REVIEWED STM 2021-07-13 Grey Sea Drainage Memo Rev1I;ECIL
ASOCIATES
MEMORANDUM
Date: April 23, 2021 (Revised 7/13/21) Project #: #21-001
To: Zack Richardson, Stormwater Engineer
From: Roger J. Cecil, P.E.
cc: Meredith Kelly, DeForest Architects
Subject: Grey Sea Residence - 729 Laurel Street
Memorandum of Stormwater Management Compliance/26/2021
Grey Sea Residence Project Summary
The project includes the expansion and renovation of the existing residence at 729 Laurel Street in
Edmonds. The existing site contains existing impervious areas, a large portion of which currently
drains into the City's MS4 system. Currently, approximately 2,606 sf of roof area, and
approximately 1,000 sf of pavement drain into the MS4 system in Laurel Street, at the SW corner of
the property. Additional paved areas, (approximately 1,534 sf) drain to the north to the stream in the
alley, just off of the property. In the proposed condition, the amount if impervious draining to the MS4
is increased by 317 sf. See Exhibit 1.
Two small expansions are proposed, one on the SW corner of the basement level for the garage
(300sf), and one on the north end of the first -floor level, cantilevered over an existing outdoor
concrete patio (266sf). Site improvements for the project include the addition of a driveway, as well as
concrete walkways, porches, and stairs at the main entry of the house.
Drainage Review analysis
Edmonds Community Development Code (ECDC), Section 18.30, addresses Stormwater Management
from construction and development sites. ECDC 18.30 also references the 2014 Stormwater
management Manual for Western Washington (SWMMWW) and the Edmonds Stormwater
Addendum, which further detail requirements for projects in the City of Edmonds. In accordance with
ECDC 18.30.060 and Figure 3.1:
1. ALL development shall be required to comply with Minimum Requirement No. 2. ECDC
18.30.060.D.2.d.i references the SWMMMWW chapter 2, Section 2.5.2 for construction
Stormwater Pollution Prevention Plans (SWPPP's) and Details. The project complies with this
requirement. Please refer to the Civil Plans, Sheet C1.00 and C1.10 for Demolition and
Temporary Erosion & Sedimentation Control (TESC) Plans and Details, which comply with
Minimum Requirement No. 2.
2. Projects that result in 2,000 sf or more of new plus replaced hard surface area shall comply
with Minimum Requirements No. 1 through No. 5. The project proposes a total of new plus
replaced hard surface areas of 1,545 sf, which does not meet the 2,000 sf threshold for this
requirement. See Figure 1 on the following page for a detailed graphical depiction of
proposed new + replaced hard surface areas. Of note is a recent interpretation provided by
the stormwater engineer; that a home expansion area located above ground, and also above
an existing exterior impervious surface that will remain in place, is NOT considered a
replaced hard surface area. Based on the project scope and the feedback from the City, this
project does not meet thresholds for this requirement, and MR No. 1 through MR No. 5 do not
apply to this project.
FIGURE 1 - HARD SURFACE EXHIBIT
E TING HARD SURFACE TO REMAIN
EXISTING ROOF SURFACE TO REMAIN -
193:181 ING HARE EaTRPAtE Tong REmourb
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