MGP Stormwater Report.pdfSTOR'MWATER REPORT cffycoi
New Shops Building RESUB,
21900 & 21904 Hwy 99
UOTOINOI
Prepared By.
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10 135 5E Sunnyside Road, Suite 200
Clackamas, OR 97015
April 2015
Revised: July 23, 2015
Updated November 12, 2015
Bryan Dickerson, P.E.
NEW 'I (;J ?015
CITY f F,'
IMYVATE
Section
Page
Section A - Project Overview..... ..... ............ ............... ........... ................ ....
Introduction......................................... ............. ____ ........ ,....................... ........... ..........
3
ExistingConditions.......................................................................... . .... .......................3
RedevelopedConditions ............................. ,............. ...,.,....................... ..... ..,,..................... 4
Section B -Minimum Requirements ......................................... ...... ......................,.......,..4
Minimum Requirement # 1: Preparation of Stormwater Site Plans........................................5
Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan (SWPPP) .....5
Minimum Requirement #3: Source Control of Pollution ....... .............. ......... ......................
..5
Minimum Requirement #4: Preservation of Natural Drainage Systems & Outfalls.................6
Minimum Requirement #5: On-site Stormwater Management.........................................„...6
Minimum Requirement #6: Runoff Treatment.........................................:...........„„,....,„...,..6
Minimum Requirement #7: Flow Control ........................................................................„,.6
Minimum Requirement #8: Wetlands Protection .................................................. ........ ..,...T
Minimum Requirement #9: Operation and Maintenance.................................................7
Minimum Requirement #10: Offsite Analysis and Mitigation...............................................7
Minimum Requirement #11: Financial Liability.................................................................7
Section C - Final Soils Evaluation .......................................................................................8
SectionD - Source Control.................................................................................................8
Section E - On-site Stormwater Management BMPs...............................................................8
Section F - Runoff Treatment Analysis and Design .......................................
8
Section G - Flow Control Analysis and Design.....................................................................9
Section H -Wetlands Protection ........................ ___ .............................. ...,....... .,,,... ,...,..,.9
Section I - Other Permits ..............................................
9
Section L - Maintenance and Operations Manual ..... ....... ..................... ,........ ,....... .,,,......,,,..9
Appendix..............................................................................,.,........,.,.,,..,,,...............,....„...10
Hwy 99 New Shops Building Page 2
Edmonds, WA
Section A - Project Overview
Introduction
This stormwater report is prepared to discuss the proposed stormwater management system and to
provide the documentation and the analysis showing that the proposed system is feasible and
designed to address the jurisdictional requirements. All components of the stormwater
management system were designed to meet the stormwater requirements of The City of Edmonds
Chapter 18.30 Edmonds Community Development Code and Exhibit "A" Stormwater Code
Supplement dated April 2010.
The project site is located in the Top Food & Drug parking lot on 220th St. SW & Hwy 99 in
Edmonds, Washington. The parcel lies on the southern edge of the existing parking lot, along the
north side of 220th St. SW. The improvements also include the addition of six (6) parking stalls
near the east driveway. A vicinity map is included in the appendix for reference (See Appendix A).
According to the FEMA Flood Insurance Rate Map Number 53061 C1315E, dated November 9,
1999, the site is located within Zone X, described as areas determined to be outside the 0.2%
annual chance floodplain.
Existing Conditions
The site is approximately 0.83 acres and is currently developed with an existing asphalt parking lot
and limited vegetation. The site is west of the existing Starbucks on the corner of 220'h St. SW &
Hwy 99. According to the Natural Resources Conservation Services (NCRS), the native soil
underlying the site consists of Alderwood-Urban Land Complex (2-8% slopes). The Geotechnical
Engineering Investigation report by GeoTest, dated 12/4/2014, found that soils within the site are
glacial till.
Stormwater runoff on the site and surrounding streets are managed through a system of catch
basins and pipes. Within the subject site, runoff from the existing parking lot flows to catch basins
throughout the proposed site. The stormwater drains to an existing underground stormwater vault
where the flows are controlled and water is detained. The existing underground detention vault
located north of.the project site, was constructed with the original Top Foods development. The
underground vault provides stormwater detention for the runoff from the Top Foods building and
the associated asphalt parking lot surrounding the building. The inside dimensions of the existing
vault are 44 feet wide and 200 feet long. The internal height is 5.75 feet. The existing detention
facility discharges runoff into a biofiltration swale west of Hwy 99. Stormwater that flows through
the swale is collected by an 18 -inch pipe which also collects overflow from the detention vault,
and connects to the existing public storm drainage system located within Hwy 99.
Hwy 99 New Shops Building Page 3
Edmonds, WA
Redeveloped Conditions
The project proposes to develop an approximate 6,162 square foot retail pad building, with
associated parking, landscaping, lighting, stormwater and utility improvements. The project will
also include the addition of 6 parking stalls in the Top Foods parking lot, adjacent to the east
driveway. The project will consist of approximately 0.83 acres of total land disturbance.
An existing biofiltration swale is proposed to continue to manage runoff quality prior to discharge
into the public storm system. Stormwater runoff from the developed site will be conveyed to the
underground detention vault via curb and gutter and surface flow. To account for the 0.15 acres of
new impervious area, an underground detention facility will be constructed in the area east of the
building below the parking area. The rest of the site drains to the existing catchbasins located at the
northeast limits of the project. Two catchbasins will be replaced with FloGard Perk Filter
catchbasins to provide Phosphorus Treatment for the 17,758 SF of new/replaced asphalt within the
project area as described below. After the stormwater is released it flows through a water quality
Swale located northeast of the site along the Hwy 99 right of way.
The stormwater system for this project has been designed in accordance with regulatory criteria
described above and is consistent with sound engineering practice. This system's design has
incorporated stormwater treatment BMP's for the mitigation of stormwater runoff quality impacts.
Section B - Minimum Requirements
The proposed site improvements will increase the amount of impervious surface in the project area
by approximately 6,592 sf. The existing project area consists of approximately 23,284 SF of
impervious area, with 12,842 SF of pervious area. All existing site improvements will be
demolished as needed to accommodate the proposed development. The redeveloped project area
will consist of approximately 29,876 SF of new/replaced impervious area and 6,250 SF of
landscape area.
Table 1 below summarizes each land disturbing activity for the proposed development and
provides a Total Effective Impervious Surface for the Threshold Drainage Area (TDA).
Table 1. Land -Disturbing Activity
Existing Conditions (0.83 acres±)
Existing Impervious Surface
Area (SF)
23,284
Existing Landscaped Area
12,842
Proposed Conditions (0.83 acres±)
Site Impervious Area
Area (SF)
29,876*
Site Pervious Area
Total Land Disturbing Activity
6,250
36,126
Total Effective Impervious Surface
17,758**
*Note the replacers rntpenrrnus area rncruaes i z, i i o sr or new ouilaing, plaza arru siueavdlK.
**Effective Impervious Surface is new/replaced asphalt only.
Hwy 99 New Shops Building Page
Edmonds, WA
The Minimum Requirements applicable for the site are determined by Section 2 of the 2010
Edmonds Stormwater Code Supplement (ESCS). Based on the flowchart, Minimum Requirements
#1 through #10 apply to the Effective Impervious Surface.
Based on coordination with City Engineering, the replaced impervious surface that meets the Top
Foods flow control standard can continue to be routed to the existing detention vault. The new
impervious area (6,592 SF) is detained and treated in the proposed underground detention and
stormwater treatment catchbasins.
The Western Washington Hydrologic Model (WWHM2012) was used to determine treatment
flows proposed for the mitigated developed conditions. The required treatment flow for the
Effective Impervious Area is 0.0544 CFS or 24.4 GPM. This treatment rate is achieved with the
addition of 2 FloGard Perk Filter catchbasins. For these systems, WSDOE has approved treatment
rates of 6.8 GPM/cartridge for the 12 -inch cartridges. Four (4) 12 -inch cartridges are required for
treatment. Results of the continuous runoff simulation are provided as part of the WWHM2012
Project Report in the appendix (See Appendix Q.
The project has been classified per Section 2 of Exhibit "A" Stormwater Code Supplement 2010 as
a Category 2 Small Site Project. The Small Site Minimum Requirements that apply to the proposed
development are as follows:
Minimum Requirement #1: Preparation of Stormwater Site Plans
The Stormwater Site Plan has been prepared in accordance with Section 5.1 — Preparation of
Stormwater Site Plan in the Edmonds Stormwater Code Supplement. This Stormwater Site Plan
summarizes the methods and analysis for design of the stormwater system for during and after
construction.
Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan
(SWPPP)
An Erosion Control Plan is included with the application. The Construction Stormwater Pollution
Prevention Plan (SWPPP) is a combination of the Temporary Erosion and Sediment Control (TESC)
Plan and a Stormwater Spill Prevention Plan (SSPP). Per Section 5.2 of the ESCS, since the project
is classified as a small site, only a TESC Plan is required.
Minimum Requirement #3: Source Control of Pollution
Available and reasonable source control BMPs have been selected, designed, and maintained in
accordance with the 2010 Edmonds Stormwater Code Supplement (ESCS). All potential pollutant
sources within the building will be routed to the sanitary sewer system. The Garbage dumpster
area is enclosed and isolated from stormwater intrusion. The dumpster area has also been isolated
such that any leakage from the dumpsters will be routed to a drain connected to the sanitary sewer
system.
Hwy 99 New Shops Building Page 5
Edmonds, WA
Minimum Requirement #4: Preservation of Natural Drainage Systems & Outfalls
The site is located within the Halls Creek Watershed according to Figure B-1 of Appendix B in the
Edmonds Stormwater Code Supplement. All stormwater runoff from new/replaced impervious
areas will receive phosphorus stormwater treatment prior to discharge downstream. The new
impervious area's impact is mitigated with the addition of an underground detention facility that
will control the release of stormwater. The areas of replaced impervious pavement will continue to
drain to the existing underground detention vault and have zero impact to the downstream system.
Minimum Requirement #5: On-site Stormwater Management
The proposed project will employ on-site stormwater management BMPs to treat stormwater runoff
in accordance with the requirements of 2010 Edmonds Stormwater Code Supplement (ESCS)
without causing flooding and erosion. The proposed project increases the impervious area by
6,592 SF and is mitigated by the use of an underground detention facility that is sized using
WWHM 2012 and does not negatively affect the watershed basin.
Minimum Requirement #6: Runoff Treatment
The project proposes approximately 14,315 SF of replaced pollutant generating impervious
surfaces (PCIS) and 3,443 SF of new PGIS. The project proposes approximately 6,592 SF of total
new impervious area (both PGIA and Non-PGIS). Through coordination with the City Engineer,
phosphorus treatment will be required for the new and replaced PGIS. Under this storm, report,
stormwater runoff from an equivalent area to that of the replaced paved areas will drain to Kristar
FloGard Perk Filters (using ZPC Filter Media for Enhanced Treatment) catch basins for phosphorus
treatment. Two FloGard Perk Filter catchbasins will be used to meet and exceed the required
treatment areas. Catchbasin #1 will treat 10,318 SF and Catchbasin #2 will treat 10,690 SF of
runoff area. See Basin Map Exhibit B-4 in Appendix B.
The total treated area is 21,008 SF, which exceeds the required 17,758 SF of PGIS (see Appendix C
for Water Quality Modeling). The proposed project exceeds the water quality requirements.
Minimum Requirement #7: Flow Control
Per Figure B-1 from the 2010 ESCS, the project is located in the Halls Creek drainage basin, which
is tributary to Lake Ballinger. The total new and replaced impervious surface area associated with
the project is 29,876 square feet. The underground detention facility will provide mitigation of
storm water runoff from the roof of the building and surrounding area. Runoff from the remaining
replaced impervious surface will continue to be mitigated by the existing detention vault. Based
upon the construction drawings of the detention vault, the City determined that the vault can be
used for Minimum Requirement #7 Flow Control for the replaced impervious associated with the
project.
Hwy 99 New Shops Building Page 6
Edmonds, WA
Minimum Requirement #8: Wetlands Protection
This requirement does not apply since the proposed project will not discharge to any known
wetlands directly or indirectly through a conveyance system.
Minimum Requirement #9: Operation and Maintenance
An operation and maintenance manual (O&M Manual) is included per provisions outlined in
Volume V of the DOE Stormwater Manual, for all proposed stormwater facilities and BMPs (See
Appendix D) necessary for the project. The property owner will be responsible for the cost of
installation, as well as operation and maintenance of the proposed onsite stormwater facilities. See
the appendix for the O&M manual.
Minimum Requirement #10: Offsite Analysis and Mitigation
Based on previous reports prepared for redevelopment within the Top Foods property, the
following downstream drainage course was outlined:
The outlet from the flow control structure located within the existing detention vault discharges to
the east via an 18 -inch CMP pipe. The pipe daylights into the biofiltration swale along the east side
of the project site. During the time of the investigation, there was a visible flow of stormwater
discharge through the swale. The swale flows north and is collected by an 18 -inch concrete pipe
that continues north into a catch basin located at north end of the swale. The catch basin combines
flows from the swale, the overflow from the detention vault, and the flow collected by two catch
basins in the north entry drive. The combined flow from the catch basin connects with the existing
drainage system located in the west side of Highway 99. The flow continues east to a catch basin
located within the gutter flow line along the east side of Highway 99. The drainage system along
the east side of Highway 99, continues north through a series of catch basins and pipes. The
drainage system continues east along the south side of 216th Street SW for approximately 500 feet.
The drainage system continues south and discharges into Halls Creek. There was no observed
flooding or erosion within the approximate area of the outfall. The outfall into Halls Creek is
located approximately 1,550 feet downstream from the project site. Halls Creek continues south
within a vegetated channel and through various culvert crossings underneath roadways. Halls
Creek eventually discharges to Lake Ballinger, located approximately 7,700 feet (1.5 miles)
downstream from the project site.
It does not appear that the proposed development will negatively impact the downstream drainage
course. The new impervious area drains to the underground detention facility to mitigate flows
prior to discharging to the downstream basin.
Minimum Requirement #11: Financial Liability
The project is a commercial project, which would normally require that a performance bond be
posted as a financial guarantee for the required stormwater systems and BMPs related to the
Construction Stormwater Pollution Prevention Plan. However, there are no public stormwater
improvements onsite or in the public right of way. Therefore, no performance bond should be
required.
Hwy 99 New Shops Building Page 7
Edmonds, WA
Section C —Soils Evaluation
According to the Natural Resources Conservation Services (NCRS), the native soil underlying the
site consists of Alderwood-Urban Land Complex (2-8% slopes), a Hydrologic Soil Group (HSG) B
designation. A Web Soil Survey for the site is provided in the appendix (See Appendix A-2).
The site is currently developed with asphalt parking covering over 90% of the area. Only a small
landscape area currently exists within the limits of disturbance.
Section D — Source Control
Dust control and appropriate soil erosion control
the construction phase of the proposed project.
be handling hazardous material.
measures shall be implemented as needed during
The proposed commercial development will not
Section E — On-site Stormwater Management BMPs
Selection and design criteria for the on-site stormwater management BMPs are found in Volume III,
Chapter 3 and Volume V, Chapter 5 of the DOE Stormwater Manual. The stormwater management
BMP locations are shown on the Grading and Drainage Plan, Sheet C-2.0 (See Appendix B-2).
Section F — Runoff Treatment Analysis and Design
The pollution generating surfaces for the proposed project are summarized in Table 2,
Table 2. Pollution Generating Surfaces
Pollution Generating Surfaces
Treatment Method
Condition
Area (SF)
Existing - Pollution Generating Impervious
Asphalt
23,284
Surfaces (PGIS)
Pavement
13.6
Proposed - Pollution Generating Impervious
Asphalt
17,758
Surfaces (PGIS)
Pavement
13.6
Total Net PGIS Reduction
Asphalt
-5,526
Pavement
Through coordination with the City Engineer, phosphorus treatment will be required for the new
and replaced PGIS. Stormwater runoff from an equivalent area to that of the replaced paved areas
will drain to FloGard Perk Filter catch basins for treatment. See Table 3b for Perk Filter sizing
requirements.
Table 3b. Equivalent Replaced PGIS Treatment Area
New Impervious Area Equivalent Drainage Basins
Treatment Method
Drainage
Treatment
Area (SF)
Flow (GPM)
Catchbasin #1 Basin Perk Filter 12 -in
1 0,31 8
13.6
Double Cartridge
Catchbasin #2 Basin Perk Filter 12 -in
10,690
13.6
Double Cartridge
Hwy 99 New Shops Building Page 8
Edmonds, WA
The required treatment is 24.4 GPM based on the WWHM on-line target treatment flow. The
proposed system is approved for a treatment rate of 6.8 GPM/cartridge and will utilize two (2)
double cartridge systems for a 27.2 GPM total treatment rate.
Section G — Flow Control Analysis and Design
Site Suitability for Stormwater Infiltration
Based on the native soil classification the soils are classified as Hydrologic Soils Group B, which
provides moderate infiltration rates of approximately 0.25 in/hr. However, the project does not
propose any infiltration.
Flow Control Facilities for the TDA
Not Applicable per Section B, minimum requirement #7,.
Section H — Wetlands Protection
This requirement does not apply since the proposed project will not discharge to any wetlands
directly or indirectly through a conveyance system.
Section I — Other Permits
Based on coordination with Ecology, an NPDES permit will not be required for this project since
the project limit of land disturbance is expected to be less than 1 acre.
Section L — Maintenance and Operation Manual
An operation and maintenance manual (O&M Manual) is included per provisions outlined in
Volume V of the DOE Stormwater Manual, for all proposed stormwater facilities and BMPs (See
Appendix D). The property owner will be responsible for the cost of installation, as well as
operation and maintenance of the proposed onsite stormwater facilities.
Hwy 99 New Shops Building Page 9
Edmonds, WA
Appendix
Appendix A: Maps
A-1: Vicinity Map
A-2: Web Soil Survey
A-3: FEMA Flood Insurance Rate Map Number 53061C1315E
Appendix B: Site Plans
B-1: Existing Site Topographic Survey
B-2: Grading and Drainage Plan
B-3: Erosion Control Plan
B-4: Basin Map
Appendix C: Data Output
C-1: WWHM Water Quality Project Output
C-2: WWHM Detention Facility Sizing
Appendix D: Operation and Maintenance Manual
Hwy 99 New Shops Building Page 10
Edmonds, WA
APPENDIX AM MAPS
A-1: Vicinity Map
A-2: Web Soil Survey
A-3: FEMA Flood Insurance Rate Map Number 53061C1315E
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5—Alderwood-Urban land complex, 2 to 8 percent slopes
Map Unit Setting
• National map unit symbol: 2hz9
• Elevation: 50 to 800 feet
Mean annual precipitation: 25 to 60 inches
Mean annual air temperature: 48 to 52 degrees F
Frost -free period: 180 to 220 days
Farmland classification: Not prime farmland
Map (last Composition
• Alderwood and similar soils: 60 percent
• Urban land: 25 percent
• Minor components: 6 percent
• Estimates are based on observations, descriptions, and transects of the mapunit.
Description ofAldeo-wood
Setting
• Landform: Till plains
• Parent material: Basal till
Typical profile
• H1 - 0 to 7 inches: gravelly ashy sandy loam
• H2 - 7 to 35 inches: very gravelly ashy sandy loam
• H3 - 35 to 60 inches: gravelly sandy loam
Properties and qualities
• Slope: 2 to 8 percent
• Depth to restrictive feature: 20 to 40 inches to densic material
• Natural drainage class: Moderately well drained
• Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low
(0.00 to 0.06 in/hr)
• Depth to water table: About 18 to 36 inches
• Frequency of flooding: None
• Frequency of ponding: None
• Available water storage in profile: Low (about 3.0 inches)
Interpretive groups
• Land capability classification (irrigated): None specified
• Land capability classification (nonirrigated): 4s
• Hydrologic Soil Group: B
Other vegetative classification: Limited Depth Soils (G002XN302WA)
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AEN'IX C: data Out �t
C-1: WWHM Water Quality Project Output
C-2: WWHM Detention Facility Sizing
Mitigated Land Use
Basin 1
Bypass:
Yes
GroundWater:
No
Pervious Land Use
Acres
Pervious Total
0
Impervious Land Use
Acres
PARKING FLAT
0.41
Impervious Total
0.41
Basin Total
0.41
Element Flows To:
Surface Interflow Groundwater
Trapezoidal Pond 1
.41 acres 2015-11-12 11/12/2015 2:24:59 PM C-1
Water Quality
Water Quality BM�P Flow and Volume for • O
M r0.0365
acre-feet
On-line-0.0544
cfs.
Adjusted for 15 min:
0.0544 cfs.
•ff-1,ine facility target flow,01.0307
cfs.
AdwiUsted' o
.41 acres 2015-11-12 11/12/2015 2:26:52 PM Page 18
MCG EDMONDS, WA
Flows Summary
t
Event
Pre -developed
Post Developed
Stage (ft)
Outlet Mitigated
Allowed
(0501)
(0701)
(CFS)
* (CFS)
2
0.0032
0.0451
1.22
0.0074
0.0075
10
0.0065
0.0727
1.79
0.0135
0.015
100
1 0.0111
0.1172
2.53 1
0.0256
0.027
* Allowable discharge - 0.05,0.10 and 0.18 cfs/acre impervious
"� 'T'ank 1 Miflqated
Facility Name
Outlet 1
Downstream Connection
Precipitation Appfied to Facility
F, Evaporation Applied to Facility
Facility Dimensions
Facility Bottom Elevation (ft)
Tank Type c cular ..
Diameter (ft)
Length (ft)
Infiltration NO
Facility Type
Outlet 2 Outlet 3
Auto Tank OuickTank
Facility Dimension Dia ram
Outlet Structure Data I
Riser Height (ft) r ---.=I
Riser Diameter (in) 12
Riser Type Flat ^�
Notch Type
Orifice Diameter Height
Number (in) (ft)
7 0.5 ^H Fo--- ^�
2 r4 ^6-1 2. Z ^�
Tank Volume at Riser Head (ac -ft) .029
Show Tank TableOpen Table
Intitial Stacie (ft)
r
IC -2
W HM2 1.2
PROJECT REPORT
General Model Information
Project Name:
MCG Edmonds Pipes
Site Name:
MCG
Site Address:
City:
Edmonds
Report Date:
12/9/2015
MGS Region:
Puget East
Data Start:
1901/10/1
Data End:
2058/09/30
Timestep:
15 Minute
DOT Data Number02
Version:
2014/01/24
POC Thresholds
Low Flow Threshold for POC1
High Flow Threshold for POC1
50 Percent of the 2 Year
50 Year
MCG Edmonds Pipes 12/9/2015 8:49:06 AM Page 2
Landuse Basin Data
Predeveloped Land Use
Basin 1
Bypass:
No
GroundWater:
No
Pervious Land Use
Acres
C, Pasture, Mod
0.15
Pervious Total
0.15
Impervious Land Use
Acres
Impervious Total
0
Basin Total
0.15
Element Flows To:
Surface Interflow Groundwater
MCG Edmonds Pipes 12/9/2015 8:49:06 AM Page 3
Mitigated Land Use
Basin 1
Bypass: No
GroundWater: No
Pervious Land Use
Acres
Pervious Total
0
Impervious Land Use
Acres
PARKING FLAT
0.15
Impervious Total
0.15
Basin Total
0.15
Element Flows To:
Surface
Tank 1
Interflow Groundwater
MCG Edmonds Pipes 12/9/2015 8:49:06 AM Page 4
Routing Elements
Predeveloped Routing
MCG Edmonds Pipes 12/9/2015 8:49:06 AM Page 5
Mitigated Routing
Tank 1
Dimensions
Depth:
Tank Type:
Diameter:
Length:
Discharge Structure
Riser Height:
Riser Diameter:
Orifice 1 Diameter:
Orifice 2 Diameter:
Element Flows To:
Outlet 1
3 ft.
Circular
3 ft.
180 ft.
3 ft.
12 in.
0.5 in. Elevation:0 ft.
4 in. Elevation:2.2 ft.
Outlet 2
Tank Hydraulic Table
Stage(ft)
Area(ac)
Volume(ac-ft)
Discharge(cfs)
Infilt(cfs)
0.0000
0.000
0.000
0.000
0.000
0.0333
0.002
0.000
0.001
0.000
0.0667
0.003
0.000
0.001
0.000
0.1000
0.004
0.000
0.002
0.000
0.1333
0.005
0.000
0.002
0.000
0.1667
0.005
0.000
0.002
0.000
0.2000
0.006
0.000
0.002
0.000
0.2333
0.006
0.001
0.003
0.000
0.2667
0.007
0.001
0.003
0.000
0.3000
0.007
0.001
0.003
0.000
0.3333
0.007
0.001
0.003
0.000
0.3667
0.008
0.002
0.004
0.000
0.4000
0.008
0.002
0.004
0.000
0.4333
0.008
0.002
0.004
0.000
0.4667
0.009
0.002
0.004
0.000
0.5000
0.009
0.003
0.004
0.000
0.5333
0.009
0.003
0.004
0.000
0.5667
0.009
0.003
0.004
0.000
0.6000
0.009
0.004
0.005
0.000
0.6333
0.010
0.004
0.005
0.000
0.6667
0.010
0.004
0.005
0.000
0.7000
0.010
0.005
0.005
0.000
0.7333
0.010
0.005
0.005
0.000
0.7667
0.010
0.005
0.005
0.000
0.8000
0.011
0.006
0.005
0.000
0.8333
0.011
0.006
0.006
0.000
0.8667
0.011
0.007
0.006
0.000
0.9000
0.011
0.007
0.006
0.000
0.9333
0.011
0.007
0.006
0.000
0.9667
0.011
0.008
0.006
0.000
1.0000
0.011
0.008
0.006
0.000
1.0333
0.011
0.008
0.006
0.000
1.0667
0.011
0.009
0.006
0.000
1.1000
0.011
0.009
0.006
0.000
1.1333
0.012
0.010
0.007
0.000
1.1667
0.012
0.010
0.007
0.000
1.2000
0.012
0.010
0.007
0.000
MCG Edmonds Pipes 12/9/2015 8:49:06 AM
Page 6
1.2333
0.012
0.011
0.007
0.000
1.2667
0.012
0.011
0.007
0.000
1.3000
0.012
0.012
0.007
0.000
1.3333
0.012
0.012
0.007
0.000
1.3667
0.012
0.013
0.007
0.000
1.4000
0.012
0.013
0.007
0.000
1.4333
0.012
0.013
0.007
0.000
1.4667
0.012
0.014
0.008
0.000
1.5000
0.012
0.014
0.008
0.000
1.5333
0.012
0.015
0.008
0.000
1.5667
0.012
0.015
0.008
0.000
1.6000
0.012
0.015
0.008
0.000
1.6333
0.012
0.016
0.008
0.000
1.6667
0.012
0.016
0.008
0.000
1.7000
0.012
0.017
0.008
0.000
1.7333
0.012
0.017
0.008
0.000
1.7667
0.012
0.017
0.008
0.000
1.8000
0.012
0.018
0.008
0.000
1.8333
0.012
0.018
0.008
0.000
1.8667
0.012
0.019
0.009
0.000
1.9000
0.011
0.019
0.009
0.000
1.9333
0.011
0.019
0.009
0.000
1.9667
0.011
0.020
0.009
0.000
2.0000
0.011
0.020
0.009
0.000
2.0333
0.011
0.021
0.009
0.000
2.0667
0.011
0.021
0.009
0.000
2.1000
0.011
0.021
0.009
0.000
2.1333
0.011
0.022
0.009
0.000
2.1667
0.011
0.022
0.009
0.000
2.2000
0.011
0.023
0.009
0.000
2.2333
0.010
0.023
0.086
0.000
2.2667
0.010
0.023
0.118
0.000
2.3000
0.010
0.024
0.142
0.000
2.3333
0.010
0.024
0.163
0.000
2.3667
0.010
0.024
0.181
0.000
2.4000
0.009
0.025
0.198
0.000
2.4333
0.009
0.025
0.213
0.000
2.4667
0.009
0.025
0.227
0.000
2.5000
0.009
0.026
0.240
0.000
2.5333
0.009
0.026
0.253
0.000
2.5667
0.008
0.026
0.265
0.000
2.6000
0.008
0.026
0.276
0.000
2.6333
0.008
0.027
0.287
0.000
2.6667
0.007
0.027
0.297
0.000
2.7000
0.007
0.027
0.307
0.000
2.7333
0.007
0.027
0.317
0.000
2.7667
0.006
0.028
0.327
0.000
2.8000
0.006
0.028
0336
0.000
2.8333
0.005
0.028
0.345
0.000
2.8667
0.005
0.028
0.354
0.000
2.9000
0.004
0.028
0.362
0.000
2.9333
0.003
0.029
0.371
0.000
2.9667
0.002
0.029
0.379
0.000
3.0000
0.000
0.029
0.387
0.000
3.0333
0.000
0.000
0.454
0.000
MCG Edmonds Pipes 12/9/2015 8:49:06 AM Page 7
Analysis Results
POC 1
UV
MW_ m.._ ----- W.n.._...........I � 9-
05 1 2 „ 10 g; ,� bYrn '4C1 95 98 99 995 tl."�
+ Predeveloped x Mitigated
Predeveloped Landuse Totals for POC #1
Total Pervious Area: 0.15
Total Impervious Area: 0
Mitigated Landuse Totals for POC #1
Total Pervious Area: 0
Total Impervious Area: 0.15
Flow Frequency Method: Log Pearson Type III 17B
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period
Flow(cfs)
2 year
0.003173
5 year
0.005111
10 year
0.006488
25 year
0.008299
50 year
0.009688
100 year
0.011103
Flow Frequency Return Periods for Mitigated. POC #1
Return Period
Flow(cfs)
2 year
0.007351
5 year
0.010659
10 year
0.013483
25 year
0.017896
50 year
0.021888
100 year
0.026567
Annual Peaks
Annual Peaks for Predeveloped and Mitigated. POC #1
Year
Predeveloped
Mitigated
1902
0.004
0.008
1903
0.002
0.007
1904
0.004
0.007
1905
0.002
0.007
1906
0.001
0.006
1907
0.005
0.009
1908
0.003
0.007
1909
0.003
0.007
1910
0.005
0.008
1911
0.003
0.007
MCG Edmonds Pipes 12/9/2015 8:49:06 AM
Page 8
1912
0.015
0.008
1913
0.004
0.007
1914
0.001
0.007
1915
0.002
0.006
1916
0.003
0.007
1917
0.001
0.007
1918
0.003
0.007
1919
0.002
0.006
1920
0.003
0.007
1921
0.003
0.007
1922
0.003
0.008
1923
0.002
0.007
1924
0.002
0.006
1925
0.002
0.006
1926
0.003
0.007
1927
0.003
0.007
1928
0.002
0.007
1929
0.005
0.008
1930
0.003
0.007
1931
0.003
0.007
1932
0.002
0.007
1933
0.003
0.007
1934
0.007
0.009
1935
0.003
0.006
1936
0.004
0.007
1937
0.004
0.008
1938
0.003
0.007
1939
0.001
0.006
1940
0.003
0.008
1941
0.003
0.006
1942
0.004
0.008
1943
0.002
0.007
1944
0.006
0.066
1945
0.003
0.007
1946
0.003
0.006
1947
0.002
0.007
1948
0.006
0.009
1949
0.006
0.018
1950
0.003
0.007
1951
0.003
0.006
1952
0.009
0.029
1953
0.007
0.031
1954
0.003
0.007
1955
0.002
0.006
1956
0.002
0.005
1957
0.004
0.007
1958
0.008
0.011
1959
0.005
0.007
1960
0.002
0.006
1961
0.005
0.009
1962
0.003
0.008
1963
0.002
0.006
1964
0.007
0.007
1965
0.006
0.009
1966
0.001
0.007
1967
0.003
0.006
1968
0.003
0.008
1969
0.003
0.007
MCG Edmonds Pipes
12/9/2015 8:56:58 AM Page 9
1970
0.004
0.008
1971
0.006
0.009
1972
0.012
0.008
1973
0.005
0.009
1974
0.003
0.008
1975
0.006
0.009
1976
0.003
0.008
1977
0.002
0.006
1978
0.006
0.009
1979
0.002
0.007
1980
0.003
0.006
1981
0.003
0.007
1982
0.002
0.006
1983
0.005
0.008
1984
0.002
0.007
1985
0.003
0.007
1986
0.003
0.007
1987
0.006
0.009
1988
0.003
0.007
1989
0.003
0.007
1990
0.004
0.008
1991
0.003
0.008
1992
0.004
0.008
1993
0.004
0.008
1994
0.006
0.009
1995
0.002
0.006
1996
0.007
0.009
1997
0.003
0.007
1998
0.003
0.008
1999
0.000
0.006
2000
0.002
0.007
2001
0.002
0.006
2002
0.006
0.007
2003
0.004
0.008
2004
0.003
0.007
2005
0.005
0.007
2006
0.002
0.006
2007
0.003
0.008
2008
0.003
0.007
2009
0.002
0.007
2010
0.002
0.009
2011
0.002
0.006
2012
0.004
0.009
2013
0.002
0.007
2014
0.002
0.006
2015
0.014
0.007
2016
0.001
0.006
2017
0.005
0.028
2018
0.008
0.037
2019
0.011
0.063
2020
0.003
0.007
2021
0.004
0.008
2022
0.002
0.006
2023
0.003
0.007
2024
0.014
0.008
2025
0.003
0.007
2026
0.005
0.008
2027
0.003
0.007
MCG Edmonds Pipes 12/9/2015 8:56:58 AM Page 10
2028
0.001
0.006
2029
0.003
0.007
2030
0.006
0.009
2031
0.002
0.006
2032
0.002
0.005
2033
0.002
0.006
2034
0.002
0.007
2035
0.007
0.026
2036
0.004
0.008
2037
0.001
0.007
2038
0.004
0.009
2039
0.001
0.006
2040
0.002
0.007
2041
0.002
0.007
2042
0.008
0.046
2043
0.004
0.008
2044
0.004
0.008
2045
0.003
0.007
2046
0.003
0.007
2047
0.002
0.006
2048
0.003
0.008
2049
0.003
0.008
2050
0.002
0.007
2051
0.004
0.009
2052
0.002
0.008
2053
0.003
0.007
2054
0.008
0.008
2055
0.002
0.006
2056
0.001
0.007
2057
0.002
0.007
2058
0.003
0.006
Ranked Annual Peaks
Ranked Annual Peaks for Predeveloped and Mitigated. POC #1
Rank
Predeveloped
Mitigated
1
0.0149
0.0665
2
0.0141
0.0628
3
0.0140
0.0455
4
0.0124
0.0372
5
0.0108
0.0307
6
0.0091
0.0292
7
0.0083
0.0280
8
0.0083
0.0257
9
0.0078
0.0184
10
0.0076
0.0113
11
0.0075
0.0094
12
0.0074
0.0092
13
0.0074
0.0090
14
0.0069
0.0090
15
0.0066
0.0089
16
0.0064
0.0089
17
0.0063
0.0089
18
0.0061
0.0088
19
0.0061
0.0087
20
0.0061
0.0087
21
0.0060
0.0086
22
0.0058
0.0086
23
0.0058
0.0086
MCG Edmonds Pipes 12/9/2015 8:56:58 AM Page 11
24
0.0058
0.0086
25
0.0057
0.0086
26
0.0055
0.0086
27
0.0053
0.0085
28
0.0051
0.0085
29
0.0051
0.0084
30
0.0049
0.0083
31
0.0048
0.0083
32
0.0048
0.0083
33
0.0048
0.0081
34
0.0047
0.0081
35
0.0047
0.0081
36
0.0045
0.0081
37
0.0045
0.0081
38
0.0044
0.0080
39
0.0044
0.0080
40
0.0043
0.0080
41
0.0043
0.0079
42
0.0042
0.0079
43
0.0042
0.0079
44
0.0041
0.0078
45
0.0040
0.0078
46
0.0039
0.0078
47
0.0039
0.0078
48
0.0038
0.0078
49
0.0038
0.0078
50
0.0038
0.0077
51
0.0038
0.0077
52
0.0037
0.0077
53
0.0037
0.0076
54
0.0037
0.0076
55
0.0035
0.0075
56
0.0035
0.0075
57
0.0035
0.0075
58
0.0035
0.0075
59
0.0034
0.0075
60
0.0034
0.0075
61
0.0034
0.0075
62
0.0034
0.0075
63
0.0033
0.0075
64
0.0033
0.0074
65
0.0033
0.0074
66
0.0032
0.0074
67
0.0032
0.0074
68
0.0032
0.0074
69
0.0032
0.0074
70
0.0032
0.0074
71
0.0032
0.0074
72
0.0032
0.0074
73
0.0032
0.0073
74
0.0031
0.0073
75
0.0031
0.0073
76
0.0031
0.0073
77
0.0031
0.0072
78
0.0031
0.0072
79
0.0031
0.0072
80
0.0030
0.0072
81
0.0030
0.0071
MCG Edmonds Pipes 12/9/2015 8:56:58 AM Page 12
82
0.0030
0.0071
83
0.0030
0.0071
84
0.0030
0.0071
85
0.0030
0.0071
86
0.0029
0.0071
87
0.0029
0.0070
88
0.0029
0.0070
89
0.0029
0.0070
90
0.0029
0.0070
91
0.0028
0.0070
92
0.0028
0.0070
93
0.0028
0.0069
94
0.0028
0.0069
95
0.0028
0.0069
96
0.0027
0.0069
97
0.0027
0.0069
98
0.0027
0.0069
99
0.0027
0.0069
100
0.0027
0.0069
101
0.0026
0.0069
102
0.0026
0.0069
103
0.0026
0.0069
104
0.0025
0.0068
105
0.0025
0.0068
106
0.0025
0.0068
107
0.0025
0.0068
108
0.0025
0.0068
109
0.0024
0.0068
110
0.0024
0.0068
111
0.0023
0.0068
112
0.0023
0.0068
113
0.0023
0.0067
114
0.0023
0.0067
115
0.0022
0.0067
116
0.0022
0.0067
117
0.0022
0.0067
118
0.0022
0.0067
119
0.0022
0.0066
120
0.0022
0.0066
121
0.0022
0.0066
122
0.0022
0.0066
123
0.0021
0.0065
124
0.0020
0.0065
125
0.0020
0.0064
126
0.0020
0.0064
127
0.0020
0.0064
128
0.0019
0.0064
129
0.0019
0.0064
130
0.0019
0.0063
131
0.0019
0.0063
132
0.0018
0.0063
133
0.0018
0.0063
134
0.0018
0.0062
135
0.0018
0.0062
136
0.0017
0.0062
137
0.0017
0.0062
138
0.0017
0.0062
139
0.0017
0.0062
MCG Edmonds Pipes
12/9/2015 8:56:58 AM Page 13
140
0.0017
0.0061
141
0.0017
0.0061
142
0.0016
0.0061
143
0.0016
0.0061
144
0.0016
0.0061
145
0.0016
0.0061
146
0.0016
0.0060
147
0.0015
0.0060
148
0.0015
0.0060
149
0.0015
0.0060
150
0.0014
0.0059
151
0.0013
0.0057
152
0.0012
0.0057
153
0.0011
0.0057
154
0.0009
0.0056
155
0.0009
0.0056
156
0.0006
0.0055
157
0.0002
0.0054
MCG Edmonds Pipes 12/9/2015 8:56:58 AM Page 14
Analysis Results
POC 1
001
001
0
L 000
0' 11,5 10E-4 10E-3 10E-2 10E-1 ,1 .,. 1'0 -_. 1M
P�ro�r�t Time FEE o—
+ Predeveloped
Predeveloped Landuse Totals for POC #1
��.�.m.m.............
Ar+hry 'K k
A6.iwe'" 4
e Cb P 2 19 „„ „4 a, 90 95 96 99 99.5 1 $
IINA i to
Total Pervious Area:
0.15
Total Impervious Area:
0
Mitigated Landuse Totals for POC #1
Total Pervious Area:
0
Total Impervious Area:
0.15
Flow Frequency Method:
Log Pearson Type III 17B
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period
Flow(cfs)
2 year
0.003173
5 year
0.005111
10 year
0.006488
25 year
0.008299
50 year
0.009688
100 year
0.011103
Flow Frequency Return Periods for Mitigated. POC #1
Return Period
Flow(cfs)
2 year
0.007333
5 year
0.010473
10 year
0.013121
25 year
0.017216
50 year
0.020884
100 year
0.02515
Annual Peaks
Annual Peaks for Predeveloped
and Mitigated. POC #1
Year
Predeveloped Mitigated
1902
0.004
0.008
1903
0.002
0.007
1904
0.004
0.007
1.905
0.002
0.007
1906
0.001
0.006
1907
0.005
0»009
1908
0.003
0.007
1909
0.003
0.007
1910
0.005
0.008
1911
0.003
0.007
MCG Edmonds Pipes 11/12/2015 2:32:06 PM Page 8