22-102749-UP-Level One Downstream Storm Analysis-06-15-2022-V1
LEVEL ONE DOWNSTREAM
STORM DRAINAGE ANALYSIS
FOR
PLANT 2 RELOCATION
JUNE 9, 2022
LEVEL ONE DOWNSTREAM
STORM DRAINAGE ANALYSIS
FOR
PLANT 2 RELOCATION
A portion of the Southeast Quarter of the Southeast Quarter of Section 20,
Township 21 North, Range 4 East, of the Willamette Meridian, City of Federal Way, Washington
Prepared for: Prepared by:
35000 Pacific Hwy South LLC Apex Engineering LLC
PO Box 94176 2601 South 35th Street, Suite 200
Seattle, WA 98124-6476 Tacoma, Washington 98409
(253) 473-4494
File #35072
June 9, 2022
Project Engineer:
Gabe L. Jellison, P.E.
1
LEVEL ONE DOWNSTREAM STORM DRAINAGE ANALYSIS
Task 1. Study Area Definition and Maps
Federal Way as-built/record drawings and GIS maps were obtained for the off-site areas
and are referenced for the downstream drainage path . The site discharges to a catch
basin within Pacific Highway South to the west, which conveys the drainage to the south
where it discharges to a City regional storm facility located approximately one-quarter
mile downstream. These facilities discharge to Hylebos Creek where drainage would
flow generally to the south to a point one mile downstream. Refer to the Downstream
Drainage Path map and associated documentation in this section for additional
information.
The Federal Way Crossings commercial development is located upstream of the project
site and has separate stormwater facilities. Run-on from adjacent properties is assumed
to be negligible.
Task 2. Resource Review
The project site is located within the Hylebos Creek and Lower Puget Sound Basin Plan
area. The requirements of the Basin Plan should not be more restrictive than the
requirements of the KCSMDM and COFA.
The project is not located within a known floodplain and/or floodway per FEMA
mapping. Refer to the FEMA FIRM included as Figure 3.2.
There are no other known offsite analysis reports within the same subbasin.
There are no known erosion hazard or landslide hazard areas located on the project site
or within one mile downstream of the site per City of Federal Way critical area mapping.
There are no known wetlands on the project site, but the Hylebos wetland and creek is
located approximately one-half mile downstream of the site. Refer to Figure 3.3 for the
City of Federal Way Critical Areas Map.
Per King County GIS, there are no listed drainage complaints within one mile
downstream of the project site. One drainage complaint is listed for a parcel south of
the project site that is not within the downstream drainage path . The complaint was for
a water quality audit inspection and was closed in June 2013. Refer to Figure 3.4 for
further information.
There are no known road drainage problems within one mile downstream of the project
site.
2
NRCS’ web soil survey information was referenced for the soil mapping of the site. The
site consists of Everett-Alderwood gravelly sandy loams for the northern portion of the
site and Urban land for the southern portion of the site per the mapping.
Per King County GIS, there are no channel migration hazard areas within one mile
downstream of the project site.
The Washington State Department of Ecology’s (ECY) published Clean Water Act Section
303d list of polluted waters has identified an unnamed water body in the area of the
project site as a Category 5 water due to temperature and dissolved oxygen. The water
body is listed as unmappable and it is unclear from the available information if the
project site drains to this water body. Additionally, Hylebos Creek greater than a mile
downstream of the project is identified as a Category 5 water due to temperature,
dissolved oxygen, and bacteria. No additional requirements from these assessments
have been identified at this time. Refer to Figure 3.5 for reports of the assessed water
quality areas.
There are no known designated water quality problems, and no additional requirements
from adopted stormwater compliance plans downstream of the project site have been
identified at this time.
Task 3. Field Inspection
A Level 1 field inspection was performed on February 11, 2022. The weather was
overcast and approximately 45 degrees. The drainage path to a point more than one-
quarter mile downstream was observed. Refer to the Downstream Drainage Path Map
and associated Drainage System Table in this section for additional information.
From the field inspection, it was determined that run-on from adjacent properties can
be considered negligible. The Federal Way Crossings commercial development is located
upstream of the project site on the north and east sides and has separate stormwater
facilities that will collect runoff. Pacific Highway South to the west and South 351st
Street to the south is located downgrade of the project site.
Task 4. Drainage System Description and Problem Descriptions
The majority of the project site is proposing infiltration for water quantity control. The
western portion of the 351st Street improvements is unable to gravity flow to the onsite
storm facilities and will discharge to the existing conveyance system within Pacific
Highway South, which is the current discharge location for the existing site.
The field inspection was aided by King County GIS information and City of Federal Way
record drawings. Runoff from the site discharges to a catch basin within the
3
easternmost Pacific Highway South/State Route 99 (SR99) northbound travel lane.
Runoff would then continue generally south within 36-inch pipes for approximately 253
feet. Runoff would then continue generally south within 48-inch pipes for approximately
354 feet to a catch basin within the eastern sidewalk of SR99. Runoff would then
continue generally east within a 48-inch pipe for approximately 173 feet to a flow
splitter for a City regional stormwater facility. Runoff would then continue generally
south within 48-inch and 60-inch pipes for approximately 39 feet where it enters the
City regional stormwater facility. Runoff would continue generally south within the City
facility for approximately 650 feet to a point more than one-quarter mile downstream.
Refer to the Downstream Drainage Path Map and associated Drainage System Table in
this section for additional information.
Task 5. Mitigation of Existing or Potential Problems
No existing or potential problems within a mile downstream have been identified at this
time.
4
FIGURE 3.1 – DOWNSTREAM ANALYSIS
Hylebos Creek -- 45 degrees, overcast 9:30 AM 2/11/2022BasinSubbasin Name Subbasin Number Weather ConditionsDateDrainage Component Type, Name, and SizeDrainage Component Description Slope Existing Problems Potential Problems Observations of field inspector, resource reviewer, or residentType: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface areaDrainage basin, vegetation, cover, depth, type of sensitive area, volume+/-, %Tributary area, likelihood of problem, overflow pathways, potential impactsCatchbasinExisting 10' +/- deep cb(1)(2)None observed Sedimentation Impacts not expected1 - 2 36-inch pipe0.70(1)0 - 29 None observed Under capacity Impacts not expectedCatchbasinExisting 10' +/- deep cb(1)(2)None observed Sedimentation Impacts not expected2 - 3 36-inch pipe0.64(1)29 - 203 None observed Under capacity Impacts not expectedStorm ManholeExisting 7' +/- deep sdmh(1)(2)None observed Sedimentation Impacts not expected3 - 4 36-inch pipe0.60(1)203 - 253 None observed Under capacity Impacts not expectedCatchbasinExisting 11' +/- deep cb(1)(2)None observed Sedimentation Impacts not expected4 - 5 48-inch pipe1.66(1)253 - 494 None observed Under capacity Impacts not expectedCatchbasin Existing 11' +/- deep cbNone observed Sedimentation Impacts not expected5 - 6 48-inch pipe1.15(1)494 - 607 None observed Under capacity Impacts not expectedCatchbasin Existing 12' +/- deep cbNone observed Sedimentation Impacts not expected6 - 7 48-inch pipe0.81(1)607 - 780 None observed Under capacity Impacts not expected7 Diversion ManholeExisting 10' +/- deep cb - Flow splitter prior to regional storm facility(1)(3)None observed Sedimentation Impacts not expected7 - 8 60-inch pipe4.62(1)780 - 793 None observed Under capacity Impacts not expected8 CatchbasinExisting 17' +/- deep cb(1)(3)None observed Sedimentation Impacts not expected8 - 9 48-inch pipe0.92(1)793 - 819 None observed Under capacity Impacts not expectedPond InletInlet to existing City of Federal Way regional storm facility(1)(3)None observed Erosion/scouring Impacts not expected9 - 10 Regional pondExisting City of Federal Way regional storm facilityN/A 819 - 1469 None observed Under capacity Impacts not expectedPond outlet structureControl structure for existing City of Federal Way regional storm facility(1)(3)None observed Sedimentation Impacts not expected10 - 11 48-inch pipe0.20(1)1469 - 1520 None observed Under capacity Impacts not expectedCatchbasinExisting 5' +/- deep cb with debris cage top(1)(3)None observed Sedimentation Impacts not expected11 - 12 48-inch pipe0.37(1)1520 - 1574 None observed Under capacity Impacts not expectedCatchbasinExisting 7.5' +/- deep cb(1)(3)None observed Sedimentation Impacts not expected12 - 13 48-inch pipe0.37(1)1574 - 1672 None observed Under capacity Impacts not expectedCatchbasin Existing 7.5' +/- deep cbNone observed Sedimentation Impacts not expected13 - 14 48-inch pipe0.46(1)1672 - 1803 None observed Under capacity Impacts not expectedCatchbasin Existing 7.5' +/- deep cbNone observed Sedimentation Impacts not expected14 - 15 48-inch pipe0.37(1)1803 - 1825 None observed Under capacity Impacts not expectedPipe end Outlet to unnamed stream w/ rip rapNone observed Erosion/scouring Impacts not expectedNotes:(1) Slope/inverts per City of Federal Way Record Drawings(2) Unable to access/open structure, located within SR99 travel lane(3) Unable to access/open structure, located within fenced/locked City facility111520121574OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLEKING COUNTY SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosionPlant 2 Relocation (Job #35072) - Downstream Analysis229SymbolDistance from Site Discharge (+/-, ft)See Map1/4 mi = 1,320 ft1010146932034253549466079819780793131672141803151825
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FIGURE 3.2 – FEMA FIRM
PROJECT
SITE
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FIGURE 3.3 – CRITICAL AREAS MAP
Critical Areas!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! !!!!!!!!!!!!!!!!!!!!!! ! ! !! ! ! ! ! !! ! ! ! !! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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11th Pl S1st Av S8th Av SPavillionsCenter
CelebrationCenter
SeaTacVillage
Pal-doWorldPlaza
The Commons atFederal Way
GatewayCenter
Twin LakesVillage
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SilverLakeElem.
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BrigadoonElem.
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IllaheeMiddle School
LakotaMiddleSchool
SacajaweaMiddle School
KiloMiddleSchool
SaghalieMiddleSchool
SequoyahMiddleSchool
PublicAcademy
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ThomasJeffersonHigh School
Todd BeamerHigh School
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TotemMiddle School
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Twin LakesPark &Ride
South FederalWay Park &Ride
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Federal WayCommunityCenter
SteelLakeAnnex
CityHall
Dumas BayCentre
KnutzenTheatre
ParkLakota
SacajaweaPark
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CamelotPark
Dash PointState Park
SaghaliePark
LakeGenevaPark
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WestHylebosWetlandsPark
FiveMileLakePark
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City of Federal Way Critical Areas Map Map Date: May 2016City of Federal Way,GIS Division33325 8th Ave SFederal Way, WA 98003(253) 835-7000www.cityoffederalway.com
´
This map is accompanied by NO warranties, and is simply a graphic representation.J:\standard\reference\sensitive.mxd
KingCounty
Vicinity MapHylebos Creek
Lower Green River
Lower Puget Sound
Mill Creek
White River
Erosion Hazard Area
Landslide Hazard Areas
Wetlands (1998 City Survey)
Lakes
Streams
Drainage Basins:Critical Areas:Water Features:
Legend:
Boundaries are approximate. Remember, ADDITIONAL SENSITIVE AREAS MAY EXIST. See Map Notes below for more information.Please Note:Map Notes: Wetlands and streams were identified in a1998 City of Federal Way survey. Data for the Landslide hazard and erosion hazard areas is provided by King County. Drainage basin boundaries within city limits havebeen verified by the City of Federal Way. Basin boundaries outside of city limits are provided by King County and have not been verified by the City of Federal Way. Critical area information is provided forillustrative purposes ONLY.
Actual boundaries are subject of field verification. ADDITIONAL CRITICAL AREAS MAY EXIST. Critical areas in Pierce County are not shown. The City of Federal Wayshall not be liable for any damages due to the use or misuse of the information represented on this map. Wetlands are onlyshown in Federal Way and its Potential Annexation Area.Contact the City for an explanation of these areas and theregulations that govern them.Source: City of Federal Way, King County
0 0.5 10.25
Miles
Scale:
50 Acres
5
20
47°15'5.46831"N122°25'3.78156"W47°21'46.42899"N
122°25'3.78156"W47°21'46.42899"N
122°16'19.25508"W47°15'5.46831"N 122°16'19.25508"WA B C D E F
A B C D E F
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FIGURE 3.4 – DRAINAGE COMPLAINTS
K in g
Date : 3/18/20 22 Notes:
±The informati on included on this map has been c ompil ed by King County s taff from a variety of sources and issubject to change without notice. King County makes no repr esentations or warr anties, ex press or implied,as to accurac y, completeness, timel iness, or rights to the us e of such information. T hi s doc ument i s not intendedfor use as a s urvey product. Ki ng County shall not be l iable for any general , special, indirect, incidental, orconsequential damages i ncl uding, but not li mited to, lost revenues or los t profits resulting from the us e or mi sus eof the information contained on this map. Any sale of thi s map or informati on on this map is prohi bited exc ept bywritten permi ss i on of Ki ng County.
King C ou nty iMap
PROJECT
SITE
Figure 3.4: Downstream Drainage Complaints
PLANT 2 RELOCATION
Apex Job #35072
#Parcel Address Type Problem Date Closed Comments
2013-0132 2021049059 1393 S 351st St WQAL WQAI 6/11/2013 N/A
14
FIGURE 3.5 – ASSESSED WATER QUALITY AREAS
Fed Way
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS,FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, EsriJapan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and
March 17, 2022
0 0.5 10.25Miles
K
Assessed Water/SedimentWater
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
Sediment
Category 5 - 303d
Category 4C
Category 4B
Category 4A
Category 2
Category 1
PROJECT
SITE