Stormwater Memo.pdfFrom: Rob Long, PE
RAM Engineering
Subject: Burleigh Short Plat- Lot 2— 22932102nd PI W
Stormwater Memo
RAM Job No. 15-016
Memorandum
Date: October 7, 2016
This memo provides the design analysis of the stormwater drainage control system for Lot 2 of the Burleigh Short Plat
(22932 102nd PI W). A gravelless chamber system is proposed to control the proposed addition of 3,300 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 = 3,300 sf
Building Rooftop, Covered Deck and Patio (roof line) = 2,830 sf
Uncovered Patio and Walks = 110 sf
Driveway (pollution generating) = 360 sf
Individual Lot Gravelless Chamber Sizing Summary:
Individual Lot
Total Impervious = 3,300 sf
Required Chamber Length (3,300 sf x 0.014)1 46.2 ft
Required Chamber Storage (46.2 ft @ 2.6 cf/ft) 120.1 cf
Required Chamber Surface Area (46.2 ft @ 2.8 sf/ft) 129.4 sf
Proposed System Hancor Arc 36 HC Storage 59.0 ft
Provided Chamber Storage [59.0 ft @ 2.04 cf/ft (10.7 cf / 5.25 ft)z ] 120.4 cf
Provided Chamber Surface Area [59.0 ft @ 2.34 cf/ft (12.27 cf / 5.25 ft)Z ] 138.1 sf
Gravelless Chamber Size: 59.0 ft long Hancor Arc 36 HCz
1. 1.4% impervious surface sizing factor per Edmonds simplified sizing charts (with 2.0 in/hr soils and Category 2 Site)
2. See Hancor Arc 36 HC specification brochure (segment length 63 in., capacity 10.7 cf, open bottom area 12.27 sf)
EINGIG DIVISION
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Infiltration Trenc qeg cgi . Criteria Edmond's Handout #E72B:OCT 1. 01
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Attachment A. Edmond's Handout #E728, Figure A-4 Typical Gravelless Chamber Detail
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AI ravel s ianfil, n �hjmt,wr txg la dicaigned pee fugure 5-27. 71w Void sps= per l" ex foot shall be at
cubic i s The infltm ivc surface per linear foot shall be at Veaaat 2.8 sq ft.
T c, following products are kftow�n to I. c t thr Scav Dem chs n crit is
InfiltratorO Miglu pa by by infiltrator Systems, Inc,
Enva.roCba;rr.bcr0 Hisfn Capacityby Hemor, Inc,
stanxrtn rcln S("-3 10 by lu iltrater Systents, Inc
Figure A-4. Ty ical gravelless chamber (Figure 5.27 in Appendix 5A of the Kitsap County Slormorater
. anagement Design Manual [ ,:itsaj) County 1997]),
A-1
RAM Engineering 16S3113`hAve W,Suite A108 Lynnwood WA 98037 (425)678-6960 RAMengineeringinc.com
Leaching chambers are rapidly becoming the product of choice for
leachfield applications over conventional pipe and gravel systems.
Their lightweight construction offers lower installed costs and less
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,
. . . . . . . . . . .
installation and simplified contouring capabilities.
FEATURES & BENEFITS:
(HDPE) for lightweight and sturdy design
• 20 -degree integral articulating joint that is ideal
for either straight or contoured sepfic leachfield
applications
• True corrugated chamber design eliminates
flat surfaces and provides increased load
bearing capability in the trench
• Designed to accommodate both gravity -fed
and pressure -dosed 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
• Increased plumbing option with Side Port Coupler
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
T ---
B-1
RAM Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (4115) 678-6960 RAMengineeringinc.com
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