RESP0NSE LETTER - PREL SUBMITTAL.pdfSITE DEVELOPMENT SERVICES
August 7, 2018
City of Edmonds
Development Services Department
121 5t11 Ave N
Edmonds, WA 98020
Subject: Lee Short Plat, PLN 20180013
Attn: Mike Clugston, Senior Planner
Dear Mr. Clugston:
This letter is presenting the responses to the comments from Engineering that were
included with your letter dated May 24, 2018.
Memo from Jennifer Lambert:
GENERAL:
1. Added Special Note 94 to Sheet 1 stating that all building will be demolished.
2. Site address corrected.
3. Added new sheet 1 to show existing conditions.
4. Existing irrelevant information removed from Drainage Plan and the added Utility
Plan.
5. All known utilities have been shown except for water services within the site.
That information is not needed, as all such lines will be abandoned in place and
will not represent any hazard if they remain. There is no gas on the site.
UTILITIES:
1. As stated above, all known existing utilities have been shown. Existing dry
utilities are above ground. Proposed utility routing has been added.
2. Requested utility information has been added.
3011 Raven Crest, Bellingham, WA 98226 425-481-9687
STORMWATER ENGINEER:
Per discussions with the reviewer, the permeable pavement has been modeled as a
separate element. Because the geotechnical engineer stated that the existing site
fill material is unsuitable for use under pavements, it will be removed and
replaced with engineered material meeting the requirements for treatment and
traffic support. A discussion of this has been added to the TIR. No underdrain is
being used. Through a combination of check dams and an overflow pipe, the
drainage reservoir under the pavement will store and average of 3 inches of water.
This was described in the TIR and modeled accordingly.
2. The controlling factor in the design of the permeable pavement is the depth to the
seasonal water table. This depth was measured in many places by the
geotechnical engineer and is plotted in the profile. The top of the permeable
pavement has been revised and is shown in the profile to be adequate to provide
the minimum one foot of suitable soil above the ground water.
3. Drainage Report Revisions for Category 2 review:
a. Each of the minimum requirements has been addressed in the revised
reports as required. An explanation was added under MR44 stating that
the retaining wall is being placed very close to the top of the channel
located along the east property line. It shows that very little if any of the
channel below the high water mark will be affected. However, the option
to deepen the wall as necessary to enable widening of the channel bottom
can be used to maintain the same or greater cross sectional area.
b. Infeasibility criteria has been presented under the MR45 discussion, as
requested.
c. Using the soil under the permeable pavement was thoroughly researched
with the geotechnical engineer and the reviewer. As presented in the TIR,
the existing fill material will be removed and replaced with engineered fill
that meets the requirements for treatment and traffic support. The
specifications for treatment have been added to the Special Notes on Sheet
3.
4. The address on the report cover has been corrected.
5. An assumed driveway area for each lot was added to Sheet 3.
6. Offsite analysis comments:
a. The downstream analysis was revised to explain where the runoff from the
ROW goes. The conclusion from both the survey and site review was that
it sheet flows to the open channel before the channel enters the piped
system. The completed design will capture this water, convey it to the
detention vault, and release it to the same drainage system at a point just
off of the southeast corner of the site.
3011 Raven Crest, Bellingham, WA 98226 425-481-9687
b. The current drainage system below the channel outfall was clarified to the
extent that the systems could be exposed. The effect of the block wall was
added to the TIR as explained above. This project will not add any flow to
the channel
c. The pipe sizes were verified an explanation was added to the downstream
analysis. Some pipes are not 18 inches as verified in the revised report.
7. A structural engineer was consulted relative to the retaining wall design without a
wall drain. This can be done, but it should be revisited during final design to
ensure the most effective system is utilized.
The reason for the dead storage was added to the Detention Design section of the
TIR. It is because the vault must be 7 feet high, minimum, but we can only use
some of that for live storage because of the elevation of the existing storm drain to
which we are connecting. The dead storage is not used for treatment. It would
have been if that treatment level was all that was required.
9. The vault dimensions in the report match the modelled vault.
10. Pavement hatch has been added to Sheet 3.
END OF MEMO
3011 Raven Crest, Bellingham, WA 98226 425-481-9687