HomeMy WebLinkAboutRE_Drainage_Technical_Information_Report_250327_v2Patrick E. Carroll, P.E.
PEC Design and Consulting LLC
2621 NE 109th Street
Vancouver, WA 98686
(503) 849-1646
pat@pecdesign.net
Date: August 23, 2022
Rev: March 25, 2025
Subject: Technical Information Report (TIR) – Billings 2
Lot Short Plat, 14103 160th Avenue SE, Renton, WA 98059
Table of Contents:
Project Overview
Conditions and Requirements Summary / Core Requirements
Off Site Analysis
Flow Control and Water Quality Facility Analysis and Design
Conveyance System Analysis and Design
Special Reports and Studies
Other Permits
ESC Analysis and Design
Bond Quantities, Facility Summaries and Declarations of Covenant
Operations Manual
Special Requirements
Project Description:
The proposed project will divide the existing 36,469 sf parcel into 2 Lots. An existing single family
residence is on the proposed parcel B and a future residence will be constructed on parcel A. A 20-foot-
wide access driveway will be constructed to parcel A. A driveway with a fire department required hammer
head will be constructed in the future and included in the building permit submittal for the residence. The
total new impervious area for the driveway, road improvements on 160th Avenue SE (road asphalt paving,
driveway drop and sidewalk improvements) is a total of 6,146 sf.
The general grade of the residence site slopes gently to the west. The existing soils consist of fine to
medium sand (based upon a geotechnical report from Nelson Geotechnical Associates, Inc. (NGA)),
therefore runoff from the new driveway impervious area will flow into a gravel trench infiltration /
Bioretention facility adjacent to the 20’ driveway on the south side of the lot in the landscaping area. An
overflow for the infiltration / planter bed will be the proposed inlet and into the existing storm system
inlet in 160th Ave. SE. The street improvements, and sidewalk will flow into the existing roadside ditch on
160th Ave. SE. The runoff from the future fire turnaround and the proposed residence will flow from to a
future infiltration trench area on Parcel A. The individual system design will be provided at time of the
building permit application.
Under this permit, it is assumed that the only area to be disturbed, will be for the installation of the
proposed driveway to parcel A, and for the installation of the street, sidewalk, and driveway drop on 160th
Avenue SE. The approximate area to be disturbed during the installation of the improvements is
approximately 7,000 sf. No existing native growth areas or significant trees will be disturbed.
Docusign Envelope ID: 62D86DA9-EC63-4203-A23D-A92308805918
The proposed site earthwork is estimated as follows.
Earthwork Calculations:
Access Driveway Exc. = 2,879 sf = 160 cy
Residence Exc. = 1,013 sf = 50 cy
Total excavation to be spread onsite. = 210 cy.
Conditions and Requirements Summary:
The following specifics about the site apply:
The site will use the City of Renton/King County Stormwater Manual allow for sheet flow from the
driveway to the proposed Bioretention facility with an overflow into the existing storm system.
Due to the size of the site and area disturbed, a Full Drainage Review format will be used.
The following sections address the project as relates to the nine Core Requirements and the five
Special Requirements.
Core Requirement #1 - Discharge at the Natural Location
The impervious areas will flow to the proposed Bioretention facility along the south side of the
driveway to Lot 2 and have an overflow discharge to the existing storm system via the inlet at the east
end of the facility near 160th Avenue SE.
Core Requirement #2 – Offsite Analysis
There are no identified drainage problems “downstream” of the site.
Core Requirement #3 - Flow Control
The proposed project will utilize an LID infiltration trench design in conjunction with the Bioretention
facility, Flow control will occur onsite since the additional runoff generated from impervious surfaces
will be infiltrated onsite. The inlet at the east end of the driveway near 160th Avenue will be for
overflow discharge.
Core Requirement #4 - Conveyance System
The use of PVC pipe for runoff collection and routing to the existing storm system provides accepted
and common conveyance practice. Three feet of cover is provided under pavement. Any storm piping
under 3 feet of cover will be Ductile Iron Pipe.
Core Requirement #5 - Construction Stormwater Pollution Prevention
A TESCP Plan is provided integral with the drainage design drawing. The site is small and warrants only
the normal placement of a downslope silt fence at its perimeter. A standard stabilized construction
entrance BMP is provided for site entrance silt and debris protection of adjacent pavement.
Core Requirement #6 - Maintenance and Operations
Docusign Envelope ID: 62D86DA9-EC63-4203-A23D-A92308805918
An Operations and Maintenance Manual will be provided as part of the building permit process. A
new manual will be provided in Exhibit B of a new Declaration of Covenant which is required by the
City of Renton.
Core Requirement #7 - Financial Guarantees and Liability
The STE and Performance and Maintenance Bonds are required, and a right-of-way driveway installation.
Core Requirement #8 - Water Quality
The project will utilize Basic WQ Option 9 – Bioretention. The stormwater from the proposed driveway
will sheet flow into the Bioretention facility. The use of a catch basin with downturned elbows at the
discharge overflow to the east protects the infiltration trenches (and groundwater) from serious oil
and other contaminant spills or seeps from vehicular areas. Also, the roof is considered a non-polluting
impervious surface. This site meets the criteria for a Surface Area Exemption.
Core Requirement #9 - Flow Control BMP's
Flow control will be obtained by the use of a Bioretention area with infiltration, The LID infiltration
trench will infiltrate runoff from the proposed driveway to Lot 2.
Core Requirement #10 - Special Reports and Studies:
No previous reports or studies have been identified for this site, except for the older and more recent
short plat. Copies of these documents were not available for review.
Other Permits:
Permits for normal residential construction such as plumbing, electrical, etc. will be required. A right-
of-way permit is required for driveway installation.
Special Requirements for Full Drainage Review:
Special Requirement #1 - Other Adopted Requirements - None
Special Requirement #2 - Flood Hazard Area - None
Special Requirement #3 - Flood Protection - None
Special Requirement #4 - Source Control - None
Special Requirement #5 - Oil Control - None
Flow Control and Water Quality Facility Analysis and Design:
Per the Core Requirements above, the stormwater from the impervious roof areas will flow to the existing
storm system.
Conveyance System Analysis and Design:
6” and 4” PVC pipe will be used in all stormwater locations. All slopes will be in excess of 2 percent due to
the site topography, and are adequate by inspection. Minimum cover of 3 feet will be provided in any
paved or concrete driveway areas.
Special Reports and Studies:
No special reports of studies were performed for this site. Previous short plat documents were not
available for review.
Docusign Envelope ID: 62D86DA9-EC63-4203-A23D-A92308805918
Other Permits:
No special permits are required for site. The building permits are the only required permits for the
construction.
ESC Analysis and Design:
As noted in the Core Requirements, the site is small and only requires the normal placement of
downslope filter fence. A standard stabilized construction entrance will be used at the residence
construction site entrance.
Bond Quantities, Facility Summaries and Declaration of Covenant:
A Declaration of Covenant with attached Operations and Maintenance Manual will be provided if previous
documents are not considered applicable.
Operations and Maintenance Manual:
Provided with the Declaration of Covenant (see above note).
Any questions, or comments may be sent via email or mail to the above address.
Patrick E. Carroll, P.E.
PEC Design and Consulting LLC
2621 NE 109th Street
Vancouver, WA 98686
pat@pecdesign.net
Docusign Envelope ID: 62D86DA9-EC63-4203-A23D-A92308805918
3/25/2025