HomeMy WebLinkAboutRS_Technical Information Report_170426_v1Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. i January, 2017
TABLE OF CONTENTS
SECTION A PROJECT OVERVIEW .............................................................................. 1
SECTION B CONDITIONS AND REQUIREMENTS SUMMARY ................................... 2
LARGE LOT BMP REQUIREMENTS EVALUATION .............................................................................. 2
SECTION C SMALL SITE ESC PLAN & REPORT ........................................................ 4
SECTION D DECLARATION OF COVENANT ............................................................... 5
SECTION E OPERATIONS & MAINTENANCE MANUAL ............................................. 5
APPENDIX
1. Geotechnical Report
2. Construction and TESC Plans
3. Declaration of Covenant
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 1 January, 2017
SECTION A
PROJECT OVERVIEW
The proposed project is to subdivide an existing parcel into two residential lots, leaving both of
the existing houses. Onsite construction will be limited to the addition of an emergency vehicle
turnaround, addition of a fire hydrant, two new water service lines and one new sewer service for
the easterly home.
The parcel is located at 3106 Talbot Road South and is approximately 2.3 acres in size with the
dimensions of 100’x1000’. Current zoning is R8, which requires a minimum lot size of 5,445 sf
per lot. Additionally, an NGPA will be dedicated along the eastern 100’ of the site to encompass
an existing wetland.
The required emergency vehicle turnaround will be located onsite between Lots 1 and 2, and will
connect to South 32nd Place via and existing dedicated ingress/egress easement area (Tract H)
within the Winsper Division No. 1 Subdivision.
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 2 January, 2017
SECTION B
CONDITIONS AND REQUIREMENTS SUMMARY
The drainage design will be in accordance with the City of Renton Standards and the 2016 King
County Surface Water Design Manual (“KCSWDM”). City standards and the KCSWDM outline
specific and other requirements which must be addressed. Since the project adds more than
1,999 sf but less than 5,000 sf of new plus replaced impervious surface, and less than ¾ acres of
new pervious surface, this project will follow the Simplified Drainage Review Requirements as
described in Appendix C of the KCSWDM.
The proposed construction associated with the project will add 4,163 sf in new impervious surface
and is proposed on a project site/lot larger than 22,000 square feet. Therefore, per Table C.1.1.A,
the Large Lot BMP requirements per Section C.1.3 and Implementation Requirements in Section
C.1.3.4 will be followed. Additionally, the ESC and SWPPS measures in accordance with Section
C.1.4 and Simplified submittal requirements of C.1.5 will be followed.
LARGE LOT BMP REQUIREMENTS EVALUATION
Full Dispersion
As described in C.1.3.2 (1), the feasibility and applicability of full dispersion must be first evaluated
for all targeted impervious surfaces.
This BMP is not feasible on this site due to the existing slope that is greater than 15% downslope
(west) of the proposed targeted impervious surface. Additionally, a 100-foot flow path meeting
the requirements of Section C.2.1, cannot be provided.
Full Infiltration
Full infiltration per Section C.2.2, is considered infeasible if it is not recommended by the project
geotechnical engineer. Per the geotechnical evaluation provided by Geotech Consultants Inc.,
dated May 27, 2014, page 3, paragraph 8, the onsite soil type and groundwater conditions are
not suitable for infiltration. The geotechnical report is provided in the Appendix. Additionally,
perched ground water was found in Test Pit No. 4 during the geotechnical investigation, see page
2, Groundwater Conditions. Therefore, full infiltration is not a proposed BMP for this project.
Limited Infiltration
Limited infiltration per C.2.3, is not a recommend BMP for this project for the same reasons
discussed in the full infiltration evaluation.
Bioretention
If bioretention per C.2.6 were utilized, the cell volume would be approximately 2,520 cf, utilizing
0.6 inches of rainfall per C.2.6.1 for till soils and rainfall region ST-1.0. Utilizing a maximum
containment depth of 12-inches, this would require a cell bottom footprint of approximately
50’x50’. In order to have adequate slope for conveyance piping, the bottom of the cell would need
to be placed at an elevation of 170’. With 3:1 side slopes, the grading would be well within existing
15% slopes on the west side of the proposed turnaround. Therefore, this BMP is not considered
to be feasible per item #11 on infeasibility criteria list.
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 3 January, 2017
Permeable Pavement
Permeable pavement per C.2.7 is infeasible to due to the existing poor infiltrating soils and
existing perched ground water as discussed in the full infiltration BMP evaluation. Portions of the
new access will be within a few feet of existing properties. As discussed in the geotech report
page 3, paragraph 6, shallow perched ground water is a concern when constructing new homes.
Therefore, infiltrating water near any existing structure would be a concern and have potential for
liability, and a valid reason to consider this BMP infeasible.
Additionally, the design considerations for the utilization of pervious surfacing do not allow for run-
on from pervious surfaces. With the existing site grades sloping east to west and the location of
the required turnaround, this design criteria cannot be met, which would also make this BMP
infeasible.
Basic Dispersion
Per C.1.3.2-Large Lot BMP Requirements, #4, all impervious surfaces not mitigated using items
1,2, or 3, must be mitigated to the maximum extent feasible utilizing basic dispersion per C.2.4.
Basic dispersion consisting of sheet flow per C.2.4.5 can be provided for approximately 55% of
the new impervious surface, meeting the requirements of item #5, a). This will be accomplished
by utilizing a gravel strip on the westerly side of the new impervious area that is located within the
project site. The portion of impervious that is located within the existing Tract H will be collected
in a catch basin and conveyed to the existing City stormwater system located in S. 32nd Place,
which is where runoff from the area currently flows.
Per design criteria 3 and 4 in Section C.2.4.5, 10-feet of vegetated flow path is to be provided for
up to a 20 foot strip of impervious surface. An additional 10-feet of flow path is required for every
additional 20-feet of impervious surface. The widest portion of the turnaround is 53’, therefore,
26.5-feet of flow path will be provided west of the targeted surface, which will provide adequate
flow path for entire turnaround.
Summary: Basic dispersion per Section C.2.4.5 and Figure C.2.4.D will be provided to mitigate
runoff from approximately 2,306 sf (55%) of the new impervious surface. The remaining area
that cannot be mitigated (1,857 sf) will be collected and conveyed to the City’s existing storm
drainage system. Please see the attached drawing 3 which depicts the proposed stormwater
improvements.
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 4 January, 2017
SECTION C
SMALL SITE ESC PLAN & REPORT
Erosion and Sediment Control
Development of the project site will require earth disturbance. As a result, special attention needs
to be given to the construction stages of development. This section of the report, along with the
Temporary Erosion and Sedimentation Control (TESC) plans, serve as a guide to minimize
the effects of erosion onsite and off-site. The temporary erosion and sediment control plan is in
conformance with the King County Surface Water Design Manual (2009). The following elements
discuss how the project site will conform to County erosion and sedimentation control standards.
Element #1: Mark Clearing Limits
Clearing Limits will be flagged by the surveyor and/or fenced by the contractor prior to
commencement of construction activity. In addition, tree protection fencing will be installed.
Element #2: Establish Construction Access
A rock-construction entrance (or equivalent) shall be installed in conformance with City erosion
control standards.
Element #3: Detain Flows
All surface runoff generated during construction will be controlled by perimeter filter fabric fence
prior to release.
Element #4: Install Sediment Controls
Sediment controls for the project site shall consist of catch basin protection and filter fabric
fencing installed around the site perimeter.
Element #5: Stabilize Soils
The temporary erosion and sediment control plan calls for the stabilization of exposed soils
through mulching and/or hydroseeding when the soils are not to be worked for a significant period
of time. The plan also calls for the establishment of permanent vegetation through hydroseeding
once the site has reached final grade.
Element #6: Protect Slopes
The temporary erosion and sediment control plan calls for the installation of filter fabric fencing
along the downstream limits of construction. Side slopes of soil stockpiles shall be temporarily
covered with plastic until the stockpile materials are used or exported from the site.
Element #7: Protect Drain Inlets
The Temporary Erosion and Sediment Control Plan calls for a filter fabric socks to be installed at
all newly constructed catch basin inlets and all existing inlets which lie immediately downstream
of areas under construction.
Element #8: Stabilize Channels and Outlets
There are no nearby channels.
Element #9: Control Pollutants
All waste materials shall be disposed of in an approved location, in accordance with City
Standards. In order to reasonably prevent a contamination event (such as a fuel spill), vehicle
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 5 January, 2017
maintenance shall occur off-site to the greatest extent practicable. Any contamination event that
occurs should be immediately contained and remedied to the satisfaction of the City.
Element #10: Control De-Watering
No significant amount of dewatering is expected to occur during this project.
Element #11: Maintain BMPs
All BMPs should be monitored and maintained regularly to insure adequate operation. A TESC
supervisor shall be identified at the beginning of the project, to provide monitoring and direct
appropriate maintenance activities. As site conditions change, all BMPs shall be updated as
necessary to maintain compliance with City standards.
Element #12: Manage the Project
The project will begin with a pre-construction conference, in which an onsite TESC supervisor
shall be identified. The onsite supervisor shall monitor all TESC facilities regularly and maintain
a log of inspections and improvements to demonstrate compliance with City standards. It is
important to ensure that the entire site is in conformance with City erosion control standards at
all times. The TESC supervisor shall notify Land Development Advisors, LLC of any problems
with the proposed erosion control elements, or if any revisions to the plans need to be made.
Additional erosion control materials, such as filter fabric fencing, plastic cover and straw bales,
shall be kept onsite at all times in the event that an erosion control feature needs to be replaced
or installed.
The TESC Plans are included in the Appendix.
SECTION D
DECLARATION OF COVENANT
A declaration of covenant will be executed and is included in the attached documents at
the end of this report.
SECTION E
OPERATIONS & MAINTENANCE MANUAL
Operations and Maintenance
Operations and maintenance guidelines for the onsite storm system are covered in the DOE
Manual.
Drainage Assessment Valley Vue Short Plat
LAND DEVELOPMENT ADVISORS, LLC. 6 January, 2017
APPENDIX
Return Address:
City Clerk’s Office
City of Renton
1055 S Grady Way
Renton, WA 98057
DECLARATION OF COVENANT FOR INSPECTION AND
MAINTENANCE OF STORMWATER FACILITIES AND BMPS
Grantor:
Grantee: City of Renton
Legal Description:
Assessor's Tax Parcel ID#:
IN CONSIDERATION of the approved City of Renton ___________________________ permit
for application file No. LUA/SWP_______________________ relating to the real property ("Property")
described above, the Grantor(s), the owner(s) in fee of that Property, hereby covenants(covenant) with the
City of Renton, a political subdivision of the state of Washington, that he/she(they) will observe, consent
to, and abide by the conditions and obligations set forth and described in Paragraphs 1 through 10 below
with regard to the Property, and hereby grants(grant) an easement as described in Paragraphs 2 and 3.
Grantor(s) hereby grants(grant), covenants(covenant), and agrees(agree) as follows:
1. The Grantor(s) or his/her(their) successors in interest and assigns ("Owners of the described
property") shall at their own cost, operate, maintain, and keep in good repair, the Property's stormwater
facilities and/or best management practices ("BMPs") constructed as required in the approved
construction plans and specifications __________ on file with the City of Renton and submitted to the
City of Renton for the review and approval of permit(s) _____________________________. The
property's stormwater facilities and/or best management practices ("BMPs") are shown and/or listed on
Exhibit A. The property’s stormwater facilities and/or BMPs shall be maintained in compliance with the
operation and maintenance schedule included and attached herein as Exhibit B. Stormwater facilities
include pipes, swales, tanks, vaults, ponds, and other engineered structures designed to manage and/or
treat stormwater on the Property. Stormwater BMPs include dispersion and infiltration devices, native
vegetated areas, permeable pavements, vegetated roofs, rainwater harvesting systems, reduced impervious
surface coverage, and other measures designed to reduce the amount of stormwater runoff on the
Property.
2. City of Renton shall have the right to ingress and egress over those portions of the Property
necessary to perform inspections of the stormwater facilities and BMPs and conduct maintenance
activities specified in this Declaration of Covenant and in accordance with RMC 4-6-030.
3. If City of Renton determines that maintenance or repair work is required to be done to any of
the stormwater facilities or BMPs, City of Renton shall give notice of the specific maintenance and/or
repair work required pursuant to RMC 4-6-030. The City shall also set a reasonable time in which such
Page 1 of 3 Form Approved by City Attorney 10/2013
work is to be completed by the Owners. If the above required maintenance or repair is not completed
within the time set by the City, the City may perform the required maintenance or repair, and hereby is
given access to the Property, subject to the exclusion in Paragraph 2 above, for such purposes. Written
notice will be sent to the Owners stating the City’s intention to perform such work. This work will not
commence until at least seven (7) days after such notice is mailed. If, within the sole discretion of the
City, there exists an imminent or present danger, the seven (7) day notice period will be waived and
maintenance and/or repair work will begin immediately.
4. If at any time the City of Renton reasonably determines that a stormwater facility or BMP on
the Property creates any of the hazardous conditions listed in RMC 4-4-060 G or relevant municipal
successor's codes as applicable and herein incorporated by reference, the City may take measures
specified therein.
5. The Owners shall assume all responsibility for the cost of any maintenance or repair work
completed by the City as described in Paragraph 3 or any measures taken by the City to address hazardous
conditions as described in Paragraph 4. Such responsibility shall include reimbursement to the City
within thirty (30) days of the receipt of the invoice for any such work performed. Overdue payments will
require payment of interest at the current legal rate as liquidated damages. If legal action ensues, the
prevailing party is entitled to recover reasonable litigation costs and attorney’s fees.
6. The Owners are hereby required to obtain written approval from City of Renton prior to
filling, piping, cutting, or removing vegetation (except in routine landscape maintenance) in open
vegetated stormwater facilities (such as swales, channels, ditches, ponds, etc.), or performing any
alterations or modifications to the stormwater facilities and BMPs referenced in this Declaration of
Covenant.
7. Any notice or consent required to be given or otherwise provided for by the provisions of this
Agreement shall be effective upon personal delivery, or three (3) days after mailing by Certified Mail,
return receipt requested.
8. With regard to the matters addressed herein, this agreement constitutes the entire agreement
between the parties, and supersedes all prior discussions, negotiations, and all agreements whatsoever
whether oral or written.
9. This Declaration of Covenant is intended to protect the value and desirability of the real
property described above, and shall inure to the benefit of all the citizens of the City of Renton and its
successors and assigns. This Declaration of Covenant shall run with the land and be binding upon
Grantor(s), and Grantor's(s') successors in interest, and assigns.
10. This Declaration of Covenant may be terminated by execution of a written agreement by the
Owners and the City that is recorded by King County in its real property records.
IN WITNESS WHEREOF, this Declaration of Covenant for the Inspection and Maintenance of
Stormwater Facilities and BMPs is executed this _____ day of ____________________, 20_____.
GRANTOR, owner of the Property
GRANTOR, owner of the Property
Page 2 of 3 Form Approved by City Attorney 10/2013
STATE OF WASHINGTON ) COUNTY OF KING )ss.
On this day personally appeared before me:
, to me known to be the individual(s) described in
and who executed the within and foregoing instrument and acknowledged that they signed the same as
their free and voluntary act and deed, for the uses and purposes therein stated.
Given under my hand and official seal this _____ day of ____________________, 20_____.
Printed name
Notary Public in and for the State of Washington,
residing at
My appointment expires
Page 3 of 3 Form Approved by City Attorney 10/2013