Stormwater Memo.pdfFrom: Rob Long, PE
RAM Engineering
Subject: Burleigh Short Plat- Lot 4^' 22936102nd pl W
Stormwater Memo
Memorandum
'p p Date: December 6, 2016
t
RAM Job No. 15-016o
t
This memo provides the design analysis of the stormwater drainage control system for Lot 4 of the Burleigh Short Plat
(22936 102nd PI W). A gravelless chamber system is proposed to control the proposed addition of 2,910 sf of
impervious area for Lot 4 (300 sf of Lot 4's driveway is accounted for in the private road infiltration trench system). 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 = 2,910 sf
Building Rooftop, Covered Deck and Patio (roof line) = 2,260 sf
Driveway; and Uncovered Patio and Walks = 650 sf
(note: 300 sf of lot 4's driveway is accounted for in the private road infiltration trench system)
Individual Lot Gravelless Chamber Sizing Summary:
Individual Lot
Total Impervious = 2,910 sf
Required Chamber Length (2,910 sf x 0.014)' 40.7 ft
Required Chamber Storage (40.7 ft @ 2.6 cf/ft) 105.9 cf
Required Chamber Surface Area (40.7 ft @ 2.8 sf/ft) 114.1 sf
Proposed System Hancor Arc 36 HC Storage 52.0 ft
Provided Chamber Storage [52.0 ft @ 2.04 cf/ft (10.7 cf / 5.25 ft)z] 106.1 cf
Provided Chamber Surface Area [52.0 ft @ 2.34 cf/ft (12.27 cf / 5.25 ft)Z ] 121.7 sf
Gravelless Chamber Size: 52.0 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 1 Site)
2. See Hancor 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:
Native Soil Design
Infiltration Rate
BMP Facility Overflow Depth I (inches/hour)
Sizing Factor
(�/ of contributing
impervious area)
Category Category
Sites ' '.. 2 Slleti b Sizing Equation
Design Criteria for All BMPs
■ These. BMPS shall not be used in:
The North Edmonds Earth Subsidence and Landslide Hazard Area (ESLHA)'
Upgradient (east) of the ESLHA
In it Landslide Hazard Area°
Within 5 feet of property lines and easements
Within 10 feel from underground storage tanks
Within 50 feel from proposed or existing septic systems or drain fields.
Where the depth to the top of the seasonal groundwater level is less than I foot from the bottom ol'the
facility.
• The BMP must meet the following setback requimuerus from buildings:
- If runoff is from an area less than 5,000 square feet, setback is 5 feet frown a structure without a
basement and 10 feet for a structure with a basement.
- If runoff is front an area greater than or equal to 5,000 square feet, a structure shall not intersect
with a I Horizontal: I Vertical slope from the bottom edge of the facility. Minimum 5 feet from a
structure without a basement and 10 feet fora structure with a basement.
w An overflow path must be specified such that runoff above the facility's design capacity does not cause:
Flooding of a building or emergency access
Erosion or downstream sedimentation
Slope failure.
12/6/16
Attachments:
A. Edmond's Handout #E72B, Figure A-4 Typical Gravelless Chamber Detail
B. Hancor Arc 36 HC System Brochure (2 pages).
M Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425)678-6900
RAM engineeringi nc.com
0.25
3.796
3.7%
0 5
""""""`�"`
2.700
2.70/6
Gravelless Chamber Length (feet)
Gravelless
NA
L
0
1.9%
1..9%
= Impervious Area (square feet) x
Chamber `
Sizutg Factor (0'u)t100
1.5
1.596
L6 °i6
BMP length is calculated as
a function of intinrvious arca draining to it: BMP Length (feeo = Impervious Area (square feet) x Sizing Factor
OkY 100,
Design Criteria for All BMPs
■ These. BMPS shall not be used in:
The North Edmonds Earth Subsidence and Landslide Hazard Area (ESLHA)'
Upgradient (east) of the ESLHA
In it Landslide Hazard Area°
Within 5 feet of property lines and easements
Within 10 feel from underground storage tanks
Within 50 feel from proposed or existing septic systems or drain fields.
Where the depth to the top of the seasonal groundwater level is less than I foot from the bottom ol'the
facility.
• The BMP must meet the following setback requimuerus from buildings:
- If runoff is from an area less than 5,000 square feet, setback is 5 feet frown a structure without a
basement and 10 feet for a structure with a basement.
- If runoff is front an area greater than or equal to 5,000 square feet, a structure shall not intersect
with a I Horizontal: I Vertical slope from the bottom edge of the facility. Minimum 5 feet from a
structure without a basement and 10 feet fora structure with a basement.
w An overflow path must be specified such that runoff above the facility's design capacity does not cause:
Flooding of a building or emergency access
Erosion or downstream sedimentation
Slope failure.
12/6/16
Attachments:
A. Edmond's Handout #E72B, Figure A-4 Typical Gravelless Chamber Detail
B. Hancor Arc 36 HC System Brochure (2 pages).
M Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425)678-6900
RAM engineeringi nc.com
Attachment A. Edmond's Handout #E72B, Figure A-4 Typical Grovelless Chamber Detail
UUM
Profile View
UVffRPLUWU Solid lid nrith surface access
ON 6C0
MIN S FT OF OGFM BELOW &a0V0
Cross -Section
M
A, PAyr) letr tetiiltrzstiOu C113zUbct jmtmh d swignM per figure 5-27. ''l. c Void spaoc per 1znt4 " foot %hall bc: at leant 2',6
cubic, tcLt, j,he itrtitarrttiVC SLI,rtzcc per Izrr A Itz t Isball be sit leust 2.8 e
InflItTatorep 11it#1 Capacity by Isifilbut Systcnl%, Inc.
1 nviroChamhor t kh8h CaPecity ICY I°140c0t, Ittic,
StvrtntechC SC -310 by infitm/or Systems. Inc
Figure A-4. Typical gravelless chamber (Figure 5.27 in Appendix 5A of the Kitsap County . t raaaat}nter
Management Design Manual [Kitsap County 1997]).
A-1
IMAM Engineering 16531131hAve W,Suite A108 Lynnwood WA 98037 (425)678-6960 RAM engineeringinc.com
Arc
I'M
Leachfield Chamber
SAVE, TIME AND LABO,R
WITH, THE ARC 36, HC
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.
ENGINEERED FOR OPTIMAL PERFORMANCE.
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
performance and improved structural integrity as well as ease of
installation and simplified contouring capabilities.
FEATURES & BENEFITS:
• Injection -molded from High 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 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
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B-1
RAM Engineering 1653113" Ave W, Suite A108 Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com
HANCOR ARCw 36 HC SEPTIC LEACHING CHAMBER SPECIFICATIONS
SCOPE
This specification describes the Arc chamber units for use in onsite wastewater
disposal applications.
CHAMBER REQUIREMENTS
Arc chambers are manufactured from high-density polyethylene with an open
bottom, solid top and louvered sidewalls. Sidewall louvers shall be designed to
minimize soil intrusion.
Chamber shall meet the load rating of H-10 (16,000 Ib per axle) with a minimum
of 12 inches of cover when tested in accordance with IAPMO PS 63 and installed
in accordance with manufacturers installation procedures.
CHAMBER CONNECTION
Each chamber shall interlock with an integral articulating joint. Articulating joints
shall have a free range of horizontal rotation of 20 degrees, with a maximum of 10
degrees in either direction. Articulating joint shall be constructed by placing the dome with
engaging knuckle of the incoming chamber over the post end of the previously-instalted
chamber, with final engagement occurring when, the lower base flanges of the incoming.
chamber under -lap the raised base flanges of the previous lyinstalled chamber.
MATERIAL PROPERTIES
Each chamber shall be manufactured from high-density polyethylene as defined
and described in IAPMO PS 63.
INSTALLATION
Installation shall be in accordance with Hancor installation procedures and those
issued by the local health department regulations.
1
DOS,-CV4r $VITH DOME ENDWITH
RECEMN3 AREA 'KNJCKLE'
II
A
B-2
M Engineering 1653113`hAve W,Suite A108 Lynnwood WA 98037 (425)673-6960 RAMengineeringinc.com