STORMWATER REPORT FOR 244TH ST.pdfINSIGHT ENGINEENNG M
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PRELIMINARY STORMWATER SITE PLAN
For
244th ST.
Prepared for
The City of Edmonds
121 5th Ave N
Edmonds, WA 98020
425-771-0220
Project Site Location:
8609 244th SW
Edmonds, WA 9,8026-9062
Applicant:
Meitzner Brothers Properties, UC
11611 Air of t Rd., Ste. B- I
Everett, WA 98204
Contact:
IECO
P.O. Box 1478
Everett, WA98206
425-303-9363
Tax Id: 00463303100103
IE,CO Project: 16-0800
Certified Erosion and Sedimentation Control Lead:
To be named b,y contractor
Stormwater Site Plan Prepared By:
Jacob D. Mealey, P.E.
Stoirnwater Site Plan Preparation Date:
March 8, 2017
Approximate Construction Date:
May 1, 2017
ROBox 1478 oEverett, WA98206,, P-1425,30&9363
F-425,303.9362 o hnfo@insightengineering.n t
1.0 Executive Summary...................:............................................................................................3
1.1 Drainage Information Summary..................................................................................................6
1.2 Minimum Requirements Summary.............................................................................................. 8
2.0 Existing Conditions..............................................................................................................10
3.0 Offsite Analysis.....................................................................................................................14
3.1 Upstream Analysis.....................................................................................................................14
3.2 Downstream Analysis................................................................................................................14
4.0 Developed Conditions..........................................................................................................17
5.0 Site Hydraulic Analysis.........................................................................................................19
5.1 Existing Basin Summary............................................................................................................20
5.2 Developed Basin Summary ........................................................................................................20
5.3 Water Quality.............................................................................................................................21
6.0 Appendix..............................................................................................................................22
Figures
Figure 1- Minimum Requirements Flow Chart.........................................................................5
Figure2 - Vicinity Map.................................................................................................................7
Figure3 - Soil Map......................................................................................................................11
Figure4 - Downstream Analysis Map-1...................................................................................16
Figure5 - Downstream Analysis Map-2...................................................................................17
Figure 6 - Downstream Analysis Man-3...................................................................................18
Insight Engineering Co. - Stormwater Site Plan 03/08/2017
Acronyms and Abbreviations
BLA
Boundary Line Adjustment
BMP
Best Management Practices
DOE
Department of Ecology
EDDS
Engineering Design and Development Standards
ESC
Erosion and Sediment Control
TECO
Insight Engineering Company
MR
Minimum Requirement
SCDM
SnohomishCounty Drainage Manual
SWPPP
Stormwater Pollution Prevention Plan
SWMMWW
Stormwater Management Manual for Western Washington
TESC
Temporary Erosion and Sediment Control
W WHM
Western Washington Hydrology Model
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1.0 Executive Summary
The proposed project 244th St. is located at 8609 244th SW, Edmonds, Washington.
More generally, the site is located in Section 31, Township 27 North, and Range 4 East of the
Willamette Meridian in Snohomish County, Washington. Please refer to the Vicinity Map
attached later in the section. This report follows the City of Edmond's requirements and the
requirements defined in DOE's 2012 SWMMWW as amended in Dec 2014.
The existing site contains two existing houses with garage, shed and an existing asphalt
driveway from the 244th St. S. W. There also exists a third house with a shed and an existing
gravel driveway from the 244th St. S. W. A shop along with a shed is also present in the site. The
remainder of the site contains lawn and few trees. The site is generally flat and appears to slope
slightly towards the north. Please refer to the downstream analysis map for more details. Per
NRCS survey of Snohomish County, the project site contains Alderwood soil that have a
hydrologic classification of Type "C". Please refer to the soils map and descriptions attached
later in this report for more details.
The site area contains 0.90 Acres. The proposal is to construct eleven new single family
homes and an access drive aisle that have a total onsite impervious area of 9,778 SF. The project
is greater than 5,000 SF, and therefore per Figure 2.2, (flow chart for new development
requirements) Volume I SWMMWW, Minimum requirements #1 through 9 shall apply for this
project. Perforated stub -out connections per section 3.1.3 of Vol III of the DOE's 2012
SWMMWW will provide onsite stormwater management for the roof and yard runoff. The
developed site will be connected to the onsite detention system. The perforated pipe shall be a
10 -ft — 4 -in dia. pipe to be lain in a level, 2 -ft wide trench backfilled with washed drain rock.
Flow control requirements will be met by a Storm- tank system of depth 3 -ft and a 1 -ft layer of
gravel. The Storm -tank system and the gravel for this project will provide a total storage capacity
of 9,995 CF. The storm tank will be located beneath the drive aisle and to the south of the site.
Water quality for the site will be provided by a MWS filter located downstream of stormtank.
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The outlet from the stormtank will be connected to the existing storm drainage system along
244' St.
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Figure l Minimum Requirements (MR's) for New Development Projects
Does tlue site have Yes dear l ewle«wvelw.wlrmeurt
% or r v)re of lawsirr:lnrwrcrr
existing inqmn"Vious Requirements and
eove rage'i" Flcyw Chart
r -t
�. Doe re prgject Convert (Figure 2.3)
No acres or nrt re of native
vegetation to lawn or
Nx,s Ott: project add No Lndscaped areas, or
„filth square, are, t e;t or convert 2,5 acres rur rnore
inorre. of new atf n tine vegetation to
huperviw u's surfaces? ew.s? : acture"
RM
All tw,tirrirrrum,
ltregUireurrrnts apply, to
the new Impervious
surfaces and wr.arn:verle
i wnT^w ions s rtusees.
To's No
Does the Project have
2,0tlti square, feet or
rurore of new, replaced.,
or new plus replaced
uw°urlreu°°wFrrrus Sw. rfaccs" ?
Yes No
Mirwmurru m
Requirements it l
through li apply to
the nw«W v and replaced
imperw+icni Surl" ewr r
and the land rlisturrlre,wt,
Does the proJect have
land -disturbing
.m ..m ctiwriti,e s of ,i;tii i
yes, tiqwire" fe t or rrw4:wre"'a
m
Sce Minimum,
RequGriTenrerrt #2,
t, "rwruwwtr•uret ion
Strrrrrwww ater Pollution
Prevention
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1.1 Drainage Information Summary
Project Name: 244th St
Project Engineer: INSIGHT ENGINEERING COMPANY
Project Applicant: Kenneth & Audrey Darwin
Total Site Area: 0.9 Ac
Project Development Area Including Frontage Improvements: 0.9 Ac I Number of Units:11
Summary Table
Drainage Basin Information
Individual Basin Designation
A B C D
Basin Area (Acres)
0.9
Type of Storage Proposed
Storm tank
Approximate Storage Volume (CF)
9,995
Soil types
(Type C)
Pre -developed Runoff Rate
Q (cfs) 2 -year
0.02
10 -year
0.03
50 -year
0.05
Post -developed Runoff Rate
Q (cfs) 2 -year
0.01
10 -year
0.04
50 -year
0.11
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TAKEN FROMTHE BING MAPS
,f08l2�:� d'f
—7—
1.2 Minimum Requirements Summary
MR Minimum Requirement
SWPPP : Stormwater Pollution Prevention Plan
MR #1 Stormwater Site Plan Narrative. The Stormwater Site Plan preparation follows the
City of Edmonds requirements and in accordance with DOE's 2012 SWMMWW as amended in
Dec 2014. Refer to the executive summary within Section 1.0 .
MR 92 SWPPP Narrative: A SWPPP has been included in the Appendix B under Section 6.
MR 93 Water Pollution Source Control for New Development: No source control pollutants
pertains to the proposed single family project, therefore no BMP's are required for the project.
MR #4 Preservation of Natural Drainage Systems and Outfalls: The outfall from the onsite
detention and water quality system will be connected to the existing drainage system along 244th
St. S. W. to follow the site's natural drainage course.
MR #5 Onsite Stormwater Management: Perforated stub -out connections per section 3.1.3 of
Vol III of the DOE's 2012 SWMMWW will provide onsite stormwater management for the roof
and yard runoff. The developed site will be connected to the onsite detention system. The
perforated pipe shall be a 10 -ft — 4 -in dia. pipe to be lain in a level, 2 -ft wide trench backfilled
with washed drain rock. Post construction soil quality and depth per BMP T 5.13 will provide
onsite stormwater management for the yard runoff.
MR #6 Runoff Treatment: The developed site will be connected to the MWS filter.
MR #7 Flow Control: Flow control requirements will be met by a Storm- tank system of depth
3 -ft and a 1 -ft layer of gravel. The Storm -tank system and the gravel for this project will provide
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a total storage capacity of 9,995 CF. The storm tank will be located beneath the drive aisle and to
the south of the site.
MR #S Wetlands Protection: There are no wetlands contained within the site.
MR 49 Operations and Maintenance A complete Operations and Maintenance Manual will be
provided along with the construction submittal.
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2.0 Existing Conditions
The proposed project 244th St. is located at 8609 244th SW, Edmonds, Washington.
More generally, the site is located in Section 31, Township 27 North, and Range 4 East of the
Willamette Meridian in Snohomish County, Washington.
The existing site contains two existing houses with garage, shed and an existing asphalt
driveway from the 244th St. S. W. There also exists a third house with a shed and an existing
gravel driveway from the 244th St. S. W. A shop along with a shed is also present in the site. The
remainder of the site contains lawn and few trees. The site is generally flat and appears to slope
slightly towards the north. Please refer to the downstream analysis map for more details. Per
SCC survey of Snohomish County, the project site contains Alderwood soil that have a
hydrologic classification of Type "C". Please refer to the soils map and descriptions attached
later in this report for more details.
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SOILS LEGEND
5— Alderwood-Urban land complex 2-8% slopes
Insight Enc` rneer�ng Co Stounwater &te Ran 03)()8/2017
Snohomish County Area, Washington
S--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 Unit Composition
• Alderwvood 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 of Alderwood
Setting
• Landform: Till plains
Parent material: Basal till
Typical profile
• HI - 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 offlooding: 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)
• Hydric soil rating: No
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Minor Components
Mckenna
Percent of reap unit: 2 percent
Landform: Depressions
Hydric soil rating: Yes
Norma
Percent of map unit• 2 percent
Landform: Depressions
Hydric soil rating: Yes
Terric medisaprists
Percent of map unit: 2 percent
Landform: Depressions
Hydric soil rating: Yes
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3.0 Offsite Analysis
A site reconnaissance was performed by Jacob D. Mealey of Insight engineering on
December 20, 2016 to verify the downstream flow paths and observe any drainage problems
downstream of the site. The sky was partly cloudy overcast with a temperature of 48 degrees.
The existing site contains two existing houses with garage, shed and an existing asphalt
driveway from the 244th St. S. W. There also exists a third house with a shed and an existing
gravel driveway from the 244th St. S. W. A shop along with a shed is also present in the site. The
remainder of the site contains lawn and few trees. The site is generally flat and appears to slope
slightly towards the north. No visible on-site drainage problems were observed at the time of
field investigations.
3.1. Upstream Analysis
Based on the site reconnaissance and the topographic survey of the site, the upstream
flows are minimal. Refer to the Downstream Analysis Map attached in the next page for more
details.
3.2 Downstream Analysis
3.2.1. Downstream Analysis for the Existing Flow
Refer to the Downstream Analysis Maps attached to the next page for a visual description
of the downstream flow.
The site is generally flat and appears to slope slightly towards the north. The drainage
flows into the existing drainage system east along the 242nd St SW for about 200 -ft. It passes
through a ditch and reenters the existing system that turns north west along the Edmonds Way.`
The drainage flows north west through the existing system along the Edmonds Way upto 1 mile
of the site. There did not appear to be any restrictions or erosional problems within 1 mile of the
site. Refer to the downstream analysis map for more information.
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3.2.2 Downstream Analysis for the Mitigated Flow
For the mitigated flow the drainage enters the existing drainage system along 2441h St and
flows east along the 205th St SW up to 4,300 -ft and turns north. It ultimately passes through a
culvert and discharges into the Lake Ballinger.
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FIGURE 4, DOWNSTREAM ANALYSIS AP -l14112 24 1 M.
4C 24
X177 01co
...,. R
2 ria 74126
�..
�,.��....8k7
2 F ;
� ei ..
86,0
,V
8
8614
70 6
42 lD6 3:
r it rr y 1 ._c._.,.;.. 8772 G 24 217 . "'14A77 62
Ir
i)7
e271X42 7870LO
��;fi7u
ro
ca
03 com vs
vm eq
ca
,224al 5- 2431
243 201 (3
a }
2 n 8603
m
0 � CO ...I,.. � 4 � 7 � 24326, 1 7` �fi�� Er a�' . $42 51 � `,
SIT......
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13F
11114SIGHTENGINEERUNG M
WIC
244th St
Edmonds, Washington
SCALE: DATE: 3/16/17 JOB H: 16-01800
NONE I
FILE NAME:
BY: JDM I 16-08001/do c/Stormwater Site Plan
... . ......... .
Hns4ghf. Erghnee"Ing Clo, Stormwater Se Pbn 03/08/2017
4.0 Developed Conditions
The proposed project 244th St. is located at 8609 244th SW, Edmonds, Washington.
More generally, the site is located in Section 31, Township 27 North, and Range 4 East of the
Willamette Meridian in Snohomish County, Washington. Per NRCS survey of Snohomish
County, the project site contains Alderwood soil that have a hydrologic classification of Type
"C 7.
The proposal is to construct eleven new single family homes and an access drive
aisle that have a total onsite impervious area of 9,778 SF. The project is greater than 5,000 SF,
and therefore per Figure 2.2, (flow chart for new development requirements) Volume I
SWMMWW, Minimum requirements #1 through 9 shall apply for this project. Perforated stub -
out connections per section 3.1.3 of Vol III of the DOE's 2012 SWMMWW will provide onsite
stormwater management for the roof and yard runoff. The developed site will be connected to the
onsite detention system. The perforated pipe shall be a I0 -ft — 4 -in dia. pipe to be lain in a level,
2 -ft wide trench backfilled with washed drain rock. Flow control requirements will be met by a
Storm- tank system of depth 3 -ft and a 1 -ft layer of gravel. The Storm -tank system and the gravel
for this project will provide a total storage capacity of 9,995 CF. The storm tank will be located
beneath the drive aisle and to the south of the site. Water quality for the site will be provided by
a MWS filter located downstream of stormtank. The outlet from the stonntank will be connected
to the existing storm drainage system along 244th St.
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5.0 Site Hydraulic Conditions to Determine Flow Control Constraints
Total Site Area = 0.90Acres
Total Area Included in the Analysis = 0.90Arces
From the Soil Conservation Service Map of Snohomish County, the majority of the site contains
Alderwood soil that have a hydrologic classification of Type "C"
5.1 Existing Basin Summary
_Existing Basin = 0.90 Acres
Total area included in the analysis =0.90 Acres
Entire existing basin was modeled as forested areas.
Refer to the Existing Basin Map and the following pages for more details.
5.2 Developed Basin Summary
Developed Basin = 0.90 Acres
Total area included in the analysis =0.90 Acres
Refer to the Developed Basin Map for representation.
Impervious:
Roof Area = 0.44 Acres (19,117 SF)
Road = 0.22 Acres ( 9,778 SF)
Total Existing Impervious = 0.66 Acres (28,895 SF)
Pervious:
Pervious Area (Lawn)= 0.90 - 0.66 = 0.24 Acres
Detention Volume Required: 9,943 CF
Detention Volume Provided: 9,995 CF
Refer to the Appendix A for WWHM Report.
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6.0 Appendix
olk
B. Stormwater Pollution Prevention Plain.
C. Operations and Maintenance Manual
D. Geotechnical Report
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A. WWHM REPORT
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General Model Infoirmatioil
10�roject Name: stormtank
Site Name:
244th
Site Address,:
8609 244TH SW, EDMONDS, WA 98,026,-9062
City:
Edmonds
Report Date:
3/14/2017
Gage:
Everett
Data Start:
1948/10/01
Data End:
2009/09/3,0
Timestep:
15 Minute
Precip Scale:
1.00
Version Date:
2016/02/25
Version:
4212
POC Thresholds
Low Flow Threshold for POC1: 501 Percent of the 2 Year
High Flow Threshold for POC1: 59 Year
stountank, 3/14/20,17 4A4:48 PM Page 2
Landuse Bas
to
Predeveloped Land
Use
Exisitng
Bypass:
No
Gro�undWater-.
No
Pervious Land Use
acre
C. Forest, Flat
0.9
Pervious Total
0.9
Impervious Land Use acre
Impervious Total 0
Basin Total 0.9
El'emenit Flows To. -
Surface Interflow Groundwater
stornitank 3/'W2017 4:44:48 P'N/11 Page 3
Mitigated Land Use
Developed
Bypass:
No
GroundWater:
No
Pervious Land Use
acre
C, Pasture, Flat
0.24
Pervious Total
0.24
Impervious Land Use
acre
ROADS FLAT
0.22
ROOF TOPS FLAT
0.44
Impervious Total
0.66
Basin Total
0.9
Element Flows To:
Surface Interflow Groundwater
Storrntank Stormtank
stormtaik 3/'14/2017 4:44A8 PM Page 4
Routing Elements
Predeveloped Routing
storr"titank 3/14/2017 4:44:48 PM Page 5
Mitigated Routing
Stormtank
Bottom Length:
Bottom Width:
Trench bottom slope 1:
Trench Left de slope 0:
Trench right side slope 2:
Material thickness of first layer:
Pour Space of material for first layer:
Material thickness of second layer
F-
F.ovi�101,tw-
Material thickness of third' layer:
Pour Space of material for third layer:
Discharge Structure
Riser Height.
Riser Diameter: 12 in.
54.81 ft.
54.8,1 ft.
0 To 1
0 To 1
0 To 1
3
0.97
1
0.4
0
0
1 Offi i i �ce �ia m e Uer
�in06vation:0 ft.
*rifice 2 Diameter:
01.7 in. Elevation:2.998 ft.
*rifice 3 Diameter-.,
O.42 in., Elevation:3.33 ft.
Element Flows To:
#utlet I
Outlet 2
0.0000
0.01556
0.1111
0.1667
0.2222
0.2778
0.3333
0.3889
0.4444
01.5000
0.5556
0,6111
0.6667
0.7222
0.7778
#.8333
4.8889
*.9444
1.0000
1.0556
11111
1. 1 6,6i7
1.2222
1.2778
1 -3333
1.388i9
1.4444
1.5000
1 5556
1.6111
0.069
0.,069
Oi.069
0.069
0.069
0.069
0.069
0.0169
0.069
0.069
0.069
0.0619
0,069
0.069
0.069
0.069
0.069
0.069
01.069
01.069
0.1069
0.069
0.069
0.069
0.069
0.0169
0.069
0.0169
0.0169
0.069
Volume(ac-ft.)
0.000
0.003
0.007
0.011
0.0114
0.018
0.022
0.026
0.029
0.033
0.037
0.040
0.044
0.048
0.052
01.055
01.,059
0.063
0.066
0.070
0,074
0.073
0.081
0.0185
0.0189
0.092
0.096
0.1010,
0.1014
0.107
Discharge(cfs)
0.000
0.01011
0.0:012
0.0012
0.00,2
0.003
0.003
0.003
0,004
0.004
0.,004
0.004
0.004
0.005
01.005
0.005
0.005
0.005
0,006
0.006
0.006
0-006
0.006
0.006
0.006
0.007
0,007
0.007
0.007
0.007
mmm MI
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000,
0,0100
0.000
0.000
0.000
U00
0.000
0.0010
0.000
0.000
#.000
000
#1.000
#.000
#i.000
#.000
#.,000
1.000
stormtank 3114/20'17 4A4:48 PM Page 6
1.6667
0.069
0.111
0.007
0.000
1.7222
0.069
0.115
0.007
0.000
1.7778
0.069
0.118
0.008
0.000
1.8333
0.069
0.122
0.008
0.000
1.8889
0.069
0.126
0.008
0.000
1.9444
0.069
0.130
0.008
0.000
2.0000
0.069
0.133
0.008
0.000
2.0556
0.069
0.137
0.008
0.000
2.1111
0.069
0.141
0.008
0.000
2.1667
0.069
0.144
0.008
0.000
2.2222
0.069
0.148
0.008
0.000
2.2778
0.069
0.152
0.009
0.000
2.3333
0.069
0.156
0.009
0.000
2.3889
0.069
0.159
0.009
0.000
2.4444
0.069
0.163
0.009
0.000
2.5000
0.069
0.167
0.009
0.000
2.5556
0.069
0.171
0.009
0.000
2.6111
0.069
0.174
0.009
0.000
2.6667
0.069
0.178
0.009
0.000
2.7222
0.069
0.182
0.009
0.000
2.7778
0.069
0.185
0.010
0.000
2.8333
0.069
0.189
0.010
0.000
2.8889
0.069
0.193
0.010
0.000
2.9444
0.069
0.197
0.010
0.000
3.0000
0.069
0.200
0.011
0.000
3.0556
0.069
0.202
0.013
0.000
3.1111
0.069
0.203
0.015
0.000
3.1667
0.069
0.205
0.016
0.000
3.2222
0.069
0.206
0.017
0.000
3.2778
0.069
0.208
0.017
0.000
3.3333
0.069
0.209
0.018
0.000
3.3889
0.069
0.211
0.020
0.000
3.4444
0.069
0.213
0.021
0.000
3.5000
0.069
0.214
0.022
0.000
3.5556
0.069
0.216
0.023
0.000
3.6111
0.069
0.217
0.024
0.000
3.6667
0.069
0.219
0.025
0.000
3.7222
0.069
0.220
0.025
0.000
3.7778
0.069
0.222
0.026
0.000
3.8333
0.069
0.223
0.027
0.000
3.8889
0.069
0.225
0.028
0.000
3.9444
0.069
0.226
0.028
0.000
4.0000
0.069
0.228
0.029
0.000
4.0556
0.069
0.232
0.168
0.000
4,1111
0.069
0.235
0.420
0.000
4.1667
0.069
0.239
0.734
0.000
4.2222
0.069
0.243
1.077
0A00
4.2778
0.069
0.247
1.415
0.000
4.3333
0.069
0.251
1.716
0.000
4.3889
0.069
0.255
1.954
0.000
4.4444
0.069
0.258
2.121
0.000
4.5000
0.069
0.262
2.237
0.000
4.5556
0.069
0.266
2.382
0.000
4.6111
0.069
0.270
2.497
0.000
4.6667
0.069
0.274
2.607
0.000
4.7222
0.069
0.278
2.712
0.000
4.7778
0.069
0.281
2.814
0.000
4.8333
0.069
0.285
2.912
0.000
starmtan€c 3/14/2017 4:44:48 PM Page 7
4.8889 0.069 0.289 3.007
4.9444 0.069 0.293 3.098
5.0000 0.069 0.297 3.188
stormta nk 3/14/2017 4:44:48 PM Page 8
Analysis Results
POC I
O
+ Predleveloped
Predeveloped La9use Totals for PO,C #1
Total Pervious Area: 069
Total Impervious Area: 0
x MIIflga.-ited
Flow Frequency Method: Loig Pearson Type III 17B
-low Frequency Return Periods for Predeveloped, POC #1
Re urn Period
Flow(cfs)
2 year
0.019292
5 year
0.0128556
10 year
0.034898
25 year
01.043077
50 year
0,049265
100 year
0.05552
Return Period
Flow(cfs)
2 year
0.0112043
5 year
0.026489
101 year
0.042854
25 year
0.075602
50 year
0.,112506
100 year
0.164293
AnnualPeaks
Annual Peaks for Predeveloped and Mitigated. PO,C #1
Year
Predevelloped
Mitigated
1949
0,0111
0.009
1950
0.021
0.010
1951
0.017
0.008
1952
0.014
0.0108
1953
0.011
0.0018
1954
0.043
0.009
1955
0.029
0.030
1'956
0.026
0,069
1957
0.0128
0.010
1958
0.019
0.009
stornitank 3/14/2017 4:44:48 PM Page, 9
1959
0.021
0.009
1960
0.018
0.009
1961
0.019
0.0:24
1962
0.017
0.008
1963
0.020
0.009
1964
0.017
0.007
1965
01.019
0.010
1966
0.010
0.,008
1967
0.024
0.009
1968
0.028
0.010
1969
0.021
0.009
1970
0.015
0.009
1971
0.021
0.052
1972
0.019
0-008
1973
0.015
0.010
1974
0.026
0.010
1975
0,015
0.008
1976
0.014
0.009
1977
0.012
0.008
1978
0.01:5
0.008
1979
0.027
0.008
1980
0.017
0.008
1981
0.014
0.008
1982
0.018
0.010
1983
0.026
0.009
1984
0.019
0.066
1985
0.025
0.028
1'986
0.062
0,203
1987
0.027
0.088
1988
0.015
0.010
1989
0.013
0.008
1990
0.020
0.010
1 '991
0.021
0.010
1992
0.016
0-010
1993
0.011
0.007
1994
0.010
0.010
1995
0.020
0.017
1996
0.035
0.015
1997
0,067
0.316
1998
0.013
0.009
1999
0.019
0.010
2000
0.010
0.018
2001
0.003
0.006
2002
0.019
0.,027
2003
0.014
0.009
2004
0.022
0.010
2005
0.016
0.009
200:6
0.038
0.027
2007
0.,032
0.019
2008
0.052
0.144
2009
0.0,16
0.010
Ranked Annual Peaks
Ranked Annual Peaks for Predeveloped and Mitigated. POC #1
an Predeveloped Mitigated
1 0.,0674 0.3160
2 0.0617 0.2027
3 0,0516 0.1438
storn,itank, 3/14/2017 4:45-27 PI\A Page 10
4
0.0427
0.0877
5
0.0381
0.0687
6
0.0353
0.0658
7
0.0325
0.0519
8
0.0289
0.0296
9
0.0284
0.0285
10
0.0276
0.0270
11
0.0274
0.0265
12
0.0272
0.0238
13
0.0264
0.0195
14
0.0258
0.0178
15
0.0256
0.0172
16
0.0250
0.0148
17
0.0235
0.0104
18
0.0223
0.0103
19
0.0213
0.0102
20
0.0212
0.0101
21
0.0212
0.0101
22
0.0207
0.0100
23
0.0206
0.0100
24
0.0203
0.0100
25
0.0201
0.0100
26
0.0200
0.0100
27
0.0195
0.0099
28
0.0192
0.0098
29
0.0192
0.0098
30
0.0191
0.0097
31
0.0190
0.0096
32
0.0188
0.0094
33
0.0185
0.0093
34
0.0183
0.0093
35
0.0183
0.0092
36
0.0173
0.0092
37
0.0170
0.0092
38
0.0170
0.0091
39
0.0167
0.0091
40
0.0164
0.0090
41
0.0162
0.0089
42
0.0162
0.0088
43
0.0152
0.0088
44
0.0152
0.0088
45
0.0151
0.0085
46
0.0151
0.0085
47
0.0150
0.0084
48
0.0145
0.0083
49
0.0142
0.0082
50
0.0139
0.0081
51
0.0137
0.0081
52
0.0128
0.0080
53
0.0128
0.0078
54
0.0121
0.0078
55
0.0113
0.0077
56
0,0109
0.0077
57
0.0106
0.0076
58
0.0104
0.0076
59
0.0102
0.0071
60
0.0099
0.0069
61
0.0034
0.0059
stormtank 3/14/2017 4:45:27 PM Page 11
stormtank 3/1412017 4:45:27 PM Page 12
Flow(cfs)
re 'era
mit
Percentage
Pass/Fall
0.0096
22629
16264
71
Pass
0.0100
20563
9283
45
Pass
0.0104
18617
5405
29
Pass
0.0108
16818
4502
26
Pass
0.0112
15177
4128
27
Pass
0.0116
13732
4028
29
Pass
0.0120
'12474
3933
31
Pass
0.0124
11317
3850
34
Pass
0.0128
10260
3760
36
Pass
0.0132
9319
3687
39
Pass
0.0136
8466
3600,
42
Pass
0.0140
7691
3480
45
Pass
0.0144
6953
3373
48
Pass
0.0148
6323
3245
51
Pass
0.,0152
5784
3133
54
Pass
0.0156
5292
3001
56
Pass
0.0160
4857
2858
58
Pass
0,0164
4447
2582
58
Pass
0.0168
4098
2432
59
Pass
0.0172
3709
2278
61
Pass
0.0176
3379
2158
63
Pass
0.0181
3050,
2051
67
Pass
0.0185
2748
'1964
711
Pass
0.0189
2505
1891
75
Pass
01.0193
2299
1832
79
Pass
0.0197
2107
1779
84
Pass
0.0201
1949
1735
89
Pass
0.0205
1820,
1683
92
Pass
0.0209
1698
1621
95
Pass
0.0213
1581
1570
99
Pass
0.02117
1480
1527
103
Pass
0.0221
1398
1468
105
Pass
0.0225
1329
1409
106
Pass
0.0229
1260
1342
106
Pass
01.0233
1197
1279
106
Pass
0.0237
1138
11202
105
Pass
0.0241
1081
1122
103
Pass
0,0245
1025
1066
104
Pass
0.0249
954
1010
105
Pass
0.0253
915
928
101
Pass
0.0257
8,79
861
97
Pass
0.0261
845,
809
95
Pass
0.0265
808
745
92
Pass
0.0269
767
685
89
Pass
01.0273
732
623
85
Pass
0.0277
700
577
82
Pass
0.0281
676
524
77
Pass
0.0285
655
436
66
Pass
0.0289
639
363
56
Pass
0.0293
620
297
47
Pass
0.0297
604
290
48
Pass
0.0301
588
286
48
Pass
0.01305
573
2,81
49
Pass
stormiank 3/14/2017 4.A527 PM Page 13
0.0309
560
281
50
Pass
0.0313
551
279
50
Pass
0.0317
539
277
51
Pass
0.0321
523
274
52
Pass
0.0325
511
271
53
Pass
0.0329
496
267
53
Pass
0.0333
473
264
55
Pass
0.0337
458
263
57
Pass
0.0341
448
263
58
Pass
0.0345
438
260
59
Pass
0.0349
427
257
60
Pass
0.0353
417
256
61
Pass
0.0357
402
254
63
Pass
0.0361
396
250
63
Pass
0.0365
385
248
64
Pass
0.0369
375
245
65
Pass
0.0373
362
240
66
Pass
0.0377
355
239
67
Pass
0.0381
349
238
68
Pass
0.0385
338
233
68
Pass
0.0389
329
229
69
Pass
0.0393
320
227
70
Pass
0.0397
310
223
71
Pass
0.0401
306
220
71
Pass
0.0405
300
219
73
Pass
0.0409
296
213
71
Pass
0.0413
288
208
72
Pass
0.0417
283
204
72
Pass
0.0421
276
201
72
Pass
0.0425
270
198
73
Pass
0.0429
260
197
75
Pass
0.0433
252
195
77
Pass
0.0437
245
192
78
Pass
0.0441
239
191
79
Pass
0.0445
234
189
80
Pass
0.0449
227
187
82
Pass
0.0453
215
184
85
Pass
0.0457
205
180
87
Pass
0.0461
200
177
88
Pass
0.0465
194
173
89
Pass
0.0469
188
171
90
Pass
0.0473
184
170
92
Pass
0.0477
176
168
95
Pass
0.0481
170
166
97
Pass
0.0485
165
163
98
Pass
0.0489
158
160
101
Pass
0.0493
152
158
103
Pass
stormtank 3/1412017 4:45:27 PM Page 14
Water Quality
Water Quality BMP F»2i» «efor POC #1
On-line facility volume:
Oacre-feet
On-line facility target flow:
0! cfs.
Adjusted', for 15 min:
e.»
e\m® facility target flow:
0c
Adjusted for 15 mini:
0 efs.
stountank 3/14/2017 4:45:27 PM Page 15
UD Technique Used for TOM 'Volume Volume
Tireatmenr � Needs Through
Treatment Faciflity
(ac. -ft) (ac -ft)
infiftration Cumidialive Percent WalvQualiVy Percent Comrnen�
Vo lurne, vorume Waler Quafity
(ac -ft) Infiltrahon Infiltrated Treated
� credA
ped
storrntank 3114/2017 4:45,'27 PM Plage 16
Model Default Modifications
�- M
PERLND Changes
IMPLND Changes
No IMPLNQ changes have been made.
L,
stormtaink 3/14/2017 4:45:38 PM Page 17
Appendix
Predeveloped Schematic
sforn-itank 311412017 4:45:38 P'M Page 18
Mitigated Schematic
storaltank 3/1412017 4A538 PIV Page 19
Disclaimer
Legal No,tice
This program and accompanying documentation are provid ed 'as-iswithout warranty of any kind�. The
entire risk regarding the performance and results of this program is assumed by End User, Clear
Creek Solutions Inc. and the governmental licensee or sublicenisees disclaim all warranties, either
expressed or implied, including but not limited to implied warranties Of Drogram and accompanying
documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever
(inicluding without limitation to damages for loss of business profits, loss of business information,
business interruiption, and the like) arising out of the use of, or inabprogram even
if Clear Creek Solutions Inc. oir their authorized representatives have been advised of the
possibility of such damages. Software Copyright @ by: Clear Creek Solutions, Inc. 2010;5-2017; All
Rights Reserved.
EMMMM �
storm�ank 3/14-12017 4'45;38 PM Page, 29
B. STORMWATER POLLUTION PREVENTION PLAN
This Stormwater Pollution Prevention Plan (S WPPP) has been prepared as part of the
Construction stormwater permit requirements for the 244th St. project in SW, Edmonds,
Washington. Itis located in Section 31, Township 27 North, and Range 4 East of the Willamette
Meridian in Snohomish County, Washington. The existing site contains two existing houses with
garage, shed and an existing asphalt driveway from the 244th St. S. W. There also exists a third
house with a shed and an existing gravel driveway from the 244th St. S. W. A shop along with a
shed is also present in the site. The remainder of the site contains lawn and few trees. The site is
generally flat and appears to slope slightly towards the north. Please refer to the downstream
analysis map for more details. Per SCC survey of Snohomish County, the project site contains
Alderwood soil that have a hydrologic classification of Type "C". Please refer to the soils map
and descriptions attached later in this report for more details.
The proposal is to construct eleven new single family homes and an access drive aisle. The
project is exempt from flow control.
The purpose of this SWPPP is to describe the proposed construction activities and all temporary
and permanent erosion and sediment control (TESC) measures, pollution prevention measures,
inspection/monitoring activities, and recordkeeping that will be implemented during the
proposed construction project. The objectives of the SWPPP are to:
1. Implement Best Management Practices (BMPs) to prevent erosion and
sedimentation, and to identify, reduce, eliminate or prevent stormwater
contamination and water pollution from construction activity.
2. Prevent violations of surface water quality, ground water quality, or
sediment management standards.
3. Prevent, during the construction phase, adverse water quality impacts
including impacts on beneficial uses of the receiving water by controlling
peak flow rates and volumes of stormwater runoff at the Permittee's
outfalls and downstream of the outfalls.
Insight Engineering Co. - Stormwater Site Plan
-24-
03/08/2017
This S WPPP was prepared using the Ecology S WPPP Template. This S WPPP was prepared
based on the requirements set forth in the Construction Stormwater General Permit and in the
Stormwater Management Manual for Western Washington (SWMMWW 2005).
The 12 BMP Elements
Element #1— Mark Clearing Limits
To protect adjacent properties and to reduce the area of soil exposed to construction, the
limits of construction will be clearly marked before land -disturbing activities begin.
Element #2 — Establish Construction Access
Construction access or activities occurring on unpaved areas shall be minimized, yet
where necessary, access points shall be stabilized to minimize the tracking of sediment
onto public roads, and wheel washing, street sweeping, and street cleaning shall be
employed to prevent sediment from entering state waters.
Install the temporary construction entrance, according to the approved construction plans,
prior to any clearing or grading activities. Maintain until the access road is paved.
Element #3 — Control Flow Rates
In order to protect the properties and waterways downstream of the project site,
stormwater discharges from the site will be controlled. In general, discharge rates of
stormwater from the site will be controlled where increases in impervious area or soil
compaction during construction could lead to downstream erosion, or where necessary to
meet local agency stormwater discharge requirements.
Element #4 — Install Sediment Controls
Install silt fencing, according to the approved plans, prior to any clearing or grading activities.
Maintain until all construction activities are completed.
Install catch basin filters, according to the approved construction plans, as catch basins become
operable. Maintain until all construction activities are completed.
Element #5 — Stabilize Soils
Exposed and un -worked soils shall be stabilized with the application of effective BMPs to
prevent erosion throughout the life of the project.
Apply temporary hydro -seed to exposed and un -worked soils, according to the approved
construction plans, as needed to prevent erosion during site grading. Apply permanent hydro -
seed to areas at final grade as site grading is completed.
Apply mulching to exposed and un -worked soils, according to the approved construction plans,
as needed to prevent erosion during site grading. Maintain until site grading is completed and
permanent hydro -seed is applied.
Cover stockpiles with plastic sheeting, according to the approved construction plans, as needed
to prevent erosion during site grading. Maintain until stockpiles are removed from site.
Insight Engineering Co. - Stormwater Site Plan 03/08/2017
-25-
Element #b — Protect Slopes
All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes
erosion. The following specific BMPs will be used to protect slopes for this project.
Element #7 — Protect Drain Inlets
All storm drain inlets and culverts made operable during construction shall be protected to
prevent unfiltered or untreated water from entering the drainage conveyance system. However,
the first priority is to keep all access roads clean of sediment and keep street wash water separate
from entering storm drains until treatment can be provided.
Element #8 -- Stabilize Channels and Outlets
Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural
drainage point, efforts will be taken to prevent downstream erosion.
Element 99 — Control Pollutants
All pollutants, including waste materials and demolition debris, that occur onsite shall be
handled and disposed of in a manner that does not cause contamination of stormwater. Good
housekeeping and preventative measures will be taken to ensure that the site will be kept clean,
well organized, and free of debris.
Element 410 — Control Dewatering
There will be no dewatering expected as part of this proposal. If it occurs, Baker tanks will be
used for dewatering.
Element 911 — Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be maintained and
repaired as needed to assure continued performance of their intended function. Maintenance and
repair shall be conducted in accordance with each particular BMP's specifications. Visual
monitoring of the BMPs will be conducted at least once every calendar week and within 24 hours
of any rainfall event that causes a discharge from the site. If the site becomes inactive, and is
temporarily stabilized, the inspection frequency will be reduced to once every month. All
temporary erosion and sediment control BMPs shall be removed within 30 days after the final
site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped
sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs
or vegetation shall be permanently stabilized.
Element #12 — Manage the Project
Erosion and sediment control BMPs for this project have been designed based on the following
principles:
Design the project to fit the existing topography, soils, and drainage patterns; Emphasize erosion
control rather than sediment control; Minimize the extent and duration of the area exposed; Keep
runoff velocities low; Retain sediment on site; Thoroughly monitor site and maintain all ESC
measures and Schedule major earthwork during the dry season. The SWPPP shall be modified as
necessary to include additional or modified BMPs designed to correct problems identified.
Insight Engineering Co. _ Stormwater Site Flan 03/08/2017
-26-
Revisions to the SWPPP shall be completed within seven (7) days following the inspection.
Insight Engineering Co. - Stormwater Site Plan 03/0812017
-27-
C. OPERATIONS AND MAINTENANCE MANUAL
An operation and maintenance manual shall be submitted for the construction
submittal.
Insight Engineering Co. - Storrnwater Site Plan
-28-
03/08/2017
D. GEOTECENICAL REPORT
Insight Engineering Co. - Storrnwater Site Plan
-29-
03/08/2017
& ASSOCIATES, ENC.
Geotechnical Engineering Engineering Geology Earth Science
August 4, 2016
Mr. Mike Mietzaer
Mietzner Home Builders, LLC
11611 Airport Road, Suite B-1
Everett, WA 98204
Dear Mr. Mietzner:
Subject: preliminary Geotechnical Investigation
Mietzner Plat
8609/8611/8615 - 244th Street SW
Edmonds, Washington.
L&A. Job No. 16-117
We understand that the development a 16 -lot plat residential project is proposed for the
subject property located at the above addresses in Edmonds, Washington. At your
request, we have completed a preliminary geotechnical investigation for the subject
project. The purpose of this investigation is to explore and characterize subsurface (soil
and groundwater) conditions of the project site and evaluate feasibility of onsite
stormwater disposal. Presented in this report are our findings of subsurface conditions
and recommendations for onsite stormwater disposal.
A. three-story, above -grade, wood -framed, single-family residence is to be constructed on
each of the lots. The residence structures are to be supported on perimeter concrete
sternwalls, interior load-bearing walls, beams, and columns. The lots are to be accessed
from 244th Street SW with a paved driveway entering the south side and traversing
19213 Kenlake Place NE - Kenmore, ...oE
:.
August 4, 2016
Mietzner Plat
L&A Job No. 16-117
Page 2
northward into the interior of the site with a hammerhead at the north end of this
driveway.
The general location of the project site is shown on Plate 1 — Vicinity Map, attached
hereto. The site is situated on a gentle, southerly -declining slope. It is bounded by North
184th Street to the north and a joint -use paved driveway to the east, and is adjoined by
residential development to the south and west_ The project site is a rectangle -shaped land
elongated in the north -south direction. The townhomes are to be accessed via driveways
of porous concrete pavement northward from the j flint -use driveway.
The ground within the project site generally slopes down gently westward towards its
west side. An existing house occupies the middle of the site. The open area of the site is
mostly covered by over-grawn grass and brush and is dotted with scattered ornamental
trees throughout.
The Geologic trap of _ he Edmonds East and Part of the Edmonds West Quadrangles,
Washington, by James P. Minard, published by U. S. Geological Stuvey in 1983, was
referenced for the geologic and soil conditions at the project site. According to this
publication, the surficial soil unit at and in the vicinity of the site is mapped as Vashon
Till (Qvt) deposits.
August 4, 2016
Mietzner Plat
L&A Job No. 16-117
Page 3
The geology of the Puget Sound Lowland has been modified by the advance and retreat of
several glaciers in the past one million years or so and the subsequent deposits and
erosions. The latest glacier advanced to the Puget Sound Lowland is referred to as the
Vashon Stade of the Fraser glaciation which had occurred during the later stages of the
Pleistocene Epoch, and retreated .from the region some 12,500 years ago_
The deposits of the Vashon till soil unit were plowed directly wider glacial ice during the
most recent glacial period as the glacier advanced over an eroded. irregular surface of
older fon-nations and sediments. This soil unit is composed of a mixture of unsorted clay,
silt, sand, gravel, and scattered cobbles and boulders. The Vashon till soil over the top
two to four feet is nonnally weathered to a medium -dense state, and is moderately
permeable and compressible. The underlying fxesh till soil, commonly referred to as
"hard pan", is very -dense and weakly -cemented. The fresh till soil possesses a
compressive strength comparable to that of low-grade concrete and can remain stable on
steep natural slopes or roan -make cuts for a long period. The fresh trill deposits can
provide excellent foundation support with little or no settlement, but are of extremely low
permeability and would hardly allow stormwater to seep through.
Subsurface conditions of the project site were explored with two backhoe test pits
excavated on July 5, 2016, with a tire -mounted backhoe to depths of 8.0 and 10.0 feet.
The approximate locations of the test pits are shown on Plate 2 - Site and Exploration
Location. Plan. The test pits were located with either a tape measure or by visual
August 4, 2016
Mietzner Plat
L&A Job No. 16-117
Page 4
reference to existing topographic features in the field and on the topographic survey snap,
and their locations should be considered as only accurate to the measuring method used.
A geotechnical engineer from our office was present during subsurface exploration,
examined the sail and geologic conditions encountered, and completed logs of test pits.
Soil samples obtained from each sail layer in the test pits were visually classified in
general accordance with United Soil Classification System;, a copy of which is presented
on Plate 3. Detailed descriptions of soils encountered during site exploration are
presented in test pit logs on Plate 4.
The test pits encountered a layer of topsoil, about 8 to 12 inches thick, mantling the site.
The topsoil is underlain by a layer of weathered sail of light -brown to brown, medium -
dense, silty fine sand with trace to some gravel, about 2.3 to 3.5 feet thick. Underlying
the weathered soil is underlain to the depths explored by a glacial till deposit of light -gray,
very -dense, cemented, gravelly, silty, fine sand with occasional cobble.
Groundwater was not encountered in any of the three test pits excavated on the site. The
very -dense, cemented, glacial till deposit underlying the site at shallow depth is of
extremely low permeability and would hardly allow stormwater to seep through.. This till
deposit would perch stormwater infiltrating into the more permeable surficial soils. The
arnount of and the depth to the near -surface perched groundwater would fluctuate
seasonally, depending on precipitation, surface runoff, ground vegetation cover, site
August 4, 2016
Mietzner Plat
L&A Job No. 16-1 J 7
Page 5
utilization, and other factors. The perched groundwater would accumulate and rise in the
wet winter months and may dry up completely during the dryer summer months.
Low hnpact Development (LID) methods for onsite stormwater disposal, include storage
and reuse, splash blocks, surface dispersion; infiltration trenches, rain gardens (bio -
retention cells), porous pavement may be considered for onsite stormwater disposal.
These methods are discussed below.
Storage and Reuse
Roof runoff may be stored in cisterns or barrels during rainstorms. Mater stored inky be
used later for watering plants and irrigating lawns.
The proposed residences are of limited totat impervious area. Therefore, using splash
blocks under roof downspouts to spread roof runoff onto grass covered yards would be
sufficient to dispose roof runoff: Downspouts should be extended to at least 6 feet away
from the structures where splash blocks are placed to create sheet flag onto the yards_
The yards should be re -graded as necessary to allow disposed stonnwater to flow away
from the townhomes_
August 4, 2016
Mietrner Plat
L&A Job No. 16-11.7
Page 6
Infiltration Trenches
The project site is underlain at shallow depth by a very -dense, cemented, glacial till
deposit of extremely low permeability. Therefore, using infiltration trenches or rain
gardens to dispose stormwater solely by infiltration would require a large infiltration
bottom area., will be inefficient and may not work well. If used, infiltration trenches
should be sized based on a design infiltration rate of 4.15 iph (inches per hour).
Infiltration trenches should be located on the downhill side of adjacent structures, and
should be set back at least 5 feet from property lines and 10 feet from nearby structure
foundations or utility trenches. Also, thetrenchbottom should be at least 12 inches lower
than the adjacent footing foundations and utility trenches. The sightlines conveying
stormwater into infiltration trenches should have sufficient grade (1% minimum) to
generate flaw by gravity. Tightlines conveying storinwater into infiltration trenches
should have sufficient gradient (1% minimum) to generate flow by gravity. A clay or
lean concrete dam should be constructed in the tightline trenches to farm an impermeable
barrier to keep water in infiltration trenches from flowing backward to adjacent
structures.
The side walls (but not the bottom) of the infiltration trenches should be lined by a layer
of non -woven filter fabric (Mirafi 140NS). The trenches are then filled with clean, 3/4 to
1-112 inch washed gravel to within about 12 inches of the finish grade. The dispersing
pipes, consisting of 4 -inch, perforated PVC pipes, spaced at no more than 4 feet on
centers, should be embedded in the gravel fill at about 2 feet below top of trenches. The
top of the gravel fill should then be covered with the same filter fabric and the remaining
i
August 4, 2016
lli.etzner Plat
L&A Job No. 16.117
Page 7
trenches filled with onsite clean sandy soil. Infiltration trenches, if installed under
driveways should have gravel fill placed in 10 -inch lifts with each lift densified to a non -
yielding state with a vibratory mechanical compactor.
Rain Gardens (Bio -retention Cells)
In addition to infiltration, rain gardens may also rely on evaporation into the air and
absorption by vegetation roots for stormwater disposal. Rain gardens should be about 3
feet deep with their bottom cut into weathered soil. If used, rain gardens should be sized
based on a design infiltration rate of 0.20 iph (inches per hour). Rain gardens should be
located on the downhill side of adjacent structures and should be set back at least 5 feet
from property lines and 10 feet from adjacent structure foundations and utility trenches.
Tightlines conveying stormwater into rain gardens should have sufficient gradient (1%
minimum) to generate flow by gravity. A clay or lean concrete dam should be
constructed in the tightline trenches to form an impermeable barrier to keep water from.
flowing backward to adjacent structures.
Rain garden ponds should be lined with a layer of amended soil at least 18 inches thick.
The amended soil should consist of 40% of compost by volume mixed with clean medium
to coarse sand to achieve an organic content of at least 10% by dry weight.
Rain garden ponds should be vegetated for erosion control and the vegetation should be
fully established before the ponds can be put: in use for stormwater disposal. Planted
vegetation should be tolerant of ponding water and saturated soil conditions in the winter
months and drought in the summer months. In general, the predominant plants should be
IU & ASSOCIATES, INC.
August 4, 2016
Mietzner Plat
L&A. Job No. 16-117
Page 8
of facultative species adapted to stresses associated with -wet and dry conditions.
Typically, the plants may comprise of red twig dogwood, rushes, sedges, salmonberry and
twinbeny and ornamentals such as royal ferns, big -leaved ligularias or various primroses.
Surface Dispersion
Runoff over roofs and paved driveways may be disposed onsite by surface dispersion. A
surface dispersion system should consist of a distribution trench and a vegetated flowpath
on the downhill side of the houses to be constructed on the lots. This method will work
well only if there is sufficient open space to install this surface dispersion system on each
lot.
Porous pavement may be used for driveways of the proposed development to allow runoff
to infiltrate into the ground. A design infiltration rate of 0.25 iph (inch per hour) may be
used for design of porous pavement. A 10 -inch thick layer of railroad ballast rocks (3/4
to 2-1/2 inch crushed rock) is to be placed over prepared subgrade soils and compacted to
a firm condition with a vibratory compactor. The railroad road ballast rocks should be
covered with a layer of non -woven filter fabric (Miraf 140NS) and topped with a 4 -inch
layer of 5/8 -inch crushed rock. This crushed rock base should also be compacted to a
non -yielding state. The porous pavement with a minimum thickness of 4 inches should
then be constructed over the crushed 5/8 -inch crush rock base.
LIU & ASSOCIATES, INC.
August 4., 2016
Mietmer Plat
L&A Job No� 16-1,17
Page 9
C�
LIMITATIONS
'11"his report has been preparedfor the specific application to thispro.ject 1-br the exclusive
use by Mietzries .1--lome Builders, 1'11,C, and its associates, representatives, consultants and
contractors. The conclusions and interpretations in this rcport, however, should not be
construed as a wamanty of subsurface conditions of the site, 'rhe scone of this
irwestigation does not InChicle services related to construction safety precautions and our
recommendations are not intended to direct the contract o:A rnethods, techniques,
,,;equen cL ofi,ca
r procedures, except as specilly described in this report -for design
considerations. All geotechnical construction work should be monitored by a
gcotechnical engineer during constniction.
CLOSURE
We are pleased to ofservice to you on this prqject. Please feel free to contact ris if you have
questions regardin this report gar r .ftirther consalitation.
4�1 9
I-','ive plates attached
Yours Vely Imly,
HU & ASSOCIAI-ES, INC.
J. S, (Julian)'Liu, Ph.D., RE,
Principal,
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SITE AND EXPLORATION LOCATION PLAN
LIU & ASSOCIATES, INC. MIETZNER PLAT
8615 - 24TH STREET SW
000technical Engineering - Engineering Geology - Earth science EDMONDS, WASHINGTON
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SITE AND EXPLORATION LOCATION PL4
LIU & ASSOCIATES, INC. MIETZNER PLAT
8615 - 24TH STREET SW
Geotechnical Erlgineering Engineering Gealogy •Earth Science EDMONDS WASHINGTON
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UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
COARSE-
GRAINED
SOILS
MORE THAN 50%
RETAINED ON THE
NO, 200 SIEVE
GRAVEL
MORE THAN 50% OF
COARSE FRACTION
RETAINED ON NO, 4 SIEVE
CLEAN
GRAVEL
GW
WELL -GRADED GRAVEL, FINE TO COARSE GRAVEL
GP
POORLY -GRADED GRAVEL
GRAVEL WITH
FINES
GIM
SILTY GRAVEL
GC
CLAYEY GRAVEL
SAND
MORE THAN 50% OF
COARSE FRACTION
PASSING NO, 4 SIEVE
CLEAN
SAND
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SP
POORLY -GRADED SAND
SAND WITH
EINES
Shy
SILTY SAND
SC
CLAYEY SAND
PINE-
GRAINED
SOILS
SILT AND CLAY
LIQUID LIMIT
LESS THAN 50%
INORGANIC
ML
SILT
CL
CLAY
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
MORE THAN 50%
PASSING ON THE
NO. 200 SIEVE
Sl LTY AND CLAY
LIQUID LIMIT
50% OR MORE
INORGANIC
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
CH
CLAY OF HIGH PLASTICITY, FAT CLAY
ORGANIC
OH
ORGANIC SILT, ORGANIC SILT
HIGHLY ORGANIC SOILS
PT
PEAT AND OTHER HIGHLY ORGANIC SOILS
NOTES, SOIL MOISTURE MODIFIERS.
t. FIELD CLASSIFICATION IS BASED ON VISUAL EXAMINATION DRY - ABSENCE OF MOISTURE, DUSTY, DRY TO
OF SOIL IN GENERAL ACCORDANCE WITH ASTM D2488-83. THE TOUGH
2, SOIL CLASSIFICATION USING LABORATORY TESTS IS BASED SLIGHTLY MOIST - TRACE MOISTURE, NOT DUSTY
ON ASTM D2487-83.
MOIST - DAMP, BUT NO VISIBLE WATER
3, DESCRIPTIONS OF SOIL DENSITY OR CONSISTENCY ARE VERY MOIST - VERY DAMP, MOISTURE FELT TO THE TOUCH
BASED ON INTERPRETATION OF BLOW -COUNT DATA, VISUAL WET - VISIBLE FREE WATER OR SATURATED,
APPEARANCE OF SOILS, AND/OR TEST DATA, USUALLY SOIL IS OBTAINED FROM BELOW
WATER TABLE
Geotechnical Engineering Engineering Geology • Earth Science
UNIFIED SOIL CLASSIFICATION SYSTEM
PLATE 3
TEST PIT NO. 1
Logged By:
JSL Date: 81112016 Ground EI. ±
Depth
USCS
Sample
w
Other
ft.
CLASS.
Soil Description
No.
%
Test
OL
Dark -brown, loose, organic, silty fine SAND, some roots, moist
—
(TOPSOIL
SM
Light -brown, medium-dense, silty fine SAND, some gravel, dry
2
3
4
1
___
SM
L€ght-gray, very-dense, gravelly, siity, fine SAND, occasional----
5
cobble, cemented, slightly-moist (VASHON TILL)
7
8
9
Test pit terminated at 9.0 it; groundwater not encountered.
10
TEST PIT NO. 2
Logged By:
JSL Date_ 8/1/2016 Ground El.
Depth
USCS
Sample
w
Other
tt.
CLASS.
Soil Description
No.
%
Test
OL
Dark -brown, loose, organic, silty fine SAND, some roots, moist
------------------------------------------
(T-OPSOIL)
2
SM
Brown, medium-dense, silty fine SAND, trace gravel, moist to wet
3
4
5
-----------------------------------------
---T
-------------_..... ------..-.----------------
SM
SM
Light-gray, very-dense, gravelly, silty, fine SAND, occasional
6
cobble, cemented, very-moist to moist (VASHON TILL)
7
8
9
10
TEST PIT LOGS
L IU & ASSOCIATES, INC.
MIETZNER PLAT
8615 - 24TH STREET SSV
Geotechnical Engineering - Engineering Geology • Earth Science
11
EDMOND5 ASHINGTO,
aoB NO. 15-117
DATE 811112015 PLATE 4
TEST PIT NO. 3
Logged By:
JSL Date: 811/21116 Ground El. ±
Depth
USCS
Sample
W
Other
ti.
CLASS.
Sou Description
No.
%
Test
OL
Dark -brown, loose, organic, silty fine SAND, dry
1
____
_ MqUF
-S-OiILLI________________________
SM
Light -brown, loose, silty fine SAND, some gravel, with gravel and
2
cobble size angular rocks, glass bottles, brick fragments, dry
3
4
-------------------------------------------
SM
Light -gray, very -dense, gravelly, silty, tine SAND, occasional
cobble, cemented, slightly -moist (VASHON TILL)
5
6
7
8
9
Test pit terminated at 7.5 ft-, groundwater not encountered.
90
TEST PIT" NO.
Logged By:
Date: Ground El.
Depth
I USCS
Sample
W
Other
ft.I
CLASS.
Soil Description
No.
%
Tesi
7
2
3
4
5
6
7
8
9
10
TEST PIT LOGS
LIQ & ASSOCIATES, INC. MIETZNER PLAT
8615 - 24TH STREET SW
Geotechnical Engineering - Engineering Geology - Earth Science EDMONDS WASHINGTON
J013 N0. 16-117
HATE 8/1112018
PLATE 5