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August 2019 | Renton Sunset Community Area Reevaluation and Addendum 1
Reevaluation / Addendum
Renton Sunset Terrace Redevelopment | August 2019
Prepared By: BERK Consulting in association with Transpo Group
1 Background/Need for Reevaluation .................................................................................... 2
2 Sunset Area Alternatives ..................................................................................................... 6
2.1 Study Area ........................................................................................................................................ 6
2.2 Land Use Proposals ......................................................................................................................... 8
2.3 Development Standards ............................................................................................................... 11
2.4 Facility and Infrastructure Proposals .......................................................................................... 13
2.5 Updated Land Cover / Impervious Analysis ............................................................................. 13
2.6 Phasing ............................................................................................................................................. 15
2.7 Master Site Plan and Other Discretionary Applications ......................................................... 16
3 Environmental Analysis ....................................................................................................18
3.1 Land Use .......................................................................................................................................... 18
3.2 Aesthetics ......................................................................................................................................... 18
3.3 Cultural Resources .......................................................................................................................... 18
3.4 Transportation................................................................................................................................. 18
3.5 Parks and Recreation .................................................................................................................... 18
3.6 Public Services ................................................................................................................................ 18
3.7 Utilities .............................................................................................................................................. 18
3.8 Other FEIS Topics ........................................................................................................................... 19
3.9 Monitoring and Review ................................................................................................................. 19
4 Conclusions .......................................................................................................................23
Attachments
Attachment A Transportation Analysis - Reevaluation
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 2
1 Background/Need for Reevaluation
The City of Renton, along with the Renton Housing Authority (RHA), and other public, private, and
nonprofit agencies and developers, is redeveloping the Sunset Terrace public housing community
plus some peripheral sites that have been master planned for redevelopment along with Sunset
Terrace for a total of about 12.7 acres. See Exhibit 1.
The Master Site Plan envisions a mixed-use, mixed-income community with park and library and
other civic and commercial uses. Mixed-use sites will have both market rate and affordable rental
housing in multi-story, multi-family townhomes and apartments, along with commercial and retail
space.
The Master Site Plan is located within the Renton Sunset neighborhood that has been included in the
Renton Comprehensive Plan as a center for new housing, commercial, recreation, education, and
other uses. See Exhibit 2.
In order to meet National Environmental Policy Act (NEPA) and State Environmental Policy Act (SEPA)
requirements, the City of Renton issued the Draft Environmental Impact Statement (DEIS) for the City
of Renton Sunset Area Community Planned Action on December 17, 2010 and the Final Environmental
Impact Statement (FEIS) for the City of Renton Sunset Area Community Planned Action on April 1,
2011.1 The City served as the Responsible Entity (RE) for NEPA compliance, and the lead agency
for SEPA compliance.
The Sunset Terrace Master Site Plan Area was also the subject of subsequent revaluations/addenda
in 2014 and 2016. The Master Site Plan completed in 2014 provides a coordinated plan of
development for both the Sunset Terrace and Replacement sites. The 2016 Master Site Plan
amendment added properties into the Master Site Plan, and redistributed some dwelling units, but
retained the same overall number of units as approved by the 2014 Master Site Plan. See Exhibit
3 for the Sunset Terrace redevelopment area and housing replacement sites.
In 2019, RHA2 is proposing an amended Master Site Plan that would:
▪ Shift units between a site on the west (Site C/18: Edmonds Apartments/Homestead Willow
Crest Townhomes) to a site in the north of the Master Site Plan area (Site E/14,16/17: Sunset
Park West Townhomes 2014/Harrington Park 2016/Sunset Oaks 2019).
This 2019 reevaluation also assesses the future removal of a site from the Master Site Plan
boundaries (Site G/11 known previously as the Sunset Park East (Piha) Townhomes & Apartments
2014/Suncrest Homes 2016/Solera 2019). The site would remain within the Sunset Area
Community neighborhood. This Master Site Plan boundary amendment proposal is evaluated for
potential implementation at a later date. It would require a Major Site Plan amendment and
Planned Action Ordinance (PAO) amendment when accomplished. The reevaluation identifies
implications of the site’s future removal should the City or RHA desire that amendment.
The 2019 proposals would not add housing units in the Master Site Plan area or in the Sunset Area
neighborhood. However, consistent with the flexibility allowed by the adopted Master Site Plan,
some units would be redistributed.
1 CH2MHill and ICF International. 2011. Sunset Area Community Planned Action NEPA/SEPA Environmental Impact
Statement. Final. April. (ICF 00593.10.) Bellevue and Seattle, WA. Prepared for City of Renton and the Renton Housing
Authority, Renton, WA.
2 RHA owns Sites C and E. The applicant for Site E is Sunset Oakes LLLP.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 3
As amended, development in the Master Site Plan area would meet City standards for density,
height, setbacks, transportation levels of service, connection to utilities, and would be subject to City
parking codes, including procedures for modifying applicable standards.
The amended Master Site Plan would be consistent with RMC Title IV. Also, the SEPA PAO would
be amended in the future to include the revised Master Site Plan concept should Site G/11 (Solera)
site be removed. The total development levels and mitigation measures in the PAO remain
unchanged.
Exhibit 1. Sunset Terrace Master Site Plan 2016
Source: Mithun, City of Renton 2016
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 4
Exhibit 2. Planned Action Area: 2011
Source: CH2MHill and ICF International, 2011; BERK, 2016.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 5
Exhibit 3. Renton Sunset Terrace Redevelopment Area and Swap Sites: 2016
Source: CH2MHill and ICF International, 2011; BERK, 2016.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 6
As with the changes previously evaluated in 2014 and 2016, the 2019 revisions proposed to the
Master Site Plan at this time are the focus of this NEPA Reevaluation and SEPA Addendum to provide
additional information about the proposal, to determine whether the proposed changes would result
in any new or substantially different environmental impacts, and to assess whether the conclusions
of the original EIS are still valid.
This analysis would also provide the basis for amendments to the Record of Decision (ROD) and/or
PAO, if any. This Reevaluation and Addendum document is structured as follows:
1. Introduction
2. Sunset Area Alternatives
3. Environmental Analysis
4. Conclusions
2 Sunset Area Alternatives
2.1 STUDY AREA
The primary Sunset Terrace redevelopment
area as well as housing Replacement sites,
and areas of public investment are illustrated
on Exhibit 4.
All Master Site Plan sites, plus the Sunset Area
neighborhood, were evaluated in the 2011
EIS for the Sunset Area Community Planned
Action Area. See Exhibit 5.
The 2014 Master Site Plan area totaled about
12.4 acres. The updated 2016 Master Site
Plan area equaled about 14 acres.
In this 2019 reevaluation, the Master Site Plan
area is about 14 acres with the same sites, or
12.9 acres if Site G/11 is removed.
Exhibit 4. Lettered Master Plan Sites
# - Master Plan Sites /// - Sunset Terrace Public Housing
Boundaries
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 7
Exhibit 5. Revitalization Projects: 2019
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 8
2.2 LAND USE PROPOSALS
In total, 722 dwelling units are being proposed in the study area in this 2019 Reevaluation, which
is to the same as the number of units considered in the 2014 and 2016 Reevaluations. See Exhibit
6. Future commercial square feet are the same for each Master Site Plan Reevaluation. The Master
Site Plan acres vary between the alternatives with more added in 2016 compared with 2014. In
2019, the total acres are similar to 2016, with slight adjustments due to the availability of specific
site plans completed since 2016. If Site G/11 is removed, the acres would equal 15.74 closer to
the 2014 Master Site Plan extent.
Exhibit 6. Summary of Total Units, Commercial Square Feet, and Acres: Studied in Reevaluation
Location
See Exhibit 4 for Site Letters
Total
Dwelling
Units: 2014,
2016, 2019
Commercial
Square Feet:
2014, 2016,
2019
Land Area
(acres):
2014
Land Area
(acres):
2016
Land Area
(acres):
2019
Master Site Plan Sites
Sunset Terrace and Replacement Sites: C through J 671 4,500-
39,500
7.63 9.23 9.17
Library (Site K), Developed 15,000
Sunset Park (Site M) and Regional Stormwater
Facility (Site L), Installed
3.20 3.20 3.21
NE 10th and Sunset Lane Loop (Site N and O) 1.61 1.61 1.61
Total Master Site Plan Sites 19,500-
54,500
12.44 14.04 13.99
Other Sunset Terrace Study Area Sites: Glenwood
(Site A) - Developed
671
0.65 0.65 0.65
Swap Sites: Kirkland Avenue (B) - Developed,
Library Site for Future Surplus (X)
8
2.18 2.18 2.18
Other Employment potential in Sunset Terrace and
Replacement Sites
43
4,500
Total All Sites 722 19,500-
59,000
15.28 16.88 16.83
Source: King County Assessor; ICF Jones & Stokes et al. 2011; BERK Consulting 2015 and 2019
Two alternatives were addressed in the NEPA Record of Decision (ROD) and the PAO as “selected”
alternatives: Alternative 3 and a Preferred Alternative. See Exhibit 7 for a list of net dwelling units.
These alternatives represented the higher growth levels studied in the EIS. The mitigation documents
contained in the ROD and PAO were based on the range of growth of the two Selected Sunset
Area Alternatives.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 9
Exhibit 7. Comparison of Net Growth in Sunset Terrace and Neighborhood Alternatives
Dwelling
Units/Jobs
Net New Growth
FEIS Alternative 3
FEIS Preferred
Alternative
Reevaluation
Alternative: 2014
Reevaluation
Alternative: 2016, 2019
Neighbor
-hood
Sunset
Terrace
Neighbor
-hood
Sunset
Terrace
Neighbor
-hood
Sunset
Terrace
Neighbor
-hood
Sunset
Terrace
Dwelling units 2,506 479c 2,339 266a 2,506 554b 2,506 519b
Population 5,789 1,106 5,403 614a 5,789 1,279 5,789 1,199
Employment SF 1,310,113 59,000 1,247,444
–
1,259,944
38,100 1,310,113 19,500-
59,000
1,310,113 19,500-
59,000
Jobs 3,330 182 3,154–
3,192
117 3,330 60-182 3,330 60-182
a Does not include approximately 90-100 units to be developed on land swap/housing replacement sites.
b Similar to the FEIS, includes the sites shaded purple in Exhibit 2 and Exhibit 3, considered Potential Sunset Terrace
Redevelopment subarea. This equates to Master Site Plan sites C, D, E, G to O, plus site A. Sites B, F, and X
considered swap sites and included within neighborhood dwelling units.
C Does not include swap sites B, F, and X.
Source: FEIS 2011, BERK 2014, 2016, 2019.
The purpose of identifying two “Selected Sunset Area Alternatives” in the FEIS was to define a
range of acceptable growth and designs considering the conceptual nature of the Sunset Terrace
redevelopment plans in 2011, as well as the 20-year horizon of the broader neighborhood planned
action. The Preferred Alternative was similar to Alternative 3 with slightly lower growth and a
reconfiguration of park space and road network. The two alternatives were similar in terms of
potential beneficial and adverse impacts and required mitigation measures.
Since the original FEIS analysis, additional site planning for Sunset Terrace and other properties
has occurred and some changes in the number or location of units have been considered. In 2014,
90 units were added to in the Sunset Terrace Master Site Plan area (Exhibit 8), compared to
Alternative 3 in the FEIS, but the total number of units in the overall Sunset Area neighborhood
remained the same. As well, other site planning considerations were addressed regarding building
height, etc. as described above. The NEPA/SEPA Reevaluation conducted in 2014 showed no
substantive changes in impacts or required mitigation were needed as a result of the revised
alternative, which is termed the “Reevaluation Alternative.” Per the approved 2014 Master Site
Plan, dwelling units may be redistributed among sites provided the Reevaluation conclusions are
maintained.
The net units in Sunset Terrace are lower in 2016 and 2019 than in 2014 per Exhibit 7. This is a
reflection of the boundaries of the 2011 Potential Sunset Terrace Redevelopment Area (sites
shaded purple in Exhibit 2 and Exhibit 3) that excluded Site 19 (also lettered Site F). Site F/19 is
included in the Sunset Area neighborhood units.
Some potential dwelling units are proposed to be transferred among five individual Master Site
Plan sites; these are identified with the “box” on Exhibit 8. However, the total number of units that
could be developed in the Master Site Plan area would remain the same.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 10
Exhibit 8. Summary of Total Units Proposed for Study in Reevaluation
Sources: Veer, Schemata, Third Place Design, Mithun, Colpitts, City of Renton, Renton Housing Authority, BERK 2014, 2016, 2019
Neighbor-
hood Site
Letter
Master
Plan Site Development Title Status Acres:
2014
Total Units
Reviewed in
Reevaluation:
2014
Acres:
2016
Total Units
Reviewed in
Reevaluation:
2016
Acres:
2019
Total Units
Reviewed in
Reevaluation:
2019
A Glennwood Townhomes Constructed RHA 0.65 8 0.65 8 0.65 8
B Kirkland Avenue Townhomes Constructed RHA 0.77 18 0.77 18 0.77 18
C 18 Edmonds Apartments/Sunset Crest Part of Master Site Plan 1.70 112 1.70 68 1.70 25
D 5 Sunset Terrace Apartments Part of Master Site Plan 0.51 54 0.51 47 0.51 47
E 14, 16/17 Sunset Park West Townhomes 2014 /
Harrington Park 2016/ Sunset Oaks 2019
Part of Master Site Plan 0.55 10 1.06 19 1.05 62
F 19 Sunset Court Townhomes 2014 / Sunset
Court Apartments 2016
Part of Master Site Plan 0.88 15 1.95 50 1.95 50
G 11 Sunset Park East (Piha) Townhomes & Apts
2014 / Suncrest Homes 2016 / Solera 2019
Part of Master Site Plan (Remove in Future)1.09 57 1.09 64 1.09 64
H 9 Sunset Terrace Dev. Building A Part of Master Site Plan 0.99 117 0.99 117 0.58 117
I 7/8 Sunset Terrace Dev. Building B Part of Master Site Plan 1.18 196 1.18 196 1.18 196
J 6/7 Sunset Terrace Dev. Building C Part of Master Site Plan 0.74 110 0.74 110 0.74 110
K 10 Renton Highlands Library Constructed, King County Library System See H See H 0.37
L Regional Stormwater Facility Constructed, City See M See M See M
M Sunset Park Consturcted, City 3.20 3.2 3.2
N Sunset Lane Loop Improvements Constructed, City 1.41 1.41 1.41
O NE 10th Street Extension Improvements Constructed, City 0.20 0.20 0.20
X Library Site (2013)Future Development 1.41 25 1.41 25 1.41 25
Total - Master Plan Sites 12.44 671 14.04 671 13.99 671
Total - All Sites 15.28 722 16.88 722 16.83 722
= Master Plan Properties
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 11
The 2019 Reevaluation alternative is similar to the 2016 Reevaluation alternative except potential
dwelling units would be transferred as follows:
▪ Site C/18 would be reduced from 68 to 25 units and Site E/14,16/17 would be increased
from 19 to 62 units.
The eastern half of Site C is planned for 12 townhomes in a development currently known as
Homestead Willow Crest Townhomes. The development is seeking Self-Help Homeownership
Opportunity Program (SHOP) funding. This development has been reviewed in its own NEPA
documentation.
The reduced number of units allocated to Site C accommodates the 12-unit townhome development
on the east. The western portion of Site C has not yet been planned but could accommodate another
13 units with the balance of the 25-unit allocation.
The City considered a Comprehensive Plan future land use map change and rezone for Site E in
2018. The Future Land Use Map was changed from Residential High Density to Commercial Mixed
Use. The site was also correspondingly rezoned from R-14 to Center Village (CV). The reallocation
of the units is consistent with the density allowed by the CV zone.
Site E is proposed for affordable attached dwelling units in a development called Sunset Oakes. It
is anticipated that units will be rented with project-based vouchers using RHA operating subsidies;
there is no direct federal capital funding.
The Master Site Plan concept would be retained per Exhibit 1 at this time. In the future, it is possible
that Site G/11 will be removed from the Master Site Plan; however, it would still be located in the
Sunset Area neighborhood, retain its zoning, and be allowed development similar to that in the
Master Site Plan. It may develop with public housing, privately developed housing, mixed uses, or
other forms of development allowed by the CV zoning district. The boundary reduction would
require a Major Site Plan amendment and PAO amendment if proposed in the future.
2.3 DEVELOPMENT STANDARDS
Sites C/18 and E/14,16/17 proposed for unit reallocations are addressed below together with
cumulative development allowed in the Master Site Plan area and the Sunset Area neighborhood.
Other sites in the study area were addressed in the 2011 EIS and the 2014 and 2016 NEPA/SEPA
Reevaluations.
2.3.1 Building Height
All sites would be designed to meet allowable heights of their respective zones.
Site E/14,16/17 was considered to be developed at three stories in the 2016 Reevaluation and
associated Master Site Plan height analysis. While the CV zone allows heights of 50 feet with 10
feet more for retail on the ground floor, the proposed Sunset Oaks development would be 33 feet
maximum consistent with the 2016 height analysis; thus, no further height or shade/shadow analysis
is needed.
Site C/18 was evaluated in the 2016 Master Site Plan with conceptual buildings extending up to
50-60 feet in height consistent with the CV zone. Detailed site plans have been prepared for the
eastern portion of the property with three-story townhomes, less than the maximum height of the
zone. The western portion of the site is undesigned and subject to the maximum 50-60 feet in height.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 12
2.3.2 Density
All sites are consistent with the density requirements of the zoning code or density transfer
agreements. Sites D, H, I, and J were allowed to exceed site-specific density in 2014 based on the
density transfer from the larger park via the Master Site Plan approval. With detailed development
site plans for Sites H and K, the density increased on Site H since the lot is a little smaller than
originally projected. However, the 2014 Master Site Plan transferred density from the park to the
sites since it was conceptually planned together and part of the original Sunset Terrace public
housing site. Density for sites part of original Sunset Terrace (D, H-M) including the Sunset
Neighborhood Park is 76.6 units per acre less than the maximum 80 units (7.3 acres and 559 units).
See Exhibit 9.
Exhibit 9. Density Standards and Results
Notes:
R-14 zone allows a bonus density: Per 4-9-065 Density Bonus Review: Up to 4 additional dwelling units per net acre.
Densities of greater than eighteen (18) units per net acre are prohibited.
CV Zone: RMC 4-9-065 allows a bonus of 50% above maximum density in the CV zone.
Source: City of Renton Municipal Code; BERK Consulting 2019.
2.3.3 Parking
Subject sites will be required to meet City parking standards. The standards for parking are as
follows:
Attached dwellings in RM-F, R-14, and R-10 Zones: A minimum and maximum of
1.6 per 3 bedroom or large dwelling unit; 1.4 per 2 bedroom dwelling unit; 1.0
per 1 bedroom or studio dwelling unit. In addition to the minimum parking stalls
required, a minimum 10% of the total number of required parking spaces shall be
provided for guest parking and located in a common area accessible by guests.
Attached dwellings within all other zones: 1 per dwelling unit is required. A
maximum of 1.75 per dwelling unit is allowed.
Attached dwellings for low income: A minimum of 1 for each 4 dwelling units is
required [0.25]. A maximum of 1.75 per dwelling unit is allowed.
Project Name
Total
Proposed
Units with
Reevaluation
Density
Reevaluation
Zone
Maximum
Density
Greater or
Lesser than
Maximum
Density
Proposed
Building
Height in
Feet
RHA Sunset Terrace- Sunset Area Replacement and Affordable Housing Units
C Edmonds Apartments/Homestead Willow Crest 1.70 25 14.7 80.0 (65.3) 60.0 60.00 -
D Sunset Terrace Apartments 0.51 47 93.0 80.0 13.0 60.0 50.00 10.0
E Sunset Park West Townhomes 2014 / Harrington
Park 2016/ Sunset Oaks 2019
1.05 62 59.2 80.0 (20.8)
33.0 50.00 (17.0)
F Sunset Court Townhomes 2014 / Sunset Court 1.95 50 25.6 80.0 (54.4) 39.0 50.00 (11.0)
G Sunset Park East (Piha) Townhomes & Apts 2014 /
Suncrest Homes 2016 / Solera 2019
1.09 64 58.6 80.0 (21.4)
48.0 50.00 (2.0)
Other Sunset Terrace Public and Private Projects -
H Sunset Terrace Dev. Building A 0.58 117 202.4 80.0 122.4 68.0 60.00 8.0
I Sunset Terrace Dev. Building B 1.18 196 166.0 80.0 86.0 62.0 50.00 12.0
J Sunset Terrace Dev. Building C 0.74 110 148.3 80.0 68.3 58.0 50.00 8.0
K Renton Highlands Library 0.37 27.0 60.00 (33.0)
L Regional Stormwater Facility See park
M Sunset Park 3.21
N Sunset Lane Loop Improvements 1.41
O NE 10th Street Extension, Improvements 0.20
Total Sunset Terrace Improvement Projects 13.99 671 48.0
Density Exlcluding Rights of Way 671 52.5
Greater or
Lesser Than
Maximum
Height
Property
Area per Site
Plans
Zone
Maximum
Height
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 13
Public housing sites propose parking consistent with the standards for low-income attached dwellings
which may range from 0.25 to 1.75 per dwelling unit.
2.3.4 Onsite Open Space
In the CV zone, common open space is required to be provided at a rate of fifty (50) square feet
per unit. The City may allow substitutions in light of the public park provided adjacent to the
properties. See RMC 4-1-240 for Common Open Space Substitutions. This would likely require
payment of a Fee-in-Lieu of Common Open Space. This would be addressed in future Site Plan
Review applications.
▪ Site C/18 would require 1,250 square feet of onsite open space. The eastern portion of the
site with 12 homes proposes 3,886 square feet, which is more than the number for 25 total
future units. It is likely the western portion of the site would add to the onsite open space.
▪ Site E/14, 16/17 would require 3,100 square feet of open space. Conceptual site plans show
a central tree and mix of hardscape and plantings in the center of the site that would equal at
least half of that with other areas of plantings that are beyond the setback areas.
Private open space is required to be provided for each dwelling unit. Site plans for site C/18 show
townhome units with patio space. Site E plans shows balconies; first floor units appear to have
windows/balconies higher than ground level.
At the time of Site Plan Review, the Director may approve modifications such as a percentage of
units that may have alternative private open space standards if meeting the overall intent of design
standards and other criteria at 4-3-100(F) and RMC 4-9-250(D).
2.3.5 Setbacks
The CV zone requires a minimum 10-foot setback which may be reduced to 0 feet as part of the
site plan development review process, provided blank walls are not located within the reduced
setback.
Site C/18 on the west facing Edmonds Ave NE has not yet been designed but would be subject to
CV zone setbacks.
The proposed Sunset Oaks plan for Site E/14,16/17 provides 15 feet setbacks from streets. The
northern property line setback includes a 16-foot alley and about 10 feet of plantings or parking
access areas.
2.4 FACILITY AND INFRASTRUCTURE PROPOSALS
Detailed infrastructure plans will be required to meet City standards for utility hookups, fire flow
pressure, and stormwater standards including the conceptual utility plan that was part of the PAO.
2.5 UPDATED LAND COVER / IMPERVIOUS ANALYSIS
The FEIS included an analysis of changes in impervious surfaces. Additionally, consistent with the
requirements of Section 7 of the Endangered Species Act (ESA), the original 2011 proposal was
evaluated with respect to potential effects on species listed or proposed for listing under the ESA. A
biological assessment was prepared and submitted to the National Marine Fisheries Service (NMFS)
in December 2010 for its concurrence with a finding that the proposal may affect, but is not likely
to adversely affect, anadromous fish protected under the ESA, and would have no effect on any
ESA-protected species under U.S. Fish and Wildlife Service jurisdiction. The City and NMFS
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 14
corresponded in January, February, and April 2011 on NMFS questions. The City received a letter
of concurrence in May 2011.
Exhibit 10 shows the land cover analysis associated with the 2011 FEIS Alternative 3, and Exhibit
11 shows the analysis associated with the Preferred Alternative; both were addressed in the FEIS,
ROD, and NMFS correspondence.
Exhibit 10. FEIS Alternative 3 Land Cover Analysis
Location
Total Area
(acres)
Total
Impervious
Area (acres)
Total
Pervious Area
(acres)
Total PGIS
(acres)
Total
Untreated
PGIS (acres)
Effective
Impervious
(acres)
Potential Replacement Sites 3.06 2.28 0.78 0.62 0.26 2.14
Potential Sunset Terrace Redevelopment
Subarea
12.64 7.04 6.02 2.43 0 4.22
Total 15.70 9.32 6.80 3.05 0.26 6.36
Notes: PGIS = Pollutant generating impervious surfaces
Source: CH2MHill, April 29, 2011, memo to Erika Conkling, City of Renton, Summary of Sunset Terrace Land
Coverage Analysis in Response to NMFS Comments
Exhibit 11. FEIS Preferred Alternative Land Cover Analysis
Location
Total Area
(acres)
Total Impervious
Area (acres)
Total Pervious
Area (acres)
Total PGIS
(acres)
Total Untreated
PGIS (acres)
Effective
Impervious
(acres)
Potential Replacement Sites 3.06 2.57 0.49 0.41 0 2.39
Potential Sunset Terrace
Redevelopment Subarea
12.64 6.1 6.54 1.7 0 3.66
Total 15.70 8.67 7.03 2.11 0 6.15
Notes: PGIS = Pollutant generating impervious surfaces
Source: CH2MHill, April 29, 2011, memo to Erika Conkling, City of Renton, Summary of Sunset Terrace Land
Coverage Analysis in Response to NMFS Comments
The following table shows an updated analysis of the 2019 Reevaluation Proposal, including sites
that are amended regarding unit reallocations but also other sites that have been constructed using
approved site plans, and sites under planning with updated site plans. Results show the total
impervious area, pollutant generating impervious surfaces (PGIS), and effective impervious area is
less than FEIS Alternative 3.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 15
Exhibit 12. Reevaluation 2019 Land Cover Analysis
Location
Total
Area
(acres)
Total
Impervious
Area (acres)
Total
Pervious
Area
(acres)
Total
PGIS
(acres)
Total
Untreated
PGIS (acres)
Effective
Impervious
(acres)*
Potential Replacement Sites 4.14 1.38 2.76 0.45 0.26 0.83
Potential Sunset Terrace
Redevelopment Subarea
12.69 6.99 5.74 1.64 0 4.19
Total 16.83 8.37 8.50 2.09 0.26 5.02
Notes: PGIS = Pollutant generating impervious surfaces .
Sources: Veer, Schemata, Colpitts, City of Renton, Renton Housing Authority, CH2MHill, BERK , 2014; Schemata, Renton
Housing Authority, BERK 2015; Third Place Design, Lank Tree Land Surveying, BERK, 2019.
Notes: *Per FEIS & BA, assumes that 40% of the impervious area in the site would be mitigated with flow control best
management practices.
Total acres within the study area as a whole are higher than in 2011 due to properties for
replacement housing added in 2016. However, with updated site plan information across the
Master Site Plan area, total impervious area is lower due to the proposed designs of the sites many
of which have pervious sidewalks and pavement (e.g. Glenwood Townhomes, Sunset Court), lesser
Sunset Terrace right-of-way, and the larger park.
To keep within impervious limits, the following features are included with sites where units are being
reallocated in this 2019 Reevaluation:
▪ Site C/18: Sidewalk dedication is assumed to be pervious due to green street designation of
Edmonds Avenue NE as a “green street” in the City’s plans for the Sunset Area.
▪ Site E/14, 16/17: The Sunset Oakes development would include pervious parking and pervious
sidewalks, if necessary to meet any impervious requirements and to be consistent with the
cumulative impervious range and cap evaluated for the Sunset Area NEPA/SEPA Record of
Decision.
Therefore, the 2019 Reevaluation Alternative is in the range of the prior analysis and no further
analysis or conditions are needed in association with the proposal.
The City communicated with NOAA in 2019 and received confirmation that no new formal
consultation is needed with regard to the ESA as the results are within the range previously received
in the 2011 letter of concurrence. (pers com, Janet Curran, NOAA to Rocale Timmons, City of Renton,
October 30, 2015) The analysis updated in 2019 has been submitted to NOAA and is anticipated
to receive a similar confirmation of consistency with prior conditions.
Should Site G/11 site be removed from the Master Site Plan in the future, the base impervious area
would not change as the site is undeveloped. The future impervious area would be reduced within
the Master Site Plan area. The site would be subject still to the City’s stormwater regulations. Once
removed the total area subject to the impervious surfaces limits would be reconfigured but more
similar in land area to the 2011 and 2014 acres.
2.6 PHASING
The redevelopment of the study area and broader neighborhood was anticipated to occur over a
number of years. The Master Site Plan sites are being phased over an approximate 10-year period
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 16
in approximately 5 phases. Phase 1 sites have approved site plans or are in active permit review.
Other phases are approximately estimated based on prior Master Site Plan evaluations. See
Exhibit 13.
Exhibit 13. Site Phasing
= Master Site Plan Sites
Sources: Veer, Schemata, Colpitts, City of Renton, Renton Housing Authority, BERK 2016; BERK, 2019
2.7 MASTER SITE PLAN AND OTHER DISCRETIONARY APPLICATIONS
RHA proposes to amend the Master Site Plan per RMC 4-9-200 to reallocate units. For each Master
Site Plan site, a number of current and future permits are also anticipated. See Exhibit 14.
This Reevaluation and Addendum for the revised proposal will also result in minor revisions of the
ROD. Minor housekeeping amendments could be made to the PAO to update information about the
2019 reevaluation though there is no change to total dwellings or PAO mitigation measures.
Should Site G/11 be removed from the Master Site Plan in the future, a major Master Site Plan
amendment would be needed. In addition, the same conceptual site plan attached to the PAO would
be amended.
Other development permits and approvals would be required for implementing projects. These
could include lot line adjustments/subdivisions, right-of-way dedications and easements,
phased/detailed site plans and associated design modifications where appropriate. Lastly,
building and construction permits would be sought.
Neighbor-
hood Site
Letter
Master
Plan Site Phasing
RHA Sunset Terrace- Sunset Area Replacement and Affordable Housing Units
A Glennwood Townhomes Completed
B Kirkland Avenue Townhomes Completed
C 18 Edmonds Apartments/Homestead Willow Crest Townhomes Phase 1 Sunset Crest,
Phase 4 Edmonds
D 5 Sunset Terrace Apartments Phase 5
E 14,16/17 Sunset Park West Townhomes 2014 / Harrington Park 2016/ Sunset Oaks 2019 Phase 1
F 19 Sunset Court Townhomes 2014 / Sunset Court Apartments 2016 Completed
G 11 Sunset Park East (Piha) Townhomes & Apts 2014 / Suncrest Homes 2016 / Solera 2019 Phase 1
Other Sunset Terrace Public and Private Projects
H 9 Sunset Terrace Dev. Building A Phase 1
I 7/8 Sunset Terrace Dev. Building B Phase 2
J 6/7 Sunset Terrace Dev. Building C Phase 3
K 10 Renton Highlands Library Completed
L Regional Stormwater Facility Completed
M Sunset Park Completed
N Sunset Lane Loop Improvements Extended with Utilities
O NE 10th Street Extension, Improvements Extended with Utilities
X Library Site Phase 5
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 17
Exhibit 14. Matrix of Permits
= Sites permitted/constructed.
Sources: Veer, Schemata, Colpitts, City of Renton, Renton Housing Authority, BERK 2016 , BERK 2019.
Neighbor-
hood Site
Letter
Master
Plan Site
Project Name Master PlanHeight CUPDensity InterpretationParking Rate InterpretationStreet Reclass-ificationsNEPA/SEPA ReevaluationROD/Planned Action AmendmentLot Line Adjustment or SubdivisionROW Dedication / EasementsSite Plan ReviewDensity BonusMod: Open SpaceMod: TransparencyMod: Blank WallMod: ModulationBuilding & Construction PermitsRHA Sunset Terrace- Sunset Area Replacement and Affordable Housing Units
C 18 Edmonds Apartments/Homestead Willow Crest Townhomes X X X X X
D 5 Sunset Terrace Apartments X X X X X X X X
E 14, 16/17 Sunset Park West Townhomes 2014 / Harrington Park 2016/ Sunset Oaks 2019 X X X X X X X
F 19 Sunset Court Townhomes 2014 / Sunset Court Apartments 2016
G 11 Sunset Park East (Piha) Townhomes & Apts 2014 / Suncrest Homes 2016 / Solera 2019
Other Sunset Terrace Public and Private Projects
H 9 Sunset Terrace Dev. Building A X X X X X X X X X X X
I 7/8 Sunset Terrace Dev. Building B X X X X X X X X X X X X
J 6/7 Sunset Terrace Dev. Building C X X X X X X X X X X X X
K Renton Highlands Library
L Regional Stormwater Facility
M Sunset Park
N Sunset Lane Loop Improvements
O NE 10th Street Extension, Improvements
Approvals and Permits Summer 2014 Future Permits Permits with Site Plan Review
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 18
3 Environmental Analysis
The analysis of each element of the environment below compares the conclusions from the FEIS regarding
Alternative 3 and the Preferred Alternative to the 2019 Reevaluation Alternative. It concludes that the
revised Master Site Plan would not change results of the impact analysis or mitigation measures in the FEIS.
3.1 LAND USE
The Land Use analysis in the FEIS concluded that the Sunset Area subarea would advance the purposes of
the Comprehensive Plan and Center Village (CV) zoning district. It would serve as an incentive for other
redevelopment opportunities near the study area. Anticipated growth would also help the City meet its
2031 (now 2035) housing and employment targets. These conclusions are still valid for the 2019
Reevaluation Alternative which proposes housing and mixed uses consistent with zoning and developed in
coordination with the Master Site Plan.
3.2 AESTHETICS
As described in Section 2.2, the Reevaluation Alternative will reallocate dwelling units among sites, but all
sites will meet zoning densities, building heights and setbacks, open space, and landscaping per the code
or per the Master Site Plan approval in 2014. Design standards will apply.
3.3 CULTURAL RESOURCES
The Master Site Plan area was evaluated for cultural resources in the 2011 EIS and again with the Master
Site Plan expansion in 2016. No sites were determined eligible. The ROD includes inadvertent discovery
conditions applicable throughout the study area.
3.4 TRANSPORTATION
Based on the results of the 2019 Reevaluation traffic analysis, overall transportation conditions are
expected to operate similarly to the FEIS Preferred Alternative, Alternative 3, and the 2014 Reevaluation
Alternative. The 2019 evaluation includes the Sunset Court site added in 2016. See Appendix A.
3.5 PARKS AND RECREATION
The Sunset Neighborhood Park has been constructed in accordance with the adopted Master Site Plan.
There are no changes to the FEIS results or prior Reevaluations in 2014 or 2016.
3.6 PUBLIC SERVICES
The overall conclusions of the FEIS for Selected Alternatives is expected to be similar for the Reevaluation
Alternative since growth is the same as projected for the overall neighborhood and is similar to the 2014
and 2016 Reevaluation proposal.
3.7 UTILITIES
3.7.1 Water and Sewer
Conceptual utility plans in the FEIS, City design manuals, and code requirements will apply to future
development.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 19
3.8 OTHER FEIS TOPICS
Generally, regarding natural environment topics (earth, air quality, water resources, plants and animals),
there are no anticipated changes to the overall conclusions or mitigation measures identified in the ROD
and PAO since the proposed mixed use development activities are essentially occurring within the same
footprint and the range of impervious estimates in the FEIS and ROD will be maintained.
Conditions, mitigation measures, and conclusions regarding Environmental Health and Historic/Cultural
Features are likewise unchanged. No environmental health conditions or cultural resources features are
known in the Potential Sunset Terrace Redevelopment Subarea, but in case such features are uncovered
mitigation measures would apply.
Lastly, regarding socio-economics, housing, and environmental justice, overall conditions and impacts
regarding the potential for change in the neighborhood, need for replacement housing or vouchers, etc.
identified in the FEIS are still valid, as the study area continues to redevelop to a mixed use, amenity-rich
environment.
3.9 MONITORING AND REVIEW
The PAO includes monitoring and review measures to be considered within five years of the ordinance
adoption; some measures are to be considered at the time of a NEPA Reevaluation (compliance with
neighborhood goals and Leadership in Environmental and Energy Design rating system for Neighborhood
Development [LEED-ND] criteria or equivalent), though monitoring and review are directed to the Planned
Action area as a whole. The City conducted a review in the 2014 Reevaluation and 2016 Reevaluation.
The next 5-year milestone, based on the effective date of the amended ordinance in 2016, would occur in
2021.
Consistent with the PAO monitoring provisions, this Reevaluation provides a review of the Planned Action
Study Area Goals and Objectives and to the LEED-ND criteria in relation to the Reevaluation Alternative.
See Exhibit 15 and Exhibit 16. Results show the 2019 Reevaluation Alternative continues to create a mixed
use, mixed income neighborhood supported by park, library, road, and stormwater improvements that
increase quality of life.
Exhibit 15. Goals and Objectives Reevaluation
FEIS Goals and Objectives Reevaluation Alternative: Potential Sunset
Terrace Redevelopment Subarea
Transformation of private and public properties in
the Planned Action Study Area …is expected to
meet the Sunset Area Community vision, as
expressed in the Highlands Phase II Task Force
Recommendations (City of Renton 2008a) and the
CIS (City of Renton 2009b).
The Highlands is a destination for the rest of the
city and beyond.
The neighbors and businesses here are engaged
and involved in the community.
Neighborhood places are interconnected and
walkable.
The neighborhood feels safe and secure.
The Reevaluation Alternative is based on the prior
studied alternatives and continues to promote a
mixed-income, mixed-use development with parks,
library, and green streets to promote an
affordable, connected, walkable, and attractive
area for residents and businesses.
Since the approval of the Planned Action and
implementing Master Site Plan, affordable housing
has been developed at Sunset Court.
Neighborhood civic facilities have been built
including the library. The City has developed a
more walkable place with streets and streetscapes
improved consistent with the Master Site Plan. The
Sunset Neighborhood Park has been completed.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 20
FEIS Goals and Objectives Reevaluation Alternative: Potential Sunset
Terrace Redevelopment Subarea
Neighborhood growth and development is
managed in a way that preserves quality of life.
The neighborhood is an attractive place to live
and conduct business.
The neighborhood is affordable to many incomes.
The neighborhood celebrates cultural and ethnic
diversity.
For each of the major components of the proposal,
the following specific goals and objectives were
developed to be consistent with this vision.
The entire Renton Sunset neighborhood is
considered a planned action area since 2011 per
Exhibit 2; growth and general types of land uses
are consistent with the City’s Comprehensive Plan.
The PAO, effective in 2011 and amended in 2014
and 2016, remains in effect. The City may update
the PAO with the amended 2019 Master Site Plan
results.
The Reevaluation/Addendum demonstrates that the
Planned Action EIS conclusions remain valid. City
infrastructure investments for the planned action
area continue. For example, regional stormwater
and green streets have bene implemented and are
expected to continue to be implemented in the
neighborhood. A loop road has been implemented;
the Library site has been developed. The park was
enlarged and has been constructed.
1. Through designation of a Planned Action and
infrastructure investments, support and stimulate
public and private development.
2. Ensure that redevelopment is planned to conform
to the City’s Comprehensive Plan.
The Reevaluation Alternative implements the City’s
Comprehensive Plan Commercial Mixed-Use
designation and furthers the intent of the CV zone
for a mixed-use center, providing housing, civic,
retail, and park uses.
3. Through the Planned Action and early
environmental review, accelerate the transformation
of the Potential Sunset Terrace Redevelopment
Subarea with mixed-income housing and mixed uses
together with places for community gathering. This
will also be accomplished in part by using this EIS to
achieve a NEPA Record of Decision, which will
enable RHA to submit a HUD Demolition and
Disposition application in 2015.
See Response to #1. A Demolition and Disposition
permit was obtained for the Library site and a
second permit was obtained for the balance of the
site.
4. Ensure that the Planned Action covers
environmental review of Sunset Area roadway,
drainage, parks and recreation, and other
infrastructure improvements, and analyze impacts of
anticipated private development in addition to
Sunset Terrace.
See Response to #1. The total amount of growth
studied across the Planned Action study area
remains unchanged under the 2019 Reevaluation
Alternative; redistribution of some units was
evaluated in 2014, 2016, and 2019. Both public
and private development is promoted in the
Potential Sunset Terrace Redevelopment Subarea
as well as the broader neighborhood.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 21
FEIS Goals and Objectives Reevaluation Alternative: Potential Sunset
Terrace Redevelopment Subarea
5. Build on previous City, RHA, and Renton School
District efforts and current projects. Leverage
relationships and partner with existing community
outreach activities and resources. Recognize
community desires documented in:
Report and Recommendation of the Highlands
Area Citizen’s Zoning Task Force (City of Renton
2006),
Report and Recommendation of the Highlands
Phase II Task Force (City of Renton 2008a),
Highlands Action Plan (City of Renton 2009c),
Sunset Area Community Investment Strategy (City
of Renton 2009b),
Renton Trails and Bicycle Master Site Plan (City
of Renton 2009d),
Renton Parks, Recreation, Open Space and
Natural Resources Plan (estimated completion
date September 2011),
Utility system plans, and
Library replacement (in process).
The Reevaluation Alternative continues to further the
prior planning efforts. The following has been
developed:
Replacement affordable housing at Sunset Court
A new library
A new larger neighborhood park
A regional stormwater facility
Harrington Avenue NE Greenstreet
Sunset Lane improvements
Early childhood education center has been
redeveloped
The subarea will have additional mixed income,
mixed use development as anticipated in the
Community Investment Strategy.
6. Create a Great Street on NE Sunset Boulevard,
as described in the CIS. Implement the City
Complete Streets policy for the NE Sunset
Boulevard corridor and the Sunset Area green
connections. Extend conceptual design of
improvements between the Interstate 405 limited
access right-of-way and Monroe Avenue NE and
include them in the Planned Action effort.
The Reevaluation Alternative Master Site Plan
concept anticipates and recognizes the multimodal
design of NE Sunset Boulevard by matching the
future right of way boundary studied in the FEIS.
7. Encourage low-impact stormwater management
methods and area-wide solutions as part of a
master drainage plan to support development.
The Reevaluation Alternative would be developed
consistent with the Sunset Area drainage plan.
Regional stormwater in the central park and green
streets (e.g. Harrington Avenue NE) have been
accomplished with more green infrastructure
planned in future phases.
8. Engage the community in a transparent process
using available outreach opportunities and tools
successfully used in prior planning efforts.
The Reevaluation Alternative is similar to prior
studied alternatives that were developed with
public engagement opportunities. Public comment
opportunities are offered with some types of land
use permits (e.g. Notices of Application), or
amendments to the PAO.
9. Optimize funding strategies by leveraging
partnerships, innovation and sustainable
development for a healthy community. Recognize
the importance and timing of integrating housing,
transportation, infrastructure, expanded economic
The Reevaluation Alternative has resulted from a
public/private Master Site Plan coordination effort.
See response to #1 regarding infrastructure and
civic investments.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 22
FEIS Goals and Objectives Reevaluation Alternative: Potential Sunset
Terrace Redevelopment Subarea
opportunity, parks and recreation, and the
environment.
Source: FEIS, Appendix A, 2011; BERK 2014
The official 2014 LEED ND project scorecard3 published by the U.S. Green Building Council is used as a
guide to address green design issues in relation to the proposed redevelopment. For each criteria group
on the scorecard, a brief discussion of how the proposed redevelopment is consistent with the principles of
LEED ND is provided in Exhibit 16.
Exhibit 16. LEED for Neighborhood Development Criteria
Summary of Criteria Reevaluation Alternative: Potential Sunset Terrace
Redevelopment Subarea
The intent of the Smart Location and Linkage
criteria of the LEED ND rating system is to
encourage development to avoid environmentally
sensitive areas and to be focused within and near
existing communities where there are opportunities
to access services and reach destinations. There is a
preference for housing proximate to jobs. Access to
public transit is promoted to reduce vehicle trips.
Development in smart locations also encourages a
greater degree of walking of bicycling, which has
personal health benefits.
The Sunset Terrace site is located along a major
transportation and transit corridor within the City of
Renton. Redevelopment of the site under the
Reevaluation Alternative would contribute to a
mixed-use, mixed-income development already
served by the full range of public services on a
previously developed infill site on a major transit
corridor – a “smart location.” The Master Site Plan
concept anticipates and recognizes the multimodal
design of NE Sunset Boulevard by matching the
future right of way boundary studied in the FEIS.
The intent of the Neighborhood Pattern and
Design criteria of the LEED ND rating system is to
promote safe, diverse, walkable, compact
neighborhoods with high-quality design with a mix
of land uses.
The Master Site Plan furthers the intent of the
Comprehensive Plan Mixed Use Commercial
designation and CV zone for a mixed-use center,
providing housing, civic, retail, and park uses. The
neighborhood is compact and furthers walkability
and quality design with a loop road, green streets,
and a new park and library.
The intent of the Green Infrastructure and
Buildings criteria is to encourage development that
implements green building practices or introduces
green infrastructure. This includes using certified
green building techniques, increasing building water
and energy efficiency, controlling pollution from
construction activities, implementing adaptive reuse
of historic buildings, and using green methods of
stormwater management.
The Reevaluation Alternative as expressed in the
amended Master Site Plan would implement FEIS
mitigation measures and retain green features of
prior studied alternatives, including:
Green Connections for Stormwater Management:
The Reevaluation Alternative continues the City’s
investment in Green Connections (Harrington
Avenue NE implemented), a regional stormwater
facility (built), and the drainage Master Site Plan
for the study area.
Construction Emission Control: The FEIS
recommends that the City require all construction
contractors to implement air quality control plans
3 See: Checklist: LEED v4 for Neighborhood Development. https://www.usgbc.org/resources/leed-v4-neighborhood-
development-checklist. Accessed: July 22, 2019.
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 23
Summary of Criteria Reevaluation Alternative: Potential Sunset Terrace
Redevelopment Subarea
for construction activities in the study area,
including measures for reducing engine emissions
and fugitive dust.
Energy Efficiency: The FEIS recommends that the
City encourage or require implementation of
energy and greenhouse gas reduction measures
in the study area such as compliance with the
Northwest ENERGY STAR Homes program and
the Seattle Energy Code for non-residential
buildings.
Source: FEIS, Appendix A, 2011; BERK, 2014 and 2019.
4 Conclusions
The City of Renton (City) is the Responsible Entity and lead agency for NEPA purposes. In accordance with
specific statutory authority and the U.S. Department of Housing and Urban Development’s (HUD’s)
regulations at 24 Code of Federal Regulations (CFR) part 58, the City is authorized to assume responsibility
for environmental review, decision-making, and action that would otherwise apply to HUD under NEPA.
Additionally, the City is the lead agency and proponent of the broader Planned Action for the Sunset area
which has had environmental review under Washington State Environmental Policy Act (SEPA) Revised Code
of Washington [RCW] 43.21(C).
The City has performed joint NEPA/SEPA environmental review in cooperation with the Recipient, the Renton
Housing Authority (RHA). Accordingly, the City prepared a Draft and Final EIS to analyze potential impacts
of redevelopment of the Sunset Terrace public housing community. The Final Environmental Impact Statement
(FEIS) supporting both milestones was issued April 1, 2011.
The City initiated consultation with agencies and tribes regarding permit requirements and to identify any
areas of concerns regarding the Sunset Terrace public housing redevelopment as well as the overall
Planned Action. Federal and state agencies were notified of comment opportunities through the scoping
process and were offered comment opportunity on the Draft EIS. Two agencies were particularly consulted
consistent with NEPA, the National Historic Preservation Act (Section 106), and the Endangered Species Act
(Section 7). As documented in the ROD and Environmental Review Record, the City received a letter of
concurrence from NMFS in May 2011. The Biological Assessment and NMFS memoranda are included in
the Environmental Review Record. The City also completed Section 106 consultation for Sunset Terrace
redevelopment and all properties fronting NE Sunset Boulevard as documented in the ROD and
Environmental Review Record. In addition, consistent with the federal Coastal Zone Management Act, the
City received a letter of consistency from the State of Washington Department of Ecology (16 U.S.C. 1451-
1464).
In May 2011, the City of Renton completed a ROD in accordance with the National Environmental Policy
Act and adopted a PAO in accordance with the State Environmental Policy Act.
The ROD and PAO identified mitigation measures from the FEIS. The Record of Decision (ROD) concluded
that “[w]ith the application of City-adopted development regulations and recommended mitigation
measures, and application of other federal and state requirements, no significant unavoidable adverse
impacts are anticipated. Pursuant to 40 CFR 1505.3, this decision to proceed with Sunset Terrace and
actions in the broader area will be implemented and mitigation measures imposed through appropriate
August 2019 | Renton Sunset Community Area Reevaluation and Addendum 24
conditions in any land use or related permits or approvals issued by the City of Renton and through
conditions of federal funding.” This Reevaluation and Addendum maintains the mitigation measures from
the EIS, ROD, and Planned Action and identifies where the application of such mitigation measures (e.g.,
design guidelines) is particularly relevant and could be included in permit conditions.
The City finds by this re-evaluation, after considering the effects of the revised Master Site Plan, as well
as existing and supplemental environmental documentation, that no substantive change to the findings in
the ROD would occur. The Sunset Area Community Planned Action NEPA/SEPA EIS adequately examines
the impacts of the overall project, and the proposed changes in the Master Site Plan would not result in
modification to those conclusions. No new or significantly different impacts to the environment would occur.
Mitigation measures incorporated in the proposal and identified in the EIS, and additional consultation and
mitigation documented in the ROD, represent reasonable steps to reduce adverse environmental effects of
the proposed project. Together, these measures and would reduce effects to acceptable levels. No
additional mitigation is warranted as a result of changes proposed in the Master Site Plan.
Responsible Entity Certifying Officer
City of Renton Environmental Review Committee (ERC)
Date: Signature:
Signature:
Signature:
Signature:
BASIS OF BEARINGSREFERENCESSURVEYOR'S NOTESVICINITY MAPN.T.S.SURVEYOR'S CERTIFICATESCHEDULE B ITEMSLEGAL DESCRIPTIONVERTICAL DATUMLEGENDALTA/NSPS LAND TITLE SURVEY ALTA/NSPS LAND TITLE SURVEYSUNSET OAKS N.T.S.CONTROL MAP
LEGENDALTA/NSPS LAND TITLE SURVEY ALTA/NSPS LAND TITLE SURVEYSUNSET OAKS
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
5705'6.#0'0'4'06109#
5705'61#-5#2#46/'065coterra
321 3rd Ave South, Suite 406
Seattle, Washington 98104
ph 206.596.7115
coterraengineering.com
ENGINEERING PLLC
5705'61#-5#2#46/'065
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
5705'6.#0'0'4'06109#
5705'61#-5#2#46/'065coterra
321 3rd Ave South, Suite 406
Seattle, Washington 98104
ph 206.596.7115
coterraengineering.com
ENGINEERING PLLC
5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
July 23, 2019
Project: Pre-construction assessment for property re-development at 1073 Harrington Ave NE,
Renton, WA. Parcel numbers 7227801315, 1310, and 1290.
Contact: Brent Chastain - Third Place Design 341 NE 91st Street Seattle, WA 98115
Phone – 206 920 9996 Email – Brent@thirdplacedesigncoop.com
Objectives: Evaluate health of existing trees and establish criteria for the preservation of those
to be retained.
Description: The proposed development is formed from a modified combination of six previous
lots which the Renton Housing Authority purchased between 2011 and 2014 (Figures 1 and 2).
Until 2015 five properties had numerous trees present, mainly along the lot lines (see Figure 2).
The same canopy configuration goes back at least twenty years as shown in Figure 3. The City of
Renton had the existing houses demolished in 2016. Post demolition the tree cover was reduced
by roughly sixty percent and the area bulldozed where the houses had been (Figure 4).
The RHA is now ready to proceed with developing the site and contracted with Third Place
Design. Their proposed site plan is shown in Figure 5. They in turn contacted Superior NW and
asked that a formal assessment of the remaining tree be made. The provided plan shows a large
evergreen in the center of the development and four others on the west side that currently exist.
There are a number of trees shown which will be installed post construction.
The following itemized list begins in the northwest corner of the property. It includes the trees
currently on the property and those within 10’ of the borders. The numeric designations are
reflected in the tree plot shown in Figure 6. The diameters measured were taken at the standard
height of 54” above grade (DSH) and the trees were tagged with 1” green circular markers.
1) Douglas Fir (Pseudotsuga menziesii) 26.5” DSH, 25’ tall standing 10’ E of the rough
curb line/parking area along Glenwood Avenue and 16’ S of the NW corner marker.
The tree has been topped multiple times for power line clearance (Figure 7). It has a
full canopy which descends to near the 10’ level. The branches are somewhat
overextended and are encroaching on a utility pole in its NW quadrant as shown in
Figure 8. It has good new growth and color.
Enterprises
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
2) Douglas Fir 29” DSH, 70’ tall standing 65’ S of the #1 tree and 8’ E of the rough curb
line. It is in fair condition with average new growth and color. There is some
deadwood present and it has been pruned multiple times for power line clearance on
its west face. Its canopy extends down to the 12’ level. The SW corner of the previous
house was less than 15’ away from the base of the tree and the driveway ran fully
beneath its canopy as shown in Figure 9.
3) Douglas Fir 24” DSH, 65’ tall standing 36’ S of #2, 8’ E of the rough curb line, and at
the north end of a small stand. It is in fair condition and its canopy extends down to
the 12’ level although it mainly extends to north and is slightly over extended. There
is ivy present in the tree. It has been pruned for wire clearance multiple times. The
NW corner of the previous house was around 15’ back from the tree and its driveway
ran beneath the tree.
4) Douglas Fir 17.5” DSH, 65’ tall standing 4’ SW of the #3 tree. All its canopy extends
to the west except for at the very top. It has somewhat limited new growth and decent
color. It has been pruned multiple times for wire clearance. There is ivy present in the
tree.
5) Douglas Fir 18” DSH, 60’ tall standing 7’ S of the #4 tree. There is not much canopy
on this tree. Most of it is on the east side in a narrow column and then there is a little
foliage on the west side starting at the half way point and running nearly in a single
branch width. It has noticeably limited new growth and poor color. It has been pruned
multiple times for wire clearance. There is ivy present in the tree. A crow’s or hawk’s
nest is visible at the very top.
6) Douglas Fir 25” DSH, 65’ tall standing 5’ S of #5, 8’ E of the existing edge of the
asphalt for Glenwood Avenue, 24’ N of a set of new water meters, and at the south
end of the stand. It has fair color but below average new growth. Its canopy extends
down to the 12’ level, almost entirely extends to the south, and is slightly over
extended. There is ivy present in the tree. It has been pruned for wire clearance
multiple times. The west side of the previous house was close to 20’ back from the
tree.
7) Silver Maple (Acer saccharinum) 40” DSH, 55’ tall, 28’ radial spread standing 65’
nearly due east of the #2 fir. The tree is in decline with poor color, stunted new
growth, deadwood and die back throughout the canopy, and it is already showing
color changes at the extremities. It has a cavity low on the west side with a 7”
diameter opening. The previous house was 25’ west of the maple’s base. There had
been several smaller trees or quite large shrubs standing between this tree and the #8
fir to its east prior to the demolition event as shown in Figure 2.
8) Douglas Fir 28” DSH, 70’ tall standing 55’ ESE of the #7 maple. The top of the tree
was damaged near the 55’mark and it now exhibits multiple stems above that level
(see Figure 10). It has average new growth and color. There have been recent
breakouts along the SE quadrant probably due to snow loading.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
9) Pacific Dogwood (Cornus nuttalli) 13” DSH, 35’ tall, 9’ spread standing near the
center line on the south side of the parcel. The tree is in weak condition with little to
no new growth and poor color. An 8” caliper branch cracked out low on the stem and
tore into the quick of the tree. Another 6” caliper branch broke out about 18” higher
on the stem. The tree is nearly engulfed in English Laurel and holly.
10) Red Alder (Alnus rubra) 36” DSH, 45’ tall, 25’ spread standing 45’ W of the #9 tree
at the south end of the parcel. It has advanced decay present along the column and
the main scaffolds. The upper half of the canopy is dead. Before the demolition event
this tree was surrounded by a dense thicket of other shrubs/small trees. Currently
there is nothing around the tree but grass and weeds.
Methods: Tree assessment is both an art and a science. To properly perform, an arborist must
have an extensive background in biology, tree mechanics, and tree structure that is equal parts
academic and field knowledge. It takes years of study to recognize and correctly diagnose the
subtle signs trees exhibit before their failure, whether it be partial or total. The process begins
with a visual inspection (visual tree assessment, VTA) which is followed up as necessary with
soundings, core testing, and/or other detection means. Each tree is examined and evaluated
according to several factors including species type, size, vigor, injuries present, root and grade
disturbance, deadwood, location and extent of decay, stem taper, exposure, and targets that are at
risk.
Discussion: Of the ten trees listed only the #3-6 and #8 firs are noted for retention. The other
trees currently present are located in areas which will be occupied by structures.
The #8 Douglas Fir is shown in Figure 5 with a 20’ radial space (a little more in the NE and SW
quadrants) left within which it is to live. Trees can accept some loss of rooting space and still
survive but the arboricultural industry accepted threshold is thirty percent. In the given scenario
the tree will lose over 50% of its Critical Rooting Area. If the tree is meant to be a long term
asset for the campus then this area has to be increased to at least a 23.5’ radial circle. This could
be accomplished by making the pathways around the tree fully permeable.
Pre-grading and excavation a hard fence will have to be set up around this tree at a distance of
25’ radial feet. The area within the fence should be covered with 6-8” of arbormulch. When it is
time to do the improvement work within the fencing (the paths, the parking, the corner of
Building B East’s foundation forms) it will have to be overseen by an arborist to document the
degree and nature of the impact. The path should be cut and set by hand if in any way possible.
All the mulch would be left around the tree once construction is finished. No grass should be
planted. The only plants which should be installed would be those commonly found around firs
naturally. Salal, evergreen or deciduous huckleberries, rhododendron species, vine maples
(native or Japanese varietals), and the like would be acceptable choices.
The top of the tree will have to be pruned to create a stronger long term structure. Depending on
what the climbing arborist finds it could be that the tree will need ongoing care on a five to seven
year basis. The tree would definitely benefit from a deep root feed at the end of the construction
process to help it cope with impact stress.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Based on the historical imagery shown in Figure 2 it is clear that the #3-6 firs incurred root
disturbance well within their Critical Root Zones (CRZ). This is the area defined as one radial
foot per inch of tree diameter. Trenching type incursion, that is excavation that occurs along
only one sector of a tree’s CRZ, can reach significantly into the root growth area without having
a detrimental long term effect. What does have to be absolutely protected is a tree’s Structural
Root Plate (SRP). This radial area is related to the diameter inches of the tree in question but not
quite in such a direct proportion. Figure 11 below illustrates the relationship.
Figure 11. Size of the Structural Root Plate in relation to tree stem diameter. Note
that the SRP levels off at 10’ for any tree over 24” in diameter (Coder, 1996).
In the case of the four firs mentioned above, the excavation of the existing house’s foundation on
their east side occurred between 12’ and 17’ from their bases. This would have been well outside
any of the fours’ SRP. The proposed walkway to their north is 20’ away; again well outside the
SRP for the #3 tree. The new foundation work for Building B West could come as near as 18’ to
the base of the trees. This will still not affect the Structural Root Plates of any of the four trees.
However, if the City of Renton is going to ask that a sidewalk is installed on the west side of the
trees or that any other hardscaping improvement be made which requires a change in grade, these
trees will be severely impacted. Installing sidewalk will necessitate the removal of all four due to
compromising their structural stability. Any other improvements on the west side will have to be
evaluated on a case by case basis.
Protection fencing for the stand should be set at the full CRZ distance for the larger two, namely
twenty-five radial feet on three sides. On the west it will have to be limited to being at the curb
line or just slightly beyond as traffic safety dictates. The area within the protection fencing
should be filled with 6-8” of arbormulch and arborist oversite is dictated when work has to occur
within the protection zone.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Waiver of Liability Because the science of tree risk assessment is constantly broadening its
understanding, it cannot be said to be an exact science. Every tree is different and performing
tree risk assessment is a continual learning process. Many variables beyond the control, or
immediate knowledge, of the arborist involved may adversely affect a tree and cause its
premature failure. Internal cracks and faults, undetectable root rot, unexposed construction
damage, interior decay, and even nutrient deficiencies can be debilitating factors. Changes in
circumstance and condition can also lead to a tree’s rapid deterioration and resulting instability.
All trees have a risk of failure. As they increase in stature and mass their risk of breakdown also
increases, eventual failure is inevitable.
While every effort has been taken to provide the most thorough and accurate snapshot of the
trees’ health, it is just that, a snapshot, a frozen moment in time. These findings do not guarantee
future safety nor are they predictions of imminent events. It is the responsibility of the property
owner to adequately care for the tree(s) in question by utilizing the proper professionals and to
schedule future assessments in a timely fashion.
This report and all attachments, enclosures, and references, are confidential and are for the use of
Brent Chastain, Third Place Design, the Renton Housing Authority, and their representatives
only. They may not be reproduced, used in any way, or disseminated in any form without the
prior consent of the client concerned.
Anthony Moran, BS
Certified Arborist
Qualified Tree Risk Assessor
ISA #PN-5847A
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 1. New parcel configuration.
Figure 2. Aerial view of the six lots circa 2015 showing prevoius configuration.
Note the concentration of trees along the perimeter of the properties.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 3. Aerial view from 2000 showing nearly the same canopy coverage.
Figure 4. Aerial view circa 2017 showing the new parcel post demolition.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 5. Concept of site redevelopment.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 6. Current aerial view of subject property. The white numerals correspond to the
nomenclature in the description section and show rough placement of the indicated trees.
Please refer to the most recent survey for exact locations.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 7. Photo of the #1 Douglas Fir taken during the July 2019 site visit.
Figure 8. Photo of the #1 fir showing encroachment on the utility pole at the NW
corner of the parcel.
13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com
206-930-5724
Figure 9. Enlargement of the 2015 aerial photo showing driveways
running under the #2 and #3 firs.
Figure 10. Photo of the top of the #8 fir showing the weak structural formation.
coterra
321 3rd Avenue South, Suite 406
Seattle, Washington 98104
206.596.7115
TECHNICAL INFORMATION REPORT
Project: Renton Housing Authority
Sunset Oaks Apartments
Renton, WA 98056
Prepared For: Renton Housing Authority
2900 NE 10th St
Renton, WA 98056
Prepared By: Max Berde, PE
Reviewed By: Peter Apostol, PE
Date: September 3, 2019
ENGINEERING PLLC
TABLE OF CONTENTS
Section No. Subject Page No.
SECTION I PROJECT OVERVIEW .....................................................................1
SECTION II CONDITIONS AND REQUIREMENTS SUMMARY ...................15
SECTION III OFFSITE ANALYSIS ......................................................................19
SECTION IV FLOW CONTROL AND WATER QUALITY
FACILITY ANALYSIS AND DESIGN ..........................................23
SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN ................27
SECTION VI SPECIAL REPORTS AND STUDIES .............................................27
SECTION VII OTHER PERMITS ...........................................................................27
SECTION VIII EROSION AND SEDIMENT CONTROL ......................................27
SECTION IX BOND QUANTITIES AND
DECLARATION OF COVENANTS ...............................................28
SECTION X OPERATIONS AND MAINTENANCE MANUAL .......................28
LIST OF FIGURES
FIGURE 1 VICINITY MAP .................................................................................4
FIGURE 2 TIR WORKSHEET ............................................................................5
FIGURE 3 EXISTING SITE SOILS...................................................................12
FIGURE 4 EXISTING LAND COVER .............................................................13
FIGURE 5 DEVELOPED LAND COVER ........................................................14
LIST OF APPENDICIES
APPENDIX A CIVIL PLANS
APPENDIX B FLOW CONTROL/DETENTION CALCULATIONS
APPENDIX C WATER QUALITY CALCULATIONS
APPENDIX D GEOTECHNICAL REPORT
APPENDIX E CONVEYANCE CALCULATIONS
APPENDIX F DRAINAGE REVIEW FLOWCHART
Sunset Oaks Apartments Page 1 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION I – PROJECT OVERVIEW
General Description:
The proposed Sunset Oaks Apartment project includes the construction of three multi-
story apartment buildings on a proposed 1.053 acre lot currently consisting of five
currently-undeveloped parcels. The existing five parcels were previously developed as
single-family homes and previously demolished. Proposed project includes on-site
parking, landscaping, frontage improvements on Glennwood Ave NE and Harrington
Ave NE, and associated utility and storm drainage improvements. The project proposes to
construct a public alley between Glennwood Ave NE and Harrington Ave NE on the
northern margin of the site. The alley will be dedicated to the City of Renton. The project
site, located in the City of Renton, is bounded by Glennwood Ave NE to the west,
Harrington Ave NE to the east, Sunset Lane NE (NE 10th Street) to the south, and
residential parcels to the north (see Figure 1 for vicinity map).
The proposed project has been designed to meet the requirements of the 2017 City of
Renton Surface Water Design Manual (SWDM). A summary of the project data is
provided in the TIR worksheet (see Figure 2).
Site Soils:
The NRCS map (see Figure 3) of the site shows a majority of the site consisting of
“Arents, Alderwood material “ with a small portion of the west side of the site consisting
of “Ragnar-Indianola” soils. Additional information on the site’s soils is provided in a
geotechnical report prepared by Zipper Geo Associates, LLC, and dated May 15, 2019.
The findings of the report are based on soil samples taken from five borings that were
excavated on-site. In general, the results of the borings uncovered 3’-12” of medium
dense to dense sand with variable silt and gravel contents. Below that layer the borings
encountered very dense sand with variable silt and gravel contents that the geotechnical
engineer interprets to be glacial till. For more information, see the geotechnical report
included in Appendix D.
Predeveloped Conditions:
The existing site is currently undeveloped with areas of impervious remaining from
demolition and clearing of the former single-family residences on the 5 project parcels.
The remainder of the site is considering to be pervious, former landscaping, consisting of
till grass for stormwater modeling purposes. There are several significant trees spread
throughout the site. The project site consists of one Threshold Discharge Area which is
defined by the City of Renton Surface Water Design Manual as: “an onsite area draining
to a single natural discharge location, or multiple natural discharge locations that
combine within one-quarter –mile downstream.”
The site is generally flat with stormwater runoff draining overland generally north to
south towards Sunset Lane NE.
Sunset Oaks Apartments Page 2 Project No. 19003
Renton, WA Coterra Engineering PLLC
The existing land coverage of the project site is presented in the table below. The
existing site is presented graphically in Figure 4 which follows this section. The
downstream path of stormwater runoff is described in the offsite analysis in Section III.
Table 1 – Existing Site Land Coverage (Acres)
Impervious
(Acres)
Pervious
Till Grass
(Acres)
Total
(Acres)
Project Site 0.250 0.803 1.053
Developed Conditions:
The proposed developed condition includes three apartment buildings with at-grade
parking stalls adjacent to and within the buildings; a public alley at the northern margin
of the site; pedestrian walkways; and associated storm drainage, utility, and landscape
improvements. The following table quantifies the areas of the proposed land coverage.
The proposed site is presented graphically in Figure 5 which follows this section.
Table 2 – Developed Site Land Coverage (Acres)
Rooftop
(Acres)
Hardscape
(Acres)
Grass/
Landscape
(Acres)
Total
(Acres)
Project Site 0.433 0.380 0.240 1.053
The existing site topography will not be dramatically altered in the proposed condition.
In general, the site will continue to drain from north to south towards Sunset Lane NE as
it currently does in the existing condition.
The proposed improvements within the project site described above and delineated in
Table 2 trigger both flow control and water quality mitigation per the City of Renton
Surface Water Design Manual.
Stormwater runoff will be collected by roof drains, catch basins, and area drains. Per
Core Requirement #4 of the 2017 City of Renton Surface Water Design Manual, the
proposed conveyance system will be designed to convey runoff resulting from the peak
rates resulting from the 25-year storm event. The proposed flow control facility is a
detention tank located under the northwest parking lot and which will discharge to the
existing 18” storm drainage main in Glennwood Ave NE to the west. Permeable
pavements throughout the project site, including pervious asphalt and pervious concrete
sidewalks, will provide water quality treatment. See Section IV for a detailed description
of the design of the flow control and water quality facilities.
Sunset Oaks Apartments Page 3 Project No. 19003
Renton, WA Coterra Engineering PLLC
FIGURE 1 – VICINITY MAP
Sunset Oaks Apartments Page 4 Project No. 19003
Renton, WA Coterra Engineering PLLC
FIGURE 2
CITY OF RENTON
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
CITY OF RENTON SURFACE WATER DESIGN MANUAL
2017 City of Renton Surface Water Design Manual 12/12/2016 8-A-1
REFERENCE 8-A
TECHNICAL INFORMATION REPORT (TIR)
WORKSHEET
Part 1 PROJECT OWNER AND
PROJECT ENGINEER Part 2 PROJECT LOCATION AND
DESCRIPTION
Project Owner _____________________________
Phone ___________________________________
Address __________________________________
_________________________________________
Project Engineer ___________________________
Company _________________________________
Phone ___________________________________
Project Name __________________________
CED Permit # ________________________
Location Township ________________
Range __________________
Section _________________
Site Address __________________________
_____________________________________
Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS
Land Use (e.g., Subdivision / Short Subd.)
Building (e.g., M/F / Commercial / SFR)
Grading
Right-of-Way Use
Other _______________________
DFW HPA
COE 404
DOE Dam Safety
FEMA Floodplain
COE Wetlands
Other ________
Shoreline
Management
Structural
Rockery/Vault/_____
ESA Section 7
Part 5 PLAN AND REPORT INFORMATION
Technical Information Report Site Improvement Plan (Engr. Plans)
Type of Drainage Review
(check one):
Date (include revision
dates):
Date of Final:
Full
Targeted
Simplified
Large Project
Directed
__________________
__________________
__________________
Plan Type (check
one):
Date (include revision
dates):
Date of Final:
Full
Modified
Simplified
__________________
__________________
__________________
REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-2
Part 6 SWDM ADJUSTMENT APPROVALS
Type (circle one): Standard / Blanket
Description: (include conditions in TIR Section 2)
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Approved Adjustment No. ______________________ Date of Approval: _______________________
Part 7 MONITORING REQUIREMENTS
Monitoring Required: Yes / No
Start Date: _______________________
Completion Date: _______________________
Describe: _________________________________
_________________________________________
_________________________________________
Re: SWDM Adjustment No. ________________
Part 8 SITE COMMUNITY AND DRAINAGE BASIN
Community Plan: ____________________________________________________________________
Special District Overlays: ______________________________________________________________
Drainage Basin: _____________________________________________________________________
Stormwater Requirements: _____________________________________________________________
Part 9 ONSITE AND ADJACENT SENSITIVE AREAS
River/Stream ________________________
Lake ______________________________
Wetlands ____________________________
Closed Depression ____________________
Floodplain ___________________________
Other _______________________________
_______________________________
Steep Slope __________________________
Erosion Hazard _______________________
Landslide Hazard ______________________
Coal Mine Hazard ______________________
Seismic Hazard _______________________
Habitat Protection ______________________
_____________________________________
REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-3
Part 10 SOILS
Soil Type
______________________
______________________
______________________
______________________
Slopes
________________________
________________________
________________________
________________________
Erosion Potential
_________________________
_________________________
_________________________
_________________________
High Groundwater Table (within 5 feet)
Other ________________________________
Sole Source Aquifer
Seeps/Springs
Additional Sheets Attached
Part 11 DRAINAGE DESIGN LIMITATIONS
REFERENCE
Core 2 – Offsite Analysis_________________
Sensitive/Critical Areas__________________
SEPA________________________________
LID Infeasibility________________________
Other________________________________
_____________________________________
LIMITATION / SITE CONSTRAINT
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
Additional Sheets Attached
Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet
per Threshold Discharge Area)
Threshold Discharge Area:
(name or description)
Core Requirements (all 8 apply):
Discharge at Natural Location Number of Natural Discharge Locations:
Offsite Analysis Level: 1 / 2 / 3 dated:__________________
Flow Control (include facility
summary sheet)
Standard: _______________________________
or Exemption Number: ____________
On-site BMPs: _______________________________
Conveyance System Spill containment located at: _____________________________
Erosion and Sediment Control /
Construction Stormwater Pollution
Prevention
CSWPP/CESCL/ESC Site Supervisor: _____________________
Contact Phone: _________________________
After Hours Phone: _________________________
REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-4
Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet
per Threshold Discharge Area)
Maintenance and Operation Responsibility (circle one): Private / Public
If Private, Maintenance Log Required: Yes / No
Financial Guarantees and Liability Provided: Yes / No
Water Quality (include facility
summary sheet)
Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog
or Exemption No. _______________________
Special Requirements (as applicable):
Area Specific Drainage
Requirements
Type: SDO / MDP / BP / Shared Fac. / None
Name: ________________________
Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None
100-year Base Flood Elevation (or range): _______________
Datum:
Flood Protection Facilities Describe:
Source Control
(commercial / industrial land use)
Describe land use:
Describe any structural controls:
Oil Control High-Use Site: Yes / No
Treatment BMP: _________________________________
Maintenance Agreement: Yes / No
with whom? _____________________________________
Other Drainage Structures
Describe:
REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-5
Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS
MINIMUM ESC REQUIREMENTS
DURING CONSTRUCTION
Clearing Limits
Cover Measures
Perimeter Protection
Traffic Area Stabilization
Sediment Retention
Surface Water Collection
Dewatering Control
Dust Control
Flow Control
Control Pollutants
Protect Existing and Proposed
BMPs/Facilities
Maintain Protective BMPs / Manage
Project
MINIMUM ESC REQUIREMENTS
AFTER CONSTRUCTION
Stabilize exposed surfaces
Remove and restore Temporary ESC Facilities
Clean and remove all silt and debris, ensure
operation of Permanent BMPs/Facilities, restore
operation of BMPs/Facilities as necessary
Flag limits of sensitive areas and open space
preservation areas
Other _______________________
Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch)
Flow Control Type/Description Water Quality Type/Description
Detention
Infiltration
Regional Facility
Shared Facility
On-site BMPs
Other
________________
________________
________________
________________
________________
________________
Vegetated Flowpath
Wetpool
Filtration
Oil Control
Spill Control
On-site BMPs
Other
________________
________________
________________
________________
________________
________________
________________
Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS
Drainage Easement
Covenant
Native Growth Protection Covenant
Tract
Other ____________________________
Cast in Place Vault
Retaining Wall
Rockery > 4′ High
Structural on Steep Slope
Other _______________________________
REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-6
Part 17 SIGNATURE OF PROFESSIONAL ENGINEER
I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were
incorporated into this worksheet and the attached Technical Information Report. To the best of my
knowledge the information provided here is accurate.
____________________________________________________________________________________
Signed/Date
Sunset Oaks Apartments Page 11 Project No. 19003
Renton, WA Coterra Engineering PLLC
FIGURE 3 – EXISTING SITE SOIL CONDITIONS
Arents, Alderwood material
Ragnar-Indianola
association
coterra
321 3rd Avenue South, Suite 406
Seattle, Washington 98104
206.596.7115 coterraengineering.com
ENGINEERING PLLC
coterra
321 3rd Avenue South, Suite 406
Seattle, Washington 98104
206.596.7115 coterraengineering.com
ENGINEERING PLLC
Sunset Oaks Apartments Page 14 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION II – CONDITIONS AND REQUIREMENTS SUMMARY
The proposed project is subject to a Full Drainage Review per the 2017 City of Renton
Surface Water Design Manual and is therefore subject to all nine core requirements and
all six special requirements. These requirements are listed below along with a discussion
of their applicability to this project. See Appendix F for drainage review type flow chart.
Core Requirements:
Req. #1 Discharge at Natural Location:
Existing discharge locations will be maintained.
Req. #2 Offsite Analysis:
See Section III below.
Req. #3 Flow Control:
The project is required to meet the Peak Rate Flow Control Standard.
The proposed improvements exceed the threshold of 5,000 sf of new and replaced
impervious surface, therefore triggering the requirement of a flow control facility
and on-site flow control BMPs.
A detention tank is proposed to meet the Peak Rate Flow Control Standard
requirement. Onsite BMPs are also required as part of the project and are
discussed below in Core Requirement #9.
For further details see Section IV.
Req. #4 Conveyance System:
The new conveyance system has been designed to convey the 25-year peak flow
from the developed site conditions.
Req. #5 Erosion and Sediment Control:
Construction erosion and sediment control systems will be designed and provided
for review at civil construction permit submittal.
Sunset Oaks Apartments Page 15 Project No. 19003
Renton, WA Coterra Engineering PLLC
Req. #6 Maintenance and Operations:
A Declaration of Covenant is required for this project and will be submitted for
review by City of Renton staff before recording. The proposed facilities will be
owned and maintained by Renton Housing Authority.
Req. #7 Financial Guarantees:
A financial guarantee will be necessary for this project. Bonding will be required
for the construction of improvements and will be obtained prior to construction.
Req. #8 Water Quality:
The proposed improvements located on the project site exceed 5,000 sf of new
and replaced Pollution-Generating Impervious Surface (PGIS), therefore
triggering the requirement of a water quality facility.
Based on the proposed site usage, multi-family housing, Enhanced Basic Water
Quality treatment is required per Core Requirement #8 of the 2017 City of Renton
Surface Water Design Manual for targeted PGIS.
Permeable pavement will be installed throughout the project site and for concrete
sidewalks in any frontage improvements on Glennwood Ave NE and Harrington
Ave NE. Porous asphalt, porous concrete sidewalks, and permeable parking lot
pavers, underlain with a 6” sand layer, will provide water quality treatment for all
proposed PGIS on the project.
For further details see Section IV.
Req. #9 On-Site BMPs:
The proposed improvements exceed the threshold of 5,000 sf of new and replaced
impervious surface, therefore triggering the requirements of Core Requirement #9
to implement on-site flow control facilities to the maximum extent feasible.
Following the City of Renton SWDM required list method for Individual Large
Lots implementing on-site BMPs to comply with Core Requirement #9, all listed
BMPs were determined to be infeasible for the proposed project site.
Despite infeasibility determinations for listed on-site BMP facilities, the proposed
project plans to implement perforated pipe connections on all roof drains from the
Sunset Oaks Apartments Page 16 Project No. 19003
Renton, WA Coterra Engineering PLLC
three proposed apartment buildings per the recommendation of the City of Renton
SWDM.
For further details see Section IV.
Special Requirements:
Req. #1 Area Specific Requirements:
Proposed project site is part of the Sunset Terrace Redevelopment Project within
the City of Renton. Master Site Plan was reviewed and approved by City of
Renton. Additionally, Sunset Terrace Redevelopment Project was reviewed by
NOAA for compliance with requirements of Section 7 of the Endangered Species
Act (ESA) with respect to its potential effects on species listed or proposed for
listing under the ESA. Project must maintain specific impervious coverage limits
for overall Sunset Terrace Redevelopment Project which were approved as part of
previous reviews and agreements. To meet these approved impervious coverage
thresholds, proposed Sunset Oaks Apartments project must implement permeable
pavement throughout project site and for sidewalks on any frontage
improvements.
Req. #2: Floodplain/Floodway Delineation
This project is not adjacent to any floodplains or floodways. Therefore no
delineation is necessary.
Req. #3 Flood Protection Facilities:
This project is not adjacent to any applicable areas and will not affect any
applicable facility.
Req. #4 Source Controls:
This project is a multi-family project and will provide appropriate source controls.
Req. #5 Oil Control:
No oil control requirements are applicable to this project.
Sunset Oaks Apartments Page 17 Project No. 19003
Renton, WA Coterra Engineering PLLC
Req. #6 Aquifer Protection Area
The proposed project is within Zone 2 of the APA. The contractor will be
required to obtain imported fill material from a Washington Department of
Transportation approved source. There are no open flow control or water quality
facilities which will introduce stormwater to groundwater given the project soil
conditions.
Sunset Oaks Apartments Page 18 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION III – OFFSITE ANALYSIS
Task 1 – Study Area Definition and Maps
Maps of the project site and surrounding area were obtained from the King County GIS
website. Topographical site information is from the topographical survey for the project.
Storm drainage system maps were compiled from City of Renton GIS maps and as-built
plans. Aerial images were obtained from Google Earth.
Task 2 – Resource Review
The City of Renton Public Works Department was contacted regarding the resources
listed in section 2.3.1.1 of the 2017 City of Renton Surface Water Design Manual. The
following is a summary of the resource review:
• Adopted Basin Plans
o City of Renton Basin Name: John’s Creek Basin
• Basin Reconnaissance Summary Reports
o None completed to our knowledge.
• Floodplain/Floodway (FEMA) Maps
o The site is not within a floodplain or floodway per FEMA mapping.
• Other Offsite Analysis Reports
o Sunset Terrace Regional Stormwater Facility Final TIR
• Environmentally Sensitive Areas Map
o There are no Environmentally Sensitive areas mapped within the vicinity
of the site.
• USDA Soils Survey
o A geotech report has been completed and site soils are primarily medium
dense sand with silt that was underlain by impermeable glacial till soil.
• Wetlands Inventory Maps
o There are no Wetlands mapped within the vicinity of the site.
Sunset Oaks Apartments Page 19 Project No. 19003
Renton, WA Coterra Engineering PLLC
Task 3 – Field Inspection
A full Level 1 downstream analysis will be performed for civil construction permit
submittal.
Based on review of City of Renton GIS Utility Mapping, due to recent construction of the
Sunset Terrace Regional Stormwater Facility and associated storm drainage lines
surrounding it, the downstream storm drainage system from the Sunset Oaks Apartments
site has not been updated in the GIS system. It is believed that storm drainage is
conveyed south and west from Glennwood Ave NE before connecting into the existing
system on NE Sunset Blvd, where larger diameter conveyance piping flows west towards
Lake Washington beyond ¼ mile downstream from the site.
No known open drainage complaints are associated with the downstream conveyance
system.
Task 4 – Drainage System Description and Problem Description
There are no known problems with the downstream system.
Task 5 – Mitigation of Existing or Potential Problems
Based on the requirements for the design of the proposed drainage systems, no negative
impacts to the systems downstream of the project site are anticipated.
Existing Upslope Drainage Areas
There is no significant upslope unmitigated drainage areas flowing onto the proposed
project site.
Sunset Oaks Apartments Page 22 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION IV – FLOW CONTROL AND WATER QUALITY FACILITY
ANALYSIS AND DESIGN
Flow Control
The project site is located in a Peak Flow Control Standard area per the 2017 City of
Renton Surface Water Design Manual. This standard requires that the developed site
discharge rates match the existing site conditions discharge rates for the 2-, 10-, and 100-
year return periods. The proposed improvements will create more than 2,000 SF of new
plus replaced imperious surfaces, therefore the project is required to meet the flow
control standard and implement on-site flow control BMPs.
MGS Flood stormwater modeling program – utilizing a continuous hydrologic model –
was implemented to size a detention facility which matched the existing site discharge
rates for the 2-, 10-, and 100-year return events. At this preliminary stage of design, a
detention tank was sized in MGS Flood to meet the flow control requirement. As the
project stormwater design is refined, the type of detention structure on the project may be
revised.
Based on the MGS Flood analysis, an approximately 970 CF detention tank is required
for the proposed project. The MGS Flood calculations are included in Appendix B of this
report. The proposed detention tank was designed per the City of Renton SWDM
requirements including 0.5’ sediment storage (dead storage). Sizing details are shown on
the Utility Plan and the future civil construction permit submittal.
On-Site Flow Control BMPs
The proposed site is classified as a Large Lot BMP Site as the proposed site is over
22,000 SF. Implementation of On-Site Flow Control BMPs is therefore required per
Core Requirement #9.
On-site BMPs are evaluated for targeted surfaces, per the list from section 1.2.9.2.2 for
Large Lot BMP Projects in the 2017 City of Renton Surface Water Design Manual.
Analysis of feasibility of the on-site BMPs from the SWDM list follow in order per
SWDM feasibility determination instructions.
• Full Dispersion: Infeasible. Per on-site BMP infeasibility criteria in section C.2.1.1,
the total area of impervious surfaces plus non-native pervious surfaces on the project
site exceed 35% of the total site area.
• Full Infiltration: Infeasible. Per Minimum Design Requirements for Full Infiltration
in section C.2.2.2, existing soils must be “coarse sands or cobbles or medium sands.”
Soils collected in on-site borings per the Geotechnical Engineering Report prepared
by Zipper Geo Associates, LLC, dated 5/15/2019, are classified dense to dense sand
with variable silt and gravel contents. Below this layer was encountered very dense
sand with variable silt and gravel contents that the geotechnical engineer interpreted
to be glacial till. These soils were found at a depth of typical on-site infiltration
facilities or infiltration BMPs.
Sunset Oaks Apartments Page 23 Project No. 19003
Renton, WA Coterra Engineering PLLC
• Bioretention: Infeasible. Bioretention is considered infeasible for projects that cannot
meet the minimum design requirements for bioretention. Per section C2.6 of the City
of Renton SWDM, “ Many locations in the City have soils that are underlain by a
compacted layer of soil (i.e., glacial till or hardpan) which severely limits soaking
capacity and causes water to perch on the relatively impervious layer during the wet
season. This can make bioretention impracticable, unreliable, and reduce plant
survivability in the bioretention system.”
Per the Geotechnical Engineering Report prepared by Zipper Geo Associates, LLC,
dated 5/15/2019, “Our explorations encountered glacial till at a depth of about 3 to 5
feet below existing site grade. For purposes of stormwater infiltration, glacial till (or
hardpan) is generally considered a hydraulically restrictive layer, or essentially
impermeable for purposes of stormwater infiltration. As such, it is our opinion that
sufficient permeable soils do not exist at the site and therefore stormwater infiltration
is not feasible, in our opinion.”
Based on the project geotechnical engineer guidance, bioretention is not feasible on
the project site.
• Permeable Pavement: Required Implementation Per Project Conditions. Per agreed
upon terms between Sunset Oaks Apartments project owner/agents (Renton Housing
Authority) and reviewing agencies (City of Renton, NOAA, NMFS) to maintain
compliance with existing conditions of approval for the Sunset Terrace
Redevelopment Project, Sunset Oaks Apartments project will implement permeable
pavements for all at-grade hard surfaces throughout project site and any proposed
sidewalks as part of required frontage improvements.
• Basic Dispersion:
o Splash blocks: Infeasible. Required 50’ vegetated flow path is infeasible
based on proposed site design.
o Rock pads: Infeasible. Required 50’ vegetated flow path is infeasible
based on proposed site design.
o Gravel-filled trenches: Infeasible. Per section C.2.4.4, setbacks of at least
10’ from buildings and 5’ from property line are required. Proposed site
layout cannot accommodate 25’ flowpath with required setbacks.
o Sheet flow: Infeasible. Required 10’ vegetated flow path located on the
project property is infeasible based on proposed site design.
• Soil Amendment: Feasible. New and replaced pervious surfaces within the project
limits will implement soil amendment per the soil quality and depth requirements of
section C2.13
In addition to utilization of permeable pavement throughout project site, perforated pipe
connections from roof drain leaders from each of the three proposed buildings, upstream
of detention, are proposed. These perforated pipe connections are shown on the current
Utility Plan.
Sunset Oaks Apartments Page 24 Project No. 19003
Renton, WA Coterra Engineering PLLC
Water Quality
The proposed new and replaced pollution-generating impervious surfaces (PGIS) on the
project site trigger the requirement for water quality treatment of targeted surfaces. Per
the City of Renton SWDM, the project site is within the Basin Water Quality Area; but
the proposed site land use of multi-family housing triggers the Enhanced Basic Water
Quality Menu.
The proposed project will provide mitigation of on-site PGIS using permeable pavements
throughout the project site. All proposed PGIS is either porous asphalt, porous concrete
sidewalk, or permeable pavers. Any proposed sidewalk for frontage improvements on
Glennwood Ave NE and Harrington Ave NE is porous concrete sidewalk. All permeable
pavement surfaces follow City of Renton standard details and specifications.
Sunset Oaks Apartments Page 25 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION V – CONVEYANCE SYSTEM DESIGN AND ANALYSIS
The new conveyance system has been designed to convey at least the 25-year peak flow
rate from the developed site. Conveyance capacity calculations will be included with the
civil construction permit submittal.
SECTION VI – SPECIAL REPORTS AND STUDIES
A geotechnical analysis of the project site was performed and is included in Appendix D.
SECTION VII – OTHER PERMITS
In addition to the Site Plan Review, a Civil Construction Permit from the City of Renton
is required, as well as an NPDES permit from the Washington State DOE for the
discharge of construction stormwater from the project site.
SECTION VIII – EROSION AND SEDIMENT CONTROL
ESC Measures are being addressed as follows:
• Clearing Limits: Clearing limits are being delineated by perimeter silt fencing and
chain link fencing.
• Cover Measures: Temporary cover shall be installed if an area is to remain
unworked for more than seven days during the dry season (May 1 to September
30) or for more than two consecutive working days during the wet season
(October 1 to April 30). Any area to remain unworked for more than 30 days shall
be seeded or sodded, unless the City of Renton determines that winter weather
makes vegetation establishment infeasible.
• Perimeter Protection: Perimeter protection will be implemented by silt fencing
around the site perimeter where drainage paths require.
• Traffic Area Stabilization: A stabilized construction entrance will be built for
construction traffic.
• Sediment Retention: Catch basin protection will be provided on all drainage inlets
on, adjacent to, and downstream of the project site.
• Surface Water Control: Surface water will be collected and conveyed via swales
with check dams as necessary.
• Dust Control: Dust control, if required, will be provided through the limited use
of water trucks.
Sunset Oaks Apartments Page 26 Project No. 19003
Renton, WA Coterra Engineering PLLC
SECTION IX – BOND QUANTITIES AND DECLARATION OF COVENANTS
A bond quantity worksheet for the proposed improvements will be included with the civil
construction permit submittal.
There are two Declaration of Covenants which are required for the proposed project; one
for inspection and maintenance of proposed stormwater facilities; and one for the
inspection and maintenance of the proposed on-site BMPs. A draft version of these
Declaration of Covenants will be provided for review and approval by City of Renton
prior to recording. They will be signed and notarized prior to recording.
SECTION X – OPERATIONS AND MAINTENANCE MANUAL
An operation and maintenance manual which outlines required regular maintenance
necessary for the proposed stormwater facilities will be provided with the civil
construction permit submittal. The maintenance of the stormwater facilities will by be
performed by Renton Housing Authority.
Appendix A
Civil Plans
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
5705'6.#0'0'4'06109#
5705'61#-5#2#46/'065coterra
321 3rd Ave South, Suite 406
Seattle, Washington 98104
ph 206.596.7115
coterraengineering.com
ENGINEERING PLLC
5705'61#-5#2#46/'065
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
5705'6.#0'0'4'06109#
5705'61#-5#2#46/'065coterra
321 3rd Ave South, Suite 406
Seattle, Washington 98104
ph 206.596.7115
coterraengineering.com
ENGINEERING PLLC
5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
NO.DATEREMARKISSUE DATE:DRAWN BY:CHECKED BY:Sunset CrestTownhomesGlennwood Ave,Renton, WA.....................12.19.18MBPAPPUD SUBMITTALSHEET NO:SHEET TITLE:177 Western Avenue West Suite 266Seattle, WA 98119coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLCIN COMPLIANCE WITH CITY OF RENTON STANDARDS5705'6.#0'0'4'06109#5705'61#-5#2#46/'065coterra321 3rd Ave South, Suite 406Seattle, Washington 98104ph 206.596.7115coterraengineering.comENGINEERING PLLC5705'61#-5#2#46/'065
Appendix B
Flow Control/Detention Calculations
—————————————————————————————————
MGS FLOOD
PROJECT REPORT
Program Version: MGSFlood 4.38
Program License Number: 201510001
Project Simulation Performed on: 09/03/2019 9:15 AM
Report Generation Date: 09/03/2019 9:26 AM
—————————————————————————————————
Input File Name:XXXX-MGS Flood - revised areas.fld
Project Name:19003 - RHA Sunset Oaks
Analysis Title:Preliminary Detention Sizing
Comments:60" CMP - approx 50 lf
48" CMP - approx 90 lf
———————————————— PRECIPITATION INPUT ————————————————
Computational Time Step (Minutes): 15
Extended Precipitation Time Series Selected
Climatic Region Number:13
Full Period of Record Available used for Routing
Precipitation Station :96004005 Puget East 40 in_5min 10/01/1939-10/01/2097
Evaporation Station :961040 Puget East 40 in MAP
Evaporation Scale Factor : 0.750
HSPF Parameter Region Number:1
HSPF Parameter Region Name :USGS Default
********** Default HSPF Parameters Used (Not Modified by User) ***************
********************** WATERSHED DEFINITION ***********************
Predevelopment/Post Development Tributary Area Summary
Predeveloped Post Developed
Total Subbasin Area (acres)1.053 1.053
Area of Links that Include Precip/Evap (acres) 0.000 0.000
Total (acres)1.053 1.053
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
---------- Subbasin : EX ----------
-------Area(Acres) --------
Till Forest 0.000
Till Pasture 0.000
Till Grass 0.803
Outwash Forest 0.000
Outwash Pasture 0.000
Outwash Grass 0.000
Wetland 0.000
Green Roof 0.000
User 2 0.000
Impervious 0.250
----------------------------------------------
Subbasin Total 1.053
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
---------- Subbasin : PR ----------
-------Area(Acres) --------
Till Forest 0.000
Till Pasture 0.000
Till Grass 0.240
Outwash Forest 0.000
Outwash Pasture 0.000
Outwash Grass 0.000
Wetland 0.000
Green Roof 0.000
User 2 0.000
Impervious 0.813
----------------------------------------------
Subbasin Total 1.053
************************* LINK DATA *******************************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
************************* LINK DATA *******************************
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
------------------------------------------
Link Name: Prelim Det 60 in-50 lf
Link Type: Structure
Downstream Link: None
User Specified Elevation Volume Table Used
Elevation (ft) Pond Volume (cu-ft)
99.00 0.
99.20 26.
99.40 74.
99.60 134.
99.80 203.
100.00 280.
100.20 362.
100.40 450.
100.60 542.
100.80 637.
101.00 734.
101.20 832.
101.40 932.
101.60 1032.
101.80 1132.
102.00 1230.
102.20 1327.
102.40 1422.
102.60 1514.
102.80 1601.
103.00 1684.
103.20 1761.
103.40 1830.
103.60 1890.
103.80 1937.
104.00 1964.
104.20 1965.
104.40 1966.
104.60 1967.
104.80 1968.
105.00 1969.
Massmann Infiltration Option Used
Hydraulic Conductivity (in/hr) : 0.00
Depth to Water Table (ft): 100.00
Bio-Fouling Potential : Low
Maintenance : Average or Better
Riser Geometry
Riser Structure Type : Circular
Riser Diameter (in): 24.00
Common Length (ft): 0.280
Riser Crest Elevation : 104.00 ft
Hydraulic Structure Geometry
Number of Devices: 3
---Device Number 1 ---
Device Type : Circular Orifice
Control Elevation (ft) : 100.50
Diameter (in): 2.21
Orientation : Horizontal
Elbow : No
---Device Number 2 ---
Device Type : Circular Orifice
Control Elevation (ft) : 102.50
Diameter (in): 2.90
Orientation : Horizontal
Elbow : Yes
--- Device Number 3 ---
Device Type : Rectangular Weir that Intersects the Riser Top
Invert Elevation (ft): 103.50
Length (ft): 0.280
**********************FLOOD FREQUENCY AND DURATION STATISTICS*******************
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
Number of Links: 1
********** Link: Prelim Det 60 in-50 lf ********** Link WSEL Stats
WSEL Frequency Data(ft)
(Recurrence Interval Computed Using Gringorten Plotting Position)
Tr (yrs) WSEL Peak (ft)
======================================
1.05-Year 101.341
1.11-Year 101.496
1.25-Year 101.589
2.00-Year 102.049
3.33-Year 102.443
5-Year 102.563
10-Year 102.755
25-Year 103.199
50-Year 103.335
100-Year 103.834
***********Groundwater Recharge Summary *************
Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures
Total Predeveloped Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: EX 98.135
_____________________________________
Total:98.135
Total Post Developed Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: PR 29.331
Link: Prelim Det 60 in-50 0.000
_____________________________________
Total: 29.331
Total Predevelopment Recharge is Greater than Post Developed
Average Recharge Per Year, (Number of Years= 158)
Predeveloped: 0.621 ac-ft/year, Post Developed: 0.186 ac-ft/year
***********Water Quality Facility Data *************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
********** Link: Prelim Det 60 in-50 lf **********
Basic Wet Pond Volume (91% Exceedance): 3843. cu-ft
Computed Large Wet Pond Volume, 1.5*Basic Volume: 5765. cu-ft
Infiltration/Filtration Statistics--------------------
Inflow Volume (ac-ft): 412.77
Inflow Volume Including PPT-Evap (ac-ft): 412.77
Total Runoff Infiltrated (ac-ft): 0.00, 0.00%
Total Runoff Filtered (ac-ft): 0.00, 0.00%
Primary Outflow To Downstream System (ac-ft): 414.39
Secondary Outflow To Downstream System (ac-ft): 0.00
Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00%
***********Compliance Point Results *************
Scenario Predeveloped Compliance Subbasin: EX
Scenario Postdeveloped Compliance Link: Prelim Det 60 in-50 lf
*** Point of Compliance Flow Frequency Data ***
Recurrence Interval Computed Using Gringorten Plotting Position
Predevelopment Runoff Postdevelopment Runoff
Tr (Years)Discharge (cfs)Tr (Years)Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.166 2-Year 0.162
5-Year 0.234 5-Year 0.241
10-Year 0.320 10-Year 0.303
25-Year 0.442 25-Year 0.392
50-Year 0.573 50-Year 0.414
100-Year 0.659 100-Year 0.633
200-Year 0.702 200-Year 0.654
** Record too Short to Compute Peak Discharge for These Recurrence Intervals
Detention Pipe Volume Calculator
Blue Indicates Data Entry Cells, the rest are calculated.
Storage Volume Provided by Horizontal Pipe of Diameter d
Pipe Diameter (d)5.0 ft
Pipe Length 100 ft
Overflow Elevation:104.00 ft
Pond Volume at Overflow (cu ft):1937
Target Volume from MGSFlood:700
Note: Volume is increased by 1 for Elevations Greater than Pipe Diameter
Pond Volume Table Because Routing Routine Requires Increasing Pond Volume
Circular Section Geometry Read from CircularSections Tab *** Copy Table below to MGSFlood Program Elevation Volume Input Screen
elev.Wetted Area storage storage DON'T INCLUDE THE COLUMN HEADINGS!
ft y/d s.f.cu.ft.(ac.ft)ELEV (FT)Top Area (Dummy) VOLUME (CU FT)
99.00 0.000 0.000 0 0 99.00 10.0 0.0.
99.20 0.040 0.263 26 0.001 99.20 10.1 26.3.
99.40 0.080 0.735 74 0.002 99.40 10.2 73.5.
99.60 0.120 1.335 134 0.003 99.60 10.3 133.5.
99.80 0.160 2.028 203 0.005 99.80 10.4 202.8.
100.00 0.200 2.795 280 0.006 100.00 10.5 279.5.
100.20 0.240 3.623 362 0.008 100.20 10.6 362.3.
100.40 0.280 4.500 450 0.010 100.40 10.7 450.0.
100.60 0.320 5.418 542 0.012 100.60 10.8 541.8.
100.80 0.360 6.365 637 0.015 100.80 10.9 636.5.
101.00 0.400 7.335 734 0.017 101.00 11.0 733.5.
101.20 0.440 8.320 832 0.019 101.20 11.1 832.0.
101.40 0.480 9.318 932 0.021 101.40 11.2 931.8.
101.60 0.520 10.318 1032 0.024 101.60 11.3 1031.8.
101.80 0.560 11.315 1132 0.026 101.80 11.4 1131.5.
102.00 0.600 12.300 1230 0.028 102.00 11.5 1230.0.
102.20 0.640 13.270 1327 0.030 102.20 11.6 1327.0.
102.40 0.680 14.218 1422 0.033 102.40 11.7 1421.8.
102.60 0.720 15.135 1514 0.035 102.60 11.8 1513.5.
102.80 0.760 16.010 1601 0.037 102.80 11.9 1601.0.
103.00 0.800 16.840 1684 0.039 103.00 12.0 1684.0.
103.20 0.840 17.608 1761 0.040 103.20 12.1 1760.8.
103.40 0.880 18.300 1830 0.042 103.40 12.2 1830.0.
103.60 0.920 18.900 1890 0.043 103.60 12.3 1890.0.
103.80 0.960 19.373 1937 0.044 103.80 12.4 1937.3.
104.00 1.000 19.635 1964 0.045 104.00 12.5 1963.5.
104.20 1.040 19.635 1964 0.045 104.20 12.6 1964.5.
104.40 1.080 19.635 1964 0.045 104.40 12.7 1965.5.
104.60 1.120 19.635 1964 0.045 104.60 12.8 1966.5.
104.80 1.160 19.635 1964 0.045 104.80 12.9 1967.5.
105.00 1.200 19.635 1964 0.045 105.00 13.0 1968.5.
9/3/2019 PondPipe.xls
Appendix C
Water Quality Calculation
Appendix D
Geotechnical Report
GEOTECHNICAL ENGINEERING REPORT
HARRINGTON AVE APARTMENTS
NE 10TH STREET AND HARRINGTON AVENUE NE
RENTON, WASHINGTON
PROJECT NO. 2072.01
May 15, 2019May 15, 2019
Prepared for:
Renton Housing Authority
Prepared by:
19019 36th Avenue W., Suite E
Lynnwood, WA 98036
19019 36th Avenue West, Suite E Lynnwood, WA 98036 (425) 582-9928
Project No. 2072.01
May 15, 2019
Renton Housing Authority
P.O. Box 2316
Renton, Washington 98056-0316
Attn: Mr. Mark Gropper
Subject: Geotechnical Engineering Report
Harrington Ave Apartments
NE 10th Street and Harrington Avenue NE
Renton, Washington
Dear Mr. Gropper,
In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has
completed the subsurface exploration and geotechnical engineering evaluation for the Harrington Ave
Apartments project. This report presents the results of the subsurface exploration, as well as our
geotechnical engineering recommendations for the project. Our services were completed in general
accordance with our Proposal for Geotechnical Engineering Services (Proposal No. P18283) dated August
23, 2018. Written authorization to proceed on our proposed scope of services was provided by Renton
Housing Authority on August 27, 2018. We appreciate the opportunity to be of service to you on this
project. If you have any questions concerning this report, or if we may be of further service, please contact
us.
Sincerely,
Zipper Geo Associates, LLC
Robert A. Ross, P.E.
Principal
5/15/19
TABLE OF CONTENTS
Page
INTRODUCTION ........................................................................................................................................... 1
PROJECT UNDERSTANDING..................................................................................................................... 1
SITE CONDITIONS ....................................................................................................................................... 1
Surface Conditions .......................................................................................................................................... 1
Subsurface Conditions ..................................................................................................................................... 2
Groundwater Conditions ................................................................................................................................. 2
LABORATORY TESTING ............................................................................................................................ 3
CONCLUSIONS AND RECOMMENDATIONS ............................................................................................ 3
General Considerations ................................................................................................................................... 3
Geologically Hazardous Areas ......................................................................................................................... 3
Seismic Design Considerations ........................................................................................................................ 4
Site Preparation ............................................................................................................................................... 5
Structural Fill Materials, Placement, and Compaction .................................................................................... 7
Utility Trenching and Backfilling ...................................................................................................................... 8
Construction Dewatering ................................................................................................................................ 9
Shallow Foundation Recommendations .......................................................................................................... 9
On-Grade Concrete Slabs .............................................................................................................................. 10
Permanent Drainage Considerations ............................................................................................................ 11
Retaining Wall ............................................................................................................................................... 11
Stormwater Infiltration Feasibility ................................................................................................................ 12
Pavements ..................................................................................................................................................... 12
CLOSURE ................................................................................................................................................... 14
FIGURES
Figure 1 – Site and Exploration Plan
APPENDICES
Appendix A – Subsurface Exploration Procedures and Logs
Appendix B – Laboratory Testing Procedures and Results
Cover Page Photo Credit: Google Earth Pro, 2018 Aerial Photo
Page 1
GEOTECHNICAL ENGINEERING REPORT
HARRINGTON AVE APARTMENTS
RENTON, WASHINGTON
Project No. 2072.01
May 15, 2019
INTRODUCTION
This report documents the surface and subsurface conditions encountered at the project site and our
geotechnical engineering recommendations for the current proposed Harrington Ave Apartments in
Renton, Washington. Our geotechnical engineering scope of services for the project included subsurface
explorations, laboratory testing, geotechnical engineering analysis, and preparation of this report.
The observations and conclusions summarized herein are based in part upon conditions observed in our
subsurface explorations and site observations. In the event that site conditions change, it may be
necessary to modify the conclusions and recommendations presented in this report. This report is an
instrument of service and has been prepared in general accordance with locally accepted geotechnical
engineering practice. This report has been prepared for the exclusive use of the Renton Housing
Authority, and its agents, for specific application to the subject property and stated purpose.
PROJECT UNDERSTANDING
The project site consists of five undeveloped parcels zoned as R-14 and located at the northwest corner of
the intersection of NE 10th Street and Harrington Ave NE in Renton, Washington. The project site was
previously developed with single-family homes that were demolished. We understand the project will
consists of developing the site with a 62 unit, 3-story, wood-framed apartment building and related site
improvements including underground utilities, pavements, and stormwater management facilities. We
expect that the finished floor elevation of the building will be near existing site grades. Grading for the
project is expected to consist of cuts and fills with a maximum anticipated depth/thickness of about 5 feet.
However, deeper cuts may be required for underground utilities and stormwater management facilities.
Design drawings for the proposed apartment building and associated site improvements were not available
at the time this report was prepared. Once details regarding the proposed apartment building and
additional site improvements are known, we should be consulted to review the details and revise this report
if necessary.
SITE CONDITIONS
Surface Conditions
The project site consists of five parcels with a total area of slightly above one acre. The site is bordered to
the north by single-family residences, to the east by Harrington Ave NE, to the south by the new extension
of NE 10th Street, and to the west by Glennwood Ave NE. Parcel number 7227801305 overlaps with the new
construction of the NE 10th Street extension with a portion remaining to the north of the road construction.
We anticipate that this portion will be included in the project area.
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Topographically, the site is relatively flat. Ground cover consists primarily of grass with a few scattered large
deciduous and coniferous trees. The northwest corner of the project site was used as a staging area for
construction equipment associated with the extension of NE 10th Street and is covered with medium gravel.
A plan view of the project site is shown on the attached Figure 1, Site and Exploration Plan.
Subsurface Conditions
Mapped Geology: We reviewed published geologic mapping of the site vicinity through the Washington
State Department of Natural Resource’s web-based mapping application Washington Geologic
Information Portal (https://geologyportal.dnr.wa.gov/). The published mapping indicates the site is
underlain by Vashon glacial till (Qgt). The mapping describes this soil as mostly thin ablation till over
lodgment till, deposited by the Puget glacial lobe consisting of a generally compact, coherent unsorted
mixture of sand, silt clay and gravel. The mapping notes that north of the Cedar River, where the project
site is located, the till is mostly sand.
Subsurface Exploration: The subsurface evaluation for this project included advancement of five borings
(B-1 through B-5) completed throughout the area of the project site. The borings were extended to depths
of about 16 to 26½ feet below the existing ground surface (bgs) and their approximate locations are shown
on Figure 1, Site and Exploration Plan.
Soils were visually classified in general accordance with the Unified Soil Classification System. Descriptive
logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are
presented in Appendix A. A generalized description of soil conditions encountered in the explorations is
presented below. Please refer to the exploration logs in Appendix A for a more detailed description of the
conditions encountered at each exploration location.
Soil conditions observed in the borings generally consisted of three to twelve feet of medium dense to dense
sand with variable silt and gravel contents. Below this layer we encountered very dense sand with variable
silt and gravel contents that we interpret to be glacial till. All the explorations terminated within the glacial
till. The upper 4 to 5 feet of soils observed in our explorations was interpreted to be possibly undocumented
fill associated with previous development of the site and possibly demolition of the previously existing homes.
Groundwater Conditions
Groundwater was not encountered within our explorations. Fluctuations in groundwater levels will likely
occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time
the exploration was performed. Therefore, groundwater levels during construction or at other times in
the life of the structure may be higher than indicated on the logs. The possibility of groundwater level
fluctuations should be considered when developing the design and construction plans for the project.
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May 15, 2019
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LABORATORY TESTING
Laboratory testing included soil moisture content, grain size distribution, and modified proctor tests on
selected samples obtained from our explorations. The results of the moisture content tests are presented on
the boring logs in Appendix A and the grain size distribution and modified proctor test results are presented
in Appendix B. In general, moisture content testing indicates the sands within the upper 10 feet of existing
site grade had moisture contents ranging from about 4 to 12 percent with an average of about 9 percent.
Grain size distribution testing indicates the sands within the upper 7 feet of existing site grade had fines
contents ranging from about 19 to 30 percent. We collected cuttings from the auger and performed a
modified proctor test on the material. The modified proctor test yielded a maximum dry density of 136.2 pcf
and an optimum moisture content of 8.3 percent.
CONCLUSIONS AND RECOMMENDATIONS
General Considerations
Based on the results of our subsurface investigation as described in previous sections, it is our opinion the
proposed building can be supported on conventional shallow foundations bearing on medium dense to
very dense native soil or structural fill placed on properly prepared native soils, contingent on proper
design and construction practices and implementation of the recommendations presented in this report.
Geotechnical engineering recommendations for conventional shallow foundations and other earthwork
related phases of the project are presented below. The recommendations contained in this report are
based upon the results of field and laboratory testing (which are presented in Appendices A and B),
engineering analyses, and our current understanding of the proposed project. ASTM and Washington
State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the
current manual published by the American Society for Testing & Materials and the 2016 edition of the
Standard Specifications for Road, Bridge, and Municipal Construction (M41-10).
Geologically Hazardous Areas
As part of our services, we evaluated the presence of regulated geologically hazardous areas (GHAs) at
the site. Chapter 4-3-050 of the Renton Municipal Code (the Code) designates GHAs as Erosion, Landslide,
Seismic, and Coal Mine Hazard Areas.
Steep Slope Hazard Areas: The code defines steep slope hazard areas as areas with an average slope of
25 percent or greater with a total relief of 15 feet or greater, or having an average slope of 40 percent or
greater. The project site does not meet the definition of a steep slope area.
Landslide Hazard Areas: The code defines a low landslide hazard area as an area with slopes less than
fifteen percent. Based on the relative flat topography, the site classifies as having a “low landslide
hazard”, based on the code definition.
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Erosion Hazard Areas: The code characterizes sites as having a low or high erosion hazard based on
information available through the Natural Resource Conservation Service (NRCS). The NRCS maps the site
as being 70% Arents, Alderwood material (AmC) and 30% Ragnar-Indianola association both with a slope
less than 15 percent. Therefore, the site classifies as having a “low erosion hazard”, based on the code
definition.
Seismic Hazard Areas: The code characterizes sites as having either “low seismic hazard” or “high seismic
hazard” based on the subsurface conditions. A low seismic hazard area is defined as an area underlain by
dense soils or bedrock, generally having site classifications of A through D, as defined in the International
Building Code, 2012. It is our opinion that the project site classifies as having a “low seismic hazard”,
based on the code definition. More detailed information regarding seismic hazards is provided in the
seismic design considerations section of this report.
Coal Mine Hazard Areas: The code defines areas with low coal mine hazards as areas with no known mine
workings and no predicted subsidence. We reviewed the King County iMap for coal mine hazard mapping
as well as the Coal Mine Map Database located within the Washington State Department of Natural
Resources online Washington Geologic Information Portal. Based on a review of the readily available
information provided by these sources, no coal mine workings are documented within close vicinity of the
project site. Therefore, in our opinion the project site classifies as having a “low coal mine hazard”,
based on the code definition.
Seismic Design Considerations
The tectonic setting of western Washington is dominated by the Cascadia Subduction Zone formed by the
Juan de Fuca plate subducting beneath the North American Plate. This setting leads to intraplate, crustal,
and interplate earthquake sources. Seismic hazards relate to risks of injury to people and damage to
property resulting from these three principle earthquake sources.
Ground Surface Rupture: Based on our review of the USGS Quaternary age fault database for Washington
State, an inferred fault trace of the Seattle Fault Zone is located approximately 1 ½-miles to the north and
northwest of the project site. As the fault does not appear to cross the site, it is our opinion that the risk
of ground surface rupture at the site is low.
Landsliding: Based on the relatively flat topography of the site and surrounding vicinity, it is our opinion
that the risk of earthquake-induced landsliding is low.
Soil Liquefaction: Liquefaction is a phenomenon wherein cohesionless soils below the groundwater table
build up excess pore water pressures during earthquake loading. Liquefaction typically occurs in loose,
cohesionless soils, but may occur in denser soils if the ground shaking is sufficiently strong. The potential
hazardous impacts of liquefaction include liquefaction-induced settlement and lateral spreading. Soil
conditions observed in our explorations consisted of dense to very dense sands with variable silt/gravel
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contents. We did not encounter groundwater within our explorations. Based on the subsurface
conditions we encountered on the site, it is our opinion that the risk of liquefaction is low.
IBC Seismic Design Parameters: Based on site location and soil conditions, the values provided below are
recommended for seismic design. The values provided below are based on the 2015 IBC as the building
code reference document.
Site Preparation
Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments.
We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped
areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet
weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion,
whereas soil stockpiles should be protected with anchored plastic sheeting.
Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a
manner and sequence that will provide drainage at all times and provide proper control of erosion. The
site should be graded to prevent water from ponding in construction areas and/or flowing into and/or
over excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each
day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from
subgrades and work areas immediately and prior to performing further work in the area. Equipment
access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly
increased if drainage efforts are not accomplished in a timely manner.
Description Value
2015 IBC Site Classification 1 C
Ss Spectral Acceleration for a Short Period 1.430 g (Site Class B)
S1 Spectral Acceleration for a 1-Second Period 0.537 g (site Class B)
SMS Maximum considered spectral response
acceleration for a Short Period 1.430 g (Site Class C)
SM1 Maximum considered spectral response
acceleration for a 1-Second Period 0.699 g (Site Class C)
SDS Five-percent damped design spectral response
acceleration for a Short Period 0.953 g (Site Class C)
SD1 Five-percent damped design spectral response
acceleration for a 1-Second Period 0.466 g (Site Class C)
1. In general accordance with the 2015 International Building Code, Table 1613.5.2. IBC Site Class is based on
the average characteristics of the upper 100 feet of the subsurface profile. The borings completed for this
study extended to a maximum depth of 26½ feet below grade. ZGA therefore determined the Site Class
assuming that similar density soils extend to 100 feet as suggested by published geologic maps for the
project area.
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Clearing and Stripping: Once TESC measures are installed, we expect site preparation to continue with
clearing and grubbing brush and trees, and stripping of organic rich topsoil. We recommend all tree
stumps and roots larger than ½ inch in diameter be cleared and grubbed from the areas planned for
improvement. Based on our explorations, stripping depths to remove topsoil is estimated to be about 6
inches. Stripping depths may be greater near trees and brush to fully remove root systems. All clearing
and stripping debris should be wasted off site or, if approved, used for topsoil in landscape areas.
Subgrade Preparation: Once site preparation is complete, all areas that are at design subgrade elevation
or areas that will receive new structural fill should be moisture conditioned to a moisture content within
plus or minus two percent of optimum moisture content for compaction. The subgrade should then be
compacted to a firm and unyielding condition.
The existing near-surface site soils consist of loose to dense silty sand or sand with silt at or generally
somewhat above optimum moisture content for compaction. During wet weather, achieving a moisture
content adequate for compaction will be impossible. Therefore, we recommend subgrade preparation
and earthwork, in general, be completed during drier periods of the year when the soil moisture content
can be controlled by aeration and drying. If earthwork or construction activities take place during
extended periods of wet weather, or if the in situ moisture conditions are elevated above the optimum
moisture content, the soils will become unstable and not compactable. In the event the exposed subgrade
becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend
that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be
compacted to the minimum recommended levels. The severity of construction problems will be
dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils.
Once compacted, subgrades should be evaluated through density testing and proof rolling with a loaded
dump truck or heavy rubber-tired construction equipment weighing at least 20 tons to assess the
subgrade adequacy and to detect soft and/or yielding soils. In the event that compaction fails to meet
the specified criteria, the upper 12 inches of subgrade should be scarified and moisture conditioned as
necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D1557). Those soils
which are soft, yielding, or unable to be compacted to the specified criteria should be over-excavated and
replaced with suitable material as recommended in the Structural Fill section of this report. As an
alternate to subgrade compaction during wet site conditions or wet weather, the upper 12 inches of
subgrade should be overexcavated to a firm, non-yielding and undisturbed condition and backfilled with
compacted imported structural fill consisting of free-draining Gravel Borrow or crushed rock.
Freezing Conditions: If earthwork takes place during freezing conditions, exposed subgrades should be
allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively,
the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing
subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill
until allowed to thaw and adjusted to the proper moisture content, which may not be possible during
winter months.
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Structural Fill Materials, Placement, and Compaction
Structural fill includes any material placed below or adjacent to foundations, below concrete slabs, within
utility trenches, or other areas to support settlement-sensitive site improvements. Prior to the placement
of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site
Preparation section of this report.
Laboratory Testing: Representative samples of on-site and imported soils to be used as structural fill
should be submitted for laboratory testing at least 4 days in advance of its intended use in order to
complete the necessary Proctor tests.
Reuse of Site Soils as Structural Fill: We expect that the finished grade will stay very close to the existing
grade and therefore no substantial fill placement will be required. However, we expect the reuse of site
soils as structural fill will be desirable for underground utilities.
The suitability for reuse of site soils as structural fill depends on the composition and moisture content of
the soil. Soils encountered in excavations at the site are expected to consist of silty sand or sand with silt.
As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture
content. Soils containing more than about 5 percent fines cannot be consistently compacted to the
appropriate levels when the moisture content is more than approximately 2 percent above or below the
optimum moisture content (per ASTM D1557). Optimum moisture content is the moisture content which
results in the greatest compacted dry density with a specified compactive effort.
Laboratory testing of select soil samples indicates the in-place moisture content of site soils ranges from
about 4 to 12 percent. Based on the results of the modified proctor test, the optimum moisture content
of site soils is 8.3 percent. Therefore, site soils appear near the optimum moisture content for
compaction. Site soils should be suitable for structural fill during periods of dry weather with some slight
moisture conditioning. However, during wet weather, site soils will quickly become too wet for reuse as
structural fill. Therefore, we recommend earth work for the project be scheduled for the drier summer
months.
Imported Structural Fill: The appropriate type of imported structural fill will depend on weather
conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet
the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2016 Washington State
Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction
(WSDOT Standard Specifications). During wet weather and/or wet site conditions, higher-quality
structural fill might be required, as Common Borrow may contain sufficient fines to be moisture-sensitive.
During wet conditions, we recommend that imported structural fill consist of a “clean”, free-draining pit-
run sand and gravel. Such material should generally contain less than 5 percent fines, based on that soil
fraction passing the U.S. No. 4 sieve, and not contain discrete particles greater than 3 inches in maximum
dimension. Alternatively, Crushed Surfacing Base Course or Gravel Borrow conforming to Sections 9-
03.9(3) and 9-03.14(1), respectively, of the WSDOT Standard Specifications could be used during wet
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weather. It should be noted that the placement of structural fill is, in many cases, is weather-dependent.
Delays due to inclement weather are common, even when using select granular fill. We recommend that
site grading and earthwork be scheduled for the drier months, if possible.
Fill Placement and Compaction: Structural fill should be placed in horizontal lifts of a thickness adequate
for adequate compaction throughout the entire lift thickness with the compaction equipment used.
Typically, the maximum loose lift thickness that can be adequately compacted with typical compaction
equipment is 12 inches. However, in cases where large vibratory rollers and imported fill with less than
5% fines are used, the lift thickness can be increased. Increasing the loose lift thickness beyond 12 inches
should be based on field performance testing during construction prior to placement of production fills.
Thinner lifts may be necessary, depending on the size and weight of the compaction equipment. Each lift
of fill should be compacted to the minimum levels recommended in the table below based on the
maximum laboratory dry density as determined by the ASTM D 1557 Modified Proctor Compaction Test.
Structural fill placed in municipal rights-of-way should be placed and compacted in accordance with the
jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading
so that an adequate number of density tests may be conducted as structural fill placement occurs. In this
way, the adequacy of the earthwork may be evaluated as it proceeds.
Recommended Soil Compaction Levels
Location Minimum Percent Compaction*
Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95
All fill below building floor slabs and foundations 95
Upper two feet of fill below pavement finished grade 95
Pavement fill below two feet from finished grade 92
Utility trench backfill greater than two feet from finished grade 92
Upper two feet of trench backfill from finished grade 95
Landscape Areas 90
* ASTM D 1557 Modified Proctor Maximum Dry Density
Utility Trenching and Backfilling
We recommend that utility trenching conform to all applicable federal, state, and local regulations, such
as OSHA and WISHA, for open excavations. Trench excavation safety guidelines are presented in WAC
Chapter 296-155 and WISHA RCW Chapter 49.17.
Utility Subgrade Preparation: We recommend that all utility subgrades be firm and unyielding and free of
soils that are loose, disturbed, or pumping. Soils that pump or yield should be removed and replaced. All
structural fill used to replace over-excavated soils should be compacted as recommended in the Structural
Fill section of this report.
Bedding and Initial Backfill: We recommend that a minimum of 4 inches of bedding material be placed
below and at least 12 inches above all utilities or in general accordance with the utility manufacturer’s
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recommendations and local ordinances. We recommend the bedding consist of granular material free
from particles greater than 3 inches. All trenches should be wide enough to allow for compaction around
the haunches of the pipe, or material such as pea gravel should be used below the spring line of the pipes
to eliminate the need for mechanical compaction in this portion of the trenches. If water is encountered
in the excavations, it should be removed prior to fill placement.
Trench Backfill: Materials, placement and compaction of utility trench backfill should be in accordance
with the recommendations presented in the Structural Fill section of this report. In our opinion, the initial
lift thickness should not exceed 1 foot unless recommended by the manufacturer to protect utilities from
damage by compacting equipment. Light, hand operated compaction equipment may be utilized directly
above utilities if damage resulting from heavier compaction equipment is of concern.
Construction Dewatering
Groundwater was not encountered in our explorations. If groundwater is encountered during
construction, some form of temporary dewatering may be required. Conventional dewatering methods,
such as pumping from sump pits, should likely be adequate for temporary removal of groundwater
encountered during shallow excavation at the site. Construction dewatering systems should be designed,
maintained, and permitted by the contractor.
Shallow Foundation Recommendations
We recommend the building foundations be supported on the medium dense to very dense soils
encountered in our explorations at a depth of 2.5 to 4 feet below existing site grades. Based on the results
of our explorations, some loose, undocumented fill may be encountered at footing subgrade elevations.
As such, some over-excavation and replacement of loose, undocumented fill with structural fill may be
required. The need for over-excavation and replacement of loose, undocumented fill should be evaluated
by a representative from Zipper Geo Associates during construction. Where over-excavation is required,
the width of the over-excavation beyond footing edges should be equal to the required over-excavation
depth. For example, if the footing width is 12 inches and an over-excavation depth of two feet is required,
the total width of the over-excavation should be five feet. As an alternative, the width of over-excavations
can be limited to the footing width provided the over-excavation is backfilled with controlled density fill
or lean mix concrete having a minimum 28 day compressive strength of 100 psi. Over-excavation and
replacement with structural fill shall be in accordance with the recommendations provided in the
Structural Fill Materials, Placement and Compaction section of this report. Recommendations for shallow
spread footings are provided below.
Subgrade Preparation: Where loose, undocumented fill is not encountered at footing subgrade elevation,
we recommend that the subgrade exposed at the bottom of foundation excavations be compacted to a
firm and non-yielding condition and to at least 95 percent of the modified Proctor maximum dry density
determined in accordance with ASTM D 1557. If the exposed subgrade cannot be compacted to the
required density, we recommend that it be removed to an adequate depth as recommended by a
representative from ZGA and replaced with compacted structural fill placed in accordance with this report.
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Allowable Bearing Pressure: Continuous and isolated column footings bearing on subgrades prepared as
recommended above may be designed for a maximum allowable, net, bearing pressure of 3,000 psf if
supported as recommended in this report. A one-third increase of the bearing pressure may be used for
short-term transient loads such as wind and seismic forces.
Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear
at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings
should bear at least 12 inches below the surrounding slab surface level. We recommend that all
continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively.
Lateral Resistance: Resistance to lateral loads can be calculated assuming a ultimate passive resistance of
405 pcf equivalent fluid pressure (triangular distribution) for footings backfilled with structural fill as
recommended in this report. We recommend an ultimate base friction coefficient of 0.50. If allowable
stress design is used, we recommend a minimum safety factor of 1.5 be used for lateral resistance
calculations. We recommend that passive resistance be neglected in the upper 18 inches of embedment.
Estimated Settlement: Assuming the foundation subgrade soils and structural fill compaction are
completed in accordance with recommendations presented herein, we estimate that total static footing
settlements will be 1 inch or less. We estimate that differential footing settlement will be ½ inch or less
in 40 feet.
Subsurface Drainage: Although no groundwater was encountered in our explorations, as a precautionary
measure, we recommend a perimeter footing drain be installed around the building to collect surface
water infiltration if impermeable hard surfacing, such as asphalt pavement, is not extended to the
foundation walls of the building. The perimeter footing drain should consist of a 4-inch-diameter
perforated pipe within an envelope of pea gravel or washed rock, extending at least 6 inches on all sides
of the pipe. The gravel envelope should be wrapped with filter fabric (such as Mirafi 140N) to reduce the
migration of fines from the surrounding soil. The invert of the footing drain should be placed no higher
than the bottom of the footing. The perforations should be placed down. The perimeter foundation drain
with cleanouts should not be connected to roof downspout drains and should be constructed to discharge
into the site storm water system or other appropriate outlet.
On-Grade Concrete Slabs
Subgrade Preparation: Subgrades for on-grade slabs should be prepared in accordance with the Site
Preparation and Structural Fill sections of this report.
Slab Base: To provide a uniform slab bearing surface, capillary break, and even working surface, we
recommend that on-grade slabs be underlain by a 6-inch thick layer of clean, compacted crushed rock
meeting the requirements of Crushed Surfacing Top Course as specified in Section 9-03.9(3) of the WSDOT
Standard Specifications with the modification that a maximum of 7.5 percent of the material passes the
U.S. No 200 sieve.
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Vapor Barrier: From a geotechnical perspective, a vapor barrier is not considered necessary beneath the
slab on grade floor unless moisture sensitive floor coverings and/or adhesives are used. If a vapor barrier
is used, we recommend using a 10-mil (minimum), puncture-resistant proprietary product such as Stego
Wrap, or an approved equivalent that is classified as a Class A vapor retarder in accordance with ASTM E
1745. Overlap lengths and the appropriate tape used to seal the laps should be in accordance the vapor
retarder manufacturer’s recommendations. When conditions warrant the use of a vapor retarder, the
slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions
regarding the use and placement of a vapor retarder/barrier.
Permanent Drainage Considerations
Surface Drainage: Final site grades should be sloped to carry surface water away from buildings and other
drainage-sensitive areas. Additionally, site grades should be designed such that concentrated runoff on
softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected
at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents
erosion.
Retaining Wall
Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the
nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth
loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at
least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding
walls (i.e. walls that are not free to translate or rotate) should be designed for at-rest earth pressures.
Non-yielding walls include walls that are braced to another wall or structure, and wall corners.
Assuming that walls are backfilled and drained as described in the following paragraphs, we recommend
that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf
(active earth pressure). Non-yielding walls should be designed using an equivalent fluid density of 50 pcf
(at-rest earth pressure).
Surcharge pressures due to sloping backfill, adjacent footings, vehicles, construction equipment, etc. must
be added to these lateral earth pressure values. For traffic loads, we recommend using an equivalent
two-foot soil surcharge of about 250 psf.
For yielding and non-yielding walls with level backfill conditions, we recommend that a uniformly
distributed seismic pressure of 7H psf for the active case and 12H psf for the at-rest case, where H is the
height of the wall, be applied to the walls.
The above equivalent fluid pressures are based on the assumption of no buildup of hydrostatic pressure
behind the wall. If groundwater is allowed to saturate the backfill soils, hydrostatic pressures will act
against a retaining wall; however, if the recommended drainage system is included with each retaining
wall, we do not expect that hydrostatic pressures will develop.
Harrington Ave Apartments
ZGA Project No. 2072.01
May 15, 2019
Page 12
Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade
walls. All backfilled walls should include a drainage aggregate zone extending a minimum of two feet from
the back of wall for the full height of the wall and wide enough at the base of the wall to allow seepage
to flow to the footing drain. The drainage aggregate should consist of material meeting the requirements
of WSDOT 9-03.12(2), Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe
should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate
discharge point. We recommend placing a non-woven geotextile, such as Mirafi 140N, or equivalent,
around the free draining backfill material.
Stormwater Infiltration Feasibility
With respect to stormwater infiltration, the City of Renton adopts the 2016 King County Surface Water
Design Manual (KCSWDM) with amendments. Based on our review of the 2016 KCSWDM, the applicant
must demonstrate, through the opinion of a geotechnical professional, that sufficient permeable soil
exists to allow construction of a properly functioning infiltration facility. Our explorations encountered
glacial till at a depth of about 3 to 5 feet below existing site grade. For purposes of stormwater infiltration,
glacial till (or hardpan) is generally considered a hydraulically restrictive layer, or essentially impermeable
for purposes of stormwater infiltration. As such, it is our opinion that sufficient permeable soils do not
exist at the site and therefore stormwater infiltration is not feasible, in our opinion.
Pavements
Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance-
free. The following pavement sections represent our minimum recommendations for an average level of
performance during a 20-year design life; therefore, an average level of maintenance will likely be
required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years.
Thicker asphalt, base, and subbase courses would offer better ling-term performance, but would cost
more initially. Conversely, thinner courses would be more susceptible to “alligator” cracking and other
failure modes. As such, pavement design can be considered a compromise between a high initial cost and
low maintenance costs versus a low initial cost and higher maintenance costs. The recommendations
presented below are based on AASHTO Low-Volume Road Design methodologies as presented in the 1993
AASHTO Guide for Design of Pavement Structures.
Traffic and Reliability: Our design assumes 100,000, 18-kip equivalent single axle loads over the life of the
pavement along the main access roads and a 75% reliability.
Soil Design Values: Pavement subgrade soils are anticipated to consist of the medium stiff silt deposit we
encountered in our explorations. Our analysis assumes a minimum California Bearing Ration (CBR) value
of 10 is appropriate for this material.
Recommended Pavement Sections: For light duty pavements (parking stalls), we recommend 2 inches of
asphalt concrete over 4 inches of crushed rock base course. For heavy duty pavements (main access
roads, truck delivery routes, etc.), we recommend 3 inches of asphalt concrete over 6 inches of crushed
Harrington Ave Apartments
ZGA Project No. 2072.01
May 15, 2019
Page 13
rock base course. A thicker asphalt section or concrete pavements should be considered in front of
dumpster enclosures.
Materials and Construction: We recommend the following regarding asphalt pavement materials and
pavement construction.
• Subgrade Preparation: Upper 24 inches of pavement subgrade should be prepared in accordance
with the recommendations presented in the Subgrade Preparation section of this report.
• Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG
58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the WSDOT Standard
Specifications. We also recommend that the gradation of the asphalt aggregate conform to the
aggregate gradation control points for ½-inch mixes as presented in Section 9-03.8(6), HMA
Proportions of Materials.
• Base Course: We recommend that the crushed aggregate base course conform to Section
9-03.9(3) of the WSDOT Standard Specifications.
• Compaction: All base material should be compacted to at least 95 percent of the maximum dry
density determined in accordance with ASTM D1557. We recommend that asphalt be compacted
to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall
(Maximum laboratory) density.
We recommend that a Portland cement concrete pavement (CCP) be utilized in entrance and exit sections,
dumpster pads, loading dock areas, drive-thru areas or other areas where extensive wheel maneuvering
or repeated loading are expected. The dumpster pad should be large enough to support the wheels of
the truck which will bear the load of the dumpster. We recommend a minimum of 6 inches of CCP
underlain by 4 inches of crushed aggregate base. Although not required for structural support, the base
course layer is recommended to help reduce potentials for slab curl, shrinkage cracking, and subgrade
“pumping” through joints. Proper joint spacing will also be required to prevent excessive slab curling and
shrinkage cracking. All joints should be sealed to prevent entry of foreign material and dowelled where
necessary for load transfer.
Portland cement concrete should be designed with proper air-entrainment and have a minimum
compressive strength of 4,000 psi after 28 days of laboratory curing. Adequate reinforcement and
number of longitudinal and transverse control joints should be placed in the rigid pavement in accordance
with ACI requirements. The joints should be sealed as soon as possible (in accordance with sealant
manufacturer’s instructions) to minimize water infiltration into the soil.
Harrington Ave Apartments
ZGA Project No. 2072.01
May 15, 2019
Page 14
CLOSURE
The analysis and recommendations presented in this report are based, in part, on the explorations
completed for this study. The number, location, and depth of the explorations for the current phase of
the project were completed within the constraints of budget and site access so as to yield the information
to formulate our recommendations. Project plans were not available at the time this report was prepared.
We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans
and specifications when they become available in order to assess that the recommendations and design
considerations presented in this report have been properly interpreted and implemented into the project
design.
The performance of shallow foundations and slabs on grade depend greatly on proper site preparation
and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide
geotechnical engineering services during the site preparation and foundation construction phases of the
project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer
could provide additional geotechnical recommendations to the contractor and design team in a timely
manner as the project construction progresses.
This report has been prepared for the exclusive use of Renton Housing Authority, and its agents, for
specific application to the project discussed and has been prepared in accordance with generally accepted
geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety,
excavation support, and dewatering requirements are the responsibility of others. In the event that
changes in the nature, design, or location of the project as outlined in this report are planned, the
conclusions and recommendations contained in this report shall not be considered valid unless Zipper
Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in
writing.
B-4GLENNWOOD AVE NE
HARRINGTON AVE NENE 10TH STB-1B-2B-3B-5FIGUREJob No.Zipper Geo Associates, LLC19019 36th Ave. W.,Suite ELynnwood, WASHT. of11SITE AND EXPLORATION PLAN2072.01SEPTEMBER 20181HARRINTON APARTMENTSNE 10TH ST AND HARRINGTON AVE NERENTON, WASHINGTONAPPROXIMATE SCALE IN FEET0808040LEGENDB-1BORING NUMBER ANDAPPROXIMATE LOCATIONAPPROXIMATE PROPERTY LINEREFERENCE: GOOGLE MAPS 2018.
APPENDIX A
SUBSURFACE EXPLORATION PROCEDURES AND LOGS
APPENDIX A
SUBSURFACE EXPLORATION PROCEDURES AND LOGS
Field Exploration Description
Our field exploration for this project included advancing five borings across the proposed site of the
project on September 12, 2018. The approximate locations of the explorations are presented on Figure
1, the Site and Exploration Plan. Exploration locations were determined in the field based on hand
measurements from existing site features. As such, the exploration locations should be considered
accurate only to the degree implied by the measurement method. Descriptive logs of the borings are
enclosed in this appendix. A current topographic survey of the site was not available at the time of this
report. Therefore, ground surface elevations of the explorations were not determined.
The borings were advanced using a truck-mounted drill rig operated by an independent drilling company
(Holocene Drilling Inc.) working under subcontract to ZGA. The borings were advanced using the hollow-
stem auger drilling method. An engineer from our firm continuously observed the borings, logged the
subsurface conditions encountered, and obtained representative soil samples. All samples were stored
in moisture-tight containers and transported to our laboratory for further evaluation and testing. Samples
were obtained by means of the Standard Penetration Test at 2.5- to 5-foot intervals throughout the drilling
operation.
The Standard Penetration Test (ASTM D 1586) procedure consists of driving a standard 2-inch outside
diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches.
The number of blows required to drive the sampler through each 6-inch interval is recorded, and the total
number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or
“blow count” (N value). If a total of 50 blows is struck within any 6-inch interval, the driving is stopped
and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard
Penetration Resistance values indicate the relative density of granular soils and the relative consistency
of cohesive soils.
The enclosed boring logs describe the vertical sequence of soils and materials encountered in the borings,
based primarily upon our field classifications. Where a soil contact was observed to be gradational, our
log indicates the average contact depth. Where a soil type changed between sample intervals, we inferred
the contact depth. Our logs also graphically indicate the blow count, sample type, sample number, and
approximate depth of each soil sample obtained from the borings. If groundwater was encountered, the
approximate groundwater depth, and date of observation, are depicted on the logs.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-1
Page 1 of 2
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-1
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 18
S-2 18
S-3 0
S-4 8
S-5 18
S-6 18
47
30
20
20
76
72
GSA
MC
MC
5 inches of organics
Dense, damp, light brown, Silty SAND, with gravel
(Possible fill)
Medium dense, moist, brown, SAND, with silt, trace gravel
No Recovery
Medium dense, moist, brown-gray, SAND, with silt, some
gravel, slight mottling (Weathered Glacial Till)
Grades to very dense
Very dense, moist, tan, SAND, some silt (Glacial till)
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
25
30
35
40
45
50
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-1
Page 2 of 2
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-1
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-7 18 65 GSA
Very dense, moist, gray, SAND, with silt, some gravel
(Glacial till)
Boring terminated at approximately 26 1/2 feet.
No groundwater observed during exploration.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-2
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-2
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 inches
Auto
SNM
11/2/120 602040
S-1 12
S-2 12
S-3 16
S-4 18
S-5 11
49
60
63
73
50/5
MC
MC
MC
MC
6 inches of organics
Dense, damp, brown, Silty SAND, with gravel slight
mottling (Possible fill)
Dense, damp, gray, SAND, with silt and gravel (Weathered
Glacial Till)
Very dense, moist, gray, SAND, with silt, trace gravel
(Glacial Till)
Very dense, moist, gray, SAND, with silt, some gravel,
slight mottling (Glacial till)
Boring terminated at approximately 16 ft.
No groundwater observed during time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-3
Page 1 of 1
GROUNDWATER LEGEND
Harrington Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-3
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 0
S-2 6
S-3 18
S-4 9
S-5 11
S-6 10
50/2
23
74
50/3
50/5
50/4
GSA
MC
MC
4 inches of organics
Light brown, silty SAND, some gravel (Possible fill)
No recovery (Blow counts overstated)
Medium dense, moist, gray-tan, SAND, with silt, some
gravel (Weathered glacial till)
Very dense, moist, gray, silty SAND, some gravel (Glacial
till)
Grades to with silt and gravel
Grades to trace gravel
Grades to some silt and gravel
Boring terminated at approximately 21 ft. No groundwater
observed at the time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-4
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-4
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 inches
Auto
SNM
11/2/120 602040
S-1 6
S-2 18
S-3 12
S-4 0
S-5 8
S-6 4
7
26
50/6
50/3
50/2
50/3
GSA
MC
MC
2 inches of organics
Loose, damp, orange-brown, Gravelly SAND, with silt,
trace organics (Possible fill)
Medium dense, moist, gray, SAND, with silt, some gravel
(Weathered glacial till
Very dense, moist, gray-brown, SAND, with silt and gravel
(Glacial till)
No recovery (Blow counts overstated)
Grades to gray, some gravel
Grades to with gravel, some silt
Boring terminated at approximately 20 1/2 feet.
No groundwater observed at the time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-5
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-5
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 9
S-2 10
S-3 9
S-4 6
S-5 14
S-6 6
32
25
50/3
50/6
50/6
50/6
MC
MC
MC
MC
6 inches of organics
Dense, moist, tan, SAND, with silt, some gravel (Possible
fill)
Medium dense, moist, gray, SAND, with silt, some gravel
(Weathered glacial till)
Very dense, moist, gray, SAND, with silt, trace gravel
(Glacial till)
Grades to some gravel
Grades to some silt
Boring terminated at approximately 20 1/2 feet. No
groundwater observed at the time of drilling.
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
A series of laboratory tests were performed by ZGA during the course of this study to evaluate the index
and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests
performed are given below.
Visual Classification
Samples recovered from the exploration locations were visually classified in the field during the
exploration program. Representative portions of the samples were carefully packaged in moisture tight
containers and transported to our laboratory where the field classifications were verified or modified as
required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil
classification includes evaluation of color, relative moisture content, soil type based upon grain size, and
accessory soil types included in the sample. Soil classifications are presented on the exploration logs in
Appendix A.
Moisture Content Determinations
Moisture content determinations were performed on representative samples obtained from the
explorations to aid in identification and correlation of soil types. The determinations were made in
general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented
on the exploration logs in Appendix A.
Grain Size Distributions
A grain size analysis determines the range in diameter of soil particles included in a particular sample.
Grain size analyses were performed on representative samples in general accordance with ASTM D 422.
The results of the grain size determinations for the samples were used in classification of the soils, and
are presented in this appendix.
Modified Proctor
A modified proctor test determines the maximum dry density and optimum moisture to obtain a
maximum density under a certain compaction effort. The modified proctor test was performed on
representative samples in general accordance with ASTM D1557. The results of the modified proctor test
are presented in Appendix B.
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartment
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-1 2 1/2-4 9.3 Silty SAND, with
gravelS-1 30.5
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-1 25-26 1/2 8.3 SAND, with silt,
some gravelS-7 12.7
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-3 5-6 1/2 7.3 SAND, with silt,
some gravelS-2 27.6
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-4 2 1/2-4 9.1 Gravelly SAND,
with siltS-1 19.3
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
90
95
100
105
110
115
120
125
130
135
140
145
150
0 5 10 15 20 25 30 35 40 45Dry Unit Weight (pcf)Moisture Content (%)
LABORATORY
COMPACTION
CURVE
Compaction Size
Test Standard Mold
Harrington Ave Apartments
Job No.
Job Name
Date Tested
Sample No.
Location
Test Results
Zipper Geo Associates, LLC 19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Test No.Field Moist.2 3 4
Dry Density (lbs/cu.ft.)132.9 129.4 130.4 #DIV/0!
Moisture Content (%)9.3 10.1 6.5 #DIV/0!
1557-B 4-inch
2.80
2.70
2.60
2.50
2.40
Zero Air Voids Curves For
Various Specific Gravities
2072.01
Depth / Elevation9/14/2018
09122018
Cuttings 5-7 1/2 ft
134.0 136.2
8.38.3
Maximum Dry Density / Oversize Corrected (pcf)
Opt. Moisture Content / Oversize Corrected (%)
Sample Description:
Comments:
Oversize Fraction (%) / Sieve Used 3/49
Appendix E
Conveyance Calculations
Appendix F
Drainage Review Flow Chart
SECTION 1.1 DRAINAGE REVIEW
12/12/2016 2017 City of Renton Surface Water Design Manual
1-14
FIGURE 1.1.2.A FLOW CHART FOR DETERMINING TYPE OF DRAINAGE REVIEW REQUIRED
12131 113th Avenue NE, Suite 203, Kirkland, WA 98034 | 425.821.3665 |
FINAL MEMORANDUM
Date: September 11, 2019 TG:1.19223.00
To: Brianne Bannwarth – City of Renton
From: Stefanie Herzstein PE, PTOE and Francesca Liburdy – Transpo Group
cc: Bob Baldwin – McCullough Allen
Lisa Grueter, AICP – BERK Consulting
Subject: Renton Sunset Oaks Final Transportation Impact Analysis
This analysis identifies potential transportation-related impacts associated with the proposed
Sunset Oaks residential development north of NE 10th Street between Glenwood Avenue NE and
Harrington Avenue NE in Renton, WA. This final transportation impact analysis incorporates City
staff’s review of the study.
Background
The project is sites 14, 16 and 17 in the Sunset Terrace Master Plan as shown on Figure 1.
Figure 1 – Sunset Terrace Master Plan
2
Transportation-related impacts of the Master Plan were documented in the Sunset Area
Community Planned Action Update: Traffic Analysis Results - May 2014 Redevelopment Master
Site Plan Alternative (CH2MHill, 2014). The proposed project includes more dwellings than
included in the current Master Plan and requires Master Plan revisions to reallocate dwelling units
to the Renton Housing Authority Sunset Oaks properties and reflect other public, private and non-
profit development activities that have been permitted or constructed in the last several years.
Transportation analysis associated with the Sunset Terrace Master Plan reallocation of 87
dwelling units including 52 dwelling units to the Sunset Oaks properties was documented in the
memorandum Sunset Oaks and Master Site Plan: Transportation Analysis prepared by Transpo
Group dated July 23, 2019. The analysis of the Master Plan dwelling unit reallocation found that
there would be no new transportation impacts and the mitigation measures identified in the
previous Master Plan analysis would be appropriate. Based on the 2030 build-out of the Master
Plan, mitigation measures identified include potential improvements to the Edmonds Avenue
NE/NE 12th Street and Harrington Avenue NE/NE 12th Street intersections to maintain LOS D
operations. As an affordable housing residential project, payment of the City’s transportation
impact fees would not be required, These findings are being incorporated into updated
SEPA/NEPA analysis for the Sunset Terrace Master Plan.
The following documents the project-specific transportation impact analysis (TIA) for the Sunset
Oaks property.
Project Description
The proposed project includes up to 62 affordable multifamily housing units located in the Sunset
Area neighborhood of Renton. The site vicinity is shown on Figure 2.
Figure 2 – Site Vicinity
The project site is currently undeveloped and the project is anticipated to be constructed and
occupied by 2021. Vehicle access to the site is proposed via Harrington Avenue NE and
3
Glennwood Avenue NE. There would also be a non-motorized connection via Sunset Lane NE.
Figure 3 shows the site plan depicting the proposed site and driveways.
Figure 3 – Preliminary Site Plan
Study Scope
The scope of the analysis is consistent with the City of Renton’s Traffic Impact Analysis Policy
Guidelines for New Developments (2016) and was reviewed and approved by the City through a
scoping process. Based on coordination with the City, the analysis focuses on the weekday PM
peak hour. Considering anticipated trip distribution patterns described later in the study and the
City’s guidelines stating the study area should include intersections experiencing a 5 percent
increase in peak hour traffic volumes as a result of the proposed development, the analysis
focuses on the two site access locations under future with-project conditions.
As described previously, the proposed project is part of the Sunset Terrace Master Plan
Amendment1 and a separate transportation analysis was conducted related to the reallocation of
dwelling units. The Master Plan analysis evaluated traffic volume impacts at the NE 12th Street/
Harrington Avenue NE, NE Sunset Boulevard/NE 10th Street, and NE Sunset Boulevard/
Harrington Avenue NE intersections and found that there would be a 0.5 to 2.4 percent in total
intersection volumes at these locations as a result of the proposed Master Plan Amendment. This
increase in traffic volumes is less than the City’s 5 percent threshold used to determine the study
area for project-specific TIAs. This analysis supports limiting the study intersections for the Sunset
Oaks development TIA to the site accesses.
1 Memorandum Sunset Oaks and Master Site Plan: Transportation Analysis, Transpo Group, July 2019.
4
Existing Transportation Context
The following section summarizes the existing transportation context of the proposed project,
including the surrounding roadway network, non-motorized facilities, transit, traffic safety, and
vehicle volumes.
Roadway Network
The project site is located in the City of Renton and is bounded by Glennwood Avenue NE,
Harrington Avenue NE, and Sunset Lane NE. Descriptions of the roadways within the project area
are provided below.
Glennwood Avenue NE is classified as a local street and has a narrow travel way. On-street
parking occurs on the shoulder on both sides of the street narrowing the travel way further. The
posted speed limit is 25 miles per hour (mph). No sidewalks are provided along Glennwood
Avenue NE in the vicinity of the project.
Harrington Avenue NE is classified as a local street and has two lanes per direction. The posted
speed limit is 25 mph. Sidewalks and on-street parking are provided on both sides of the street.
Sunset Lane NE is classified as a local street with a posted speed of 25 mph. It has a narrow
travel way. Sidewalks and on-street parking are provided on both sides of the street.
Non-Motorized Facilities
Sidewalks are provided throughout the study area with the exception of Glennwood Avenue NE.
Marked crosswalks are provided at the Glennwood Avenue NE/Sunset Lane NE and Harrington
Avenue NE/Sunset Lane NE intersections. No bicycle facilities are provided in the vicinity of the
project site; however, the roadways are local streets with low traffic volumes.
Transit
The project site is located in proximity to transit operated by King County Metro. There are
numerous stops along NE Sunset Blvd and NE 12th Avenue, nearby principal arterial roadways.
The closest bus stops are located a 0.2 mile walking distance or an approximately 5-minute walk
from the project site. Connections to King County Metro routes near the project site are
summarized in Table 1.
Table 1. Existing Transit Service
Approximate Weekday
Operating Hours
AM Peak
Period Trips
PM Peak
Period Trips
Headways
(minutes) Routes Area Served
111 Maplewood to Lake Kathleen to
Downtown Seattle
5:50 a.m. – 8:45 a.m.
4 4 30
4:00 p.m. – 7:00 p.m.
240 Bellevue to Renton 5:00 a.m. – 12:00 a.m. 7 7 15
105 Renton Highlands to Renton TC 4:30 a.m. – 12:10 a.m. 3 3 30
Source: King County Metro (August 2019).
The King County Metro transit service provides access to the Renton Transit Center, which is
located approximately 3-miles south of the Sunset Terrace neighborhood. Connections at Renton
Transit Center provide bus access to SeaTac, Kent, Auburn, Bellevue, and Overlake via both King
County Metro and Sound Transit. There is a proposed bus rapid transit (BRT) expansion along I-
405 slated to be completed by Sound Transit in year 2024. There would be a stop at the Renton
Transit Center.
5
Traffic Safety
Collision records were reviewed within the study area to document potential traffic safety issues.
The collision data from Washington State Department of Transportation (WSDOT) is for the most
recent 5-year period between January 1, 2014 and December 31, 2018. A historical review of
collisions was conducted at the roadways directly surrounding the site. Only one collision was
reported along the roadways and intersections directly adjacent to the project area. In 2016, a
vehicle making a northbound left-turn onto Sunset Lane NE out of a driveway 200-feet east of
Harrington Avenue NE had a collision with a bicyclist. There were no reported fatalities within or
surrounding the study area.
Trip Generation
The proposed project includes up to 62-multifamily affordable housing units. Trip generation
estimates have been prepared for the development based on trip rates identified using the Institute
of Transportation Engineers (ITE) Trip Generation Manual, 10th Edition (2017). Table 2 provides a
summary of the trip generation for the proposed land use.
Table 2. Estimated Weekday Vehicle Trip Generation
Land Use Size
Daily
Trips
AM Peak Hour Trips PM Peak Hour Trips
In Out Total In Out Total
Multifamily Housing Mid-Rise (LU #221) 62 du 337 6 16 22 16 11 27
Notes: du = dwelling units
As shown in Table 2, the proposed project is anticipated to generate approximately 337 daily
vehicle trips with approximately 22 trips during the weekday AM peak hour and 27 trips during the
weekday PM peak hour.
Trip Distribution and Assignment
Weekday PM peak hour trip distribution patterns to and from the project site were based on
existing vehicle travel patterns and the U.S. Census Bureau’s OnTheMap tool. OnTheMap is a
web-based mapping and reporting application, which shows where residents in the area work
based on census data. Project traffic was assigned to the site driveways based on the trips’
anticipated final destination and the location of the dwelling units. Anticipated trip distribution and
assignment for the proposed project are shown on Figure 4.
Traffic Volumes
Existing weekday PM (4 to 6 p.m.) peak period traffic counts were collected at the Harrington
Avenue NE/Glennwood Avenue NE, Glennwood Avenue NE/NE 10th Street, and Harrington
Avenue NE/NE 10th Street intersections in August 2019. These volumes were used to develop
future traffic forecasts at the proposed site accesses. Detailed intersection traffic counts are
provided in Attachment A.
Future (2021) with-project weekday PM peak hour traffic volumes were estimated by growing
existing traffic volumes by three (3) percent per year to 2021 conditions, consistent with other
projects completed in the City. No pipeline projects were identified within the study area. The
resulting future (2021) with-project volumes at the site accesses are summarized on Figure 4.
6
Figure 4 – Trip Distribution, Assignment & Future Weekday PM Peak Hour Traffic Volumes
Site Access Analysis
The traffic operations at each of the site driveways was analyzed under future with-project
conditions for the weekday PM peak hour. At unsignalized side-street stop-controlled
intersections, LOS is measured by the average delay per vehicle of the worst-movement. Traffic
operations and average vehicle delay for an intersection can be described qualitatively with a
range of levels of service (LOS A through LOS F), with LOS A indicating free-flowing traffic and
LOS F indicating extreme congestion and long vehicle delays. The operational analysis is
consistent with Highway Capacity Manual (HCM) 6th Edition method and evaluated in Synchro 10.
Synchro 10 is a software program that uses the HCM method to evaluate intersection LOS and
average vehicle delays.
Under future (2021) with-project conditions, both site accesses are anticipated to operate at LOS
A during the weekday PM peak hour with approximately 9 seconds of delay. LOS worksheets are
included in Attachment B.
7
Mitigation Measures
As discussed previously, mitigation measures identified for the Sunset Terrace Master Plan
include potential improvements to the Edmonds Avenue NE/NE 12th Street and Harrington
Avenue NE/NE 12th Street intersections to maintain LOS D operations. As an affordable housing
residential project, payment of the City’s transportation impact fees will not be required.
Intersection Improvements
The proposed project’s anticipated increase in traffic volumes at the Edmonds Avenue NE/NE
12th Street and Harrington Avenue NE/NE 12th Street intersections is anticipated to be small and
less than 5 percent as demonstrated in the Master Plan Amendment analysis and shown on
Figure 4 of this study.
A review of the Sunset Court project-specific TIA2 shows that the Edmonds Avenue NE and
Harrington Avenue NE intersections along NE 12th Street were anticipated to operate at LOS B or
better during the weekday PM peak hour under future 2017 conditions. A sensitivity analysis was
conducted by Transpo to understand potential future 2021 with-project conditions at the Edmonds
Avenue NE/NE 12th Street and Harrington Avenue NE/NE 12th Street intersections. The
sensitivity analysis uses the Sunset Court traffic volumes to project 2021 conditions assuming a
three (3) percent per year growth rate and adding the project traffic. The Edmonds Avenue NE/NE
12th Street and Harrington Avenue NE/NE 12th Street intersections would operate at LOS B
during the weekday PM peak hour in 2021; therefore, no mitigation would be needed with the
proposed project.
Conclusions
Key findings of this TIA include:
· The proposed project would generate approximately 337 daily vehicle trips with 22
weekday AM peak hour and 27 weekday PM peak hour trips.
· Both site accesses are forecast to operate at LOS A during the weekday PM Peak
hour under future (2021) with-project conditions.
· No significant impacts requiring mitigation are anticipated with the proposed project.
2 Ally Community Development, LLC Traffic Impact Analysis Sunset Court, Perteet, September 10, 2015.
8
Attachment A: Traffic Counts
Peak Hour:05:00 PM - 06:00 PM
HARRINGTON AVE NE HARRINGTON AVE NEGLENWOOD AVE NEGLENWOOD AVE NE
(303) 216-2439
www.alltrafficdata.net
Location:1 HARRINGTON AVE NE & GLENWOOD AVE NE PM
Thursday, August 1, 2019Date:
All Vehicles Pedestrians/Bicycles in Crosswalk
Traffic Counts - All Vehicles
Heavy Vehicles
Peak Hour
Traffic Counts - Heavy Vehicles and Pedestrians/Bicycles in Crosswalk3120
0
1
1
0
4
39 41
1
2
3735
5
4 N
S
EW
0
0 3313600GLENWOOD AVE NE
GLENWOOD AVE NEHARRINGTON AVEHARRINGTON AV82
0
214N
S
EW 1110
0 0
40Interval
Start Time RightLeft Thru Total
Eastbound Westbound Northbound Southbound
U-Turn
Rolling
HourRightLeft ThruU-Turn RightLeft ThruU-Turn RightLeft ThruU-Turn
4:00 PM 630 2 0 0 0 0 0 0 4 0 1 1 90 0 0 1
4:15 PM 730 2 0 0 0 0 0 0 4 0 0 9 170 0 0 2
4:30 PM 750 3 0 0 0 0 0 0 5 0 0 5 160 0 0 3
4:45 PM 780 0 0 0 1 0 0 1 10 0 0 5 210 0 0 4
5:00 PM 820 1 0 0 0 0 0 1 11 0 1 4 191 0 0 0
5:15 PM 0 0 0 0 0 0 0 0 6 1 0 12 190 0 0 0
5:30 PM 0 0 0 0 0 0 0 0 8 0 0 9 190 0 0 2
5:45 PM 0 3 0 0 1 0 0 0 11 0 1 8 250 0 0 1
Count Total 0 11 0 0 2 0 0 2 59 1 3 53 1451 0 0 13
Peak Hour 0 4 0 0 1 0 0 1 36 1 2 33 821 0 0 3
HV% PHF
0.42
0.25
0.77
0.75
0.0%
0.0%
2.7%
5.1%
3.7% 0.82
EB
WB
NB
SB
All 0000
0
0
0
0
0
2 1
0
0
12
0
0 N
S
EW
0
0 20100Heavy VehiclesInterval
Start Time EB NB TotalWB SB
4:00 PM 0 0 0 0 0
4:15 PM 0 0 0 0 0
4:30 PM 0 0 0 0 0
4:45 PM 0 0 0 0 0
5:00 PM 0 0 0 0 0
5:15 PM 0 1 0 2 3
5:30 PM 0 0 0 0 0
5:45 PM 0 0 0 0 0
Count Total 0 1 0 2 3
Peak Hour 0 1 0 2 3
Pedestrians/Bicycles on CrosswalkInterval
Start Time EB NB TotalWB SB
4:00 PM 0 0 4 1 5
4:15 PM 0 0 2 1 3
4:30 PM 1 0 3 0 4
4:45 PM 3 0 0 0 3
5:00 PM 4 0 1 0 5
5:15 PM 0 0 0 0 0
5:30 PM 0 0 0 0 0
5:45 PM 0 1 1 0 2
Count Total 8 1 11 2 22
Peak Hour 4 1 2 0 7
Peak Hour:05:00 PM - 06:00 PM
GLENWOOD AVE NESUNSET LN NESUNSET LN NE
(303) 216-2439
www.alltrafficdata.net
Location:2 GLENWOOD AVE NE & SUNSET LN NE PM
Thursday, August 1, 2019Date:
All Vehicles Pedestrians/Bicycles in Crosswalk
Traffic Counts - All Vehicles
Heavy Vehicles
Peak Hour
Traffic Counts - Heavy Vehicles and Pedestrians/Bicycles in Crosswalk3034
6
0
0
2
5
6 9
10
57
9 N
S
EW
0
0 0SUNSET LN NE
SUNSET LN NE GLENWOOD AVE 23
1
02N
S
EW 000 1
02Interval
Start Time RightLeft Thru Total
Eastbound Westbound Northbound Southbound
U-Turn
Rolling
HourRightLeft ThruU-Turn RightLeft ThruU-Turn RightLeft ThruU-Turn
4:00 PM 170 0 1 0 0 1 0 0 0 40 2 0
4:15 PM 220 0 0 0 0 2 0 0 0 50 1 2
4:30 PM 200 1 1 0 0 1 0 1 0 50 1 0
4:45 PM 180 0 1 0 0 1 0 0 0 30 0 1
5:00 PM 230 2 0 0 0 3 0 2 0 90 1 1
5:15 PM 0 0 1 0 0 1 0 0 0 30 1 0
5:30 PM 0 2 0 0 0 1 0 0 0 30 0 0
5:45 PM 0 1 1 0 0 1 0 1 0 80 2 2
Count Total 0 6 5 0 0 11 0 4 0 400 8 6
Peak Hour 0 5 2 0 0 6 0 3 0 230 4 3
HV% PHF
0.88
0.63
0.50
0.0%
0.0%
0.0%
0.0% 0.64
EB
WB
NB
SB
All 0000
0
0
0
0
0
0 0
0
00
0 N
S
EW
0
0 0Heavy VehiclesInterval
Start Time EB NB TotalWB SB
4:00 PM 0 0 0 0
4:15 PM 0 0 0 0
4:30 PM 0 0 0 0
4:45 PM 0 0 0 0
5:00 PM 0 0 0 0
5:15 PM 0 0 0 0
5:30 PM 0 0 0 0
5:45 PM 0 0 0 0
Count Total 0 0 0 0
Peak Hour 0 0 0 0
Pedestrians/Bicycles on CrosswalkInterval
Start Time EB NB TotalWB SB
4:00 PM 0 0 0 0
4:15 PM 0 0 0 0
4:30 PM 0 0 1 1
4:45 PM 0 0 1 1
5:00 PM 0 0 0 0
5:15 PM 1 0 1 2
5:30 PM 1 0 0 1
5:45 PM 0 0 0 0
Count Total 2 0 3 5
Peak Hour 2 0 1 3
Peak Hour:05:00 PM - 06:00 PM
HARRINGTON AVE NENE 10TH STSUNSET LN NE
(303) 216-2439
www.alltrafficdata.net
Location:3 HARRINGTON AVE NE & NE 10TH ST PM
Thursday, August 1, 2019Date:
All Vehicles Pedestrians/Bicycles in Crosswalk
Traffic Counts - All Vehicles
Heavy Vehicles
Peak Hour
Traffic Counts - Heavy Vehicles and Pedestrians/Bicycles in Crosswalk303039
8
0
0
4
1
33 40
47
345
11 N
S
EW
0
0 0SUNSET LN NE
NE 10TH ST HARRINGTON AV85
1
69N
S
EW 421 0
90Interval
Start Time RightLeft Thru Total
Eastbound Westbound Northbound Southbound
U-Turn
Rolling
HourRightLeft ThruU-Turn RightLeft ThruU-Turn RightLeft ThruU-Turn
4:00 PM 540 1 0 0 0 2 0 1 0 80 3 1
4:15 PM 690 0 0 0 0 1 0 7 0 140 3 3
4:30 PM 670 0 3 0 0 0 0 4 0 150 6 2
4:45 PM 700 1 0 0 0 1 0 4 0 170 11 0
5:00 PM 850 0 2 0 0 3 0 4 0 230 13 1
5:15 PM 0 0 1 0 0 2 0 5 0 120 4 0
5:30 PM 0 0 0 0 0 1 0 7 0 180 9 1
5:45 PM 0 1 1 0 0 2 0 14 0 320 13 1
Count Total 0 3 7 0 0 12 0 46 0 1390 62 9
Peak Hour 0 1 4 0 0 8 0 30 0 850 39 3
HV% PHF
0.63
0.73
0.55
0.0%
0.0%
3.0%
1.2% 0.66
EB
WB
NB
SB
All 0010
0
0
0
0
0
1 0
0
10
0 N
S
EW
0
0 0Heavy VehiclesInterval
Start Time EB NB TotalWB SB
4:00 PM 0 0 0 0
4:15 PM 0 0 0 0
4:30 PM 0 0 0 0
4:45 PM 0 0 0 0
5:00 PM 0 0 0 0
5:15 PM 0 0 0 0
5:30 PM 0 0 0 0
5:45 PM 0 0 1 1
Count Total 0 0 1 1
Peak Hour 0 0 1 1
Pedestrians/Bicycles on CrosswalkInterval
Start Time EB NB TotalWB SB
4:00 PM 0 1 0 1
4:15 PM 0 0 0 0
4:30 PM 0 1 0 1
4:45 PM 2 0 0 2
5:00 PM 5 4 0 9
5:15 PM 1 0 1 2
5:30 PM 0 0 0 0
5:45 PM 3 2 0 5
Count Total 11 8 1 20
Peak Hour 9 6 1 16
9
Attachment B: LOS Worksheets
HCM 6th TWSC Sunset Oaks Apartments
4: Glennwood Ave NE & Site Access Future (2021) With-Project PM Peak Hour
Transpo Group Synchro 10 Report
Intersection
Int Delay, s/veh 1.8
Movement WBL WBR NBT NBR SBL SBT
Lane Configurations
Traffic Vol, veh/h 4 1 10 7 1 5
Future Vol, veh/h 4 1 10 7 1 5
Conflicting Peds, #/hr 0 0 0 0 0 0
Sign Control Stop Stop Free Free Free Free
RT Channelized - None - None - None
Storage Length 0 - - - - -
Veh in Median Storage, # 0 - 0 - - 0
Grade, % 0 - 0 - - 0
Peak Hour Factor 92 92 92 92 92 92
Heavy Vehicles, % 2 2 2 2 2 2
Mvmt Flow 4 1 11 8 1 5
Major/Minor Minor1 Major1 Major2
Conflicting Flow All 22 15 0 0 19 0
Stage 1 15 - - - - -
Stage 2 7 - - - - -
Critical Hdwy 6.42 6.22 - - 4.12 -
Critical Hdwy Stg 1 5.42 - - - - -
Critical Hdwy Stg 2 5.42 - - - - -
Follow-up Hdwy 3.518 3.318 - - 2.218 -
Pot Cap-1 Maneuver 995 1065 - - 1597 -
Stage 1 1008 - - - - -
Stage 2 1016 - - - - -
Platoon blocked, % - - -
Mov Cap-1 Maneuver 994 1065 - - 1597 -
Mov Cap-2 Maneuver 994 - - - - -
Stage 1 1008 - - - - -
Stage 2 1015 - - - - -
Approach WB NB SB
HCM Control Delay, s 8.6 0 1.2
HCM LOS A
Minor Lane/Major Mvmt NBT NBRWBLn1 SBL SBT
Capacity (veh/h) - - 1007 1597 -
HCM Lane V/C Ratio - - 0.005 0.001 -
HCM Control Delay (s) - - 8.6 7.3 0
HCM Lane LOS - - A A A
HCM 95th %tile Q(veh) - - 0 0 -
HCM 6th TWSC Sunset Oaks Apartments
5: Harrington Ave NE & Site Access Future (2021) With-Project PM Peak Hour
Transpo Group Synchro 10 Report
Intersection
Int Delay, s/veh 1.2
Movement EBL EBR NBL NBT SBT SBR
Lane Configurations
Traffic Vol, veh/h 1 5 7 40 35 1
Future Vol, veh/h 1 5 7 40 35 1
Conflicting Peds, #/hr 0 0 0 0 0 0
Sign Control Stop Stop Free Free Free Free
RT Channelized - None - None - None
Storage Length 0 - - - - -
Veh in Median Storage, # 0 - - 0 0 -
Grade, % 0 - - 0 0 -
Peak Hour Factor 92 92 92 92 92 92
Heavy Vehicles, % 2 2 2 2 2 2
Mvmt Flow 1 5 8 43 38 1
Major/Minor Minor2 Major1 Major2
Conflicting Flow All 98 39 39 0 - 0
Stage 1 39 - - - - -
Stage 2 59 - - - - -
Critical Hdwy 6.42 6.22 4.12 - - -
Critical Hdwy Stg 1 5.42 - - - - -
Critical Hdwy Stg 2 5.42 - - - - -
Follow-up Hdwy 3.518 3.318 2.218 - - -
Pot Cap-1 Maneuver 901 1033 1571 - - -
Stage 1 983 - - - - -
Stage 2 964 - - - - -
Platoon blocked, % - - -
Mov Cap-1 Maneuver 896 1033 1571 - - -
Mov Cap-2 Maneuver 896 - - - - -
Stage 1 978 - - - - -
Stage 2 964 - - - - -
Approach EB NB SB
HCM Control Delay, s 8.6 1.1 0
HCM LOS A
Minor Lane/Major Mvmt NBL NBT EBLn1 SBT SBR
Capacity (veh/h) 1571 - 1007 - -
HCM Lane V/C Ratio 0.005 - 0.006 - -
HCM Control Delay (s) 7.3 0 8.6 - -
HCM Lane LOS A A A - -
HCM 95th %tile Q(veh) 0 - 0 - -
GEOTECHNICAL ENGINEERING REPORT
HARRINGTON AVE APARTMENTS
NE 10TH STREET AND HARRINGTON AVENUE NE
RENTON, WASHINGTON
PROJECT NO. 2072.01
May 15, 2019May 15, 2019
Prepared for:
Renton Housing Authority
Prepared by:
19019 36th Avenue W., Suite E
Lynnwood, WA 98036
19019 36th Avenue West, Suite E Lynnwood, WA 98036 (425) 582-9928
Project No. 2072.01
May 15, 2019
Renton Housing Authority
P.O. Box 2316
Renton, Washington 98056-0316
Attn: Mr. Mark Gropper
Subject: Geotechnical Engineering Report
Harrington Ave Apartments
NE 10th Street and Harrington Avenue NE
Renton, Washington
Dear Mr. Gropper,
In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has
completed the subsurface exploration and geotechnical engineering evaluation for the Harrington Ave
Apartments project. This report presents the results of the subsurface exploration, as well as our
geotechnical engineering recommendations for the project. Our services were completed in general
accordance with our Proposal for Geotechnical Engineering Services (Proposal No. P18283) dated August
23, 2018. Written authorization to proceed on our proposed scope of services was provided by Renton
Housing Authority on August 27, 2018. We appreciate the opportunity to be of service to you on this
project. If you have any questions concerning this report, or if we may be of further service, please contact
us.
Sincerely,
Zipper Geo Associates, LLC
Robert A. Ross, P.E.
Principal
5/15/19
TABLE OF CONTENTS
Page
INTRODUCTION ........................................................................................................................................... 1
PROJECT UNDERSTANDING..................................................................................................................... 1
SITE CONDITIONS ....................................................................................................................................... 1
Surface Conditions .......................................................................................................................................... 1
Subsurface Conditions ..................................................................................................................................... 2
Groundwater Conditions ................................................................................................................................. 2
LABORATORY TESTING ............................................................................................................................ 3
CONCLUSIONS AND RECOMMENDATIONS ............................................................................................ 3
General Considerations ................................................................................................................................... 3
Geologically Hazardous Areas ......................................................................................................................... 3
Seismic Design Considerations ........................................................................................................................ 4
Site Preparation ............................................................................................................................................... 5
Structural Fill Materials, Placement, and Compaction .................................................................................... 7
Utility Trenching and Backfilling ...................................................................................................................... 8
Construction Dewatering ................................................................................................................................ 9
Shallow Foundation Recommendations .......................................................................................................... 9
On-Grade Concrete Slabs .............................................................................................................................. 10
Permanent Drainage Considerations ............................................................................................................ 11
Retaining Wall ............................................................................................................................................... 11
Stormwater Infiltration Feasibility ................................................................................................................ 12
Pavements ..................................................................................................................................................... 12
CLOSURE ................................................................................................................................................... 14
FIGURES
Figure 1 – Site and Exploration Plan
APPENDICES
Appendix A – Subsurface Exploration Procedures and Logs
Appendix B – Laboratory Testing Procedures and Results
Cover Page Photo Credit: Google Earth Pro, 2018 Aerial Photo
Page 1
GEOTECHNICAL ENGINEERING REPORT
HARRINGTON AVE APARTMENTS
RENTON, WASHINGTON
Project No. 2072.01
May 15, 2019
INTRODUCTION
This report documents the surface and subsurface conditions encountered at the project site and our
geotechnical engineering recommendations for the current proposed Harrington Ave Apartments in
Renton, Washington. Our geotechnical engineering scope of services for the project included subsurface
explorations, laboratory testing, geotechnical engineering analysis, and preparation of this report.
The observations and conclusions summarized herein are based in part upon conditions observed in our
subsurface explorations and site observations. In the event that site conditions change, it may be
necessary to modify the conclusions and recommendations presented in this report. This report is an
instrument of service and has been prepared in general accordance with locally accepted geotechnical
engineering practice. This report has been prepared for the exclusive use of the Renton Housing
Authority, and its agents, for specific application to the subject property and stated purpose.
PROJECT UNDERSTANDING
The project site consists of five undeveloped parcels zoned as R-14 and located at the northwest corner of
the intersection of NE 10th Street and Harrington Ave NE in Renton, Washington. The project site was
previously developed with single-family homes that were demolished. We understand the project will
consists of developing the site with a 62 unit, 3-story, wood-framed apartment building and related site
improvements including underground utilities, pavements, and stormwater management facilities. We
expect that the finished floor elevation of the building will be near existing site grades. Grading for the
project is expected to consist of cuts and fills with a maximum anticipated depth/thickness of about 5 feet.
However, deeper cuts may be required for underground utilities and stormwater management facilities.
Design drawings for the proposed apartment building and associated site improvements were not available
at the time this report was prepared. Once details regarding the proposed apartment building and
additional site improvements are known, we should be consulted to review the details and revise this report
if necessary.
SITE CONDITIONS
Surface Conditions
The project site consists of five parcels with a total area of slightly above one acre. The site is bordered to
the north by single-family residences, to the east by Harrington Ave NE, to the south by the new extension
of NE 10th Street, and to the west by Glennwood Ave NE. Parcel number 7227801305 overlaps with the new
construction of the NE 10th Street extension with a portion remaining to the north of the road construction.
We anticipate that this portion will be included in the project area.
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Topographically, the site is relatively flat. Ground cover consists primarily of grass with a few scattered large
deciduous and coniferous trees. The northwest corner of the project site was used as a staging area for
construction equipment associated with the extension of NE 10th Street and is covered with medium gravel.
A plan view of the project site is shown on the attached Figure 1, Site and Exploration Plan.
Subsurface Conditions
Mapped Geology: We reviewed published geologic mapping of the site vicinity through the Washington
State Department of Natural Resource’s web-based mapping application Washington Geologic
Information Portal (https://geologyportal.dnr.wa.gov/). The published mapping indicates the site is
underlain by Vashon glacial till (Qgt). The mapping describes this soil as mostly thin ablation till over
lodgment till, deposited by the Puget glacial lobe consisting of a generally compact, coherent unsorted
mixture of sand, silt clay and gravel. The mapping notes that north of the Cedar River, where the project
site is located, the till is mostly sand.
Subsurface Exploration: The subsurface evaluation for this project included advancement of five borings
(B-1 through B-5) completed throughout the area of the project site. The borings were extended to depths
of about 16 to 26½ feet below the existing ground surface (bgs) and their approximate locations are shown
on Figure 1, Site and Exploration Plan.
Soils were visually classified in general accordance with the Unified Soil Classification System. Descriptive
logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are
presented in Appendix A. A generalized description of soil conditions encountered in the explorations is
presented below. Please refer to the exploration logs in Appendix A for a more detailed description of the
conditions encountered at each exploration location.
Soil conditions observed in the borings generally consisted of three to twelve feet of medium dense to dense
sand with variable silt and gravel contents. Below this layer we encountered very dense sand with variable
silt and gravel contents that we interpret to be glacial till. All the explorations terminated within the glacial
till. The upper 4 to 5 feet of soils observed in our explorations was interpreted to be possibly undocumented
fill associated with previous development of the site and possibly demolition of the previously existing homes.
Groundwater Conditions
Groundwater was not encountered within our explorations. Fluctuations in groundwater levels will likely
occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time
the exploration was performed. Therefore, groundwater levels during construction or at other times in
the life of the structure may be higher than indicated on the logs. The possibility of groundwater level
fluctuations should be considered when developing the design and construction plans for the project.
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LABORATORY TESTING
Laboratory testing included soil moisture content, grain size distribution, and modified proctor tests on
selected samples obtained from our explorations. The results of the moisture content tests are presented on
the boring logs in Appendix A and the grain size distribution and modified proctor test results are presented
in Appendix B. In general, moisture content testing indicates the sands within the upper 10 feet of existing
site grade had moisture contents ranging from about 4 to 12 percent with an average of about 9 percent.
Grain size distribution testing indicates the sands within the upper 7 feet of existing site grade had fines
contents ranging from about 19 to 30 percent. We collected cuttings from the auger and performed a
modified proctor test on the material. The modified proctor test yielded a maximum dry density of 136.2 pcf
and an optimum moisture content of 8.3 percent.
CONCLUSIONS AND RECOMMENDATIONS
General Considerations
Based on the results of our subsurface investigation as described in previous sections, it is our opinion the
proposed building can be supported on conventional shallow foundations bearing on medium dense to
very dense native soil or structural fill placed on properly prepared native soils, contingent on proper
design and construction practices and implementation of the recommendations presented in this report.
Geotechnical engineering recommendations for conventional shallow foundations and other earthwork
related phases of the project are presented below. The recommendations contained in this report are
based upon the results of field and laboratory testing (which are presented in Appendices A and B),
engineering analyses, and our current understanding of the proposed project. ASTM and Washington
State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the
current manual published by the American Society for Testing & Materials and the 2016 edition of the
Standard Specifications for Road, Bridge, and Municipal Construction (M41-10).
Geologically Hazardous Areas
As part of our services, we evaluated the presence of regulated geologically hazardous areas (GHAs) at
the site. Chapter 4-3-050 of the Renton Municipal Code (the Code) designates GHAs as Erosion, Landslide,
Seismic, and Coal Mine Hazard Areas.
Steep Slope Hazard Areas: The code defines steep slope hazard areas as areas with an average slope of
25 percent or greater with a total relief of 15 feet or greater, or having an average slope of 40 percent or
greater. The project site does not meet the definition of a steep slope area.
Landslide Hazard Areas: The code defines a low landslide hazard area as an area with slopes less than
fifteen percent. Based on the relative flat topography, the site classifies as having a “low landslide
hazard”, based on the code definition.
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Erosion Hazard Areas: The code characterizes sites as having a low or high erosion hazard based on
information available through the Natural Resource Conservation Service (NRCS). The NRCS maps the site
as being 70% Arents, Alderwood material (AmC) and 30% Ragnar-Indianola association both with a slope
less than 15 percent. Therefore, the site classifies as having a “low erosion hazard”, based on the code
definition.
Seismic Hazard Areas: The code characterizes sites as having either “low seismic hazard” or “high seismic
hazard” based on the subsurface conditions. A low seismic hazard area is defined as an area underlain by
dense soils or bedrock, generally having site classifications of A through D, as defined in the International
Building Code, 2012. It is our opinion that the project site classifies as having a “low seismic hazard”,
based on the code definition. More detailed information regarding seismic hazards is provided in the
seismic design considerations section of this report.
Coal Mine Hazard Areas: The code defines areas with low coal mine hazards as areas with no known mine
workings and no predicted subsidence. We reviewed the King County iMap for coal mine hazard mapping
as well as the Coal Mine Map Database located within the Washington State Department of Natural
Resources online Washington Geologic Information Portal. Based on a review of the readily available
information provided by these sources, no coal mine workings are documented within close vicinity of the
project site. Therefore, in our opinion the project site classifies as having a “low coal mine hazard”,
based on the code definition.
Seismic Design Considerations
The tectonic setting of western Washington is dominated by the Cascadia Subduction Zone formed by the
Juan de Fuca plate subducting beneath the North American Plate. This setting leads to intraplate, crustal,
and interplate earthquake sources. Seismic hazards relate to risks of injury to people and damage to
property resulting from these three principle earthquake sources.
Ground Surface Rupture: Based on our review of the USGS Quaternary age fault database for Washington
State, an inferred fault trace of the Seattle Fault Zone is located approximately 1 ½-miles to the north and
northwest of the project site. As the fault does not appear to cross the site, it is our opinion that the risk
of ground surface rupture at the site is low.
Landsliding: Based on the relatively flat topography of the site and surrounding vicinity, it is our opinion
that the risk of earthquake-induced landsliding is low.
Soil Liquefaction: Liquefaction is a phenomenon wherein cohesionless soils below the groundwater table
build up excess pore water pressures during earthquake loading. Liquefaction typically occurs in loose,
cohesionless soils, but may occur in denser soils if the ground shaking is sufficiently strong. The potential
hazardous impacts of liquefaction include liquefaction-induced settlement and lateral spreading. Soil
conditions observed in our explorations consisted of dense to very dense sands with variable silt/gravel
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contents. We did not encounter groundwater within our explorations. Based on the subsurface
conditions we encountered on the site, it is our opinion that the risk of liquefaction is low.
IBC Seismic Design Parameters: Based on site location and soil conditions, the values provided below are
recommended for seismic design. The values provided below are based on the 2015 IBC as the building
code reference document.
Site Preparation
Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments.
We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped
areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet
weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion,
whereas soil stockpiles should be protected with anchored plastic sheeting.
Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a
manner and sequence that will provide drainage at all times and provide proper control of erosion. The
site should be graded to prevent water from ponding in construction areas and/or flowing into and/or
over excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each
day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from
subgrades and work areas immediately and prior to performing further work in the area. Equipment
access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly
increased if drainage efforts are not accomplished in a timely manner.
Description Value
2015 IBC Site Classification 1 C
Ss Spectral Acceleration for a Short Period 1.430 g (Site Class B)
S1 Spectral Acceleration for a 1-Second Period 0.537 g (site Class B)
SMS Maximum considered spectral response
acceleration for a Short Period 1.430 g (Site Class C)
SM1 Maximum considered spectral response
acceleration for a 1-Second Period 0.699 g (Site Class C)
SDS Five-percent damped design spectral response
acceleration for a Short Period 0.953 g (Site Class C)
SD1 Five-percent damped design spectral response
acceleration for a 1-Second Period 0.466 g (Site Class C)
1. In general accordance with the 2015 International Building Code, Table 1613.5.2. IBC Site Class is based on
the average characteristics of the upper 100 feet of the subsurface profile. The borings completed for this
study extended to a maximum depth of 26½ feet below grade. ZGA therefore determined the Site Class
assuming that similar density soils extend to 100 feet as suggested by published geologic maps for the
project area.
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Clearing and Stripping: Once TESC measures are installed, we expect site preparation to continue with
clearing and grubbing brush and trees, and stripping of organic rich topsoil. We recommend all tree
stumps and roots larger than ½ inch in diameter be cleared and grubbed from the areas planned for
improvement. Based on our explorations, stripping depths to remove topsoil is estimated to be about 6
inches. Stripping depths may be greater near trees and brush to fully remove root systems. All clearing
and stripping debris should be wasted off site or, if approved, used for topsoil in landscape areas.
Subgrade Preparation: Once site preparation is complete, all areas that are at design subgrade elevation
or areas that will receive new structural fill should be moisture conditioned to a moisture content within
plus or minus two percent of optimum moisture content for compaction. The subgrade should then be
compacted to a firm and unyielding condition.
The existing near-surface site soils consist of loose to dense silty sand or sand with silt at or generally
somewhat above optimum moisture content for compaction. During wet weather, achieving a moisture
content adequate for compaction will be impossible. Therefore, we recommend subgrade preparation
and earthwork, in general, be completed during drier periods of the year when the soil moisture content
can be controlled by aeration and drying. If earthwork or construction activities take place during
extended periods of wet weather, or if the in situ moisture conditions are elevated above the optimum
moisture content, the soils will become unstable and not compactable. In the event the exposed subgrade
becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend
that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be
compacted to the minimum recommended levels. The severity of construction problems will be
dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils.
Once compacted, subgrades should be evaluated through density testing and proof rolling with a loaded
dump truck or heavy rubber-tired construction equipment weighing at least 20 tons to assess the
subgrade adequacy and to detect soft and/or yielding soils. In the event that compaction fails to meet
the specified criteria, the upper 12 inches of subgrade should be scarified and moisture conditioned as
necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D1557). Those soils
which are soft, yielding, or unable to be compacted to the specified criteria should be over-excavated and
replaced with suitable material as recommended in the Structural Fill section of this report. As an
alternate to subgrade compaction during wet site conditions or wet weather, the upper 12 inches of
subgrade should be overexcavated to a firm, non-yielding and undisturbed condition and backfilled with
compacted imported structural fill consisting of free-draining Gravel Borrow or crushed rock.
Freezing Conditions: If earthwork takes place during freezing conditions, exposed subgrades should be
allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively,
the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing
subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill
until allowed to thaw and adjusted to the proper moisture content, which may not be possible during
winter months.
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Structural Fill Materials, Placement, and Compaction
Structural fill includes any material placed below or adjacent to foundations, below concrete slabs, within
utility trenches, or other areas to support settlement-sensitive site improvements. Prior to the placement
of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site
Preparation section of this report.
Laboratory Testing: Representative samples of on-site and imported soils to be used as structural fill
should be submitted for laboratory testing at least 4 days in advance of its intended use in order to
complete the necessary Proctor tests.
Reuse of Site Soils as Structural Fill: We expect that the finished grade will stay very close to the existing
grade and therefore no substantial fill placement will be required. However, we expect the reuse of site
soils as structural fill will be desirable for underground utilities.
The suitability for reuse of site soils as structural fill depends on the composition and moisture content of
the soil. Soils encountered in excavations at the site are expected to consist of silty sand or sand with silt.
As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture
content. Soils containing more than about 5 percent fines cannot be consistently compacted to the
appropriate levels when the moisture content is more than approximately 2 percent above or below the
optimum moisture content (per ASTM D1557). Optimum moisture content is the moisture content which
results in the greatest compacted dry density with a specified compactive effort.
Laboratory testing of select soil samples indicates the in-place moisture content of site soils ranges from
about 4 to 12 percent. Based on the results of the modified proctor test, the optimum moisture content
of site soils is 8.3 percent. Therefore, site soils appear near the optimum moisture content for
compaction. Site soils should be suitable for structural fill during periods of dry weather with some slight
moisture conditioning. However, during wet weather, site soils will quickly become too wet for reuse as
structural fill. Therefore, we recommend earth work for the project be scheduled for the drier summer
months.
Imported Structural Fill: The appropriate type of imported structural fill will depend on weather
conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet
the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2016 Washington State
Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction
(WSDOT Standard Specifications). During wet weather and/or wet site conditions, higher-quality
structural fill might be required, as Common Borrow may contain sufficient fines to be moisture-sensitive.
During wet conditions, we recommend that imported structural fill consist of a “clean”, free-draining pit-
run sand and gravel. Such material should generally contain less than 5 percent fines, based on that soil
fraction passing the U.S. No. 4 sieve, and not contain discrete particles greater than 3 inches in maximum
dimension. Alternatively, Crushed Surfacing Base Course or Gravel Borrow conforming to Sections 9-
03.9(3) and 9-03.14(1), respectively, of the WSDOT Standard Specifications could be used during wet
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weather. It should be noted that the placement of structural fill is, in many cases, is weather-dependent.
Delays due to inclement weather are common, even when using select granular fill. We recommend that
site grading and earthwork be scheduled for the drier months, if possible.
Fill Placement and Compaction: Structural fill should be placed in horizontal lifts of a thickness adequate
for adequate compaction throughout the entire lift thickness with the compaction equipment used.
Typically, the maximum loose lift thickness that can be adequately compacted with typical compaction
equipment is 12 inches. However, in cases where large vibratory rollers and imported fill with less than
5% fines are used, the lift thickness can be increased. Increasing the loose lift thickness beyond 12 inches
should be based on field performance testing during construction prior to placement of production fills.
Thinner lifts may be necessary, depending on the size and weight of the compaction equipment. Each lift
of fill should be compacted to the minimum levels recommended in the table below based on the
maximum laboratory dry density as determined by the ASTM D 1557 Modified Proctor Compaction Test.
Structural fill placed in municipal rights-of-way should be placed and compacted in accordance with the
jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading
so that an adequate number of density tests may be conducted as structural fill placement occurs. In this
way, the adequacy of the earthwork may be evaluated as it proceeds.
Recommended Soil Compaction Levels
Location Minimum Percent Compaction*
Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95
All fill below building floor slabs and foundations 95
Upper two feet of fill below pavement finished grade 95
Pavement fill below two feet from finished grade 92
Utility trench backfill greater than two feet from finished grade 92
Upper two feet of trench backfill from finished grade 95
Landscape Areas 90
* ASTM D 1557 Modified Proctor Maximum Dry Density
Utility Trenching and Backfilling
We recommend that utility trenching conform to all applicable federal, state, and local regulations, such
as OSHA and WISHA, for open excavations. Trench excavation safety guidelines are presented in WAC
Chapter 296-155 and WISHA RCW Chapter 49.17.
Utility Subgrade Preparation: We recommend that all utility subgrades be firm and unyielding and free of
soils that are loose, disturbed, or pumping. Soils that pump or yield should be removed and replaced. All
structural fill used to replace over-excavated soils should be compacted as recommended in the Structural
Fill section of this report.
Bedding and Initial Backfill: We recommend that a minimum of 4 inches of bedding material be placed
below and at least 12 inches above all utilities or in general accordance with the utility manufacturer’s
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recommendations and local ordinances. We recommend the bedding consist of granular material free
from particles greater than 3 inches. All trenches should be wide enough to allow for compaction around
the haunches of the pipe, or material such as pea gravel should be used below the spring line of the pipes
to eliminate the need for mechanical compaction in this portion of the trenches. If water is encountered
in the excavations, it should be removed prior to fill placement.
Trench Backfill: Materials, placement and compaction of utility trench backfill should be in accordance
with the recommendations presented in the Structural Fill section of this report. In our opinion, the initial
lift thickness should not exceed 1 foot unless recommended by the manufacturer to protect utilities from
damage by compacting equipment. Light, hand operated compaction equipment may be utilized directly
above utilities if damage resulting from heavier compaction equipment is of concern.
Construction Dewatering
Groundwater was not encountered in our explorations. If groundwater is encountered during
construction, some form of temporary dewatering may be required. Conventional dewatering methods,
such as pumping from sump pits, should likely be adequate for temporary removal of groundwater
encountered during shallow excavation at the site. Construction dewatering systems should be designed,
maintained, and permitted by the contractor.
Shallow Foundation Recommendations
We recommend the building foundations be supported on the medium dense to very dense soils
encountered in our explorations at a depth of 2.5 to 4 feet below existing site grades. Based on the results
of our explorations, some loose, undocumented fill may be encountered at footing subgrade elevations.
As such, some over-excavation and replacement of loose, undocumented fill with structural fill may be
required. The need for over-excavation and replacement of loose, undocumented fill should be evaluated
by a representative from Zipper Geo Associates during construction. Where over-excavation is required,
the width of the over-excavation beyond footing edges should be equal to the required over-excavation
depth. For example, if the footing width is 12 inches and an over-excavation depth of two feet is required,
the total width of the over-excavation should be five feet. As an alternative, the width of over-excavations
can be limited to the footing width provided the over-excavation is backfilled with controlled density fill
or lean mix concrete having a minimum 28 day compressive strength of 100 psi. Over-excavation and
replacement with structural fill shall be in accordance with the recommendations provided in the
Structural Fill Materials, Placement and Compaction section of this report. Recommendations for shallow
spread footings are provided below.
Subgrade Preparation: Where loose, undocumented fill is not encountered at footing subgrade elevation,
we recommend that the subgrade exposed at the bottom of foundation excavations be compacted to a
firm and non-yielding condition and to at least 95 percent of the modified Proctor maximum dry density
determined in accordance with ASTM D 1557. If the exposed subgrade cannot be compacted to the
required density, we recommend that it be removed to an adequate depth as recommended by a
representative from ZGA and replaced with compacted structural fill placed in accordance with this report.
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Allowable Bearing Pressure: Continuous and isolated column footings bearing on subgrades prepared as
recommended above may be designed for a maximum allowable, net, bearing pressure of 3,000 psf if
supported as recommended in this report. A one-third increase of the bearing pressure may be used for
short-term transient loads such as wind and seismic forces.
Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear
at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings
should bear at least 12 inches below the surrounding slab surface level. We recommend that all
continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively.
Lateral Resistance: Resistance to lateral loads can be calculated assuming a ultimate passive resistance of
405 pcf equivalent fluid pressure (triangular distribution) for footings backfilled with structural fill as
recommended in this report. We recommend an ultimate base friction coefficient of 0.50. If allowable
stress design is used, we recommend a minimum safety factor of 1.5 be used for lateral resistance
calculations. We recommend that passive resistance be neglected in the upper 18 inches of embedment.
Estimated Settlement: Assuming the foundation subgrade soils and structural fill compaction are
completed in accordance with recommendations presented herein, we estimate that total static footing
settlements will be 1 inch or less. We estimate that differential footing settlement will be ½ inch or less
in 40 feet.
Subsurface Drainage: Although no groundwater was encountered in our explorations, as a precautionary
measure, we recommend a perimeter footing drain be installed around the building to collect surface
water infiltration if impermeable hard surfacing, such as asphalt pavement, is not extended to the
foundation walls of the building. The perimeter footing drain should consist of a 4-inch-diameter
perforated pipe within an envelope of pea gravel or washed rock, extending at least 6 inches on all sides
of the pipe. The gravel envelope should be wrapped with filter fabric (such as Mirafi 140N) to reduce the
migration of fines from the surrounding soil. The invert of the footing drain should be placed no higher
than the bottom of the footing. The perforations should be placed down. The perimeter foundation drain
with cleanouts should not be connected to roof downspout drains and should be constructed to discharge
into the site storm water system or other appropriate outlet.
On-Grade Concrete Slabs
Subgrade Preparation: Subgrades for on-grade slabs should be prepared in accordance with the Site
Preparation and Structural Fill sections of this report.
Slab Base: To provide a uniform slab bearing surface, capillary break, and even working surface, we
recommend that on-grade slabs be underlain by a 6-inch thick layer of clean, compacted crushed rock
meeting the requirements of Crushed Surfacing Top Course as specified in Section 9-03.9(3) of the WSDOT
Standard Specifications with the modification that a maximum of 7.5 percent of the material passes the
U.S. No 200 sieve.
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Vapor Barrier: From a geotechnical perspective, a vapor barrier is not considered necessary beneath the
slab on grade floor unless moisture sensitive floor coverings and/or adhesives are used. If a vapor barrier
is used, we recommend using a 10-mil (minimum), puncture-resistant proprietary product such as Stego
Wrap, or an approved equivalent that is classified as a Class A vapor retarder in accordance with ASTM E
1745. Overlap lengths and the appropriate tape used to seal the laps should be in accordance the vapor
retarder manufacturer’s recommendations. When conditions warrant the use of a vapor retarder, the
slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions
regarding the use and placement of a vapor retarder/barrier.
Permanent Drainage Considerations
Surface Drainage: Final site grades should be sloped to carry surface water away from buildings and other
drainage-sensitive areas. Additionally, site grades should be designed such that concentrated runoff on
softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected
at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents
erosion.
Retaining Wall
Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the
nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth
loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at
least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding
walls (i.e. walls that are not free to translate or rotate) should be designed for at-rest earth pressures.
Non-yielding walls include walls that are braced to another wall or structure, and wall corners.
Assuming that walls are backfilled and drained as described in the following paragraphs, we recommend
that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf
(active earth pressure). Non-yielding walls should be designed using an equivalent fluid density of 50 pcf
(at-rest earth pressure).
Surcharge pressures due to sloping backfill, adjacent footings, vehicles, construction equipment, etc. must
be added to these lateral earth pressure values. For traffic loads, we recommend using an equivalent
two-foot soil surcharge of about 250 psf.
For yielding and non-yielding walls with level backfill conditions, we recommend that a uniformly
distributed seismic pressure of 7H psf for the active case and 12H psf for the at-rest case, where H is the
height of the wall, be applied to the walls.
The above equivalent fluid pressures are based on the assumption of no buildup of hydrostatic pressure
behind the wall. If groundwater is allowed to saturate the backfill soils, hydrostatic pressures will act
against a retaining wall; however, if the recommended drainage system is included with each retaining
wall, we do not expect that hydrostatic pressures will develop.
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Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade
walls. All backfilled walls should include a drainage aggregate zone extending a minimum of two feet from
the back of wall for the full height of the wall and wide enough at the base of the wall to allow seepage
to flow to the footing drain. The drainage aggregate should consist of material meeting the requirements
of WSDOT 9-03.12(2), Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe
should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate
discharge point. We recommend placing a non-woven geotextile, such as Mirafi 140N, or equivalent,
around the free draining backfill material.
Stormwater Infiltration Feasibility
With respect to stormwater infiltration, the City of Renton adopts the 2016 King County Surface Water
Design Manual (KCSWDM) with amendments. Based on our review of the 2016 KCSWDM, the applicant
must demonstrate, through the opinion of a geotechnical professional, that sufficient permeable soil
exists to allow construction of a properly functioning infiltration facility. Our explorations encountered
glacial till at a depth of about 3 to 5 feet below existing site grade. For purposes of stormwater infiltration,
glacial till (or hardpan) is generally considered a hydraulically restrictive layer, or essentially impermeable
for purposes of stormwater infiltration. As such, it is our opinion that sufficient permeable soils do not
exist at the site and therefore stormwater infiltration is not feasible, in our opinion.
Pavements
Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance-
free. The following pavement sections represent our minimum recommendations for an average level of
performance during a 20-year design life; therefore, an average level of maintenance will likely be
required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years.
Thicker asphalt, base, and subbase courses would offer better ling-term performance, but would cost
more initially. Conversely, thinner courses would be more susceptible to “alligator” cracking and other
failure modes. As such, pavement design can be considered a compromise between a high initial cost and
low maintenance costs versus a low initial cost and higher maintenance costs. The recommendations
presented below are based on AASHTO Low-Volume Road Design methodologies as presented in the 1993
AASHTO Guide for Design of Pavement Structures.
Traffic and Reliability: Our design assumes 100,000, 18-kip equivalent single axle loads over the life of the
pavement along the main access roads and a 75% reliability.
Soil Design Values: Pavement subgrade soils are anticipated to consist of the medium stiff silt deposit we
encountered in our explorations. Our analysis assumes a minimum California Bearing Ration (CBR) value
of 10 is appropriate for this material.
Recommended Pavement Sections: For light duty pavements (parking stalls), we recommend 2 inches of
asphalt concrete over 4 inches of crushed rock base course. For heavy duty pavements (main access
roads, truck delivery routes, etc.), we recommend 3 inches of asphalt concrete over 6 inches of crushed
Harrington Ave Apartments
ZGA Project No. 2072.01
May 15, 2019
Page 13
rock base course. A thicker asphalt section or concrete pavements should be considered in front of
dumpster enclosures.
Materials and Construction: We recommend the following regarding asphalt pavement materials and
pavement construction.
• Subgrade Preparation: Upper 24 inches of pavement subgrade should be prepared in accordance
with the recommendations presented in the Subgrade Preparation section of this report.
• Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG
58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the WSDOT Standard
Specifications. We also recommend that the gradation of the asphalt aggregate conform to the
aggregate gradation control points for ½-inch mixes as presented in Section 9-03.8(6), HMA
Proportions of Materials.
• Base Course: We recommend that the crushed aggregate base course conform to Section
9-03.9(3) of the WSDOT Standard Specifications.
• Compaction: All base material should be compacted to at least 95 percent of the maximum dry
density determined in accordance with ASTM D1557. We recommend that asphalt be compacted
to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall
(Maximum laboratory) density.
We recommend that a Portland cement concrete pavement (CCP) be utilized in entrance and exit sections,
dumpster pads, loading dock areas, drive-thru areas or other areas where extensive wheel maneuvering
or repeated loading are expected. The dumpster pad should be large enough to support the wheels of
the truck which will bear the load of the dumpster. We recommend a minimum of 6 inches of CCP
underlain by 4 inches of crushed aggregate base. Although not required for structural support, the base
course layer is recommended to help reduce potentials for slab curl, shrinkage cracking, and subgrade
“pumping” through joints. Proper joint spacing will also be required to prevent excessive slab curling and
shrinkage cracking. All joints should be sealed to prevent entry of foreign material and dowelled where
necessary for load transfer.
Portland cement concrete should be designed with proper air-entrainment and have a minimum
compressive strength of 4,000 psi after 28 days of laboratory curing. Adequate reinforcement and
number of longitudinal and transverse control joints should be placed in the rigid pavement in accordance
with ACI requirements. The joints should be sealed as soon as possible (in accordance with sealant
manufacturer’s instructions) to minimize water infiltration into the soil.
Harrington Ave Apartments
ZGA Project No. 2072.01
May 15, 2019
Page 14
CLOSURE
The analysis and recommendations presented in this report are based, in part, on the explorations
completed for this study. The number, location, and depth of the explorations for the current phase of
the project were completed within the constraints of budget and site access so as to yield the information
to formulate our recommendations. Project plans were not available at the time this report was prepared.
We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans
and specifications when they become available in order to assess that the recommendations and design
considerations presented in this report have been properly interpreted and implemented into the project
design.
The performance of shallow foundations and slabs on grade depend greatly on proper site preparation
and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide
geotechnical engineering services during the site preparation and foundation construction phases of the
project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer
could provide additional geotechnical recommendations to the contractor and design team in a timely
manner as the project construction progresses.
This report has been prepared for the exclusive use of Renton Housing Authority, and its agents, for
specific application to the project discussed and has been prepared in accordance with generally accepted
geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety,
excavation support, and dewatering requirements are the responsibility of others. In the event that
changes in the nature, design, or location of the project as outlined in this report are planned, the
conclusions and recommendations contained in this report shall not be considered valid unless Zipper
Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in
writing.
B-4GLENNWOOD AVE NE
HARRINGTON AVE NENE 10TH STB-1B-2B-3B-5FIGUREJob No.Zipper Geo Associates, LLC19019 36th Ave. W.,Suite ELynnwood, WASHT. of11SITE AND EXPLORATION PLAN2072.01SEPTEMBER 20181HARRINTON APARTMENTSNE 10TH ST AND HARRINGTON AVE NERENTON, WASHINGTONAPPROXIMATE SCALE IN FEET0808040LEGENDB-1BORING NUMBER ANDAPPROXIMATE LOCATIONAPPROXIMATE PROPERTY LINEREFERENCE: GOOGLE MAPS 2018.
APPENDIX A
SUBSURFACE EXPLORATION PROCEDURES AND LOGS
APPENDIX A
SUBSURFACE EXPLORATION PROCEDURES AND LOGS
Field Exploration Description
Our field exploration for this project included advancing five borings across the proposed site of the
project on September 12, 2018. The approximate locations of the explorations are presented on Figure
1, the Site and Exploration Plan. Exploration locations were determined in the field based on hand
measurements from existing site features. As such, the exploration locations should be considered
accurate only to the degree implied by the measurement method. Descriptive logs of the borings are
enclosed in this appendix. A current topographic survey of the site was not available at the time of this
report. Therefore, ground surface elevations of the explorations were not determined.
The borings were advanced using a truck-mounted drill rig operated by an independent drilling company
(Holocene Drilling Inc.) working under subcontract to ZGA. The borings were advanced using the hollow-
stem auger drilling method. An engineer from our firm continuously observed the borings, logged the
subsurface conditions encountered, and obtained representative soil samples. All samples were stored
in moisture-tight containers and transported to our laboratory for further evaluation and testing. Samples
were obtained by means of the Standard Penetration Test at 2.5- to 5-foot intervals throughout the drilling
operation.
The Standard Penetration Test (ASTM D 1586) procedure consists of driving a standard 2-inch outside
diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches.
The number of blows required to drive the sampler through each 6-inch interval is recorded, and the total
number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or
“blow count” (N value). If a total of 50 blows is struck within any 6-inch interval, the driving is stopped
and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard
Penetration Resistance values indicate the relative density of granular soils and the relative consistency
of cohesive soils.
The enclosed boring logs describe the vertical sequence of soils and materials encountered in the borings,
based primarily upon our field classifications. Where a soil contact was observed to be gradational, our
log indicates the average contact depth. Where a soil type changed between sample intervals, we inferred
the contact depth. Our logs also graphically indicate the blow count, sample type, sample number, and
approximate depth of each soil sample obtained from the borings. If groundwater was encountered, the
approximate groundwater depth, and date of observation, are depicted on the logs.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-1
Page 1 of 2
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-1
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 18
S-2 18
S-3 0
S-4 8
S-5 18
S-6 18
47
30
20
20
76
72
GSA
MC
MC
5 inches of organics
Dense, damp, light brown, Silty SAND, with gravel
(Possible fill)
Medium dense, moist, brown, SAND, with silt, trace gravel
No Recovery
Medium dense, moist, brown-gray, SAND, with silt, some
gravel, slight mottling (Weathered Glacial Till)
Grades to very dense
Very dense, moist, tan, SAND, some silt (Glacial till)
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
25
30
35
40
45
50
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-1
Page 2 of 2
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-1
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-7 18 65 GSA
Very dense, moist, gray, SAND, with silt, some gravel
(Glacial till)
Boring terminated at approximately 26 1/2 feet.
No groundwater observed during exploration.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-2
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-2
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 inches
Auto
SNM
11/2/120 602040
S-1 12
S-2 12
S-3 16
S-4 18
S-5 11
49
60
63
73
50/5
MC
MC
MC
MC
6 inches of organics
Dense, damp, brown, Silty SAND, with gravel slight
mottling (Possible fill)
Dense, damp, gray, SAND, with silt and gravel (Weathered
Glacial Till)
Very dense, moist, gray, SAND, with silt, trace gravel
(Glacial Till)
Very dense, moist, gray, SAND, with silt, some gravel,
slight mottling (Glacial till)
Boring terminated at approximately 16 ft.
No groundwater observed during time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-3
Page 1 of 1
GROUNDWATER LEGEND
Harrington Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-3
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 0
S-2 6
S-3 18
S-4 9
S-5 11
S-6 10
50/2
23
74
50/3
50/5
50/4
GSA
MC
MC
4 inches of organics
Light brown, silty SAND, some gravel (Possible fill)
No recovery (Blow counts overstated)
Medium dense, moist, gray-tan, SAND, with silt, some
gravel (Weathered glacial till)
Very dense, moist, gray, silty SAND, some gravel (Glacial
till)
Grades to with silt and gravel
Grades to trace gravel
Grades to some silt and gravel
Boring terminated at approximately 21 ft. No groundwater
observed at the time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-4
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-4
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 inches
Auto
SNM
11/2/120 602040
S-1 6
S-2 18
S-3 12
S-4 0
S-5 8
S-6 4
7
26
50/6
50/3
50/2
50/3
GSA
MC
MC
2 inches of organics
Loose, damp, orange-brown, Gravelly SAND, with silt,
trace organics (Possible fill)
Medium dense, moist, gray, SAND, with silt, some gravel
(Weathered glacial till
Very dense, moist, gray-brown, SAND, with silt and gravel
(Glacial till)
No recovery (Blow counts overstated)
Grades to gray, some gravel
Grades to with gravel, some silt
Boring terminated at approximately 20 1/2 feet.
No groundwater observed at the time of drilling.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
0
5
10
15
20
25
SAMPLE LEGEND % Fines (<0.075 mm)
2-inch O.D. Split spoon Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube Bentonite Plastic Limit Liquid Limit
Grout/Concrete Natural Water Content
Screened Casing
Blank Casing
GSA = Grain Size Analysis Date:Project No.:
200W = 200 Wash Analysis
Cons. = Consolidation Test
Att. = Atterberg Limits
NE 10th St & Harrington Ave NE
TESTING KEY Groundwater level at time of
drilling (ATD) or on date of
measurement.
Renton, WA
Sep-18 2072.01
19019 36th Ave. W, Suite E
Lynnwood, WA
BORING
LOG:B-5
Page 1 of 1
GROUNDWATER LEGEND
Harrington Ave Apartments
The stratification lines represent the approximate
boundaries between soil types. The transition may be
gradual. Refer to report text and appendices for additional
information.
Boring Location:
B-5
Date Drilled:Depth (ft)SOIL DESCRIPTION
Sample Number SAMPLES Recovery (Inches)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsSoil TestingSee Site and Exploration Plan
N/A
September 12, 2018
Holocene
H.S.A.
D90 Truck Rig
8 in.
Auto
SNM
11/2/120 602040
S-1 9
S-2 10
S-3 9
S-4 6
S-5 14
S-6 6
32
25
50/3
50/6
50/6
50/6
MC
MC
MC
MC
6 inches of organics
Dense, moist, tan, SAND, with silt, some gravel (Possible
fill)
Medium dense, moist, gray, SAND, with silt, some gravel
(Weathered glacial till)
Very dense, moist, gray, SAND, with silt, trace gravel
(Glacial till)
Grades to some gravel
Grades to some silt
Boring terminated at approximately 20 1/2 feet. No
groundwater observed at the time of drilling.
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
A series of laboratory tests were performed by ZGA during the course of this study to evaluate the index
and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests
performed are given below.
Visual Classification
Samples recovered from the exploration locations were visually classified in the field during the
exploration program. Representative portions of the samples were carefully packaged in moisture tight
containers and transported to our laboratory where the field classifications were verified or modified as
required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil
classification includes evaluation of color, relative moisture content, soil type based upon grain size, and
accessory soil types included in the sample. Soil classifications are presented on the exploration logs in
Appendix A.
Moisture Content Determinations
Moisture content determinations were performed on representative samples obtained from the
explorations to aid in identification and correlation of soil types. The determinations were made in
general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented
on the exploration logs in Appendix A.
Grain Size Distributions
A grain size analysis determines the range in diameter of soil particles included in a particular sample.
Grain size analyses were performed on representative samples in general accordance with ASTM D 422.
The results of the grain size determinations for the samples were used in classification of the soils, and
are presented in this appendix.
Modified Proctor
A modified proctor test determines the maximum dry density and optimum moisture to obtain a
maximum density under a certain compaction effort. The modified proctor test was performed on
representative samples in general accordance with ASTM D1557. The results of the modified proctor test
are presented in Appendix B.
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartment
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-1 2 1/2-4 9.3 Silty SAND, with
gravelS-1 30.5
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-1 25-26 1/2 8.3 SAND, with silt,
some gravelS-7 12.7
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-3 5-6 1/2 7.3 SAND, with silt,
some gravelS-2 27.6
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
0
10
20
30
40
50
60
70
80
90
100
0.0010.0100.1001.00010.000100.0001000.000PERCENT FINER BY WEIGHTPARTICLE SIZE IN MILLIMETERS
GRAIN SIZE ANALYSIS
Comments:
36"12"6"3"1 1/2"3/4"3/8"4 10 20 40 60 140 200
Coarse Medium Fine Silt ClayFineCoarse
COBBLESBOULDERS GRAVEL SAND FINE GRAINED
SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER
Project No.:PROJECT NAME:
Harrington Ave
Apartments
DATE OF TESTING:
Exploration Sample Depth (feet) Moisture (%)Fines (%) Description
B-4 2 1/2-4 9.1 Gravelly SAND,
with siltS-1 19.3
2072.01
9/13/2018
ASTM D 422Test Results Summary
Zipper Geo Associates, LLC
Geotechnical and Environmental Consultants
90
95
100
105
110
115
120
125
130
135
140
145
150
0 5 10 15 20 25 30 35 40 45Dry Unit Weight (pcf)Moisture Content (%)
LABORATORY
COMPACTION
CURVE
Compaction Size
Test Standard Mold
Harrington Ave Apartments
Job No.
Job Name
Date Tested
Sample No.
Location
Test Results
Zipper Geo Associates, LLC 19023 36th Avenue West, Suite D Lynnwood, Washington 98036 (425) 582-9928
Test No.Field Moist.2 3 4
Dry Density (lbs/cu.ft.)132.9 129.4 130.4 #DIV/0!
Moisture Content (%)9.3 10.1 6.5 #DIV/0!
1557-B 4-inch
2.80
2.70
2.60
2.50
2.40
Zero Air Voids Curves For
Various Specific Gravities
2072.01
Depth / Elevation9/14/2018
09122018
Cuttings 5-7 1/2 ft
134.0 136.2
8.38.3
Maximum Dry Density / Oversize Corrected (pcf)
Opt. Moisture Content / Oversize Corrected (%)
Sample Description:
Comments:
Oversize Fraction (%) / Sieve Used 3/49