1021 2ND AVE S-Impervious Surface Calcs.pdfREAM Engineering Memorandum
To
City of Edmonds Development Services Department
1215th Avenue North
Edmonds, WA 98020
From: Rob Long, PE
Subject:
RAM Engineering
16531 13th Ave W, Suite A108
Lynnwood WA 98037
Date: December 18, 2015
Select Homes SFR at 10xx 2"d Ave S (PN# 005820 003 002 00)
Plan Check #BLD 2015
Impervious Surface Area and Stormwater Detention Pipe Calculations
RAM Job No. 15-040
12/18/15
This memo provides the proposed site impervious areas and stormwater detention pipe calculations for the
construction of a new single family residence at 10xx 2nd Ave S. The stormwater control detention tank has be sized
using the City of Edmonds Simplified Sizing Approach. The pre -sized approach for sizing flow control BMPs has been
developed for Small Site Projects in Edmonds with between 2,000 and 10,000 square feet of new and replaced
impervious surface area. Edmonds handout E72-A provide simplified sizing guidelines.
Project Area Summary:
Total Site Area = 9,735 sf
Proposed Impervious = 3,500 sf
Building Rooftop, Covered Deck and Patio (roof line) = 2,550 sf
Uncovered Patio and Walks = 50 sf
Driveway (pollution generating) = 900 sf
Underground Detention Tank Sizing: Per Table 1 of handout E72-A, 3,500 sf if impervious requires 24 ft length of 30 inch
diameter detention pipe with a 5/8 in diameter orifice:
3,500 sf
Table 1
Detention Pipe Look -Up Table
Category 1 Small Site Projects
Contributing New Plus
Replaced Impervious
Surface Area (sf)
Len ii, or Five (ft) For Own Insi
Ie Diameter
18-Inch
24-inch
36-inch
30-Inch
2.000
41
22
15
11
2.500
49
30
18
12
3.000
61
33
23
16
—� 3.500
74
38
1 24
1 17
4.000
81
45
29
20
4.500
95
49
32
23
5,000
112
56
35
25
St — square Im
Orifice Size:
= 0.5 ( 112( inch diameter = 0.75 (3/4) inch diameter
= 0.625 (5/8) inch diameter = 0.875 (718) inch diameter
Proposed Detention Tank: 24 ft — 30" Pipe with 518" orifice size.
RAM Engineering 1653113`hAve W,Suite A108 Lynnwood WA 98037 (425)678-6960 RAMengineeringinc.com
RAM Engineering
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Select Homes SFR at 10xx 2"d Ave S (PN# 005820 003 002 00)
Plan Check #BLD 2015
Project Area Summary:
Total Site Area = 9,735 sf
Proposed Impervious = 3,500 sf
Building Rooftop, Covered Deck and Patio (roof line) = 2,550 sf
Uncovered Patio and Walks = 50 sf
Driveway (pollution generating) = 900 sf
EVS-C
NOV-W
RAM Engineering 1653113`I' Ave W, Suite A108 Lynnwood WA 98037 (425) 678-6960 RAM engineeringinc.conn