HomeMy WebLinkAboutPre-Comments_Tranport_Stormwater_09-151 QT - Ron StrakaPUBLIC WORKS DEPARTMENT City of
M E M O R A N D U M
DATE: September 14, 2009 [h 1 a Zoog
TO: Arneta Henninger, Plan Reviewer
FROM: Ronald J. Straka, Surface Water Utility Supervisor
SUBJECT: QUENDALL TERMINALS STORMWATER REQUIREMENTS
Please see my comments below regarding the drainage report and plans, dated August
271 2009, for Quendall Terminals.
1. The project shall be required to comply with the 2009 King County Surface Water
Design Manual (KCSWDM) standards as a condition of SEPA.
2. A compete TIR for the project site will be required with submittal of the civil
engineering plans for the site that includes all information required by the 2009
King County Surface Water Design Manual. This includes information related to
satisfying all core requirements and applicable special requirements in the 2009
KCSWDM.
3. The proposed projects must submit an offsite analysis report that assesses
potential offsite drainage and water quality impacts associated with
development of the project site and proposes appropriate mitigation of those
impacts.
4. The report must include a KCRTS printout of all land use input values for pre- and
post -developed impervious and pervious areas. The report should also include a
basin summary table for the existing condition and developed condition land
use. The basin summary table should identify the wetlands.
5. The wetland area needs to be included in the pre- and post -developed time
series analysis.
6. Since the project will result in more than 5,000 square feet of new impervious
surfaceI the project must comply with section 1.2.3 of the 2009 KCSWDM Flow
Control. The direct discharge exemption may apply to the project if it meets all
of the following criteria:
a. The flowpath from the project site discharge point to the edge of the
100 -year floodplain of the major receiving water will be no longer than a
quarter mile.
b. The conveyance system
between
the
project
site and the major receiving
water will extend to the
ordinary
high
water
mark, and will be comprised
Henninger/Quendall Terminal Stormwater Requirements
Page 2 of 2
September 14, 2009
of manmade conveyance elements (pipes, ditches, etc.) and will be within
public right-of-way or a public or private drainage easement
c. The conveyance system will have adequate capacity per Core
Requirement #4, Conveyance System, for the entire contributing
drainage area, assuming build -out conditions to current zoning for the
equivalent area portion and existing conditions for the remaining area
d. The conveyance system will be adequately stabilized to prevent erosion,
assuming the same basin conditions as assumed in Criteria (c) above.
NOTE: The major receiving waters do not include wetlands.
The engineer proposes to discharge runofffrom the north and west portions of
the site into the wetlands located at the north and west corners of the site. The
engineer needs to conduct an analysis of the wetland to determine the existing
hydrology, including the hydroperiod, and base the recharge on that analysis.
Typically, the wetland report would include a recommendation from the
biologist as to the proper recharge rate.
8. The proposed roadway improvements shall betaken into consideration when
calculating the post development site condition and sizing the water quality and
flow control facilities, if required.
9. The project will be required to provide enhanced water quality treatment per
section 1.2.8.1. Application of the Enhanced Basic Water Quality menu may be
waived for treatment of any runoff that is discharged entirely by pipe all the way
to the ordinary high water mark to the major receiving waters, listed on pages 1-
37 of the 2009 KCSWDM. Enhanced Basic Water Quality treatment is required
for any discharges to the existing wetlands on site.
10. Does the project have an expected average daily traffic (ADT) count of 100 or
more vehicles per square feet of gross building area, per section 1.2.8.1 of the
2009 KCSWDM? If yes, the project must provide oil control in addition to any
other water quality facility required.
If you have any questions contact Hebe Bernardo, Surface Water Utility Engineer
(x7264).
cc: Lys Hornsby, Utility Systems Director
Kayren Kittrick, Development Engineering Supervisor
Chip Vincent, Planning Director
Neil Watts, Development Services Director
h:\file sys\swp -surface water projects\swp 27 -surface water projects (plan review)\quendall terminals\first review.doc\HBaw
1. Introduction
Quendall Terminals is a proposed mixed-use development in Renton,
Washington. The development
ncludes five stories of
residential or
office space above two levels of
above -grade parking or retail and
restaurant space. The
development
project anticipates entitlement of the following:
Table 1-1: Proposed Development
Use
Residential
Note: All areas shown are moss buil
Quantity/Area
800 Units
Office
245,000 Square Feet
Retail
21,600 Square Feet
Restaurant
9,000 Square Feet
Parking
2,215 Spaces
ding areas (GBA).
The project site is located west of Interstate 405 near the northern city limits of Renton. The site is
bounded by the Seahawks Training Facility to the north, BNSF railroad tracks to the east, and the
Barbee Mill residential community to the south. Ripley Lane is located east of the BNSF railroad
tracks and Lake Washington Boulevard is located southeast of the project site. See Figure 1 in the
Appendix for the site location.
This report is intended to support City of Renton entitlement processingfor Master Site Plan Approval.
The scope of this report is to address the sanitary sewer system for the proposed development.
Design criteria will be outlined and a sewerage approach will be evaluated.
2. Predeveloped Site Conditions
The existing site is vacant and is the former location of a log sort
ing and storage yard. The main site is
approximately 20.30 acres in size, and the parcel east of the main project site across Ripley Lane
North is approximately 1.15 acres in size. An existing 12 -inch sanitary sewer main runs from south to
north along the east side of the site within a 60 -foot roadway and utility easement. The invert
elevation of the existing sewer pipe is generally 10 to 13 feet below the existing ground surface. The
existing Baxter Lift Station serves Quendall Terminals as well as the Seahawks Training Facility to the
north and Barbee Mill to the South. There are no other sewers located on the project site. An 84 -inch
Metro sewer main is located approximately 100 feet east of the site's east property line. See Figure 2
in the Appendix for existing site conditions.
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3. Developed Site Conditions
The proposed site improvements include amixed-use development consisting of residential, office,
retail, and restaurant uses, as well as new public and private streets and parking. Sewer mains will be
constructed within the proposed public streets Sewage from the buildings will discharge to the new
sewer mains vla slde sewers. The new sewer mains will discharge to the existing 12 -inch sewer main
at the east side of the project site at a new manhole constructed over the existing main. No
improvements are planned for the 1.15 -acre parcel east of Ripley Lane. See Figures 3 and 4 in the
Appendix for proposed site plan and proposed sewer plan, respectively.
4. Basis of Design
An on-site sanitary sewer system will collect and convey flows from Quendall Terminals. Adjacent sites
are already developed and served by separate sanitary sewer systems. This report has utilized
programmed project areas and Department of Ecology (DOE) criteria to establish projected sewer flows
without provisions for future growth or connections. See Figures 3 and 4 in the Appendix for proposed
site plan and proposed sewer plan, respectively.
Gross building areas have been used for this report.
An allowance of 1,100 gallons/acre/day (gpad) has been made for infiltration and inflow since the
proV osed sanitary sewer system is expected to be below seasonal high groundwater elevations.
The 1.15 acre parcel east of Ripley Lane has not been included in the infiltration calculation.
A peaking factor of 4.0 was included in the design flows. This factor should account for the
daily and
seasonal fluctuations in waste generation. Thisfactor should also mitigate the impact of the varying
flow generations for the different uses proposed with this project.
The sanitary sewer system was designed to convey the estimated peak flows by gravity to the project
discharge location at a new manhole installed on an existing City of Renton sanitary sewer pipe. The
sewer capacities were established using Manning's Equation, with an "n" factor of 0.013. Sewer lines
have been designed using the minimum slope requirements of the Washington State DOE. The pipe
slopes used in the final design and future construction documents may be greater than the minimum
slope to accommodate potential settlement, depending on the recommendation of the geotechnical
engineer.
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3. Developed Site Conditions
The proposed site improvements include amixed-use development consisting of residential, office,
retail, and restaurant uses, as well as new public and private streets and parking. Sewer mains will be
constructed within the proposed public streets Sewage from the buildings will discharge to the new
sewer mains vla slde sewers. The new sewer mains will discharge to the existing 12 -inch sewer main
at the east side of the project site at a new manhole constructed over the existing main. No
improvements are planned for the 1.15 -acre parcel east of Ripley Lane. See Figures 3 and 4 in the
Appendix for proposed site plan and proposed sewer plan, respectively.
4. Basis of Design
An on-site sanitary sewer system will collect and convey flows from Quendall Terminals. Adjacent sites
are already developed and served by separate sanitary sewer systems. This report has utilized
programmed project areas and Department of Ecology (DOE) criteria to establish projected sewer flows
without provisions for future growth or connections. See Figures 3 and 4 in the Appendix for proposed
site plan and proposed sewer plan, respectively.
Gross building areas have been used for this report.
An allowance of 1,100 gallons/acre/day (gpad) has been made for infiltration and inflow since the
proV osed sanitary sewer system is expected to be below seasonal high groundwater elevations.
The 1.15 acre parcel east of Ripley Lane has not been included in the infiltration calculation.
A peaking factor of 4.0 was included in the design flows. This factor should account for the
daily and
seasonal fluctuations in waste generation. Thisfactor should also mitigate the impact of the varying
flow generations for the different uses proposed with this project.
The sanitary sewer system was designed to convey the estimated peak flows by gravity to the project
discharge location at a new manhole installed on an existing City of Renton sanitary sewer pipe. The
sewer capacities were established using Manning's Equation, with an "n" factor of 0.013. Sewer lines
have been designed using the minimum slope requirements of the Washington State DOE. The pipe
slopes used in the final design and future construction documents may be greater than the minimum
slope to accommodate potential settlement, depending on the recommendation of the geotechnical
engineer.
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Quendall Terminals 2
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EXISTING BAXTER LIFT STATION
The Baxter Lift Station is an existing sewer lift station located at the northeast corner of the project site
within a sanitary sewer easement. The lift station was designed in 2006 and was constructed in
2009. The lift station was designed for an overall peak flow of 594 gpm for the Seahawks Training
Facility, Barbee Mill community, and the Quendall Terminals site. The lift station was designed and
constructed with the following assumptions for future development of the Quendall Terminals site:
Table 5.3: Lift Station Design Assumations for Quendall irrmi., .l"E. a,
Developable Acres
5
Tributary Area
5.0 Acres
Flow Rate
2,800 gpad
Number of Units
75
Tributary Area
3.0 Acres
Persons/Unit
2.4
Flow Rate
100 gpad
Average Sewerage Flow
22.2 gpm
Design 1/1 Rate
1,500 gpad
Peaking Factor
4
Design Sewage Flow
88.9 gpm
Design VI Flow
8.3 gpm
Total Design Flow
97.2 gpm
Total Design Flow
Q peak hourly
The sewer lift station was designed for a flow of 97.2 gpm from the Quendall project site. The
anticipated flow from the Quendall project site is 614 gpm. The sewer lift station capacity will need to
be increased by approximately 517 gpm to 1,111 gpm to accommodate development of the Quendall
Terminals site. Per discussion with the City of Renton Public Works, the existing lift station has the
ability to be modified to increase capacity by changing pump impellers and increasing the wet well
capacity. See Figure 6 in the Appendix for Baxter Lift Station design details and Figure 7 for a record
of discus0on with the City.
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• Other available options are installing larger pumps but Dave did not believe that would be necessary
as the existing pumps were specifically chosen to allow impeller modifications as they anticipated the
need for additional capacity in the future.
Fees:
Quendall has recently been assessed a capacity charge of $166k for their "fair share" of the Baxter
Pump Station. This assessment was based on 111gpm of capacity. I asked Dave if future
assessments would be required if the flows exceeded the 111 gpm. Dave indicated there would be NO
additional capacity charge assessments for the Quendall site only mechanical pump station upgrades
to increase the pump station pipacity to meet' o^qlr proposed site demand. o•5T�9
KPFF Consulting Engineers Page 2 Telephone Record November 77, 2009
Figure 7
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