IECO Response dated 6.22.16-Storm.pdfINSIGHT ENGINEERING M
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June 22, 2016
JoAnne Zulauf
121 5"' Ave. N
Edmonds, WA 98020
(425) 771-0220
Re: Mueller 4 Lot SP — PLN #20150007
IECO No. 14-0675
Dear JoAnne,
The project referenced above is revised in response to the review comments dated April 27,
2016. The review comments are numbered on the letter and have been addressed in italics as
follows:
1. The Stormwater Site Plan report (4/7/16), WWHM output report (4/7/16), Sheet C3.0
(4/6/16), and Sheet C3.1 (4/6/16) contain different rain garden bottom areas. Please
update for consistency.
The dimensions within the Stormwater Site Plan report were the correct values. The
plans and WWHM report have been changed to reflect the Stormwater Site Plan report.
2. The top and bottom elevations and groundwater elevation for Rain Garden 4 are
inconsistent between the comment response letter (4/6/16), Sheet C3.0 (4/6/16), and
Sheet C3.1 (4/6/16). Please update for consistency.
Stormwater Site
Plan report
(4/7/16)
WWHM
Output Report
(4/7/16)
Road, Drainage
and Utility Plan
C3.0 (4/6/16)
Raingarden Plan
and Details C3.1
(4/6/16)
Rain Barden 1
10' x 10'
12'x 10'
98 sf
12'x 10'
Rain arden 2
10' x 10'
12'x 10'
98 sf
12' x 10'
Rain garden 3
10'x 10'
12'x 10'
98 sf
12'x 10'
Rain garden 4
13' x 13'
15' x 13'
98 sf
15' x 13'
Rain garden 5
12' x 12'
14' x 12'
185 sf
14'x 12'
The dimensions within the Stormwater Site Plan report were the correct values. The
plans and WWHM report have been changed to reflect the Stormwater Site Plan report.
2. The top and bottom elevations and groundwater elevation for Rain Garden 4 are
inconsistent between the comment response letter (4/6/16), Sheet C3.0 (4/6/16), and
Sheet C3.1 (4/6/16). Please update for consistency.
Comment
Road, Drainage
Raingarden Plan
response letter
and Utility Plan
and Details C3.1
(4/6/16)
C3.0 (4/6/16)
(4/6/16)
Top elevation
33'
32.5'
33'
Bottom elevation
32'
31'
32'
Groundwater elevation
28.5'
NA
29'
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The elevations on sheet C3.1 were the correct values, the elevations on sheet C3.0 have
been revised accordingly. Rain Garden — 4 has been relocated to the western side of
driveway for lot 4, and Rain Garden — S has been relocated to the eastern side of the
turn -around. Test pit locations still applies. Rain Gardens I and 5 will collect runoff front
the proposed tract and therefore will be constructed along with the Short Plat
construction. The remaining rain gardens will be constructed along with the construction
of the homes and have been "grayed out" on the plans. Refer to the revised plans.
Rain Garden — I elevations have been revised to:
Rain Garden -1
Top elevation 33.5'
Bottom elevation 32.5'
Groundwater elevation 30.0'
Invert elevations are inconsistent between Sheet C3.0 (4/6/16) and Sheet C3.1 (4/6/16).
Please update for consistency.
The invert elevations have been revised and are now consistent.
4. The WWHM model output report lists the WWHM version as Version 4.2.11 (2015-11-
13). There have been several model updates since that time. The current version of the
model is Version 4.2.12 (2016-02-25):
http://www. cey.wa.gov/Programs/wq/stormwater/wwhmtraining/index.html
The latest version of WWHM has been used for the latest calculation. The drainage
report has been revised. Please refer to the revised WWHMprintout within the
Stormwater Site Plan report.
5. The WWHM model output report includes a 10" diameter riser; however, the Raingarden
Plan and Details, Sheet C3.1 (4/6/16) shows a 6" diameter riser.
The model has been revised to include 6" diameter risers.
6. The test pit locations have not been provided as referenced in the geotechnical report.
Please provide Plat 2 to verify the test pit locations. Grain size distributions from the test
pits also has not been provided (see comment #9 under status of previous comments
blow).
PO Box 1478 • Everett, WA 98206 s Phone: (425) 303-9363
Fax: (425) 303-9362 • Email:info@insightengineering.net
Road, Drainage
Raingarden Plan
and Utility Plan
and Details C3.1
C3.0 (4/6/16)
(4/6/16)
Rain garden 1
31.9'
29.24'
Rain garden 2
28.9'
28.5'
Rain Qarden 3
28.9'
1 28.5'
Rain garden 4
31.9'
1 29.24'
The invert elevations have been revised and are now consistent.
4. The WWHM model output report lists the WWHM version as Version 4.2.11 (2015-11-
13). There have been several model updates since that time. The current version of the
model is Version 4.2.12 (2016-02-25):
http://www. cey.wa.gov/Programs/wq/stormwater/wwhmtraining/index.html
The latest version of WWHM has been used for the latest calculation. The drainage
report has been revised. Please refer to the revised WWHMprintout within the
Stormwater Site Plan report.
5. The WWHM model output report includes a 10" diameter riser; however, the Raingarden
Plan and Details, Sheet C3.1 (4/6/16) shows a 6" diameter riser.
The model has been revised to include 6" diameter risers.
6. The test pit locations have not been provided as referenced in the geotechnical report.
Please provide Plat 2 to verify the test pit locations. Grain size distributions from the test
pits also has not been provided (see comment #9 under status of previous comments
blow).
PO Box 1478 • Everett, WA 98206 s Phone: (425) 303-9363
Fax: (425) 303-9362 • Email:info@insightengineering.net
..........e......... '7........... ,, .111".
Test pits and grain size distributions have been provided. Refer to the geotechnical
reports located in the appendix of the Stormwater Site Plan report.
7. For bioretention facilities/rain gardens, the Edmonds Stormwater Supplement (Appendix
Q states that there shall be one test pit per 5,000 square feet of contributing area;
however, only three test pits were included in the geotechnical investigation.
Test pits at the proposed locations of each lot and tract has been provided. Refer to the
geotechnical report by Earth Solutions NW LLC dated 1/27/2016 located in the appendix
of the Stormwater Site Plan report.
8. Post construction soil quality and depth is described on sheet 3.0, but is not currently
mentioned in the Stormwater Site Plan report.
Post construction soil quality and depth has been added to MR#5 of the Storinwater Site
Plan report.
Comment from Jerry Shusher
9. Rain Garden sizing
The geotechnical report does not contain all the site characterization criteria found in
Volume III, Section 3.3 of the SWMMWW. The design infiltration rate used in the
modeling is from two Test pit sample. The location and depth of these test pits as well as
the grain size distribution are not included on the submittal. For design purposes, soil
samples must be collected at the location of the proposed bioretention/rain gardens at or
below the proposed depth of the native soil bioretention soil interface.
4/25/16 — The locations of the test pits still have not been provided.
Test pits at the proposed locations of each lot and tract has been provided. Refer to the
geotechnical report by Earth Solutions NWLLC dated 1/27/2016 located in the appendix
of the Stormwater Site Plan report.
Please feel free to contact me with any questions or comments you may have.
Sincerely,
Jacob Mealey
PO Box 1478 • Everett, WA 98206 • Phone: (425) 303-9363
Fax: (425) 303-9362 • Email:info@insightengineering.net