HomeMy WebLinkAboutC_Response_Letter_Greystoke_LLC_180410_v2.pdf
Western Washington Division Eastern Washington Division
165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922
Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419
www.EncompassES.net
April 10, 2018
Ian Fitz-James/Jill Ding
City of Renton
1055 S Grady Way, 6th Floor
Renton, WA 98057
RE: 28 Hundred Unit Lot Subdivision/ LUA17 -000163,PP, -ECF, SA-A,CU-A
May 1, 2017 Review Comments
Dear Ian and Jill:
The plans and TIR were revised per you r May 1, 2017 memo, meetings at the City on March
1, 2018 and April 5, 2018, and a couple of review redlined plans emailed a few days later, as
follows:
WATER COMMENTS
1. The Renton Regional Fire Authority has determined that the preliminary fire flow
demand for the development is 2,500 gallons per minute (gpm) with the use of
approved automatic fire sprinkler systems for the buildings. Three fire hydrants are
required within 300 feet of the buildings. Any new fire hydrants required to meet
Renton Regional Fire Authority standards shall be per City Standard Plan 310.1. Noted.
2. The preliminary utility plan submitted with the land use application by Encompass
Engineering and Surveying shows approximately 295 LF of new 4" water main in a 25'
water/sewer easement east of the proposed town homes in the private drive aisle
connecting from the existing 8" main in NE 12th Street to the 6" main in NE 13th
Street.
The new water main shall be 8" and contained in a 25' water/ sewer
easement. A new hydrant shall be installed near the south driveway connected
to the above new 8" water main. The new water main is now 8" and
contained in a 25' water/ sewer easement. A new hydrant is shown to be
installed adjacent to the south end of the onsite driveway.
3. Each new townhome shall be served by a 1" water service from the new 8" main. Each
water meter will need to be contained in a water I utilities easement. A double check
valve assembly (DCVA) will be required behind each meter as the townhomes are three
stories in height. The DCVA will be privately maintained. A pressure reducing valve
behind the meter is required as static water pressure exceeds 80 psi. The DCVAs and PRVs
were added to each of the units.
4. A residential fire sprinkler system shall be installed for each townhome unit with a double
check valve assembly (DDCVA) for backflow prevention on the water supply line to the fire
sprinkler piping. The DDCVAs were added to each of the units
5. A separate meter is required for landscape irrigation. A double check valve assemb ly is
required downstream of the meter. For services 2" or smaller, the DCVA shall be installed
per COR Standard Plan 340.8. The meter shall be contained in a water I utilities easement.
Irrigation is not being proposed.
6. Water system improvements shall be designed in accordance with Appendix J of the City's
2012 Water System Plan. Adequate horizontal and vertical separation between new
mains and other existing and proposed utilities {sewer lines, storm drains, gas lines, power
and communication ducts) shall be provided for operation and maintenance of the water
main; Retaining walls, rockeries, or similar structures cannot be installed over the water
main unless the water main is installed inside of a steel casing. Noted.
7. The site is located in Zone 2 of the Aquifer Protection Area. Noted.
8. The development is subject to system development charges {SDCs) for water service. The
2017 water SOC for a lot with a 3/4" or 1" water meter is $3,486.00. Credit will be issued
for existing water services. Water SDCs that are current will be collected at the time of
construction permit issuance. Fees for work done by City crews are also collected at the
time of construction permit issuance. Work done by City crews includes connections of
new mains to the existing system, chlorination of new lines, and cut and caps of existing
lines and/ or services. Noted.
The drop-in meter cost is $400.00 for a 3/4" meter and $460.00 for a 1" meter. Drop-in
meters are installed by City forces under a separate permit. Noted.
SEWER COMMENTS
1. The preliminary sewer plan submitted with the land use application by Encompass
Engineering and Surveying shows approximately 225 LF of new 8" sewer main flowing
from north to south in a 25' water/sewer easement east of the proposed town homes
in the private drive aisle connecting to the existing 8" sewer main in NE 12th Street.
The northern terminus of the new sewer main shall be a sanitary sewer manhole. The
Cleanout was changed to a manhole.
2. Each new townhome is served by an individual side sewer. All new side sewers shall
be 6". All side sewers shall flow by gravity to the main at a minimum slope of 2%.
Each new townhome is shown to be served by an individual side sewer
3. The development is subject to system development charges {SDCs) for sewer service.
The SOC far sewer service is based on the size of the domestic water service. The 2017
SOC for sewer service with a 3/4" or 1" water meter is $2,540.00 . Credit will be
issued for existing sewer services. Sewer SDCs that are current will be collected at
the time of construction permit issuance. Noted.
STORM DRAINAGE COMMENTS
1. A Preliminary Drainage Plan and Technical Information Report (TIR) prepared by
Encompass Engineering and Surveying dated February 20, 2017 were submitted to
the City as part of the site plan submittal. The site is located in the City's Peak Rate
Flow Control Standard (Existing Site Conditions). The site is located in the East Lake
Washington drainage basin. The TIR was completed in accordance with the
standards found in the 2017 Renton Surface Water Design Manual (RSWDM). All
nine core requirements and five of the six special requirements were addressed.
Special Requirement #6: Aquifer Protection Area was not addressed in the TIR.
Special Requirement #6: Aquifer Protection Area is now addressed in the TIR. This
site is located in in Zone 2 of the Aquifer Protection Area. Because we are not
proposing open stormwater facilities or ditches, this project meets the Zone 2
Aquifer Protection Area restrictions/requirements.
Infiltration trenches are proposed to infiltrate the all roof drainage from the site. A
combination bioswale infiltration trench is shown to infiltrate all runoff from the
paved drive aisle. Infiltration of all runoff from target impervious surfaces will satisfy
Core Requirement #3: Flow Control Facilities. Infiltration facilities shall be sized and
designed in accordance with the standards found in Section 5.2 of the 2017 RSWDM.
Where stormwater from pollution generating impervious surface (PGIS) is being
infiltrated, the groundwater protection requirements found in Section 5.2 need to be
met as the site in located in Zone 2 of the Aquifer Protection Area. If soils on-site do
not meet the criteria found in this section, the project should implement groundwater
protection measures per Section 5.2.1 prior to the infiltration facility or install a facility
liner per Section 6.2.4. The infiltration facility will exempt the project from Core
Requirement #9: On-Site BMPs for the site. Because of infiltration test issues, we are
now proposing a detention only stormwater vault together with a Filterra
biofiltration device w/presedimentation chamber and/or Vortechs hydrodynamic
separator to provide flow control and enhanced water quality treatment for runoff
(no infiltration). Infiltration trench BMPs are shown that will provide the required
flow control BMPs.
The infiltration facilities were sized using infiltration rates provided in the
geotechnical report completed by Earth Solutions NW dated August 24, 2014: The
geotechnical report that was submitted used older sizing standards from the 2005
Washington Department of Ecology (DOE) Stormwater Manual for Western
Washington (SWMMWW).
A bioswale is proposed to satisfy Core Requirement #8: Water Quality Facilities. The
bioswale was sized using 60% of the 2 - year flow using 15 minute time steps in KCRTS.
A bioswale is an approved Basic Water Quality treatment option. Multifamily
developments require Enhanced Basic Water Quality treatment. As discussed above,
a Filterra biofiltration device w/presedimentation chamber and/or Vortechs
hydrodynamic separator will be used to provide enhanced water quality treatment
for runoff from the driveway.
Below is a summary of revisions required for the TIR prior to construction permit review.
• Update the TIR to address Special Requirement #6, Aquifer Protection area. The site is
located in Zone 2 of the Aquifer Protection Area. Update the TIR to discuss how the
bioswale I infiltration trench is meeting the soil requirements mentioned above or if a
treatment liner is being proposed as it is infiltrating PGIS. This site is located in in Zone 2
of the Aquifer Protection Area. Because we are not proposing open stormwater
facilities or ditches, this project meets the Zone 2 Aquifer Protection Area
restrictions/requirements. We are assuming that infiltration BMPs will provide the
required flow control BMPs for roof water only. It is not clear if this clean roof wa ter
is subject the infiltration limitations for the Aquifer Protection Area requirements
but may turn out to need to have a treatment liner or drain into soil that meets
treatment liner specifications. The measured infiltration rate was in the area of
infiltration rates specified for treatment liners in the RSWDM. This will be analyzed
with the final engineering design
• Infiltration testing shall be done in accordance with the standards found in Section 5.2 of
the 2017 RSWDM. Testing was performed in accordance with the Seattle-modified 2005
DOE SWMMWW. Update the geotechnical report accordingly. Infiltrating tests will be
performed with the final engineering design to see if infiltration will work for providing
flow control other than infiltration BMPs.
• Infiltration testing shall be done when the water level is expected to be at a
maximum (later winter or early spring). Infiltration testing was previously completed
in August. Update the geotechnical report accordingly. Infiltrating tests will be
performed with the final engineering design to see if infiltration will work for providing
flow control other than infiltration BMPs.
• A minimum of one test shall be performed at each proposed infiltration facility
location. Only two test locations were used. There are six proposed infiltration
trenches. More testing is needed in the facility locations. Update the geotechnical
report accordingly. Noted.
• Test pits need to extend a minimum of 5' below the bottom of the infiltration
facility. Confirm that the test pits meet these requirements. Noted.
• The design infiltration rate needs to be determined per the standards foun d in
Section 5.2. Update the geotechnical report accordingly. Infiltrating tests will be
performed with the final engineering design to see if infiltration will work for providing
flow control other than infiltration BMPs.
• The sizing of the infiltration trenches shall be done with an approved continuous
hydrologic model. WWHM and MGS Flood are the approved continuous hydrologic
models. KCRTS is no longer an approved model. Revise design calculations in TIR with
an approved model. WWHM2012 is now being used to design the stormwater
facility.
• This project requires Enhanced Basic Water Quality treatment. A bioswale is not an
approved Enhanced Basic Water Quality treatment option. Update the TIR and plans
to show an approved water quality treatment option. If a bioswale is used as part of
a treatment train to meet the Enhanced Basic Water Quality treatment standards,
the following applies:
o The sizing of the bioswale shall be done with an approved continuous
hydrologic model. WWHM and MGS Flood are approved continuous
hydrologic models. KCRTS is no longer an approved model. Calculations shall
clearly show that 91% of the total runoff volume is treated by the facility.
Revise design calculations in TIR with an approved model. WWHM2012 is now
being used to design the stormwater facility. We are now proposing a
detention only stormwater vault together with a Filterra biofiltration device
w/presedimentation chamber and/or Vortechs hydrodynamic separator to
provide flow control and enhanced water quality treatment for runoff.
• Infiltration trenches need to meet all of the design criteria found in Section 5.2.5. In
particular, a 20' setback is required from trenches to structures. This setback may be
reduced if the facility soils report addresses potential impacts of trench phreatic
surface on structures located within 20'. If a reduced setback is desired please
include discussion in the TIR. Trenches also need to be set back at least 5' from
property lines. Please see the transportation comments regarding right of way
dedication along NE 12th Street and NE 13th Street as the property lines for the
project will change. Update the drainage plans to show conformance with this
requirement. Noted. We are now proposing a detention vault.
2. A geotechnical report evaluating the feasibility of infiltration on-site was
prepared by Earth Solutions NW dated August 24, 2014. The report described the
soils located on site as silty sand with gravel. Infiltration testing was performed in
accordance with the Seattle-modified 2005 DOE SWMMWW, Section 3.6.
Infiltration testing was done at two locations. The measured infiltration rates
were 4.0 inches per hour in the central portion of the site and 8.0 inches per hour
in the northern portion of the site. A design infiltration rate was determined
using correction factors from Table 3.9 of the 2005 SWMMWW. The design
infiltration rate was determined to be 1.0 inches per hour. Noted.
3. Storm drainage i mprovements along public street frontages are required to
conform to the City's Street standards. New storm structures may be required to
capture storm w ater along the street frontages per Section 4.2 .1. New storm drain
shall be designed and sized i n accordance with the standards found in Section
4.2.1. Storm drain with a minimum diamete r of 12" is required in the public right of
way. No new CBs are needed along the frontages to capture gutter flows—flows
along 12th and 13th will continue to flow west to existing CBs. A 12” pipe is
proposed in the Harrington Avenue NE ROW to outfall the proposed stormwater
vault into the City storm system
4. The development is subject- to system development charges (SDCs) for stormwater.
The 2017 SDC for stormwater is $1,608.00 per lot. Credit will be issued for any
existing homes. Stormwater SDCs that are current will be collected at the time of
construction permit issuance. Noted.
TRANSPORTATION/STREET COMMENTS
1. Each new lot is subject to a transportation impact fee. The 2017 transportation
impact fee is $2,822.61 per townhome. A credit of $2,822.61 will be issued for each
of the existing units in the existing duplex and for the two former units in the duplex
that was demolished. The transportation impact fee is due at the time of building
permit issuance. Noted.
2. NE 12th Street is classified a collector arterial a nd is designated as a Green
Connection in the City's adopted Sunset Area Surface Water Master Plan. The
Master Plan was adopted in April 2011.
Per the adopted Master Plan, NE 12th Street shall have a right of way width of 83'.
City staff has determined a modified Collector Green Connection section is more
appropriate for this portion of NE 12th Street. The modified street section shall
have a right of way width of 69'. The paved roadway width shall remain 40'
consisting of 2 -14' shared share vehicular I bike lanes and 1-12' center two way
left turn lane. A 0.5' curb, 8' rain garden, and 6' sidewalk are required along both
sides of the roadway. A right of way dedication of approximately 9.5' is required
along the NE 12th Street frontage to provide the required 34.5' half right of way
section.
The plans should be updated to show the right of way dedication, new curb, 8' rain
garden, and 6' sidewalk along the project frontage. A street modification is
required to be submitted to adhere to the modified Collector Green Connection
section described above. Please submit the street modification with the updates to
the civil plans and TIR. A street modification would not be granted to keep the
existing frontage improvements along NE 12th Street. As agreed by City staff, we
show NE 12th Street to have the curb replaced in its present location, a 6’
planter/infiltration strip and a 5’ sidewalk. A 7.5’ dedication will provide the
necessary room in the ROW for said improvements.
3. Harrington Avenue NE is classified as a residential access street and is designate d as
a Green Connection in the City's adopted Sunset Area Surface Water Master Plan.
The portion of Harrington Avenue NE adjacent to this site was improved by a City
capital improvement project. The driveway entrances constructed for 2801 NE 13th
Street shall be removed as part of this project. A concrete curb per City of Renton
Standards shall be constructed whe re the driveway entrances are removed. No
further improvements would be required along the Harrington Avenue NE frontage.
The driveway curbcut is shown to be removed and replace with curb.
4. NE 13th Street is classified as a residential access street. Per RMC 4-6-060, the required
right of -way width for a residential access street is 53'. The paved roadway width
shall be 26' consisting of 2 -10' lanes and 1-6' parking lane. A 0.5 curb, 8' planter strip,
and 5' sidewalk are required along both side of the roadway. The new curb line shall be
set at 13' from the center line of the existing right of way. A dedication of approximately
1.5' is required along the NE 13th Street frontage to provide the required 26.5' half right
of way section. The plans now show the existing NE 13th Street widened to 13’ of paving
from the centerline, a curb, an 8’ planter strip and a 5’ sidewalk, with a 1.5’ dedication.
5. Curb radii of 25' were installed at the intersections of NE 12th Street and Harrington
Avenue NE and NE 13th Street and Harrington Avenue NE. These curb radii can remain
as part of this project. Noted.
6. Per RMC 4-6-060, street lighting is required as the. project is larger than four residential
units. A photometric study and street lighting plan per City standard shall be
submitted at the time of construction permit review. Required street lights shall be
per current City of Renton standards. A lighting plan will be part of the construction
plans. - . -
7. The project does not require a Traffic Impact Analysis as the project produces less than
20 vehicles per hour in both the AM and PM peak periods. Noted.
8. Paving and trench restoration within the City of Renton right of way shall comply with
the City's Restoration and Overlay requirements. Noted.
GENERAL COMMENTS
1. The fees listed are for 2017. The fees that are current at the time of the
respective permit issuance will be levied. Please see the City of Renton website for the
current fee schedule. Noted.
2. Retaining walls that are 4' or taller from bottom of footing and stormwater detention
vaults will require a separate building permit. Structural calculations and plans
prepared by a licensed engineer will be required as part of the building permit review.
Noted.
3. All civil plans shall conform to the current City of Renton survey and drafting standards.
Current drafting standards can be found on the City of Renton website. Noted.
4. A separate plan submittal will be required for a construction permit for utility work
and street improvements. All plans shall be prepared by a licensed Civil Engineer in
the State of Washington. Noted.
5. Please see the City of Renton Development Engineering website for the Construction
Permit Application and Construction Permit Process and Submittal Requirements.
Please contact the City to schedule a construction permit intake meeting. Noted.
If you have questions or need additional information, please call me at 425 -392-0250 or email me
at tredding@encompasses.net
Sincerely,
Encompass Engineering
Tom Redding
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