Report (8) FOR OFFICE USE ONLY—SITE ADDRESS:
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Please complete this form when submitting information for plan review responses and revisions.
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City of Tigard • COMMUNITY DEVELOPMENT DEPARTMENT
.IN a Transmittal Letter
TIGARD 13125 SW Hall Blvd. • Tigard,Oregon 97223 • 503.718.2439 • www.tigard-or.gov
TO: l�2Rr'oEi4) iA&Ci4 .t DATE RECEIVED:
DEPT: BUILDING DIVISION RECEIVED
/� APR 2 9 2019
FROM: �jo�{ I2-t PL.E'f
CITY OF TIGARD
COMPANY: ts-t PD CS{p,ov p BUILDING DIVISION
PHONE: (vol. 710-5 (02'2 By:/7 ./•
RE: l(62d p
(Site Address) ( i tl{N 1ii%er)
(Project name or subdivision name and lot number)
ATTACHED ARE THE FOLLOWING ITEMS:
Copies: Description: Copies: Description:
Additional set(s)of plans. 3 Revisions: .j66 woiC-4o Pi. •+S
Cross section(s)and details. Wall bracing and/or lateral analysis.
Floor/roof framing. Basement and retaining walls.
Beam calculations. Engineer's calculations.
2 Other(explain): \-DR,14.,n)4.c„ {248 r'
REMARKS:
FOR OFFICE USE ONLY
Routed to Permit Technician: Date:S C- Initials: 1)
Fees Doer Yes El No Fee Description: Amount Due:
s- 1-) tr io $ yr—�
$
$
Special
Instructions:
Reprint Permit(per PE): ❑ Yes A No 0 Done
Applicant Notified: Date: Initials:
I:\Building\FormslTransmittalLetter-Rcvisions.doc 05/25/2012
520 South Main Street,Suite 2531 Phone 330.572.2100 v
Akron,Ohio 44311 www.gpdgroup.com
GPD Engineering and Architecture ^
Professional Corporation \)( \
r/
February 25, 2019
Job #2016355.42
Storm Water Quality Review and Analysis
Starbucks - Tigard Towne Square
16200 SW Pacific Highway RECEIVED
Tigard, OR 97224
APR 2 9 2019
Prepared For:
Starbucks CITY OF TIGARD
BUILDING DIVISION
Civil Designer: •
�D PROF
Tyler Budd ��¢ GINg ve r .
t.IProject Manager: r44
t 9Pd61P P
Tom Conner ,n , ,, , .�a
Design Date: OREGON:
April 24, 2019
j 'A 1
Project Number: 04/26/2019
2016355.42
EXPIRES:06/30/2020
1.06
CAI PPpC°ved �t� ,--
Tyler Budd, Civil Designer 2 February 25, 2019
Table of Contents
Section 1:
• Project Information
• Design and Analysis
Section 2:
• Drainage Map
• USDA Web Soil Survey Report
Section 3:
• Excerpt from Chapter 4 (Section 4.05), Runoff Treatment and Control
of the R&O 17-05 Manual
Tyler Budd, Civil Designer 3 February 25, 2019
Section 1
Project Information
The project is located at 16200 SW Pacific Highway, Suite Z3, Tigard, OR 97224 as
part of a larger shopping center. The proposed improvements consist of renovating
an existing bank building, reconfiguring part of the parking lot and adding a
dumpster enclosure and concrete pad. Because the project consists of adding or
modifying over 1,000 SF of impervious area, the City of Tigard and Clean Water
Services requires water quality to be addressed with the development. It is not
known whether the existing site has water quality treatment already, so it is
assumed that the full amount of required treatment area, as calculated below, will
need to be treated in the proposed water quality treatment plan. Runoff is currently
pitched to (2).inlets on site. The storm water runoff will either be directed through
an ADS Bayfilter or a LIDA Rain Garden before being released back into the existing
storm water system or into the groundwater.
Design and Analysis
The water quality requirements for City of Tigard are governed by Chapter 4 of the
current Clean Water Services Design and Construction Standards (see section 3). To
determine the amount of impervious area needed to be treated in design, we
referred to section 4.05.5, which gives the formula shown below for all
developments other than single family and duplex, which result in the permanent
removal of 1,000 SF or greater of impervious area.
Treatment =New Imp. +3(Modified Imp. - Permanently Removed Imp.)
New Impervious 1,150 SF
Removed Impervious 2,650 SF
Modified Impervious 6,760 SF
Using this formula and the numbers shown, we are able to determine 13,480 SF of
impervious area is required to be treated for water quality. Refer to the drainage
map in section 2 to show the amount of impervious area being treated by the
Bayfilter and the amount being treated by the rain garden to satisfy this
requirement. For the purpose of this report and following Clean Water Services
guidelines, modified impervious pavement is considered to be any pavement or
concrete that is removed and replaced full depth. The area being milled and overlaid
is not considered full depth replacement and therefore not included in this modified
impervious number. New impervious surface is any area being turned into
impervious surface that was existing landscaping and removed impervious is any
impervious area being replaced with landscaping.
Tyler Budd, Civil Designer 4 February 25, 2019
A review of section 4.05.3 c.1 of the R&O manual for water quality indicates a list of items that
can be used for treatment:
A) Vegetated Swale
B) Extended Dry Basin
C) Constructed Water Quality Wetland
D) Structural Infiltration Planter
E) Non-structural Infiltration Planter (rain garden)
F) Flow-through Planter
G) LIDA Swale
H) Street-Side Planter
I) Landscape Filter Strip
J) Vegetated Corridor as a Filter Strip
After reviewing these items and the site layout, it was determined that is it not
feasible to install one of these items and be able to treat the required amount of
impervious area required without unnecessary grading and construction.
Section 4.05.8 in the R&O Manual states proprietary treatment systems shall be
used in conjunction with a LIDA treatment method in certain situations. This project
falls under section 4.05.8.c.2 to make it qualified to use a proprietary treatment
device:
Treatment of runoff from an adjoining commercial, industrial, or multi-family, or
condominium parcels which share a common parking lot.
In order to minimize construction and maximize efficient water quality treatment,
we have recommended the use of an ADS Bayfilter device in addition to a small rain
garden along the drive-thru near the pickup window. Based on site conditions, the
impervious treatment area for the Bayfilter is 13,720 SF, therefore the required
water quality volume is 411.6 cf as calculated by the formula below:
Water Quality Volume(cull.) = 0.36(in.) x Area(sy.ft.1
12(in It.)
From here, we calculated the water quality flow from the formula below:
Water Water Quality Volume(cu.11.)
Quality Flow(cfs) = 14,400 seconds
The required water quality flow for this project was determined to be 0.029 cfs.
After this is determined, the ADS Bayfilter can be sized based on their flow
specifications.
•
Tyler Budd, Civil Designer 5 February 25, 2019
BayFiltern'Model :'.ecast Number of Treatment Capacity- Treatment Capacity- Treatment Capacity-
Cartridges 522(cfs) 530(cfs) 545(cis)
BF-48-1 48' 1 0.05 0.067 C
BF-60-2 6D" 2 0.10 0.13 0.20
BF-72-3 3 0 15 0.20 0 30
BF-84-4 26 0.27 0.40
BF-96-5 76" 5 0.33 0.50
BF-96-6 86 6 C 30 0 46 0.6C
BF-96-7 7 .tb 5.47 0.70
•
Based on this table, the required Bayfilter to accommodate the necessary water
quality flow is the BF-48-1 model with (1) 522 cartridge. This requires a 48"
manhole, as detailed by ADS, to be installed on site with the cartridge inside. See
utility plan for placement and invert information. The ADS Installation Manual shall
be referenced for additional information.
Based on site conditions, the impervious treatment area for the rain garden is 1,240
SF. According to the LIDA Handbook, the required rain garden surface area is 6% of
the impervious treatment area, therefore the required bottom surface area of the
rain garden must be 75 SF. See drainage map in section 2 for the rain garden
impervious treatment area.
Conclusion
After reviewing the City of Tigard water quality requirements and LIDA approaches,
it was determined the most practical approach is to install an ADS Bayfilter and a
LIDA rain garden as described above. These improvements will require some storm
sewer to be replaced, but we believe it is more practical than the regrading and
maintenance that would be needed for installing a singular LIDA water quality
approach to accommodate the whole site. The Bayfilter and rain garden approach
will provide sufficient capacity for treating the necessary impervious area on-site,
along with providing a recommended LIDA water quality approach which is required
when installing a proprietary treatment system.
Tyler Budd, Civil Designer 6 February 25, 2019
•
Section 2
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USDA Natural Resources Web Soil Survey 2/11/2019
Conservation Service National Cooperative Soil Survey Page 1 of 3
Soil Map—Washington County,Oregon
MAP LEGEND MAP INFORMATION
Area of Interest(AOI) Spoil Area The soil surveys that comprise your AOI were mapped at
Area of Interest(AOI) 1:20,000.
® Stony Spot
Soils CO Very Stony Spot Warning:Soil Map may not be valid at this scale.
Soil Map Unit Polygons
7 Wet spot Enlargement of maps beyond the scale of mapping can cause
.0. Soil Map Unit Lines misunderstanding of the detail of mapping and accuracy of soil
Other line placement.The maps do not show the small areas of
• Soil Map Unit Points contrasting soils that could have been shown at a more detailed
.•• Special Line Features
Special Point Features scale.
V Blowout Water Features
Streams and Canals Please rely on the bar scale on each map sheet for map
Borrow Pit measurements.
Transportation
Clay Spot Rails Source of Map: Natural Resources Conservation Service
''4 Web Soil Survey URL:
p Closed Depression
ti Interstate Highways Coordinate System: Web Mercator(EPSG:3857)
X Gravel Pit
US Routes Maps from the Web Soil Survey are based on the Web Mercator
,• Gravelly Spot Major Roads projection,which preserves direction and shape but distorts
distance and area.A projection that preserves area,such as the
® Landfill Local Roads Albers equal-area conic projection,should be used if more
Lava Flow Background accurate calculations of distance or area are required.
dlb Marsh or swamp . Aerial Photography This product is generated from the USDA-NRCS certified data as
of the version date(s)listed below.
* Mine or Quarry
Soil Survey Area: Washington County,Oregon
O Miscellaneous Water Survey Area Data: Version 16,Sep 18,2018
O Perennial Water Soil map units are labeled(as space allows)for map scales
Rock Outcrop 1:50,000 or larger.
▪ Saline Spot Date(s)aerial images were photographed: Aug 3,2014—Aug
23,2014
Sandy Spot
The orthophoto or other base map on which the soil lines were
Severely Eroded Spot compiled and digitized probably differs from the background
• Sinkhole imagery displayed on these maps.As a result,some minor
shifting of map unit boundaries may be evident.
0 Slide or Slip
Sodic Spot
i a \ Natural Resources Web Soil Survey 2/11/2019
Conservation Service National Cooperative Soil Survey Page 2 of 3
Soil Map—Washington County,Oregon
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AO1
37A Quatama loam,D to 3 percent 1.8 59.2%
slopes
37B Quatama loam,3 to 7 percent 1.3 40.8%
slopes
Totals for Area of Interest 3.1 100.0%
USDA Natural Resources Web Soil Survey 2/11/2019
Conservation Service National Cooperative Soil Survey Page 3 of 3
Tyler Budd, Civil Designer 7 February 25, 2019
Section 3
b. Approaches shall be designed so that flow from the development is treated
off-line from the storm conveyance system and reconnected to upstream
flows following treatment. If an off-line approach is not feasible, additional
capacity in the approach may be required for upstream flow.
c. Discharges to sensitive areas shall maintain the hydro period and flows of
pre-development site conditions to the extent necessary to protect the
characteristic functions of the sensitive area. Conversely, discharge of
flows that may be critical to downstream water quality sensitive areas into
other catchments will not be permitted unless addressed in the applicant's
Service Provider Letter.
d. The stormwater quality approaches shall be designed for a dry weather
storm event totaling 0.36 inches of precipitation falling in 4 hours with an
average storm return period of 96 hours.
e. All water quality approaches shall be designed in accordance with this
Chapter.
4.05.5 Impervious Area Used In Design
The following apply for development which creates or modifies 1,000 square
feet or greater of impervious surface: Development which results in both new
and modified impervious surface will result in a combined treatment
requirement, as described below:
a. For new home construction on a single family or duplex lot of record the
water quality approach shall be sized based on 2,640 square feet of
impervious surface per dwelling unit. The actual impervious surface may
be utilized when the lot size is less than 2,000 square feet, or the
development creates or modifies impervious surface not associated with
new home construction,up to a maximum of 2,640 square feet.
b. For single family and duplex residential partitions and subdivisions,
stormwater quality approaches shall be sized for all impervious area
created by the development and for all existing impervious area proposed
to remain on site. All existing and proposed residences on individual lots
shall be sized at the rate of 2,640 square feet of impervious surface area per
dwelling unit. For the purpose of design calculations, the actual
impervious surface can be utilized as an alternative to 2,640 square feet per
dwelling unit when the average lot size on a single-family residential
project is less than 2,000 square feet.
c. For all developments other than single family and duplex, including row
houses and condominiums, the stormwater quality approaches shall be
sized to treat all new impervious surfaces and three times the modified
R&O 17-5 RUNOFF TREATMENT AND CONTROL
April 2017 Chapter 4—Page 11
impervious surface,up to the total existing impervious surface on the site.
The area requiring treatment is shown in the formula below:
Treatment=New Impervious+3(Modified Impervious)
When modification results in the permanent removal of 1,000 square feet
or greater of impervious surface,the treatment approach shall be sized for
three times the replaced impervious surface, in addition to the new
impervious surface. In this case,the area requiring treatment is shown in
the formula below:
Treatment=New Imp. + 3(Modified Imp. -Permanently Removed Imp.)
Impervious areas shall be determined based upon building permits,
construction plans, or other appropriate methods of measurement deemed
reliable by District and/or City.
4.05.6 Water Quality Approach Sizing Methods
a. Water Quality Volumes and Flows (applies to approaches in Section
4.05.3.c.1 (A)-(C))
1. Water Quality Storm
The water quality storm is the storm required by regulations to be
treated. The storm defines both the volume and rate of runoff. The
water quality storm is defined in Subsection 4.05.4 (d).
2. Water Quality Volume(WQV) •
The WQV is the volume of water that is produced by the water
quality storm. The WQV equals 0.36 inches over the impervious
area that is required to be treated as shown in the formula below:
Water Quality Volume (cu.ft.) = 0.36(in.) x Area(sq.ft.)
12 (in./ft.)
3. Water Quality Flow (WQF)
The WQF is the average design flow anticipated from the water
quality storm as shown in the formulas below:
Water Quality Flow (cfs) = Water Quality Volume(cu.ft.)
14,400 seconds
or
Water Quality Flow (cfs) = 0.36(in.) x Area(sq.ft.)
12(in/ft)(4 hr)( 60 min/hr)(60 sec/min)
R&O 17-5 RUNOFF TREATMENT AND CONTROL
April 2017 Chapter 4—Page 12
b. Water Quality Surface Area(applies to facilities in Section 4.05.3.c.1(D)-
(1))
A 6% sizing factor shall be used to calculate the required water quality
surface area of the selected treatment facility. A sizing factor of 6%
assumes the site infiltration rate is less than 2 inches/hour. A site specific
design for the site shall be required for any of the following situations:
1. An alternate sizing factor is used;
2. The impervious area contributing to an individual water quality
approach is greater than 15,000 square feet; or
3. The treatment facility is used for quantity control.
c. Water Quality for Vegetated Corridor as a Filter Strip (applies to Section
4.05.3.c.1(J)).
The sizing of a Vegetated Corridor as a Filter Strip must meet all of the
following criteria:
1. The maximum contributing impervious surface is 2,640 square feet
per 50 feet of Vegetated Corridor width.
2. The contributing impervious surface must be adjacent to the
Vegetated Corridor, or within the outer 40% and approved as an
allowed use consistent with the Service Provider Letter.
3. The minimum depth is three times the depth of the contributing
impervious surface, or one single family residence. The depth of the
Vegetated Corridor treatment area shall be measured from the edge
of the Sensitive Area and in the direction of stormwater flow.
4.05.7 Pretreatment
a. Pretreatment Required
Unless approved by the District, flow from impervious surfaces to water
quality approaches shall not be allowed without pretreatment or as
specified in the design criteria for specific approaches in Section 4.06.
Incoming flows to the water quality approach shall be pretreated using a
water quality manhole in accordance with Subsection 4.06.1 or as specified
within the design criteria for specific approaches. Other pre-treatment
methods such as proprietary devices, filter strip, or trapped catch basin may
be approved by the District or City.
R&O 17-5 RUNOFF TREATMENT AND CONTROL
April 2017 Chapter 4—Page 13
b. Proprietary Pre-Treatment Devices
1. The use of proprietary pre-treatment devices shall be permitted on a
case by case basis with approval by the District or City.
2. The devices will be sized in accordance with the manufacturer's
recommendations; however, the minimum treatment flow must be
the water quality flow.
3. Technical submittals from the manufacturer are required, including
hydraulic design criteria, particulate removal efficiency, and
maintenance requirements and schedule.
4.05.8 Proprietary Treatment Systems
a. Proprietary treatment systems shall meet the removal efficiency
requirement defined in Section 4.05.3(a) and be approved by the District
for use in the situations identified in Subsection(c)below.
b. Maintenance
1. Proprietary treatment systems shall be maintained by the District or
Cities except those systems used in the situations specified in
Section 4.05.8(c)(1) and(2) below.
2. Proprietary systems require a long-term maintenance plan
identifying maintenance techniques, schedule, and responsible
parties. This maintenance plan shall be submitted and approved
with the drainage report for a project.
c. Proprietary treatment systems shall be allowed in situations meeting one of
the following criteria:
1. Treatment of runoff from a single parcel.
2. Treatment of runoff from an adjoining commercial, industrial, or
multi-family, or condominium parcels which share a common
parking lot.
3. Treatment of runoff from new and expanded collector and arterial
roadways where no other opportunities exist for treatment without
necessitating the removal of homes or businesses.
4. Treatment of runoff from new developments in transit-oriented or
similar high-density zoning classifications where the development
is primarily single-family residential and the average lot size is less
than 2,500 square feet.
5. Treatment of runoff as part of a master planned regional facility
approved by the District.
R&O 17-5 RUNOFF TREATMENT AND CONTROL
April 2017 Chapter 4—Page 14