13-102906FILE
Rev August 15, 2013
G EOTECHNICAL REPORT
FOR STORMWATER RESIGN, APPENDIX C
KING COUNTY SWM
Tim Johnson Residence
44thAve SW and SW 310th°Street
Federal Way, WA 98023
Parcel# 112103-9009
Prepared for
Tryge Pohlman
RESUBMITTED 122 Pershing Ave
Carbonado, WA 98323
SEP 0 4 2013
CITY OF FEDERAL WAY
CDS
-1 WAJason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall / Pavement Design Project Tim Johnson, 44th
7�d
Consulting Construction Management Ave SW and SW 3101h St,
Business, Inc. WABO/ AASHTO Inspection & Testing Federal Way
File #:13024
TM Pohlman Construction Inc
122 Pershing Ave
Carbonado, WA 98323
Attu Tim Johnson c/o Mr. Tryge Pohlman:
Re: Johnson Residence, Parcel# 112103-9009
At your request, we have conducted a soils exploration for the above mentioned project. During our exploration,
two test pits were advanced to determine soil characteristic per KCSWM, Appendix C.
Permeability is expected to be rapid, on the order of 5 minutes/inch. The remaining results of this investigation are
found in the following report ,
We would be pleased to continue our role as geotechnjcal engineers during the project We appreciate this
I
pportunity to be of service to you and we look forward to working with you in the future. If you have any
questions concerning this report, the procedures used, or if we can be of any further assistance please call us at
(206) 786-8645.
Respectfully,
JASON ENGINEERING &CONS NG BUSINESS, INC
0 ; %VA
President �� a
trr 7_
373439.
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 2 of 18
PO Box 181 Auburn WA. 98071
Jason
IgEngineering &
Consulting
Business, Inc
Table of Contents
Geotechnical Engineering
Retaining Wall / Pavement Design
Construction Management
WABO/ AASHTO Inspection & Testing
Table of Contents
Investigation Information
Introduction
Scope:
Sampling & Laboratory Testing Procedures:
,Site Tnformatinn
Project Description
Geology of Area Alderwood gravelly sandy loam (AgC)
Geoseismic Setting -
Liquefaction Potential
Description of Foundation Materials:
Groundwater and Surface Runoff "Control•
Climate of Area:
Conclusion
Appendix I: TestPit Logs
Log, Typical
SCS Soil Survey
Vicinity Map
Site Plan
Rev Date. 8-15-2013
Project: .Tim Johnson, 44th
Ave SW and SW 310th St,
Federal Way
File #:13024
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 3 of 18
PO Box 181 Auburn WA. 98071
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Jason
Engineering &
Consulting
Business, Inc.
Geotechnical Engineering Rev Date: 8-15-2013
Retaining Wall / Pavement Design Pr°ject-Tim Johnson, 44th
Construction Management Ave SW and SW 310f St,
WABO / AASHTO Inspection & Testing Federal Way
Investigation Information
Introduction:
This report presents the results of a soils exploration and analysis for the proposed new construction located at
44fl,ave SW and SW 3101h Street in Federal Way. The provides the soil profile components, the engineering
characteristics of the foundation materials and provides criteria for the design engineers and architects to prepare
or verify aspects of the stormwater design per AppendixC of the King County Storm Water manual. This report
was requested by Tryge Pohhnan Written authorization to perform this exploration and analysis was provided by
Tryge Pohlman
Legal Description
BEG 523 FT N & 40 FT W OF SE COR GL 3 TH W 556.64 FT TH N 470 FT TH N 87-23-30 E 255.14 FT TH S TO PT
860 FT N & 341.76 FT W OF SE COR OF GL 3 TH S 89-54-50 E TO ELY MGN OF 44TH AVE SW HOIT RD 132.90
FT TH SLY ALG A 413.07 FT RAD CURVE TO RGT AN ARC DIST OF 107.72 FT TH S 84-43-40 E 205.14 FT TO W
LN OF E 40 FT OF GL 3 TH S ALG SD W LN 217 FT TO POB LESS POR PLTD AS DUMAS HEIGHTS
Scope:
The scope of this report and analysis included; a review of geological maps of the area, review of geologic and
related literature, a reconnaissance of the immediate site, subsurface exploration, and laboratory testing.
We were not requested to provide an Environmental Site Assessment for this property. Any comments concerning
onsite conditions and/or observations, including soil appearances and odors, are provided as general information
Information in this report is not intended to describe, quantify or evaluate any environmental concern or situation
We were not requested to provide landslide or slope stability analysis. The soils engineer warrants that the
findings, recommendations, specifications, or professional advice contained herein, have been promulgated after
being prepared according to generally accepted professional engineering practice in the fields of foundation
engineering, soil mechanics and engineering geology. No other warranties are implied or expressed.
This investigative report has been prepared for the exclusive use of Tryge Pohhnan and retained design consultants
thereof. Findings and recommendations within this report are for specific application to the proposed project. All
recommendations are in accordance with generally accepted soils and foundation engineering practices.
Sampling & Laboratory Testing Procedures:
The test pits were performed by hand excavation. Representative samples were obtained from the test pits at
various soil intervals. The samples obtained by this procedure were classified in the field by a soils technician,
identified according to test pit number and depth, placed in plastic bags to protect against moisture loss and
transported to the laboratory for additional testing.
Along with the field investigation, a supplemental laboratory testing program was conducted to determine
additional pertinent engineering characteristics of the foundation materials necessary in analyzing the behavior of
the proposed building structure. The laboratory testing program included supplementary visual classification and
water content determinations on all samples. In addition, selected samples were subjected to: Moisture Content
Analysis - D4959, and Grain Size Analysis - ASTM designation C-117, C 136. All phases of the laboratory testing
program were conducted according to applicable ASTM Specifications and the results of these tests are to be found
on the accompanying logs located in the Appendix.
Phone: 206-786-8645 Email:- Jason@jasonengirneering.com Page 4 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall / Pavement Design Project Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
Site Information
Project Description
The purpose of this section is to provide details of the proposed structure. The following information was provided
by the project contractor. The building will be a wood framed, single family residence structure. A large garage
basement is planned. The site topography consists of mostly flat ground to the west There is a slope on the east
side of the property downward to a ravine. The slope is approximately 50% with a vertical elevation difference of
about 30 feet. A large retaining wall is to be constructed to create the driveway on the north side.
Geology of Area: Alderwood gravelly sandy loam (AgC)
The geology of the site and surrounding, area as taken from the USDA Soil Conservation Service Survey consists of
Alderwood gravelly sandy loam (AgC). Typical Alderwood soils are moderately well drained, undulating to hilly
soils that have dense, very slowly permeable glacial till at a depth of 20 to 40 inches; on uplands and terraces
formed under conifers in glacial deposits. This soil is rolling. Areas are irregular in shape and range from 10 to
about 600 acres in size. A typical profile is a very dark brown gravelly sandy loam on the top two inches. It is weak,
fine, granular structure, friable, non sticky and non plastic. Layers at 2 to 12 inches are a dark brown; dry, slightly
hard, friable soil. It is non sticky, non plastic strongly acidic, with a sub angular blocky structure. From 12 to 27
inches the soil is grayish brown to light gray hard friable, non sticky, non plastic and medium acidic. Boundaries
are wavy with distinct mottles of light olive. At 27 to 60 inches the soil is grayish brown to light gray weakly to
strongly consolidated till. It is dry, medium acidic with distinct mottles of light olive and yellowish brown.
Permeability is moderately rapid in the surface layer and subsoil, however it is very slow within the cemented
layer and dense glacial till. Roots penetrate easily to the consolidated substratum where they tend to mat on the
surface. Alderwood soils are in a cool marine climate. The summers are cool and dry, and the winters are mild and
wet. Water moves on top of the substratum in winter. A perched water table is as high as 18 to 36 inches at times
from January through March. Runoff is slow to medium and erosion hazard is moderate.
Geoseismic Setting:
EXPLANATION
El
Site class F
Reywres sire -specific
inir+iigaiwm
❑ Site class E
Site class D to E
❑ z
7R
❑ Site class D
Site class C to D
❑ c
❑ Site class C
Site class B to C
❑ y
❑ Site class B
Foundation soils on this site are designated a Site Class C, from Table 1615.1.1 per the International
Building Code (I.B.C.). All building structures on this project should be designed per the Code
Requirements for such a seismic classification. These types of soils have a shear wave velocity in the
Phone: 206-786-8645 Email: Jason@jasoneogineering.com Page 5 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/ Pavement Design pt_oject: Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
File #:13024
range of 1,200 to 2,500 ft/sec. The undrained shear strength is typically greater than 2000 psf with blow
counts greater than 50 blows per foot. The following may be used for the seismic coefficients.
Design Response Spectrum
90.00
N
c 80.00
_O
70.00
m
60.00
s0.00
$ 40.00
30.00
Q
20.00
10.00
N 0.00
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Period, T
Liquefaction Potential:
EXPLANATION
ElLiquefaction susceptibility: HIGH
Liquefaction susceptibility: MODERATE to HIGH
❑ Liquefaction susceptibility: MODERATE
❑ Liquel'action susceptibility: LOW to MODERATE
❑ Liquefaction susceptibility: LOW
❑ Liquefaction susceptibility: VERY LOW to LOW
❑ Liquefaction susceptibility: VERY LOW
Period,
T Sa Sds Sms
0
0.00
33.33
To
0.08
83.33
83.33
125.00
Ts
0.42
83.33
83.33
125.00
1
1.00
34.67
2
2.00
1 17.33
• Sds and Sms values
acceleration
o Sm1 = 52, Sd1= 34.7
given at max
Liquefaction is when saturated, cohesionless soils are temporarily turned in to a liquid state usually from a seismic
event. If ground motion lasts for extended amounts of time, the grain to grain contact shifts and the grain structure
can collapse. If the water within the soil cannot flow easily between the grain and out of a collapsing area, the
water pressure increases. When pore pressures build up within the soil and exceed the effective contact pressure of
the soil, the water can push the soil particles apart When the particles lose contact with each other, the soil mass
can behave like a liquid. If pore pressures are great enough, water may discharge out of the ground like a geyser
leaving characteristic signs, such as sand boils. Liquefaction is generally related to; soil characteristics, water table
depths and the degree of seismic activity. The results are lower bearing capacities, increased settlement issues,
landslides, and lateral spreading to name a few things. Liquefaction potential for this site is provided within the
boundaries of the site. Seismic events which affect land masses on a greater scale are beyond the scope of this
report.
The Liquefaction Susceptibility Map of King County Washington provided by the Department of natural Resources
classifies the area as VERY LOW to LOW. We are in agreement with this susceptibility rating and have used this
information within our design recommendations.
Phone: 206-786-8645 Email: JasonOjasonengineering.com Page 6 of 18
PO Box 181 Auburn WA. 98071
It
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall / Pavement Design Prrniect Trim Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
File #:13024
Description of Foundation Materials:
Test pit #1
Test Pit #2
The surface of the proposed construction site is covered with about 2 to 6 inches of topsoil that should be removed
prior to the start of any construction due to the high compressibility of these soils. Silt with sand layers were
encountered beneath the existing topsoil and extended to depths beyond the scope of this investigation. Lines of
demarcation represent the approximate boundary between the soil types, but the transition may be gradual
Below 4 feet, the excavation was difficult for the machine to excavate the dense silty sandy till layers.
Groundwater and Surface Runoff Control:
Groundwater was not encountered when the field exploration was conducted. Groundwater is not expected to
cause difficulties during construction of this project.
The on -site drainage (roof downspouts& catch basins for pavement areas) should be collected and directed away
from the property. This can be acconiplislied by tight -lining the drainage toan on -site storm drainage system. All
impervious surfaces are expected to connect to the storm drain system
Mottled soil indicates seasonal soil saturation (alternate oxidizing and reducing conditions). In other words, water
flows through this layer periodically creating a saturated soil condition at times and at other times the soil may be
dry. This can create a soft, saturated yard area, problems for basements and septic fields, and poor aeration for
landscape plantings. Implementation of perimeter footing drains should alleviate many difficulties associated with
these soil conditions. Proper grading of the ground surface to direct runoff to the collection points is required.
Phone: 206-786-8645 Email:- Jason@jasanengineering.com Page 7 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Of/
Engineering & Retaining Wall/ Pavement Design Project Tim Johnson, 44th
_ Consulting Construction Management Ave SW and SW 3101h St,
Business, Inc. WABO/ AASHTO Inspection & Testing Federal Way
Climate of Area:
The climate of the site and surrounding area as taken from the USDA Soil Conservation Service Survey consists of
mean annual precipitation ranging from 35 to 60 inches, most of which falls as rain from November through March.
Mean January temperature is 38 degrees F, mean July temperature is. 60 degrees F, and mean annual temperature is
50 degrees F. The frost free season (28 degrees F) is about 200 days.
Conclusion
The on -site drainage (new and existing, roof downspouts & catch basins for pavement areas) should be collected
and directed away from the property by tight -lining the drainage to the bottom of the slope. A retaining wall is
scheduled to constructed to create a driveway to the property. This area could serve as a large drywell reservoir to
collect roof runoff and allow it to filtrate into the ground. Any overflow could be dispersed to the existing drain
trench on the north side of the property. Proper grading of the ground surface to direct runoff to the collection
points is also required.
When the plans and specifications are complete, or if significant changes are made in the character or location of
the proposed structures, a consultation should be arranged to review them regarding the prevailing soil conditions.
Then, it may be necessary to submit supplementary recommendations.
While the recommendations made herein are considered sufficient in detail for the construction of the proposed
project, there are many alternative methods of construction which are available. We can discuss various other
options for construction at your request.
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 8 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/ Pavement Design Project Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 3101h St,
Business, Inc. WABO/ AASHTO Inspection & Testing Federal Way
Appendix I: TestPit Logs
Log Typical
Boring ID: Typical for 1,2 Method of Sample: Track Excavator
Date of Excavation: 4-12-2013 Surface Elevation (ft): 75
Project Name: Tim Johnson Total depth (ft): 6
File #: 13024-001 Technician: JECB
Depth(ft):
Profile
SPT (N)
Moisture
Percent passing
Sample
Description
3/4"
#4
#200
(feet) (meters)
USC S
(blows/ft)
%
Type
1 0.30
'Topsoil
2 0.61
ML
10
Silt with Sand, dense, mottled in top 12 inches
3 0.91
(estimated)
30
Silt with Sand, very dense,
4 1.22
ML
5 1.52
(estimated)
6 1.83
7 2.13
8 2.44
9 2.74
10 3.05
End Boring
Boring ID: Typical for 3,4 Method of Sample: Track Excavator
Date of Excavation: 8-15-2013 Surface Elevation (ft): 75
Project Name. Tim Johnson Total depth (ft): 6
File #: 13024-001 Technician: JECB
Depth(ft):
Profile
SPT (i)
Moisture
Percent passing
Sample
Description
3/4"
#4
#200
(feet) (meters)
USCS
(blows/ft)
%
Type
1 0.30
Topsoil
2 0.61
ML
Silt with Sand, med dense, slightly mottled
3 0.91
4 1.22
ML
;Silt with Sand, medium dense,
5 1.52
6 1.83
7 2.13
8 2.44
9 2.74
10 3.05
End Boring
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 9 of 18
PO Box 181 Auburn WA. 98071
Rev August 15, 2013
GEOTECHNICAL REPORT
FOR STORMWATER DESIGN, APPENDIX _C
KING COUNTY SWM
Tim Johnson Residence
44til Ave SW and SW 310th Street
Federal Way, WA 98023
Parcel# 112103-9009
Prepared for
Tryge Pohlman
122 Pershing Ave
Carbonado, WA 98323
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall / Pavement Design Project: Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 310h St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
Appendix II: Drywell Area
C.2.24 USE OF DRYWELLS FOR FULL INFILTRATION (2009 SWDM Appdx C)
Drywells are gravel filled holes as opposed to trenches and therefore may allow for a more compact design in areas
where the depth to the maximum wet -season water table is relatively deep (e.g., 6 feet or greater). Figure C.2.2.0 on
page C-47 illustrates the specifications for drywell infiltration systems as outlined below:
1. When located in coarse sands and cobbles, drywells must contain a volume of gravel equal to or greater
than 60 cubic feet per 1,000 square feet of impervious surface served. When located in medium sands,
drywells must contain at least 90 cubic feet of gravel per 1,000 square feet of impervious surface served.
2. Drywells must be at least 48 inches in diameter and deep enough to contain the gravel amounts specified
above for the soil type and impervious surface area served.
3. The gravel used for drywells must be 1-1/2-inch to 3-inch washed drain rock The drain rock may be
covered with backfill material as shown in Figure C.2.2.0 (p. C-47) or remain exposed at least 6 inches
below the lowest surrounding ground surface.
4. Filter fabric (geotextile) must be placed on top of the drain rock (if proposed to be covered with backfill
material) and on the drywell sides prior to filling with the drain rock
5. Spacing between drywells shall be a minimum of 10 feet.
6. Drywells must be setback at least 15 feet from buildings with crawl space or basement elevations that are
below the overflow point of the drywell
Soils is the drywell area are a medium dense, sandy loam. Limited infiltration may be used.
Per C.2.3.4 USE OF DRYWELLS FOR LIMITED INFILTRATION, the specifications for use of drywells for limited
infiltration are the same as those used for full infiltration, except that every 1,000 square feet of tributary
impervious surface requires different gravel volumes as follows:
(a) 230 cubic feet if the soil is a fine sand/loamy sand,
(b) 380 cubic feet if the soil is a sandy loam, or
(c) 570 cubic feet if the soil is a loam
Impervious
(SF)
Req'd CF/SF impervious
House 5460
Driveway
3180
Gravel required for dryweU
Fine loamy sand (a)
230
1256
731
Sandy loam (b)
Loam (c)
380
570
2075
3112
1208
1813
Totals 8640 1 1987 1 3283 4925
Various configurations and/or dimensions may be used to obtain the required 3,283 cubic foot volume, however
the overall volume is the goal. For instance;
15 x 15x 15 feet = 3,375 CF (125 Cubic yards)
20 x 20 x 8.5 feet = 3,400 CF (125 Cubic yards)
Phone: 206- 886-8645 Email: Jason@jasonengineering.com Page 11 of 18
PO Box 181 Auburn WA. 98071
Jason w 'Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/Pavement Design Project: Tim Johnson, 44th
__ Consulting Construction Management Ave SW and SW 310thSt,
T Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
File #13024
Drywelllocation'-pic 1
Drpi location pic.2
Phone: 206-786-8645Email•,Jason@jasonengineering.com I Page 12 of 18
PO Box 181 , Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/ Pavement Design Project: Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
File #:13024
SECTION C? FLOW CONTROL 111`Ps
FIGURE C.2.2.0 TYPICAL DRYR'ELL Lk;FILTRATIO\ SYSTE-1I
` f Roof Downspout
House If'
—0
Roof flow
Downspout
Catch Basin
(Yard Drain)
r112V W=t I
PLAN VIEW
NTS
} Roof Downspout
House l Overflow
l Splash Block
—1►
flow 't
Fine Mesh Screen'
Catch Basin
(Yard Drain)
15' min.
DRY WELL
SECTION
NTS
Topsoil
Min. 4" dia.
PVC Pipe
Sides of Hole '
Lined with
Filter Fabric
O
48 Inch Diameter
Hole Filled with
11/2-3" Washed
Drain Rock
Mark Center of Hole
with 1" Capped PVC
or Other means
Flush with Surface
I r
I'min.
48 Inch Diameter 4' min_
Hole Filled with
11/2-3" Washed
Drain Rock
Min. V above Seasonal
High Groundwater Table
t
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 13 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering
Engineering & -Retaining Wall/Pavement Design
Consulting Construction Management
Business, Inc. WABO/ AASHTO Inspection & Testing
Site Plan — Dry well
Phone: 206-786-8645, Email• jasongaksonengineering.com
PO Box 181 Auburn WA. 98071
Rev Date: 845-2013
Project: Tim Johnson, 44th
Ave SW and SW 310!h St,
Federal Way
File #:13024
Page 14 of T8
DUMAS BAY PARK ENTRANCE ROAD
OVERFLOW TOEMSPING
DITCH LINE
/ LOCATION. ENCLOSED IN CONCRETE
FILLED WITH CRUSHED GRAVEL
NO F1I3ES (1-1/2'to 3' AGG)
WN 15 FOOT SEPARATION FROM HOUSE
-WN DRYWELL DIMENSIONS SHOWN
�`,t0'x20'x8.5'�$ItUCP
— ' Yx15'z15'9,VSCF(optional)
x ,
3oa T�o 1
2ra tt
1
i ♦�
r
SURVEY PROVIDED BY JEFF DALQUIST, ARCHITECT • IMPERVIOUS (SF) GRAVEL FOR DRYWELL (CF)
HOUSE 5460 2075
DRIVEWAY 918A 1206
TOTALS 8640 3283
0 20 40 60
0
w
n m g
^
^ E2.
E m
�a
Tim Johnson Residence
44th Ave SW and SW 310th Street
�' 8 aeon
Geotechnical En eerieMIC:
_
L
Federal Way, WA 98023
Retaining Wall / Pavement Designngineering &
Parcel#112103-9009
Construction Managementonsulting
WABO / AASHTO Inspection & TestingBasiness, Inc
o
W
PO Box 781 Anbuai WA- 96071'(206)78h-8613 `jason�jasonengincYing.com
..
@
DRY WELL
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/ Pavement Design Proiec - Tim Johnson, 44th
-_ Consulting Construction Management Ave SW and SW 310th St, Z�d Business, Inc. WABO / AASHTO Inspection & Testing Federal Way
File #:13024
Appendix III: Full Dispersion (with city permission)
Full dispersion of the full 8,640 impervious surface may be handled with a single 50 foot gravel trench, IFF there is
a 200 foot vegetated flow path from the trench. Since the property line is only 30 feet from the house, there is
insufficient room on the property. The neighboring property is owned by the City of Federal Way as Dumas Bay
park
Typically, homeowners are expected to maintain their own runoff on their own property. The options of limited
infiltration (125 cubic yards of material) and a 50 foot trench (about 19 cubic yards) are both acceptable per the
design manual Special permission must be granted for dispersion to accepted as noted in the design manual;
Section C.3 Storm Water Design Manual
The intent of ESC measures is to prevent, to the maximum extent practicable, the transport of sediment and
other construction -related pollutants to streams, wetlands, lakes, drainage systems, and adjacent ro erties
during and after construction. Erosion of disturbed areas on construction sites can result in excessive sediment
transport to adjacent properties and to surface waters. This sediment can result in major adverse impacts, such
as flooding due to obstructed drainage ways, smothering of salmonid spawning beds, creation of algal blooms in
lakes, and violation of State water quality standards for turbidity. In addition to sediment, other construction -
related pollutants can be generated by uncovered waste materials, stockpiles, and demolition debris, de -
watering; maintenance and operation of heavy equipment; chemical spills; oil spills; placement of concrete; and
application of fertilizers andpesticides. Such pollutants can be toxic to both fish and humans and may violate
State water quality standards and the prohibited discharges section of KCC 9.12.
TABLE C.2.1.A SU_ BNURY OF DISPERSION DEVICE FLO'%VPATH LENGTHS & CAPACITIES
Full Dispersion
Device
Native Vegetated
Flowpath Length
Maximum Impervious
Surface Amount
Maximum Non -Native Pervious
Surface Amount
Non -Pasture
Pasture
Splash Block
100 feet
700 sq ft
NA
NA
200 feet
1,400 sq ft
NA
NA
Rock Pad
100 feet
700 sq ft
2,500 sq ft
8,000 sq ft
200 feet
1,400 sq ft
5,000 sq ft
16,000 sq ft
10-foot Gravel
Trench
100 feet
1,400 sq ft
5,000 sq ft
16,000 sq ft
200 feet
2,800 sq It
10,000 sq ft
32,000 sq ft
50-foot Gravel
Trench
100 feet
5,000 sq ft
17.500 sq ft
54,450 sq It
200 feet
10,000 sq ft
35,000 sq ft
108,900 sq ft
Sheet Flow from
Impervious Surface
100 feet*
25-ft strip width
NA
NA
200 feet"
50-ft strip width
NA
NA
Sheet Flow from
Non -Native Pervious
Surface
25 feet
NA
25 feet of width in direction of flow
50 feet
NA
100 feet of width in direction of flow
75 feet
NA
175 feet of width in direction of flow
100 feet
NA
250 feet of width in direction of flow
' Reducible to 10 feet for each 20 feet of strip width when dispersing over outwash soils outside the UGA.
Phone: 206-786-8645 Email- Jason@jasonengineering.com j Page 15 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall / Pavement Design Pr�0'im Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
File #:13024
FIGURE C.2.1.1) 50-FOOT DISPERSION TRENCH IVITH -NOTCHED BOARD
pipe O.D.
in Mill end cap or plug
7 clean out wye from pipe
a r vain I 4" or 6- perforated pipe laid flaVli
notched
grade board a a"
P7 M77)
2"x 2" notches ra 7 type I CB w/solid cover (locking)
18" O.C. A
a t
a influent pipe (max design
a° a flow!:-, 0.5 CFS per trench)
C d 7°
v; vclean out wye from pipe
Q 8
n
a
PLAN
NTS
galvanized bolts
y51� ma�1
2" X12" t
pressure
treated grade -
board
4" x 4' support post
filter fabric
pipe O.D.
l 1'-0 1'-0
ax
Mini illin 31". M
4" or 6" perforated
v , v pipe laid flat
as clean (<_5%fines)
° A 1112" - 3l4 "washed rock
SECTION A -A
NTS
flow to second
dispersal trench
if necessary
B
:over
-.0--
flow to other
branching CB's
as necessary
18" O.C.
�.1 2"
2" grade
board notches 2"
NOTES:
1. This trench shall be constructed so
as to prevent point discharge and/or
erosion.
2. Trenches may be placed no closer
than 50 feet to one another. (100 feet
along flowline)
3. Trench and grade board must be
level. Align to follow contours of site.
4. Support post spacing as required by
soil conditions to ensure grade board
remains level.
Phone: 206-786-8645 Email: Jason@jasonengineering.com Page 16 of 18
PO Box 181 Auburn WA. 98071
Jason Geotechnical Engineering Rev Date. 8-15-2013
0/71 Engineering & Retaining WaR.1- Pavement Design Project Tim Johnson, 44th
Qf-_ Consulting Construction Management Ave SW and SW,310Ih St, z�Business, Inc. WAB-O/AASHTO-Iftgpection & Testing Federal Way
File #:13024
AMP contours of site and adjacent property, Dumas Bay Park
Federal Way
Phone: 206-786-8645 Email: Jason@Jasonengineering-com Page 17 of 18
PO Box 181 Auburn WA. 98091 ' I
Jason Geotechnical Engineering Rev Date: 8-15-2013
Engineering & Retaining Wall/ Pavement Design Project Tim Johnson, 44th
Consulting Construction Management Ave SW and SW 310th St,
Business, Inc. WABO/AASHTO Inspection & Testing Federal Way
Site Plan - 50 foot dispersion trench
Phone: 206-786-8645 Email: Jason@jasonengineering.com I Page 18 of 18
PO Box 181 Auburn WA. 98071
DUMASBAY PARK ENTRANCEROAD
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