response to eng. comments 1.pdf1001 Fifth Avenue, Suite 1808 Seattle, VVA98181 206.622.5822 kpficnm
May 2S.2O15
Ms. Jeanie McConnell
City VfEdmonds
Public Works Department
Engineering Division -
121 Fifth Avenue North
Edmonds, VVAQ8O2O
GUbieCL: Permit Application #BLD2O15O4AO
Edmonds School District Sherwood Elementary School
Response to Public Works Comments
Dear Jeanie:
The following outlines our response to City of City of Edmonds Civil Plan Review comments
date May 19, 2015. Your original comment letter is enclosed for reference.
1. Please provide an itemized engineers cost estimate, including units and unit prices, for
both onsite and off-site /hght-Of+w8y\improvements, including all utilities and traffic
C8DfnOl. Please use the King County Site Improvement Bond Quantity Worksheet and
utilize the "write-in" sections where appropriate.
8. A bond is required to be p|8C0d for all erosion Don(nJ| Dl88SUre8. and
StOrO0vv@te[management improvements. The amount Vfthe bond will bebased OD
12Of6Ofthe City approved estimate. The City will inform you Ofthe appropriate bond
amount after review 0fthe cost estimate. Please obtain the appropriate subdivision
improvement bond forms from the City.
b. |fyou intend t0post Gbond inorder i0record the subdivision and ahead of
constructing required improvements, the bond amount will be based on the entire
scope Ofthe project.
o. Inspection fees for this project will be C8|CU|8ted at 3.3% of the 120% City approved
estimate for all improvements.
Engineers cost estimate using King County Site Improvement Bond Quantity
Worksheet is forthcoming. We will provide when we are complete.
2. |DdUde aCity Engineering Division approval block 0Oall plan sheets. Refer tOsample
on City website.
3. Please add @ note tOplans stating "A separate i construction permit iG
naqUi[8d for all work within the Cih/ right-of-way." Please Dote, 8 ROW permit application
with contractor's signature shall beprovided t0the city prior tVissuance of civil
cODBt[UCtioD p|@DG.
Ms. Jeanie McConnell
May 29, 2015
Page 2
Response: Note added. See note 12 on sheet C4.01
4. Please provide a traffic control plan for work within City right-of-way.
Response: Contractor will provide the traffic control plan when they apply for the right-
of-way permit. Note 13 on C4.01 added to reflect this.
5. Existing improvements throughout plan set are in a very light font/line type, which makes
it difficult to figure out how the proposed improvements fit in with the existing
improvements. Please darken fine/line type throughout plan set. Please note, a new
plan set that was printed in house at KPFF was delivered to the City. This submittal is
readable = thank you. The cover memo states "This set is not signed as it is intended to
supplement the official review documents". Future submittals will need to be signed as
those plans will become the official permit set. We are not able to provide project
approval based off the plan set that was submitted with the original permit application.
Response: We believe the attached plan set is more -legible. Our apologies for the poor
print -quality of the previous submittal.
6. Please note, a rain garden covenant will be required for this project. The covenant will
need to be recorded at Snohomish County prior to final construction approval for project
(not prior to building permit issuance). The City has a template covenant and will
forward this soon.
Response: Covenant will be recorded prior to final construction.
Sheet G0.02:
1. Update General Construction Notes. Refer to sample on City website.
Response: Notes updated per notes on city website.
Sheet C0.01:
1. Please include a project description explaining the proposed layout and intended traffic
flow. Are there parent only or bus only areas?
Response: Project description note added. There are both parent only (portion adjacent
to 106th) and bus only (circle lot to the east) areas on-site.
Sheet C1.02:
1. Please move construction sequence notes from this detail plan sheet to the TESC plan
sheet.
Response: Sequence notes moved.
Sheet C3.01:
1. Revise sheet title to include "utilities". See comment under Sheet 4.01 regarding fire
hydrant relocation.
Response: Sheet title revised and information added for utilities.
2. Remove storm drain line shown as to be removed on demolition plan.
Response: Existing utilities are part of the project survey which is used as a background
to our plans. We are uncomfortable modifying the project survey to remove elements.
Ms. Jeanie McConnell
May 29, 2015
Page 3
With the revised prints and updated color -scheme we believe the plan is more -clear with
the survey data left untouched.
3. The storm drainage crossing downstream of proposed SDCB #6 has incorrect
elevations. Please revise.
Response: Per discussion with Jerry Shuster, the elevations have been updated.
4. Verify that existing SDCB #9 connects to the existing 18" diameter storm drain. It
appears to be a tee connection. Verify that this is an operational connection.
Response: Per discussion with Jerry Shuster, the as -built records indicate that this is a
tee connection to the 18 -inch storm drain. Edmonds School District acknowledges this
is an atypical connection and takes on responsibility for maintaining and/or replacing this
connection on their property if any damage or clogging is experienced
5. Provide an impervious surface area chart consistent with City handout E72.
Response: Impervious surface area summary chart has been added as detail 7 on
sheet C3.02
6. Please note whether the fire hydrant installation is proposed to be done as a wet/hot tap
or cut in.
Response: Hydrant will be cut -in. The school will be closed and unoccupied during time
of work. Note 17 has been added to sheet C3.01.
Sheet C3.02:
1. It is unclear the purpose of Detail 2 on this sheet (very poor quality reproduction as well).
Please note, the quality issue was corrected in the sheets that were submitted to the City
May 19, 2015.
Response: The swale adjacent to the new bus lane is a replace -in-kind system. This
swale provides infiltration for field drainage. Per discussion with Jerry Shuster on May
11, 2015, this detail is reused from as -built drawings. Reuse of this detail indicates that
the system is not a proposed means of flow control for the playfield, but instead a
relocation of the existing field drainage system.
Sheet C3.03 (note this comment was listed as #2 under C3.02):
1. Detail 2 — Inlets to bioretention/rain gardens should have 3-4" of "catch" at the inlet pipe
to collect sediment. Please revise.
Response: Per discussion with Jerry Shuster on May 11, 2015, storm pipe outlets to
rain gardens are revised to include 3 inches of "catch" above the bottom of the rain
garden facilities.
Sheet C3.03:
1. Typical Rain Garden Section:
a. There should be 18 inches of bioretention soil mix for treatment not 15" plus the
mulch layer.
Response: Section modified to 18 inches.
Ms. Jeanie McConnell
May 29, 2015
Page 4
b. A geotextile should not be placed under bioretention soil (See LID guidance); they
tend to clog. A solution used by Seattle is Seattle mineral aggregate type 26
between the bioretention soil and the gravel. It is a %" washed sandy gravel. See
pages 9-11 and 914in https://www.ecobuilding.org/olympia/flyers-
forms/903SR51110Revised.pdf
Response: Per discussion with Jerry Shuster on May 11, 2015, mineral aggregate
type 26 (3/4" washed sandy gravel) is now included in the rain garden soil profile, in
place of geotextile fabric between the infiltration basin and bioretention soil.
c. Also, geotextile on the bottom of an infiltration trench tends to clog (top and sides
OK).
Response: Geotextile removed from bottom.
Sheet C4.01:
1. For clarity, please do not show existing features that were noted for removal on the
demolition plan sheet.
Response: Existing utilities are part of the project survey which is used as a background
to our plans. We are uncomfortable modifying the project survey to remove elements.
With the revised prints and updated color -scheme we believe the plan is more -clear with
the survey data left untouched.
2. Please remove the note that states "sidewalk and ADA curb ramp improvement being
coordinated with 2015 ramp upgrades project". The school district will be responsible for
installation of this ramp in conjunction with the proposed project.
Response: Note removed.
3. The new sidewalk on 106th Ave W could be constructed of asphalt to match existing
conditions. The ramp will still need to be constructed of concrete.
a. Revise plans as needed.
Response: Plans revised. New sidewalk on 106th Ave W will be constructed of
asphalt to match existing conditions. The curb ramp and landing will still be
constructed of concrete.
b. See notes below under Sheet C7.01 regarding curb ramp details. The new curb
ramp on 106th will need to be modified slightly to meet ADA standards. A modified
detail has been requested for this ramp.
Response: Curb ramp R5 modified to be COS Std E2.17. A 4 -ft minimum width
landing area is provided at the top of the ramp and at the edge of the ramp wings to
connect all three sidewalk/walkway sections. The layout and additional dimensions
are included on the paving enlargement (detail 8, sheet C4.02).
4. Please provide a detail or explanation of what the center island area is in the lower
parking lot. A pedestrian island is called out and then a 15 -foot aisle (appears to be for
traffic?) and then a walkable pedestrian area south of that (at grade?).
Response: The center concrete island is a drop-off area for ADA vehicles and daycare
shuttles. It is flush with adjacent grade per ADA requirements. The 15 -foot drive aisle is
Ms. Jeanie McConnell
May 29, 2015
Page 5
for daycare shuttle van and ADA traffic. The 5 -foot walkway is intended for pedestrian
traffic from the staff parking area north of the ADA/Shuttle aisle. These features are now
identified on sheet C0.01 — Master Site Plan and better explained on C4.01.
5. If the 15 -foot center aisle is intended for traffic, please show turning movements can be
achieved with proposed curb radii at each end of the aisle.
Response: The 15 -foot center aisle is intended for ADA vehicles and daycare shuttle
vans. The interior turning radius at each end of the drive aisle is 20 feet, providing
sufficient space for vans turning into and out of the aisle. Turning movements are now
included on sheet C0.02 — Master Site Plan.
6. Dimension drive aisle width between the proposed curb island (at the west end of the
proposed bank of parking stalls in the lower lot) and the curb radius with C12 reference.
Response: Dimension added.
7. Note drive aisle width between the existing sidewalk on the south side the building and
the proposed pedestrian island concrete sidewalk.
Response: Drive aisle width added. Also refer to C5.01 Striping Plan for drive aisle
striping information.
8. Provide truncated domes where the crosswalk meets the pedestrian path on the north
side of the 15 -foot center aisle.
Response: Truncated domes added.
9. At the south end of the 228th St access the vertical curb is shown to taper down to 1" for
a distance of 12 -feet. It appears as though this is for access to the field via a chain-link
gate. Please add note that clarifies the purpose of the curb drop and reference detail 2
on Sheet L1.02. Is an asphalt approach proposed in this area or will the surface
transition from the curb to lawn?
Response: This curb drop is intended for mower and maintenance access to the
playfield. Note 14 on sheet C4.01 now clarifies the intent of the curb drop and
references landscape sheets for installation of the chain link gate. The surface transition
will be from curb to lawn, additional clarification for this transition is also included in note
14.
10. Show installation of a stop sign, to MUTCD standards, at the access to 228th St SW.
Response: Refer to sheet C5.01 for signage locations, and sheet C6.01 for type of
signs. A stop sign is provided at the access to 228th St SW.
11. The new fire hydrant location is noted on this plan, but the water main is not shown.
Please move fire hydrant related notes to the grading and drainage (and utility) plan.
Response: Fire hydrant and related notes are now included on the Grading, Drainage,
and Utility Plan (sheet C3.01).
12. The constructability of paving what shown on this drawing will be difficult. The amount of
saw cutting and sealing just to have so many areas of existing remain pavement seems
unwarranted. The site has more than enough room to manage the stormwater from the
areas that are current plan to remain in place. Sealing so many edges is never 100%
Ms. Jeanie McConnell
May 29, 2015
Page 6
and the long-term viability of this paving plan is not very good. The site will also look a lot
better if less of the existing pavement remains.
Response: As coordinated with Jerry Shuster, only those areas of pavement needing
replacement for grading or utility cuts will be fully replaced. Smaller localized areas that
were not previously included in full depth pavement replacement are now included and
the total disturbed area quantity is updated. An additive alternative for a 1.5 -inch grind
and overlay and crack sealing is now included in the set. The full site asphalt grind and
overlay will increase pavement life and provide better aesthetics, without a full depth
replacement of all pavements. (NOTE: It appears the contractor bids will allow for this
element to be constructed with the project)
Sheet 04.02:
1. Please revise sheet number reference for detail 1 to indicate which plan sheet(s) this
detail applies to.
Response: Detail reference revised.
2. Detail 8 — Ramp Paving Enlargement:
a. Will curb be constructed along the perimeter of the path?
Response: No, curb will not be constructed along the perimeter of the path. 2010
ADA Standards for Accessible Design manual section 405.9.2 — Curb or Barrier
Edge Protection requires edge curb or barrier that prohibits passage of a 4" diameter
sphere. Detail 3 on sheet C4.03 shows typical edge rail on ramp runs and landings.
The lowest 2 -inch diameter rail (interior diameter of steel pipe) is detailed to be 5" on
center above the finished grade surface. The clearance from the bottom of this steel
pipe rail to the ramp/landing surface will be less than 4". Therefore, the current ramp
detail complies with ADA standards.
b. FYI - The curb ramp wings (R6) are not needed in this instance as the transition on
the sides of the ramp is to landscaping instead of concrete sidewalk.
Response: Curb ramp R6 is removed from the plan. The ADA landing for the
concrete ramp is now at the elevation of the asphalt drive aisle. Vertical curb will
taper down at 1:1 on each side of the ramp. Steel pipe handrail is located on all
sides of the landing.
Sheet 05.01:
1. For clarity, please do not show existing features that were noted for removal on the
demolition plan sheet.
Response: Existing utilities are part of the project survey which is used as a background
to our plans. We are uncomfortable modifying the project survey to remove elements.
With the revised prints and updated color -scheme we believe the plan is more -clear with
the survey data left untouched.
2. Indicate signage that will be added to the site to further direct the flow of traffic through
the site.
a. Will there be a designated parent pick-up/drop-off area?
Ms. Jeanie McConnell
May 29, 2015
Page 7
Response: Parent loading/unloading zones now include "No Parking — Loading
Zone" signs. See sheet C5.01, C5.02, and C6.01 for signage type, location, and
details.
b. Will there be a designated bus loop?
Response: There is a designated one-way bus loop in the lower parking area. This
is now identified with signage and directional arrows. See sheet C5.01, C5.02, and
C6.01 for channelization and signage details.
c. Will there be any designated teacher parking?
Response: Staff parking is in the lower parking area. This is now indicated with a
sign at the entrance to the new asphalt drive aisle. Two-way directional arrows are
included in the staff parking area. See sheets C5.01, C5.02, and C6.01 for
channelization and signage details.
d. Will there be any loading/unloading stalls?
Response: There are loading/unloading zones in the upper and lower parking areas.
These are signed with "No Parking — Loading Zone" signs. See sheet C5.01, C5.02,
and C6.01 for signage type, location, and details.
3. Signage at pedestrian crossings in high travel areas could be beneficial. Please
consider.
Response: Signage added.
4. Are there any one-way drive aisles in the lower parking lot? If so, striping and signage
should be added as appropriate.
Response: Striping and signage added.
5. Is the outside loop of the lower parking lot intended for one lane of traffic or two?
Response: Outside loop of the lower parking lot is intended for one lane bus traffic.
Description of site layout has been added to sheet C0.01.
6. It appears as though a stripe is to be painted on the north side of the 15 -foot access
aisle to provide pedestrian area boundary. Please clarify on plans.
Response: The 15 -foot daycare shuttle van drive loop and 5 -foot pedestrian walkway
have been clarified on sheet C0.01. The paint stripe around the pedestrian walkway is
intended to indicate the boundary for the drive aisle and the parking spaces.
7. Please show the extension of the existing painted fogline on 106th Ave W in the area
where the driveway will be removed.
Response: Extension of painted fog line now shown on 106`" Ave in the area where the
driveway will be removed.
8. Will the driveway access egress for the site onto 106th merge into one lane or will there
be two lanes all the way to 106th? If two lanes, one shall be striped as right only and the
other as left only. If turning movements are restricted then signage shall be added prior
to entering the queue lanes indicating appropriate lanes to use for south bound 106th
traffic and north bound 106th traffic.
Ms. Jeanie McConnell
May 29, 2015
Page 8
Response: The driveway access egress onto 106th will be two lanes, one right turn only
lane and one left turn only lane. Broken lane striping is added to delineate turn lanes
and allow cars to switch lanes before exiting the site. Directional arrows and signs S1
and S2 are updated to indicate the "right/left turn only" designation of each lane.
9. Add "Do Not Enter" signage at the 106th egress point.
Response: Signage added
10. Please confirm that the existing curb ramp on the east side of the new crosswalk in the
upper parking lot meets ADA standards. Show replacement of the ramp as needed.
Response: The existing curb ramp is 3 -ft wide, has 6 -ft wings (1:12 slope on a '/2' curb)
and has a 3 -ft landing at the top of the ramp. This curb ramp meets ADA standards
outlined in section 406 — Curb Ramps of the 2010 ADA Standards for Accessible Design
manual.
Sheet 06.01:
1. Revise curb ramp table to note which plan sheet details are provided on.
Response: Curb ramp table indicates which sheets details are provided on. Format of
detail reference to plan sheets is "detail #/sheet #". For example, curb ramp R1 has a
detail reference of 5/C4.02, indicating that this curb ramp references detail 5 on sheet
C4.02.
Sheet C7.01:
1. Detail 6 — City standard detail E2.16 is not the appropriate detail for the curb ramps R2,
R3, R5 and R6. City standard detail E2.17 (or WSDOT equivalent) could be used for
ramps R2, R3, and R6. Ramp R5 could also be constructed utilizing detail E2.17, but a
modified detail is requested addressing construction of this ramp as a 4 -foot minimum
width landing area will need to be provided at the top of the ramp connecting all three
sidewalk/walkway sections together.
Response: Detail 6 on sheet C7.01 is updated to be City of Edmonds Curb Ramp Type
4 (Std E2.17). This detail is used for curb ramps R2, R3, and R5. For curb ramp R5, a
4 -ft minimum width landing area is now provided at the top of the ramp and at the edge
of the ramp wings to connect all three sidewalk/walkway sections. The layout and
additional dimensions for curb ramp R5 are included on the paving enlargement (detail
8, sheet C4.02). Curb ramp R6 now references detail 5 on sheet C4.02.
2. Detail 3 — City standard detail E2.13 — replace with detail E2.12 if asphalt walk is
proposed along 106th instead of concrete.
Response: COE Std E2.12 is added under detail 5 on sheet C7.02. Asphalt walk is
proposed on 106th instead of concrete. Detail 3 on sheet C7.01 remains as is, because
this detail will be used for construction of concrete sidewalk on site.
Sheet C7.02:
1. Detail 3 — Reference sheet C3.01 instead of C4.01.
Response: Reference updated.
Sheet L1.01:
Ms. Jeanie McConnell
May 29, 2015
Page 9
1. Several dimensions are provided along the east side of the access drive connecting to
228th St SW. Please clarify what this represents.
Response: Dimensions clarified
2. Sheet L1.02 indicates installation of a chain link with 20 -foot wide gate, but this plan
sheet indicates an 8 -foot wide gate. Please revise.
Response: Detail 2 on sheet L1.02 has been revised to indicate chain link gate width as
shown on sheet L1.01.
Stormwater Report (these responses were previously coordinated with Jerry Shuster via
phone call on May 11, 2015):
Provide an exhibit that shows the extent of land disturbing activity for the project. Note
that land disturbing activity is defined as: "Any activity that results in a change in the
existing soil cover (both vegetative and non -vegetative) and/or the existing soil
topography. Land disturbing activities include, but are not limited to clearing, grading,
filling, and excavation. Compaction that is associated with stabilization of structures and
road construction shall also be considered a land disturbing activity. Vegetation
maintenance practices, including landscape maintenance and gardening, are not
considered land -disturbing activity. Stormwater facility maintenance is not considered
land disturbing activity if conducted according to established standards and procedures."
Please review the comment for plan sheet C4.01 prior to producing this exhibit.
Response: Per discussion on May 11, 2015, an exhibit showing the extent of all land
disturbing activity will be added as an Appendix to the Drainage Report.
2. Provide a table with the following information for the post -development scenario:
Area in Acres of Sub -Basin
Surface Type A B C D Grand
Totals
New + Replaced
Impervious
PCIS
Non PCIS
Subtotal
Existing Impervious
Not Disturbed
PGIS
Non PGIS
Subtotal
Grand Totals
Ms. Jeanie McConnell
May 29, 2015
Page 10
Response: Per discussion on May 11, 2015, a table with the above information for the
post -developed scenario will be added to the Drainage Report.
3. The Drainage Report from 1995 when existing sub -basin B was constructed has 1.37
acres (0.85 acres impervious plus 0.52 acres pervious) going to the existing swale and
the detention facility (available in City files). The Drainage Report for this proposed
project has 0.99 acres existing going to the swale/detention. Please reconcile.
Response: The 0.99 acres only represents the area within the limit of work. The total
1.37 acres includes additional area outside the limits of work for this project. Per
discussion on May 11, 2015, a description of this case will be added to the Drainage
Report.
4. Infiltration is the preferred method of stormwater management for the City. Sherwood
Elementary is located in the area of the City that has the best soils for infiltration. Since
the infiltration rate is favorable and the School District has the space, the City would
prefer 100% infiltration up to the 50 year event. Note that the City plans to construct an
infiltration gallery in the summer of 2015 on 228th St SW near the proposed entrance to
the school to infiltrate runoff from the adjacent neighborhood.
Response: Per discussion on May 11, 2015, the infiltration systems are designed to the
Edmonds Stormwater Supplement requirements for a Small Site Project. The
preference of Edmonds School District is to minimize the extent of playfield area taken
for infiltration facilities. It is expected that 100% infiltration up to the 50 year event would
require additional infiltration facilities in the playfield area, which is not preferable to the
School District. Infiltration above the Edmonds Stormwater Supplement requirements
for a Small Site Project is not proposed for this project.
5. Per volume V, Section 4.1 of the 2005 Ecology Stormwater Management Manual for
Western Washington, "If runoff from non -pollution generating surfaces reaches a runoff
treatment BMP, flows from those areas must be included in the sizing calculations for
the facility. Once runoff from non -pollution generating areas is mixed with runoff from
pollution -generating areas, it cannot be separated before treatment." Rain Gardens 1 &
2 are modeled for treatment only using the PCIS, when the flows to these facilities
insides non-PGIS. Remodel/resize for the combined flows.
Response: Per discussion on May 11, 2015, the rain gardens are revised to include
treatment for both PGIS and non-PGIS areas. Revised model outputs are included in
the Drainage Report to reflect the revisions.
6. The modeling needs a few modifications to represent what is designed. The bioretention
cells (rain gardens) in Appendix G needs the following changes:
a. The surface areas of the rain garden needs to be subtracted from the tributary area
in the post -development run.
Response: The surface area of the rain garden is not included in the tributary area
for runoff. The MGSFlood model accounts for the additional surface area of the rain
garden for evaporation from the facility. Per discussion on May 11, 2015, an
explanation of the model will be added to the Drainage Report, see response to
comment #7.
Ms. Jeanie McConnell
May 29, 2015
Page 11
b. Bioretention soil porosity should be 40% per the LID Technical guidance manual.
Response: Per discussion on May 11, 2015, bioretention soil porosity is revised to
be 40%.
c. An underdrain is not present.
Response: An underdrain is present in the model. See response to comment #7 for
a full description of the model.
d. Bioretention cells treat runoff by passing it vertically through the bioretention soil mix
(BSM) and infiltrating the water; not filling up the pond and overflowing it to the layer
below. The runs show 0% infiltrated. Add the 2.5 ft of gravel below the BSM and the
design infiltration rate of 1 inch per hour.
Response: The model accounts for both treated and untreated flows distributed to
the infiltration basin. See response to comment #7 for a full description of the model.
e. A circular riser 12 inches in diameter is modeled. The plan shows the riser is a Type
1 CB with a beehive grate.
Response: Dimensions of the overflow structure are changed to match the
dimensions of a Type 1 Catch Basin.
7. The Infiltration Basins modeled in Appendix H needs the following changes:
a. It does not appear that the MGS Flood model is capable of modeling the proposed
bioretention/infiltration/overflow system. Runoff gets to the infiltration layer by two
routes from the bioretention layer 1) infiltration through the bottom and 2) via the
overflow structure. Please verify that the model accounts for this. If this cannot be
accurately modeled in MGS Flood, WWHM2012 or WWHM4 can do this.
Response: Per discussion on May 11, 2015, the MGSFIood model accurately
reflects the design of the rain garden/infiltration systems and accounts for all treated
and untreated waters flowing from the rain garden layer to the infiltration basin.
• The rain garden/infiltration facilities are designed to receive stormwater flows
from upland basins via a pipe outlet from the proposed stormwater systems.
This is modeled in MGSFIood by a link connection from the post -developed
runoff cell to the rain garden cell.
The rain garden facilities are designed to infiltrate treated stormwater through the
bottom of the rain garden layer to the infiltration basin below. This is modeled in
MGSFIood through an underdrain that directs all treated flows from the rain
garden cell to the infiltration cell in the model. The rain garden cell is linked to
the downstream infiltration trench cell to model flows moving from the rain garden
facility to the infiltration basin. The 0% infiltration that is shown in the model for
the rain garden cell indicates that no treated waters are infiltrating to native soil.
All treated waters are modeled as being collected by an underdrain and directed
to the infiltration cell. The model properly accounts for all treated waters passing
from the rain garden facility to the infiltration basin with the underdrain.
• The rain garden facilities are designed to pass all untreated flows in excess of
the rain garden capacity through an overflow structure (Type 1 Catch Basin) to
Ms. Jeanie McConnell
May 29, 2015
Page 12
the infiltration basin below. The infiltration basin is designed with a series of 6 -
inch diameter perforated pipes that evenly distribute untreated waters from the
rain garden layer that pass through the overflow structure. This is modeled in
MGSFIood through the overflows structure that directs all untreated flows from
the rain garden cell to the infiltration cell in the model. The rain garden cell is
linked to the downstream infiltration trench cell to model flows moving from the
rain garden facility to the infiltration basin. The model properly accounts for all
untreated waters passing from the rain garden layer to the infiltration basin
through the overflow structure.
The infiltration facilities are designed to receive stormwater form the rain garden
through infiltration from the bottom of the rain garden layer (treated flows) and
through the overflow structure (untreated flows). This is modeled in MGSFIood
by linking the upstream rain garden cell to the downstream infiltration trench cell.
Treated flows from the rain garden cell are collected by the underdrain and
untreated flows are collected by the overflow structure. The link in the model
directs flows from the underdrain and overflow structure to the infiltration trench
cell. The model properly accounts for all waters moving from the rain garden to
the infiltration basin as it is designed.
® The infiltration basins are designed to discharge flows in excess of infiltration
capacity by means of a storm drain pipe with the invert at the top of the infiltration
basin layer. This is modeled in MGSFIood through an overflow structure. The
point of compliance in the model is set at the outflow of the infiltration trench,
which properly accounts for all flows in excess of infiltration that are leaving the
system. The model reports indicate the 2 -yr, 10 -yr, and 100 -yr flows that leave
the system, and a description of flow control compliance for the requirements of a
Small Site Project per the Edmonds Stormwater Supplement is provided in the
report.
A detailed description of how the model accounts for the design of the rain
garden/infiltration basins will be added to the Drainage Report. Snapshots of the
model layout will be provided in an Appendix to the Drainage Report.
b. The bioretention soil saturated hydraulic conductivity should be 1.5 in/hr
Response: The saturated hydraulic conductivity of the rain garden soil is updated in
the models to be 1.5 in/hr.
c. The bioretention soil porosity should be 40% per the LID Technical guidance manual.
Response: Per discussion on May 11, 2015, bioretention soil porosity is revised to
be 40%.
d. An underdrain is not present.
Response: An underdrain is present in the model. See above comment response
for a full description of the model.
e. The infiltration trench does not appear to be a "Trench on Embankment Slope."
Choosing the "Trench Located Beneath Ditch" option may be more representative.
Ms. Jeanie McConnell
May 2Q.20i5
Page 13
Per discussion oDMay 11,2U15,the model ieupdated h0include the
"Trench Located Beneath Ditch" option. The model reports indicate "Trench Located
GtToe nfEmbankment" when this option iSchosen.
f. Acircular riser 12inches indiameter iomodeled. The plan shows @D8"pipe outlet.
The outlet from the system iSupdated iDthe model to begO8"overflow
O[0c8.
Hopefully these responses meet with your approval. Please feel free to contact me directly at
(206) 622-5822 with any questions or comments.
TJE:N|
Enclosures
114407.21
E'sr. I A9�J
DATE: May 19, 2015
ENGINEERING DIVISION
(425) 771-0220
City Website: www.edmondswa.gov
TO: Thaddeus Egging
thaddeus.egging@kpff.com
FROM: Jeanie McConnell, Engineering Program Manager
jc�_aid .nicc~��iineil(��1edi' o ids a, ov
Jerry Shuster, Stormwater Program Manager
Bertrand Hauss, City Traffic Engineer
RE; Application #: bld20150490
Project: Sherwood Elementary
Project Address: 22901 — 106`x' Ave W
During review of the above noted application, it was found that the following information,
corrections, or clarifications are needed. Please redline plans or submit three (3) sets of revised
plans/documents with a written response to each of the items below to a permit coordinator.
Resubmittals can be made at the Development Services Department on the 2nd floor of City Hall.
Permit Center hours are M, T, Th & F from 8am-4:30pm and on Wednesdays from 8am-noon.
Please note, starting June 3rd, the Pen -nit Center will be closed on Wednesdays.
City of Edmonds handouts, standard details and development code can be referenced on the City
website.
GENERAL
1. Please provide an itemized engineers cost estimate, including units and unit prices, for both on-
site and off-site (right-of-way) improvements, including all utilities and traffic control. Please
use the Ding County Site Improvement Bond Quantity Worksheet and utilize the "write-in"
sections where appropriate.
® A bond is required to be placed for all erosion control measures, right-of-way and
stormwater management improvements. The amount of the bond will be based on 1.20% of
the City approved estimate. The City will inform you of the appropriate bond amount after
review of the cost estimate. Please obtain the appropriate subdivision improvement bond
forms from the City.
® If you intend to post a bond in order to record the subdivision and ahead of constructing
required improvements, the bond amount will be based on the entire scope of the project.
Inspection fees for this project will be calculated at 3.3% of the 120% City approved
estimate for all improvements.
2. Include a City Engineering Division approval block on all plan sheets. Reler to san
-g2le oq_(,—
.... .... ..... . .... ... . . . ............ ty
Nvebsite.
3. Please add a note to plans stating "A separate right-of-way construction permit is required for all
work within the city right-of-way." Please note, a ROW permit application with contractor's
signature shall be provided to the city prior to issuance of civil construction plans.
4. Please provide a traffic control plan for work within City right-of-way.
5. Existing improvements throughout plan set are in a very light font/line type, which makes it
difficult to figure out how the proposed improvements fit in with the existing improvements.
Please darken fine/line type throughout plan set. Please note, a new plan set that was printed in
house at IUFF was delivered to the City. This submittal is readable — thank you. The cover
memo states "This set is not signed as it is intended to supplement the official review
documents". Future submittals will need to be signed as those plans will become the official
permit set. We are not able to provide project approval based off the plan set that was submitted
with the original permit application.
6. Please note, a rain garden covenant will be required for this project. The covenant will need to
be recorded at Snohomish County prior to final construction approval for project (not prior to
building permit issuance). The City has a template covenant and will forward this soon.
Sheet G0.02 — GENERAL NOTES
1. Update General Construction Notes. Refert(sample --.ol.Ci . v ��si-te--
. -- -- - - ---------- ------ �
Sheet C0.01 — MASTER SITE PLAN
1. Please include a project description explaining the proposed layout and intended traffic flow.
Are there parent only or bus only areas?
Sheet C1.02 — TESC DETAILS
1. Please move construction sequence notes from this detail plan sheet to the TESC plan sheet.
Sheet C3.01 — GRADING AND DRAINAGE PLAN
1. Revise sheet title to include "utilities". See comment under Sheet 4.01 regarding fire hydrant
relocation.
2. Remove storm drain line shown as to be removed on demolition plan.
3. The storm drainage crossing downstream of proposed SDCB #6 has incorrect elevations. Please
revise.
4. Verify that existing SDCB #9 connects to the existing 18" diameter storm drain. It appears to
be a tee connection. Verify that this is an operational connection.
5. Provide an impervious surface area chart consistent with City handout E72.
6. Please note whether the fire hydrant installation is proposed to be done as a wet/hot tap or cut in.
Sheet C3.02 — GRADING AND DRAINAGE DETAILS
1. It is unclear the purpose of Detail 2 on this sheet (very poor quality reproduction as well).
Please note, the quality issue was Corrected in the sheets that were submitted to the City May 19,
2015.
2. Detail 2 — Inlets to bioretention/rain gardens should have 34" of "catch" at the inlet pipe to
collect sediment. Please revise.
Page 2 of 6
Sheet C3.03 — GRADING AND DRAINAGE ENLARGEMENTS AND DETAILS
1. Typical Rain Garden Section:
a. There should be 18 inches of bioretention soil mix for treatment not 15" plus the mulch
layer.
b. A geotextile should not be placed under bioretention soil (See LID guidance); they tend
to clog. A solution used by Seattle is Seattle mineral aggregate type 26 between the
bioretention soil and the gravel. It is a 3/a" washed sandy gravel. See pages 9-11 and 9-
14 in VM.1...ff w ,. obg_r1ci6; f«➢: z � y/. � c � j'6rjns/903,51 1 ll__I ORey'4p�°cl 1xff
c. Also, geotextile on the bottom of an infiltration trench tends to clog (top and sides OK).
Sheet C4.01 — PAVING AND UTILITY PLAN
1. For clarity, please do not show existing features that were noted for removal on the demolition
plan sheet.
2. Please remove the note that states "sidewalk and ADA curb ramp improvement being
coordinated with 2015 ramp upgrades project". The school district will be responsible for
installation of this ramp in conjunction with the proposed project.
3. The new sidewalk on 106"' Ave W could be constructed of asphalt to match existing conditions.
The ramp will still need to be constructed of concrete.
a. Revise plans as needed.
b. See notes below under Sheet C7.01 regarding curb ramp details. The new curb ramp on
100" will need to be modified slightly to meet ADA standards. A modified detail has
been requested for this ramp.
4. Please provide a detail or explanation of what the center island area is in the lower parking lot.
A pedestrian island is called out and then a 15 -foot aisle (appears to be for traffic?) and then a
walkable pedestrian area south of that (at grade?).
5. If the 15 -foot center aisle is intended for traffic, please show turning movements can be
achieved with proposed curb radii at each end of the aisle.
6. Dimension drive aisle width between the proposed curb island (at the west end of the proposed
bank of parking stalls in the lower lot) and the curb radius with C12 reference.
7. Note drive aisle width between the existing sidewalk on the south side the building and the
proposed pedestrian island concrete sidewalk.
8. Provide truncated domes where the crosswalk meets the pedestrian path on the north side of the
15 -foot center aisle.
9. At the south end of the 228`x' St access the vertical curb is shown to taper down to 1" for a
distance of 12 -feet. It appears as though this is for access to the field via a chain-link gate.
Please add note that clarifies the purpose of the curb drop and reference detail 2 on Sheet L1.02.
Is an asphalt approach proposed in this area or will the surface transition from the curb to lawn?
10. Show installation of a stop sign, to MUTCD standards, at the access to 228" St SW.
11. The new fire hydrant location is noted on this plan, but the water main is not shown. Please
move fire hydrant related notes to the grading and drainage (and utility) plan.
12. The constluctability of paving what shown on this drawing will be difficult. The amount of saw
cutting and sealing just to have so many areas of existing remain pavement seems
unwarranted. The site has more than enough room to manage the stormwater from the areas that
are current plan to remain in place. Sealing so many edges is never 100% and the long-term
viability of this paving plan is not very good. The site will also look a lot better if less of the
existing pavement remains.
Page 3 of 6
Sheet C4.02 — PAVING DETAILS
1. Please revise sheet number reference for detail 1 to indicate which plan sheet(s) this detail
applies to.
2. Detail 8 — Ramp Paving Enlargement:
a. Will curb be constructed along the perimeter of the path?
b. FYI - The curb ramp wings (R6) are not needed in this instance as the transition on the
sides of the ramp is to landscaping instead of concrete sidewalk.
Sheet C5.01 — STRIPING AND SIGNAGE PLAN
1. For clarity, please do not show existing features that were noted for removal on the demolition
plan sheet.
2. Indicate signage that will be added to the site to further direct the flow of traffic through the site.
a. Will there be a designated parent pick-up/drop-off area?
b. Will there be a designated bus loop?
c. Will there be any designated teacher parking?
d. Will there be any loading/unloading stalls?
3. Signage at pedestrian crossings in high travel areas could be beneficial. Please consider.
4. Are there any one-way drive aisles in the lower parking lot? If so, striping and signage should
be added as appropriate.
5. Is the outside loop of the lower parking lot intended for one lane of traffic or two?
6. It appears as though a stripe is to be painted on the north side of the 15 -foot access aisle to
provide pedestrian area boundary. Please clarify on plans.
7. Please show the extension of the existing painted fogline on 106th Ave W in the area where the
driveway will be removed.
8. Will the driveway access egress for the site onto 106th merge into one lane or will there be two
lanes all the way to 106th? If two lanes, one shall be striped as right only and the other as left
only. If turning movements are restricted then signage shall be added prior to entering the
queue lanes indicating appropriate lanes to use for south bound 106th traffic and north bound
106t11 traffic.
9. Add "Do Not Enter" signage at the 106"' egress point.
10. Please confirm that the existing curb ramp on the east side of the new crosswalk in the upper
parking lot meets ADA standards. Show replacement of the ramp as needed.
Sheet C6.01— HORIZONTAL CONTROL TABLES
1. Revise curb ramp table to note which plan sheet details are provided on.
Sheet C7.01 — CITY OF EDMONDS DETAILS
1. Detail 6 — City standard detail E2.16 is not the appropriate detail for the curb ramps R2, R3, R5
and R6. City standard detail E2.17 (or WSDOT equivalent) could be used for ramps R2, R3,
and R6. Ramp R5 could also be constructed utilizing detail E2.17, but a modified detail is
requested addressing construction of this ramp as a 4 -foot minimum width landing area will
need to be provided at the top of the ramp connecting all three sidewalk/walkway sections
together.
2. Detail 3 — City standard detail E2.13 — replace with detail E2.12 if asphalt walk is proposed
along 106th instead of concrete.
Sheet C7.02 — CITY OF EDMONDS DETAILS
1. Detail 3 — Reference sheet C3.01 instead of C4.01.
Page 4 of 6
Sheet 1,1.01 — LANDSCAPE PLAN
1. Several dimensions are provided along the east side of the access drive connecting to 228"' St
SW. Please clarify what this represents.
2. Sheet L1.02 indicates installation of a chain link with 20 -foot wide gate, but this plan sheet
indicates an 8 -foot wide gate. Please revise.
RN Eel tu'ri,
The following comments are provided from Jerry Shuster, Stormwater Engineer. These are
the same comments that were provided via email on May G, 2015. Please contact Jerry
directly at 425-771-0220 or by email at trr 'W.wi W u ~(d±dp� epi, sy a g��y with any specific
..... .
questions you may have regarding these comments.
Drainage Report, dated April 2015
® Provide an exhibit that shows the extent of land disturbing activity for the project. Note that
land disturbing activity is defined as: "Any activity that results in a change in the existing
soil cover (both vegetative and non -vegetative) and/or the existing soil topography. Land
disturbing activities include, but are not limited to clearing, grading, filling, and excavation.
Compaction that is associated with stabilization of structures and road construction shall
also be considered a land disturbing activity. Vegetation maintenance practices, including
landscape maintenance and gardening, are not considered land -disturbing
activity. Stormwater facility maintenance is not considered land disturbing activity if
conducted according to established standards and procedures." Please review the comment
for plan sheet C4.01 prior to producing this exhibit.
• Provide a table with the following information for the post -development scenario:
Page 5 of 6
• The Drainage Report from 1995 when existing sub -basin B was constructed has 1.37 acres
(0.85 acres impervious plus 0.52 acres pervious) going to the existing swale and the
detention facility (available in City files). The Drainage Report for this proposed project has
0.99 acres existing going to the swale/detention. Please reconcile.
• Infiltration is the preferred method of stormwater management for the City. Sherwood
Elementary is located in the area of the City that has the best soils for infiltration. Since the
infiltration rate is favorable and the School District has the space, the City would prefer
100% infiltration up to the 50 year event. Note that the City plans to construct an infiltration
gallery in the summer of 2015 on 228"' St SW near the proposed entrance to the school to
infiltrate runoff from the adjacent neighborhood.
• Per volume V, Section 4.1 of the 2005 Ecology Stormwater Management Manual for
Western Washington, "If runoff from non -pollution generating surfaces reaches a runoff
treatment BMP, flows from those areas must be included in the sizing calculations for the
facility. Once runoff from non -pollution generating areas is mixed with runoff from
pollution -generating areas, it cannot be separated before treatment." Rain Gardens 1 & 2 are
modeled for treatment only using the PGIS, when the flows to these facilities insides non-
PGIS. Remodel/ esize for the combined flows.
The modeling needs a few modifications to represent what is designed. The bioretention cells (rain
gardens) in Appendix G needs the following changes:
• The surface areas of the rain garden needs to be subtracted from the tributary area in the
post -development run.
• Bioretention soil porosity should be 40 % per the LID Technical guidance manual.
• An underdrain is not present.
• Bioretention cells treat runoff by passing it vertically though the bioretention soil mix
(BSM) and infiltrating the water; not filling up the pond and overflowing it to the layer
below. The runs show 0% infiltrated. Add the 2.5 ft of gravel below the BSM and the
design infiltration rate of 1 inch per hour.
• A circular riser 12 inches in diameter is modeled. The plan shows the riser is a Type 1 CB
with a beehive grate.
The Infiltration basins modeled in Appendix H needs the following changes:
• It does not appear that the MGS Flood model is capable of modeling the proposed
bioretention/infiltration/overflow system. Runoff gets to the infiltration layer by two routes
from the bioretention layer 1) infiltration though the bottom and 2) via the overflow
structure. Please verify that the model accounts for this. If this cannot be accurately
modeled in MGS Flood, WWHM2012 or WWHM4 can do this.
• The Bioretention soil Saturated Hydraulic Conductivity should be 1.5 in/hr.
• Bioretention soil porosity should be 40 % per the LID Technical guidance manual.
• An underdrain is not present.
• The infiltration trench does not appear to be a "Trench on Embankment Slope." Choosing
the "Trench Located Beneath Ditch" option may be more representative.
• A circular riser 12 inches in diameter is modeled. The plan shows an 8" pipe (orifice) outlet.
Page 6 of 6