20150212153455985.pdfCity of Edmonds Public Works Department
121 - 5th Ave. North
Edmonds, WA. 98020
Re: Plan Check # BLD 20140613
622 Bell Street — Phoenix United 4 -plea
Attn: JoAnne Zulauf — Engineering Division
Dear JoAnne;
10"' February 2015
This is a response to your correction letter of January 22"d 2015 for the above noted
project along with our discussion at the city January 7"' 2015. The responses are shown
per the Ws shown on the letter., The responses marked "done" are not included. Some
additional notes have been added to address comments. Several revisions have been
made in drafting mainly to sheet 3 to present a plan that is more clear and readable.
1. A revised Cost Estimate for the Site Improvement Bond Quantity Worksheet has
been completed and is signed and attached
Q
6. The landscaping plan revised to show revisions on the site plan
9. Comments by stormwater engineer have been addressed
10. 44 cc 44 44 44 Gc 44
All done
1� Ms FMgil)c-crirq�211.01 .. 80"' Ave T4 . 1/13 WA, 98026
SHEET 2 OF 2: STORMWATER DRAINAGE (AND UTILITY) PLAN
The Construction Notes have been revised as requested per the following:
1. The side sewer slope has been revised to 2%.
2. The pipe type has been noted as "ACSP" Aluminum Corrugated Steel Pipe which
is an option as provided in a earlier comment by the stormwater engineer
5. "E5.4 " removed
8. 4" down spout drain pipe rerouted to CB # 3
12. 2 revise "I "concrete driveway
13. The landscaping strip is shown on both sides of the driveway and the sidewalks
are shown the full 59.97 frontage of the property — note 26 was removed
15. Romac Saddle added to note # 18
18. Romac Saddle added and Inserta-Tee removed
23. The pipe inverts have been revised to show a 2.0 % slope on side sewer
25. The footing drain outlet was connected to the inch outlet pipe from CB 4 before
it enters the right - Away
Additional notes 25, 26, 27, 28 and 29 have been added to detail the drainage engineers
requirements.
18. The detail on L-1 shows a concrete block wall is to be constructed on top of the
reinforced concrete wall on the west, north and east side of the dumpster enclosure
which will screen off the area — a double gate is shown on sheet 3 of the civil plans
23. The water lines cross the sewer line in the middle of the 20 -foot sleeve enveloping
the sewer line
24. No reduction requested for detention pipe reduction — pavers treated as impervious
26. The engineer requires that the pipe in the pavement is a DIP even if it has more
than 2 feet of cover
28. The pipe length has been corrected
29. The footing drain has been revised to connect to the outlet pipe on private property
32. The 6 -inch side pipe has been revised to a 2.0 % slope and a invert is called out at
the clean out at the alleys edge
Addition comments
CB 4 2 has additional inverts added
CB 4 6 invert removed
CB # 4"invert added
34. The sidewalk is shown along all street 59.97 foot of frontage - changed to sheet 3
plans are also shown
35. Landscaping is more clearly noted in the planter strip
36. a) The plans show that the tree will be "replaced "
IMl L`ngincoi,in- 21101 - 90"' Ave, 'N. 11B"F�,dinoiids,, WA. 980'-6
37. c) The new trees show a 3 x 3' tree grate in the note
38. d) The tree species have been noted on the plan
A revised DRAINAGE & DETENTION DESIGN NARRATIVE and Requirements for
Small Sites Category 4 2 Development is attached which clarifies most of the issues
requested.
Minimum Requirements # 6 and # 7 have been revised and requirement # 8, 9, 10 and I I
have been added.
The following enclosures are noted:
* Drainage Detention Design Narrative ( I page)
* Requirements for Small Site Category # 2 Development 2 pages
* WWHM 2012 Detention Calculations Printout 4 pages
* Design Sheets 1, 2, 3, 4 & 5 ( 24 x 36
Respectfully ibinitte
R. Micha I Span, PE
RMS Engineering
11101 - 8V'Avc,.,"�,4. IM WA� 98026
The site is an existing family lot 59.97 by 109.94 foot single family lot consisting of 6593
square feet. It contains a house and garage, short driveway and patio of about 2600
square feet. The site is relatively flat with an average down slope of about 4% south to
north. The lot is bordered on the south by a paved alley and the north by Bell Street.
The proposal is to remove the house, garage and patio and construct a 4-plex. The design
is to take vehicular access from both the alley and the street with a 2 -car garage for all the
units. The 39 by 76.5 foot footprint of a three story building will be place in the middle
of the lot and have a 4 -foot wide walkways of pervious pavers on the east and west sides
of the building. Concrete driveways paced on the north and south sides contain about 580
square feet. The proposed building rooftop including alb -inch overhangs contains 3339
square feet. The pervious pavers will encompass, excluding the area under the roof
overhang, 848 square feet. The total impervious area including the pavers is 5493 square
feet or 0.126 acres. The remained area of the site being landscaped area of about 1100
square feet.
The total site development contains more than 5000 square feet and less than 10,000
square feet of proposed impervious pavement and therefore is classified as a Category 2
Small Project. A stormwater detention system is requires for the project to mitigate the
5493 square feet of proposed roof, driveway, trash enclosure and sidewalks impervious
areas.
A 30 -inch diameter detention pipe with a 0.5% slope placed along the north and east
property lines has been chosen for stormwater runoff mitigation. Calculation using the
DOE WWHM 2012 program was used to determine a 30 -inch pipe 105 feet long is
required. Three 48 -inch catchbasins (3) placed in the system will reduce the required pipe
length by 18 linear feet per the attached calculations. Two outlet orifices of 0.56 inches
and 1.65 inches diameter are required for the restrictor in the down stream catchbasin # 2.
The locations of the pipe and catchbasin are shown on the plans. The collection system in
designed to drain all the onsite roof and driveways and sidewalks.
N
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1NIS F"Ilginecring 21110 - 80"' Ave W. �# B Edniiondsl. WA. 98026
Requirement for Small Sites Category # 2 Development
for a four-plex design at 622 Bell Street in the City of Edmonds
Small Site Minimum Requirement #1— Preparation of Stormwater Site Plan: Five
design sheets are enclosed of civil engineering plans. The first is a Cover and Notes, the
second a Erosion Control and Grading plan, the third a Drainage and Storm water
/Details plan, the fourth a Street Improvement plan and the fifth a Detail sheet.
Small Site Minimum Requirement #2 — Construction Stormwater Pollution Prevention
Plans: The seconds sheet shown the Silt Fencing and Construction Entrance details
which are both proposed to meet this requirement.
Small Site Minimum Requirement #3 — Source Control of Pollution: There are no
source control measures that are proposed for this residential duplex lot design.
Small Site Minimum Requirement #4 — Preservation of the Natural Drainage System
Outfall: All the drainage from the site will flow north via a new pipe into the right -away
of Bell Street. This is the existing outfall for the site. There is almost no upland drainage
onto from the alley or the adjacent property to the east. The site drainage outlet will enter
a new inline catch basin across the right -away in Bell Street. Installation of a new 8 -inch
pipe will connect the site to the new catch basin. This existing storm drainage consists of
a 12 -inch pipe/ catch basin system which drains west in the city maintained closed
system. The system eventually outlet into Shell Creek about 12 blocks north and west of
the property.
Small Site Minimum Requirement #5 — Onsite Stormwater Management: The duplex
lot design contains very little impervious area to install any large LID options found in
table # 4-2 to be utilized. The walkways are designed with pervious pavers along both
sides of the building for some infiltration water quality treatment. The Traditional
detention pipe method is used for mitigating stormwater drainage. Calculations using the
DOE WWHM 2012 are attached. A 30 -inch detention pipe was used along with three
48 -inch catchbaisns provide the required storage.
Small Site Minimum Requirement #6 — Runoff Treatment: Most of the rainfall water
runoff from the site will be from the roof tops which does not require treatment. The only
storm water requiring treatment are the short driveways north and south of the duplex
structure. These areas are only about 580 square feet of PGIS which is less than the
minimum area requiring treatment. Some surface driveway oils will be collected in the
dead storage catch basins in the detention system.
Small Site Minimum Requirement #7 — Flow Control: The site is classified as a
"Category 2 Small Site" project located is the Shell Crick drainage basin. This area
requires a peak flow outlets of 0.07 cfs/acre for a 2- year storm. 0.14 cfs/acre for a 10 -
year storm and 0.33 cfs/acre for a 100 -year storm. The proposed total developed
RMS Engineering 21101 - 801h Ave. W #B Edmonds, WA. 98026
impervious area is 0.126. Therefore the calculated outlets for a 2 -year is 0.009cfs, 0.018
for a 10 -year and 0.042 for a 100 -year storm.
A detention system with a series of 2.5 foot diameter underground pipe will be installed
on the site along the north and east sides of the structure. The outlet restrictor catchbasin
will be place at the very northwest corner of the parcel. WWHM 3 modeling program is
enclosed for the detention sizing to match the outlet requirements. .
Small Site Minimum Requirement #8 — Wetland Protection: No wetlands are on or
close to the site and protection is not required.
Small Site Minimum Requirement #9 — Operation and Maintenance: The maintenance
of the 30 -inch diameter underground detention pipe, the 48 -inch diameter catch basins
and the small onsite catch basins will be the responsibility of the private property owner
using the drainage system. Seasonally the system should be inspected. Enclosed are
copies ( 4 pages) of item that should be inspected as illustrate in the 2005 DOE
Stormwater Manual in volume V section 4.6. The items that are clouded are considered
more likely to need maintenance for this system.
Small Site Minimum Requirement #10 - Offsite Analysis and Mitigation: No offsite
problems exist and no mitigation is proposed or required.
Small Site Minimum Requirement #11— Financial Liability: No critical areas are
around the site and no downstream conveyance system capacity or flooding problems
have been located which require mitigation.
RMS Engineering 21101 - 80th Ave. W #B Edmonds, WA. 98026