0958_001.pdfSTORMWATER REVIEW COMMENTS
City of Edmonds
Engineering Division
To: Applicant
Date: Apri18,2019 I MAC ENGINEERING RESPONSES: April 29, 2019
Project Name: Hicks Family Trust
Permit Number: BLD20181267
Address: 1001 OlympicAve
Review Type: Building Permit (SFR)
Submittal Date: 3/22/2019
Reviewer: Zack Richardson, PE FCITY 2ND COMMENTS
City of Edmonds, Stormwater Engineer
Recommendation: I recommend that BLD20181267 be withheld until the
comments below are adequately addressed.
Review Comments:
1. Drainage Report: It does not appear that the singular boring log
meets the minimum requirement for the site -specific soils
investigation. Update report to:
a. Extend boring to the minimum depth of 4' below finished surface.
Update: Not addressed On Jan. 28, 2019, Mac Engineering
discussed with Zack by phone the difficulty in performing the
boring by hand due to cementious soils. This has been further
explained in the Drainage Report.
b. Include a map/exhibit identifying the location of the boring on -site.
Update: Not addressed Mac Engineering prepared an exhibit for
the Drainage Report (see attached). Also shown on plan sheet C2.
i. If boring was located in the vicinity of a previous
improvement, clarify if the improvements were in -pace
or recently removed at the time of investigation.
c. Identify the USDA soils classification(s) encountered.
Update: Not addressed The USDA soil map indicated Alderwood-
Urban, however the soil encountered appeared more like
f�b,4
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Alderwood gravelly sandy loam. The soil was a very restrictive till -
like silty sand material with very little organic material and may be
compacted structural fill. This has been explained in the Drainage
Report.
d. Include a name, stamp, and signature of the professional who
performed the boring.
Update: Not addressed Mac Engineering attempted a hand dug
boring. The name, stamp, and signature are on the cover of the
Drainage Report.
2. Nothing further.
3. General: It is unclear which plan is controlling the grading for the
site; update architectural site plan or one of the civil sheets as the
"grading plan".
Update: Appears architectural site plans controls grades, but
conflicts/concerns exist as notes: MAC ENGINEERING'S SITE
PLAN CONTROLS GRADING
❑ Update civil plans and/or drainage report to include final square footages
used for sizing the BMPs and include sizing calculation for how the trench
length was determined. TRENCHES SIZED 700 SF
IMPERVIOUS=10' OF TRENCH LENGTH.
5,568/700=7.95*10=79.5 FEET OF TRENCH.
❑ Update to address which plans controls TESC; update TESC plan to
protect infiltration capability of dispersion trench bottom from construction
traffic (architectural plans shows stockpile over trench areas). Mac
Engineering's SWPP Plan shall control TESC.
o Architectural utility plan appears to propose a sewer service which is in
direct conflict with the proposed drainage system; updated/address as
needed. Wayne Malmberg will address.
❑ Building footprints appear slightly differentbetween architecturalandcivil
plans; ensure areas used for drainage design match architectural sheets.
The plans have been modified.
❑ The architectural grading appears to suggest a low spot which is slightly
offset north from the pavement joint where the civil currently proposes the
trench drains; update/address as needed. Mac Engineering has
provided proposed grading on the site plan (Sheet C1).
o Grading plan (arch) suggested the vegetated flow path varies between
11% and 20% in steepness (>15%) and may not meet the requirements
for a vegetated flow path and appears to suggest that dispersion may be
infeasible without additional geotechnical approval; updated/address (on
grading plan or in drainage report) as needed. Please refer to the
revised Mac Engineering site plan which includes proposed
grading. The vegetated flow path is compliant as proposed.
o If flow path if not compliant with requirements of , modelling credit
may not be used and the peak flow exemption from flow control
need to be updated and re-evaluated. The flow path is compliant
as proposed on the site plan.
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4. Grading plan: Provide spot elevations at the corners and grade -breaks along the
driveway surface, sufficient enough to verify drainage will function as intended
and meet maximum grade requirements.
Update: It appears that the proposal accepts road runoff sheet flow and directs
all surface flows from areas east of the structure to the west, directly toward the
proposed structure: update plans as need to address surface runoff or update
report to acknowledge condition and address why the grading plan is of no
concern to the structure. Olympic Ave has an asphalt thickened edge, so the
proposal accepts no road runoff sheet flow. Please refer to the revised
Drainage Report and upstream analysis and Mac Engineering's site plan
which includes proposed grading.
5. Nothing further.
6. Cl: Provide top/finished grade and invert elevations for the dispersion trenches.
Update: Not addressed; needs to be on design plan and consistent with the
grading plans. This as -built note was added to sheet C1, "Finished grade, catch
basin rim elevations and invert elevations of dispersion trenches system [to be
surveyed and confirmed for as -built]". Providing this on the design plans
would require survey of the site.
7. C 1: Identify location where footing drains will outlet; if they outlet to the
dispersion trench system, provide enough information to verify that the footing
drains maintain a minimum freeboard above the top -of the dispersion trench to
avoid backwatering.
Update: Not addressed; elevations not provided. This Storm Drainage note was
added to sheet C1, "Footing drains will outlet to proposed dispersion trench
system. Contractor will construct the footing drains with a minimum freeboard
of one foot from the top of the proposed dispersion trench to avoid potential
backwatering[to be surveyed and confirmed for as -built]". Providing this on the
design plans would require survey of the site.
8. Nothing further.
9. Nothing further.
10. Nothing further.
11. Nothing further.
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