 405).
There is the potential that a short segment of Stream G will be relocated as part of the proposed plan
since it appears Stream G and Stream F were joined at some time the in recent past. RMC 4-3-050.J.2.e.
allows administrative approval for stream relocation for expansion of public road or other public facility
improvements where no feasible alternative exists, provided the following:
(a) Buffer widths shall be based upon the new stream location.
(b) The provided buffer between the facility and the relocated stream shall be enhanced or
improved to provide appropriate functions given the class and condition of the stream.
ALTERNATIVE NO. 1
Thunder Hills Sanitary Sewer Interceptor
Summary of Sensitive Area Impacts
The Watershed Company
October 21, 2015
7
(c) Applicable mitigation criteria must be met.
(d) Proper notification to the City must be made.
As noted above, the project area does not include fish-bearing streams, and the downstream barrier
under Interstate 405 is very unlikely to be corrected. Nevertheless, it should be noted that the project
area is within the designated as Usual and Accustomed (U&A) fishing grounds of the Muckleshoot Tribe.
As such, the Muckleshoot Tribe may review and comment on permits through the public review period.
The Corps heavily weighs comments and recommendations from the tribes, particularly as they relate to
stream habitat and fish passage. Early and frequent coordination with Muckleshoot Tribe during the
permitting phase of this project is advised.
3.5 IMPLICATIONS OF DIRECT IMPACTS TO WETLANDS
Direct wetland impacts are those that change the physical shape or configuration of the wetland itself.
Based on the preliminary project plans, it is estimated that the project will directly impact (eliminate)
approximately 2,000 square feet of wetland. Mitigation will need to be provided for direct wetland
impacts. Frequently, wetland mitigation takes the form of replacement wetland areas rehabilitated,
constructed, or enhanced on-site. However, given the steep nature of the project site and the lack of
public ownership, on-site mitigation does not appear feasible. Additionally, the Corps and Ecology have
established a preference for use of mitigation banks or in lieu fee programs over on-site, permittee-
responsible mitigation. This is in contrast to the city’s preference for mitigation, which prioritizes re-
establishing, rehabilitating, creating, enhancing, and preserving wetlands on-site over mitigation banks
or in-lieu fee programs. The City of Renton has an approved wetland mitigation bank on Springbrook
Creek and King County operates an in lieu fee program through its Mitigation Reserves Program. The
use of either site would be permitted by local, state, and federal standards. The credits required from
either the Springbrook Creek Mitigation Bank or the Mitigation Reserves Program would be determined
by the mitigation banking agreement and/or certification process. Based on the project plans, it is
estimated that if the applicant were to use the Springbrook Creek Mitigation Bank, approximately 0.04
credits would be needed.
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WETLAND E
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WETLAND F
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EX. 12" DI SS
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APPROX. (NOT SURVEYED).
SURVEY MAY BE REQUIRED
FOR PERMITS
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THUNDER
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OPTIONAL GRAVITY WALL OR
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ADD CULVERT & DIRECT
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APPROX. (NOT SURVEYED).
SURVEY MAY BE
REQUIRED FOR PERMITS WETLAND B
THIS SECTION OF
THUNDERHILLS CREEK
APPROX. (NOT SURVEYED).
SURVEY MAY BE
WET BFR
WET BFR
WET BFR
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WET BFR
WET BF
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EX. 10
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D
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OPTIONAL GRAVITY WALL OR
ROCKERY - MAY NOT BE NEEDED
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
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EX. 10" AC SS
EX. 10" A
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EX. 10" AC SS
EX. 10" A
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THUNDER HILLS CREE
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EX. 10
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CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
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EX. 10" AC SS
STREAM F
STREAM G
EX. 10" AC SS
THUNDER HILLS CREEK
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
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SO-D
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B
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B
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B
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F
R
WET
B
F
R
WET B
F
R
WE
T
B
F
R
WET
B
F
R
WE
T
B
F
R
WET B
F
R
WETLAND A
STREAM E
THUNDER HILLS CREEK
CUT IN
T
O
T
O
E
O
F
SLOP
E
T
O
C
R
E
A
T
E
12' WI
D
E
G
R
A
V
E
L
R
D
CUT INTO TOE OF
SLOPE TO CREATE
12' WIDE GRAVEL RD
RE
-
P
A
V
E
&
W
I
D
E
N
OPTIONAL GRAVITY WALL OR
ROCKERY - MAY NOT BE NEEDED
MA
T
C
H
L
I
N
E
-
S
T
A
.
2
4
+
5
0
.
0
0
SE
E
S
H
E
E
T
7
MA
T
C
H
L
I
N
E
-
S
T
A
.
2
8
+
0
0
.
0
0
SE
E
S
H
E
E
T
9
20
0
6
6*70&'4*+..5+06'4%'2614
#.6'40#6+8'5#0#.;+5+5
WET BFR
////////////
///
////////////
///
///
///
///
///
///
///
////////////////////////
///
//////////////////
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///
SS
SS
SS
SS
SS
S
S
SS
///
///
///
///
///
///
///
////////////////////////////////////////////////////////////
///
///
///
///
///
///
///
///
///
///
///
///
///
///
///////////////////////////////////////////////////////////////
///
///
///
///
WET BFR
WET BFR
WET BFR
WET BFR
WET BFR
WET
B
F
R
WET
B
F
R
WET
B
F
R
WET
B
F
R
WET B
F
R
WET B
F
R
GRANT AVE S
S
1
8
t
h
S
T
///
///
///
///
///
///
///
RE-PAVE & WIDEN
ACCESS ROAD
M
A
T
C
H
L
I
N
E
-
S
T
A
.
2
8
+
0
0
.
0
0
S
E
E
S
H
E
E
T
8
20
0
6
#.6'40#6+8'5#0#.;+5+5
WET BFR