Stormwater Memo.pdfRAM Engineeri
To: JoAnne Zulauf
City of Edmonds
Engineering Division
emorandum
ber 7, 2016
From: Rob Long, PE FiECEIVED
RAM Engineering
Subject: Burleigh Short Plat- Lot 3— 22934102nd PI W
Stormwater Memo l SEKAG :S CTR,.
o
Y OF EDMONDS
RAM Job No. 15-016 �w•
This memo provides the design analysis of the stormwater drainage control system for Lot 2 of the Burleigh Short Plat
(22934 102nd PI W). A gravelless chamber system is proposed to control the proposed addition of 3,520 sf of
impervious area for Lot 2. A site specific 2.0 in/hr design infiltration rate was determined by the geotechnical engineer.
The stormwater gravelless chamber has been sized using the City of Edmonds Simplified Sizing Tables (handout #E72 -B).
The below tables provide the sizing information for the infiltration drywell systems.
Project Area Summary:
Proposed Impervious = 3,520 sf
Building Rooftop, Covered Deck and Patio (roof line) = 2,860 sf
Uncovered Patio and Walks = 110 sf
Driveway (pollution generating) = 550 sf
Individual Lot Gravelless Chamber Sizing Summary:
Individual Lot
Total Impervious = 3,520 sf
Required Chamber Length (3,520 sf x 0.014)1 49.3 ft
Required Chamber Storage (49.3 ft @ 2.6 cf/ft) 128.1 cf
Required Chamber Surface Area (49.3 ft @ 2.8 sf/ft) 138.0 sf
Proposed System Hancor Arc 36 HC Storage 63.0 ft
Provided Chamber Storage [59.0 ft @ 2.04 cf/ft (10.7 cf / 5.25 ft)Z ] 128.5 cf
Provided Chamber Surface Area [59.0 ft @ 2.34 cf/ft (12.27 cf / 5.25 ft)2 ] 147.4 sf
Gravelless Chamber Size: 63.0 ft long Hancor Arc 36 HC2
1. 1.4% impervious surface sizing factor per Edmonds simplified sizing charts (with 2.0 in/hr soils and Category 2 Site)
2. See Honcor Arc 36 HC specification brochure (segment length 63 in., capacity 10.7 cf, open bottom area 12.27 sf)
Infiltration Trench Design Criteria per Edmond's Handout #E72B:
%!G1 E: UN" DIVISION
Native Soil Desi!zn
Infiltration Rate
BMP Facility Overflow- Depth I (inclics/hour)
Sizin" Factor
(54 of contributing
impervious area)
Category calceory
I Sites a 1 2 Site% h Sizing EqUalion
Design Criteria for All MIN
• These WAN shall notbeused in:
The North Ednioncis Earth Subsidence and Landslide Nazar(l Area (ESLHA) 3
Up-1radient (east) of lite ESLHA
In it Landslide Hazard Area'
Within 5 feet ofVrolvi-ty lines and easements
Within 10 feet from underground storage links
Within 50 feet front proposed or existing septic systems or drain Fields.
Where the depth to the lop of the seasonal grWndwaler level is less than I foot from ilie bottom of ilie
facifily.
• The KNIP nitist meet the following setback requirenients front buildings:
- if ninoffis front an area less than 5.0'14) square 1'ect, &[back is 5 1'ect frorn a structure WillIOL11 a
basement and 10 feel for a sirticitire with a basement.
- If runoff is front an area greater than or equal to 5.000 square fee(. a structure shall not inlerwel
wills I Horizontal: [Vertical slol)e front the bottom edge of the facility. Mininitini 5 feet front
structure williotit a basenienil and 10 I'M fora sirticuire with a basement.
• An overnow I)aiii ,,list K- sieciried such that runoff above the facilily's design capacity does not cause:
Flooding ol'a building or emergency access
Erosion or (fou'risireani sedimentation
SIOI)c filliltil.c.
101-7116
Attachments:
A. Edmond's Handout #E72B, Figure A-4 Typical Gravelless Chamber Detail
B. Honcor Arc 36 HC System Brochure (2 pages).
RAM Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.corn
0,2i
3.7*0
3.7%
0�517%
. .......... .. ...... ..... . ..--- . ......Otavelless
2"70 o
Chamber Length (feet)
NA 1.0
1.900
1.900
Impervious Area (square feet) x
challiber,
..... . ..... . ........ ------
..... . ... .......... . . - ............
Sizine Factor(°6)x100
1.5
1.506
1.609
BMIPlepipili iscakiflileda,a
function of toil: 13IP(Fmi)= buivervious Area (square I'eeox Sizing Factor
t'& V I WX
Design Criteria for All MIN
• These WAN shall notbeused in:
The North Ednioncis Earth Subsidence and Landslide Nazar(l Area (ESLHA) 3
Up-1radient (east) of lite ESLHA
In it Landslide Hazard Area'
Within 5 feet ofVrolvi-ty lines and easements
Within 10 feet from underground storage links
Within 50 feet front proposed or existing septic systems or drain Fields.
Where the depth to the lop of the seasonal grWndwaler level is less than I foot from ilie bottom of ilie
facifily.
• The KNIP nitist meet the following setback requirenients front buildings:
- if ninoffis front an area less than 5.0'14) square 1'ect, &[back is 5 1'ect frorn a structure WillIOL11 a
basement and 10 feel for a sirticitire with a basement.
- If runoff is front an area greater than or equal to 5.000 square fee(. a structure shall not inlerwel
wills I Horizontal: [Vertical slol)e front the bottom edge of the facility. Mininitini 5 feet front
structure williotit a basenienil and 10 I'M fora sirticuire with a basement.
• An overnow I)aiii ,,list K- sieciried such that runoff above the facilily's design capacity does not cause:
Flooding ol'a building or emergency access
Erosion or (fou'risireani sedimentation
SIOI)c filliltil.c.
101-7116
Attachments:
A. Edmond's Handout #E72B, Figure A-4 Typical Gravelless Chamber Detail
B. Honcor Arc 36 HC System Brochure (2 pages).
RAM Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.corn
Attachment A. Edmond's Handout #E728, Figure A-4 Typical Grovelless Chamber Detail
UV2M*LCWYO Solid hd with swfice access
ISM01 MWII PC*. OMWN
0.4me, Mesm
WN s Or Mp-,)a ermyN OXCV0
Cross -Section
Na I Wt
044 I r)
cr,~BEA
r POP LWAIVIEL OrLWO
A &MvOicar. hirlftxtiou abilubeE "�_xjck dc.,.tiZw.x.et.1 tv.o figure 5-27. The Void spajoc per Linear fOOt ".I be M IcIAM 2
cabic fect 11M,
infil"tivc Sul foot per I.Inear foot ghajtl be mi Ikov 2.8 sq ft.
'InIr Colle%vi:lg pmlucts age knovm to Emck dmse
L�' 11101311101 SY90"'Vll JW'
at tato tmx lae� High Capacits by HaqwoT, hic"
Systirmls, lav
Figure A-4. Typical gravelless chamber (Figure 5.27 in Appendix 5A of the Kitsap County Stonn water
Afanal"oeonew Design .41annal [Kitsap Count% 19971).
A-1
RAMI Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com
intrusive installations.
The Arc 36 HC septic leaching chamber is a sturdy, lightweight plastic
unit that combines maximized infiltrative surface area and storage
capacity with an improved structural design to handle most any
conventional leachfield system challenge without sacrificing performance,
This unique combination allows for increased effluent dispersal
installation and simplified contouring capabilities.
"I NIIP�
P,
,I rka
UTTVUTIFTTI�
• l�ection-mOdeid from: Hoi Density Polyethylene
(HDPE) for lightweight and sturdy design
• 20 -degree integral articulating joint that is ideal
for either straight or contoured septic leachfield
applications
• True corrugated charrAw design eliminates
flat surfaces and prowdes increased load
bearing capability in the trench
• Designed to accommodate both gravity -fed
and pressure-Aosed systems
• 'Lock and Drop' joint provides a more positive
connection during installation and backfill
• A universal inlet/outlet end cap
• Inspection vent ports on every unit with
easy -to -remove knockouts for maximum
job site flexibility
• Convenient five-foot lengths are easy to handle
• Quickly installed by one person into three-foot
wide trench or bed applications
component which snaps in place to allow side
entry at any joint throughout the trench line
Diamond plate texture increases slip resistance
and enhances ease of installation
AW
RAM Engineering 1653113 Ih AveW,SuiteA108 Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com
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