HomeMy WebLinkAboutSWP272071(3) 1
TECHNICAL INFORMATION REPORT
on
FLOODPLAIN/STORMWATER
t
for
Customer Services
Training Center
Site Development,
Support Facilities and SW 16th Street
' Renton, Washington
October 1992
1 Sverdrup
C 0 R P 0 R A T 1 0 N
' 3300 Carillon Point
Kirkland, Washington 9BOB3-9762
(206) 6 2-3300
1
I
1
1
1
1TECHNICAL INFORMATIONREPORT
on the
1FLOODPLAIN/STORMWATER SYSTEM
1
for
1 Customer Services
Training Center
Site Development,
1 Support Facilities and SW 16th Street
Renton, Washington
J1D BE
October 1992 I 'S6
�`sS�ONAL
1 Sverdrup EXPIRES 2J12/92
C O R P O R A T I O N
3300 Carillon Point
Kirkland, Washington 98083-9762
(206) 822-3300
1
' CUSTOMER SERVICES TRAINING CENTER SITE DEVELOPMENT
CONTRACT NO. 90-8002-AC
TECHNICAL INFORMATION REPORT
ON THE FLOODPLAIN/STORM WATER SYSTEM
Prepared For:
BOEING SUPPORT SERVICES
' SEATTLE, WASHINGTON
' Prepared By:
SVERDRUP CORPORATION
' KIRKLAND, WASHINGTON
OCTOBER, 1992
i CUSTOMER SERVICES TRAINING CENTER SITE DEVELOPMENT
INCLUDING THE SUPPORT FACILITIES SITE AND
IMPROVEMENTS TO SW 16TH STREET
TECHNICAL INFORMATION REPORT
ON THE FLOODPLAIN/STORM WATER SYSTEM
TABLE OF CONTENTS
Page
' I. CUSTOMER SERVICES TRAINING CENTER (CSTC) 1
PROJECT OVERVIEW
' II. PRELIMINARY CONDITIONS SUMMARY 5
' III. OFF-SITE ANALYSIS 10
' A. Green River
B. Springbrook Creek
C. Black River
D. Previous Studies
IV. RETENTION/DETENTION ANALYSIS AND DESIGN 15
' A. Pre-Development Conditions
B. Post-Development Conditions
' V. CONVEYANCE SYSTEMS ANALYSIS AND DESIGN 22
' A. Proposed Conveyance System Overview
B. Conveyance System Analysis and Design
' VI. SPECIAL REPORTS AND STUDIES 28
' A. Dr. R.R. Horner Oil/Water Separator Study
B. Peter Walker & Partners Delta Design
' ii
TABLE OF CONTENTS (Cont'd)
Page
VII. BASIN AND COMMUNITY PLANNING AREAS 30
A. Tukwila Storm Drain
VIII. OTHER PERMITS 33
IX. FLOODPLAIN AND GROUNDWATER CONCERNS 34
' A. EXISTING FLOODPLAIN
B. PROPOSED FLOODPLAIN
' C. GROUND WATER INFLUENCE
X. TEMPORARY SEDIMENTATION/EROSION CONTROL DESIGN 36
A. Sedimentation/Erosion Control Plan Initial Implementation
' B. Sedimentation/Erosion Control Plan for Construction
XI. RETENTION/DETENTION FACILITY SUMMARY SHEET 40
' XII. MAINTENANCE AND OPERATIONS MANUAL 42
' A. Construction Equipment Maintenance
B. Incident Control and Reporting During Construction Activities
' C. Best Management Practices During Construction Activities
D. Employee Training for Construction Contractors
' E. Proposed Measures to Control Pollutants in Storm Water
Discharges After Construction
F. Incident Control and Reporting After Construction
' G. Description of Applicable State and Local Water
Management Controls
H. Employee Training
I. Best Management Practice
' iii
iLIST OF FIGURES
' FIGURE 1 TIR WORKSHEET
FIGURE 2 TIR WORKSHEET PAGE 2
FIGURE 3 LOCATION MAP
' FIGURE 4 VICINITY MAP
FIGURE 5 PRE-DEVELOPMENT BASIN PLAN
FIGURE 6 POST-DEVELOPMENT BASIN PLAN
' FIGURE 7 SW 16TH STREET DRAINAGE PLAN
FIGURE 8 FLOODPLAIN MAPPING (FROM CONTOUR INFORMATION
PROVIDED BY W&H PACIFIC)
' FIGURE 9 FEMA FLOODPLAIN MAPPING
FIGURE 10 GEOTECHNICAL REPORT
FIGURE 11 BASIN 1 PRE-DEVELOPMENT RUNOFF COEFFICIENTS
' FIGURE 12 BASIN 2 PRE-DEVELOPMENT RUNOFF COEFFICIENTS
FIGURE 13 BASIN 3 PRE-DEVELOPMENT RUNOFF COEFFICIENTS
' FIGURE 14 BASIN A POST-DEVELOPMENT RUNOFF COEFFICIENTS
FIGURE 15 BASIN B POST-DEVELOPMENT RUNOFF COEFFICIENTS
FIGURE 16 BASIN C POST-DEVELOPMENT RUNOFF COEFFICIENTS
' FIGURE 17 SW 16TH STREET PRE-DEVELOPMENT STA 34+85 to
STA 18+00
FIGURE 18 SW 16TH STREET POST-DEVELOPMENT STA 34+85 to
STA 18+00
FIGURE 19 BASIN 1 PRE-DEVELOPMENT PEAK FLOWS & SW 16TH
STREET PEAK FLOWS
FIGURE 20 48-INCH DIAMETER TUKWILA STORM DRAIN CAPACITY
FIGURE 21 PRE-AND POST DEVELOPMENT STORAGE AND
DISCHARGE
CONDITIONS
FIGURE 22 COMPARISON OF EXISTING VERSUS POST-
DEVELOPMENT CONDITIONS
' FIGURE 23 DISCHARGE VS. RECURRENCE EVENT FOR PRE-AND
POST-DEVELOPMENT
FIGURE 24 OUTFLOW VS. STAGE FOR PRE- AND POST-DEVELOPMENT
SITE
FIGURE 25 STAGE VS. STORAGE CURVES FOR PRE- AND POST-
DEVELOPMENT
FIGURE 26 CAPACITY OF PRE- AND POST-DEVELOPMENT
FLOODPLAIN SILLS VS. STAGE
FIGURE 27 SPRINGBROOK CREEK SITE WATER QUALITY DATA
FIGURE 28 SITE NO. 3 WATER QUALITY DATA
' iv
1
1 LIST OF FIGURES (Cont'd)
1 FIGURE 29 PUMP HOUSE AND SITE NO. 6 SITE WATER QUALITY DATA
FIGURE 30 STORM EVENT WATER QUALITY DATA
FIGURE 31 DR. HORNER REVIEW - BASIN C, FEBRUARY 29, 1992
1 FIGURE 32 DR. HORNER REVIEW - BASIN B & SW 16TH ST,
MARCH 12, 1992
FIGURE 33 DR. HORNER REVIEW - BASIN B & SW 16TH ST,
1 APRIL 1, 1992
i
1
1
1
1
i
1
1
i
1
1
i
1
1
DRAWINGS AND SCHEDULES
(Bound Separately)
CSTC SITE DEVELOPMENT
STORM DRAINAGE - SITE PLAN
' STORM DRAINAGE PLAN - GRID 7
STORM DRAINAGE PLAN - GRID 8
STORM DRAINAGE PLAN - GRID 9
' STORM DRAINAGE PLAN - GRID 12
STORM DRAINAGE PLAN - GRID 13
STORM DRAINAGE PLAN - GRID 14
' STORM DRAINAGE PLAN - GRID 15
STORM DRAINAGE PLAN - GRID 17
STORM DRAINAGE PLAN - GRID 18
STORM DRAINAGE PLAN - GRID 19
STORM DRAINAGE PLAN - GRID 20
' STORM DRAINAGE PLAN - GRID 120
STORM DRAINAGE PLAN - GRID 22
STORM DRAINAGE PLAN - GRID 23
' STORM DRAINAGE PLAN - GRID 24
STORM DRAINAGE PLAN - GRID 25
STORM DRAINAGE PLAN - GRID 125
STORM DRAINAGE DETAILS - SHEET 1
STORM DRAINAGE DETAILS - SHEET 2
STORM DRAINAGE DETAILS - SHEET 3
STORM DRAINAGE DETAILS - SHEET 4
STORM DRAINAGE DETAILS - SHEET 5
' STORM DRAINAGE DETAILS - SHEET 6
STORM DRAINAGE DETAILS - SHEET 7
STORM DRAINAGE DETAILS - SHEET 8
' STORM DRAINAGE DETAILS - SHEET 9
STORM DRAINAGE DETAILS - STRUCTURAL
iEROSION/SEDIMENTATION CONTROL - SITE PLAN
EROSION/SEDIMENTATION CONTROL - GRID 2
' EROSION/SEDIMENTATION CONTROL - GRID 3
EROSION/SEDIMENTATION CONTROL - GRID 4
EROSION/SEDIMENTATION CONTROL - GRID 7
EROSION/SEDIMENTATION CONTROL - GRID 8
EROSION/SEDIMENTATION CONTROL - GRID 9
EROSION/SEDIMENTATION CONTROL - GRID 12
' EROSION/SEDIMENTATION CONTROL - GRID 13
EROSION/SEDIMENTATION CONTROL - GRID 14
EROSION/SEDIMENTATION CONTROL - GRID 15
' vi
iDRAWINGS AND SCHEDULES (Cont'd)
(Bound Separately)
' EROSION/SEDIMENTATION CONTROL - GRID 17
EROSION/SEDIMENTATION CONTROL - GRID 18
EROSION/SEDIMENTATION CONTROL - GRID 19
EROSION/SEDIMENTATION CONTROL - GRID 20
EROSION/SEDIMENTATION CONTROL - GRID 120
' EROSION/SEDIMENTATION CONTROL - GRID 22
EROSION/SEDIMENTATION CONTROL - GRID 23
EROSION/SEDIMENTATION CONTROL - GRID 24
EROSION/SEDIMENTATION CONTROL - GRID 25
EROSION/SEDIMENTATION CONTROL - GRID 125
' EROSION/SEDIMENTATION CONTROL - DETAILS SHEET 1
EROSION/SEDIMENTATION CONTROL - DETAILS SHEET 2
EROSION/SEDIMENTATION CONTROL - DETAILS SHEET 3
EROSION/SEDIMENTATION CONTROL - DETAILS SHEET 4
EROSION/SEDIMENTATION CONTROL - DETAILS SHEET 5
EROSION/SEDIMENTATION CONTROL - TEMPORARY CONNECTIONS 1
' CSTC SUPPORT FACILITIES
STORM DRAINAGE PLANS - SECTOR A
STORM DRAINAGE PLANS - SECTOR B
' STORM DRAINAGE DETAILS - SHEET 1
STORM DRAINAGE DETAILS - SHEET 2
STORM DRAINAGE DETAILS - SHEET 3
' STORM DRAINAGE DETAILS - SHEET 4
SW 16TH STREET
TUKWILA STORMDRAIN:
' 48" DIAMETER STORM DRAIN PLAN AND PROFILE - 1
48" DIAMETER STORM DRAIN PLAN AND PROFILE - 2
48" DIAMETER STORM DRAIN PLAN AND PROFILE - 3
48" DIAMETER STORM DRAIN PLAN AND PROFILE - 4
48" DIAMETER STORM DRAIN PLAN AND PROFILE - 5
' ROADWAY DRAINAGE PLAN AND PROFILE - 1
ROADWAY DRAINAGE PLAN AND PROFILE - 2
ROADWAY DRAINAGE PLAN AND PROFILE - 3
' ROADWAY DRAINAGE PLAN AND PROFILE - 4
ROADWAY DRAINAGE PLAN AND PROFILE - 5
i
' vii
DRAWINGS AND SCHEDULES (Cont'd)
(Bound Separately)
' DRAINAGE DETAILS - SHEET 1
DRAINAGE DETAILS - SHEET 2
DRAINAGE DETAILS - SHEET 3
APPENDICES
' (Bound Separately)
' APPENDIX A TECHNICAL REPORT NO. 98
APPENDIX B NELSON PLACE/LONGACRES WAY DRAINAGE STUDY
APPENDIX C FEMA RIVER FLOOD PROFILES
' APPENDIX D PRE-DEVELOPMENT RUNOFF HYDROGRAPHS
APPENDIX E POST-DEVELOPMENT RUNOFF HYDROGRAPHS
APPENDIX F 100-YEAR, 24-HOUR EVENT STORM ON SPRINGBROOK
' CREEK
APPENDIX G SW 16TH STREET DRAINAGE
APPENDIX H TUKWILA STORM DRAIN
' APPENDIX I TIME OF CONCENTRATION FORM
APPENDIX J GROUNDWATER MONITORING WELL SUMMARIES
APPENDIX K BANK STABILITY CALCULATIONS
' APPENDIX L TESC TRAP SIZING CALCULATIONS
APPENDIX M LAND USE DESCRIPTION AREA MAPS
APPENDIX N CSTC SITE DEVELOPMENT AREA PIPE CAPACITY
' CALCULATIONS
' viii
' I. CUSTOMER SERVICES TRAINING CENTER (CSTC)
PROJECT OVERVIEW
The Boeing CSTC Site Development is located in the City of Renton,
' Washington, on the northerly portion of the Longacres Park Horse Race/Track
property. The Technical Information Report (TIR) Worksheets detailing site
information and the constraints to development are included as Figures 1 & 2.
' The site location is detailed on Figures 3 and 4. All figures are located at the
conclusion of the written portion of the report. The scope of this report is to
assess the pre-development and post-development flood and storm water
t drainage conditions. A Master Storm Water Plan based on a proposed Master
Plan Development has been devised for the entire Longacres Site which
consists of slightly over 212 acres. A preliminary copy of that plan was
' previously submitted. While this portion is in keeping with the overall plan, the
CSTC development is a separate project with provisions for water quantity and
quality within the scope of this project.
' Plans for the CSTC site have been in three separate packages for
prepared
bidding and contract administration purposes and since separate permits are
' needed due to timing differences in the completion of the contract documents.
The packages are as follows:
' • CSTC Site Development, which includes all facilities south of the SW 16th
Street Improvements.
• SW 16th Street Improvements, which includes all work within the expanded
' SW 16th Street right-of-way and the proposed water quality pond serving SW
16th Street which is located north of SW 16th Street just west of Springbrook
Creek.
' • CSTC Support Facilities, which includes all facilities north of the SW 16th
Street Improvements.
These projects are interdependent. For example, the CSTC building cannot
' function without the Support Facilities that provide hot and chilled water for the
building. Additionally, the reconstruction of SW 16th Street is a mitigation
measure for the project. However, the drainage facilities for these different plan
1 sets are physically separate and independent due to the geographic and
administrative separation of the areas. The drainage basin analysis for,
detention, water quality features and floodplain storage were done for the entire
' site.
This report presents data relating to the proposed project in the following order:
The first section provides an overview of the proposed project and develops
• P P P P J P
the constraints to the project from a storm water perspective.
' 1
' 0 The second section provides a summary of the existing conditions on the
site and describes how the design addresses these conditions.
• The third section discusses off-site conditions to identify the upstream
tributary areas and downstream conditions.
' 0 The fourth section describes the retention/detention for this project.
' 0 The fifth section details the conveyance system for the project.
The sixth section details the special reports, including a discussion of Dr.
' Horner's oil/water separator study and a description of the delta design at
the pond outlet.
The seventh section discusses the Tukwila storm drain which will carry flow
from a neighboring basin - the Nelson Place/Longacres Way area.
' 0 The eighth section details additional permits needed for the project.
• The ninth section discusses the existing and proposed floodplain and the
' interaction between the proposed lake and the ground water regime.
' 0 The tenth section discusses the temporary sedimentation/erosion control
design for the project.
' 0 The eleventh section discusses the retention/detention facility summaries.
The twelfth section provides the maintenance and operations manual for
' the project.
Figures referenced in the text of the report are located after the twelfth
section of the report.
• Copies of the pertinent Construction Set drawings, details and schedules
follow the report, bound in a separate appendix.
• A second binder contains referenced reports and hydrographic data along
' with associated computer output.
There are two predominant streams in the area of the site. The Green River is
' the largest and is located in the City of Tukwila, Washington, about 1,200 feet
west of Longacres, and west of the West Valley Highway (State Highway Route
181). The Green River has a levee system along its banks protecting nearby
property. The flow is partially regulated by the Corps of Engineers', Howard
Hanson Reservoir on the headwaters of the River. This controlled flow release,
2
coupled with the levee system provides protection of the site from the Green
River for at least the 100-year flood. In the vicinity of the project site, the West
Valley Highway is higher than the levee system adjacent to the River providing
additional flood protection.
The second predominant stream is Springbrook Creek, a tributary of the Black
' River (which is a tributary to the Green River). All storm water from the project
site flows to Springbrook Creek. The CSTC site is within the watershed and
' portions of the site are within the floodplain of Springbrook Creek. The natural
stream channel for Springbrook Creek was previously replaced near the project
site by an excavated channel (Drainage District No. 1). This channel is located
' to the east of the site and is adjacent to this project.
The Federal Emergency Management Agency (FEMA) 100-year return
' frequency flood elevation for Springbrook Creek at the site has been designated
as elevation 16.4 National Geodetic Vertical Datum (NGVD) of 1929. The
proposed building floor slabs will be located a minimum of two feet above this
elevation. The storm water plan provides a system of inlets, swales, storm water
treatment/detention ponds and pipes combined with open channels to convey
storm flows. Storm flows with a frequency of once every 25 years, with a
duration of 24 hours (referred to herein as a 25-year, 24-hour storm event) is
conveyed without requiring surcharge within catch basins to drive the flow.
' The conveyance system is also analyzed for a 100-year 24-hour storm assuming
the site is a closed depression. For this analysis, runoff generated on the site
' does not leave the site through the normal outlet structure. The normal outlet
will have flood gates (similar to the existing flood gates) to prevent water from
Springbrook Creek entering the site below elevation 15.0. The closed
depression analysis assumes that the elevation of the creek is high enough to
prevent discharge from the site as well. The existing banks of Springbrook
Creek form a sill which is at or above elevation 15.0. The closed depression
analysis has been completed for two different sets of conditions, where the site
and the creek interact. The first situation assumes changing elevations in the
creek caused by a 100-year storm and a 50-year storm on the site itself. All of
' the on-site 50-year storm volume is retained onsite. When the creek elevation
exceeds 15.0, flow from the creek enters the site over the sill. This set of
circumstances yields a maximum water surface elevation that matches the creek
elevation of 16.4. The sill weir for the existing site has an area of 70.6 square
feet. The proposed weir has an area of 272.3 square feet. The proposed sill
weir will allow approximately four times more water to enter the site, compared to
the existing situation. The second situation studied was a 100-year 7-day storm
on the site with no incoming component from the creek. When elevations on the
site exceeded 15.0 flow left the site and entered the creek via the sill at a flow
rate of 43 cfs. This situation yielded a maximum water surface elevation of 15.2
on the site.
' 3
1
1 ow r o reek
A closed depression analysis without inflow from or outlet to Springb o k C
1 was also performed. This situation was studied for the 2, 5, 10, 25, 50, and
100-year 24-hour storms. The maximum water surface elevation was 12.1 which
occurred during the 100-year 24 hour storm. Note that this is below the sill
1 elevation.
Water quality controls are incorporated based on the City of Renton criteria,
1 King County Surface Water Design Manual, and correspondence with Dr.
Richard Horner, (University of Washington) including Technical Report No. 98
(included herewith as Appendix A) and the final runoff quantity/quality study.
1 Based on these reports and the planned campus atmosphere for the site,
extensive storm water treatment/detention ponds are being provided in the site
landscaping. These storm water treatment/detention ponds provide surface
1 areas in excess to that required by code resulting in lower outfall quantities post-
development than pre-development. These larger volume and surface area
storm water treatment/detention ponds provide storage area for extreme events
1 such as the 100-year, 7-day storm while maximizing water quality benefits.
i
1
1
1
1
1
1
1
1
1
1 4
II. PRELIMINARY CONDITIONS SUMMARY
' Preliminary conditions include the Core Requirements from the King County,
Washington, Surface Water Design Manual, and Special Requirements deemed
to apply to the project site as follows:
Core Requirement #1 - Discharge at the Natural Location:
' Discharge from the site will occur at three locations. The area north of SW 16th
Street, post-development basin B, will discharge north of the site on to an
' existing ditch adjacent to 1-405. Drainage leaves the site via sheet flow under
pre-development conditions. The flow will be concentrated into a pipe after
development, but the ultimate receiving water, Springbrook Creek, is very close
' to this location. There will be no appreciable changes in Basin B's runoff
quantities. Velocities in the existing riprap protected ditch are low enough that
erosion will not occur.
' The portion of the site south of SW 16th Street currently discharges into
Springbrook Creek through an existing 36" diameter Corrugated Metal Pipe
' (CMP). This pipe is located approximately 450' south of the existing SW 16th
Street Bridge. The invert elevation of the pipe at Springbrook Creek is 6.33
' NGVD. The existing culvert is in poor condition, and extensive corrosion of the
pipe is evident. The pipe has also been flattened somewhat so it no longer has
a round cross-section. We are proposing to replace the culvert with a new 36"
' diameter ductile iron pipe in the same horizontal and vertical locations. All
drainage from the site south of SW 16th Street will continue to be discharged at
this location. The existing CMP culvert has a mechanical flap gate to prevent
flows from entering the site during high creek elevations. The new culvert will
utilize a Tideflex elastomeric backwater check valve to perform the same
function.
The third discharge location is from the three stage water quality pond/roadway
storm drain for SW 16th Street. Currently the runoff from SW 16th Street flows
' into catch basins located on the south side of the street. These catch basins
discharge into the existing Tukwila Nelson Place/Longacres Way outlet culvert
located south of SW 16th Street.
' Core Requirement #2 - Off-Site Analysis:
Off-site analysis has been completed regarding the Nelson Place/Longacres
Way basin (see Appendix B) to the west of the site. This off-site flow will be
' diverted to the storm drain extension planned within SW 16th Street. See
Special Requirement #2. The on-site storm drain system will be designed to
5
accept future overflow of 18 cfs from this off-site area. This is keeping with
previously prepared drainage plans for this area.
rCore Requirement #3 - Runoff Control.-
Runoff control is accomplished by the use of storm water treatment/detention
ponds to provide water quality benefits while accomplishing water quantity
control without the need for additional water detention ponds. The large surface
t areas and volumes associated with the storm water treatment/detention ponds
south of SW 16th Street reduce the flows for all storm events to much below the
pre-development conditions.
' This core requirement also includes a requirement for biofiltration of the storm
water flows. Biofiltration is provided by the long open channel and delta located
' downstream of the three pond system.
Core Requirement#4 - Conveyance Systems:
' The conveyance system has been designed to convey the peak rate runoff for
the 100-year design storm originating on the site plus existing upstream runoff
' (that may be diverted as noted in Special Requirement #2). The 100-year flows
may require surcharged conditions for pipe systems, while the systems convey
the 25-year event without surcharge.
' Core Requirement #5 - Erosion/ edimentation Contr
ol (ESC) Plan.
' Initially an erosion/sedimentation control pond will be constructed near the
proposed outfall location to Springbrook Creek, while maintaining a levee
adjacent to the stream. This pond will allow construction and excavation of the
large storm water treatment/detention ponds associated with the site, and
related construction activity. Temporary erosion control ponds are anticipated to
' be located generally in locations where storm water treatment/detention ponds
are planned for the final design. This will allow wetland plantings to develop
adjacent to these features at an early stage for biofiltration. The
' erosion/sedimentation control plan establishes the following:
• Stabilization of construction access points.
' 0 Delineate clearing limits.
' 0 Delineate and fence existing adjacent wetlands.
Develop construction phasing to establish ESC ponds as an initial
' phase of construction.
6
' 0 Utilize construction notes on the drawings to draw attention to the
special conditions associated with the ESC plans.
' 0 Direct the revegetation and/or covering of exposed areas promptly.
' 0 Monitor the water quality before and after construction begins and
through the first year of operation.
Core Requirement #6 - Maintenance and Operation:
A maintenance and operation manual to describe the Best Management
' Practices (BMP) considered for this particular site is located in Section XII of this
report. Monitoring of the water quality from the site will continue for the first year
of operation to determine the efficiency of the system and how to operate the
' system to enhance the water quality. This will determine the optimum
maintenance schedules and the manual will be modified accordingly.
' Core Requirement #7 - Bonds and Liability:
All maintenance except for the facilities serving the SW 16th Street, will be the
Owner's responsibility and no drainage conveyance easements are
contemplated as the system is looked on as a landscaping amenity and will be
maintained privately. The SW 16th Street facilities will be turned over to the City
' of Renton for ownership and maintenance, after completion.
' Special Requirement #1 - Critical Drainage Areas:
No critical drainage area is associated with this project and this special
' requirement is considered not to apply to this project.
Special Requirement #2 - Compliance with an existing Master Drainage Plan:
rThe Nelson Place/Longacres Way drainage study was completed by the City of
Tukwila and is included as an appendix to this report. The plan is to divert the
' existing drainage from this area to a new storm drain which will be extended
within the Right-of-Way of SW 16th Street. This storm drain will be constructed
as part of the required SW 16th Street roadway improvement project. The on-
site system will be designed to accommodate a future 18 cfs overflow from the
Nelson Place/ Longacres Way area, as is recommended by the drainage study.
' Special Requirement #3 - Master Drainage Plan:
This project does not impact more than 200 acres and therefore a master
rdrainage plan is not required. A rough draft of a master drainage plan based on
a conceptual site master plan was previously transmitted to the City of Renton.
' 7
' Special Requirement #4 -Adopted Basin or Community Plan:
No adopted basin or community plan exists for this area so this special
requirement is deemed not to apply to this project.
' Special Requirement #5 - Special Water Quality Controls:
' Special water quality controls are designed into the landscaping scheme for the
CSTC site. Storm water treatment/detention pond areas are an amenity for the
site and these contribute to the overall water quality. The concept for the CSTC
' site south of SW 16th Street is to utilize a three pond system for water quality.
The first stage water quality controls consist of wet vaults to contain sediments
and provide gravity oil/water separation. The second and third stages are open
wetponds with wetland vegetation to improve the water quality with plants being
used to uptake certain constituents within the storm water stream.
The portion of site north of SW 16th Street will incorporate a biofiltration swale
for water quality enhancement. Drainage from SW 16th Street will pass through
a biofiltration swale and a three stage wetpond to improve discharge water
quality.
Special Requirement#6 - Coalescing Plate Oil/Water Separator:
' This project contemplates traffic of 2,860 ADTon the adjoining streets and within
' the parking lots. A variance from using Coalescing Plate Oil/Water Separators
is being sought. The wet vaults within the three pond system are designed to
allow placement of coalescing plate packs at any time if the water quality on the
outlet stream indicates that this would be required.
Special Requirement#7 - Closed Depressions:
' Analysis on the basis of a closed depression was accomplished for this site as
the outlet end of the culvert has a tide gate and during extreme events on
Springbrook Creek the tide gates could be closed causing the site to act as a
closed depression. Analysis has been done relating to storage of storms
including
' 2-year, 5-year, 10-year, 25-year, 50-year, and 100-year 24-hour events. The
highest water surface within the site based on these events is 12.1 feet. This
compares to an elevation of 14.4 under existing conditions as additional storage
' at lower elevations is planned.
' 8
' Special Requirement #8 - Use of Lakes, Wetlands or Closed Depressions for
Runoff Control:
rExisting wetlands within the main track are highly disturbed urban wetlands of
low quality. The plan is to enhance these wetlands while using them for the third
' stage of water quality and for water quantity control. All waters are contained
within the confines of the property so neighboring properties are not affected.
The plan also provides additional floodplain storage volume from the existing
conditions while allowing flooding to occur by overtopping a natural berm as
occurs under current conditions.
' Special Requirement #9 - Delineation of 100-Year Floodplain:
Floodplain mapping by FEMA has been accomplished for the site and is
' attached as Figure 9. Note that this is slightly different than actual field site
surveys as conducted by W&H Pacific and detailed in Figure 8. A revision letter
is being prepared for submittal to FEMA to account for this change. The
' floodplain storage is larger under post-development conditions than under pre-
development conditions. This is shown in Figure 25.
Special Requirement#10 - Flood Protection Facilities for Type 1 and 2 Streams:
No existing flood protection facilities exist for the portion of Springbrook Creek
' adjacent to the project. Therefore, this requirement does not apply. Bank
stability calculations were completed for those areas where existing stream
' banks are disturbed by significant excavation, see Appendix K.
Special Requirement #11 - Geotechnical Analysis and Report:
' A brief geotechnical report is included as Figure 10, and the complete report was
an exhibit to the Environmental Checklist. Groundwater monitoring wells were
' located on the site. Locations and water level elevations are shown in Appendix
J.
' Special Requirement #12 - Soils Analysis and Report:
The existing mapping done by King County in 1973 appears sufficient for the
' purposes of this project and this requirement does not apply therefore.
9
' III. OFF-SITE ANALYSIS
A. Green River:
t The watershed area of the Green River at Renton is 450 square miles.
Above the Howard A. Hanson Dam the watershed area is 215 square
miles. The Green River flow is controlled by the Corps of Engineers,
Seattle District, which is responsible for the regulation of dam outflows
from the Howard A. Hanson Dam at Eagle Gorge on the upper Green
River. The regulation limits the flow at Auburn to less than 12,000 cfs for
up to a 500-year storm frequency. This flow rate represents a 2-year
recurrence flood event if the stream were not regulated. The flood
profiles for the Green River in the vicinity of the Longacres site indicate
the same flood elevation for either the 10-year or 500-year flood
frequency. FEMA flood profiles are presented in Appendix C.
Flood profiles of the Green River with and without levees generally
indicate the same, elevation, elevation 23.2, in the vicinity of the CSTC
site, opposite S. 158th Street (Longacres Way). This elevation (23.2) is
' significantly below the West Valley Highway which is at approximately
elevation 25 to 29 adjacent to the project site. Therefore water from the
Green River will not enter the site during a 500 year or smaller flood.
' On July 18, 1985, the Green River Management Agreement was entered
into by King County and the cities of Auburn, Kent, Renton, and Tukwila.
' This agreement generally outlines and provides guidelines for
improvements, monitoring, operations, and financial responsibilities.
Notable are the guidelines presented for the P-1 pump station operation,
tof the Springbrook Creek/Black River as follows:
Measured Green River P-1 Black River
Flows c@ Auburn Maximum Allowable Pumping
Gage (cfs) (cfs)
' Less than 9,000 cfs As Required
9,000 cfs 2,945 cfs
' 9,500 cfs 2,900 cfs
10,000 cfs 2,400 cfs
10,500 cfs 1,900 cfs
' 11,000 cfs 1,400 cfs
11,500 cfs 900 cfs
10
rMeasured Green River P-1 Black River
Flows @ Auburn Maximum Allowable Pumping
tGage (cfs) (cfs)
12,000 cfs 400 cfs to zero depending on levee
' monitoring by King County Director of
Public Works or his signee. Further
restrictions on P-1 pumping capacity
may be required.
1 Assumes full installed capacity is
' available.
B. Springbrook Creek:
' The confluence of Springbrook Creek with the Black River is established
as the upstream end of the P-1 storage pond of the Black River. This
' confluence point is .6 miles above the Black River P-1 pumping station
and 1 mile above the confluence of the Black River with Green River.
' Watershed area of Springbrook Creek is 21.9 square miles with the
following peak discharges:
' Peak Discharges CFS at Confluence
10-Year 50-Year 100-Year 500-Year
590* 930 1,100* 1,550
' *Decreased 300 cfs due to P-1 pumping station.
FEMA flood profiles for Springbrook Creek are presented in Appendix C.
In the area of the CSTC site the 100-year flood elevation is indicated as
16.4 at SW 16th Street and 16.0 at SW 23rd Street. The FEMA flood
boundary and floodway map is shown in Figure 9 and the site contours as
field mapped are shown in Figure 8. The flooding elevation of 16.4 is
obtained by assuming that the P-1 pump station is restricted to a pumping
rate of 300 cfs, when a 100-year flood occurs on Springbrook Creek. This
' flow rate results from the small 225 cfs diesel and one of the two 75 cfs
electric pumps being on line. Although the guidelines for operation of the
' station would allow the second 75 cfs electric pump to be operating, it
was considered out of service. This restriction is considered due to
flooding on the Green River, and in accordance with the guidelines, noted
' above, for the P-1 pump station operation. The highest elevation occurs
in the forebay when the flood flow is less than the maximum of 1,400 cfs,
during the downward leg of the hydrograph at a flow rate of approximately
' 11
785 cfs. This high water elevation is 15.0. This elevation is used in a
HEC-2 (Hydraulic Engineering Model for flood way water surface profiles)
to generate upstream water levels. This results in an elevation of 16.42
at the SW 16th Street bridge.
t The FEMA data does not include provisions for the recently constructed
SW 16th Street Bridge with a 60-foot span compared to the old span of
36 feet. It also does not include the new four-barrel box culvert under
' Grady Way or the new box culvert constructed (not yet placed in service)
under 1-405. The low girder of the new SW 16th Street bridge is elevation
14.79 based on a Soil Conservation Service determination of a 100-year
' backwater elevation of 11.6 to 13.1 depending on a reduced pumping
level of 400 cfs after Green River has exceeded 12,000 cfs at the bridge
site. The Soil Conservation Service has studied potential improvements
' to Springbrook Creek, referred to as the P-1 Channel. The improvements
planned south of SW 16th Street are currently under consideration, and
include possible widening and realignment of the channel, improvement
' of Panther Creek (P-9 channel) for fisheries values, and associated
cleanup efforts. Panther Creek flows into Springbrook to the east of the
site at approximately the future location of SW 19th Street. The recently
' completed "East Side Green River Watershed Plan - Current Conditions
Document", shows a high water elevation of 8.9 or 9.9 at SW 16th Street
(depending on simulation assumptions).
C. Black River:
The Black River as it exists today is 1 mile in length and its confluence
with the Green River is 11.0 miles above Puget Sound. A pumping
' station is located on the Black River .3 miles above its confluence with the
Green River. The watershed area at the pump station is 24.8 square
miles which includes the 21.9 square miles of Springbrook Creek. The
' pumping station has no gravity flow provisions. All upstream flows must
be pumped up to a gravity open channel which discharges to the Green
River. The rated pumping capacity of the station is 2,945 cfs. There are
' eight main pumps with two of the larger currently mothballed and not
used. There are five diesel pumps rated at 514 cfs, one at 225 cfs and
two automated electric pumps at 75 cfs each. The FEMA study was
based on 875 cfs as the pump station's firm capacity of maximum
discharge. The pump station has a forebay (called the P-1 pond storage
area) that was recently expanded by the excavation of approximately 1
' million cubic yards.
' The 1989 FEMA study indicates that peak outflows from the pump station
have not exceeded 525 cfs (November, 1986 event with nominal P-1 pond
storage). On March 4, 1991, the pump station operator indicated he was
12
pumping at a rate of 750 cfs. Under standard operating conditions the
maximum water surface elevation of the P-1 storage pond is elevation 3.5
' NGVD. High water alarms are activated when the level reaches elevation
4.5. Since operation began in 1972, the highest upstream elevations
observed was 7.0 NGVD and 18.7 downstream of the pump station.
' A Green River flow of 12,000 cfs is equated to elevation 19.0 downstream
of the pump station. The pump room floor elevation is 25.0 NGVD. Since
1 all upstream flow must be pumped the electric pumps are automated by
float switches. The larger diesel pumps must be manually started and are
used as required to pump out the storage pond. Trash racks are cleaned
periodically depending on the debris build-up. There have been some
flap gate failures with the rocker arm breaking off. However, the pump
bays can be isolated from backflow with stoplogs.
' A small fish ladder is operated 24 hours a day during the upstream
migration period from September through January. Between April and
' June 15 the downstream migration is accommodated by an air lift
chamber. A simplified fish counter consisting of a paddle in the upstream
migration trough counts electronically the number of fish passing.
' Fish counts for the last 8 years were as follows:
' Season No. of Fish
83-84 155
' 84-85 119
85-86 47
86-87 82
87-88 166
88-89 95
89-90 77
' 90-91 69
D. Previous Studies:
' Numerous studies have been performed in the area of Longacres Park.
Some of the more pertinent studies are as follows:
1 1. King County, Washington FEMA Flood Insurance Study, four
volumes revised September 29, 1989.
' 2. FEMA Flood Insurance Stud of Renton, November, 1980.
Y ,
' 3. Soil Conservation Service P-1 and P-9 Channel studies.
13
i4. U.S. Department of Army Corps of Engineers Green River Flood
Reduction Study, 1984.
5. King County Department of Public Works Green River
Management Agreement, July 18, 1985.
' 6. City of Tukwila, Nelson Place/Longacres Drive Basin Drainage
Study, December, 1986.
7. City of Tukwila, Nelson Place/Longacres Way Storm Drainage
System Preliminary Design, June, 1988.
' 8. An Analysis of the Distribution and Jurisdictional Status of Waters
of the United States Including Wetlands, at Longacres Park,
' Renton, Washington.
9. Environmental Site Assessment Broadacres Property Renton,
' Washington, August 31, 1990.
10. Geotechnical Engineers Services Boeing Longacres Park, Renton,
Washington, by GeoEngineers Inc., January 23, 1991.
11. City of Tukwila, Water Resource Rating and Buffer
' Recommendations, May, 1990.
' 12. Building Regulations City of Renton, October 15, 1990.
13. City of Renton, Valley Drainage Study, 1991.
14. City of Renton Storm Water Utility, East Side Green River
Watershed Plan - Current conditions Document, October 1991.
' 15. Water Quality Monitoring and Quality Assurance Project Plan for
the Black River Water Quality Management, October 10, 1991.
' 14
IV. RETENTION/DETENTION ANALYSIS AND DESIGN
A. Pre-Development Conditions:
' Entire CSTC Site
The CSTC site is located on the site of the Longacres Race Track in the
City of Renton. The CSTC site is between the Green River Channel on
the west and the Springbrook Creek Channel on the east (see Figure 4).
To the immediate north is 1-405 and to the south is generally horse barns,
grandstands and associated items related to the Longacres Park Race
Track.
' The pre-development basins are shown in Figure 5. Included are the
three separate basins (Basins 1, 2 and 3) which contribute to the CSTC
site. These separate basins were analyzed based on the King County
"HYD" program with the generated flow numbers checked by using HEC I.
The area weighted runoff coefficient (curve numbers) for all
pre-development sites are detailed in Figures 11-13 and 17. Appendix M
contains a color coded map which shows the location and size of all the
different land use description areas. The hydrograph was then developed
for the involved basins based on storms from the water quality event, 2-
year, 5-year, 10-year, 25-year, 50-year, and 100-year, 24-hour event and
the 100-year 7-day event. Figures 11-18 show the following information:
t0 The soil group, (from mapping by King County, 1973).
' 0 The hydrologic soil grouping (Note: For conservative analysis, group
D was used for all Ur (Urban Modified Soils).
' 0 The runoff coefficient; which is based on soil group and hydrologic
group.
• The existing land use and area; which was obtained by digitizing the
pre-development condition drawings developed from aerial and
topographic surveys.
' Time of concentration was calculated b utilizing averse slopes and
Y 9 9 P
' velocities based on Mannings equation for overland sheet flow through
grasses, and checked against time for urbanized basins with the lesser
time used. The travel time within the various closed or open systems
were calculated based on average flow conditions. These two numbers
were added to develop the total lag time for the individual basins. The
15
' time of concentration for the pre-development basis are as follows, see
Appendix I for calculation sheets detailing the methodology used:
' Basin Time of Concentration
' 1 28.6
2 9.7
3 25.4
The pre-development storm water hydrographs are shown in Appendix D.
' The site is relatively level with elevations generally between 13 and 20
NGVD. Storm water runoff leaves the site and enters Springbrook Creek
at two locations (see Figure 5). The first discharge point is a 36-inch
' CMP with a steel flap gate under the northeast portion of the site
discharging directly into Springbrook Creek. This discharge point drains
Basins 1 and 3 which have a combined area of 169 acres.
Basin 1 is a 93 acre drainage outside of the project area, located between
the Burlington Northern Railroad and the West Valley Highway. Runoff
from this area enters the northwest portion of the site via a 24-inch culvert
under the railroad. This culvert restricts the flow from this basin to 18 cfs.
The 93 acre Basin 1 flow is generally overland in large vegetated swales
and an existing 2' X 5' concrete box culvert along S. 158th Street under
the Union Pacific Railroad. A portion of the off-site flow drains under a
' trestle under 1-405 to the area between the two railroads. This portion of
the off-site flow contains approximately 12.4 acres. See Section VII A, for
additional discussion.
Basin 3 contains 76 acres, this is made up of the north portion of the
grandstands, the horse racing track and the track infield. The storm water
currently flows through existing swales and conveyance structures. The
existing site detention was taken into consideration to develop the flows
for all storm conditions.
' The second drainage discharge point is located at the northeast corner of
Basin 2, an area approximately 7 acres in size. This basin drains the
area north of SW 16th Street, and outfalls to the north along the southerly
' right-of-way (ROW) line of 1-405 in a swale draining to Springbrook
Creek. The Washington Department of Transportation has installed a
small siltation pond along this channel.
' CSTC Site Development
' The CSTC Site Development area lies almost entirely within Basin 3. The
CSTC Site Development area is 50.7 acre while Basin 3 is 76 acres. The
CSTC Site Development pre-development area contains numerous
16
features associated with the horse race facility. These include horse
barns, office facilities, race track, parking lots and support buildings. The
' weighted curve number for Basin 3 is 91.15, the pre-development time of
concentration is 25.4 minutes.
' SW 16th Street Improvements
The SW 16th Street area lies partially in both Basin 2 and Basin 3. The
SW 16th Street pre-development area contains the existing 20 foot wide
asphalt roadway and gravel roadway shoulders. The total area is 3.09
acres as shown in Figure 17. The 3.09 acres includes the 1.37 acre area
of additional Right-of Way to be dedicated for SW 16th Street, this area is
currently private property to the south of SW 16th Street. Currently the
runoff from SW 16th Street flows into catch basins located on the south
side of the street. These catch basins discharge into the existing Tukwila
' Nelson Place/Longacres Way outlet culvert located south of SW 16th
Street. The weighted curve number for the SW 16th Improvements area
is 93.83, the pre-development time of concentration is 20.8 minutes.
CSTC Support Facilities
The CSTC Support Facilities area lies entirely within Basin 2. The CSTC
Support Facilities area is 3.05 acres in size as shown in Figure 12. Basin
2 is 7 acres in size. The CSTC Support Facilities area currently drains
' into an existing ditch on the north side of the site . This ditch is alongside
1-405. Drainage is conveyed to the ditch via sheetflow. The pre-
development CSTC Support Facilities area consists of, trailer roofs,
' asphalt driveways, asphalt parking areas and landscaped areas. The
weighted curve number for the CSTC Support Facilities area is 94.32, the
pre-development time of concentration is 9.7 minutes.
' B. Post-Development Conditions:
' Entire CSTC Site
The post-development basins are shown in Figure 6. Basins A, B, and C
' are the three separate basins contributing to the CSTC site. These
separate basins were analyzed based on the King County "HYD" program
with numbers checked by using HEC I. Appendix M contains a color
coded map which shows the location and size of all the different land use
description areas. The area weighted runoff coefficient (Curve Numbers)
for all post-development sites are detailed in Figures 14-16 and 18, which
show the following information:
• The soil group (from mapping by King County, 1973)
17
The hydrologic soil grouping (Note: For conservative analysis, group
D was used for all Ur (Urban Modified Soils))
t0 The runoff coefficient; which is based on soil group and hydrologic
group
' 0 Areas and development densities are based on the plans for the
proposed development.
' The post-development storm water hydrographs are shown in Appendix
E.
' The following analysis methods were utilized in this study:
' 1. The total drainage area studied is 175 acres, which includes the
Nelson Place/Longacres Way study area, Basin A, as well as off-
site land which contributes runoff to the project site. The flow from
Basin A will be routed through the 48" diameter Tukwila storm
drain pipeline described in Section VII, with only an overflow of 18
cfs directed to Basin B. For this analysis, however, the flow of 18
' cfs as occurs in the pre-development basin condition is utilized for
all flow situations.
2. The precipitation for various storm events was interpolated from
isopluvials contained within the King County Surface Water Design
' Manual, as noted below:
Frequency of Event Total Precipitation
' Water Quality 0.67 (P2/3))
2-year, 24-hour 2.00
5-year, 24-hour 2.40
10-year, 24-hour 2.90
25-year, 24-hour 3.40
50-year, 24-hour 3.45
100-year, 24-hour 3.90
100-year, 168-hour (7-day) 9.80
3. Time of concentration was calculated by utilizing average slopes
and velocities based on Mannings equation for overland sheet flow
through grasses, and checked against time for urbanized basins
with the lesser time used. The travel time within the various closed
or open systems were calculated based on average flow
' conditions. These two numbers were added to develop the total
lag time for the individual basins. The time of concentration for the
' 18
post-development basins are as follows, see Appendix I for
calculation sheets detailing methodology:
' Basin Time of Concentration (Minutes)
A 28.6
B 7.2
C 9.0
4. All basins utilized for this study are shown in Figures 5 and 6.
5. The runoff coefficients used for this study are based on Table 3.5.2
of the King County Surface Water Design Manual, with all Urban
(Ur) soils considered as hydrologic soil group D. No additional
' impervious percentage was considered within calculations beyond
that contained within the runoff coefficients.
6. The conveyance system was designed to convey the 100-year, 24-
hour storm plus existing off-site runoff that is conveyed through the
site. The system is designed to handle the 25-year, 24-hour event
' without surcharging the system, however, surcharge is allowed for
the 100-year event.
7. Channel velocities will be maintained to less than 5 fps for storms
of 25-year, 24-hour and lesser events.
8. The existing site hydrographs were directed through the existing
discharge devices using the computer program "POND" as
' developed by Haestad Methods to ascertain the amount of existing
detention on the site. The peak outflows of the post-development
were then compared to develop the required detention
requirements. The 100-year, 7-day storm event was also
considered to occur when the flow in Springbrook was below the
sill but yet high enough to close the tide gates on the existing
discharge culverts (closed depression analysis). Another situation
modeled was of a 100-year flood on Springbrook Creek yielding
backwater into the site while the site was undergoing a 50-year,
' 24-hour event. The 100-year flood hydrograph on Springbrook
Creek analysis is detailed in Appendix F.
CSTC Site Development
' The CSTC Site Development area lies entirely within Basin C. The CSTC
Site Development area is 50.7 acres while Basin C is 76.4 acres. The
CSTC Site Development post-development area contains, the CSTC
' 19
' building, asphalt roadways interior to the site, asphalt parking lots,
landscape areas and a large lake-pond -stream system.
' The detention volume required due to post-development changes in
Basins B and C are provided within the CSTC Site Development lake
' system, see Figure 21 and 22. As can be seen from these figures, the
post-development discharge rates are much lower than the pre-developed
discharge rates. Much more detention volume is provided than is
' required. This is due primarily to floodplain volume requirements. The
weighted curve number for Basin C is 92.70, the post-development time of
concentration is 25.4 minutes.
SW 16th Street Improvements
' The SW 16th Street area lies partially in both Basin B and Basin C. The
total area is 3.09 acres as shown in Figure 18. The 3.09 acres includes
the 1.37 acre area of additional Right-of Way to be dedicated for SW 16th
Street. The existing SW 16th Street roadway will be removed and
replaced in conjunction with the CSTC Site Development Project. The
roadway improvements will extend from the bridge over Springbrook
' Creek to Longacres Way, which is about 1,685 lineal feet, see Figure 7.
The existing 20-foot-wide road will be removed and will be replaced with a
44-foot-wide section. There will be curbs on both sides of the pavement
' and a sidewalk on the south side. The roadway will be crowned with a
2.0% cross slope. Area between the edge of the right-of-way and the
curbs will slope toward the curbs at a 2.0% slope. The SW 16th Street
' post-development area contains the widened asphalt roadway, concrete
curb and gutters, concrete sidewalk and landscaping.
' Substitute detention volume for the SW 16th Street Improvement area is
provided within the CSTC Site Development lake system. Flow from the
SW 16th Street area does not enter the CSTC Site Development lake
system, but enough detention volume is provided within the lake to
compensate for SW 16th Street. Detention for the SW 16th Street
' Improvements as a separate project is not required since peak flows for
the post development 100-year 24-hour storm is less than 0.5 cfs greater
than the pre-development peak, see Figure 19 and Appendix G. The
' weighted curve number for the SW 16th Street Improvement area is
95.49, the post-development time of concentration is 19.4 minutes.
CSTC Support Facilities
The CSTC Support Facilities area lies entirely within Basin B. The CSTC
' Support Facilities area is 3.05 acres in size as shown in Figure 15. The
entire Basin B area is 7 acres in size. The CSTC Support Facilities area
' 20
' will be drained into an existing ditch on the north side of the site . This
ditch is alongside 1-405. Drainage will be conveyed to the ditch via a pipe
' and catch basin system. The post-development CSTC Support Facilities
area consists of, two proposed buildings, asphalt driveways, asphalt
parking areas and landscaped areas.
' Substitute detention volume for the CSTC Support Facilities area is
provided within the CSTC Site Development lake system. Flow from the
' CSTC Support Facilities area does not enter the CSTC Site Development
lake system, but enough detention volume is provided within the lake to
compensate for CSTC Support Facilities. Detention for the CSTC
' Support Facilities as a separate project is not required since peak flows
for the post development 100-year 24-hour storm is less than 0.5 cfs
greater than the pre-development peak, see Appendix D and E . The
weighted curve number for the CSTC Support Facilities area is 93.95, the
post-development time of concentration is 6.5 minutes.
t21
' V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
A. Proposed Conveyance System Overview:
' Entire CSTC Site
Plans for the CSTC site have been prepared in three separate packages
' for bidding and contract administration purposes and since separate
permits are needed due to timing differences in the completion of the
contract documents. The packages are as follows:
' • CSTC Site Development, which includes all facilities south of the SW 16th
Street Improvements.
• SW 16th Street Improvements, which includes all work within the
expanded SW 16th Street Right-of-Way and the proposed water quality
pond serving SW 16th Street which is located north of SW 16th Street just
west of Springbrook Creek.
' • CSTC Support Facilities,which includes all facilities north of the SW 16th
Street Improvements.
These projects are interdependent. For example, the CSTC building
' cannot function without the Support Facilities that provide hot and chilled
water for the building. Additionally, the reconstruction of SW 16th Street
' is a mitigation measure for the project. However, the drainage facilities
for these different plan sets are physically separate and independent due
to the geographic and administrative separation of the areas. The
' drainage basin analysis for, detention, water quality features and
floodplain storage were done for the entire site.
' CSTC Site Development
' The proposed storm water conveyance system for the CSTC Site
Development implements the following devices for water quality and
quantity control. Approximately 40% of the site is covered by
' landscaping, and the landscaping is planted extensively with trees which
have a higher uptake of water than other ground cover. The landscape is
planned to provide a roughened edge (of wetland species) as water
' surfaces are approached, providing buffering of water flowing from
landscaped surfaces. All paved parking lots will have Type 1 P catch
' basins which provide a deep sump for catching sediments. The outlet will
include a trap (an inverted elbow) to prevent floatables from entering the
storm drainage system, and reduce the discharge of oils. From the catch
' basins, which are set off-line from the system laterals, storm water runoff
is directed to a grit removal chamber, or wet vault. This vault will serve
both as the first stage wetpond and a sediment removal chamber. A
' 22
control manhole is placed just prior to the vault. This manhole will divert
flows in excess of the water quality design storm peak flow around the wet
vault. This will prevent high flows from resuspending the sediments
' contained in the wet vault. Following the wet vault is the second stage
wetpond. This is a pond designed in accordance with the King County
Surface Water Design Manual, with wetland plantings to improve water
' quality. Another control manhole is placed upstream of the second stage
pond. This manhole diverts flow in excess of the 2-year event around the
second stage pond. From the 2nd stage ponds, the flow passes into a
' third stage wetpond (lake) to further improve water quality and provide
detention. Flows from the CSTC Building (25.01) roof drains will be
' routed directly to the third stage pond. Flows are not by passed around
the third stage pond. as it is over 4 acres in size (much greater than
required).
' Most of the CSTC site drains to a large central lowpoint. A large volume
lake (the third stage pond) is located at this low point. This lake provides
much greater detention than that required by the Manual. This excess
detention is provided so as to maintain floodplain storage volumes. The
lake will be integrated into the landscape and create a visual centerpiece
' within the site. From the third stage wetpond, flow will exit through a
stream with wetland plantings both in and around the channel. The
stream will pass through an extensive marsh (delta) area and will then
empty into Springbrook Creek at the existing discharge point through an
outlet control structure.
' SW 16th Street Improvements
' The proposed horizontal pavement alignment will shift slightly to the
south, compared to the existing. The proposed vertical profile will closely
match existing. A minimum vertical profile slope of 0.5% will be used.
' This profile will be accomplished by using two vertical curves. A sag
curve will create a low point at Station 28+90, which is about 600 feet
west of the bridge. This low point will collect drainage runoff from 1,285
' feet of the new roadway. The remaining portion of the roadway, 400
lineal feet, will slope west from the high point at Station 22+00 toward
Longacres Way.
' Drainage will be collected at the low point (Station 28+90), immediately
upstream of the intersection with Longacres Way (Station 18+60),
' upstream of driveways and every 150 feet along the roadway. Drainage
will be collected into a storm drain located along the north curb. The
storm drain will extend along the entire length of the proposed roadway
' and will flow from west to east. At the east end of the roadway
improvement, the storm drain discharges into a biofiltration swale with
t23
' wetland plantings sized per the King County Drainage Manual. The swale
discharges into a three stage wetpond, also designed per the King County
' Manual. The swale and pond are located off the right-of-way to the north,
directly adjacent to Springbrook Creek. A bypass storm drain is located
south of the pond and discharges to the creek. Only flows less than the
' water quality event enters the swale or the pond. The swale is designed
using the 2-year event per the manual, however. The pond discharges
into the overflow storm drain.
' Detention is not required since peak flows for the post development 100-
year 24-hour storm is less than 0.5 cfs greater than the pre-development
peak. Substitute detention volume for the SW 16th Street area will be
provided within the CSTC Site Development area.
Pre- and post-development areas, soil groups and the resultant Curve
Numbers are shown in Figures 17-18. Figure 19 shows the peak flows for
pre- and post-development conditions for all storm return frequencies of
interest. "HYD" output data and the hydrographs are contained in
Appendix G.
' CSTC Support Facilities
' The Support Services portion of the site, north of SW 16th Street, will be
served by a storm water collection system which will discharge into the
existing ditch located north of the site in WSDOT right of way. The storm
' water collection system consists of storm drains, catch basins, an edge
drain and a biofiltration swale with wetland plantings. The site parking lot
drainage and building roof drains are collected by storm drains which
' discharge into the biofiltration swale. All parking lot drainage will pass
through a FROP-T manhole prior to entering the swale.
The electrical substation, located on the western edge of the Support
Facilities site, is drained by a storm drain which empties into the
biofiltration swale. The portion of the substation subject to transformer oil
' spills is surrounded by a curb capable of containing one and one half
times the volume of oil contained in the transformers. This curbed area is
isolated by a valve which is electrically activated by a oil density sensitive
' float switch. This valve will prevent oil or water heavily contaminated with
oil from entering the drainage system.
' The edge drain is narrow vertical slotted drain pipe which extends to the
surface. The edge drain is located along the southern and eastern edges
of the site near the property line. This drain collects a narrow band of
landscaped area which slopes toward the property line. The edge drain
discharges to the piped storm drain system in two places.
24
The biofiltration swale is located along the north edge of the site. The
' swale is 200 feet long and is designed in accordance with the King
County Drainage Manual. The swale discharges into the WSDOT ditch
which flows into Springbrook Creek.
' A separate detention system is not required for the Support Services site,
since peak flow will increase less than 0.1 cfs in a 100 year storm.
' Substitute detention volume for the CSTC Support Facilities area will be
provided within the CSTC Site Development area. A separate wetpond
is not required for the Support Facilities site either, since the water quality
features of the CSTC Site Development area have been sized based on
the entire site area.
' B. Conveyance System Analysis and Design:
Entire CSTC Site
The proposed conveyance system for the CSTC Site is designed to
' conform with Chapter 4 of the King County Surface Water Design Manual
which provides approved methods and criteria for hydraulic analysis and
' design of storm drainage facilities.
CSTC Site Development
The predominant pipe material used throughout the site is reinforced
concrete pipe, with plain 8-inch diameter concrete used to connect inlets,
' rainwater leaders, and catch basins to system laterals. The system
laterals range in size from 12-inch to 18-inch diameter. Type 1 P catch
basins are used in all parking areas, with maximum contributing areas of
' 5,000 square feet and a typical contributing area of 4000 square feet.
Maximum flows for such inlets are 0.21 cfs and 0.24 cfs for 25- and 100-
year 24-hour storms, respectively. Typical flows for these inlets are 0.10
cfs and 0.11 cfs for 25- and 100-year 24-hour storms, respectively. The
8-inch outlet pipes from these catch basins provide over 1.0 cfs maximum
capacity based on a minimum slope of 0.60%. The largest 25-year peak
' flow carried by 12-inch pipes within the parking lots is approximately 1.4
cfs, 100-year events create peak flows up to 1.7 cfs. Maximum capacity
of the 12-inch pipes at critical locations, under gravity flow conditions, is
at least 2.1 cfs based on a slope of 0.35%. All locations upstream of
these points carry lesser flows with equal capacity pipe. Where 18-inch
' pipe is used, peak flows up to 3.7 cfs are expected during 100-year
events, a capacity of 5.1 cfs is provided based on a 0.20% slope. See
Appendix N for additional calculations.
' 25
The on-site drainage system was designed to allow for a future 18 cfs
overflow from the Tukwila storm drain (pre-development Basin 1). See
Section VII A for additional description.
' SW 16th Street Improvements
The roadway drainage system consists of 12 inch and 18 inch diameter
' conveyance storm drains, 8 inch and 10 inch diameter catch basin
connections, a biofiltration swale and a wetpond. The 12 inch diameter
storm drains have a slope of 0.2%, the 18 inch diameter storm drains
' have a slope of 0.1% or greater. The capacity of an 18 inch diameter
pipe at 0.1% is 3.32 cfs. This is far in excess of the entire area's post-
development peak flow for a 100 year storm, which is 2.29 cfs, see
Figure 19 and Appendix G. The capacity of the 12 inch diameter pipes
without surcharge is 1.59 cfs, this is very close to the entire area's post-
development peak flow for a 10 year storm ( 1.63 cfs ). The most
' downstream 12 inch diameter pipe, however, only conveys flow collected
from Sta 26+30 to Sta 18+50. This is 780 lineal feet out of the total of
1,685 lineal feet, or 46% of the total area. By inspection, the flow in the
' worst case 12 inch diameter pipe will be less than half of the entire area's
post-development peak flow. Therefore the 1.59 cfs capacity will far
' exceed estimated 100 year flow of 1.15 cfs ( one-half of 2.29 cfs - the
entire site's 100 year storm peak ).
The SW 16th Street biofiltration swale is designed per the King County
Drainage Manual for a 2 year storm, see Appendix G. A maximum design
depth of 8 inches was used since the swale will be planted with emergent
' wetland plants.
The SW 16th Street wetpond was designed per the King County Drainage
' Manual for the water quality storm, see Appendix G.
CSTC Support Facilities
The CSTC Support Facilities drainage system consists of 6, 8 and 12 inch
diameter pipes. The 6 and 8 inch diameter pipes serve very small areas
at the substation and in the front landscape areas. All of the other storm
drains are 12 inch diameter reinforced concrete pipes. The flattest of
these pipes is at a slope of 0.4% which has a capacity of 2.25 cfs. This
pipe can convey the total post-development site flow from a 25 year
storm, which is 1.83 cfs ( see Appendix E ), without surcharging. The
total post-development site flow from a 100 year storm, which is 2.62 cfs,
' could be carried in this pipe with a hydraulic gradeline of 0.54%. This
gradient would create about a 0.5 foot surcharge, which is insignificant.
' 26
Since all other pipes are at a steeper slope and carry less flow, they are
all adequate.
The Support Facilities biofiltration swale is designed per the King County
Drainage Manual for a 2 year storm, see Appendix E. A maximum design
depth of 8 inches was used since the swale will be planted with emergent
wetland plants.
1
' 27
' VI. SPECIAL REPORTS AND STUDIES
A. Dr. R.R. Homer's Report on Oil/Water Separator Study:
Dr. Horner is a research professor at the University of Washington,
Department of Civil Engineering's Environmental Engineering and
Science Program. He prepared a report in June, 1985 titled
"Performance Evaluation Of A Detention Basin and Coalescing Plate Oil
Separator For Treating Urban Storm water Runoff", a copy is located in
' Appendix A. This report documented a study conducted to evaluate the
effectiveness of a coalescing plate oil/water separator and a detention
basin at the Boeing Computer Sciences (BCS) facility in Bellevue,
' Washington. This facility is a light industrial office park very much like the
proposed CSTC site development.
This study concluded that the oil/water separator did not provide any
benefits at this site. Oil/water separators are designed for inflows which
' contain high concentrations of oil. At this site, concentrations of oil
entering the separator were less than the best possible effluent
concentration which could be expected. The oil/water separator did not
remove any significant amount of oil due to the fact the incoming
concentrations of oil were so low. In fact, the separator seemed to cause
an increase in the concentrations of zinc in the effluent. Speculation was
that this was due to some unidentified internal component. The study
recommended that coalescing plate oil/water separators not be used on
light industrial sites except possibly in areas subject to the unloading or
' handling of oils. The study further concluded that effective treatment of
oils can be more successfully obtained by use of detention and wetponds.
Furthermore the study observed that these alternative methods are more
' cost effective than oil/water separators.
The CSTC site is nearly identical in its use characteristics to the BCS site.
' The conclusions reached in Dr. Horner's study apply to this site as well.
This further supports the proposal to not use oil/water separators at the
CSTC site. The proposed wet-vaults will be sized so as to allow addition
of coalescing plate packs should water quality monitoring indicate that it
is necessary.
' B. Peter Walker & Partners Delta Design:
' Drainage after leaving the third stage wetpond (lake) flows through a
stream channel and after passing under the easterly site roadway through
a culvert, it passes into an area called by the landscape designer (Peter
' 28
' Walker & Partners), the delta. This area is landscaped to resemble a
riverine delta with wetland ground cover, water tolerant trees, and braided
' channels. This area complements the site landscaping as it provides a
large patch size, is remote from the more heavily trafficked areas of the
site, and will encourage wildlife by the use of diverse habitat. The delta
will also function as a final polishing stage for the wetpond water gravity
treatment system.
' 29
VII. BASIN AND COMMUNITY PLANNING AREAS
A. Tukwila Storm Drain:
Description:
This section of the report is concerned with pre-development drainage
' Basin No. 1, as shown on Figure 5. This basin is identical to post-
development drainage Basin A. Basin No. 1 is 92.9 acres in size and is
bounded by the Burlington Northern Railroad (BNRR) tracks on the east
' and the West Valley Highway on the west. The basin's southerly limits
are approximately SW 27th Street while the northerly limits are about 400
feet north of 1-405. The entire Basin No. 1 area lies outside of the CSTC
' site and will not be altered as a result of the proposed development. Pre-
and post-development areas, soil groups and the resultant Curve
Numbers (CN) are shown in Figures 11 and 14 (note that both figures are
' identical except for the titles).
Existing Drainage:
Existing land use in the drainage Basin No. 1 area is predominantly
' commercial and industrial. The area is generally flat and is largely
without a formal drainage collection system. There is a slight topographic
slope to the northeast. The BNRR tracks, on the east boundary of the
basin, are elevated by virtue of being constructed on an earthen
embankment. The Union Pacific Railroad (UPRR) tracks, which travel in
a north/south direction, and are located in about the middle of the basin,
' are also elevated on an embankment. Runoff from the west half of the
basin flows to the east half at one location only due to the presence of the
UPRR tracks. This location is approximately 1,400 feet south of 1-405
' and occurs where the tracks are supported by a trestle which
accommodates the S. 158th Street roadway passing beneath the tracks.
The BNRR tracks restrict the movement of runoff leaving the basin.
Runoff leaves the basin via a 24-inch diameter culvert under the tracks
located about 500 feet south of 1-405. Drainage from the basin is
collected in a large ditch on the west side of the BNRR tracks which flows
into the 24-inch diameter culvert, see Figure 5. The capacity of this
culvert is 18 cfs. This creates a flow restriction which causes
impoundment of runoff in Basin No. 1 west of the BNRR tracks.
' Downstream of the tracks (east), flow enters Basin No. 3 of the Longacres
site.
' 30
! Flow travels across the site in a ditch and culvert system, ultimately
entering Springbrook Creek through a 36-inch diameter culvert. The
! portion of Basin No. 1 located between the BNRR and UPRR tracks is in
the FEMA mapped 100-year floodplain. The entire basin experiences
periodic flooding. Most of the flooding occurrences appear to be caused
! by an inadequate drainage collection and conveyance system.
Background:
! Drainage Basin No. 1 and the adjacent area were studied in the "Nelson
Place/Longacres Drive Basin Drainage Study", December, 1986 and the
! "Nelson Place/Longacres Way Storm Drainage System Preliminary
Design", June 1988. Both of these studies were prepared for the City of
Tukwila by the engineering consulting firm of Kramer, Chin & Mayo, Inc
! (KCM). These studies were funded by separate developers whose
projects were nearby and have since been constructed.
! The 1986 study recommended that storm water runoff from drainage
Basin No. 1 be collected in a series of storm drains. These drains would
join together at SW 16th Street as a 48-inch diameter pipe. This pipe
! would then travel east on SW 16th Street increasing in size to a 60-inch
diameter pipe then discharging into Springbrook Creek.
! The 1988 study recommended a very similar system. The major
difference was that the upstream collection system consisted mostly of
! swales and ditches instead of pipes. The collection system still joined
together at a pipeline in SW 16th Street. The pipe was 42-inch diameter
instead of
' 48- and 60-inch diameter but still traveled east along SW 16th Street and
then discharged into Springbrook Creek. This study recognized that a
pipeline would increase peak flows unless detention was provided, so
' maintaining discharges to the Longacres site during periods of high flows
was recommended.
!
!
!
!
! 31
The 1988 study predicted a peak runoff rate of 45.0 cfs during a 25-year
storm. The maximum flow rate leaving the basin through the 24-inch
diameter culvert was estimated at 18 cfs during a 25-year storm and 22
cfs during a 100-year storm. The proposed 42-inch diameter storm drain
would have a capacity of 40 cfs. The maximum flow rate entering the
storm drain was to be limited to 22 cfs, (the 100-year maximum discharge
rate). Another 18 cfs (the 25-year maximum discharge rate) was to be
discharged to the Longacres site. The proposed upstream swales and
ditches provided approximately 100,000 cubic feet of detention volume.
The 1988 study recommended that low areas in the basin and east of the
BNRR tracks be filled up to elevation 15.0. A separate development
study prepared for the McLeod property owners (west of the BNRR
tracks) also recognized that the Drainage Basin No. 1 area would need to
' be raised to this elevation.
In 1991 a bridge over Springbrook Creek at SW 16th Street was
constructed. A portion of the 48-inch diameter Tukwila drain was
constructed from Springbrook Creek to a point about 200 feet west of the
bridge as part of the project. This pipe was constructed in anticipation of
' being extended as described in this section of the report. During design
of the bridge, elevation of the hydraulic gradient for Springbrook Creek at
the bridge, during a 100-year storm was determined to be 11.6. This
' elevation was used to set the minimum elevation for the bottom of the
bridge structure. This 100-year flood elevation was calculated based on
SCS data. This is substantially lower than the FEMA 100-year flood
' elevation
of 16.4.
' In October 1991 the consulting firm of R.W. Beck prepared the "East Side
Green River Watershed Plan Current Conditions Document" for the City
' of Renton. This study describes the current surface water conditions for
Springbrook Creek, as well as other watercourses in the East Green River
drainage basin. Hydrologic analysis conducted for this report predicted a
100-year flood elevation for Springbrook Creek at SW 16th Street to be
either 8.9 or 9.9 depending on the simulation assumptions. This again is
much lower than the FEMA elevation.
' 32
' Hydrologic Analysis:
King County SWM's "HYD" computer program was used to generate
hydrographs for Basin No. 1. Output for storms with a return frequency of
2, 5, 10, 25, 50, 100-year 24-hour, and 100-year 7-day is provided in
Appendix H. A summary, showing peak flows, is provided in Figure 19.
The HYD program utilizes the Santa Barbara Urban Hydrograph method
(SBUH) with a rainfall hyetograph distribution very similar to the SCS
' Type IA.
Flows leaving the basin are governed by the capacity of the 24-inch
diameter culvert crossing under the BNRR tracks. Flow rates through this
pipe were determined using Haestad Methods "Pond-2" computer
software. Pond-2 utilizes level pool routing methodology. A rating table
' for the culvert was developed based on an inlet control culvert. Upstream
storage was modeled using geometry for the ditch adjacent to the BNRR
tracks. Beyond elevation 14.0 the storage volume was increased
' dramatically to simulate spill-over onto the large relatively flat basin
floodplain. Output from this model can be found in Appendix D. A
summary of the maximum culvert capacity for different storms can be
' found in Figure 19.
Proposed System:
We propose -
p p constructing a 48 inch diameter storm drain from,
immediately east of-the BNRR tracks, along SW 16th Street to the
existing 48-inch diameter storm drain which ends about 200 feet west of
Springbrook Creek, see Figure 7. This storm drain will be designed to go
' under the BNRR tracks and intercept runoff upstream of the 24-inch
diameter culvert. An overflow weir wall would allow flow in excess of 22
cfs to be diverted to the existing 24-inch culvert. This excess flow, up to a
' maximum of 18 cfs, would be accommodated by the CSTC on-site
system. The 48-inch diameter storm drain will be designed with a
maximum capacity of 45 cfs. This is very close to the unrestricted outflow
' from Basin No. 1 during a 100-year storm, which is 47.01 cfs . This
project will not construct the 48-inch storm drain under the tracks, but will
instead intercept the downstream end of the 24-inch culvert. Construction
' of facilities under and to the west of the BNRR tracks would require BNRR
permits and easements from the adjacent private property owners, this is
beyond the scope of the CSTC project responsibilities. The CSTC on-site
tsystem will be designed to accept the future diversion of up to 18 cfs.
This design is consistent with the two Nelson Place/Longacres Way
drainage studies described in the Background section above.
33
' The proposed storm drain project will also install an elastomeric
backwater valve on the end of the existing outlet to Springbrook Creek.
This will prevent discharge of flow from the creek to Basin No. 1 during
periods of high creek elevations. Without a backwater valve the flooding
would be made worse since backflow in the pipeline would be much
' greater than what could naturally via overland flow.
As mentioned above, the maximum capacity of the proposed storm drain,
' without ponding upstream of the BNRR tracks, will be 45.0 cfs. When the
elevation of Springbrook Creek rises past elevation 6.45 (NGVD) the
pipeline will become backwatered. Maximum capacity of the pipeline will
reduce when the creek rises past elevation 6.45, again assuming no
ponding upstream of the BNRR tracks. The pipe rated capacity will vary
as follows, also see Figure 20. As the creek water surface increases the
t pipeline hydraulic grade line (HGL) will remain at 0.1% until the upstream
HGL elevation reaches 13.0. Elevation 13.0 is the lowest existing ground
surface elevation upstream of the BNRR tracks, and therefore is the
' maximum allowable upstream HGL elevation without ponding. After the
upstream HGL elevation of 13.0 is reached, the HGL will become flatter
as the creek elevation increases, thereby reducing the pipeline rated
' capacity. When the creek elevation reaches 13.0 the HGL will be flat and
the pipeline will not transport flow. Runoff occurring after this point will
begin to pond upstream of the tracks. If there is sufficient volume of
' runoff to raise the water surface upstream of the tracks to above 13.0, the
pipe will once again transport flow. With existing topography, there is a
' large expanse of area at elevation 13.0 so a tremendous quantity of runoff
would be required to raise the water surface elevation. For practical
purposes it can be said that the pipeline will not transport flow when the
' creek is at or above elevation 13.0. When the creek is above elevation
13.0, as it would be during a 100-year 24-hour event, and the upstream
water surface elevation is at 13.0, the backwater valve will be closed thus
' preventing transport of flow. Previously referenced reports recommend
raising the ground surface elevation upstream of the BNRR tracks to
elevation 15.0. When this is done, the above discussion will apply to
' elevation 15.0 instead of 13.0.
34
Vill. OTHER PERMITS
' The following is a list of government approvals or permits which may be
required.
tFederal:
' 0 404(s) (Corps of Engineers):
- Inwater Construction
- Wetlands Modification
' Letter of Ma Revision FEMA 100-Year Flood lain Designation)
• P ( ) ( P 9 )
' State of Washington:
' Department of Natural Resources: Ground Water Removal Permit
• Department of Fisheries: Hydraulics Permit
• Department of Ecology:
' - State Water Quality Certification (Only if Corps Permit Required)
- Waste Discharge Permit (Only if METRO Effluent Used for Irrigation)
- NPDES Permit
- Prevention of Significant Deterioration (of Air Quality) (PSD)
Approval
' Puget Sound Air Pollution Control Agency
• Notice and Approval of Construction of New Air Contaminant
Source(s); Registration of Air Contaminant Source(s)
' Washington State Department of Transportation (WSDOT)
Hydraulics
Permit
' City of Renton:
' Demolition Permit
• Shoreline Substantial Development Permit
' Site Plan Approval
• Clearing and Grading Permits
• Utility Permit
' Building Permits
• Sewer Hookup Permit
• Conditional Use Permit
35
' IX. FLOODPLAIN & GROUND WATER CONCERNS
' A. Existing Floodplain:
The existing floodplain for elevation 16.4 is detailed in Figure 9 and the
actual site survey conditions are shown in Figure 8. The existing
floodplain has initial storage at elevation 9.0 and has approximately 89
' acre-feet of storage at elevation 16.4, however, some of that storage is
not connected with the sill that would allow flow into the site. Therefore
the actual floodplain storage is approximately 59 acre-feet. This is
' detailed in Figure 25.
The existing outlet culvert has a tide gate that prevents inflow to the site.
However, the site has an existing sill located approximately over the outlet
culvert that allows flow into the site when the stream elevation exceeds
elevation 15.0. The area of the sill is approximately 71 square feet. This
' will allow a maximum of 475 cfs into the site. This flow was analyzed
considering that the flow within Springbrook Creek was just past its peak
' and starting to drop. This amount of flow would inundate the entire site
flooding all connected areas to elevation 16.4 even without any storm
water storage at the time of flooding.
' B. Proposed Floodplain:
' The proposed flood plain storage is detailed in Figure 25, and shows
115 acre-feet of storage at elevation 16.0. Significant storage occurs at
stages starting at elevation 8.5, and all of the storage is connected to the
' proposed sill.
The proposed outlet pipe retains the flood gate, changing the gate type to
' a Tideflex check valve. The proposed sill is located at the southeastern
end of the outlet stream. Since the inflow would now be flowing over a sill
with significantly lower elevations on the downstream (for overflow from
' Springbrook Creek conditions) side we are providing a bioengineered
slope in this area to prevent erosion. The sill is increased in size to
230 square feet, and accommodates approximately twice the flow. When
a
100 year storm flow occurs on the stream the site is flooded to elevation
16.4, however, additional storage on the site is used by the stream
' compared to existing conditions. In addition, if the pre-development sill
dimensions and areas are retained and combined with a 50 year storm on
' the site and a 100 year storm on Springbrook Creek the maximum
elevation achieved would be 15.2 feet. By expanding the sill dimensions
' 36
allows additional storage on the site of approximately 20 acre-feet and
allows flooding to elevation 16.4.
' C. Ground Water Influence
The existing ground water elevations on the site vary from location to
location. These elevations are shown in Appendix J. The existing soils
on the site have the following typical soil moisture characteristics (as
revealed in testing by Soil and Plant Laboratory, Bellevue)
Water Holding
' Infiltration Capacity
Soil Type Rate (In/Hr) (In. H2O/Ft. Soil)
Sandy loam 0.50 2.2
Silt loam 0.33 3.0
' Clay loam 0.25 3.4
' With the low permeability soils typical of this site the Geotechnical
Engineer has estimated that the maximum inflow to the lake from the
' ground water system will be on the order of 300 GPM, or 0.67 CFS.
The ground water regime at this site consists of an upper perched
' acquifer and a lower capped aquifer starting at elevation -1.5 that has a
slight artesian pressure. The proposal is to excavate the lake while
keeping the cap on the underlying aquifer. The upper perched aquifer
' should not be significantly altered as the existing site has channels that
run throughout the site at elevations approaching the proposed surface
water elevation of the lake. We have proposed a test lake to allow further
' investigation of the interaction between the lake and the ground water
regime.
1
37
' X. TEMPORARY SEDIMENTATION/EROSION CONTROL PLAN
' A. Sedimentation/Erosion Control Plan Initial Implementation:
' A temporary erosion and sedimentation control plan will be developed
which will include the following actions, many of which are taken directly
from City of Renton construction plan regulations concerning
erosion/sedimentation control. Additionally, requirements deemed
applicable from the King County Surface Water Design Manual are
included:
' All limits of clearing and areas of vegetation preservation as
prescribed in the plan shall be clearly flagged in the field and
' observed during construction.
• The Contractor shall install a temporary chain link fence to protect
' wetlands, sensitive areas and to prevent unauthorized site access.
' The Contractor shall install a filter fabric fence on the construction
side of the temporary chain link fence to prevent surface water from
leaving the construction site except at desired outfall points. Filter
' fabric fences shall be inspected immediately after each rainfall and
at least daily during prolonged rainfall. Any required repairs shall be
made immediately.
' 0 The Contractor shall excavate temporary erosion/sedimentation
control (ESC) ponds within prescribed limits prior to any demolition
' or site work activities within the construction area.
Demolition, clearing, excavation and grading may not progress to an
' area greater than 10 acres contributory to any one ESC pond or
3 acres contributory to any one ESC trap, until additional ponds have
been established.
' 0 Drainage swales and ditches shall be constructed to direct runoff
from all disturbed areas into ESC facilities.
' 38
tMost construction phases will allow ESC ponds to drain, via outlet
control structures, to a larger permanent detention pond. When this
' is not feasible, detention will be provided by an oversized ESC pond
system.
' All ponds shall have 3:1 sideslopes and 10-foot-wide, 8:1 sloped
maintenance ramps.
All rough grading slopes shall be graded to drain toward an ESC
facility. Any stockpiles of earthen materials left for more than three
days (including preload materials) shall be covered with 6 mil
' polyvinyl sheeting to prevent erosion.
• During the time period of November 1 through March 31, all project
' disturbed soil areas greater than 5,000 square feet that are to be left
unworked for more than 12 hours shall be temporarily covered with
6 mil polyvinyl sheeting, mulch, or sodding. Sheeting shall be "toed-
in" at the top of slopes 2 feet in order to prevent surface water flow
beneath the sheets.
' 0 In any area which has been stripped of vegetation and where no
further work is anticipated for a period of 30 days or more, all
' disturbed areas must be immediately stabilized with mulching, grass
planting or other approved erosion control treatment applicable to
the time of year in question. Grass seeding alone will be acceptable
only during the month of April through September, inclusive.
Seeding may proceed, but must be augmented with mulching,
netting, or other treatment approved by the City of Renton, outside
' the specified time period.
• The Contractor shall utilize existing roads for construction traffic
wherever possible. Any potholes or mudholes shall be filled with
coarse rock to prevent erosion/sedimentation. The Contractor shall
be required to provide a coarse rock overlay for any roads required
' off of existing established traffic areas. Rock protected construction
entrances are anticipated at four other points where existing ground
is less resistant to erosion.
' 39
' The Contractor shall confine operation at the site to the areas
currently being worked. At the completion of the work, the
Contractor shall remove all potential blockages from the storm
drainage system, such as grit, leaves, and associated materials.
Existing channels, drain pipes and catch basins adjacent to or
' impacted by the project shall be cleaned with materials disposed of
as indicated by the Owner's Representative.
B. Sedimentation/Erosion Control Plan for Construction:
An erosion and sedimentation control plan will be developed for all
' construction tasks, which will include the following actions, many of which
are taken directly from City of Renton construction plan regulations
concerning erosion/sedimentation control. Additionally, requirements
' deemed applicable from the King County Surface Water Design Manual
are included:
' 0 All limits of clearing and areas of vegetation preservation as
prescribed in the plan shall be clearly flagged in the field and
' observed during construction.
• The Contractor shall install a temporary chain link fence to protect
wetlands, sensitive areas and to prevent unauthorized site access.
The Contractor shall install a filter fabric fence on the construction
' side of the temporary chain link fence to prevent surface water from
leaving the construction site except at desired outfall points. Filter
fabric fences shall be inspected immediately after each rainfall and
' at least daily during prolonged rainfall. Any required repairs shall be
made immediately.
' The Contractor shall excavate temporary erosion/sedimentation
control (ESC) ponds within prescribed limits prior to any demolition
or site work activities within the construction area.
• Demolition, clearing, excavation and grading may not progress to an
area greater than 10 acres contributory to any one ESC pond or
' 3 acres contributing to any one ESC trap, until additional facilities
have been established. Calculations for the sizing of ESC traps are
presented in Appendix L.
' Drainage swales and ditches shall be constructed to direct runoff
' from all disturbed areas into ESC facilities.
' 40
' Most construction phases will allow ESC facilities to drain to a larger
permanent detention pond. When this is not feasible, detention will
be provided by an oversized ESC pond system.
• All ponds shall have 3:1 sideslopes and 10-foot-wide, 8:1 sloped
' maintenance ramps.
All rough grading slopes shall be graded to drain toward an ESC
facility. Any stockpiles of earthen materials (including preload
materials) shall be covered with 6 mil polyvinyl sheeting to prevent
erosion.
' 0 During the time period of November 1 through March 31, all project
disturbed soil areas greater than 5,000 square feet that are to be left
' unworked for more than 12 hours shall be temporarily covered with
6 mil polyvinyl sheeting, mulch, or sodding. Sheeting shall be "toed-
in" at the top of slopes 2 feet in order to prevent surface water flow
' beneath the sheets.
In any area which has been stripped of vegetation and where no
' further work is anticipated for a period of 30 days or more, all
disturbed areas must be immediately stabilized with mulching, grass
planting or other approved erosion control treatment applicable to
' the time of year in question. Grass seeding alone will be acceptable
only during the month of April through September, inclusive.
Seeding may proceed, but must be augmented with mulching,
' netting, or other treatment approved by the City of Renton, outside
the specified time period.
' 0 The Contractor shall utilize existing roads for construction traffic
wherever possible. Any potholes or mudholes shall be filled with
' coarse rock to prevent erosion/sedimentation. The Contractor shall
be required to provide a coarse rock overlay for any roads required
off of existing established traffic areas. Rock protected construction
' entrances are planned at four other points where existing ground is
less resistant to erosion.
' 0 The Contractor shall confine operation at the site to the areas
currently being worked. At the completion of the work, the
Contractor shall remove all potential blockages from the storm
' drainage system, such as grit, leaves, and associated materials.
Existing channels, drain pipes and catch basins adjacent to or
impacted by the project shall be cleaned with materials disposed of
' as indicated by the Owner's Representative.
' 41
r
rXI. RETENTION/DETENTION FACILITY SUMMARY SHEET
rFigure 21 shows the existing and post-development storage volumes, inflow
rates and outflow rates. Figure 22 also contains a summary table which
compares existing and post-development outflow rates and volume changes.
The data illustrates that post-development outflows are dramatically smaller
(38% to 49%) than pre-development outflows. The volume of storage provided
ris much greater for post-development conditions than for pre-development.
Figure 23 shows the relationship between peak discharge and recurrence event
rfor pre- and post-development conditions.
Figure 24 shows how the peak outflow rate varies as the stage of the storage
rchanges for pre- and post-development conditions.
Figure 25 illustrates the storage volume available at different stages for pre- and
rpost-development conditions.
Figure 26 shows the flow capacity of the flood sills as a function of storage. This
ris the rate at which water can enter the site from Springbrook Creek during high
creek water elevations.
rFigure 21-26 graphically shows the outflow rate reductions and storage volume
increases that post-development improvements offer.
rFigures 27 - 30 contain pre-development water quality data derived from
samples taken from Springbrook Creek and the site. This information shows the
r relatively poor water quality of the creek. The on-site retention/detention and
biofiltration system will improve the quality of runoff leaving the CSTC site and
will help move in the direction of improving Springbrook Creek water quality.
r
r
r
r
r
r
r42
Dr. Horner analyzed the performance of the CSTC site storm water system on
the basis of expected removal efficiencies for the following pollutants: total
suspended solids (TSS), total phosphorus (TP), zinc (Zn), lead (Pb) and copper
(Cu). The table below summarizes King County Surface Water Design Manual
code requirements versus expected removal efficiencies:
' Pollutant Kinq County Requirement Expected CSTC Removal
' TSS 67% - 87% 99%
TIP 32% 61%
Zn 48% - 68% 65% - 73%
' Pb 67% - 87% 95% - 96%
Cu 48% - 68% 65% - 73%
t
' 43
' XII. MAINTENANCE AND OPERATIONS MANUAL
' A. Construction Equipment Maintenance:
' The Contractor shall be required to do any major equipment maintenance
at a location remote from the project site. The project site can be used for
daily maintenance activities to ensure proper operation of the equipment
' and to ensure that the equipment is environmentally safe. Periodic oil
changes and similar activities on heavy equipment that cannot leave the
project site without being hauled on a trailer or truck can be accomplished
' on the project site provided that the work is performed in a designated
area of the Contractor's storage yard, and that all waste oil and
contaminated soil is removed from the site and disposed of in accordance
1 with applicable regulations.
B. Incident Control and Reporting During Construction Activities:
1. Fire or Explosion:
tEquipment: The Contractor shall be required to keep the
appropriate fire-fighting devices, as specified by the City of Renton
' Fire Department, on hand for fighting any fires at the site.
Response:
• Call 911 to report the incident and request emergency
assistance.
' Immediately notify the Owner's representative.
• Stay clear of the area and keep all others clear.
• Direct Fire Department personnel to the site and provide
tinformation regarding facility contents, etc. as requested.
1
' 44
' 2. Small Leaks/Small Spills:
Equipment: The Contractor shall keep on hand at all times during
construction suitable types and quantities of materials such as
absorbent materials and containers for containing and recovering
' small spills.
Response:
• By appropriate measures limit the size and site of a small leak
or spill. If a container is leaking, place it in an approved
' container and clean up the spill using the appropriate
materials.
' 0 Contact the Owner's Representative
• Call Boeing Security/Fire Protection at 655-7700.
Owner's Representative
• The O p entative shall notify Boeing
' Environmental Services explaining the extent and content of
the spill.
' 3. Large Spills on the Ground:
Equipment: The Contractor shall keep on hand at all times during
construction suitable types and quantities of materials to contain a
large (typically more than a quart of hazardous material) spill.
' Response:
• Contain the flow of material to the extent possible.
' 0 Contact the Owner's Representative
' 0 Keep all others away from the spill site.
• Call Boeing Security/Fire Protection at 655-7700.
• The Owner's Representative shall notify Boeing
Environmental Services explaining the extent and content of
the spill.
' 45
' 4. Large Spill that Reaches Water:
' Equipment: The Contractor shall keep on hand at all times during
construction suitable types and quantities of materials to contain a
large spill.
Response:
' Stop the spill at its source.
• Contain the flow of material to the extent possible.
• Contact the Owner's Representative
' Keep all others away from the spill site.
• Call 911 and explain circumstances.
' Call Boeing Security/Fire/Fire Protection at 655-7700.
• 9 Y
' The Owner's Representative shall notify Boeing
Environmental Services explaining the extent and content of
' the spill.
5. Posting:
Emergency response procedures, provisions of WAC 296-62-3000,
the above contact names and phone numbers, as well as the
' location of emergency equipment will be posted at the following
locations:
' 0 At all site offices and shops.
• On all project bulletin boards.
' 0 On any Contractor owned, subcontracted, or leased
equipment servicing equipment.
' 46
' C. Best Management Practices During Construction Activities:
' The Contractor shall include the latest Best Management Practices (BMP)
in his control of pollutants program. All provisions of the
Erosion/Sedimentation Control program shall be strictly adhered to at all
times. The Contractor shall be required to inspect all devices used for
controlling storm water quantity and quality on a regular basis and
especially after each storm. If any of the devices are found not to be
working the Contractor shall take appropriate measures.
All of the materials used in construction and demolition as well as both
' mobile and stationary equipment shall be considered as potential waste
generation materials. The majority of these wastes are generated at the
construction site. Potential waste includes solvents, paints, batteries,
strong acid and alkaline wastes, and paint and varnish removers are all
considered dangerous wastes and must be disposed of in accordance
with standards listed on the individual containers. Best Management
' Practices as published in the City of Seattle "Water Quality, Best
Management Practices Manual", shall be used as follows:
Washing or steam cleaning of vehicles shall incorporate BMP 1.20.
' 0 Transfer of fuel and other engine fluids shall comply with BMP 1.30.
Above ground storage tanks shall incorporate BMP 1.40.
• Dangerous wastes shall be segregated and disposed as required by
the Washington State Department of Ecology (RA in Part V of the
' referenced document).
• Signs shall be painted on storm drain inlets to indicate that they are
' not to receive liquid or solid wastes.
' 47
' D. Employee Training for Construction Contractors:
' The Contractor shall conduct an orientation with all employees,
subcontractors, and subcontractors' employees prior to their working on
the CSTC Site Development project. The orientations will provide
' information relating to the requirements of the contract regarding
erosion/sedimentation control, proper handling of all types of hazardous
or dangerous wastes typically generated on a construction site and any
' particular to this construct site.
E. Proposed Measures to Control Pollutants in Stone Water Discharges
After Construction:
1. Storm Water Drainage System:
' The proposed site storm waters stem as detailed in Figure 6
Y 9
outlets to Springbrook Creek at two outfall points as noted below:
' The first outlet point will drain the portion of the site r• p p e previously
' drained by the 36" Culvert, with a tide gate located
approximately 450 feet south of the SW 16th Street Bridge.
This system is directly connected to Springbrook Creek but
' will flow through a three-stage wetpond (lake) system. A
natural stream corridor with plantings within and along the
stream will be used with a final connection to Springbrook
Creek through a culvert with tide gate, located 200 feet south
of the existing location with the first culvert filled with a
controlled density fill material.
• The second outlet point will drain the area of the site north of
SW 16th Street. Runoff will flow through a three pond
wetpond system at that location prior to leaving the site to flow
in the existing drainage pathway South of 1-405.
48
1
1 2. Parking Lots:
1 Parking lots shall be maintained on a regular basis, build-up of
debris within the catch basins shall be monitored and cleaned prior
to the fall-winter storm season annually or at other intervals as
1 required to provide adequate sediment settling area. The parking
lots shall be swept at appropriate intervals to remove debris.
However, this interval shall not exceed three (3) times per year
1 unless debris build-up requires sweeping, as unnecessary stirring
of sediment will occur.
1 3. Utilities and Communications Buildings:
All floor drains within the buildings shall be connected to the
1 sanitary sewer system. Any dangerous or hazardous wastes shall
be handled in accordance with the Department of Ecology's
guidelines presented in the City of Seattle's "Water Quality Best
1 Management Practice Manual" section V. All drainage shall flow
through a biofiltration swale prior to leaving the site.
1 4. Customer Services Training Center(CSTC) Building:
1 All floor drains within the building shall be connected to the
sanitary sewer system. Any dangerous or hazardous wastes shall
be handled in accordance with the Department of Ecology's
1 guidelines presented in the City of Seattle's "Water Quality Best
Management Practice Manual" section V. Roof drains shall be
routed directly to the biofiltration channel downstream of the large
1 lake.
5. Landscape Areas:
1 All landscaped areas shall be maintained to prevent erosion.
Grass areas shall be maintained to allow a high degree of
1 roughness to encourage sheet flow and filtration. The grass shall
also be kept aerated to allow maximum infiltration. Caution shall
be used to avoid over fertilization of landscape areas.
i
1
1
1
1 49
t6. Site Utilities:
' All site utility drains shall be connected to the storm drainage
system, or sanitary sewer system as deemed appropriate (i.e. if
chilled or hot water without additives to storm drain, if glycol to
' sanitary sewer system).
F. Incident Control and Reporting After Construction:
1. Fire or Explosion:
Equipment: The Maintenance staff shall have, at the Utilities
Building, the appropriate fire-fighting devices as specified by the
City of Renton's Fire Department on hand for fighting any fires at
' the site.
' Response:
• Call 911 to report the incident and request emergency
assistance.
• Immediately notify the Boeing Security/Fire Protection at
' 655-7700.
• Stay clear of the area and keep all others clear.
• Direct Fire Department personnel to the site and provide
information regarding facility contents, etc. as requested.
50
2. Small Leaks/Small Spills:
Equipment: The Maintenance staff shall keep on hand at all times
suitable types and quantities of materials such as absorbent
materials and containers for containing and recovering small spills.
Response:
' • By appropriate measures limit the size and site of a small leak
or spill. If a container is leaking, place it in an approved
container and clean up the spill using the appropriate
materials.
• Call Boeing Security/Fire Protection at 655-7700.
' • Call Boeing Environmental Services section explaining the
extent and content of the spill.
' 3. S Large ills on the Ground:
P
' Equipment: The Maintenance staff shall keep on hand at all times
during construction suitable types and quantities of materials to
contain a large spill.
Response:
' 0 Stop the spill if possible.
' 0 Contain the flow of material to the extent possible.
• Keep all others away from the spill site.
• Call Boeing Security/Fire Protection at 655-7700.
• Call Boeing Environmental Services explaining the extent and
content of the spill.
' 51
' 4. Large Spill that Reaches Water:
' Equipment: The maintenance staff shall keep on hand at all times
suitable types and quantities of materials to contain a large spill.
' Response:
• Stop the spill if possible.
' Contain the flow of material to the extent possible.
• Keep all others away from the spill site.
• Call Boeing Security/Fire Protection at 655-7700.
' Call 911 and explain extent and content of the spill.
' Call Boeing Environmental Services explaining the extent and
content of the spill.
' S. Posting:
' Emergency response procedures, provisions of WAC 296-62-3000,
the above contact names and phone numbers, as well as the
location of emergency equipment will be posted at the following
' locations:
• At all janitorial closets in offices and shops.
' 0 On all bulletin boards in the Utilities Building.
• On any maintenance equipment used for servicing equipment
or machinery.
' 52
rG. Description of Applicable State and Local Water Management
Controls:
' The City of Renton has an ordinance (Chapter 22 Title IV RMC) in effect
relating to storm water management. The ordinance references the King
' County Surface Water Design Manual as the applicable local water
management control. This manual is more strict than the State standards,
or the Puget Sound Water Quality Manual.
H. Employee Training:
' The maintenance department shall conduct an orientation with all
employees, subcontractors, and subcontractors employees prior to their
working on the CSTC site. The orientations will provide information
t relating to the proper handling of all types of hazardous or dangerous
wastes typically generated in the CSTC, Utilities Building or
Communications Building and any particular to this site. The response
' procedures detailed above shall also be presented .
' I. Best Management Practice:
The best description for the CSTC site would be that this is a "Services"
' site. The BMP's from the City of Seattle "Water Quality Best Management
Practice Manual are as follows:
• Source Control BMP 1.30 Loading and Unloading of Liquids.
This applies to the loading of fuel products for the emergency generators
' located in the Utilities Building. All loading dock doors shall employ door
skirts. Drainage from the loading dock area shall be discharged to the
sanitary sewer system. The maintenance department shall retain on-site
' the appropriate materials for rapid cleanup.
• Source Control BMP 1.80 Emergency Spill Cleanup Plans.
' This applies to the requirement to have an emergency spill cleanup plan.
' Signs shall be painted on storm drain inlets to indicate that they are
not to receive liquid or solid wastes.
' Storm water-Treatment BMP's.
53
' The plan for the storm water treatment at the CSTC site implements the
following devices for water quality and quantity control. Over 40% of the
site will be covered by landscaping, and the landscaping planted
extensively with trees. Trees have a higher uptake of water than other
ground cover. The landscape is planned to provide a rougher edge (of
' wetland species) as water surfaces are approached, providing buffering of
water flowing from landscaped surfaces. All paved parking lots will have
catch basins of type IP (this type of catch basin has a deeper sump for
' catching sediments). The outlet will include an inverted elbow to prevent
floatables from going down the storm drainage system. From the catch
basins, the storm water flow is sent to a sedimentation control wet vault.
' A control manhole is placed just prior to entering the wet vault to allow
high volume flows to bypass the wet vault and flow directly to the second
stage pond to prevent these high flows from resuspending the sediments
' contained in the wet vault. Following the wet vault is the second stage
wetpond. Roof drainage is routed around the wet vault and tied directly to
the biofiltration channel leaving the lake. This is a pond designed in
accordance with the King County Surface Water Design Manual, with
plantings to control water quality. From this stage the flow passes into a
third stage wetpond to control water quality. Most of the site drains to the
' central drainage basin. This basin is dominated by a large volume lake
that provides detention greater than that required by the Manual. From
the third stage wetpond the flow exits out through an outlet structure,
through a stream with plantings in and alongside.
' Storm water-Treatment BMP 2.10 Oil/Water Separation.
Type 1 P catch basins with inverted elbows are used in all parking lots to
' limit the amount of oil entering the system. The wet vaults will also trap
oil. Due to this dual gravity oil/water separation scheme, at a meeting
held in July, the City of Renton decided to use coalescing plate
' technology. However, the outflow water quality will be closely monitored
and, if the oils exceed the limits established, coalescing plates separators
will be added to the system.
• Storm water-Treatment BMP 2.30 Constructed Wetlands.
' 54
' The three-stage pond system is used for all but roof runoff, which
bypasses the sediment vaults. The ponds are connected by swales and
' portions of the ponds (especially the edges) will become constructed
wetlands.
Storm water-Treatment BMP 2.40 Wet Settling Basins.
The wet vaults will act as wet settling basins.
Storm water-Treatment BMP 2.50 Vegetated Biofilter
' Grass-lined swales are used wherever possible on the site. However,
due to the extreme flatness of the site and the low hydraulic slope, swales
were not feasible within most parts of the system.
' 55